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Sample records for prevalent flow regime

  1. Boolean logic analysis for flow regime recognition of gas–liquid horizontal flow

    International Nuclear Information System (INIS)

    Ramskill, Nicholas P; Wang, Mi

    2011-01-01

    In order to develop a flowmeter for the accurate measurement of multiphase flows, it is of the utmost importance to correctly identify the flow regime present to enable the selection of the optimal method for metering. In this study, the horizontal flow of air and water in a pipeline was studied under a multitude of conditions using electrical resistance tomography but the flow regimes that are presented in this paper have been limited to plug and bubble air–water flows. This study proposes a novel method for recognition of the prevalent flow regime using only a fraction of the data, thus rendering the analysis more efficient. By considering the average conductivity of five zones along the central axis of the tomogram, key features can be identified, thus enabling the recognition of the prevalent flow regime. Boolean logic and frequency spectrum analysis has been applied for flow regime recognition. Visualization of the flow using the reconstructed images provides a qualitative comparison between different flow regimes. Application of the Boolean logic scheme enables a quantitative comparison of the flow patterns, thus reducing the subjectivity in the identification of the prevalent flow regime

  2. Flow regimes

    International Nuclear Information System (INIS)

    Kh'yuitt, G.

    1980-01-01

    An introduction into the problem of two-phase flows is presented. Flow regimes arizing in two-phase flows are described, and classification of these regimes is given. Structures of vertical and horizontal two-phase flows and a method of their identification using regime maps are considered. The limits of this method application are discussed. The flooding phenomena and phenomena of direction change (flow reversal) of the flow and interrelation of these phenomena as well as transitions from slug regime to churn one and from churn one to annular one in vertical flows are described. Problems of phase transitions and equilibrium are discussed. Flow regimes in tubes where evaporating liquid is running, are described [ru

  3. Flow regimes

    International Nuclear Information System (INIS)

    Liles, D.R.

    1982-01-01

    Internal boundaries in multiphase flow greatly complicate fluid-dynamic and heat-transfer descriptions. Different flow regimes or topological configurations can have radically dissimilar interfacial and wall mass, momentum, and energy exchanges. To model the flow dynamics properly requires estimates of these rates. In this paper the common flow regimes for gas-liquid systems are defined and the techniques used to estimate the extent of a particular regime are described. Also, the current computer-code procedures are delineated and introduce a potentially better method is introduced

  4. Refrigeration. Two-Phase Flow. Flow Regimes and Pressure Drop

    DEFF Research Database (Denmark)

    Knudsen, Hans-Jørgen Høgaard

    2002-01-01

    The note gives the basic definitions used in two-phase flow. Flow regimes and flow regimes map are introduced. The different contributions to the pressure drop are stated together with an imperical correlation from the litterature.......The note gives the basic definitions used in two-phase flow. Flow regimes and flow regimes map are introduced. The different contributions to the pressure drop are stated together with an imperical correlation from the litterature....

  5. Flow regime classification in air-magnetic fluid two-phase flow.

    Science.gov (United States)

    Kuwahara, T; De Vuyst, F; Yamaguchi, H

    2008-05-21

    A new experimental/numerical technique of classification of flow regimes (flow patterns) in air-magnetic fluid two-phase flow is proposed in the present paper. The proposed technique utilizes the electromagnetic induction to obtain time-series signals of the electromotive force, allowing us to make a non-contact measurement. Firstly, an experiment is carried out to obtain the time-series signals in a vertical upward air-magnetic fluid two-phase flow. The signals obtained are first treated using two kinds of wavelet transforms. The data sets treated are then used as input vectors for an artificial neural network (ANN) with supervised training. In the present study, flow regimes are classified into bubbly, slug, churn and annular flows, which are generally the main flow regimes. To validate the flow regimes, a visualization experiment is also performed with a glycerin solution that has roughly the same physical properties, i.e., kinetic viscosity and surface tension, as a magnetic fluid used in the present study. The flow regimes from the visualization are used as targets in an ANN and also used in the estimation of the accuracy of the present method. As a result, ANNs using radial basis functions are shown to be the most appropriate for the present classification of flow regimes, leading to small classification errors.

  6. Capacitance densitometer for flow regime identification

    International Nuclear Information System (INIS)

    Shipp, R.L. Jr.

    1978-01-01

    This invention relates to a capacitance densitometer for determining the flow regime of a two-phase flow system. A two-element capacitance densitometer is used in conjunction with a conventional single-beam gamma densitometer to unambiguously identify the prevailing flow regime and the average density of a flowing fluid

  7. Dynamic Modeling Strategy for Flow Regime Transition in Gas-Liquid Two-Phase Flows

    Directory of Open Access Journals (Sweden)

    Xia Wang

    2012-12-01

    Full Text Available In modeling gas-liquid two-phase flows, the concept of flow regimes has been widely used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are flow regime dependent. Current nuclear reactor safety analysis codes, such as RELAP5, classify flow regimes using flow regime maps or transition criteria that were developed for steady-state, fully-developed flows. As two-phase flows are dynamic in nature, it is important to model the flow regime transitions dynamically to more accurately predict the two-phase flows. The present work aims to develop a dynamic modeling strategy to determine flow regimes in gas-liquid two-phase flows through introduction of interfacial area transport equations (IATEs within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation of the interfacial area, fluid particle (bubble or liquid droplet disintegration, boiling and evaporation, and the destruction of the interfacial area, fluid particle coalescence and condensation. For flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shapes, namely group-1 and group-2 bubbles. A preliminary approach to dynamically identify the flow regimes is discussed, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration. The flow regime predicted with this method shows good agreement with the experimental observations.

  8. The application of neural networks to flow regime identification

    International Nuclear Information System (INIS)

    Embrechts, M.; Yapo, T.C.; Lahey, R.T. Jr.

    1993-01-01

    This paper deals with the application of a Kohonen map for the identification of two-phase flow regimes where a mixture of gas and fluid flows through a horizontal tube. Depending on the relative flow velocities of the gas and the liquid phase, four distinct flow regimes can be identified: Wavy flow, plug flow, slug flow and annular flow. A schematic of these flow regimes is presented. The objective identification of two-phase flow regimes constitutes an important and challenging problem for the design of safe and reliable nuclear power plants. Previous attempts to classify these flow regimes are reviewed by Franca and Lahey. The authors describe how a Kohonen map can be applied to distinguish between flow regimes based on the Fourier power spectra and wavelet transforms of pressure drop fluctuations. The Fourier power spectra allowed the Kohonen map to identify the flow regimes successfully. In contrast, the Kohonen maps based on a wavelet transform could only distinguish between wavy and annular flows. An analysis of typical two-phase pressure drop data for an air/water mixture in a horizontal pipe is presented. Use of the wavelet transform and the Kohonen feature map are discussed

  9. Zero-G two phase flow regime modeling in adiabatic flow

    International Nuclear Information System (INIS)

    Reinarts, T.R.; Best, F.R.; Wheeler, M.; Miller, K.M.

    1993-01-01

    Two-phase flow, thermal management systems are currently being considered as an alternative to conventional, single phase systems for future space missions because of their potential to reduce overall system mass, size, and pumping power requirements. Knowledge of flow regime transitions, heat transfer characteristics, and pressure drop correlations is necessary to design and develop two-phase systems. This work is concerned with microgravity, two-phase flow regime analysis. The data come from a recent sets of experiments. The experiments were funded by NASA Johnson Space Center (JSC) and conducted by NASA JSC with Texas A ampersand M University. The experiment was on loan to NASA JSC from Foster-Miller, Inc., who constructed it with funding from the Air Force Phillips Laboratory. The experiment used R12 as the working fluid. A Foster-Miller two phase pump was used to circulate the two phase mixture and allow separate measurements of the vapor and liquid flow streams. The experimental package was flown 19 times for 577 parabolas aboard the NASA KC-135 aircraft which simulates zero-G conditions by its parabolic flight trajectory. Test conditions included bubbly, slug and annular flow regimes in 0-G. The superficial velocities of liquid and vapor have been obtained from the measured flow rates and are presented along with the observed flow regimes and several flow regime transition predictions. None of the predictions completely describe the transitions as indicated by the data

  10. Unified flow regime predictions at earth gravity and microgravity

    International Nuclear Information System (INIS)

    Crowley, C.J.

    1990-01-01

    This paper illustrates the mechanistic models developed to predict flow regime transitions at earth gravity for various pipe inclinations can be successfully applied to existing microgravity flow regime data from several experiments. There is a tendency in the literature for flow regime comparisons in several inclination ranges and at various gravity (acceleration) levels to be treated by separate models, resulting in a proliferation of models for the prediction of flow regimes. One set of mechanistic models can be used to model the transitions between stratified, slug, bubbly, and annular flow regimes in pipes for all acceleration vectors and magnitudes from earth gravity to microgravity

  11. Flow regimes in vertical gas-solid contact systems

    Energy Technology Data Exchange (ETDEWEB)

    Yerushalmi, J.; Cankurt, N. T.; Geldart, D.; Liss, B.

    1976-01-01

    The flow characteristics in fluidized beds, i.e., gas-solid systems, was studied to determine the flow regimes, the interaction of gas and solid in the various flow regimes and the dependence of this interaction and of transition between flow regimes on the properties of the gas and solid, on the gas and solid flow rates, and on the containing vessel. Fluidized beds with both coarse and fine particles are considered. Test results using high speed photography to view the operation of a 2-dimensional bed are discussed. (LCL)

  12. Comparison of differential pressure model based on flow regime for gas/liquid two-phase flow

    International Nuclear Information System (INIS)

    Dong, F; Zhang, F S; Li, W; Tan, C

    2009-01-01

    Gas/liquid two-phase flow in horizontal pipe is very common in many industry processes, because of the complexity and variability, the real-time parameter measurement of two-phase flow, such as the measurement of flow regime and flow rate, becomes a difficult issue in the field of engineering and science. The flow regime recognition plays a fundamental role in gas/liquid two-phase flow measurement, other parameters of two-phase flow can be measured more easily and correctly based on the correct flow regime recognition result. A multi-sensor system is introduced to make the flow regime recognition and the mass flow rate measurement. The fusion system is consisted of temperature sensor, pressure sensor, cross-section information system and v-cone flow meter. After the flow regime recognition by cross-section information system, comparison of four typical differential pressure (DP) models is discussed based on the DP signal of v-cone flow meter. Eventually, an optimum DP model has been chosen for each flow regime. The experiment result of mass flow rate measurement shows it is efficient to classify the DP models by flow regime.

  13. Flow and heat transfer in laminar–turbulent transitional flow regime under rolling motion

    International Nuclear Information System (INIS)

    Yuan, Hongsheng; Tan, Sichao; Zhuang, Nailiang; Lan, Shu

    2016-01-01

    Highlights: • Flow and heat transfer experiment in transitional flow regime under rolling motion. • Increases of average friction factor and Nu were found. • Periodic breakdown of laminar flow contributes to the increase. • Nonlinear variation of pressure drop or Nu with Re also contributes to the increase. • Effect of critical Reynolds number shift was discussed. - Abstract: Flow and heat transfer characteristics under rolling motion are extremely important to thermohydraulic analysis of offshore nuclear reactors. An experimental study was conducted in a heated rectangular channel to investigate flow and heat transfer in laminar–turbulent transitional flow regime under rolling motion. The results showed that the average friction factor and Nusselt number are higher than that of the corresponding steady flow as the flow rate fluctuates in transitional flow regime. Larger relative flow rate fluctuation was observed under larger rolling amplitude or higher rolling frequency. In the same manner, larger increases of average friction factor and Nusselt number were achieved under larger rolling amplitude or higher rolling frequency. The increases were mainly caused by the flow rate fluctuation through periodic breakdown of laminar flow and development of turbulence in laminar–turbulent transitional flow regime. First, turbulence, which enhances the rate of momentum and energy exchange, occurs near the crest of flow rate wave even the flow is still in laminar flow regime according to the average Reynolds number. Second, as a result of rapid increases of the friction and heat transfer with Reynolds number in transitional flow regime, the increases of the friction and the heat transfer near the crest of flow rate wave are larger than the decreases of them near the trough of flow rate wave, which also contributes to increases of average friction and heat transfer. Additionally, the effect of critical Reynolds number shift under unsteady flow and heating

  14. Flow Regime Identification of Co-Current Downward Two-Phase Flow With Neural Network Approach

    International Nuclear Information System (INIS)

    Hiroshi Goda; Seungjin Kim; Ye Mi; Finch, Joshua P.; Mamoru Ishii; Jennifer Uhle

    2002-01-01

    Flow regime identification for an adiabatic vertical co-current downward air-water two-phase flow in the 25.4 mm ID and the 50.8 mm ID round tubes was performed by employing an impedance void meter coupled with the neural network classification approach. This approach minimizes the subjective judgment in determining the flow regimes. The signals obtained by an impedance void meter were applied to train the self-organizing neural network to categorize these impedance signals into a certain number of groups. The characteristic parameters set into the neural network classification included the mean, standard deviation and skewness of impedance signals in the present experiment. The classification categories adopted in the present investigation were four widely accepted flow regimes, viz. bubbly, slug, churn-turbulent, and annular flows. These four flow regimes were recognized based upon the conventional flow visualization approach by a high-speed motion analyzer. The resulting flow regime maps classified by the neural network were compared with the results obtained through the flow visualization method, and consequently the efficiency of the neural network classification for flow regime identification was demonstrated. (authors)

  15. Flow visualization study of post critical heat flux region for inverted bubbly, slug and annular flow regimes

    International Nuclear Information System (INIS)

    Denten, J.G.; Ishii, M.

    1988-11-01

    A visual study of film boiling using still photographic and high- speed motion picture methods was carried out in order to analyze the post-CHF hydrodynamics for steady-state inlet pre-CHF two-phase flow regimes. Pre-CHF two-phase flow regimes were established by introducing Freon 113 liquid and nitrogen gas into a jet core injection nozzle. An idealized, post-CHF two-phase core initial flow geometry (cylindrical multiphase jet core surrounded by a coaxial annulus of gas) was established at the nozzle exit by introducing nitrogen gas into the annular gap between the jet nozzle two-phase effluent and the heated test section inlet. For the present study three basic post-CHF flow regimes have been observed: the rough wavy regime (inverted annular flow preliminary break down), the agitated regime (transition between inverted annular and dispersed droplet flow), and the dispersed ligament/droplet regime. For pre-CHF bubbly flow in the jet nozzle, the post-CHF flow (beginning from jet nozzle exit/heated test section inlet) consists of the rough wavy regime, followed by the agitated and then the dispersed ligament/droplet regime. In the same way, for pre-CHF slug flow in the jet core, the post-CHF flow is comprised of the agitated regime at the nozzle exit, followed by the dispersed regime. Pre-CHF annular jet core flow results in a small, depleted post-CHF agitated flow regime at the nozzle exit, immediately followed by the dispersed ligament/droplet regime. Observed post dryout hydrodynamic behavior is reported, with particular attention given to the transition flow pattern between inverted annular and dispersed droplet flow. 43 refs., 20 figs., 5 tabs

  16. Visualized investigation on flow regimes for vertical upward steam–water flow in a heated narrow rectangular channel

    International Nuclear Information System (INIS)

    Wang Junfeng; Huang Yanping; Wang Yanlin; Song Mingliang

    2012-01-01

    Highlights: ► Flow regimes were visually investigated in a heated narrow rectangular channel. ► Bubbly, churn, and annular flow were observed. Slug flow was never observed. ► Flow regime transition boundary could be predicted by existing criteria. ► Churn zone in present flow regime maps were poorly predicted by existing criteria. - Abstract: Flow regimes are very important in understanding two-phase flow resistance and heat transfer characteristics. In present work, two-phase flow regimes for steam–water flows in a single-side heated narrow rectangular channel, having a width of 40 mm and a gap of 3 mm, were visually studied at relatively low pressure and low mass flux condition. The flow regimes observed in this experiment could be classified into bubbly, churn and annular flow. Slug flow was never observed at any of the conditions in our experiment. Flow regime maps at the pressure of 0.7 MPa and 1.0 MPa were developed, and then the pressure effect on flow regime transition was analyzed. Based on the experimental results, the comparisons with some existing flow regime maps and transition criteria were conducted. The comparison results show that the bubbly transition boundary and annular formation boundary of heated steam–water flow were consistent with that of adiabatic air–water flow. However, the intermediate flow pattern between bubbly and annular flow was different. Hibiki and Mishima criteria could predict the bubbly transition boundary and annular formation boundary satisfactorily, but it poorly predicted churn zone in present experimental data.

  17. Regimes of Two-Phase Flow in Short Rectangular Channel

    Science.gov (United States)

    Chinnov, Evgeny A.; Guzanov, Vladimir V.; Cheverda, Vyacheslav; Markovich, Dmitry M.; Kabov, Oleg A.

    2009-08-01

    Experimental study of two-phase flow in the short rectangular horizontal channel with height 440 μm has been performed. Characteristics of liquid motion inside the channel have been registered and measured by the Laser Induced Fluorescence technique. New information has allowed determining more precisely the characteristics of churn regime and boundaries between different regimes of two-phase flow. It was shown that formation of some two-phase flow regimes and transitions between them are determined by instability of the flow in the lateral parts of the channel.

  18. Online recognition of the multiphase flow regime and study of slug flow in pipeline

    International Nuclear Information System (INIS)

    Guo Liejin; Bai Bofeng; Zhao Liang; Wang Xin; Gu Hanyang

    2009-01-01

    Multiphase flow is the phenomenon existing widely in nature, daily life, as well as petroleum and chemical engineering industrial fields. The interface structure among multiphase and their movement are complicated, which distribute random and heterogeneously in the spatial and temporal scales and have multivalue of the flow structure and state. Flow regime is defined as the macro feature about the multiphase interface structure and its distribution, which is an important feature to describe multiphase flow. The energy and mass transport mechanism differ much for each flow regimes. It is necessary to solve the flow regime recognition to get a clear understanding of the physical phenomena and their mechanism of multiphase flow. And the flow regime is one of the main factors affecting the online measurement accuracy of phase fraction, flow rate and other phase parameters. Therefore, it is of great scientific and technological importance to develop new principles and methods of multiphase flow regime online recognition, and of great industrial background. In this paper, the key reasons that the present method cannot be used to solve the industrial multiphase flow pattern recognition are clarified firstly. Then the prerequisite to realize the online recognition of multiphase flow regime is analyzed, and the recognition rules for partial flow pattern are obtained based on the massive experimental data. The standard templates for every flow regime feature are calculated with self-organization cluster algorithm. The multi-sensor data fusion method is proposed to realize the online recognition of multiphase flow regime with the pressure and differential pressure signals, which overcomes the severe influence of fluid flow velocity and the oil fraction on the recognition. The online recognition method is tested in the practice, which has less than 10 percent measurement error. The method takes advantages of high confidence, good fault tolerance and less requirement of single

  19. Problems of mixed convection flow regime map in a vertical cylinder

    International Nuclear Information System (INIS)

    Kang, Gyeong Uk; Chung, Bum Jin

    2012-01-01

    One of the technical issues by the development of the VHTR is the mixed convection, which is the regime of heat transfer that occurs when the driving forces of both forced and natural convection are of comparable orders of magnitude. In vertical internal flows, the buoyancy force acts upward only, but forced flows can move either upward or downward. Thus, there are two types of mixed convection flows, depending on the direction of the forced flow. When the directions of the forced flow and buoyancy are the same, the flow is a buoyancy aided flow; when they are opposite, the flow is a buoyancy opposed flow. In laminar flows, buoyancy aided flow shows enhanced heat transfer compared to the pure forced convection and buoyancy opposed flow shows impaired heat transfer due to the flow velocity affected by the buoyancy forces. In turbulent flows, however, buoyancy opposed flows shows enhanced heat transfer due to increased turbulence production and buoyancy aided flow shows impaired heat transfer at low buoyancy forces and as the buoyancy increases, the heat transfer restores and at further increases of the buoyancy forces, the heat transfer is enhanced. It is of primary interests to classify which convection regime is mainly dominant. The methods most used to classify between forced, mixed and natural convection have been to refer to the classical flow regime map suggested by Meta is and Eckert. During the course of fundamental literature studies on this topic, it is found that there are some problems on the flow regime map in a vertical cylinder. This paper is to discuss problems identified through reviewing the papers composed in the classical flow regime map. We have tried to reproduce the flow regime map independently using the data obtained from the literatures and compared with the classical flow regime map and finally, the problems on this topic were discussed

  20. Identification of two-phase flow regimes under variable gravity conditions

    International Nuclear Information System (INIS)

    Kamiel S Gabriel; Huawei Han

    2005-01-01

    Full text of publication follows: Two-phase flow is becoming increasingly important as we move into new and more aggressive technologies in the twenty-first century. Some of its many applications include the design of efficient heat transport systems, the transfer and storage of cryogenic fluids, and condensation and flow boiling processes in heat exchangers and energy transport systems. Two-phase flow has many applications in reduced gravity environments experienced in orbiting spacecraft and earth observation satellites. Examples are heat transport systems, the transfer and storage of cryogenic fluids, and condensation and flow boiling processes in heat exchangers. A concave parallel plate capacitance sensor has been developed to measure void fraction for the purpose of objectively identifying flow regimes. The sensor has been used to collect void-fraction data at microgravity conditions aboard the NASA and ESA zero-gravity aircraft. It is shown that the flow regimes can be objectively determined from the probability density functions of the void fraction signals. It was shown that under microgravity conditions four flow regimes exist: bubbly flow, characterized by discrete gas bubbles flowing in the liquid; slug flow, consisting of Taylor bubbles separated by liquid slugs which may or may not contain several small gas bubbles; transitional flow, characterized by the liquid flowing as a film at the tube wall, and the gas phase flowing in the center with the frequent appearance of chaotic, unstable slugs; and annular flow in which the liquid flows as a film along the tube wall and the gas flows uninterrupted through the center. Since many two-phase flow models are flow regime dependent, a method that can accurately and objectively determine flow regimes is required. (authors)

  1. Identification of two-phase flow regimes under variable gravity conditions

    Energy Technology Data Exchange (ETDEWEB)

    Kamiel S Gabriel [University of Ontario Institute of Technology 2000 Simcoe Street North, Oshawa, ON L1H 7K4 (Canada); Huawei Han [Mechanical Engineering Department, University of Saskatchewan 57 Campus Dr., Saskatoon, Saskatchewan, S7N 5A9 (Canada)

    2005-07-01

    Full text of publication follows: Two-phase flow is becoming increasingly important as we move into new and more aggressive technologies in the twenty-first century. Some of its many applications include the design of efficient heat transport systems, the transfer and storage of cryogenic fluids, and condensation and flow boiling processes in heat exchangers and energy transport systems. Two-phase flow has many applications in reduced gravity environments experienced in orbiting spacecraft and earth observation satellites. Examples are heat transport systems, the transfer and storage of cryogenic fluids, and condensation and flow boiling processes in heat exchangers. A concave parallel plate capacitance sensor has been developed to measure void fraction for the purpose of objectively identifying flow regimes. The sensor has been used to collect void-fraction data at microgravity conditions aboard the NASA and ESA zero-gravity aircraft. It is shown that the flow regimes can be objectively determined from the probability density functions of the void fraction signals. It was shown that under microgravity conditions four flow regimes exist: bubbly flow, characterized by discrete gas bubbles flowing in the liquid; slug flow, consisting of Taylor bubbles separated by liquid slugs which may or may not contain several small gas bubbles; transitional flow, characterized by the liquid flowing as a film at the tube wall, and the gas phase flowing in the center with the frequent appearance of chaotic, unstable slugs; and annular flow in which the liquid flows as a film along the tube wall and the gas flows uninterrupted through the center. Since many two-phase flow models are flow regime dependent, a method that can accurately and objectively determine flow regimes is required. (authors)

  2. THE INFLUENCED FLOW REGIMES

    Directory of Open Access Journals (Sweden)

    Gavril PANDI

    2011-03-01

    Full Text Available The influenced flow regimes. The presence and activities ofhumanity influences the uniform environmental system, and in this context, therivers water resources. In concordance with this, the natural runoff regime suffersbigger and deeper changes. The nature of these changes depending on the type anddegree of water uses. The multitude of the use cause different types of influence,whit different quantitative aspects. In the same time, the influences havequalitative connotations, too, regarding to the modifications of the yearly watervolume runoff. So the natural runoff regime is modified. After analyzing thedistribution laws of the monthly runoff, there have been differenced four types ofinfluenced runoff regimes. In the excess type the influenced runoff is bigger thanthe natural, continuously in the whole year. The deficient type is characterized byinverse rapports like the first type, in the whole year. In the sinusoidal type, theinfluenced runoff is smaller than the natural in the period when the water isretained in the lake reservoirs, and in the depletion period the situation inverts. Atthe irregular type the ratio between influenced and natural runoff is changeable ina random meaner monthly. The recognition of the influenced regime and the gradeof influence are necessary in the evaluation and analysis of the usable hydrologicalriver resources, in the flood defence activities, in the complex scheme of thehydrographic basins, in the environment design and so on.

  3. Study on flow regimes of high-pressure and dense-phase pneumatic conveying

    International Nuclear Information System (INIS)

    Lu Peng; Chen Xiaoping; Liang Cai; Pu Wenhao; Zhou Yun; Xu Pan; Zhao Changsui

    2009-01-01

    High-pressure and dense-phase pneumatic conveying of pulverized coal is a key technology in the field of large-scale entrained bed coal gasification. Flow regime plays an important role in two-phase flow because it affects not only flow behavior and safety operation, but also the reliability of practical processes. Few references and experiences in high-pressure and dense-phase conveying are available, especially for the flow regimes. And because of the high stickiness and electrostatic attraction of pulverized coal to the pipe wall, it is very difficult to make out the flow regimes in the conveying pipe by visualization method. Thus quartz powder was chosen as the conveyed material to study the flow regime. High-speed digital video camera was employed to photograph the flow patterns. Experiments were conducted on a pilot scale experimental setup at the pressure up to 3.6MPa. With the decrease in superficial gas velocity, three distinguishable flow regimes were observed: stratified flow, dune flow and plug flow. The characteristics of pressure traces acquired by high frequency response pressure transmitter and their EMD (Empirical Mode Decomposition) characteristics were correlated strongly with the flow regimes. Combining high-speed photography and pressure signal analysis together can make the recognition of flow patterns in the high-pressure and dense-phase pneumatic conveying system more accurate. The present work will lead to better understanding of the flow regime transition under high-pressure.

  4. Early Regimes of Water Capillary Flow in Slit Silica Nanochannels

    DEFF Research Database (Denmark)

    Oyarzua, Elton; Walther, Jens Honore; Mejia, Andres

    2015-01-01

    on the dynamics of capillaryfilling. The results indicate that the nanoscale imbibition process is divided into three main flow regimes:an initial regime where the capillary force is balanced only by the inertial drag and characterized by aconstant velocity and a plug flow profile. In this regime, the meniscus...... velocity profiles identify the passage froman inviscid flow to a developing Poiseuille flow. Gas density profiles ahead of the capillary front indicatea transient accumulation of air on the advancing meniscus. Furthermore, slower capillary filling ratescomputed for higher air pressures reveal a significant...... retarding effect of the gas displaced by the advancing meniscus....

  5. Two-phase flow regimes and mechanisms of critical heat flux under subcooled flow boiling conditions

    International Nuclear Information System (INIS)

    Le Corre, Jean-Marie; Yao, Shi-Chune; Amon, Cristina H.

    2010-01-01

    A literature review of critical heat flux (CHF) experimental visualizations under subcooled flow boiling conditions was performed and systematically analyzed. Three major types of CHF flow regimes were identified (bubbly, vapor clot and slug flow regime) and a CHF flow regime map was developed, based on a dimensional analysis of the phenomena and available experimental information. It was found that for similar geometric characteristics and pressure, a Weber number (We)/thermodynamic quality (x) map can be used to predict the CHF flow regime. Based on the experimental observations and the review of the available CHF mechanistic models under subcooled flow boiling conditions, hypothetical CHF mechanisms were selected for each CHF flow regime, all based on a concept of wall dry spot overheating, rewetting prevention and subsequent dry spot spreading. Even though the selected concept has not received much attention (in term or theoretical developments and applications) as compared to other more popular DNB models, its basis have often been cited by experimental investigators and is considered by the authors as the 'most-likely' mechanism based on the literature review and analysis performed in this work. The selected modeling concept has the potential to span the CHF conditions from highly subcooled bubbly flow to early stage of annular flow and has been numerically implemented and validated in bubbly flow and coupled with one- and three-dimensional (CFD) two-phase flow codes, in a companion paper. [Le Corre, J.M., Yao, S.C., Amon, C.H., in this issue. A mechanistic model of critical heat flux under subcooled flow boiling conditions for application to one and three-dimensional computer codes. Nucl. Eng. Des.].

  6. Development of objective flow regime identification method using self-organizing neural network

    International Nuclear Information System (INIS)

    Lee, Jae Young; Kim, Nam Seok; Kwak, Nam Yee

    2004-01-01

    Two-phase flow shows various flow patterns according to the amount of the void and its relative velocity to the liquid flow. This variation directly affect the interfacial transfer which is the key factor for the design or analysis of the phase change systems. Especially the safety analysis of the nuclear power plant has been performed based on the numerical code furnished with the proper constitutive relations depending highly upon the flow regimes. Heavy efforts have been focused to identify the flow regime and at this moment we stand on relative very stable engineering background compare to the other research field. However, the issues related to objectiveness and transient flow regime are still open to study. Lee et al. and Ishii developed the method for the objective and instantaneous flow regime identification based on the neural network and new index of probability distribution of the flow regime which allows just one second observation for the flow regime identification. In the present paper, we developed the self-organized neural network for more objective approach to this problem. Kohonen's Self-Organizing Map (SOM) has been used for clustering, visualization, and abstraction. The SOM is trained through unsupervised competitive learning using a 'winner takes it all' policy. Therefore, its unsupervised training character delete the possible interference of the regime developer to the neural network training. After developing the computer code, we evaluate the performance of the code with the vertically upward two-phase flow in the pipes of 25.4 and 50.4 cmm I.D. Also, the sensitivity of the number of the clusters to the flow regime identification was made

  7. Salix response to different flow regimes in controlled experiments: first results

    Science.gov (United States)

    Gorla, Lorenzo; Signarbieux, Constant; Buttler, Alexandre; Perona, Paolo

    2013-04-01

    Dams and water management for hydropower production, agriculture and other human activities alter the natural flow regime of rivers. The new river hydrograph components depend on the type of impoundment and the policy of regulation but such a different flow regime will likely affect the riparian environment. The main challenge in order to define sustainable flow releases is to quantify hydrological effects in terms of geomorphology and ecosystem response. A considerable lack of knowledge still affects the link hydrology-ecology and inadequate flow rules (e.g., minimal or residual flows) are consequently still widespread: further research in this direction is urgently required. We present an experiment, which aims to investigate the effects of different water stage regimes on riparian vegetation (salix Viminalis cuttings) development in a temperate region (Switzerland). This work describes the installation setup, together with the first results concerning the first of the two scheduled seasons of campaign. Sixty Salix cuttings were planted in non-cohesive sandy-gravel sediment within 1 meter tall plastic pots installed outside in the EPFL campus. After grouping them in three batteries, the water level within them has been varying following three river regimes simulated by adjusting the water level within the pots by means of an automatic hydraulic system. The three water level regimes reproduce a natural flow regime, a minimum residual flow policy, which only conserves peaks during flooding conditions, and an artificial regime conserving only low frequencies (e.g., seasonality) of the natural dynamic. The natural flow regime of the first battery has been applied for two months to the entire system; the three regimes above said started in June 2012. This triggered a plant response transitory regime, which we monitored by measuring plant growth, soil and atmospheric variables. Particularly, measures concern with branches development leaves photosynthesis and

  8. A solution algorithm for fluid-particle flows across all flow regimes

    Science.gov (United States)

    Kong, Bo; Fox, Rodney O.

    2017-09-01

    Many fluid-particle flows occurring in nature and in technological applications exhibit large variations in the local particle volume fraction. For example, in circulating fluidized beds there are regions where the particles are close-packed as well as very dilute regions where particle-particle collisions are rare. Thus, in order to simulate such fluid-particle systems, it is necessary to design a flow solver that can accurately treat all flow regimes occurring simultaneously in the same flow domain. In this work, a solution algorithm is proposed for this purpose. The algorithm is based on splitting the free-transport flux solver dynamically and locally in the flow. In close-packed to moderately dense regions, a hydrodynamic solver is employed, while in dilute to very dilute regions a kinetic-based finite-volume solver is used in conjunction with quadrature-based moment methods. To illustrate the accuracy and robustness of the proposed solution algorithm, it is implemented in OpenFOAM for particle velocity moments up to second order, and applied to simulate gravity-driven, gas-particle flows exhibiting cluster-induced turbulence. By varying the average particle volume fraction in the flow domain, it is demonstrated that the flow solver can handle seamlessly all flow regimes present in fluid-particle flows.

  9. Methodology for local verification of flow regimes in fuel assemblies charts

    International Nuclear Information System (INIS)

    Igor, Sharaevsky; Elena, Sharaevskaya; Domashev, E.D.; Alexander, Arkhypov; Vladimir, Kolochko

    2003-01-01

    The best estimate thermal hydraulic codes describe adequately two-phase flows in nuclear energy facilities if there is proper system of closed relations. It could be obtained from the reliable information on structure forms of two-phase flows, its boundaries and reliable regime charts. In the paper the methodology of automatic recognition of the boundaries of the main types of two phase flows for rod fuel assemblies is presented. The methodology is based on definition of thermal hydraulic parameters distribution in experimental fuel assembly. The measurements were carried out using ASD signals of acoustic noise. In the paper data on two-phase flow regimes boundaries recognition especially low boundaries of bubble flow are summarized for experimental fuel assembly. The methodology of flow regimes charts applied to recognition of upper boundaries of boiling crisis regime was verificated. The satisfactory coincidence with experimental results have been shown. (author)

  10. Review of Mixed Convection Flow Regime Map of a Vertical pipe

    International Nuclear Information System (INIS)

    Chae, Myeong-Seon; Chung, Bum-Jin; Kang, Gyeong-Uk

    2015-01-01

    In a vertical pipe, the natural convective force due to buoyancy acts upward only, but forced convective force can be either upward or downward. This determines buoyancy-aided and buoyancy-opposed flows depending on the direction of forced flow with respect to the buoyancy forces. Furthermore, depending on the exchange mechanism, the flow condition is classified into laminar and turbulent. In laminar mixed convection, buoyancy-aided flow presents enhanced heat transfer compared to the pure forced convection and buoyancy-opposed flow shows impaired heat transfer as the flow velocity affected by the buoyancy forces. However, in turbulent mixed convection, buoyancy-aided flow shows an impairment of the heat transfer rate for small buoyancy, and a gradational enhancement for large buoyancy. In this study, the existing flow regime map on mixed convection in a vertical pipe was reviewed through an analysis of literatures. Using the investigated data and heat transfer correlations, the flow regime map was reconstructed independently, and compared with the existing one. This study reviewed the limitations of the classical mixed convection flow regime map. Using the existing data and heat transfer correlations by Martinelli and Boelter and Watzinger and Johnson, the flow regime map was reconstructed independently. The results revealed that the existing map used the data selectively among the experimental and theoretical results, and a detailed description for lines forming mixed convection and transition regime were not given. And the information about uncertainty analysis and the evidentiary data were given insufficiently. The flow regime map and investigator commonly used the diameter as the characteristic length for both Re and Gr in place of the height of the heated wall, though the buoyancy forces are proportional to the third power of the height of heated wall

  11. Theoretical investigation of flow regime for boiling water two-phase flow in horizontal rectangular narrow channels

    International Nuclear Information System (INIS)

    Zhang Chunwei; Qiu Suizheng; Yan Mingyu; Wang Bulei; Nie Changhua

    2005-01-01

    The flow regime transition criteria for the boiling water two-phase flow in horizontal rectangular narrow channels (1 x 20 mm, 2 x 20 mm) were theoretically explored. The discernible flow patterns were bubble, intermittent slug, churn, annular and steam-water separation flow. By using two-fluid model, equations of conservation of momentum were established for the two-phase flow. New flow-regime criteria were obtained and agreed well with the experiment data. (authors)

  12. Flow regimes and mechanistic modeling of critical heat flux under subcooled flow boiling conditions

    Science.gov (United States)

    Le Corre, Jean-Marie

    Thermal performance of heat flux controlled boiling heat exchangers are usually limited by the Critical Heat Flux (CHF) above which the heat transfer degrades quickly, possibly leading to heater overheating and destruction. In an effort to better understand the phenomena, a literature review of CHF experimental visualizations under subcooled flow boiling conditions was performed and systematically analyzed. Three major types of CHF flow regimes were identified (bubbly, vapor clot and slug flow regime) and a CHF flow regime map was developed, based on a dimensional analysis of the phenomena and available data. It was found that for similar geometric characteristics and pressure, a Weber number (We)/thermodynamic quality (x) map can be used to predict the CHF flow regime. Based on the experimental observations and the review of the available CHF mechanistic models under subcooled flow boiling conditions, hypothetical CHF mechanisms were selected for each CHF flow regime, all based on a concept of wall dry spot overheating, rewetting prevention and subsequent dry spot spreading. It is postulated that a high local wall superheat occurs locally in a dry area of the heated wall, due to a cyclical event inherent to the considered CHF two-phase flow regime, preventing rewetting (Leidenfrost effect). The selected modeling concept has the potential to span the CHF conditions from highly subcooled bubbly flow to early stage of annular flow. A numerical model using a two-dimensional transient thermal analysis of the heater undergoing nucleation was developed to mechanistically predict CHF in the case of a bubbly flow regime. In this type of CHF two-phase flow regime, the high local wall superheat occurs underneath a nucleating bubble at the time of bubble departure. The model simulates the spatial and temporal heater temperature variations during nucleation at the wall, accounting for the stochastic nature of the boiling phenomena. The model has also the potential to evaluate

  13. A study of Two-Phase Flow Regime Maps in Vertical and Horizontal Pipes

    International Nuclear Information System (INIS)

    Kim, Kyung Doo; Kang, Doo Hyuk

    2007-10-01

    A safety analysis code to design a pressurized water reactor and to obtain the licences including entire proprietary rights is under development in domestic research and development project. The purpose and scope of this report is to develop the flow regimes related models for inter-phase friction, wall frictions, wall heat transfer, and inter-phase heat and mass transfer in two-phase three-field equations. In order to choose choose the flow regime criteria, we have investigated various exiting best-estimate T/H codes in this chapter 2. They are the RELAP5-3D, TRAC-M, CATHARE, MARS codes. Around 500 references used in these codes have been collected and reviewed. Also we have investigated eleven papers in detail. In chapter 3, based on the selected flow regimes, the flow regime maps for a gas-liquid flow in horizontal and vertical tubes have decided including the mechanisms of flow regime transition regions. Conclusively, the process will be presented for choosing the best flow regime maps which occur in gas-liquid two-phase flow in horizontal and vertical pipes. We will look forward to decide the constitutive relations based upon the flow regime maps that are determined in this works. The constitutive relations will be used for the code under development

  14. Flow regime, void fraction and interfacial area transport and characteristics of co-current downward two-phase flow

    Energy Technology Data Exchange (ETDEWEB)

    Lokanathan, Manojkumar [School of Mechanical Engineering, Purdue University, 585 Purdue Mall, West Lafayette, IN 47907-2088 (United States); Hibiki, Takashi [School of Nuclear Engineering, Purdue University, 400 Central Drive, West Lafayette, IN 47907-2017 (United States)

    2016-10-15

    Highlights: • Downward flow regime maps and models were studied for 25.4 to 101.6 mm pipe diameters. • Effect of flow inlet on flow transition, void & interfacial area profile were studied. • Bubble void profiles were associated with the interfacial forces for downward flow. • Flow regime pressure drop and interfacial friction factor were studied. • The most applicable and accurate downward drift-flux correlation was determined. - Abstract: Downward two-phase flow is observed in light water reactor accident scenarios such as loss of coolant accident (LOCA) and loss of heat sink accident (LOHS) due to loss of feed water or a secondary pipe break. Hence, a comprehensive literature review has been performed for the co-current downward two-phase flow with information on the flow regime transitions and flow characteristics for each regime in the downward flow. The review compares the experimental data of the flow regime map and the current available transition models. Objectivity of the data varies on the method utilized as a certain degree of subjectivity is still present in the most objective method. Nevertheless, experimental data through subjective methods such as direct visualization or analysis of a wire mesh sensor (WMS) data were still studied in this review. Despite the wide range of flow regime data for numerous pipe sizes, a consensus was not reached for the effect of pipe sizes on flow regime transition. However, it is known that a larger pipe results in greater degree of coalescence at lower gas flow rates (Hibiki et al., 2004). The introduction of a flow straightener at the inlet led to less coring and fluid rotation and inevitably, reduced bubble coalescence. This also resulted in the disappearance of the kinematic shock wave phenomenon, contrary to an inlet without a flow straightener. The effect of flow inlet, flow location, pipe diameter and bubble interfacial forces on the radial distribution as well as bubble coalescence and breakup rate

  15. Two-phase flow regimes for counter-current air-water flows in narrow rectangular channels

    International Nuclear Information System (INIS)

    Kim, Byong Joo; Sohn, Byung Hu; Jeong, Si Young

    2001-01-01

    A study of counter-current two-phase flow in narrow rectangular channels has been performed. Two-phase flow regimes were experimentally investigated in a 760 mm long and 100 mm wide test section with 2.0 and 5.0 mm gap widths. The resulting flow regime maps were compared with the existing transition criteria. The experimental data and the transition criteria of the models showed relatively good agreement. However, the discrepancies between the experimental data and the model predictions of the flow regime transition became pronounced as the gap width increased. As the gap width increased the transition gas superficial velocities increased. The critical void fraction for the bubbly-to-slug transition was observed to be about 0.25. The two-phase distribution parameter for the slug flow was larger for the narrower channel. The uncertainties in the distribution parameter could lead to a disagreement in slug-to-churn transition between the experimental findings and the transition criteria. For the transition from churn to annular flow the effect of liquid superficial velocity was found to be insignificant

  16. Flow regime and deposition pattern of evaporating binary mixture droplet suspended with particles.

    Science.gov (United States)

    Zhong, Xin; Duan, Fei

    2016-02-01

    The flow regimes and the deposition pattern have been investigated by changing the ethanol concentration in a water-based binary mixture droplet suspended with alumina nanoparticles. To visualize the flow patterns, Particle Image Velocimetry (PIV) has been applied in the binary liquid droplet containing the fluorescent microspheres. Three distinct flow regimes have been revealed in the evaporation. In Regime I, the vortices and chaotic flows are found to carry the particles to the liquid-vapor interface and to promote the formation of particle aggregation. The aggregates move inwards in Regime II as induced by the Marangoni flow along the droplet free surface. Regime III is dominated by the drying of the left water and the capillary flow driving particles radially outward is observed. The relative weightings of Regimes I and II, which are enhanced with an increasing load of ethanol, determine the motion of the nanoparticles and the formation of the final drying pattern.

  17. Flow Regimes of Air-Water Counterflow Through Cross Corrugated Parallel Plates

    Energy Technology Data Exchange (ETDEWEB)

    de Almeida, V.F.

    2000-06-07

    Heretofore unknown flow regimes of air-water counterflow through a pair of transparent vertical parallel cross corrugated plates were observed via high-speed video. Air flows upward driven by pressure gradient and water, downward driven by gravity. The crimp geometry of the corrugations was drawn from typical corrugated sheets used as filling material in modern structured packed towers. Four regimes were featured, namely, rivulet, bicontinuous, flooding fronts, and flooding waves. It is conceivable that the regimes observed might constitute the basis for understanding how gas and liquid phases contend for available space in the interstices of structured packings in packed towers. Flow regime transitions were expressed in terms of liquid load (liquid superficial velocity) and gas flow factor parameters commonly used in pressure drop and capacity curves. We have carefully examined the range of parameters equivalent to the ill-understood high-liquid-flow operation in packed towers. More importantly, our findings should prove valuable in validating improved first-principles modeling of gas-liquid flows in these industrially important devices.

  18. Flow Regime Classification and Hydrological Characterization: A Case Study of Ethiopian Rivers

    Directory of Open Access Journals (Sweden)

    Belete Berhanu

    2015-06-01

    Full Text Available The spatiotemporal variability of a stream flow due to the complex interaction of catchment attributes and rainfall induce complexity in hydrology. Researchers have been trying to address this complexity with a number of approaches; river flow regime is one of them. The flow regime can be quantified by means of hydrological indices characterizing five components: magnitude, frequency, duration, timing, and rate of change of flow. Similarly, this study aimed to understand the flow variability of Ethiopian Rivers using the observed daily flow data from 208 gauging stations in the country. With this process, the Hierarchical Ward Clustering method was implemented to group the streams into three flow regimes (1 ephemeral, (2 intermittent, and (3 perennial. Principal component analysis (PCA is also applied as the second multivariate analysis tool to identify dominant hydrological indices that cause the variability in the streams. The mean flow per unit catchment area (QmAR and Base flow index (BFI show an incremental trend with ephemeral, intermittent and perennial streams. Whereas the number of mean zero flow days ratio (ZFI and coefficient of variation (CV show a decreasing trend with ephemeral to perennial flow regimes. Finally, the streams in the three flow regimes were characterized with the mean and standard deviation of the hydrological variables and the shape, slope, and scale of the flow duration curve. Results of this study are the basis for further understanding of the ecohydrological processes of the river basins in Ethiopia.

  19. Asymptotic preserving and all-regime Lagrange-Projection like numerical schemes: application to two-phase flows in low mach regime

    International Nuclear Information System (INIS)

    Girardin, Mathieu

    2014-01-01

    Two-phase flows in Pressurized Water Reactors belong to a wide range of Mach number flows. Computing accurate approximate solutions of those flows may be challenging from a numerical point of view as classical finite volume methods are too diffusive in the low Mach regime. In this thesis, we are interested in designing and studying some robust numerical schemes that are stable for large time steps and accurate even on coarse meshes for a wide range of flow regimes. An important feature is the strategy to construct those schemes. We use a mixed implicit-explicit strategy based on an operator splitting to solve fast and slow phenomena separately. Then, we introduce a modification of a Suliciu type relaxation scheme to improve the accuracy of the numerical scheme in some regime of interest. Two approaches have been used to assess the ability of our numerical schemes to deal with a wide range of flow regimes. The first approach, based on the asymptotic preserving property, has been used for the gas dynamics equations with stiff source terms. The second approach, based on the all-regime property, has been used for the gas dynamics equations and the homogeneous two-phase flows models HRM and HEM in the low Mach regime. We obtained some robustness and stability properties for our numerical schemes. In particular, some discrete entropy inequalities are shown. Numerical evidences, in 1D and in 2D on unstructured meshes, assess the gain in term of accuracy and CPU time of those asymptotic preserving and all-regime numerical schemes in comparison with classical finite volume methods. (author) [fr

  20. A mechanistic determination of horizontal flow regime bound using void wave celerity

    Energy Technology Data Exchange (ETDEWEB)

    Park, J.W. [Ajou Univ., Suwon (Korea, Republic of)

    1995-09-01

    The two-phase flow regime boundaries in a horizontal channel has been investigated by using the behavior of the second order void wave celerities. The average two-fluid model has been constituted with closure relations for horizontally stratified and bubbly flows. A vapor phase turbulent stress model for a smooth interface geometry has been included. It is found that the second order waves (i.e., eigenvalues) propagate in opposite direction with almost the same speed when the liquid phase is stationary. Using the well-posedness limit of the two-phase system, the dispersed-stratified flow regime boundary has been modeled. Two-phase Froude number has been theoretically found to be a convenient parameter in quantifying the flow regime boundary as a function of the void fraction. It is found that interaction between void wave celerities become stronger as the two-phase Froude number is reduced. This result should be interpreted as that gravity and the relative velocity are key parameters in determining flow regime boundaries in a horizontal flow. The influence of the vapor phase turbulent stress found to stabilize the flow stratification. This study clearly shows that the average two-fluid model is very effective for a mechanistic determination of horizontal flow regimes if appropriate closure relations are developed.

  1. A mechanistic determination of horizontal flow regime bound using void wave celerity

    International Nuclear Information System (INIS)

    Park, J.W.

    1995-01-01

    The two-phase flow regime boundaries in a horizontal channel has been investigated by using the behavior of the second order void wave celerities. The average two-fluid model has been constituted with closure relations for horizontally stratified and bubbly flows. A vapor phase turbulent stress model for a smooth interface geometry has been included. It is found that the second order waves (i.e., eigenvalues) propagate in opposite direction with almost the same speed when the liquid phase is stationary. Using the well-posedness limit of the two-phase system, the dispersed-stratified flow regime boundary has been modeled. Two-phase Froude number has been theoretically found to be a convenient parameter in quantifying the flow regime boundary as a function of the void fraction. It is found that interaction between void wave celerities become stronger as the two-phase Froude number is reduced. This result should be interpreted as that gravity and the relative velocity are key parameters in determining flow regime boundaries in a horizontal flow. The influence of the vapor phase turbulent stress found to stabilize the flow stratification. This study clearly shows that the average two-fluid model is very effective for a mechanistic determination of horizontal flow regimes if appropriate closure relations are developed

  2. Two-phase interfacial area and flow regime modeling in FLOWTRAN-TF code

    International Nuclear Information System (INIS)

    Smith, F.G. III; Lee, S.Y.; Flach, G.P.; Hamm, L.L.

    1992-01-01

    FLOWTRAN-TF is a new two-component, two-phase thermal-hydraulics code to capture the detailed assembly behavior associated with loss-of-coolant accident analyses in multichannel assemblies of the SRS reactors. The local interfacial area of the two-phase mixture is computed by summing the interfacial areas contributed by each of three flow regimes. For smooth flow regime transitions, the code uses an interpolation technique in terms of component void fraction for each basic flow regime

  3. Trickle/pulse flow regime transition in downflow packed tower involving foaming liquids

    Directory of Open Access Journals (Sweden)

    Sodhi Vijay

    2012-01-01

    Full Text Available The most of past studies in foaming trickle bed reactors aimed at the improvement of efficiency and operational parameters leads to high economic advantages. Conventionally most of the industries rely on frequently used gas continuous flow (GCF where operational output is satisfactory but not yields efficiently as in pulsing flow (PF and foaming pulsing flow (FPF. Hydrodynamic characteristics like regime transitions are significantly influenced by foaming nature of liquid as well as gas and liquid flow rates. This study’s aim was to demonstrate experimentally the effects of liquid flow rate, gas flow rates and liquid surface tension on regime transition. These parameters were analyzed for the air-aqueous Sodium Lauryl Sulphate and air-water systems. More than 240 experiments were done to obtain the transition boundary for trickle flow (GCF to foaming pulsing flow (PF/FPF by use excessive foaming 15-60 ppm surfactant compositions. The trickle to pulse flow transition appeared at lower gas and liquid flow rates with decrease in liquid surface tension. All experimental data had been collected and drawn in the form of four different transitional plots which are compared and drawn by using flow coordinates proposed by different researchers. A prominent decrease in dynamic liquid saturation was observed especially during regime transitional change. The reactor two phase pressure evident a sharp rise to verify the regime transition shift from GCF to PF/FPF. Present study reveals, the regime transition boundary significantly influenced by any change in hydrodynamic as well as physiochemical properties including surface tension.

  4. Flow regime effects on non-cavitating injection nozzles over spray behavior

    Energy Technology Data Exchange (ETDEWEB)

    Payri, R., E-mail: rpayri@mot.upv.e [CMT-Motores Termicos, Universidad Politecnica de Valencia, Camino de Vera s/n, Valencia E-46022 (Spain); Salvador, F.J.; Gimeno, J.; Novella, R. [CMT-Motores Termicos, Universidad Politecnica de Valencia, Camino de Vera s/n, Valencia E-46022 (Spain)

    2011-02-15

    This paper deals with the influence of flow regime (laminar, transition or turbulent) on the internal flow behavior, and how it affects the spray development in diesel nozzles. In particular, the research described here aims at studying and quantifying the internal flow regime effects on the spray behavior. With this purpose, internal flow results, based on mass flow rate and momentum flux measurements performed on three different tapered nozzles and which helped to determine the flow regime, has been taken into account as a point of departure for the spray behavior analysis. Thus, in this work, spray macroscopic visualization tests have been performed and analyzed which clearly revealed a change in the behavior of the angle and penetration of the spray related to the change of the flow nature. Moreover, with all the experimental data available, it has been possible to relate macroscopic parameters of the spray with those describing the internal flow (momentum and effective velocity) or the geometry of the nozzle (length or diameter) through correlations.

  5. Hydrodynamic flow regimes, gas holdup, and liquid circulation in airlift reactors

    Energy Technology Data Exchange (ETDEWEB)

    Abashar, M.E.; Narsingh, U.; Rouillard, A.E.; Judd, R. [Univ. of Durban (South Africa)

    1998-04-01

    This study reports an experimental investigation into the hydrodynamic behavior of an external-loop airlift reactor (ALR) for the air-water system. Three distinct flow regimes are identified--namely homogeneous, transition, and heterogeneous regimes. The transition between homogeneous and heterogeneous flow is observed to occur over a wide range rather than being merely a single point as has been previously reported in the literature. A gas holdup correlation is developed for each flow regime. The correlations fit the experimental gas holdup data with very good accuracy (within {+-}5%). It would appear, therefore, that a deterministic equation to describe each flow regime is likely to exist in ALRs. This equation is a function of the reactor geometry and the system`s physical properties. New data concerning the axial variation of gas holdup is reported in which a minimum value is observed. This phenomenon is discussed and an explanation offered. Discrimination between two sound theoretical models--namely model 1 (Chisti et al., 1988) and model 2 (Garcia Calvo, 1989)--shows that model 1 predicts satisfactorily the liquid circulation velocity with an error of less than {+-} 10%. The good predictive features of model 1 may be due to the fact that it allows for a significant energy dissipation by wakes behind bubbles. Model 1 is now further improved by the new gas holdup correlations which are derived for the three different flow regimes.

  6. A Risk-Based Ecohydrological Approach to Assessing Environmental Flow Regimes

    Science.gov (United States)

    Mcgregor, Glenn B.; Marshall, Jonathan C.; Lobegeiger, Jaye S.; Holloway, Dean; Menke, Norbert; Coysh, Julie

    2018-03-01

    For several decades there has been recognition that water resource development alters river flow regimes and impacts ecosystem values. Determining strategies to protect or restore flow regimes to achieve ecological outcomes is a focus of water policy and legislation in many parts of the world. However, consideration of existing environmental flow assessment approaches for application in Queensland identified deficiencies precluding their adoption. Firstly, in managing flows and using ecosystem condition as an indicator of effectiveness, many approaches ignore the fact that river ecosystems are subjected to threatening processes other than flow regime alteration. Secondly, many focus on providing flows for responses without considering how often they are necessary to sustain ecological values in the long-term. Finally, few consider requirements at spatial-scales relevant to the desired outcomes, with frequent focus on individual places rather than the regions supporting sustainability. Consequently, we developed a risk-based ecohydrological approach that identifies ecosystem values linked to desired ecological outcomes, is sensitive to flow alteration and uses indicators of broader ecosystem requirements. Monitoring and research is undertaken to quantify flow-dependencies and ecological modelling is used to quantify flow-related ecological responses over an historical flow period. The relative risk from different flow management scenarios can be evaluated at relevant spatial-scales. This overcomes the deficiencies identified above and provides a robust and useful foundation upon which to build the information needed to support water planning decisions. Application of the risk assessment approach is illustrated here by two case studies.

  7. Precise Void Fraction Measurement in Two-phase Flows Independent of the Flow Regime Using Gamma-ray Attenuation

    Directory of Open Access Journals (Sweden)

    E. Nazemi

    2016-02-01

    Full Text Available Void fraction is an important parameter in the oil industry. This quantity is necessary for volume rate measurement in multiphase flows. In this study, the void fraction percentage was estimated precisely, independent of the flow regime in gas–liquid two-phase flows by using γ-ray attenuation and a multilayer perceptron neural network. In all previous studies that implemented a multibeam γ-ray attenuation technique to determine void fraction independent of the flow regime in two-phase flows, three or more detectors were used while in this study just two NaI detectors were used. Using fewer detectors is of advantage in industrial nuclear gauges because of reduced expense and improved simplicity. In this work, an artificial neural network is also implemented to predict the void fraction percentage independent of the flow regime. To do this, a multilayer perceptron neural network is used for developing the artificial neural network model in MATLAB. The required data for training and testing the network in three different regimes (annular, stratified, and bubbly were obtained using an experimental setup. Using the technique developed in this work, void fraction percentages were predicted with mean relative error of <1.4%.

  8. Flow regime identification methodology with MCNP-X code and artificial neural network

    International Nuclear Information System (INIS)

    Salgado, Cesar M.; Instituto de Engenharia Nuclear; Schirru, Roberto; Brandao, Luis E.B.; Pereira, Claudio M.N.A.

    2009-01-01

    This paper presents flow regimes identification methodology in multiphase system in annular, stratified and homogeneous oil-water-gas regimes. The principle is based on recognition of the pulse height distributions (PHD) from gamma-ray with supervised artificial neural network (ANN) systems. The detection geometry simulation comprises of two NaI(Tl) detectors and a dual-energy gamma-ray source. The measurement of scattered radiation enables the dual modality densitometry (DMD) measurement principle to be explored. Its basic principle is to combine the measurement of scattered and transmitted radiation in order to acquire information about the different flow regimes. The PHDs obtained by the detectors were used as input to ANN. The data sets required for training and testing the ANN were generated by the MCNP-X code from static and ideal theoretical models of multiphase systems. The ANN correctly identified the three different flow regimes for all data set evaluated. The results presented show that PHDs examined by ANN may be applied in the successfully flow regime identification. (author)

  9. Lava Fountaining Discharge Regime driven by Slug-to-Churn Flow Transition. (Invited)

    Science.gov (United States)

    Ripepe, M.; Pioli, L.; Marchetti, E.; Ulivieri, G.

    2013-12-01

    Lava fountaining episodes at Etna volcano appear characterized by the transition between Strombolian and Hawaiian end-member eruptive styles. There is no evidence for this transition in the seismic (i.e. seismic tremor) signal. However, infrasonic records provide unprecedented evidence on this flow transition. Each eruptive episode is characterized by distinctive common trend in the amplitude, waveform and frequency content of the infrasonic wavefield, which evidences the shift from discrete, and transient, strombolian to sustained, and oscillatory, lava fountain dynamics. Large scale experiments on the dynamics of two-phase flow of basaltic magmas show how the transition between different regimes mainly depends on gas volume flow, which in turn controls pressure distribution within the conduit and also magma vesicularity. In particular, while regular large bubble bursting is associated with slug flow regime, large amplitude and low frequency column oscillations are associated with churn flow. In large pipes, transition from slug to churn flow regime is independent on conduit diameter and it is reached at high superficial gas velocity. Lava fountaining episodes at Etna can be thus interpreted as induced by the transition from the slug (discrete strombolian) to churn flow (sustained lava fountain) regimes that is reflecting an increase in the gas discharge rate. Based on laboratory experiments, we calculate that transition between these two end-member explosive regimes at Etna occurs when gas superficial velocity is 76 m/s for near-the-vent stagnant magma conditions.

  10. Flow regimes in a T-mixer operating with a binary mixture

    Science.gov (United States)

    Camarri, Simone; Siconolfi, Lorenzo; Galletti, Chiara; Salvetti, Maria Vittoria

    2015-11-01

    Efficient mixing in small volumes is a key target in many processes. Among the most common micro-devices, passive T-shaped micro-mixers are widely used. For this reason, T-mixers have been studied in the literature and its working flow regimes have been identified. However, in most of the available theoretical studies it is assumed that only one working fluid is used, i.e. that the same fluid at the same thermodynamic conditions is entering the two inlet conduits of the mixer. Conversely, the practical use of micro-devices often involves the mixing of two different fluids or of the same fluid at different thermodynamic conditions. In this case flow regimes significantly different than those observed for a single working fluid may occur. The present work aims at investigating the flow regimes in a T-mixers when water at two different temperatures, i.e. having different viscosity and density, is entering the mixer. The effect of the temperature difference on the flow regimes in a 3D T-mixer is investigated by DNS and stability analysis and the results are compared to the case in which a single working fluid is employed.

  11. Flow measurement in bubbly and slug flow regimes using the electromagnetic flowmeter developed

    International Nuclear Information System (INIS)

    Cha, Jae Eun; Ahn, Yeh Chan; Seo, Kyung Woo; Kim, Moo Hwan

    2002-01-01

    In order to investigate the characteristics of electromagnetic flowmeter in two-phase flow, an AC electromagnetic flowmeter was designed and manufactured. In various flow conditions, the signals and noises from the flowmeter were obtained and analyzed by comparison with the observed flow patterns with a high speed CCD camera. The experiment with the void simulators in which rod shaped non-conducting material was used was carried out to investigate the effect of the bubble position and the void fraction on the flowmeter. Based on the results from the void simulator, two-phase flow experiments encompassed from bubbly to slug flow regime were conducted. The simple relation ΔU TP = ΔU SP /(1-α) was verified with measurements of the potential difference and the void fraction. Due to the lack of homogeneity in a real two-phase flow, the discrepancy between the relation and the present measurement was slightly increased with void fraction and also liquid volumetric flux j f . Whereas there is no difference in the shape of the raw signal between single-phase flow and bubbly flow, the signal amplitude for bubbly flow is higher than that for single-phase flow at the same water flow rate, since the passage area of the water flow is reduced. In the case of slug flow, the phase and the amplitude of the flowmeter output show dramatically the flow characteristics around each slug bubble and the position of a slug bubble itself. Therefore, the electromagnetic flowmeter shows a good possibility of being useful for identifying the flow regimes

  12. Altered stream-flow regimes and invasive plant species: The Tamarix case

    Science.gov (United States)

    Stromberg, J.C.; Lite, S.J.; Marler, R.; Paradzick, C.; Shafroth, P.B.; Shorrock, D.; White, J.M.; White, M.S.

    2007-01-01

    Aim: To test the hypothesis that anthropogenic alteration of stream-flow regimes is a key driver of compositional shifts from native to introduced riparian plant species. Location: The arid south-western United States; 24 river reaches in the Gila and Lower Colorado drainage basins of Arizona. Methods: We compared the abundance of three dominant woody riparian taxa (native Populus fremontii and Salix gooddingii, and introduced Tamarix) between river reaches that varied in stream-flow permanence (perennial vs. intermittent), presence or absence of an upstream flow-regulating dam, and presence or absence of municipal effluent as a stream water source. Results: Populus and Salix were the dominant pioneer trees along the reaches with perennial flow and a natural flood regime. In contrast, Tamarix had high abundance (patch area and basal area) along reaches with intermittent stream flows (caused by natural and cultural factors), as well as those with dam-regulated flows. Main conclusions: Stream-flow regimes are strong determinants of riparian vegetation structure, and hydrological alterations can drive dominance shifts to introduced species that have an adaptive suite of traits. Deep alluvial groundwater on intermittent rivers favours the deep-rooted, stress-adapted Tamarix over the shallower-rooted and more competitive Populus and Salix. On flow-regulated rivers, shifts in flood timing favour the reproductively opportunistic Tamarix over Populus and Salix, both of which have narrow germination windows. The prevailing hydrological conditions thus favour a new dominant pioneer species in the riparian corridors of the American Southwest. These results reaffirm the importance of reinstating stream-flow regimes (inclusive of groundwater flows) for re-establishing the native pioneer trees as the dominant forest type. ?? 2007 The Authors Journal compilation ?? 2007 Blackwell Publishing Ltd.

  13. Regimes of flow past a vortex generator

    DEFF Research Database (Denmark)

    Velte, Clara Marika; Okulov, V.L.; Naumov, I.V.

    2012-01-01

    A complete parametric investigation of the development of multi-vortex regimes in a wake past simple vortex generator has been carried out. It is established that the vortex structure in the wake is much more complicated than a simple monopole tip vortex. The vortices were studied by stereoscopic...... particle image velocimetry (SPIV). Based on the obtained SPIV data, a map of the regimes of flow past the vortex generator has been constructed. One region with a developed stable multivortex system on this map reaches the vicinity of the optimum angle of attack of the vortex generator....

  14. A Framework to Assess the Cumulative Hydrological Impacts of Dams on flow Regime

    Science.gov (United States)

    Wang, Y.; Wang, D.

    2016-12-01

    In this study we proposed a framework to assess the cumulative impact of dams on hydrological regime, and the impacts of the Three Gorges Dam on flow regime in Yangtze River were investigated with the framework. We reconstructed the unregulated flow series to compare with the regulated flow series in the same period. Eco-surplus and eco-deficit and the Indicators of Hydrologic Alteration parameters were used to examine the hydrological regime change. Among IHA parameters, Wilcoxon signed-rank test and Principal Components Analysis identified the representative indicators of hydrological alterations. Eco-surplus and eco-deficit showed that the reservoir also changed the seasonal regime of the flows in autumn and winter. Annual extreme flows and October flows changes lead to negative ecological implications downstream from the Three Gorges Dam. Ecological operation for the Three Gorges Dam is necessary to mitigate the negative effects on the river ecosystem in the middle reach of Yangtze River. The framework proposed here could be a robust method to assess the cumulative impacts of reservoir operation.

  15. Void fraction and flow regime determination by optical probe for boiling two-phase flow in a tube subchannel

    International Nuclear Information System (INIS)

    Cheng Huiping; Wu Hongtao; Ba Changxi; Yan Xiaoming; Huang Suyi

    1995-12-01

    In view of the need to determine void fraction and flow regime of vapor-liquid two-phase flow in the steam generator test model, domestic made optical probe was applied on a small-scale freon two-phase flow test rig. Optical probe signals were collected at a sampling rate up to 500 Hz and converted into digital form. Both the time signal, and the amplitude probability density function and FFT spectrum function calculated thereof were analysed in the time and frequency domains respectively. The threshold characterizing vapor or liquid contact with the probe tip was determined from the air-water two-phase flow pressure drop test results. Then, the boiling freon two-phase flow void fraction was determined by single threshold method, and compared with numerical heat transfer computation. Typical patterns which were revealed by the above-mentioned time signal and the functions were found corresponding to distinct flow regimes, as corroborated by visual observation. The experiment shows that the optical probe was a promising technique for two-phase flow void fraction measurement and flow regime identification (3 refs., 15 figs., 1 tab.)

  16. Characterizing effects of hydropower plants on sub-daily flow regimes

    Science.gov (United States)

    Bejarano, María Dolores; Sordo-Ward, Álvaro; Alonso, Carlos; Nilsson, Christer

    2017-07-01

    A characterization of short-term changes in river flow is essential for understanding the ecological effects of hydropower plants, which operate by turning the turbines on or off to generate electricity following variations in the market demand (i.e., hydropeaking). The goal of our study was to develop an approach for characterizing the effects of hydropower plant operations on within-day flow regimes across multiple dams and rivers. For this aim we first defined ecologically meaningful metrics that provide a full representation of the flow regime at short time scales from free-flowing rivers and rivers exposed to hydropeaking. We then defined metrics that enable quantification of the deviation of the altered short-term flow regime variables from those of the unaltered state. The approach was successfully tested in two rivers in northern Sweden, one free-flowing and another regulated by cascades of hydropower plants, which were additionally classified based on their impact on short-term flows in sites of similar management. The largest differences between study sites corresponded to metrics describing sub-daily flow magnitudes such as amplitude (i.e., difference between the highest and the lowest hourly flows) and rates (i.e., rise and fall rates of hourly flows). They were closely followed by frequency-related metrics accounting for the numbers of within-day hourly flow patterns (i.e., rises, falls and periods of stability of hourly flows). In comparison, between-site differences for the duration-related metrics were smallest. In general, hydropeaking resulted in higher within-day flow amplitudes and rates and more but shorter periods of a similar hourly flow patterns per day. The impacted flow feature and the characteristics of the impact (i.e., intensity and whether the impact increases or decreases whatever is being described by the metric) varied with season. Our approach is useful for catchment management planning, defining environmental flow targets

  17. Dynamics of baroclinic wave pattern in transition zones between different flow regimes

    International Nuclear Information System (INIS)

    Larcher, Thomas von; Egbers, Christoph

    2005-01-01

    Baroclinic waves, both steady and time-dependent, are studied experimentally in a differentially heated rotating cylindrical gap with a free surface, cooled from within. Water is used as working fluid. We focus especially on transition zones between different flow regimes, where complex flow pattern like mixed-mode states are found. The transition from steady wave regime to irregular flow is also of particular interest. The surface flow is observed with visualisation techniques. Velocity time series are measured with the optical laser-Doppler-velocimetry technique. Thermographic measurements are applied for temperature field visualisations

  18. The impact of interpreted flow regimes during constant head injection tests on the estimated transmissivity from injection tests and difference flow logging

    Energy Technology Data Exchange (ETDEWEB)

    Hjerne, Calle; Ludvigsson, Jan-Erik; Harrstroem, Johan [Geosigma AB, Uppsala (Sweden)

    2013-04-15

    A large number of constant head injection tests were carried out in the site investigation at Forsmark using the Pipe String System, PSS3. During the original evaluation of the tests the dominating transient flow regimes during both the injection and recovery period were interpreted together with estimation of hydraulic parameters. The flow regimes represent different flow and boundary conditions during the tests. Different boreholes or borehole intervals may display different distributions of flow regimes. In some boreholes good agreement was obtained between the results of the injection tests and difference flow logging with Posiva flow log (PFL) but in other boreholes significant discrepancies were found. The main objective of this project is to study the correlation between transient flow regimes from the injection tests and other borehole features such as transmissivity, depth, geology, fracturing etc. Another subject studied is whether observed discrepancies between estimated transmissivity from difference flow logging and injection tests can be correlated to interpreted flow regimes. Finally, a detailed comparison between transient and stationary evaluation of transmissivity from the injection tests in relation to estimated transmissivity from PFL tests in corresponding sections is made. Results from previous injection tests in 5 m sections in boreholes KFM04, KFM08A and KFM10A were used. Only injection tests above the (test-specific) measurement limit regarding flow rate are included in the analyses. For all of these tests transient flow regimes were interpreted. In addition, results from difference flow logging in the corresponding 5 m test sections were used. Finally, geological data of fractures together with rock and fracture zone properties have been used in the correlations. Flow regimes interpreted from the injection period of the tests are generally used in the correlations but deviations between the interpreted flow regimes from the injection and

  19. The difficult challenge of a two-phase CFD modelling for all flow regimes

    International Nuclear Information System (INIS)

    Bestion, D.

    2014-01-01

    Highlights: • The theoretical difficulties for modelling all flow regimes at CFD scale are identified. • The choice of the number of fields and of the time and space averaging or filtering are discussed and clarified. • Closure issues related to an all flow regime CFD model are listed and the main difficulties are identified. - Abstract: System thermalhydraulic codes model all two-phase flow regimes but they are limited to a macroscopic description. Two-phase CFD tools predict two-phase flow with a much finer space resolution but the current modelling capabilities are limited to dispersed bubbly or droplet flow and separate-phase flow. Much less experience exists on more complex flow regimes which combine the existence of dispersed fields with the presence of large interfaces such as a free surface or a film surface. A list of possible reactor issues which might benefit from an “all flow regime CFD model” is given. The first difficulty is to identify the various types of local flow configuration. It is shown that a 4-field model has much better capabilities than a two-fluid approach to identify most complex regimes. Then the choice between time averaging, space averaging, or even ensemble averaging is discussed. It is shown that only the RANS-2-fluid and a space-filtered 4-field model may be reasonably envisaged. The latter has the capabilities to identify all types of interfaces and should be privileged if a good accuracy is expected or if time fluctuations in intermittent flow have to be predicted while the former may be used when a high accuracy is not necessary and if time fluctuations in intermittent flow are not of interest. Finally the closure issue is presented including wall transfers, interfacial transfers, mass transfers between dispersed and continuous fields, and turbulent transfers. An important effort is required to model all interactions between sub-filter phenomena and the transfers from the sub-filter domain to the simulated domain. The

  20. Fluid flows of mixed regimes in porous media

    Science.gov (United States)

    Celik, Emine; Hoang, Luan; Ibragimov, Akif; Kieu, Thinh

    2017-02-01

    In porous media, there are three known regimes of fluid flows, namely, pre-Darcy, Darcy, and post-Darcy. Because of their different natures, these are usually treated separately in the literature. To study complex flows when all three regimes may be present in different portions of a same domain, we use a single equation of motion to unify them. Several scenarios and models are then considered for slightly compressible fluids. A nonlinear parabolic equation for the pressure is derived, which is degenerate when the pressure gradient is either small or large. We estimate the pressure and its gradient for all time in terms of initial and boundary data. We also obtain their particular bounds for large time which depend on the asymptotic behavior of the boundary data but not on the initial one. Moreover, the continuous dependence of the solutions on initial and boundary data and the structural stability for the equation are established.

  1. Couette flow regimes with heat transfer in rarefied gas

    Energy Technology Data Exchange (ETDEWEB)

    Abramov, A. A., E-mail: alabr54@mail.ru; Butkovskii, A. V., E-mail: albutkov@mail.ru [Zhukovski Central Aerohydrodynamics Institute (Russian Federation)

    2013-06-15

    Based on numerical solution of the Boltzmann equation by direct statistic simulation, the Couette flow with heat transfer is studied in a broad range of ratios of plate temperatures and Mach numbers of a moving plate. Flow regime classification by the form of the dependences of the energy flux and friction stress on the Knudsen number Kn is proposed. These dependences can be simultaneously monotonic and nonmonotonic and have maxima. Situations are possible in which the dependence of the energy flux transferred to a plate on Kn has a minimum, while the dependence of the friction stress is monotonic or even has a maximum. Also, regimes exist in which the dependence of the energy flux on Kn has a maximum, while the dependence of the friction stress is monotonic, and vice versa.

  2. Anthropogenic Water Uses and River Flow Regime Alterations by Dams

    Science.gov (United States)

    Ferrazzi, M.; Botter, G.

    2017-12-01

    Dams and impoundments have been designed to reconcile the systematic conflict between patterns of anthropogenic water uses and the temporal variability of river flows. Over the past seven decades, population growth and economic development led to a marked increase in the number of these water infrastructures, so that unregulated free-flowing rivers are now rare in developed countries and alterations of the hydrologic cycle at global scale have to be properly considered and characterized. Therefore, improving our understanding of the influence of dams and reservoirs on hydrologic regimes is going to play a key role in water planning and management. In this study, a physically based analytic approach is combined to extensive hydrologic data to investigate natural flow regime alterations downstream of dams in the Central-Eastern United States. These representative case studies span a wide range of different uses, including flood control, water supply and hydropower production. Our analysis reveals that the most evident effects of flood control through dams is a decrease in the intra-seasonal variability of flows, whose extent is controlled by the ratio between the storage capacity for flood control and the average incoming streamflow. Conversely, reservoirs used for water supply lead to an increase of daily streamflow variability and an enhanced inter-catchment heterogeneity. Over the last decades, the supply of fresh water required to sustain human populations has become a major concern at global scale. Accordingly, the number of reservoirs devoted to water supply increased by 50% in the US. This pattern foreshadows a possible shift in the cumulative effect of dams on river flow regimes in terms of inter-catchment homogenization and intra-annual flow variability.

  3. Enstrophy transport conditional on local flow topologies in different regimes of premixed turbulent combustion

    KAUST Repository

    Papapostolou, Vassilios

    2017-09-11

    Enstrophy is an intrinsic feature of turbulent flows, and its transport properties are essential for the understanding of premixed flame-turbulence interaction. The interrelation between the enstrophy transport and flow topologies, which can be assigned to eight categories based on the three invariants of the velocity-gradient tensor, has been analysed here. The enstrophy transport conditional on flow topologies in turbulent premixed flames has been analysed using a Direct Numerical Simulation database representing the corrugated flamelets (CF), thin reaction zones (TRZ) and broken reaction zones (BRZ) combustion regimes. The flame in the CF regime exhibits considerable flame-generated enstrophy, and the dilatation rate and baroclinic torque contributions to the enstrophy transport act as leading order sink and source terms, respectively. Consequently, flow topologies associated with positive dilatation rate values, contribute significantly to the enstrophy transport in the CF regime. By contrast, enstrophy decreases from the unburned to the burned gas side for the cases representing the TRZ and BRZ regimes, with diminishing influences of dilatation rate and baroclinic torque. The enstrophy transport in the TRZ and BRZ regimes is governed by the vortex-stretching and viscous dissipation contributions, similar to non-reacting flows, and topologies existing for all values of dilatation rate remain significant contributors.

  4. Implicit gas-kinetic unified algorithm based on multi-block docking grid for multi-body reentry flows covering all flow regimes

    Science.gov (United States)

    Peng, Ao-Ping; Li, Zhi-Hui; Wu, Jun-Lin; Jiang, Xin-Yu

    2016-12-01

    Based on the previous researches of the Gas-Kinetic Unified Algorithm (GKUA) for flows from highly rarefied free-molecule transition to continuum, a new implicit scheme of cell-centered finite volume method is presented for directly solving the unified Boltzmann model equation covering various flow regimes. In view of the difficulty in generating the single-block grid system with high quality for complex irregular bodies, a multi-block docking grid generation method is designed on the basis of data transmission between blocks, and the data structure is constructed for processing arbitrary connection relations between blocks with high efficiency and reliability. As a result, the gas-kinetic unified algorithm with the implicit scheme and multi-block docking grid has been firstly established and used to solve the reentry flow problems around the multi-bodies covering all flow regimes with the whole range of Knudsen numbers from 10 to 3.7E-6. The implicit and explicit schemes are applied to computing and analyzing the supersonic flows in near-continuum and continuum regimes around a circular cylinder with careful comparison each other. It is shown that the present algorithm and modelling possess much higher computational efficiency and faster converging properties. The flow problems including two and three side-by-side cylinders are simulated from highly rarefied to near-continuum flow regimes, and the present computed results are found in good agreement with the related DSMC simulation and theoretical analysis solutions, which verify the good accuracy and reliability of the present method. It is observed that the spacing of the multi-body is smaller, the cylindrical throat obstruction is greater with the flow field of single-body asymmetrical more obviously and the normal force coefficient bigger. While in the near-continuum transitional flow regime of near-space flying surroundings, the spacing of the multi-body increases to six times of the diameter of the single

  5. Cellular properties of slug flow in vertical co-current gas-liquid flow: slug-churn transition; Caracteristiques cellulaires du regime a poches en ecoulement gaz-liquide co-courant vertical. Transition vers le regime destructure

    Energy Technology Data Exchange (ETDEWEB)

    Lusseyran, Francois

    1990-12-13

    This research thesis reports the study and description of the structure of a slug flow regime in a co-current vertical cylindrical duct, and the characterization and prediction of its transition towards a slug-churn (de-structured) regime. Flow physical mechanisms highlighted by the measurement of two important dynamics variables (wall friction and thickness of liquid films) are related to hypotheses of cellular models. The author first proposes an overview of slug flow regimes: theoretical steady and one-dimensional analysis, mass assessment equations of cellular models, application to the assessment of the flow rate and of the thickness of the film surrounding the gas slug. In the second part, the author addresses the slug flow regime transition towards the slug-churn regime: assessment of the evolution of flow dynamic properties, use of average wall friction analysis to obtain a relevant transition criterion. The third part presents experimental conditions, and measurement methods: conductometry for thickness measurement, polarography for wall friction measurement, and gas phase detection by using an optic barrier or optic fibres [French] Les ecoulements gaz-liquide en conduite verticale presentent quatre configurations ou regimes d'ecoulement. Ce travail porte sur le regime a poches et sur la transition vers la configuration qui lui succede: le regime destructure (churn flow). Les mesures sont effectuees a 200D du point d'injection du gaz, dans une conduite de 12.2 mm de diametre et pour le couple de fluides eau-azote. Les deux principales grandeurs mesurees en fonction des flux d'entree sont: le frottement parietal instantane (methode electrochimique) et l'epaisseur de film instantanee (methode conductimetrique). Une detection optique simultanee de la presence des phases permet un traitement conditionnel de la base de donnees. Les caracteristiques de la cellule moyenne representative de chaque point de fonctionnement en sont deduites: longueur de la cellule

  6. Characterization of flow regimes in the post-dryout region

    International Nuclear Information System (INIS)

    Obot, N.T.; Ishii, M.

    1988-01-01

    A visual study of film boiling using photographic and high speed motion-picture methods was carried out to determine the flow regime transition criteria in the post-CHF region. An idealized inverted annular flow was obtained by introducing a liquid jet of Freon 113 through a nozzle, precisely centered with respect to the internal diameter of the test section, with an annual gas flow. The respective ranges for liquid and gas exit velocities were 0.05-0.5 and 0.03-8.2 m/s. Nitrogen and helium were used in the study

  7. Angra 2 small break LOCA flow regime identification through RELAP5 code

    Energy Technology Data Exchange (ETDEWEB)

    Rocha, Marcelo da Silva; Sabundjian, Gaiane; Belchior Junior, Antonio; Andrade, Delvonei Alves de; Torres, Walmir Maximo; Conti, Thadeu das Neves; Macedo, Luiz Alberto; Umbehaun, Pedro Ernesto; Mesquita, Roberto Navarro de; Masotti, Paulo Henrique Ferraz, E-mail: msrocha@ipen.br, E-mail: gdjian@ipen.br, E-mail: abelchior@ipen.br, E-mail: delvonei@ipen.br, E-mail: wmtorres@ipen.br, E-mail: tnconti@ipen.br, E-mail: lamacedo@ipen.br, E-mail: umbehaun@ipen.br, E-mail: s, E-mail: rnavarro@ipen.br, E-mail: pmasotti@ipen.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)

    2012-07-01

    The purpose of this paper is to identify the flow regimes in the core of Angra 2 nuclear reactor with RELAP5/MOD3.2.gamma code (RELAP5, 2001). The postulated accident is the loss of coolant through a small break in the primary circuit (SBLOCA), which is described in Chapter 15 of the Final Safety Analysis Report of Angra 2 - FSAR (ETN, 2006). As the primary circuit pressure decreases due to the loss of coolant, several alternating two phase flow regimes are established in the primary circuit. This paper analyses the coolant two-phase flow behavior in the nuclear reactor core during the postulated accident. (author)

  8. Flow regimes in a trapped vortex cell

    Science.gov (United States)

    Lasagna, D.; Iuso, G.

    2016-03-01

    This paper presents results of an experimental investigation on the flow in a trapped vortex cell, embedded into a flat plate, and interacting with a zero-pressure-gradient boundary layer. The objective of the work is to describe the flow features and elucidate some of the governing physical mechanisms, in the light of recent investigations on flow separation control using vortex cells. Hot-wire velocity measurements of the shear layer bounding the cell and of the boundary layers upstream and downstream are reported, together with spectral and correlation analyses of wall-pressure fluctuation measurements. Smoke flow visualisations provide qualitative insight into some relevant features of the internal flow, namely a large-scale flow unsteadiness and possible mechanisms driving the rotation of the vortex core. Results are presented for two very different regimes: a low-Reynolds-number case where the incoming boundary layer is laminar and its momentum thickness is small compared to the cell opening, and a moderately high-Reynolds-number case, where the incoming boundary layer is turbulent and the ratio between the momentum thickness and the opening length is significantly larger than in the first case. Implications of the present findings to flow control applications of trapped vortex cells are also discussed.

  9. Flow over an obstruction with the generation of nonlinear waves on the free surface: Limiting regimes

    International Nuclear Information System (INIS)

    Maklakov, D.V.

    1995-01-01

    A numerical-analytic method of calculating a subcritical flow over an obstruction is proposed. This method is based on the identification of the asymptotics of the behavior of a wave train in unknown functions. The method makes it possible to calculate both steep and long waves. The effectiveness of the method is demonstrated for the problem of flow over a vortex. The concept of the limiting flow regime as a regime with the maximum value of the perturbation parameter for which steady flow still persists is introduced. Various types of the limiting regimes obtained in the calculations are analyzed

  10. Interfacial area concentration in gas–liquid bubbly to churn-turbulent flow regime

    International Nuclear Information System (INIS)

    Ozar, B.; Dixit, A.; Chen, S.W.; Hibiki, T.; Ishii, M.

    2012-01-01

    Highlights: ► A systematic approach to predict the interfacial area concentration is presented. ► Two group approach for categorizing bubbles is used. ► Prediction of Group-1 bubble size and void fraction are key elements of this work. ► The proposed approach compares well with selected databases. - Abstract: There are very few established correlations to predict the interfacial area concentration beyond the bubbly flow regime in cap-slug and churn-turbulent flow regimes. Present study shows a systematic approach to estimate the interfacial area concentration in bubbly, cap-slug and churn-turbulent flow regimes. Ishii and Mishima’s (1980) formulation and the two group approach for categorizing bubbles (Group-1: spherical or distorted bubble, Group-2: cap bubble) are used to estimate the interfacial area concentration. The key parameters in this framework are the estimation of Group-1 bubble size and the amount of void in the liquid slug, which is a function of Group-1 void fraction. Hibiki and Ishii’s (2002) correlation is utilized to predict the size of the Group-1 bubbles. A correlation is developed to estimate the Group-1 void fraction. The developed model for the estimation of interfacial area concentration is compared with the three existing datasets. These are data for air–water flow taken in annular geometry and round tube and also for air–NaOH solution taken in round tube. The estimation accuracies for these data sets are ±36.4%, ±26.5% and ±37.4%, respectively. These datasets cover a wide range of flow regimes and different physical properties.

  11. Flow regime analysis for fluid injection into a confined aquifer: implications for CO2 sequestration

    Science.gov (United States)

    Guo, B.; Zheng, Z.; Celia, M. A.; Stone, H.

    2015-12-01

    Carbon dioxide injection into a confined saline aquifer may be modeled as an axisymmetric two-phase flow problem. Assuming the two fluids segregate in the vertical direction due to strong buoyancy, and neglecting capillary pressure and miscibility, the lubrication approximation leads to a nonlinear advection-diffusion equation that describes the evolution of the sharp fluid-fluid interface. The flow behaviors in the system are controlled by two dimensionless groups: M, the viscosity ratio of the displaced fluid relative to injected fluid, and Γ , the gravity number, which represents the relative importance of buoyancy and fluid injection. Four different analytical solutions can be derived as the asymptotic approximations, representing specific values of the parameter pairs. The four solutions correspond to: (1) Γ 1; and (4) Γ >> 1, any M values. The first two of these solutions are new, while the third corresponds to the solution of Nordbotten and Celia (2006) for confined injections and the fourth corresponds to the solution of (Lyle et al., 2005) for gravity currents in an unconfined aquifer. Overall, the various axisymmetric flows can be summarized in a Γ-M regime diagram with five distinct dynamic behaviors including the four asymptotic regimes and an intermediate regime (Fig. 1). Data from a number of CO2 injection sites around the world can be used to compute the two dimensionless groups Γ and M associated with each injection. When plotted on the regime diagram, these values show the flow behavior for each injection and how the values vary from site to site. For all the CO2 injections, M is always larger than 1, while Γ can range from 0.01 up to 100. The pairs of (Γ, M) with lower Γ values correspond to solution (3), while the ones with higher Γ values can move up to the intermediate regime and the flow regime for solution (4). The higher values of Γ correspond to pilot-scale injections with low injection rates; most industrial-scale injection

  12. Flow regime mapping of vertical two-phase downflow in a ribbed annulus

    International Nuclear Information System (INIS)

    Kielpinski, A.L.

    1992-01-01

    Two-phase flow regimes have been mapped for vertical, cocurrent downflow in a narrow annulus which is partially segmented by the presence of longitudinal ribs. This geometry and flow condition has application to the analysis of a Large-Break Loss of Coolant Accident (LB-LOCA) in the production K-Reactor at the Savannah River Site (SRS). The ribbed annular geometry, particularly the presence of non-sealing ribs, gives rise to some unique phenomenological features. The flow behavior is influenced by the partial segmentation of the annulus into four quadrants or subchannels. A random element is induced by the natural bowing of the slender tubes; the width of the azimuthal flow path between two subchannels at a given axial location is indeterminate, and can take on any value between zero and the maximum clearance of 7.6 x l0 -4 m. When the rib gap is zero at a given location, it is at a maximum 180P away at the same axial location. The range of rib gaps is spanned in a single test section, as it would be also in a reactor assembly. As a result of these effects, flow regime maps obtained by other researchers for downflow in annuli are not accurate for defining flow regimes in a ribbed annulus. Flow regime transitions similar to those noted by, e.g., Bamea, were observed; the locations of these transitions were displaced with respect to the transition equations derived by Bamea. Experimental bubble rise velocity measurements were also obtained in the same test section. The bubble rise velocities were much higher than expected from the theory developed for slug bubbles in tubes, unribbed annuli, and rectangular channels. An elliptical-cap bubble rises faster than a slug bubble of the same area. Large, slug-shaped bubbles injected into the test section were observed to reduce in size as they rose, due to interaction with a longitudinal rib. They thereby adopted a shape more like an elliptical-cap bubble, hence rising faster than the original slug bubble

  13. Two-Phase Flow Regimes and Discharge Characteristics of a Plasma Electrohydrodynamic Atomization

    International Nuclear Information System (INIS)

    Sun Ming; Borocilo, D.; Harvel, G. D.; Chang, J. S.; Ibe, M.; Matsubara, H.; Hirata, H.; Fanson, P.

    2011-01-01

    Experimental investigation was conducted to study the flow regimes and discharge characteristics of plasma electrohydrodynamic atomization (EHDA) for decane (C 10 H 22 ) under pulsed applied negative voltage. The experimental parameters were set as the flow rate of decane from 0 mL/min to 10 mL/min and the DC charging voltage from DC 0 V to 12 V with a pulse repetition rates of 200 Hz. The flow regime of decane was observed and the volume-to-electrical charge ratio was measured. Unlike a conventional EHDA system, the results show that a corona discharge was initiated at the edge of the hollow electrode at a specific corona on-set voltage of -17 kV or -20 kV in the case with or without decane flow, respectively. This phenomenon was defined as plasma EHDA.

  14. Characterisation of two-phase horizontal flow regime transition by the application of time-frequency analysis methods

    International Nuclear Information System (INIS)

    Seleghim, Paulo

    1996-01-01

    This work concerns the development of a methodology which objective is to characterize and diagnose two-phase flow regime transitions. The approach is based on the fundamental assumption that a transition flow is less stationary than a flow with an established regime. In a first time, the efforts focused on: 1) the design and construction of an experimental loop, allowing to reproduce the main horizontal two-phase flow patterns, in a stable and controlled way, 2) the design and construction of an electrical impedance probe, providing an imaged information of the spatial phase distribution in the pipe, the systematic study of the joint time-frequency and time-scale analysis methods, which permitted to define an adequate parameter quantifying the un-stationary degree. In a second time, in order to verify the fundamental assumption, a series of experiments were conducted, which objective was to demonstrate the correlation between un-stationary and regime transition. The un-stationary degree was quantified by calculating the Gabor's transform time-frequency covariance of the impedance probe signals. Furthermore, the phenomenology of each transition was characterized by the joint moments and entropy. The results clearly show that the regime transitions are correlated with local-time frequency covariance peaks, which demonstrates that these regime transitions are characterized by a loss of stationarity. Consequently, the time-frequency covariance constitutes an objective two-phase flow regime transition indicator. (author) [fr

  15. Implications of climate change on flow regime affecting Atlantic salmon

    Directory of Open Access Journals (Sweden)

    2007-01-01

    Full Text Available The UKCIP02 climate change scenarios (2070–2100 suggest that the UK climate will become warmer (an overall increase of 2.5–3°C, with temperature increases being greater in the summer and autumn than in the spring and winter seasons. In terms of precipitation, winters are expected to become wetter and summers drier throughout the UK. The effect of changes in the future climate on flow regimes are investigated for the Atlantic salmon, Salmo salar, in a case study in an upland UK river. Using a hydraulic modelling approach, flows simulated across the catchment are assessed in terms of hydraulic characteristics (discharge per metre width, flow depths, flow velocities and Froude number. These, compared with suitable characteristics published in the literature for various life stages of Atlantic salmon, enable assessment of habitat suitability. Climate change factors have been applied to meteorological observations in the Eden catchment (north-west England and effects on the flow regime have been investigated using the SHETRAN hydrological modelling system. High flows are predicted to increase by up to 1.5%; yet, a greater impact is predicted from decreasing low flows (e.g. a Q95 at the outlet of the study catchment may decrease to a Q85 flow. Reliability, Resilience and Vulnerability (RRV analysis provides a statistical indication of the extent and effect of such changes on flows. Results show that future climate will decrease the percentage time the ideal minimum physical habitat requirements will be met. In the case of suitable flow depth for spawning activity at the outlet of the catchment, the percentage time may decrease from 100% under current conditions to 94% in the future. Such changes will have implications for the species under the Habitats Directive and for catchment ecological flow management strategies.

  16. Linear stability analysis of laminar flow near a stagnation point in the slip flow regime

    Science.gov (United States)

    Essaghir, E.; Oubarra, A.; Lahjomri, J.

    2017-12-01

    The aim of the present contribution is to analyze the effect of slip parameter on the stability of a laminar incompressible flow near a stagnation point in the slip flow regime. The analysis is based on the traditional normal mode approach and assumes parallel flow approximation. The Orr-Sommerfeld equation that governs the infinitesimal disturbance of stream function imposed to the steady main flow, which is an exact solution of the Navier-Stokes equation satisfying slip boundary conditions, is obtained by using the powerful spectral Chebyshev collocation method. The results of the effect of slip parameter K on the hydrodynamic characteristics of the base flow, namely the velocity profile, the shear stress profile, the boundary layer, displacement and momentum thicknesses are illustrated and discussed. The numerical data for these characteristics, as well as those of the eigenvalues and the corresponding wave numbers recover the results of the special case of no-slip boundary conditions. They are found to be in good agreement with previous numerical calculations. The effects of slip parameter on the neutral curves of stability, for two-dimensional disturbances in the Reynolds-wave number plane, are then obtained for the first time in the slip flow regime for stagnation point flow. Furthermore, the evolution of the critical Reynolds number against the slip parameter is established. The results show that the critical Reynolds number for instability is significantly increased with the slip parameter and the flow turn out to be more stable when the effect of rarefaction becomes important.

  17. A RELAP5 study to identify flow regime in natural circulation phenomenon

    Energy Technology Data Exchange (ETDEWEB)

    Sabundjian, Gaiane; Torres, Walmir M.; Macedo, Luiz A.; Mesquita, Roberto N.; Andrade, Delvonei A.; Umbehaun, Pedro E.; Conti, Thadeu N.; Masotti, Paulo H.F.; Belchior Junior, Antonio; Angelo, Gabriel, E-mail: gdjian@ipen.b, E-mail: umbehaun@ipen.b, E-mail: wmtorres@ipen.b, E-mail: tnconti@ipen.b, E-mail: rnavarro@ipen.b, E-mail: lamacedo@ipen.b, E-mail: pmasotti@ipen.b, E-mail: abelchior@ipen.b [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2011-07-01

    There has been a crescent interest in the scientific community in the study of natural circulation phenomenon. New generation of compact nuclear reactors uses the natural circulation of the fluid as a system of cooling and of residual heat removal in case of accident or shutdown. The objective of this paper is to compare the flow patterns of experimental data and numerical simulation for the natural circulation phenomenon in two-phase flow regime. An experimental circuit built with glass tubes is used for the experiments. Thus, it allows the thermal hydraulic phenomena visualization. There is an electric heater as the heat source, a heat exchanger as the heat sink and an expansion tank to accommodate fluid density excursions. The circuit instrumentation consists of thermocouples and pressure meters to better keep track of the flow and heat transfer phenomena. Data acquisition is performed through a computer interface developed with LABVIEW. The characteristic of the regime is identified using photography techniques. Numerical modeling and simulation is done with the thermal hydraulic code RELAP5, which is widely used for this purpose. This numerical simulation is capable to reproduce some of the flow regimes which are present in the circuit for the natural circulation phenomenon. Comparison between experimental and numerical simulation is presented in this work. (author)

  18. An implicit scheme with memory reduction technique for steady state solutions of DVBE in all flow regimes

    Science.gov (United States)

    Yang, L. M.; Shu, C.; Yang, W. M.; Wu, J.

    2018-04-01

    High consumption of memory and computational effort is the major barrier to prevent the widespread use of the discrete velocity method (DVM) in the simulation of flows in all flow regimes. To overcome this drawback, an implicit DVM with a memory reduction technique for solving a steady discrete velocity Boltzmann equation (DVBE) is presented in this work. In the method, the distribution functions in the whole discrete velocity space do not need to be stored, and they are calculated from the macroscopic flow variables. As a result, its memory requirement is in the same order as the conventional Euler/Navier-Stokes solver. In the meantime, it is more efficient than the explicit DVM for the simulation of various flows. To make the method efficient for solving flow problems in all flow regimes, a prediction step is introduced to estimate the local equilibrium state of the DVBE. In the prediction step, the distribution function at the cell interface is calculated by the local solution of DVBE. For the flow simulation, when the cell size is less than the mean free path, the prediction step has almost no effect on the solution. However, when the cell size is much larger than the mean free path, the prediction step dominates the solution so as to provide reasonable results in such a flow regime. In addition, to further improve the computational efficiency of the developed scheme in the continuum flow regime, the implicit technique is also introduced into the prediction step. Numerical results showed that the proposed implicit scheme can provide reasonable results in all flow regimes and increase significantly the computational efficiency in the continuum flow regime as compared with the existing DVM solvers.

  19. The Research on Metrological Characteristics of House Water Meters during Transitional Flow Regimes

    Directory of Open Access Journals (Sweden)

    Inga Briliūtė

    2011-04-01

    Full Text Available The purpose of this research is to find the influence of transitional flow regimes on inlet water meters. Four construction types of mechanical inlet water meters (each capacity Q = 10 m3/h were investigated. The biggest additional volume 0,12–0,26% when Q = 0,2…2 m3/h shows single-jet vane wheel meter. This additional volume is less 0,06–0,13% for the multi-jet concentric water meter. The minimum influence of transitional flow regimes was for turbine water meters till 0,1% for all flow range. The volumetric meters are not sensitive for this effect.Article in Lithuanian

  20. Flow Regime Destabilizing Effect on Fluid elastic Instability of Tube Array Preferentially Flexible to the Flow Direction

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kanghee; Shin, Changhwan [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Olala, Stephen; Mureithi, Njuki [BWC/AECL/NSERC Chair of Fluid-Structure Interaction, Ecole Polytechnique, Montreal (Canada)

    2015-05-15

    U bend region of operating SG is excited by the inclined cross flow due to the gradual change of hydraulic resistance force. The effect of tube array's flexibility direction on FEI is investigated by Khalvatti for rotated triangular tube in single phase (air) cross flow. He showed that FEI strongly depend on the flexibility angle. Reducing bundle flexibility to the flow direction ranging from 90 (out-of-flow direction) to 0 (in-flow direction) degree has a nonlinearly-varying stabilizing effect. Joly studies the same problem under high void fraction in two phase cross flow over 70 % to 90 %. With the Joly's experimental work, there is oddly low-valued Conner's constant in case of higher degree of angle of attack. This gives the motivation to our experimental study for fluid elastic instability of tube array in two phase cross flow. As the flow rate goes up, tube response was measured for each steady state flow condition by the strain gauge. Damping, peak frequency, and the critical velocity were estimated from the response spectrum. It seems that the flow regime for high void fraction can destabilize tube array with preferential flexibility over 60 degree. Because an intermittent flow is inherently unstable compared to the uniform bubbly flow, thus out-of-flow motion of tubes can be more fragile to the unstably rising intermittent flow. From the visual inspection, lateral tube motion seems to block the flow path periodically. Enlarged bubble in an intermittent flow regime can be squeezed-up at the flow gap between tubes.

  1. Modeling the evolution of riparian woodlands facing climate change in three European rivers with contrasting flow regimes.

    Directory of Open Access Journals (Sweden)

    Rui P Rivaes

    Full Text Available Global circulation models forecasts indicate a future temperature and rainfall pattern modification worldwide. Such phenomena will become particularly evident in Europe where climate modifications could be more severe than the average change at the global level. As such, river flow regimes are expected to change, with resultant impacts on aquatic and riparian ecosystems. Riparian woodlands are among the most endangered ecosystems on earth and provide vital services to interconnected ecosystems and human societies. However, they have not been the object of many studies designed to spatially and temporally quantify how these ecosystems will react to climate change-induced flow regimes. Our goal was to assess the effects of climate-changed flow regimes on the existing riparian vegetation of three different European flow regimes. Cases studies were selected in the light of the most common watershed alimentation modes occurring across European regions, with the objective of appraising expected alterations in the riparian elements of fluvial systems due to climate change. Riparian vegetation modeling was performed using the CASiMiR-vegetation model, which bases its computation on the fluvial disturbance of the riparian patch mosaic. Modeling results show that riparian woodlands may undergo not only at least moderate changes for all flow regimes, but also some dramatic adjustments in specific areas of particular vegetation development stages. There are circumstances in which complete annihilation is feasible. Pluvial flow regimes, like the ones in southern European rivers, are those likely to experience more pronounced changes. Furthermore, regardless of the flow regime, younger and more water-dependent individuals are expected to be the most affected by climate change.

  2. Methodology for the selection of the regime of flow in lagoons of stabilization

    International Nuclear Information System (INIS)

    Cruz T, Luis Eduardo; Alayon Torres, Walter E; Monsegny S, Carlos Emilio

    2000-01-01

    To model biological processes, information is needed on the stoichiometry and kinetics of the reactions and about the hydraulic regime of the system. The stoichiometry of a reaction refers to the quantity of consumed reactants (such as substrates) and to the quantity of formed products (such as microorganisms). The hydraulic regime makes reference to the configuration of the flow inside of and outside of the process and to the mixture and distribution of the solids of the fluid inside the reactor. The present article it is centered in studying the different mixture regimens and its kinetic models of degradation of organic matter applied to the case specify of the lagoon of stabilization of residual waters of the Municipality of Tocancipa; also it the methodology discusses to determine the type of flow that is presented in a stabilization lagoon. The kinetic models of degradation of organic matter in stabilization lagoons are classified according with the presence or absence of oxygen in the lagoon and with the mixture regime that it is presented in this. The regimens of flow that are presented in the stabilization lagoons are those of complete mixture and the piston flow, one completely opposed to the other one. Between these two is the denominated regime of dispersed or arbitrary flow. The determination of the mixture regime is of great importance, since with this it is possible to have an idea of the behavior of the rates of removal of the nutrients that arrive to the system, of the consumption of oxygen and the kinetic pattern of removal of organic matter among others. The regime of mixture complete ideal this characterized because the mass of water that enters to the system is dispersed instantly, making that the characteristics of the water are the same ones in any point, that is to say that the reaction rates are constant in the reactor and the demand of oxygen it is identical in any sampling point, likewise it happens with the removal rate; this has big

  3. Fluid flow through replicated microcellular materials in the Darcy-Forchheimer regime

    International Nuclear Information System (INIS)

    Weber, L.; Ingram, D.; Guardia, S.; Athanasiou-Ioannou, A.; Mortensen, A.

    2017-01-01

    We extend here a “bottleneck” flow model derived earlier for incompressible fluids flowing under creeping flow conditions [Despois, J. and Mortensen, A: Acta Materialia 53 (2005) 1381] to flow regimes where inertial losses are no longer negligible, causing the governing flow law to deviate from Darcy's law and become the Darcy-Forchheimer law. The proposed law is compared with measurements of the Darcian permeability K_D and of the Forchheimer coefficient C in forced-flow of air through microcellular aluminium made by the replication process. The geometrical features of the cellular medium are varied in terms of volume fraction of porosity (in the range of 0.66–0.86) and the average cell diameter from (108–425 μm). As found previously in measurements with water, the Darcy permeability of the foams for airflow is also reasonably well captured by the model. In the Forchheimer-regime the model gives good quantitative agreement with data if one assumes that the amount of air kinetic energy that is dissipated when passing across each bottleneck linking one pore to its neighbour along the fluid flow path corresponds to the difference, in a stream of constant cross-sectional area, between a uniform fluid velocity profile and the non-uniform profile that is created by the no-slip condition along the window boundary.

  4. Vortical Structures and Turbulent Bursts Behind Magnetic Obstacles in Transitional Flow Regimes

    NARCIS (Netherlands)

    Kenjeres, S.; Ten Cate, S.; Voesenek, C.J.

    2011-01-01

    The present paper reports on numerical investigations of vortical structures in transient flow regimes generated by the local action of the Lorentz force on an electrically conductive fluid. The locally imposed non-uniform magnetic field generates similar effects as observed for flows over submerged

  5. A two-phase flow regime map for a MAPLE-type nuclear research reactor fuel channel: Effect of hexagonal finned bundle

    International Nuclear Information System (INIS)

    Harvel, G.D.; Chang, J.S.

    1997-01-01

    A two-phase flow regime map is developed experimentally and theoretically for a vertical hexagonal flow channel with and without a 36-finned rod hexagonal bundle. This type of flow channel is of interest to MAPLE-type nuclear research reactors. The flow regime maps are determined by visual observations and observation of waveforms shown by a capacitance-type void fraction meter. The experimental results show that the inclusion of the finned hexagonal bundle shifts the flow regime transition boundaries toward higher water flow rates. Existing flow regime maps based on pipe flow require slight modifications when applied to the hexagonal flow channel with and without a MAPLE-type finned hexagonal bundle. The proposed theoretical model agrees well with experimental results

  6. Sensitivity of Regulated Flow Regimes to Climate Change in the Western United States

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Tian [Pacific Northwest National Laboratory, Richland, Washington; Voisin, Nathalie [Pacific Northwest National Laboratory, Richland, Washington; Leng, Guoyong [Pacific Northwest National Laboratory, Richland, Washington; Huang, Maoyi [Pacific Northwest National Laboratory, Richland, Washington; Kraucunas, Ian [Pacific Northwest National Laboratory, Richland, Washington

    2018-03-01

    Water management activities or flow regulations modify water fluxes at the land surface and affect water resources in space and time. We hypothesize that flow regulations change the sensitivity of river flow to climate change with respect to unmanaged water resources. Quantifying these changes in sensitivity could help elucidate the impacts of water management at different spatiotemporal scales and inform climate adaptation decisions. In this study, we compared the emergence of significant changes in natural and regulated river flow regimes across the Western United States from simulations driven by multiple climate models and scenarios. We find that significant climate change-induced alterations in natural flow do not cascade linearly through water management activities. At the annual time scale, 50% of the Hydrologic Unit Code 4 (HUC4) sub-basins over the Western U.S. regions tend to have regulated flow regime more sensitive to the climate change than natural flow regime. Seasonality analyses show that the sensitivity varies remarkably across the seasons. We also find that the sensitivity is related to the level of water management. For 35% of the HUC4 sub-basins with the highest level of water management, the summer and winter flows tend to show a heightened sensitivity to climate change due to the complexity of joint reservoir operations. We further demonstrate that the impacts of considering water management in models are comparable to those that arises from uncertainties across climate models and emission scenarios. This prompts further climate adaptation studies research about nonlinearity effects of climate change through water management activities.

  7. Study of the Transition Flow Regime using Monte Carlo Methods

    Science.gov (United States)

    Hassan, H. A.

    1999-01-01

    This NASA Cooperative Agreement presents a study of the Transition Flow Regime Using Monte Carlo Methods. The topics included in this final report are: 1) New Direct Simulation Monte Carlo (DSMC) procedures; 2) The DS3W and DS2A Programs; 3) Papers presented; 4) Miscellaneous Applications and Program Modifications; 5) Solution of Transitional Wake Flows at Mach 10; and 6) Turbulence Modeling of Shock-Dominated Fows with a k-Enstrophy Formulation.

  8. Numerical analysis of flow resistance and heat transfer in the transitional regime of pipe flow with twisted-tape turbulators

    Science.gov (United States)

    Rossi, R.; Cattani, L.; Mocerino, A.; Bozzoli, F.; Rainieri, S.; Caminati, R.; Pagliarini, G.

    2017-11-01

    In this paper, we present the numerical analysis of the fully developed ow and heat transfer in pipes equipped with twisted-tape inserts in the laminar to transitional flow regime. The flow Reynolds number ranges from 210 to 3100 based on the pipe diameter, whereas the Prandtl number of the working fluid, a 40% mixture of water and ethylene glycol, is about 45 at the average film temperature. The numerical study is carried out via Scale Adaptive Simulations (SAS) where the k-ω SST model is employed for turbulence modeling. Using SAS and low-dissipation discretization schemes, the present study shows that it is possible to capture the transition from the laminar regime to the pulsating or pseudo-laminar flow regime induced by the twisted-tape at low Reynolds numbers, as well as the transition to moderate turbulent regime at the higher, yet non-turbulent for smooth pipes, range of Reynolds numbers. Numerical results, validated against experiments performed in a dedicated test rig, show very good agreement with measured data and an increase of the friction factor and Nusselt number in the range of 4 to 7 times and 6 to 15 times, respectively, of the values for an empty pipe.

  9. Evaluation of Spatial Pattern of Altered Flow Regimes on a River Network Using a Distributed Hydrological Model.

    Science.gov (United States)

    Ryo, Masahiro; Iwasaki, Yuichi; Yoshimura, Chihiro; Saavedra V, Oliver C

    2015-01-01

    Alteration of the spatial variability of natural flow regimes has been less studied than that of the temporal variability, despite its ecological importance for river ecosystems. Here, we aimed to quantify the spatial patterns of flow regime alterations along a river network in the Sagami River, Japan, by estimating river discharge under natural and altered flow conditions. We used a distributed hydrological model, which simulates hydrological processes spatiotemporally, to estimate 20-year daily river discharge along the river network. Then, 33 hydrologic indices (i.e., Indicators of Hydrologic Alteration) were calculated from the simulated discharge to estimate the spatial patterns of their alterations. Some hydrologic indices were relatively well estimated such as the magnitude and timing of maximum flows, monthly median flows, and the frequency of low and high flow pulses. The accuracy was evaluated with correlation analysis (r > 0.4) and the Kolmogorov-Smirnov test (α = 0.05) by comparing these indices calculated from both observed and simulated discharge. The spatial patterns of the flow regime alterations varied depending on the hydrologic indices. For example, both the median flow in August and the frequency of high flow pulses were reduced by the maximum of approximately 70%, but these strongest alterations were detected at different locations (i.e., on the mainstream and the tributary, respectively). These results are likely caused by different operational purposes of multiple water control facilities. The results imply that the evaluation only at discharge gauges is insufficient to capture the alteration of the flow regime. Our findings clearly emphasize the importance of evaluating the spatial pattern of flow regime alteration on a river network where its discharge is affected by multiple water control facilities.

  10. Implicit unified gas-kinetic scheme for steady state solutions in all flow regimes

    Science.gov (United States)

    Zhu, Yajun; Zhong, Chengwen; Xu, Kun

    2016-06-01

    This paper presents an implicit unified gas-kinetic scheme (UGKS) for non-equilibrium steady state flow computation. The UGKS is a direct modeling method for flow simulation in all regimes with the updates of both macroscopic flow variables and microscopic gas distribution function. By solving the macroscopic equations implicitly, a predicted equilibrium state can be obtained first through iterations. With the newly predicted equilibrium state, the evolution equation of the gas distribution function and the corresponding collision term can be discretized in a fully implicit way for fast convergence through iterations as well. The lower-upper symmetric Gauss-Seidel (LU-SGS) factorization method is implemented to solve both macroscopic and microscopic equations, which improves the efficiency of the scheme. Since the UGKS is a direct modeling method and its physical solution depends on the mesh resolution and the local time step, a physical time step needs to be fixed before using an implicit iterative technique with a pseudo-time marching step. Therefore, the physical time step in the current implicit scheme is determined by the same way as that in the explicit UGKS for capturing the physical solution in all flow regimes, but the convergence to a steady state speeds up through the adoption of a numerical time step with large CFL number. Many numerical test cases in different flow regimes from low speed to hypersonic ones, such as the Couette flow, cavity flow, and the flow passing over a cylinder, are computed to validate the current implicit method. The overall efficiency of the implicit UGKS can be improved by one or two orders of magnitude in comparison with the explicit one.

  11. Numerical study of the bubbly flow regime in micro-channel flow boiling

    Science.gov (United States)

    Bhuvankar, Pramod; Dabiri, Sadegh

    2017-11-01

    Two-phase flow accompanied by boiling in micro-channel heat sinks is an effective means for heat removal from computer chips. We present a numerical study of flow boiling in micro-channels with conjugate heat transfer with a focus on the bubbly flow regime. The bubbles are assumed to nucleate at a pre-determined location and frequency. The Navier Stokes equations are solved using a single fluid formulation with the Front tracking method. Phase change is implemented using the deficit in heat flux across the bubble interface. The analytical solution for bubble growth in a superheated liquid is used as a benchmark to validate the mentioned numerical method. Water and FC-72 are studied as the operating fluids in a micro-channel made of Copper with a focus on hotspot mitigation. The micro-channel of cross-section 231 μm × 1000 μm , is used to study the effects of vertical up-flow, vertical down-flow and horizontal flow of the mentioned fluids on the heat transfer coefficients. A simple film model accounting for mass and energy conservation is applied wherever the bubble approaches closer than a cell width to the wall. The results of the simulation are compared with existing experimental data for bubble growth rates and heat transfer coefficients.

  12. Three-dimensional investigations of the threading regime in a microfluidic flow-focusing channel

    Science.gov (United States)

    Gowda, Krishne; Brouzet, Christophe; Lefranc, Thibault; Soderberg, L. Daniel; Lundell, Fredrik

    2017-11-01

    We study the flow dynamics of the threading regime in a microfluidic flow-focusing channel through 3D numerical simulations and experiments. Making strong filaments from cellulose nano-fibrils (CNF) could potentially steer to new high-performance bio-based composites competing with conventional glass fibre composites. CNF filaments can be obtained through hydrodynamic alignment of dispersed CNF by using the concept of flow-focusing. The aligned structure is locked by diffusion of ions resulting in a dispersion-gel transition. Flow-focusing typically refers to a microfluidic channel system where the core fluid is focused by the two sheath fluids, thereby creating an extensional flow at the intersection. In this study, threading regime corresponds to an extensional flow field generated by the water sheath fluid stretching the dispersed CNF core fluid and leading to formation of long threads. The experimental measurements are performed using optical coherence tomography (OCT) and 3D numerical simulations with OpenFOAM. The prime focus is laid on the 3D characteristics of thread formation such as wetting length of core fluid, shape, aspect ratio of the thread and velocity flow-field in the microfluidic channel.

  13. SOUTH-WESTERN APUSENI MOUNTAINS SMALL RIVERS SEASONAL HYDROLOGICAL FLOW REGIME

    Directory of Open Access Journals (Sweden)

    SOROCOVSCHI V.

    2015-03-01

    Full Text Available The researched area overlaps the territory belonging to Crişul Alb and Crişul Negru river basins. The study is based on processing and interpretation data from 33 hydrometric stations of which 18 stations control hydrographic basins with surfaces of less than 150 km2. To highlight the seasonal hydrological flow regime, we took into account three time periods (1950-1967, 1950-2009 and 1970-2009. For all rivers the highest flow values appear during springtime, while the smallest contribution to the multiannual average volume is realized in autumn. The time variation of seasonal flow was highlighted by analysis and variation of extreme values coefficients and also by analysing seasonal flow trends that appeared in all three time periods.

  14. Numerical investigation of the flow over a golf ball in the subcritical and supercritical regimes

    International Nuclear Information System (INIS)

    Smith, C.E.; Beratlis, N.; Balaras, E.; Squires, K.; Tsunoda, M.

    2010-01-01

    In order to understand the role of surface dimpling on the flow over a golf ball, direct numerical simulations (DNS) are conducted within the framework of an immersed boundary approach for two physical regimes. Computations of the flow over a non-rotating golf ball are reported for a subcritical flow at a Reynolds number of 2.5 x 10 4 and a supercritical case at a Reynolds number of 1.1 x 10 5 . Grid refinement studies for both Reynolds numbers indicated that characteristics of the subcritical flow could be captured using a mesh of 337 x 10 6 points, and for the supercritical case using a grid with 1.2 x 10 9 points. Flow visualizations reveal the differences in separation characteristics between the two Reynolds numbers. Profiles of the mean velocity indicate that the flow detaches completely at approximately 84 o in the subcritical case (measured from the stagnation point at the front of the ball), while in the supercritical regime there are alternating regions of reattachment and separation within dimples with complete detachment around 110 o . Energy spectra highlight frequencies associated with vortex formation over the dimples prior to complete detachment in the supercritical regime. Reynolds stresses quantify momentum transport in the near-wall region, showing that the axial stress increases around 90 o for the subcritical case. In the supercritical regime these stress components alternately increase and decrease, corresponding to local separation and reattachment. Prediction of the drag coefficient for both Reynolds numbers is in reasonable agreement with measurements.

  15. Effects of Urbanization on the Flow Regimes of Semi-Arid Southern California Streams

    Science.gov (United States)

    Hawley, R. J.; Bledsoe, B. P.; Stein, E. D.

    2010-12-01

    Stream channel erosion and associated habitat degradation are pervasive in streams draining urban areas in the southwestern US. The prevalence of these impacts results from the inherent sensitivity of streams in semi-arid climates to changes in flow and sediment regimes, and past inattention to management of geomorphically effective flows. Addressing this issue is difficult due to the lack of data linking ranges of flow (from small to large runoff events) to geomorphic channel response. Forty-three U. S. Geological Survey gages with record lengths greater than ~15 yrs and watershed areas less than ~250 square kilometers were used to empirically model the effects of urbanization on streams in southern California. The watersheds spanned a gradient of urban development and ranged from 0 to 23% total impervious area in 2001. With little flow control at the subdivision scale to date, most impervious area in the region is relatively well-connected to surface-drainage networks. Consequently, total impervious area was an effective surrogate for urbanization, and emerged as a significant (p approach expands on previous scaling procedures to produce histogram-style cumulative flow duration graphs for ungaged sites based on urbanization extent and other watershed descriptors. Urbanization resulted in proportionally-longer durations of all geomorphically-effective flows, with a more pronounced effect on the durations of moderate flows. For example, an average watershed from the study domain with ~20% imperviousness could experience five times as many days of mean daily flows on the order of 100 cfs (3 cubic meters per second) and approximately three times as many days on the order of 1,000 cfs (30 cubic meters per second) relative to the undeveloped setting. Increased duration of sediment-transporting flows is a primary driver of accelerated changes in channel form that are often concurrent with urbanization throughout southern California, particularly in unconfined, fine

  16. Computational thermal-fluid dynamics analysis of the laminar flow regime in the meander flow geometry characterizing the heat exchanger used in high temperature superconducting current leads

    Energy Technology Data Exchange (ETDEWEB)

    Rizzo, Enrico, E-mail: enrico.rizzo@kit.edu [Institute for Technical Physics, Karlsruhe Institute of Technology, 76021 Karlsruhe (Germany); Heller, Reinhard [Institute for Technical Physics, Karlsruhe Institute of Technology, 76021 Karlsruhe (Germany); Richard, Laura Savoldi; Zanino, Roberto [Dipartimento Energia, Politecnico di Torino, 10129 Torino (Italy)

    2013-11-15

    Highlights: • The laminar regime in the meander flow geometry has been analysed with a previously validated computational strategy. • Several meander flow geometries as well as flow conditions have been analysed. • A range for the Reynolds number has been defined in which the flow can be considered laminar. • Correlations for the pressure drop and the heat transfer coefficients in the laminar regime have been derived. • A comparison between the computed the experimental pressure drop of the W7-X HTS current lead prototype is presented. -- Abstract: The Karlsruhe Institute of Technology and the Politecnico di Torino have developed and validated a computational thermal-fluid dynamics (CtFD) strategy for the systematic analysis of the thermal-hydraulics inside the meander flow heat exchanger used in high-temperature superconducting current leads for fusion applications. In the recent past, the application of this CtFD technique has shown that some operating conditions occurring in these devices may not reach the turbulent regime region. With that motivation, the CtFD analysis of the helium thermal-fluid dynamics inside different meander flow geometries is extended here to the laminar flow regime. Our first aim is to clarify under which operative conditions the flow regime can be considered laminar and how the pressure drop as well as the heat transfer are related to the geometrical parameters and to the flow conditions. From the results of this analysis, correlations for the pressure drop and for the heat transfer coefficient in the meander flow geometry have been derived, which are applicable with good accuracy to the design of meander flow heat exchangers over a broad range of geometrical parameters.

  17. Computational thermal-fluid dynamics analysis of the laminar flow regime in the meander flow geometry characterizing the heat exchanger used in high temperature superconducting current leads

    International Nuclear Information System (INIS)

    Rizzo, Enrico; Heller, Reinhard; Richard, Laura Savoldi; Zanino, Roberto

    2013-01-01

    Highlights: • The laminar regime in the meander flow geometry has been analysed with a previously validated computational strategy. • Several meander flow geometries as well as flow conditions have been analysed. • A range for the Reynolds number has been defined in which the flow can be considered laminar. • Correlations for the pressure drop and the heat transfer coefficients in the laminar regime have been derived. • A comparison between the computed the experimental pressure drop of the W7-X HTS current lead prototype is presented. -- Abstract: The Karlsruhe Institute of Technology and the Politecnico di Torino have developed and validated a computational thermal-fluid dynamics (CtFD) strategy for the systematic analysis of the thermal-hydraulics inside the meander flow heat exchanger used in high-temperature superconducting current leads for fusion applications. In the recent past, the application of this CtFD technique has shown that some operating conditions occurring in these devices may not reach the turbulent regime region. With that motivation, the CtFD analysis of the helium thermal-fluid dynamics inside different meander flow geometries is extended here to the laminar flow regime. Our first aim is to clarify under which operative conditions the flow regime can be considered laminar and how the pressure drop as well as the heat transfer are related to the geometrical parameters and to the flow conditions. From the results of this analysis, correlations for the pressure drop and for the heat transfer coefficient in the meander flow geometry have been derived, which are applicable with good accuracy to the design of meander flow heat exchangers over a broad range of geometrical parameters

  18. An ecological economic assessment of flow regimes in a hydropower dominated river basin: the case of the lower Zambezi River, Mozambique.

    Science.gov (United States)

    Fanaian, Safa; Graas, Susan; Jiang, Yong; van der Zaag, Pieter

    2015-02-01

    The flow regime of rivers, being an integral part of aquatic ecosystems, provides many important services benefiting humans in catchments. Past water resource developments characterized by river embankments and dams, however, were often dominated by one (or few) economic use(s) of water. This results in a dramatically changed flow regime negatively affecting the provision of other ecosystem services sustained by the river flow. This study is intended to demonstrate the value of alternative flow regimes in a river that is highly modified by the presence of large hydropower dams and reservoirs, explicitly accounting for a broad range of flow-dependent ecosystem services. In this study, we propose a holistic approach for conducting an ecological economic assessment of a river's flow regime. This integrates recent advances in the conceptualization and classification of ecosystem services (UK NEA, 2011) with the flow regime evaluation technique developed by Korsgaard (2006). This integrated approach allows for a systematic comparison of the economic values of alternative flow regimes, including those that are considered beneficial for aquatic ecosystems. As an illustration, we applied this combined approach to the Lower Zambezi Basin, Mozambique. Empirical analysis shows that even though re-operating dams to create environmentally friendly flow regimes reduces hydropower benefits, the gains to goods derived from the aquatic ecosystem may offset the forgone hydropower benefits, thereby increasing the total economic value of river flow to society. The proposed integrated flow assessment approach can be a useful tool for welfare-improving decision-making in managing river basins. Copyright © 2014 Elsevier B.V. All rights reserved.

  19. Evaluation of drilling fluids flow regime in annular sections; Avaliacao do regime de escoamento de fluidos de perfuracao em secoes anulares

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Maria das Gracas Pena [PETROBRAS, Rio de Janeiro (Brazil). Centro de Pesquisas. Setor de Tecnologia de Perfuracao

    1990-12-31

    The determination of the transition zone between the laminar and turbulent flow regimes of particular importance in optimizing the hydraulics of drilling operations. The principal advantage which laminar flow in the annular space has in drilling operations in the avoidance of wall enlargement (wash-outs), maintaining formation integrity as much as possible. On the other hand, a lower-energy regime such as laminar flow does not provide the same cuttings-carrying capacity as that obtained when the drilling fluid is in turbulent flow. However, to be able to optimize the hydraulics it is necessary to have determined, among other parameters, the transition zone, in order to maximize the drilling rate while obtaining the hole clear of cuttings and maintaining the hole diameter constant over the whole of the section drilled. This paper presents, based on experimental results obtained on the SHS physical simulator, the transition zone expressed through the critical Reynolds numbers and those for low stable turbulence of various drilling fluids tested over the temperature range of 25-80 deg C. (author) 20 refs., 7 figs., 4 tabs.

  20. Identification method of gas-liquid two-phase flow regime based on image wavelet packet information entropy and genetic neural network

    International Nuclear Information System (INIS)

    Zhou Yunlong; Chen Fei; Sun Bin

    2008-01-01

    Based on the characteristic that wavelet packet transform image can be decomposed by different scales, a flow regime identification method based on image wavelet packet information entropy feature and genetic neural network was proposed. Gas-liquid two-phase flow images were captured by digital high speed video systems in horizontal pipe. The information entropy feature from transformation coefficients were extracted using image processing techniques and multi-resolution analysis. The genetic neural network was trained using those eigenvectors, which was reduced by the principal component analysis, as flow regime samples, and the flow regime intelligent identification was realized. The test result showed that image wavelet packet information entropy feature could excellently reflect the difference between seven typical flow regimes, and the genetic neural network with genetic algorithm and BP algorithm merits were with the characteristics of fast convergence for simulation and avoidance of local minimum. The recognition possibility of the network could reach up to about 100%, and a new and effective method was presented for on-line flow regime. (authors)

  1. Lattice Boltzmann Simulations in the Slip and Transition Flow Regime with the Peano Framework

    KAUST Repository

    Neumann, Philipp; Rohrmann, Till

    2012-01-01

    We present simulation results of flows in the finite Knudsen range, which is in the slip and transition flow regime. Our implementations are based on the Lattice Boltzmann method and are accomplished within the Peano framework. We validate our code

  2. Theoretical and pragmatic modelling of governing equations for a two-phase flow in bubbly and annular flow regimes

    International Nuclear Information System (INIS)

    Bottoni, M.; Sengpiel, W.

    1992-01-01

    Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy, derived for a two-phase flow by volume averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration, bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities make the rigorously formulated terms useless for computational purposes, modelling of these terms is discussed. 3 figs., 15 refs

  3. Contested Regimes, Aid Flows, and Refugee Flows: The Case of Burma Umkämpfte Regime, Hilfsgelder und Flüchtlingsströme: Der Fall Burma

    Directory of Open Access Journals (Sweden)

    Susan Banki

    2009-07-01

    Full Text Available There is a substantial literature that critiques the role that international aid plays in lending support to oppressive and contested regimes. But few investigators have asked the inverse question: what happens when aid is withdrawn? Following government oppression in 1988, international aid to Burma decreased significantly, providing a case study enabling this question to be addressed. Using Burma as an example, this article asks: if the presence of aid has been shown to support oppressive and contested regimes, what is the impact when aid is withdrawn? The article reviews critiques of development and humanitarian aid and identifies three specific regime-reinforcing phenomena. It demonstrates that these have not diminished following the overall decrease of aid to Burma. The paper then addresses the related relationship between aid flows and refugee flows, and concludes with implications of the research. Es gibt mittlerweile eine ganze Reihe von Literatur, in der die Rolle von internationaler Hilfe zur Unterstützung von Unrechtsregimen kritisch diskutiert wird. Es gibt bislang aber nur wenige Untersuchungen, in denen die Frage anders herum gestellt wird. Was passiert, wenn Hilfsgelder zurückgehalten werden? Seit der Unterdrückung im Jahr 1988 ist die internationale Hilfe an Burma/ Myanmar deutlich zurückgegangen. Dieser Artikel fragt für das Fallbeispiel Burma: Welche Wirkungen hat es, wenn Hilfsgelder zurückgehalten werden? Der Artikel beleuchtet die Debatten zur humanitären Hilfe und Entwicklung und identifiziert drei besondere Regime stützende Effekte. Der Artikel zeigt, dass diese im Fall Burma nicht eingetreten sind, als Hilfe zurückgezogen wurde. Der Artikel diskutiert außerdem die Beziehung zwischen Hilfsgeldern und Flüchtlingsströmen und versucht, Folgerungen aus der Forschung zu entwickeln.

  4. The metabolic regimes of flowing waters

    Science.gov (United States)

    Bernhardt, Emily S.; Heffernan, Jim B.; Grimm, Nancy B.; Stanley, Emily H.; Harvey, Judson; Arroita, M.; Appling, Alison; Cohen, M.J.; McDowell, William H.; Hall, R.O.; Read, Jordan S.; Roberts, B.J.; Stets, Edward; Yackulic, Charles B.

    2018-01-01

    The processes and biomass that characterize any ecosystem are fundamentally constrained by the total amount of energy that is either fixed within or delivered across its boundaries. Ultimately, ecosystems may be understood and classified by their rates of total and net productivity and by the seasonal patterns of photosynthesis and respiration. Such understanding is well developed for terrestrial and lentic ecosystems but our understanding of ecosystem phenology has lagged well behind for rivers. The proliferation of reliable and inexpensive sensors for monitoring dissolved oxygen and carbon dioxide is underpinning a revolution in our understanding of the ecosystem energetics of rivers. Here, we synthesize our current understanding of the drivers and constraints on river metabolism, and set out a research agenda aimed at characterizing, classifying and modeling the current and future metabolic regimes of flowing waters.

  5. The Role of Forests in Regulating the River Flow Regime of Large Basins of the World

    Science.gov (United States)

    Salazar, J. F.; Villegas, J. C.; Mercado-Bettin, D. A.; Rodríguez, E.

    2017-12-01

    Many natural and social phenomena depend on river flow regimes that are being altered by global change. Understanding the mechanisms behind such alterations is crucial for predicting river flow regimes in a changing environment. Here we explore potential linkages between the presence of forests and the capacity of river basins for regulating river flows. Regulation is defined here as the capacity of river basins to attenuate the amplitude of the river flow regime, that is to reduce the difference between high and low flows. We first use scaling theory to show how scaling properties of observed river flows can be used to classify river basins as regulated or unregulated. This parsimonious classification is based on a physical interpretation of the scaling properties (particularly the scaling exponents) that is novel (most previous studies have focused on the interpretation of the scaling exponents for floods only), and widely-applicable to different basins (the only assumption is that river flows in a given river basin exhibit scaling properties through well-known power laws). Then we show how this scaling framework can be used to explore global-change-induced temporal variations in the regulation capacity of river basins. Finally, we propose a conceptual hypothesis (the "Forest reservoir concept") to explain how large-scale forests can exert important effects on the long-term water balance partitioning and regulation capacity of large basins of the world. Our quantitative results are based on data analysis (river flows and land cover features) from 22 large basins of the world, with emphasis in the Amazon river and its main tributaries. Collectively, our findings support the hypothesis that forest cover enhances the capacity of large river basins to maintain relatively high mean river flows, as well as to regulate (ameliorate) extreme river flows. Advancing towards this quantitative understanding of the relation between forest cover and river flow regimes is

  6. Flow Regime Changes: From Impounding a Temperate Lowland River to Small Hydropower Operations

    Directory of Open Access Journals (Sweden)

    Petras Punys

    2015-07-01

    Full Text Available This article discusses the environmental issues facing small hydropower plants (SHPs operating in temperate lowland rivers of Lithuania. The research subjects are two medium head reservoir type hydro schemes considered within a context of the global fleet of SHPs in the country. This research considers general abiotic indicators (flow, level, water retention time in the reservoirs of the stream that may affect the aquatic systems. The main idea was to test whether the hydrologic regime has been altered by small hydropower dams. The analysis of changes in abiotic indicators is a complex process, including both pre- and post-reservoir construction and post commissioning of the SHPs under operation. Downstream hydrograph (flow and stage ramping is also an issue for operating SHPs that can result in temporary rapid changes in flow and consequently negatively impact aquatic resources. This ramping has been quantitatively evaluated. To avoid the risk of excessive flow ramping, the types of turbines available were evaluated and the most suitable types for the natural river flow regime were identified. The results of this study are to allow for new hydro schemes or upgrades to use water resources in a more sustainable way.

  7. Visualization of two-phase gas-liquid flow regimes in horizontal and slightly-inclined circular tubes

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Livia Alves [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil); Nuclear Engineering Institute (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)], E-mail: livia@lasme.coppe.ufrj.br; Cunha Filho, Jurandyr; Su, Jian [Coordenacao dos Programas de Pos-Graduacao de Engenharia (COPPE/UFRJ), RJ (Brazil). Nuclear Engineering Program], Emails: cunhafilho@lasme.coppe.ufrj.br, sujian@lasme.coppe.ufrj.br; Faccini, Jose Luiz Horacio [Nuclear Engineering Institute (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)], E-mail: faccini@ien.gov.br

    2010-07-01

    In this paper a flow visualization study was performed for two-phase gas-liquid flow in horizontal and slightly inclined tubes. The test section consists of a 2.54 cm inner diameter stainless steel circular tube, followed by a transparent acrylic tube with the same inner diameter. The working fluids were air and water, with liquid superficial velocities ranging from 0:11 to 3:28 m/s and gas superficial velocities ranging from 0:27 to 5:48 m/s. Flow visualization was executed for upward flow at 5 deg and 10 deg and downward flow at 2:5 deg, 5 deg and 10 deg, as well as for horizontal flow. The visualization technique consists of a high-speed digital camera that records images at rates of 125 and 250 frames per second of a concurrent air-water mixture through a transparent part of the tube. From the obtained images, the flow regimes were identified (except for annular flow), observing the effect of inclination angles on flow regime transition boundaries. Finally, the experimental results were compared with empirical and theoretical flow pattern maps available in literature. (author)

  8. Identification method for gas-liquid two-phase flow regime based on singular value decomposition and least square support vector machine

    International Nuclear Information System (INIS)

    Sun Bin; Zhou Yunlong; Zhao Peng; Guan Yuebo

    2007-01-01

    Aiming at the non-stationary characteristics of differential pressure fluctuation signals of gas-liquid two-phase flow, and the slow convergence of learning and liability of dropping into local minima for BP neural networks, flow regime identification method based on Singular Value Decomposition (SVD) and Least Square Support Vector Machine (LS-SVM) is presented. First of all, the Empirical Mode Decomposition (EMD) method is used to decompose the differential pressure fluctuation signals of gas-liquid two-phase flow into a number of stationary Intrinsic Mode Functions (IMFs) components from which the initial feature vector matrix is formed. By applying the singular vale decomposition technique to the initial feature vector matrixes, the singular values are obtained. Finally, the singular values serve as the flow regime characteristic vector to be LS-SVM classifier and flow regimes are identified by the output of the classifier. The identification result of four typical flow regimes of air-water two-phase flow in horizontal pipe has shown that this method achieves a higher identification rate. (authors)

  9. Flow regime transition and heat transfer model at low mass flux condition in a post-dryout region

    International Nuclear Information System (INIS)

    Jeong, Hae Yong

    1996-02-01

    The post-dryout flow regime transition criterion from inverted annular flow (IAF) to agitated inverted annular flow (AIAF) is suggested based on the hyperbolicity breaking concept. The hyperbolicity breaking represents a bifurcation point where a sudden flow transition occurs. The hyperbolicity breaking concept is applied to describe the flow regime transition from IAF to AIAF by the growth of disturbance on liquid core surface. The resultant correlation has the similar form to Takenaka's empirical one. To validate the proposed model, it is applied to predict Takenake's experimental results using R-113 refrigerant with four different tube diameters of 3, 5, 7 and 10 mm. The proposed model gives accurate predictions for the tube diameters of 7 and 10 mm. As the tube diameter decreases, the differences between the predictions and the experimental results slightly increase. The flow regime transition from AIAF to dispersed flow (DF) is described by the drift flux model. It is shown that the transition criterion can be well predicted if the droplet sizes in dispersed flow are evaluated appropriately. Existing mechanistic post-dryout models result in fairly good predictions when the mass flux is high or when the film dryout occurs. However, the predictions by these models become poor at low mass flux at which the flow regime before dryout is believed to be churn-turbulent. This is because the constitutive relations and/or the imposed assumptions used in the models become erroneous at low mass flux. The droplet size predicted by the correlation used in the model becomes unrealistically large. In addition, the single phase vapor heat transfer correlation becomes invalid at low mass flux condition. To develop a mechanistic post-dryout model which is available at low mass flux condition, the entrainment mechanisms and the entrained droplet sizes with relation to the flow regimes are investigated. Through the analysis of many experimental post-dryout data, it is shown that

  10. Flow regime alterations under changing climate in two river basins: Implications for freshwater ecosystems

    Science.gov (United States)

    Gibson, C.A.; Meyer, J.L.; Poff, N.L.; Hay, L.E.; Georgakakos, A.

    2005-01-01

    We examined impacts of future climate scenarios on flow regimes and how predicted changes might affect river ecosystems. We examined two case studies: Cle Elum River, Washington, and Chattahoochee-Apalachicola River Basin, Georgia and Florida. These rivers had available downscaled global circulation model (GCM) data and allowed us to analyse the effects of future climate scenarios on rivers with (1) different hydrographs, (2) high future water demands, and (3) a river-floodplain system. We compared observed flow regimes to those predicted under future climate scenarios to describe the extent and type of changes predicted to occur. Daily stream flow under future climate scenarios was created by either statistically downscaling GCMs (Cle Elum) or creating a regression model between climatological parameters predicted from GCMs and stream flow (Chattahoochee-Apalachicola). Flow regimes were examined for changes from current conditions with respect to ecologically relevant features including the magnitude and timing of minimum and maximum flows. The Cle Elum's hydrograph under future climate scenarios showed a dramatic shift in the timing of peak flows and lower low flow of a longer duration. These changes could mean higher summer water temperatures, lower summer dissolved oxygen, and reduced survival of larval fishes. The Chattahoochee-Apalachicola basin is heavily impacted by dams and water withdrawals for human consumption; therefore, we made comparisons between pre-large dam conditions, current conditions, current conditions with future demand, and future climate scenarios with future demand to separate climate change effects and other anthropogenic impacts. Dam construction, future climate, and future demand decreased the flow variability of the river. In addition, minimum flows were lower under future climate scenarios. These changes could decrease the connectivity of the channel and the floodplain, decrease habitat availability, and potentially lower the ability

  11. Non-invasive classification of gas–liquid two-phase horizontal flow regimes using an ultrasonic Doppler sensor and a neural network

    OpenAIRE

    Abbagoni, Baba Musa; Yeung, Hoi

    2016-01-01

    The identification of flow pattern is a key issue in multiphase flow which is encountered in the petrochemical industry. It is difficult to identify the gas–liquid flow regimes objectively with the gas–liquid two-phase flow. This paper presents the feasibility of a clamp-on instrument for an objective flow regime classification of two-phase flow using an ultrasonic Doppler sensor and an artificial neural network, which records and processes the ultrasonic signals reflected from the two-phase ...

  12. Predicting ecological flow regime at ungaged sites: A comparison of methods

    Science.gov (United States)

    Murphy, Jennifer C.; Knight, Rodney R.; Wolfe, William J.; Gain, W. Scott

    2012-01-01

    Nineteen ecologically relevant streamflow characteristics were estimated using published rainfall–runoff and regional regression models for six sites with observed daily streamflow records in Kentucky. The regional regression model produced median estimates closer to the observed median for all but two characteristics. The variability of predictions from both models was generally less than the observed variability. The variability of the predictions from the rainfall–runoff model was greater than that from the regional regression model for all but three characteristics. Eight characteristics predicted by the rainfall–runoff model display positive or negative bias across all six sites; biases are not as pronounced for the regional regression model. Results suggest that a rainfall–runoff model calibrated on a single characteristic is less likely to perform well as a predictor of a range of other characteristics (flow regime) when compared with a regional regression model calibrated individually on multiple characteristics used to represent the flow regime. Poor model performance may misrepresent hydrologic conditions, potentially distorting the perceived risk of ecological degradation. Without prior selection of streamflow characteristics, targeted calibration, and error quantification, the widespread application of general hydrologic models to ecological flow studies is problematic. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

  13. Assessing flow regime alterations in a temporary river – the River Celone case study

    Directory of Open Access Journals (Sweden)

    De Girolamo Anna Maria

    2015-09-01

    Full Text Available In this paper, we present an approach to evaluate the hydrological alterations of a temporary river. In these rivers, it is expected that anthropogenic pressures largely modify low-flow components of the flow regime with consequences for aquatic habitat and diversity in invertebrate species. First, by using a simple hydrological index (IARI river segments of the Celone stream (southern Italy whose hydrological regime is significantly influenced by anthropogenic activities have been identified. Hydrological alteration has been further classified through the analysis of two metrics: the degree (Mf and the predictability of dry flow conditions (Sd6. Measured streamflow data were used to calculate the metrics in present conditions (impacted. Given the lack of data from pristine conditions, simulated streamflow time series were used to calculate the metrics in reference conditions. The Soil and Water Assessment Tool (SWAT model was used to estimate daily natural streamflow. Hydrological alterations associated with water abstractions, point discharges and the presence of a reservoir were assessed by comparing the metrics (Mf, Sd6 before and after the impacts. The results show that the hydrological regime of the river segment located in the upper part of the basin is slightly altered, while the regime of the river segment downstream of the reservoir is heavily altered. This approach is intended for use with ecological metrics in defining the water quality status and in planning streamflow management activities.

  14. Numerical Study on Bubble Dynamics and Two-Phase Frictional Pressure Drop of Slug Flow Regime in Adiabatic T-junction Square Microchannel

    Directory of Open Access Journals (Sweden)

    K. Kishor

    2017-10-01

    Full Text Available In this study, bubble dynamics and frictional pressure drop associated with gas liquid two-phase slug flow regime in adiabatic T-junction square microchannel has been investigated using CFD. A comprehensive study on the mechanism of bubble formation via squeezing and shearing regime is performed. The randomness and recirculation profiles observed in the squeezing regime are significantly higher as compared to the shearing regime during formation of the slug. Further, effects of increasing gas velocity on bubble length are obtained at fixed liquid velocities and simulated data displayed good agreement with available correlations in literature. The frictional pressure drop for slug flow regime from simulations are also obtained and evaluated against existing separated flow models. A regression correlation has also been developed by modifying C-parameter using separated flow model, which improves the prediction of two-phase frictional pressure drop data within slug flow region, with mean absolute error of 10 %. The influences of fluid properties such as liquid viscosity and surface tension on the two-phase frictional pressure drop are also investigated and compared with developed correlation. The higher liquid viscosity and lower surface tension value resulted in bubble formation via shearing regime.

  15. Identifying hydrological regime and eco-flow threshold of small and medium flood of the Xiaoqing River in Jinan city

    Science.gov (United States)

    Liu, Yang; Cao, Sheng-Le

    2017-06-01

    It was known that hydrological regime was the main influencing factor of river ecosystem, but the regime of different flow rates of urban rivers was poorly understood. We collected daily inflows at the Huangtai station of the Xiaoqing River from 1960 to 2014 and divided the data into three periods. Then we calculated hydrological parameters by the method of EFCs (Environmental Flow Components) and analyzed the tendency and change rates of each component respectively in the three periods. Combined with the ecological significance of environmental flow components, we identified the small and medium flood had the greatest impact on the river regime and ecosystem. And then we used the hydraulic parameters in the good ecosystem period as control conditions, to calculate the ecological threshold of the flow component under the current situation. This study could provide technical support for restoring and improving hydrological regime and ecological environment of the Xiaoqing River in Jinan city.

  16. Non-invasive classification of gas–liquid two-phase horizontal flow regimes using an ultrasonic Doppler sensor and a neural network

    International Nuclear Information System (INIS)

    Abbagoni, Baba Musa; Yeung, Hoi

    2016-01-01

    The identification of flow pattern is a key issue in multiphase flow which is encountered in the petrochemical industry. It is difficult to identify the gas–liquid flow regimes objectively with the gas–liquid two-phase flow. This paper presents the feasibility of a clamp-on instrument for an objective flow regime classification of two-phase flow using an ultrasonic Doppler sensor and an artificial neural network, which records and processes the ultrasonic signals reflected from the two-phase flow. Experimental data is obtained on a horizontal test rig with a total pipe length of 21 m and 5.08 cm internal diameter carrying air-water two-phase flow under slug, elongated bubble, stratified-wavy and, stratified flow regimes. Multilayer perceptron neural networks (MLPNNs) are used to develop the classification model. The classifier requires features as an input which is representative of the signals. Ultrasound signal features are extracted by applying both power spectral density (PSD) and discrete wavelet transform (DWT) methods to the flow signals. A classification scheme of ‘1-of-C coding method for classification’ was adopted to classify features extracted into one of four flow regime categories. To improve the performance of the flow regime classifier network, a second level neural network was incorporated by using the output of a first level networks feature as an input feature. The addition of the two network models provided a combined neural network model which has achieved a higher accuracy than single neural network models. Classification accuracies are evaluated in the form of both the PSD and DWT features. The success rates of the two models are: (1) using PSD features, the classifier missed 3 datasets out of 24 test datasets of the classification and scored 87.5% accuracy; (2) with the DWT features, the network misclassified only one data point and it was able to classify the flow patterns up to 95.8% accuracy. This approach has demonstrated the

  17. Non-invasive classification of gas-liquid two-phase horizontal flow regimes using an ultrasonic Doppler sensor and a neural network

    Science.gov (United States)

    Musa Abbagoni, Baba; Yeung, Hoi

    2016-08-01

    The identification of flow pattern is a key issue in multiphase flow which is encountered in the petrochemical industry. It is difficult to identify the gas-liquid flow regimes objectively with the gas-liquid two-phase flow. This paper presents the feasibility of a clamp-on instrument for an objective flow regime classification of two-phase flow using an ultrasonic Doppler sensor and an artificial neural network, which records and processes the ultrasonic signals reflected from the two-phase flow. Experimental data is obtained on a horizontal test rig with a total pipe length of 21 m and 5.08 cm internal diameter carrying air-water two-phase flow under slug, elongated bubble, stratified-wavy and, stratified flow regimes. Multilayer perceptron neural networks (MLPNNs) are used to develop the classification model. The classifier requires features as an input which is representative of the signals. Ultrasound signal features are extracted by applying both power spectral density (PSD) and discrete wavelet transform (DWT) methods to the flow signals. A classification scheme of ‘1-of-C coding method for classification’ was adopted to classify features extracted into one of four flow regime categories. To improve the performance of the flow regime classifier network, a second level neural network was incorporated by using the output of a first level networks feature as an input feature. The addition of the two network models provided a combined neural network model which has achieved a higher accuracy than single neural network models. Classification accuracies are evaluated in the form of both the PSD and DWT features. The success rates of the two models are: (1) using PSD features, the classifier missed 3 datasets out of 24 test datasets of the classification and scored 87.5% accuracy; (2) with the DWT features, the network misclassified only one data point and it was able to classify the flow patterns up to 95.8% accuracy. This approach has demonstrated the

  18. Two-phase flow regimes in a horizontal microchannel with the height of 50 μm and width of 10 mm

    Science.gov (United States)

    Fina, V. P.; Ronshin, F. V.

    2017-11-01

    Two-phase flows of distilled deionized nanofiltered water and nitrogen gas in a microchannel with a height of 50 μm and a width of 10 mm have been investigated experimentally. The schlieren method has been used to determine main features of the two-phase flow in the microchannel. This method allows detecting the liquid film on the lower and upper walls of the microchannel as well as droplets of various shapes and sizes or vertical liquid bridges. Two-phase flow regimes have been observed, and their boundaries precisely determined using post-processing of the recordings. The following flow regimes have been distinguished: bubble, churn, jet, stratified and annular. Comparison of regime maps for channels of different widths has been carried out, and this parameter showed to have a significant impact on the boundaries between the regimes in microchannels of a height of less than 100 μm.

  19. Situational Lightning Climatologies for Central Florida: Phase IV: Central Florida Flow Regime Based Climatologies of Lightning Probabilities

    Science.gov (United States)

    Bauman, William H., III

    2009-01-01

    The threat of lightning is a daily concern during the warm season in Florida. Research has revealed distinct spatial and temporal distributions of lightning occurrence that are strongly influenced by large-scale atmospheric flow regimes. Previously, the Applied Meteorology Unit (AMU) calculated the gridded lightning climatologies based on seven flow regimes over Florida for 1-, 3- and 6-hr intervals in 5-, 10-, 20-, and 30-NM diameter range rings around the Shuttle Landing Facility (SLF) and eight other airfields in the National Weather Service in Melbourne (NWS MLB) county warning area (CWA). In this update to the work, the AMU recalculated the lightning climatologies for using individual lightning strike data to improve the accuracy of the climatologies. The AMU included all data regardless of flow regime as one of the stratifications, added monthly stratifications, added three years of data to the period of record and used modified flow regimes based work from the AMU's Objective Lightning Probability Forecast Tool, Phase II. The AMU made changes so the 5- and 10-NM radius range rings are consistent with the aviation forecast requirements at NWS MLB, while the 20- and 30-NM radius range rings at the SLF assist the Spaceflight Meteorology Group in making forecasts for weather Flight Rule violations during Shuttle landings. The AMU also updated the graphical user interface with the new data.

  20. Scaling relation and regime map of explosive gas–liquid flow of binary Lennard-Jones particle system

    KAUST Repository

    Inaoka, Hajime

    2012-02-01

    We study explosive gasliquid flows caused by rapid depressurization using a molecular dynamics model of Lennard-Jones particle systems. A unique feature of our model is that it consists of two types of particles: liquid particles, which tend to form liquid droplets, and gas particles, which remain supercritical gaseous states under the depressurization realized by simulations. The system has a pipe-like structure similar to the model of a shock tube. We observed physical quantities and flow regimes in systems with various combinations of initial particle number densities and initial temperatures. It is observed that a physical quantity Q, such as pressure, at position z measured along a pipe-like system at time t follows a scaling relation Q(z,t)=Q(zt) with a scaling function Q(ζ). A similar scaling relation holds for time evolution of flow regimes in a system. These scaling relations lead to a regime map of explosive flows in parameter spaces of local physical quantities. The validity of the scaling relations of physical quantities means that physics of equilibrium systems, such as an equation of state, is applicable to explosive flows in our simulations, though the explosive flows involve highly nonequilibrium processes. In other words, if the breaking of the scaling relations is observed, it means that the explosive flows cannot be fully described by physics of equilibrium systems. We show the possibility of breaking of the scaling relations and discuss its implications in the last section. © 2011 Elsevier B.V. All rights reserved.

  1. Flow topologies in different regimes of premixed turbulent combustion: A direct numerical simulation analysis

    KAUST Repository

    Wacks, Daniel H.

    2016-12-02

    The distributions of flow topologies within the flames representing the corrugated flamelets, thin reaction zones, and broken reaction zone regimes of premixed turbulent combustion are investigated using direct numerical simulation data of statistically planar turbulent H-2-air flames with an equivalence ratio phi = 0.7. It was found that the diminishing influence of dilatation rate with increasing Karlovitz number has significant influences on the statistical behaviors of the first, second, and third invariants (i.e., P, Q, and R) of the velocity gradient tensor. These differences are reflected in the distributions of the flow topologies within the flames considered in this analysis. This has important consequences for those topologies that make dominant contributions to the scalar-turbulence interaction and vortex-stretching terms in the scalar dissipation rate and enstrophy transport equations, respectively. Detailed physical explanations are provided for the observed regime dependences of the flow topologies and their implications on the scalar dissipation rate and enstrophy transport.

  2. Flow topologies in different regimes of premixed turbulent combustion: A direct numerical simulation analysis

    KAUST Repository

    Wacks, Daniel H.; Chakraborty, Nilanjan; Klein, Markus; Arias, Paul G.; Im, Hong G.

    2016-01-01

    The distributions of flow topologies within the flames representing the corrugated flamelets, thin reaction zones, and broken reaction zone regimes of premixed turbulent combustion are investigated using direct numerical simulation data of statistically planar turbulent H-2-air flames with an equivalence ratio phi = 0.7. It was found that the diminishing influence of dilatation rate with increasing Karlovitz number has significant influences on the statistical behaviors of the first, second, and third invariants (i.e., P, Q, and R) of the velocity gradient tensor. These differences are reflected in the distributions of the flow topologies within the flames considered in this analysis. This has important consequences for those topologies that make dominant contributions to the scalar-turbulence interaction and vortex-stretching terms in the scalar dissipation rate and enstrophy transport equations, respectively. Detailed physical explanations are provided for the observed regime dependences of the flow topologies and their implications on the scalar dissipation rate and enstrophy transport.

  3. Effect of aspect ratio on relationship between flow resistance and flow regime of two-phase flow in rectangular channel

    International Nuclear Information System (INIS)

    Yan Chaoxing; Yan Changqi; Sun Licheng; Xing Dianchuan; Wang Yang

    2013-01-01

    On the basis of visual observation, the effects of aspect ratio on relationship between flow resistance and flow regime were investigated experimentally for two-phase flow in three rectangular channels with the same cross-section width of 43 mm and different heights of 1.41, 3 and 10 mm, respectively. According to the criteria in terms of restriction factor C o , the former two channels belong to narrow channel, whereas the last one is conventional channel. The experimental results show that the two-phase pressure drops in rectangular channel with different aspect ratios have different variation trends with the increase of the gas velocity. For the 10 mm channel, the gravitational pressure drop makes the major percentage of total pressure drop at low gas velocity while the frictional pressure drop is dominant for the 1.41 mm and 3 mm channels. With the increase of the gas flow rate, the frictional pressure drop contributes more to total pressure drop. The range of churn flow can be distinguished from its pressure drop characteristic in 10 mm channel. (authors)

  4. Wind-Driven Ecological Flow Regimes Downstream from Hydropower Dams

    Science.gov (United States)

    Kern, J.; Characklis, G. W.

    2012-12-01

    challenge, the following study was designed to investigate the potential for wind power integration to alter riparian flow regimes below hydroelectric dams. A hydrological model of a three-dam cascade in the Roanoke River basin (Virginia, USA) is interfaced with a simulated electricity market (i.e. a unit commitment problem) representing the Dominion Zone of PJM Interconnection. Incorporating forecasts of electricity demand, hydro capacity and wind availability, a mixed-integer optimization program minimizes the system cost of meeting hourly demand and reserve requirements by means of a diverse generation portfolio (e.g. nuclear, fossil, hydro, and biomass). A secondary 'balancing' energy market is executed if real-time wind generation is less than the day-ahead forecast, calling upon reserved generation resources to meet the supply shortfall. Hydropower release schedules are determined across a range of wind development scenarios (varying wind's fraction of total installed generating capacity, as well as its geographical source region). Flow regimes for each wind development scenario are compared against both historical and simulated flows under current operations (negligible wind power), as well as simulated natural flows (dam removal), in terms of ecologically relevant flow metrics. Results quantify the ability of wind power development to alter within-week stream flows downstream from hydropower dams.

  5. Estimating the Natural Flow Regime of Rivers With Long-Standing Development: The Northern Branch of the Rio Grande

    Science.gov (United States)

    Blythe, Todd L.; Schmidt, John C.

    2018-02-01

    An estimate of a river's natural flow regime is useful for water resource planning and ecosystem rehabilitation by providing insight into the predisturbance form and function of a river. The natural flow regime of most rivers has been perturbed by development during the 20th century and in some cases, before stream gaging began. The temporal resolution of natural flows estimated using traditional methods is typically not sufficient to evaluate cues that drive native ecosystem function. Additionally, these traditional methods are watershed specific and require large amounts of data to produce accurate results. We present a mass balance method that estimates natural flows at daily time step resolution for the northern branch of the Rio Grande, upstream from the Rio Conchos, that relies only on easily obtained streamflow data. Using an analytical change point method, we identified periods of the measured flow regime during the 20th century for comparison with the estimated natural flows. Our results highlight the significant deviation from natural conditions that occurred during the 20th century. The total annual flow of the northern branch is 95% lower than it would be in the absence of human use. The current 2 year flood has decreased by more than 60%, is shorter in duration, and peaks later in the year. When compared to unregulated flows estimated using traditional mass balance accounting methods, our approach provides similar results.

  6. Place, Capital Flows and Property Regimes: The Elites’ Former Houses in Beijing’s South Luogu Lane

    Directory of Open Access Journals (Sweden)

    Zhifen Cheng

    2014-12-01

    Full Text Available Place is seen as a process whereby social and cultural forms are reproduced. This process is closely linked to capital flows, which are, in turn, shaped by changing property regimes. However, relatively little attention has been paid to the relationship between property regimes, capital flows and place-making. The goal of this paper is to highlight the role of changing property regimes in the production of place. Our research area is South Luogu Lane (SLL in Central Beijing. We take elites’ former houses in SLL as the main unit of analysis in this study. From studying this changing landscape, we draw four main conclusions. First, the location of SSL was critical in enabling it to emerge as a high-status residential community near the imperial city. Second, historical patterns of capital accumulation influenced subsequent rounds of private investment into particular areas of SLL. Third, as laws relating to the ownership of land and real estate changed fundamentally in the early 1950s and again in the 1980s, the target and intensity of capital flows into housing in SLL changed too. Fourth, these changes in capital flow are linked to ongoing changes in the place image of SLL.

  7. A Modeling Approach for Evaluating the Coupled Riparian Vegetation-Geomorphic Response to Altered Flow Regimes

    Science.gov (United States)

    Manners, R.; Wilcox, A. C.; Merritt, D. M.

    2016-12-01

    The ecogeomorphic response of riparian ecosystems to a change in hydrologic properties is difficult to predict because of the interactions and feedbacks among plants, water, and sediment. Most riparian models of community dynamics assume a static channel, yet geomorphic processes strongly control the establishment and survival of riparian vegetation. Using a combination of approaches that includes empirical relationships and hydrodynamic models, we model the coupled vegetation-topographic response of three cross-sections on the Yampa and Green Rivers in Dinosaur National Monument, to a shift in the flow regime. The locations represent the variable geomorphology and vegetation composition of these canyon-bound rivers. We account for the inundation and hydraulic properties of vegetation plots surveyed over three years within International River Interface Cooperative (iRIC) Fastmech, equipped with a vegetation module that accounts for flexible stems and plant reconfiguration. The presence of functional groupings of plants, or those plants that respond similarly to environmental factors such as water availability and disturbance are determined from flow response curves developed for the Yampa River. Using field measurements of vegetation morphology, distance from the channel centerline, and dominant particle size and modeled inundation properties we develop an empirical relationship between these variables and topographic change. We evaluate vegetation and channel form changes over decadal timescales, allowing for the integration of processes over time. From our analyses, we identify thresholds in the flow regime that alter the distribution of plants and reduce geomorphic complexity, predominately through side-channel and backwater infilling. Simplification of some processes (e.g., empirically-derived sedimentation) and detailed treatment of others (e.g., plant-flow interactions) allows us to model the coupled dynamics of riparian ecosystems and evaluate the impact of

  8. On the definition of dominant force regimes for flow boiling heat transfer by using single mini-tubes

    Science.gov (United States)

    Baba, Soumei; Sawada, Kenichiro; Kubota, Chisato; Kawanami, Osamu; Asano, Hitoshi; Inoue, Koichi; Ohta, Haruhiko

    Recent increase in the size of space platforms requires the management of larger amount of waste heat under high heat flux conditions and the transportation of it along a long distance to the radiator. Flow boiling applied to the thermal management system in space attracts much attention as promising means to realize high-performance heat transfer and transport because of large latent heat of vaporization. In microgravity two-phase flow phenomena are quite different from those under 1-g condition because buoyancy effects are significantly reduced and surface tension becomes dominant. By the similar reason, flow boiling characteristics in mini channels are not the same as those in channels of normal sizes. In the present stage, however, the boundary between the regimes of body force dominated and of surface tension dominated is not clear. The design of space thermal devices, operated under the conditions where no effect of gravity is expected, will improve the reliability of their ground tests, provided that the boundaries of dominant force regimes are clarified quantitatively in advance. In flow boiling in mini channels or in parallel channels, back flow could be occurred because of rapid growth of bubbles in a confined space, resulting flow rate fluctuation. Flow boiling heat transfer characteristics in mini channels can be changed considerably by the existence of inlet flow rate fluctuation. It is important to pay attention to experimental accuracy and to use a single circular mini-tube to compare heat transfer characteristics with those of normal size tubes. In the present paper, effects of tube orientations, i.e. vertical upward flow, vertical downward flow and horizontal flow, on flow boiling heat transfer characteristics is investigated for FC72 flowing in single mini-tubes with inner diameters of 0.13 and 0.51 mm to establish a reliable dominant force regime map. If the regime map is described by using dimensionless groups of Bond, Weber and Froude numbers

  9. Flow regimes and heat transfer in vertical narrow annuli

    International Nuclear Information System (INIS)

    Ulke, A.; Goldberg, I.

    1993-01-01

    In shell side boiling heat exchangers narrow crevices that are formed between the tubes and the tube support structure provide areas for local thermal-hydraulic conditions which differ significantly from bulk fluid conditions. Understanding of the processes of boiling and dryout in flow restricted crevices can help in designing of tube support geometries to minimize the likelihood of tube support plate and tube corrosion observed in commercial power plant steam generators. This paper describes a one dimensional thermal-hydraulic model of a vertical crevice between a tube and a support plate with cylindrical holes. The annulus formed by the support plate hole and an eccentrically located tube has been represented by vertical strips. The formation, growth and collapse of a steam bubble in each strip has been determined. Based on the bubble history, and flow regimes characterized by ''isolated'' bubbles, ''coalesced'' bubbles and liquid deficient regions have been defined

  10. Hydrological classification of natural flow regimes to support environmental flow assessments in intensively regulated Mediterranean rivers, Segura River Basin (Spain).

    Science.gov (United States)

    Belmar, Oscar; Velasco, Josefa; Martinez-Capel, Francisco

    2011-05-01

    Hydrological classification constitutes the first step of a new holistic framework for developing regional environmental flow criteria: the "Ecological Limits of Hydrologic Alteration (ELOHA)". The aim of this study was to develop a classification for 390 stream sections of the Segura River Basin based on 73 hydrological indices that characterize their natural flow regimes. The hydrological indices were calculated with 25 years of natural monthly flows (1980/81-2005/06) derived from a rainfall-runoff model developed by the Spanish Ministry of Environment and Public Works. These indices included, at a monthly or annual basis, measures of duration of droughts and central tendency and dispersion of flow magnitude (average, low and high flow conditions). Principal Component Analysis (PCA) indicated high redundancy among most hydrological indices, as well as two gradients: flow magnitude for mainstream rivers and temporal variability for tributary streams. A classification with eight flow-regime classes was chosen as the most easily interpretable in the Segura River Basin, which was supported by ANOSIM analyses. These classes can be simplified in 4 broader groups, with different seasonal discharge pattern: large rivers, perennial stable streams, perennial seasonal streams and intermittent and ephemeral streams. They showed a high degree of spatial cohesion, following a gradient associated with climatic aridity from NW to SE, and were well defined in terms of the fundamental variables in Mediterranean streams: magnitude and temporal variability of flows. Therefore, this classification is a fundamental tool to support water management and planning in the Segura River Basin. Future research will allow us to study the flow alteration-ecological response relationship for each river type, and set the basis to design scientifically credible environmental flows following the ELOHA framework.

  11. Impacts of Land Use Change on the Natural Flow Regime: A Case Study in the Meramec River Watershed in Eastern Missouri, USA

    Science.gov (United States)

    Wu, C. L.; Knouft, J.; Chu, M.

    2017-12-01

    The natural flow regime within a watershed can be considered as the expected temporal patterns of streamflow variation in the absence of human impacts. While ecosystems have evolved to function under these conditions, the natural flow regime of most rivers has been significantly altered by human activities. Land use change, including the development of agriculture and urbanization, is a primary cause of the loss of natural flow regimes. These changes have altered discharge volume, timing, and variability, and consequently affected the structure and functioning of river ecosystems. The Meramec River watershed is located in east central Missouri and changes in land use have been the primary factor impacting flow regimes across the watershed. In this study, a watershed model, the Soil and Water Assessment Tool (SWAT), was developed to simulate a long-term time series of streamflow (1978-2014) within the watershed. Model performance was evaluated using statistical metrics and graphical technique including R-squared, Nash-Sutcliffe efficiency, cumulative error, and 1:1-ratio comparison between observed and simulated variables. The calibrated and validated SWAT model was then used to quantify the responses of the watershed when it was a forested natural landscape. An Indicator of Hydrologic Alteration (IHA) approach was applied to characterize the flow regime under the current landcover conditions as well as the simulated natural flow regime under the no land use change scenario. Differences in intra- and inter-annual ecologically relevant flow metrics were then compared using SWAT model outputs in conjunction with the IHA approach based on model outputs from current and no land use change conditions. This study provides a watershed-scale understanding of effects of land use change on a river's flow variability and provides a framework for the development of restoration plans for heavily altered watersheds.

  12. Low Flow Regimes of the Tarim River Basin, China: Probabilistic Behavior, Causes and Implications

    Directory of Open Access Journals (Sweden)

    Peng Sun

    2018-04-01

    Full Text Available Droughts are a frequent occurrence in Xinjiang, China, and therefore fundamental to determining their hydrologic characteristics is low flow analysis. To that end, 11 probability distribution functions and 26 copulas functions were employed to analyze the changing characteristics of low flow regime (defined as seven-day low flow of the Tarim River Basin. Results indicated that: (1 The Wakeby distribution satisfactorily described the probabilistic behavior of the low flow regime. According to Akaike Information Criterion (AIC, Bayesian Information Criterions (BIC, maximum likelihood, and other residual-based metrics, Tawn copula, Farlie–Gumbel–Morgenstern copula and Frank copula were the best choice and used in this current study. (2 After 1987, hydrological droughts of longer return periods were prone to higher occurrence frequency. (3 The low flow volume has been increasing in recent years due to the temperature-induced increase of snowmelt and increasing precipitation. However, hydrological droughts can be expected to occur due to the massive increase in water demand from the development of irrigated agriculture, increasing arable land and livestock farming. As a result, the water shortage in the lower Tarim River Basin will be increasingly severe under the influence of climate change and human activities. To alleviate the shortage would call for the development of water-saving agricultural irrigation, water-saving technology, conservation of eco-environment and sustainable development of local socio-economy.

  13. Flow and heat transfer regimes during quenching of hot surfaces

    International Nuclear Information System (INIS)

    Barnea, Y.; Elias, E.

    1993-05-01

    Reflooding experiments have been performed to study flow and heat transfer regimes in a heated annular vertical channel under supercooled inlet conditions. A gamma densitometer was employed to determine the void fraction as a function of the distance from the quench front. Surface heat fluxes were determined by fast measurements of the temperature spatial distribution. Two quench front is shown to lie in the transition boiling region which spreads into the dry and wet segments of the heated surface. (authors) 5 refs, 3 figs

  14. Linking Flow Regime and Water Quality in Rivers: a Challenge to Adaptive Catchment Management

    Directory of Open Access Journals (Sweden)

    Christer Nilsson

    2008-12-01

    Full Text Available Water quality describes the physicochemical characteristics of the water body. These vary naturally with the weather and with the spatiotemporal variation of the water flow, i.e., the flow regime. Worldwide, biota have adapted to the variation in these variables. River channels and their riparian zones contain a rich selection of adapted species and have been able to offer goods and services for sustaining human civilizations. Many human impacts on natural riverine environments have been destructive and present opportunities for rehabilitation. It is a big challenge to satisfy the needs of both humans and nature, without sacrificing one or the other. New ways of thinking, new policies, and institutional commitment are needed to make improvements, both in the ways water flow is modified in rivers by dam operations and direct extractions, and in the ways runoff from adjacent land is affected by land-use practices. Originally, prescribed flows were relatively static, but precepts have been developed to encompass variation, specifically on how water could be shared over the year to become most useful to ecosystems and humans. A key aspect is how allocations of water interact with physicochemical variation of water. An important applied question is how waste releases and discharge can be managed to reduce ecological and sanitary problems that might arise from inappropriate combinations of flow variation and physicochemical characteristics of water. We review knowledge in this field, provide examples on how the flow regime and the water quality can impact ecosystem processes, and conclude that most problems are associated with low-flow conditions. Given that reduced flows represent an escalating problem in an increasing number of rivers worldwide, managers are facing enormous challenges.

  15. Validating alternative methodologies to estimate the hydrological regime of temporary streams when flow data are unavailable

    Science.gov (United States)

    Llorens, Pilar; Gallart, Francesc; Latron, Jérôme; Cid, Núria; Rieradevall, Maria; Prat, Narcís

    2016-04-01

    Aquatic life in temporary streams is strongly conditioned by the temporal variability of the hydrological conditions that control the occurrence and connectivity of diverse mesohabitats. In this context, the software TREHS (Temporary Rivers' Ecological and Hydrological Status) has been developed, in the framework of the LIFE Trivers project, to help managers for adequately implement the Water Framework Directive in this type of water bodies. TREHS, using the methodology described in Gallart et al (2012), defines six temporal 'aquatic states', based on the hydrological conditions representing different mesohabitats, for a given reach at a particular moment. Nevertheless, hydrological data for assessing the regime of temporary streams are often non-existent or scarce. The scarcity of flow data makes frequently impossible the characterization of temporary streams hydrological regimes and, as a consequence, the selection of the correct periods and methods to determine their ecological status. Because of its qualitative nature, the TREHS approach allows the use of alternative methodologies to assess the regime of temporary streams in the lack of observed flow data. However, to adapt the TREHS to this qualitative data both the temporal scheme (from monthly to seasonal) as well as the number of aquatic states (from 6 to 3) have been modified. Two alternatives complementary methodologies were tested within the TREHS framework to assess the regime of temporary streams: interviews and aerial photographs. All the gauging stations (13) belonging to the Catalan Internal Catchments (NE, Spain) with recurrent zero flows periods were selected to validate both methodologies. On one hand, non-structured interviews were carried out to inhabitants of villages and small towns near the gauging stations. Flow permanence metrics for input into TREHS were drawn from the notes taken during the interviews. On the other hand, the historical series of available aerial photographs (typically 10

  16. The effects of competing trade regimes on bilateral trade flows: case of Serbia

    Directory of Open Access Journals (Sweden)

    Predrag Bjelić

    2012-12-01

    Full Text Available The aim of this paper is to investigate the effects of competing trade regimes on Serbian trade with its most significant (traditional partners, like European Union and CEFTA 2006 signatories, and other untraditional trade partners with favourable trade regime, like the USA. To this end, gravity model with bilateral and time effects is estimated by Hausman-Taylor AR(1 instrumental variable estimator, using panel data on bilateral trade between Serbia and its main trade partners during the period 2001-2010. The results indicate that overall level of development and difference in factor endowments stimulate Serbia’s exports, which is in accordance with theoretical foundation that inter-industry trade is predominant in exports of less developed countries. Moreover, competing trade regimes appear as important determinant of Serbia’s trade relations, whereas additional liberalization of trade regime with the USA as untraditional trade partner, even asymmetrical to Serbia’s favour, cannot divert trade flows from traditional partners in the long-run. This could mean that distance plays more prominent role in bilateral trade than the degree of liberalization of trade regimes in case of Serbia. The result could be due to the contemporaneous effects of trade preferences granted to Serbia by the EU and other CEFTA 2006 signatories, main trading partners of Serbia.

  17. Validating the MFiX-DEM Model for Flow Regime Prediction in a 3D Spouted Bed

    Energy Technology Data Exchange (ETDEWEB)

    Banerjee, Subhodeep [National Energy Technology Lab. (NETL), Pittsburgh, PA, and Morgantown, WV (United States). Research and Innovation Center; Oak Ridge Inst. for Science and Education (ORISE), Oak Ridge, TN (United States); Guenther, Chris [National Energy Technology Lab. (NETL), Pittsburgh, PA, and Morgantown, WV (United States). Research and Innovation Center; Rogers, William A. [National Energy Technology Lab. (NETL), Pittsburgh, PA, and Morgantown, WV (United States). Research and Innovation Center

    2018-02-08

    The spout-fluidized bed reactor with relatively large oxygen carrier particles offers several advantages in chemical looping combustion operation using solid fuels. The large difference in size and weight between the oxygen carrier particles and the smaller coal or ash particles allows the oxygen carrier to be easily segregated for recirculation; the increased solids mixing due to dynamic flow pattern in the spout-fluidization regime prevents agglomeration. The primary objective in this work is to determine the effectiveness of the MFiX-DEM model in predicting the flow regime in a spouted bed. Successful validation of the code will allow the user to fine tune the operating conditions of a spouted bed to achieve the desired operating condition.

  18. On the use of area-averaged void fraction and local bubble chord length entropies as two-phase flow regime indicators

    International Nuclear Information System (INIS)

    Hernandez, Leonor; Julia, J.E.; Paranjape, Sidharth; Hibiki, Takashi; Ishii, Mamoru

    2010-01-01

    In this work, the use of the area-averaged void fraction and bubble chord length entropies is introduced as flow regime indicators in two-phase flow systems. The entropy provides quantitative information about the disorder in the area-averaged void fraction or bubble chord length distributions. The CPDF (cumulative probability distribution function) of void fractions and bubble chord lengths obtained by means of impedance meters and conductivity probes are used to calculate both entropies. Entropy values for 242 flow conditions in upward two-phase flows in 25.4 and 50.8-mm pipes have been calculated. The measured conditions cover ranges from 0.13 to 5 m/s in the superficial liquid velocity j f and ranges from 0.01 to 25 m/s in the superficial gas velocity j g . The physical meaning of both entropies has been interpreted using the visual flow regime map information. The area-averaged void fraction and bubble chord length entropies capability as flow regime indicators have been checked with other statistical parameters and also with different input signals durations. The area-averaged void fraction and the bubble chord length entropies provide better or at least similar results than those obtained with other indicators that include more than one parameter. The entropy is capable to reduce the relevant information of the flow regimes in only one significant and useful parameter. In addition, the entropy computation time is shorter than the majority of the other indicators. The use of one parameter as input also represents faster predictions. (orig.)

  19. Final report for Fundamental study of long-short interfacial wave interactions with application for flow regime development

    CERN Document Server

    McCready, M

    2000-01-01

    The long waves that cause slugs almost always form more slowly than short waves, and linear stability always predicts that the growth rate for long waves is much less than that for short waves. However, at many conditions above neutral stability, long waves dominate the wave field. Three different studies were undertaken as part of the funded work: (1) linear interaction for unsteady flows; (2) wave evolution in oil-water channel flows; (3) retrograde stability and subcritical bifurcations. The oil-water system was used as a surrogate for gas-liquid systems because the gas phase is usually turbulent, and this complication is thus avoided although the phenomena involved are similar. The following overall conclusions about flow regime development were reached: (a) Oscillations in pressure and flow rate, due to interfacial waves or a malfunctioning pump, can cause significant growth rate changes in short waves within narrow FR-equency ranges, but probably do not have a large effect on long waves and thus regime ...

  20. The evaluation of validity of the RELAP5/Mod3 flow regime map for horizontal small diameter tubes at low pressure

    Energy Technology Data Exchange (ETDEWEB)

    Agafonova, N. [St. Petersburg State Technical Univ. (Russian Federation); Banati, J. [Lappeenranta Univ. of Technology (Finland)

    1997-12-31

    RELAP5/MOD3 code was developed for Western type power water reactors with vertical steam generators. Thus, this code should be validated also for WWER design with horizontal steam generators. In application for horizontal steam generators the situation with two-phase flow inside small diameter tubes is possible when the first circuit pressure drops in accident below the pressure level in the boiling water. It is known that computer codes have not always modelled correctly the two-phase flow inside horizontal tubes at low pressures (less than 4-6 MPa). It may be the result of erroneous prediction of the flow regime. Correct prediction of the flow regime is especially important for the fully or partly stratified flow in horizontal tubes. The aim of this study is the attempt of verification of the flow regime map, which is used in the RELAP5/MOD3 computer code for two-phase flow in horizontal small diameter tubes. `Small diameter tube` means according RELAP5/MOD3 that the inner diameter of the tube is less (or equal) than 0.018 m. The inner tube diameter in horizontal steam generators is equal 0.013 m. (orig.). 19 refs.

  1. The evaluation of validity of the RELAP5/Mod3 flow regime map for horizontal small diameter tubes at low pressure

    Energy Technology Data Exchange (ETDEWEB)

    Agafonova, N [St. Petersburg State Technical Univ. (Russian Federation); Banati, J [Lappeenranta Univ. of Technology (Finland)

    1998-12-31

    RELAP5/MOD3 code was developed for Western type power water reactors with vertical steam generators. Thus, this code should be validated also for WWER design with horizontal steam generators. In application for horizontal steam generators the situation with two-phase flow inside small diameter tubes is possible when the first circuit pressure drops in accident below the pressure level in the boiling water. It is known that computer codes have not always modelled correctly the two-phase flow inside horizontal tubes at low pressures (less than 4-6 MPa). It may be the result of erroneous prediction of the flow regime. Correct prediction of the flow regime is especially important for the fully or partly stratified flow in horizontal tubes. The aim of this study is the attempt of verification of the flow regime map, which is used in the RELAP5/MOD3 computer code for two-phase flow in horizontal small diameter tubes. `Small diameter tube` means according RELAP5/MOD3 that the inner diameter of the tube is less (or equal) than 0.018 m. The inner tube diameter in horizontal steam generators is equal 0.013 m. (orig.). 19 refs.

  2. The effect of different flow regimes on the growth and metabolic rates of the scleractinian coral Galaxea fascicularis

    NARCIS (Netherlands)

    Schutter, M.; Crocker, J.; Paijmans, A.J.; Janse, M.; Osinga, R.; Verreth, J.A.J.; Wijffels, R.H.

    2010-01-01

    To study the effect of water flow on coral growth, four series of ten coral nubbins of Galaxea fascicularis were exposed to four different flow regimes (0, 10, 20, and 25 cm s-1, bidirectional flow) for 42 weeks. Buoyant weight, surface area, and polyp number were measured at regular intervals. Net

  3. Contribution to numerical methods for all Mach flow regimes and to fluid-porous coupling for the simulation of homogeneous two-phase flows in nuclear reactors

    International Nuclear Information System (INIS)

    Zaza, Chady

    2015-01-01

    The numerical simulation of steam generators of pressurized water reactors is a complex problem, involving different flow regimes and a wide range of length and time scales. An accidental scenario may be associated with very fast variations of the flow with an important Mach number. In contrast in the nominal regime the flow may be stationary, at low Mach number. Moreover whatever the regime under consideration, the array of U-tubes is modelled by a porous medium in order to avoid taking into account the complex geometry of the steam generator, which entails the issue of the coupling conditions at the interface with the free-fluid. We propose a new pressure-correction scheme for cell-centered finite volumes for solving the compressible Navier-Stokes and Euler equations at all Mach number. The existence of a discrete solution, the consistency of the scheme in the Lax sense and the positivity of the internal energy were proved. Then the scheme was extended to the homogeneous two-phase flow models of the GENEPI code developed at CEA. Lastly a multigrid-AMR algorithm was adapted for using our pressure-correction scheme on adaptive grids. Regarding the second issue addressed in this work, the numerical simulation of a fluid flow over a porous bed involves very different length scales. Macroscopic interface models - such as Ochoa-Tapia-Whitaker or Beavers-Joseph law for a viscous flow - represent the transition region between the free-fluid and the porous region by an interface of discontinuity associated with specific transmission conditions. An extension to the Beavers-Joseph law was proposed for the convective regime. By introducing a jump in the kinetic energy at the interface, we recover an interface condition close to the Beavers-Joseph law but with a non-linear slip coefficient, which depends on the free-fluid velocity at the interface and on the Darcy velocity. The validity of this new transmission condition was assessed with direct numerical simulations at

  4. Experimental study for flow regime of downward air-water two-phase flow in a vertical narrow rectangular channel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, T. H.; Yun, B. J.; Jeong, J. H. [Pusan National University, Geunjeong-gu, Busan (Korea, Republic of)

    2015-05-15

    Studies were mostly about flow in upward flow in medium size circular tube. Although there are great differences between upward and downward flow, studies on vertical upward flow are much more active than those on vertical downward flow in a channel. In addition, due to the increase of surface forces and friction pressure drop, the pattern of gas-liquid two-phase flow bounded to the gap of inside the rectangular channel is different from that in a tube. The downward flow in a rectangular channel is universally applicable to cool the plate type nuclear fuel in research reactor. The sub-channel of the plate type nuclear fuel is designed with a few millimeters. Downward air-water two-phase flow in vertical rectangular channel was experimentally observed. The depth, width, and length of the rectangular channel is 2.35 mm, 66.7 mm, and 780 mm, respectively. The test section consists of transparent acrylic plates confined within a stainless steel frame. The flow patterns of the downward flow in high liquid velocity appeared to be similar to those observed in previous studies with upward flow. In downward flow, the transition lines for bubbly-slug and slug-churn flow shift to left in the flow regime map constructed with abscissa of the superficial gas velocity and ordinate of the superficial liquid velocity. The flow patterns observed with downward flow at low liquid velocity are different from those with upward flow.

  5. Ion-neutral Clustering of Bile Acids in Electrospray Ionization Across UPLC Flow Regimes

    Science.gov (United States)

    Brophy, Patrick; Broeckling, Corey D.; Murphy, James; Prenni, Jessica E.

    2018-02-01

    Bile acid authentic standards were used as model compounds to quantitatively evaluate complex in-source phenomenon on a UPLC-ESI-TOF-MS operated in the negative mode. Three different diameter columns and a ceramic-based microfluidic separation device were utilized, allowing for detailed descriptions of bile acid behavior across a wide range of flow regimes and instantaneous concentrations. A custom processing algorithm based on correlation analysis was developed to group together all ion signals arising from a single compound; these grouped signals produce verified compound spectra for each bile acid at each on-column mass loading. Significant adduction was observed for all bile acids investigated under all flow regimes and across a wide range of bile acid concentrations. The distribution of bile acid containing clusters was found to depend on the specific bile acid species, solvent flow rate, and bile acid concentration. Relative abundancies of each cluster changed non-linearly with concentration. It was found that summing all MS level (low collisional energy) ions and ion-neutral adducts arising from a single compound improves linearity across the concentration range (0.125-5 ng on column) and increases the sensitivity of MS level quantification. The behavior of each cluster roughly follows simple equilibrium processes consistent with our understanding of electrospray ionization mechanisms and ion transport processes occurring in atmospheric pressure interfaces. [Figure not available: see fulltext.

  6. A probabilistic approach to quantifying spatial patterns of flow regimes and network-scale connectivity

    Science.gov (United States)

    Garbin, Silvia; Alessi Celegon, Elisa; Fanton, Pietro; Botter, Gianluca

    2017-04-01

    The temporal variability of river flow regime is a key feature structuring and controlling fluvial ecological communities and ecosystem processes. In particular, streamflow variability induced by climate/landscape heterogeneities or other anthropogenic factors significantly affects the connectivity between streams with notable implication for river fragmentation. Hydrologic connectivity is a fundamental property that guarantees species persistence and ecosystem integrity in riverine systems. In riverine landscapes, most ecological transitions are flow-dependent and the structure of flow regimes may affect ecological functions of endemic biota (i.e., fish spawning or grazing of invertebrate species). Therefore, minimum flow thresholds must be guaranteed to support specific ecosystem services, like fish migration, aquatic biodiversity and habitat suitability. In this contribution, we present a probabilistic approach aiming at a spatially-explicit, quantitative assessment of hydrologic connectivity at the network-scale as derived from river flow variability. Dynamics of daily streamflows are estimated based on catchment-scale climatic and morphological features, integrating a stochastic, physically based approach that accounts for the stochasticity of rainfall with a water balance model and a geomorphic recession flow model. The non-exceedance probability of ecologically meaningful flow thresholds is used to evaluate the fragmentation of individual stream reaches, and the ensuing network-scale connectivity metrics. A multi-dimensional Poisson Process for the stochastic generation of rainfall is used to evaluate the impact of climate signature on reach-scale and catchment-scale connectivity. The analysis shows that streamflow patterns and network-scale connectivity are influenced by the topology of the river network and the spatial variability of climatic properties (rainfall, evapotranspiration). The framework offers a robust basis for the prediction of the impact of

  7. How is the impact of climate change on river flow regimes related to the impact on mean annual runoff? A global-scale analysis

    International Nuclear Information System (INIS)

    Döll, Petra; Schmied, Hannes Müller

    2012-01-01

    To assess the impact of climate change on freshwater resources, change in mean annual runoff (MAR) is only a first indicator. In addition, it is necessary to analyze changes of river flow regimes, i.e. changes in the temporal dynamics of river discharge, as these are important for the well-being of humans (e.g. with respect to water supply) and freshwater-dependent biota (e.g. with respect to habitat availability). Therefore, we investigated, in a global-scale hydrological modeling study, the relation between climate-induced changes of MAR and changes of a number of river flow regime indicators, including mean river discharge, statistical low and high flows, and mean seasonal discharge. In addition, we identified, for the first time at the global scale, where flow regime shifts from perennial to intermittent flow regimes (or vice versa) may occur due to climate change. Climate-induced changes of all considered river flow regime indicators (except seasonal river flow changes) broadly follow the spatial pattern of MAR changes. The differences among the computed changes of MAR due to the application of the two climate models are larger than the differences between the change of MAR and the change of the diverse river flow indicators for one climate model. At the sub-basin and grid cell scales, however, there are significant differences between the changes of MAR, mean annual river discharge, and low and high flows. Low flows are projected to be more than halved by the 2050s in almost twice the area as compared to MAR. Similarly, northern hemisphere summer flows decrease more strongly than MAR. Differences between the high emissions scenario A2 (with emissions of 25 Gt C yr −1 in the 2050s) and the low emissions scenario B2 (16 Gt C yr −1 ) are generally small as compared to the differences due to the two climate models. The benefits of avoided emissions are, however, significant in those areas where flows are projected to be more than halved due to climate change

  8. Application of radial basis function in densitometry of stratified regime of liquid-gas two phase flows

    International Nuclear Information System (INIS)

    Roshani, G.H.; Nazemi, E.; Roshani, M.M.

    2017-01-01

    In this paper, a novel method is proposed for predicting the density of liquid phase in stratified regime of liquid-gas two phase flows by utilizing dual modality densitometry technique and artificial neural network (ANN) model of radial basis function (RBF). The detection system includes a 137 Cs radioactive source and two NaI(Tl) detectors for registering transmitted and scattered photons. At the first step, a Monte Carlo simulation model was utilized to obtain the optimum position for the scattering detector in dual modality densitometry configuration. At the next step, an experimental setup was designed based on obtained optimum position for detectors from simulation in order to generate the required data for training and testing the ANN. The results show that the proposed approach could be successfully applied for predicting the density of liquid phase in stratified regime of gas-liquid two phase flows with mean relative error (MRE) of less than 0.701. - Highlights: • Density of liquid phase in stratified regime of two phase flows was predicted. • Combination of dual modality densitometry technique and ANN was utilized. • Detection system includes a 137 Cs radioactive source and two NaI(Tl) detectors. • MCNP simulation was done to obtain the optimum position for the scattering detector. • An experimental setup was designed to generate the required data for training the ANN.

  9. About the high flow regime of the rivers of Kosovo and Metohia

    Directory of Open Access Journals (Sweden)

    Živković Nenad

    2009-01-01

    Full Text Available The examples from Kosovo and Metohia attempted to point to some problems in the domain of hydrogeographic regionalization. The river water regime, especially the phase of high flows which marks this regime, has been the topic of almost all researches which treat water resources of drainage basins. However, the thing that has not been achieved till now is the unique solution by which the classification of rivers would be made according to this feature. On this example it has been shown that even some older methods, based on genetic analysis of hydrograms and of global type, as well as some recent ones, with lot of quantitative entry and regional approaches, cannot with certainty answer all the challenges which river regimes bring with themselves. This work shows that apart from climate, orographic and physiognomic features of drainage basins, the periods of data processing and the analysis of individual intra-annual series of discharges are very important as well. Discretization on time periods shorter than one month, as well as elimination of the extreme values of discharges in the longtime series is recommended for the future research.

  10. Consistent lattice Boltzmann modeling of low-speed isothermal flows at finite Knudsen numbers in slip-flow regime: Application to plane boundaries.

    Science.gov (United States)

    Silva, Goncalo; Semiao, Viriato

    2017-07-01

    The first nonequilibrium effect experienced by gaseous flows in contact with solid surfaces is the slip-flow regime. While the classical hydrodynamic description holds valid in bulk, at boundaries the fluid-wall interactions must consider slip. In comparison to the standard no-slip Dirichlet condition, the case of slip formulates as a Robin-type condition for the fluid tangential velocity. This makes its numerical modeling a challenging task, particularly in complex geometries. In this work, this issue is handled with the lattice Boltzmann method (LBM), motivated by the similarities between the closure relations of the reflection-type boundary schemes equipping the LBM equation and the slip velocity condition established by slip-flow theory. Based on this analogy, we derive, as central result, the structure of the LBM boundary closure relation that is consistent with the second-order slip velocity condition, applicable to planar walls. Subsequently, three tasks are performed. First, we clarify the limitations of existing slip velocity LBM schemes, based on discrete analogs of kinetic theory fluid-wall interaction models. Second, we present improved slip velocity LBM boundary schemes, constructed directly at discrete level, by extending the multireflection framework to the slip-flow regime. Here, two classes of slip velocity LBM boundary schemes are considered: (i) linear slip schemes, which are local but retain some calibration requirements and/or operation limitations, (ii) parabolic slip schemes, which use a two-point implementation but guarantee the consistent prescription of the intended slip velocity condition, at arbitrary plane wall discretizations, further dispensing any numerical calibration procedure. Third and final, we verify the improvements of our proposed slip velocity LBM boundary schemes against existing ones. The numerical tests evaluate the ability of the slip schemes to exactly accommodate the steady Poiseuille channel flow solution, over

  11. Consistent lattice Boltzmann modeling of low-speed isothermal flows at finite Knudsen numbers in slip-flow regime: Application to plane boundaries

    Science.gov (United States)

    Silva, Goncalo; Semiao, Viriato

    2017-07-01

    The first nonequilibrium effect experienced by gaseous flows in contact with solid surfaces is the slip-flow regime. While the classical hydrodynamic description holds valid in bulk, at boundaries the fluid-wall interactions must consider slip. In comparison to the standard no-slip Dirichlet condition, the case of slip formulates as a Robin-type condition for the fluid tangential velocity. This makes its numerical modeling a challenging task, particularly in complex geometries. In this work, this issue is handled with the lattice Boltzmann method (LBM), motivated by the similarities between the closure relations of the reflection-type boundary schemes equipping the LBM equation and the slip velocity condition established by slip-flow theory. Based on this analogy, we derive, as central result, the structure of the LBM boundary closure relation that is consistent with the second-order slip velocity condition, applicable to planar walls. Subsequently, three tasks are performed. First, we clarify the limitations of existing slip velocity LBM schemes, based on discrete analogs of kinetic theory fluid-wall interaction models. Second, we present improved slip velocity LBM boundary schemes, constructed directly at discrete level, by extending the multireflection framework to the slip-flow regime. Here, two classes of slip velocity LBM boundary schemes are considered: (i) linear slip schemes, which are local but retain some calibration requirements and/or operation limitations, (ii) parabolic slip schemes, which use a two-point implementation but guarantee the consistent prescription of the intended slip velocity condition, at arbitrary plane wall discretizations, further dispensing any numerical calibration procedure. Third and final, we verify the improvements of our proposed slip velocity LBM boundary schemes against existing ones. The numerical tests evaluate the ability of the slip schemes to exactly accommodate the steady Poiseuille channel flow solution, over

  12. Characterization of two-phase flow regimes in horizontal tubes using 81mKr tracer experiments.

    Science.gov (United States)

    Oriol, Jean; Leclerc, Jean Pierre; Berne, Philippe; Gousseau, Georges; Jallut, Christian; Tochon, Patrice; Clement, Patrice

    2008-10-01

    The diagnosis of heat exchangers on duty with respect to flow mal-distributions needs the development of non-intrusive inlet-outlet experimental techniques in order to perform an online fault diagnosis. Tracer experiments are an example of such techniques. They can be applied to mono-phase heat exchangers but also to multi-phase ones. In this case, the tracer experiments are more difficult to perform. In order to check for the capabilities of tracer experiments to be used for the flow mal-distribution diagnosis in the case of multi-phase heat exchangers, we present here a preliminary study on the simplest possible system: two-phase flows in a horizontal tube. (81m)Kr is used as gas tracer and properly collimated NaI (TI) crystal scintillators as detectors. The specific shape of the tracer response allows two-phase flow regimes to be characterized. Signal analysis allows the estimation of the gas phase real average velocity and consequently of the liquid phase real average velocity as well as of the volumetric void fraction. These results are compared successfully to those obtained with liquid phase tracer experiments previously presented by Oriol et al. 2007. Characterization of the two-phase flow regimes and liquid dispersion in horizontal and vertical tubes using coloured tracer and no intrusive optical detector. Chem. Eng. Sci. 63(1), 24-34, as well as to those given by correlations from literature.

  13. Characterization of two-phase flow regimes in horizontal tubes using 81mKr tracer experiments

    International Nuclear Information System (INIS)

    Oriol, Jean; Leclerc, Jean Pierre; Berne, Philippe; Gousseau, Georges; Jallut, Christian; Tochon, Patrice; Clement, Patrice

    2008-01-01

    The diagnosis of heat exchangers on duty with respect to flow mal-distributions needs the development of non-intrusive inlet-outlet experimental techniques in order to perform an online fault diagnosis. Tracer experiments are an example of such techniques. They can be applied to mono-phase heat exchangers but also to multi-phase ones. In this case, the tracer experiments are more difficult to perform. In order to check for the capabilities of tracer experiments to be used for the flow mal-distribution diagnosis in the case of multi-phase heat exchangers, we present here a preliminary study on the simplest possible system: two-phase flows in a horizontal tube. 81m Kr is used as gas tracer and properly collimated NaI (TI) crystal scintillators as detectors. The specific shape of the tracer response allows two-phase flow regimes to be characterized. Signal analysis allows the estimation of the gas phase real average velocity and consequently of the liquid phase real average velocity as well as of the volumetric void fraction. These results are compared successfully to those obtained with liquid phase tracer experiments previously presented by Oriol et al. 2007. Characterization of the two-phase flow regimes and liquid dispersion in horizontal and vertical tubes using coloured tracer and no intrusive optical detector. Chem. Eng. Sci. 63(1), 24-34, as well as to those given by correlations from literature

  14. What Do They Have in Common? Drivers of Streamflow Spatial Correlation and Prediction of Flow Regimes in Ungauged Locations

    Science.gov (United States)

    Betterle, A.; Radny, D.; Schirmer, M.; Botter, G.

    2017-12-01

    The spatial correlation of daily streamflows represents a statistical index encapsulating the similarity between hydrographs at two arbitrary catchment outlets. In this work, a process-based analytical framework is utilized to investigate the hydrological drivers of streamflow spatial correlation through an extensive application to 78 pairs of stream gauges belonging to 13 unregulated catchments in the eastern United States. The analysis provides insight on how the observed heterogeneity of the physical processes that control flow dynamics ultimately affect streamflow correlation and spatial patterns of flow regimes. Despite the variability of recession properties across the study catchments, the impact of heterogeneous drainage rates on the streamflow spatial correlation is overwhelmed by the spatial variability of frequency and intensity of effective rainfall events. Overall, model performances are satisfactory, with root mean square errors between modeled and observed streamflow spatial correlation below 10% in most cases. We also propose a method for estimating streamflow correlation in the absence of discharge data, which proves useful to predict streamflow regimes in ungauged areas. The method consists in setting a minimum threshold on the modeled flow correlation to individuate hydrologically similar sites. Catchment outlets that are most correlated (ρ>0.9) are found to be characterized by analogous streamflow distributions across a broad range of flow regimes.

  15. Scaling relation and regime map of explosive gas–liquid flow of binary Lennard-Jones particle system

    KAUST Repository

    Inaoka, Hajime; Yukawa, Satoshi; Ito, Nobuyasu

    2012-01-01

    liquid droplets, and gas particles, which remain supercritical gaseous states under the depressurization realized by simulations. The system has a pipe-like structure similar to the model of a shock tube. We observed physical quantities and flow regimes

  16. Generation of leachate and the flow regime in landfills

    Energy Technology Data Exchange (ETDEWEB)

    Bendz, D.

    1998-06-01

    In this thesis the generation of leachate and the presence and movement of water in landfilled municipal solid waste (MSW) is investigated. The precipitation-leachate discharge relationship for landfills was found to be dominated by evaporation, accumulation in the soil cover, accumulation in the solid waste and fast gravitational flow in a network of channels. The flow regime is governed by the heterogeneity of the internal geometry of the landfill, which is characterized by a discrete structure, significant horizontal stratification, structural voids, impermeable surfaces, and low capillarity. Also the boundary conditions, that is the water input pattern, has shown to be important for the flow process. Based on this, landfilled waste can be conceptualized as a dual domain medium, consisting of a channel domain and a matrix domain. The matrix flow is slow and diffusive, whereas the channel flow is assumed to be driven solely by gravity and to take place as a thin viscous film on solid surfaces. A kinematic wave model for unsaturated infiltration and internal drainage in the channel domain is presented. The model employs a two-parameter power expression as macroscopic flux law. Solutions were derived for the cases when water enters the channel domain laterally and when water enters from the upper end. The model parameters were determined and interpreted in terms of the internal geometry of the waste medium by fitting the model to one set of infiltration and drainage data derived from a large scale laboratory experiment under transient conditions. The model was validated using another set of data from a sequence of water input events and was shown to perform accurately. A solute transport model was developed by coupling a simple piston flux expression and a mobile-immobile conceptualization of the transport domains with the water flow model. Breakthrough curves derived from steady and transient tracer experiments where interpreted with the model. The transport

  17. Evaluation of piping heat transfer, piping flow regimes, and steam generator heat transfer for the Semiscale Mod-1 isothermal tests

    International Nuclear Information System (INIS)

    French, R.T.

    1975-08-01

    Selected experimental data pertinent to piping heat transfer, transient fluid flow regimes, and steam generator heat transfer obtained during the Semiscale Mod-1 isothermal blowdown test series (Test Series 1) are analyzed. The tests in this first test series were designed to provide counterparts to the LOFT nonnuclear experiments. The data from the Semiscale Mod-1 intact and broken loop piping are evaluated to determine the surface heat flux and average heat transfer coefficients effective during the blowdown transient and compared with well known heat transfer correlations used in the RELAP4 computer program. Flow regimes in horizontal pipe sections are calculated and compared with data obtained from horizontal and vertical densitometers and with an existing steady state flow map. Effects of steam generator heat transfer are evaluated quantitatively and qualitatively. The Semiscale Mod-1 data and the analysis presented in this report are valuable for evaluating the adequacy and improving the predictive capability of analytical models developed to predict system response to piping heat transfer, piping flow regimes, and steam generator heat transfer during a postulated loss-of-coolant accident (LOCA) in a pressurized water reactor (PWR). 16 references. (auth)

  18. Stream flow regime of springs in the Mantiqueira Mountain Range region, Minas Gerais State

    Directory of Open Access Journals (Sweden)

    Alisson Souza de Oliveira

    2014-09-01

    Full Text Available The stream flow regime of four springs located in the Mantiqueira Mountain Range region (MG was evaluated and correlated to the respective recharge area, relief characteristics, land cover and physical and hydrologic soil characteristics. The streamflow regime was characterized by monitoring of discharges, calculating the surface runoff and specific discharge and by modeling the discharge over the recession period using the Maillet method. As all recharge areas have similar relief the effect of it on the streamflow was not possible to identify. Analysis included determining the effect of drainage area size, soil characteristics and land cover on the indicators of the streamflow regime. Size of the recharge area had a positive influence on the indicators mean discharge and surface runoff volume and on the regulation of the streamflow regime (springs L4 and L1. The spring under the smallest area of influence provided the worst results for the above mentioned indicators (spring L3. The effect of forest cover (natural and planted, associated with soil characteristics, was evidenced by the indicators surface runoff (in depth and specific yield, both independent of the recharge area size (springs L4 and L2. The interaction of area size, soil characteristics and forest cover (natural and planted provided the best results for all indicators of streamflow regime in the springs studied in the Mantiqueira Mountain Range (spring L4.

  19. study of solid-liquid flow regimes in mining industry using gamma radiation

    International Nuclear Information System (INIS)

    Salgado, Cesar M.; Brandao, Luis E.B.; Nunes, Rogerio C.; Nascimento, Ana C. de H.; Salgado, William L.

    2013-01-01

    One of the most promising areas in the mining industry is the development of devices for measuring solid mass flowrate in pipelines, mainly in transportation of ore. These units are composed of interconnected pipes where transport of the material is accomplished by pumps capable of driving the ore pellets using water. One of the problems inherent in these systems is the stratification if a critical velocity is reached, the ore pellets begin to sediment at the bottom of the pipe and it may block the system. The solid phase displacement behavior depends on a number of factors (water flowrate, density, pipe diameter, average size of the pellet) which makes the flow regime knowledge essential to the appropriate operation of the system. An apparatus to evaluate the stratification level through of particle (ore pellets) spatial distributions inside the pipe is important because it increases the safety condition of pumping and transportation of solid phase. Therefore, this work presents a study to optimize the geometrical parameters for the identification of a possible stratification of the solid phase inside a pipeline. The detection system uses different NaI(Tl) detectors and gamma ray sources (fan beam geometry), adequately positioned in order to calculate transmitted and scattered beams. Additionally, theoretical models for different flow regimes (homogeneous and stratified) have been developed using MCNP-X mathematical code. (author)

  20. Flow regime visualization and pressure drops of HFO-1234yf, R-134a and R-410A during downward two-phase flow in vertical return bends

    International Nuclear Information System (INIS)

    Padilla, Miguel; Revellin, Rémi; Wallet, Jérémy; Bonjour, Jocelyn

    2013-01-01

    Highlights: ► Visual observation of two-phase flow regimes during downward flow in a return bend. ► Bubble and vapor slug dynamical behaviors in downward slug flow are reported. ► Perturbation lengths up- and downstream of the return bend have been investigated. ► Measurement of 285 pressure drop data points for HFO-1234yf, R-134a and R-410A. -- Abstract: This paper provides a qualitative visual observation of the two-phase flow patterns for HFO-1234yf and R-134a during downward flow in a vertical 6.7 mm inner diameter glass return bend. The different flow regimes observed are: slug, intermittent and annular flows. Bubble and vapor slug dynamical behaviors in downward slug flow are reported for HFO-1234yf. In addition, to determine the perturbation lengths up- and downstream of the return bend, the total pressure drop has been measured at different pressure tap location up- and downstream of the singularity. Furthermore, 285 pressure drop data points measured for two-phase flow of HFO-1234yf, R-134a and R-410A in vertical downward flow return bends are presented. The flow behavior in the return bend, which is subjected to the complex combined actions of gravity and centrifugal force was expressed in terms of the vapor Froude number. This experimental pressure drop database, which is included in the appendix, is compared to four well-known prediction methods available in the literature

  1. Investigation of flow regime in debris bed formation behavior with nonspherical particles

    Directory of Open Access Journals (Sweden)

    Songbai Cheng

    2018-02-01

    Full Text Available It is important to clarify the characteristics of flow regimes underlying the debris bed formation behavior that might be encountered in core disruptive accidents of sodium-cooled fast reactors. Although in our previous publications, by applying dimensional analysis technique, an empirical model, with its reasonability confirmed over a variety of parametric conditions, has been successfully developed to predict the regime transition and final bed geometry formed, so far this model is restricted to predictions of debris mixtures composed of spherical particles. Focusing on this aspect, in this study a new series of experiments using nonspherical particles have been conducted. Based on the knowledge and data obtained, an extension scheme is suggested with the purpose of extending the base model to cover the particle-shape influence. Through detailed analyses and given our current range of experimental conditions, it is found that, by coupling the base model with this scheme, respectable agreement between experiments and model predictions for the regime transition can be achieved for both spherical and nonspherical particles. Knowledge and evidence from our work might be utilized for the future improvement of design of an in-vessel core catcher as well as the development and verification of sodium-cooled fast reactor severe accident analysis codes in China.

  2. Modelling of void formation in the subcooled boiling regime in the ATHLET code to simulate flow instability for research reactors

    International Nuclear Information System (INIS)

    Hainoun, A.

    1996-01-01

    The ATHLET thermohydraulic code was developed at the Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS, Society for Plant and Reactor Safety) to analyse leaks and transients for power reactors. In order to extend the code's range of application to the safety analysis of research reactors, a model was implemented permitting a description of the thermodynamic non-equilibrium effects in the subcooled boiling regime. The aim of the extension is, on one hand, to cover the thermohydraulic instability which is particularly characteristic of research reactors owing to their high power densities and low system pressures and, on the other hand, to provide a consideration of the influence of the steam formed in this boiling regime on the neutron balance. The model developed takes into consideration the competing evaporation and condensation effects in the subcooled boiling regime. It describes the bubble production rate at the superheated heating surfaces as well as the subsequent condensation of the bubbles in the subcooled core flow. The installed model is validated by the recalculation of two extensive series of experiments. In the first series the McMaster experiments on axial void distribution in the subcooled boiling regime are recalculated. The recalculation shows that the extended programme is capable of calculating the axial void distribution in the subcooled boiling regime with good agreement with the data. The second series deals with KFA experiments on thermohydraulic instability (flow excursion) in the subcooled boiling regime, comprising a broad parameter range of heat flow density, inlet temperature and channel width. Recalculation of this experimental series shows that the programme extension ensures simulation of thermohydraulic instability. (orig.)

  3. Analytical Simulation of Flow and Heat Transfer of Two-Phase Nanofluid (Stratified Flow Regime

    Directory of Open Access Journals (Sweden)

    Mohammad Abbasi

    2014-01-01

    Full Text Available Nanofluids have evoked immense interest from researchers all around the globe due to their numerous potential benefits and applications in important fields such as cooling electronic parts, cooling car engines and nuclear reactors. An analytical study of fluid flow of in-tube stratified regime of two-phase nanofluid has been carried out for CuO, Al2O2, TiO3, and Au as applied nanoparticles in water as the base liquid. Liquid film thickness, convective heat transfer coefficient, and dryout length have been calculated. Among the considered nano particles, Al2O3 and TiO2 because of providing more amounts of heat transfer along with longer lengths of dryout found as the most appropriate nanoparticles to achieve cooling objectives.

  4. THE PECULIARITIES OF SEASONAL FLOW REGIME ON SMALL RIVERS FROM THE EASTERN APUSENI MOUNTAINS

    Directory of Open Access Journals (Sweden)

    SOROCOVSCHI V.

    2014-03-01

    Full Text Available Investigated region is overlapping the territory drained by tributaries of Someşul Mic and Arieş River and also the creeks collected by Mureş River between the mouth of Arieş and Geoagiu River. The study is based on processing and interpreting data from 24 gauging stations, of which 18 control surfaces basins below 150 km2. To highlight the features of seasonal flow regime we have considered three periods (1950-1967, 1950-2009 and 1970-2009. Thus, all rivers are recording a dominant flow during spring while the lowest annual average volume is related to winter season. Seasonal time variation of river flow was highlighted by analyzing the trends in the three periods using the variation coefficients.

  5. Investigation and visualization of liquid–liquid flow in a vertically mounted Hele-Shaw cell: flow regimes, velocity and shape of droplets

    International Nuclear Information System (INIS)

    Shad, S; Gates, I D; Maini, B B

    2009-01-01

    The motion and shape of a liquid drop flowing within a continuous, conveying liquid phase in a vertical Hele-Shaw cell were investigated experimentally. The continuous phase was more viscous and wetted the bounding walls of the Hele-Shaw cell. The gap between the Hele-Shaw plates was set equal to 0.0226 cm. Four different flow regimes were observed: (a) small-droplet flow, (b) elongated-droplet flow, (c) churn flow and (d) channel flow. At low capillary number, that is, when capillary forces are larger than viscous forces, the droplet shape was irregular and changed with time and distance, and it moved with lower velocity than that of the conveying phase. At higher capillary number, several different shapes of stabilized elongated and flattened drops were observed. In contrast to gas–liquid systems, the velocities of droplets are higher than that of conveying liquid. New correlations derived from dimensionless analysis and fitted to the experimental data were generated to predict the elongated-drop velocity and aspect ratio

  6. Investigation and visualization of liquid-liquid flow in a vertically mounted Hele-Shaw cell: flow regimes, velocity and shape of droplets

    Science.gov (United States)

    Shad, S.; Gates, I. D.; Maini, B. B.

    2009-11-01

    The motion and shape of a liquid drop flowing within a continuous, conveying liquid phase in a vertical Hele-Shaw cell were investigated experimentally. The continuous phase was more viscous and wetted the bounding walls of the Hele-Shaw cell. The gap between the Hele-Shaw plates was set equal to 0.0226 cm. Four different flow regimes were observed: (a) small-droplet flow, (b) elongated-droplet flow, (c) churn flow and (d) channel flow. At low capillary number, that is, when capillary forces are larger than viscous forces, the droplet shape was irregular and changed with time and distance, and it moved with lower velocity than that of the conveying phase. At higher capillary number, several different shapes of stabilized elongated and flattened drops were observed. In contrast to gas-liquid systems, the velocities of droplets are higher than that of conveying liquid. New correlations derived from dimensionless analysis and fitted to the experimental data were generated to predict the elongated-drop velocity and aspect ratio.

  7. Investigation of bubble flow regimes in nucleate boiling of highly-wetting liquids

    International Nuclear Information System (INIS)

    Tong, W.; Bar-Cohen, A.; Simon, T.W.

    1991-01-01

    This paper describes an investigation of the bubble flow regimes in nucleate boiling of FC-72, a highly-wetting liquid. Theoretically analysis of vapor bubble generation and departure from the heated surface reveals that the heat fluxes required for the merging of consecutive bubbles, for highly-wetting liquids, lie in the upper range of the nucleate boiling heat flux. A visual and photographic study of nucleate boiling from sputtered platinum surfaces has supported the theoretical results and shown that the isolated bubble behavior extends to at least 50-80% of the critical heat flux, considerably higher than observed by others with water. Lateral coalescence of adjacent bubbles has been found to be a more likely cause of the termination of the isolated bubble regime. These findings suggest that thermal transport models which are based on isolated bubble behavior may be applicable to nearly the entire range of nucleate boiling of electronic cooling fluids

  8. Study of volume fractions for stratified and annular regime in multiphase flows using gamma-rays and artificial neural network

    International Nuclear Information System (INIS)

    Salgado, Cesar M.; Brandao, Luis Eduardo; Pereira, Claudio M.N.A.; Ramos, Robson; Schirru, Roberto; Silva, Ademir X.

    2007-01-01

    This work presents methodology based on the use of nuclear technique and artificial intelligence for attainment of volume fractions in stratified and annular multiphase flow regime, oil-water-gas, very frequent in the offshore industry petroliferous. Using the principles of absorption and scattering of gamma-rays and an adequate geometry scheme of detection with two detectors and two energies measurement are gotten and they vary as changes in the volume fractions of flow regime occur. The MCNP-X code was used in order to provide the data training for artificial neural network that matched such information with the respective actual volume fractions of each material. (author)

  9. Study of volume fractions for stratified and annular regime in multiphase flows using gamma-rays and artificial neural network

    Energy Technology Data Exchange (ETDEWEB)

    Salgado, Cesar M.; Brandao, Luis Eduardo; Pereira, Claudio M.N.A.; Ramos, Robson [Instituto de Engenharia Nuclear (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)]. E-mail: otero@ien.gov.br; brandao@ien.gov.br; cmnap@ien.gov.br; robson@ien.gov.br; Schirru, Roberto; Silva, Ademir X. [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Coordenacao dos Programas de Pos-Graduacao de Engenharia (COPPE). Programa de Energia Nuclear (PEN)]. E-mails: ademir@con.ufrj.br; schirru@lmp.ufrj.br

    2007-07-01

    This work presents methodology based on the use of nuclear technique and artificial intelligence for attainment of volume fractions in stratified and annular multiphase flow regime, oil-water-gas, very frequent in the offshore industry petroliferous. Using the principles of absorption and scattering of gamma-rays and an adequate geometry scheme of detection with two detectors and two energies measurement are gotten and they vary as changes in the volume fractions of flow regime occur. The MCNP-X code was used in order to provide the data training for artificial neural network that matched such information with the respective actual volume fractions of each material. (author)

  10. Predicting bulk powder flow dynamics in a continuous mixer operating in transitory regimes

    OpenAIRE

    Ammarcha , Chawki; Gatumel , Cendrine; Dirion , Jean-Louis; Cabassud , Michel; Mizonov , Vadim; Berthiaux , Henri

    2012-01-01

    International audience; Over recent years there has been increasing interest in continuous powder mixing processes, due mainly to the development of on-line measurement techniques. However, our understanding of these processes remains limited, particularly with regard to their flow and mixing dynamics. In the present work, we study the behaviour of a pilot-scale continuous mixer during transitory regimes, in terms of hold-up weight and outflow changes. We present and discuss experimental resu...

  11. Characterization of two-phase flow regimes in horizontal tubes using {sup 81m}Kr tracer experiments

    Energy Technology Data Exchange (ETDEWEB)

    Oriol, Jean [LPAC, CEA Grenoble, 17, rue des Martyrs, 38054 Grenoble Cedex 9 (France); Leclerc, Jean Pierre [Laboratoire des Sciences du Genie Chimique (LSGC), Nancy-Universite, CNRS, BP 20451, F-54001 Nancy (France)], E-mail: leclerc@ensic.inpl-nancy.fr; Berne, Philippe; Gousseau, Georges [L2T, CEA Grenoble, 17, rue des Martyrs, 38054 Grenoble Cedex 9 (France); Jallut, Christian [Universite de Lyon, Universite Lyon 1, LAGEP, UMR CNRS 5007, ESCPE, 43 Bd du 11 novembre 1918, 69622 Villeurbanne Cedex (France); Tochon, Patrice; Clement, Patrice [GRETh, CEA Grenoble, 17, rue des Martyrs, 38054 Grenoble Cedex 9 (France)

    2008-10-15

    The diagnosis of heat exchangers on duty with respect to flow mal-distributions needs the development of non-intrusive inlet-outlet experimental techniques in order to perform an online fault diagnosis. Tracer experiments are an example of such techniques. They can be applied to mono-phase heat exchangers but also to multi-phase ones. In this case, the tracer experiments are more difficult to perform. In order to check for the capabilities of tracer experiments to be used for the flow mal-distribution diagnosis in the case of multi-phase heat exchangers, we present here a preliminary study on the simplest possible system: two-phase flows in a horizontal tube. {sup 81m}Kr is used as gas tracer and properly collimated NaI (TI) crystal scintillators as detectors. The specific shape of the tracer response allows two-phase flow regimes to be characterized. Signal analysis allows the estimation of the gas phase real average velocity and consequently of the liquid phase real average velocity as well as of the volumetric void fraction. These results are compared successfully to those obtained with liquid phase tracer experiments previously presented by Oriol et al. 2007. Characterization of the two-phase flow regimes and liquid dispersion in horizontal and vertical tubes using coloured tracer and no intrusive optical detector. Chem. Eng. Sci. 63(1), 24-34, as well as to those given by correlations from literature.

  12. Lattice Boltzmann Simulations in the Slip and Transition Flow Regime with the Peano Framework

    KAUST Repository

    Neumann, Philipp

    2012-01-01

    We present simulation results of flows in the finite Knudsen range, which is in the slip and transition flow regime. Our implementations are based on the Lattice Boltzmann method and are accomplished within the Peano framework. We validate our code by solving two- and three-dimensional channel flow problems and compare our results with respective experiments from other research groups. We further apply our Lattice Boltzmann solver to the geometrical setup of a microreactor consisting of differently sized channels and a reactor chamber. Here, we apply static adaptive grids to fur-ther reduce computational costs. We further investigate the influence of using a simple BGK collision kernel in coarse grid regions which are further away from the slip boundaries. Our results are in good agreement with theory and non-adaptive simulations, demonstrating the validity and the capabilities of our adaptive simulation software for flow problems at finite Knudsen numbers.

  13. Regimes of Axisymmetric Flow and Scaling Laws in a Rotating Annulus with Local Convective Forcing

    Directory of Open Access Journals (Sweden)

    Susie Wright

    2017-07-01

    Full Text Available We present a numerical study of axisymmetric flow in a rotating annulus in which local thermal forcing, via a heated annular ring on the outside of the base and a cooled circular disk in the centre of the top surface, drives convection. This new configuration is a variant of the classical thermally-driven annulus, where uniform heating and cooling are applied through the outer and inner sidewalls respectively. The annulus provides an analogue to a planetary circulation and the new configuration, with its more relaxed vertical thermal boundary conditions, is expected to better emulate vigorous convection in the tropics and polar regions as well as baroclinic instability in the mid-latitude baroclinic zone. Using the Met Office/Oxford Rotating Annulus Laboratory (MORALS code, we have investigated a series of equilibrated, two dimensional axisymmetric flows across a large region of parameter space. These are characterized in terms of their velocity and temperature fields. When rotation is applied several distinct flow regimes may be identified for different rotation rates and strengths of differential heating. These regimes are defined as a function of the ratio of the horizontal Ekman layer thickness to the non-rotating thermal boundary layer thickness and are found to be similar to those identified in previous annulus experiments. Convection without rotation is also considered and the scaling of the heat transport with Rayleigh number is calculated. This is then compared with existing work on the classical annulus as well as horizontal and Rayleigh-Bénard convection. As with previous studies on both rotating and non-rotating convection the system’s behaviour is found to be aspect ratio dependent. This dependence is seen in the scaling of the non-rotating Nusselt number and in transitions between regimes in the rotating case although further investigation is required to fully explain these observations.

  14. Gas-kinetic unified algorithm for hypersonic flows covering various flow regimes solving Boltzmann model equation in nonequilibrium effect

    International Nuclear Information System (INIS)

    Li, Zhihui; Ma, Qiang; Wu, Junlin; Jiang, Xinyu; Zhang, Hanxin

    2014-01-01

    Based on the Gas-Kinetic Unified Algorithm (GKUA) directly solving the Boltzmann model equation, the effect of rotational non-equilibrium is investigated recurring to the kinetic Rykov model with relaxation property of rotational degrees of freedom. The spin movement of diatomic molecule is described by moment of inertia, and the conservation of total angle momentum is taken as a new Boltzmann collision invariant. The molecular velocity distribution function is integrated by the weight factor on the internal energy, and the closed system of two kinetic controlling equations is obtained with inelastic and elastic collisions. The optimization selection technique of discrete velocity ordinate points and numerical quadrature rules for macroscopic flow variables with dynamic updating evolvement are developed to simulate hypersonic flows, and the gas-kinetic numerical scheme is constructed to capture the time evolution of the discretized velocity distribution functions. The gas-kinetic boundary conditions in thermodynamic non-equilibrium and numerical procedures are studied and implemented by directly acting on the velocity distribution function, and then the unified algorithm of Boltzmann model equation involving non-equilibrium effect is presented for the whole range of flow regimes. The hypersonic flows involving non-equilibrium effect are numerically simulated including the inner flows of shock wave structures in nitrogen with different Mach numbers of 1.5-Ma-25, the planar ramp flow with the whole range of Knudsen numbers of 0.0009-Kn-10 and the three-dimensional re-entering flows around tine double-cone body

  15. River flow regime and snow cover of the Pamir Alay (Central Asia) in a changing climate

    NARCIS (Netherlands)

    Chevallier, P.; Pouyaud, B.; Mojaisky, M.; Bolgov, M.; Olsson, O.; Bauer, M.; Froebrich, J.

    2014-01-01

    The Vakhsh and Pyandj rivers, main tributaries of the Amu Darya River in the mountainous region of the Pamir Alay, play an important role in the water resources of the Aral Sea basin (Central Asia). In this region, the glaciers and snow cover significantly influence the water cycle and flow regime,

  16. Structure of two-phase adiabatic flow in air sparging regime in vertical cylindrical channel with water

    Directory of Open Access Journals (Sweden)

    V. I. Solonin

    2014-01-01

    Full Text Available The article presents a research of two-phase adiabatic flow in air sparging regime in vertical cylindrical channel filled with water. A purpose of the work is to obtain experimental data for further analysis of a character of the moving phases. Research activities used the optic methods PIV (Particle Image Visualization because of their noninvasiveness to obtain data without disturbing effect on the flow. A laser sheet illuminated the fluorescence particles, which were admixed in water along the channel length. A digital camera recorded their motion for a certain time interval that allowed building the velocity vector fields. As a result, gas phase velocity components typical for a steady area of the channel and their relations for various intensity of volume air rate were obtained. A character of motion both for an air bubble and for its surrounding liquid has been conducted. The most probable direction of phases moving in the channel under sparging regime is obtained by building the statistic scalar fields. The use of image processing enabled an analysis of the initial area of the air inlet into liquid. A characteristic curve of the bubbles offset from the axis for various intensity of volume gas rate and channel diameter is defined. A character of moving phases is obtained by building the statistic scalar fields. The values of vertical components of liquid velocity in the inlet part of channel are calculated. Using the obtained data of the gas phase velocities a true void fraction was calculated. It was compared with the values of void fraction, calculated according to the liquid level change in the channel. Obtained velocities were compared with those of the other researchers, and a small difference in their values was explained by experimental conditions. The article is one of the works to research the two-phase flows with no disturbing effect on them. Obtained data allow us to understand a character of moving the two-phase flows in

  17. River adjustments under varying flow and sediment sypply regimes. The role of hydrograh shape

    Science.gov (United States)

    Ferrer-Boix, C.; Elgueta, M. A.; Hassan, M. A.

    2016-12-01

    This research aims to explore how sediment supply conditions and hydrograph shape influence bed surface evolution, vertical and downstream sediment sorting, and sediment transport in gravel bed streams. While a significant body of research has been focused on channel evolution under constant flow regimes, few studies have focused on the impacts of flow variations in channel adjustments. Particularly, we are interested in examining the impact of the sediment supply regime and hydrograph magnitude and duration on channel adjustments and sediment transport rates. To this end, we conducted a set of experiments in a 0.8 m-wide, 5 m-long tilting flume. Flow discharge during the runs was increased and decreased at steps of certain duration allowing us to vary the steepness of rising and falling limbs of hydrographs. The influence of hydrograph shape (symmetrical and asymmetrical) on river morphodynamics was tested. Flow rates during the experiments ranged from 30 l/s to 70 l/s. Some of the experiments were conducted under no feed conditions while others were carried out with sediment supply, which ranged from 10 kg/h to 80 kg/h. The feed texture in these latter runs was identical to that of the original mixture (Dmin = 0.5 mm, Dmax = 64 mm, Dg = 5.65 mm and σg = 3.05). Initial bed slope and surface configuration were obtained after varying times of conditioning under constant flow and no feed. Finally, we conducted equilibrium experiments under constant flow and sediment supply that were used as reference. All these sets of experiments benefited from a very detailed and extensive data monitoring which allowed us to provide a unique description or river adjustments under varying flow conditions. Data acquisition included: 1) bed surface images covering the entire flume, 2) bed scans at 2 mm resolution of the whole flume and 3) real-time measurements of bedload transport (rate and texture) at the outlet of the flume. This set up allows us to obtain fractional particle

  18. Effect of ac electric field on the dynamics of a vesicle under shear flow in the small deformation regime

    Science.gov (United States)

    Sinha, Kumari Priti; Thaokar, Rochish M.

    2018-03-01

    Vesicles or biological cells under simultaneous shear and electric field can be encountered in dielectrophoretic devices or designs used for continuous flow electrofusion or electroporation. In this work, the dynamics of a vesicle subjected to simultaneous shear and uniform alternating current (ac) electric field is investigated in the small deformation limit. The coupled equations for vesicle orientation and shape evolution are derived theoretically, and the resulting nonlinear equations are handled numerically to generate relevant phase diagrams that demonstrate the effect of electrical parameters on the different dynamical regimes such as tank treading (TT), vacillating breathing (VB) [called trembling (TR) in this work], and tumbling (TU). It is found that while the electric Mason number (Mn), which represents the relative strength of the electrical forces to the shear forces, promotes the TT regime, the response itself is found to be sensitive to the applied frequency as well as the conductivity ratio. While higher outer conductivity promotes orientation along the flow axis, orientation along the electric field is favored when the inner conductivity is higher. Similarly a switch of orientation from the direction of the electric field to the direction of flow is possible by a mere change of frequency when the outer conductivity is higher. Interestingly, in some cases, a coupling between electric field-induced deformation and shear can result in the system admitting an intermediate TU regime while attaining the TT regime at high Mn. The results could enable designing better dielectrophoretic devices wherein the residence time as well as the dynamical states of the vesicular suspension can be controlled as per the application.

  19. Big data analytics : predicting traffic flow regimes from simulated connected vehicle messages using data analytics and machine learning.

    Science.gov (United States)

    2016-12-25

    The key objectives of this study were to: 1. Develop advanced analytical techniques that make use of a dynamically configurable connected vehicle message protocol to predict traffic flow regimes in near-real time in a virtual environment and examine ...

  20. Direct numerical simulation of a compressible boundary-layer flow past an isolated three-dimensional hump in a high-speed subsonic regime

    Science.gov (United States)

    De Grazia, D.; Moxey, D.; Sherwin, S. J.; Kravtsova, M. A.; Ruban, A. I.

    2018-02-01

    In this paper we study the boundary-layer separation produced in a high-speed subsonic boundary layer by a small wall roughness. Specifically, we present a direct numerical simulation (DNS) of a two-dimensional boundary-layer flow over a flat plate encountering a three-dimensional Gaussian-shaped hump. This work was motivated by the lack of DNS data of boundary-layer flows past roughness elements in a similar regime which is typical of civil aviation. The Mach and Reynolds numbers are chosen to be relevant for aeronautical applications when considering small imperfections at the leading edge of wings. We analyze different heights of the hump: The smaller heights result in a weakly nonlinear regime, while the larger result in a fully nonlinear regime with an increasing laminar separation bubble arising downstream of the roughness element and the formation of a pair of streamwise counterrotating vortices which appear to support themselves.

  1. Flow regime in a restored wetland determines trophic links and species composition in the aquatic macroinvertebrate community.

    Science.gov (United States)

    González-Ortegón, E; Walton, M E M; Moghaddam, B; Vilas, C; Prieto, A; Kennedy, H A; Pedro Cañavate, J; Le Vay, L

    2015-01-15

    In a restored wetland (South of Spain), where different flow regimes control water exchange with the adjacent Guadalquivir estuary, the native Palaemon varians coexists with an exotic counterpart species Palaemon macrodactylus. This controlled m\\acrocosm offers an excellent opportunity to investigate how the effects of water management, through different flow regimes, and the presence of a non-native species affect the aquatic community and the trophic niche (by gut contents and C-N isotopic composition) of the native shrimp Palaemon varians. We found that increased water exchange rate (5% day(-1) in mixed ponds vs. 0.1% day(-1) in extensive ponds) modified the aquatic community of this wetland; while extensive ponds are dominated by isopods and amphipods with low presence of P. macrodactylus, mixed ponds presented high biomass of mysids, corixids, copepods and both shrimp species. An estuarine origin of nutrients and primary production might explain seasonal and spatial differences found among ponds of this wetland. A combined analysis of gut contents and isotopic composition of the native and the exotic species showed that: (1) native P. varians is mainly omnivorous (2) while the non-native P. macrodactylus is more zooplanktivorous and (3) a dietary overlap occurred when both species coexist at mixed ponds where a higher water exchange and high abundance of mysids and copepods diversifies the native species' diet. Thus differences in the trophic ecology of both species are clearly explained by water management. This experimental study is a valuable tool for integrated management between river basin and wetlands since it allows quantification of wetland community changes in response to the flow regime. Copyright © 2014 Elsevier B.V. All rights reserved.

  2. A numerical study on the forced convection heat transfer from an isothermal and isoflux sphere in the steady symmetric flow regime

    Energy Technology Data Exchange (ETDEWEB)

    Dhole, S.D.; Chhabra, R.P. [Department of Chemical Engineering, Indian Institute of Technology, Kanpur 208 016 (India); Eswaran, V. [Department of Mechanical Engineering, Indian Institute of Technology, Kanpur 208 016 (India)

    2006-03-15

    The effects of Reynolds and Prandtl numbers on the heat transfer characteristics of an unconfined sphere for different thermal boundary conditions (isothermal and isoflux) on the sphere surface have been investigated numerically by using a finite volume method for the range of conditions as 5=flow regime. The variation of local Nusselt number on the sphere surface shows the effect of Prandtl number on heat transfer from a sphere in this flow regime. In addition, this work also demonstrates an approach to solve such flow problems using the Cartesian form of the field equations. (author)

  3. Climate change impact assessment on flow regime by incorporating spatial correlation and scenario uncertainty

    Science.gov (United States)

    Vallam, P.; Qin, X. S.

    2017-07-01

    Flooding risk is increasing in many parts of the world and may worsen under climate change conditions. The accuracy of predicting flooding risk relies on reasonable projection of meteorological data (especially rainfall) at the local scale. The current statistical downscaling approaches face the difficulty of projecting multi-site climate information for future conditions while conserving spatial information. This study presents a combined Long Ashton Research Station Weather Generator (LARS-WG) stochastic weather generator and multi-site rainfall simulator RainSim (CLWRS) approach to investigate flow regimes under future conditions in the Kootenay Watershed, Canada. To understand the uncertainty effect stemming from different scenarios, the climate output is fed into a hydrologic model. The results showed different variation trends of annual peak flows (in 2080-2099) based on different climate change scenarios and demonstrated that the hydrological impact would be driven by the interaction between snowmelt and peak flows. The proposed CLWRS approach is useful where there is a need for projection of potential climate change scenarios.

  4. Flow regime in a restored wetland determines trophic links and species composition in the aquatic macroinvertebrate community

    International Nuclear Information System (INIS)

    González-Ortegón, E.; Walton, M.E.M.; Moghaddam, B.; Vilas, C.; Prieto, A.; Kennedy, H.A.; Pedro Cañavate, J.; Le Vay, L.

    2015-01-01

    In a restored wetland (South of Spain), where different flow regimes control water exchange with the adjacent Guadalquivir estuary, the native Palaemon varians coexists with an exotic counterpart species Palaemon macrodactylus. This controlled m/acrocosm offers an excellent opportunity to investigate how the effects of water management, through different flow regimes, and the presence of a non-native species affect the aquatic community and the trophic niche (by gut contents and C-N isotopic composition) of the native shrimp Palaemon varians. We found that increased water exchange rate (5% day −1 in mixed ponds vs. 0.1% day −1 in extensive ponds) modified the aquatic community of this wetland; while extensive ponds are dominated by isopods and amphipods with low presence of P. macrodactylus, mixed ponds presented high biomass of mysids, corixids, copepods and both shrimp species. An estuarine origin of nutrients and primary production might explain seasonal and spatial differences found among ponds of this wetland. A combined analysis of gut contents and isotopic composition of the native and the exotic species showed that: (1) native P. varians is mainly omnivorous (2) while the non-native P. macrodactylus is more zooplanktivorous and (3) a dietary overlap occurred when both species coexist at mixed ponds where a higher water exchange and high abundance of mysids and copepods diversifies the native species' diet. Thus differences in the trophic ecology of both species are clearly explained by water management. This experimental study is a valuable tool for integrated management between river basin and wetlands since it allows quantification of wetland community changes in response to the flow regime. - Highlights: • Flow regimen is a major determinant of physicochemical habitat of a wetland. • Water exchanges wetland-estuary modify its aquatic community and trophic links. • Omnivory and physiological tolerance key in the resistance of a wetland

  5. Effect of surface wettability on flow patterns in vertical gas-liquid two-phase flow

    International Nuclear Information System (INIS)

    Nakamura, D.

    2005-01-01

    To examine the effect of the surface characteristics on the flow regime in two-phase flow, visualization study was performed using three test pipes, namely a no-coating pipe, a water-attracting coating pipe, a water-shedding coating pipe. Three flow regime maps were obtained based on the visual observation in the three pipes. In the water-attracting coating pipe, the slug flow-to-churn flow transition boundary was shifted to higher gas velocity at a given liquid velocity, whereas the churn flow-to-annular flow transition boundary was shifted to lower gas velocity at a given liquid velocity. In the water shedding coating pipe, the inverted-churn flow regime was observed in the region where the churn flow regime was to be observed in a no-coating pipe, whereas the droplet flow regime was observed in the region where the annular flow regime was to be observed in a no-coating pipe. The criteria for the slug flow-to-inverted-churn flow transition and the inverted-churn flow-to-droplet flow transition were modeled by force balance approaches. The modeled transition criteria could predict the observed flow transition boundaries reasonably well. (authors)

  6. A dry-spot model for the prediction of critical heat flux in water boiling in bubbly flow regime

    International Nuclear Information System (INIS)

    Ha, Sang Jun; No, Hee Cheon

    1997-01-01

    This paper presents a prediction of critical heat flux (CHF) in bubbly flow regime using dry-spot model proposed recently by authors for pool and flow boiling CHF and existing correlations for forced convective heat transfer coefficient, active site density and bubble departure diameter in nucleate boiling region. Without any empirical constants always present in earlier models, comparisons of the model predictions with experimental data for upward flow of water in vertical, uniformly-heated round tubes are performed and show a good agreement. The parametric trends of CHF have been explored with respect to variation in pressure, tube diameter and length, mass flux and inlet subcooling

  7. Large Dam Effects on Flow Regime and Hydraulic Parameters of river (Case study: Karkheh River, Downstream of Reservoir Dam

    Directory of Open Access Journals (Sweden)

    Farhang Azarang

    2017-06-01

    Full Text Available Introduction: The critical role of the rivers in supplying water for various needs of life has led to engineering identification of the hydraulic regime and flow condition of the rivers. Hydraulic structures such dams have inevitable effects on their downstream that should be well investigated. The reservoir dams are the most important hydraulic structures which are the cause of great changes in river flow conditions. Materials and Methods: In this research, an accurate assessment was performed to study the flow regime of Karkheh river at downstream of Karkheh Reservoir Dam as the largest dam in Middle East. Karkheh River is the third waterful river of Iran after Karun and Dez and the third longest river after the Karun and Sefidrud. The Karkheh Dam is a large reservoir dam built in Iran on the Karkheh River in 2000. The Karkheh Reservoir Dam is on the Karkheh River in the Northwestern Khouzestan Province, the closest city being Andimeshk to the east. The part of Karkheh River, which was studied in this research is located at downstream of Karkheh Reservoir Dam. This interval is approximately 94 km, which is located between PayePol and Abdolkhan hydrometric stations. In this research, 138 cross sections were used along Karkheh River. Distance of cross sections from each other was 680m in average. The efficient model of HEC-RAS has been utilized to simulate the Karkheh flow conditions before and after the reservoir dam construction using of hydrometric stations data included annually and monthly mean discharges, instantaneous maximum discharges, water surface profiles and etc. Three defined discharges had been chosen to simulate the Karkheh River flow; maximum defined discharge, mean defined discharge and minimum defined discharge. For each of these discharges values, HEC-RAS model was implemented as a steady flow of the Karkheh River at river reach of study. Water surface profiles of flow, hydraulic parameters and other results of flow regime in

  8. Flow regime in a restored wetland determines trophic links and species composition in the aquatic macroinvertebrate community

    Energy Technology Data Exchange (ETDEWEB)

    González-Ortegón, E., E-mail: quique.gonzalezortegon@andaluciajunta.es [School of Ocean Sciences, Bangor University, Menai Bridge LL59 5AB (United Kingdom); IFAPA Centro El Toruño, Camino Tiro de Pichón s/n, 11500 El Puerto de Santa María (Spain); Walton, M.E.M.; Moghaddam, B. [School of Ocean Sciences, Bangor University, Menai Bridge LL59 5AB (United Kingdom); Vilas, C.; Prieto, A. [IFAPA Centro El Toruño, Camino Tiro de Pichón s/n, 11500 El Puerto de Santa María (Spain); Kennedy, H.A. [School of Ocean Sciences, Bangor University, Menai Bridge LL59 5AB (United Kingdom); Pedro Cañavate, J. [IFAPA Centro El Toruño, Camino Tiro de Pichón s/n, 11500 El Puerto de Santa María (Spain); Le Vay, L. [School of Ocean Sciences, Bangor University, Menai Bridge LL59 5AB (United Kingdom)

    2015-01-15

    In a restored wetland (South of Spain), where different flow regimes control water exchange with the adjacent Guadalquivir estuary, the native Palaemon varians coexists with an exotic counterpart species Palaemon macrodactylus. This controlled m/acrocosm offers an excellent opportunity to investigate how the effects of water management, through different flow regimes, and the presence of a non-native species affect the aquatic community and the trophic niche (by gut contents and C-N isotopic composition) of the native shrimp Palaemon varians. We found that increased water exchange rate (5% day{sup −1} in mixed ponds vs. 0.1% day{sup −1} in extensive ponds) modified the aquatic community of this wetland; while extensive ponds are dominated by isopods and amphipods with low presence of P. macrodactylus, mixed ponds presented high biomass of mysids, corixids, copepods and both shrimp species. An estuarine origin of nutrients and primary production might explain seasonal and spatial differences found among ponds of this wetland. A combined analysis of gut contents and isotopic composition of the native and the exotic species showed that: (1) native P. varians is mainly omnivorous (2) while the non-native P. macrodactylus is more zooplanktivorous and (3) a dietary overlap occurred when both species coexist at mixed ponds where a higher water exchange and high abundance of mysids and copepods diversifies the native species' diet. Thus differences in the trophic ecology of both species are clearly explained by water management. This experimental study is a valuable tool for integrated management between river basin and wetlands since it allows quantification of wetland community changes in response to the flow regime. - Highlights: • Flow regimen is a major determinant of physicochemical habitat of a wetland. • Water exchanges wetland-estuary modify its aquatic community and trophic links. • Omnivory and physiological tolerance key in the resistance of a

  9. Effects of flow regime and flooding on heavy metal availability in sediment and soil of a dynamic river system

    NARCIS (Netherlands)

    Poot, A.; Gillissen, F.; Koelmans, A.A.

    2007-01-01

    The acid volatile sulphide (AVS) and simultaneously extracted metals (¿SEM) method is increasingly used for risk assessment of toxic metals. In this study, we assessed spatial and temporal variations of AVS and ¿SEM in river sediments and floodplain soils, addressing influence of flow regime and

  10. Dune growth under multidirectional wind regimes

    Science.gov (United States)

    Gadal, C.; Rozier, O.; Claudin, P.; Courrech Du Pont, S.; Narteau, C.

    2017-12-01

    Under unidirectional wind regimes, flat sand beds become unstable to produce periodic linear dunes, commonly called transverse dunes because their main ridges are oriented perpendicular to the air flow. In areas of low sediment availability, the same interactions between flow, transport and topography produce barchan dunes, isolated sand-pile migrating over long distances with a characteristic crescentic shape. For the last fifteen years, barchan dunes and the instability at the origin of transverse dunes have been the subject of numerous studies that have identified a set of characteristic length and time scales with respect to the physical properties of both grains and fluid. This is not the case for dunes developing under multidirectional wind regimes. Under these conditions, dune orientation is measured with respect to the direction of the resultant sand flux. Depending on the wind regime, dunes do not always line up perpendicularly to the resultant sand flux, but can also be at an oblique angle or even parallel to it. These oblique and longitudinal dunes are ubiquitous in all deserts on Earth and planetary bodies because of the seasonal variability of wind orientation. They are however poorly constrained by observations and there is still no complete theoretical framework providing a description of their orientation and initial wavelength. Here, we extend the linear stability analysis of a flat sand of bed done in two dimensions for a unidirectional flow to three dimensions and multidirectional flow regimes. We are able to recover transitions from transverse to oblique or longitudinal dune patterns according to changes in wind regimes. We besides give a prediction for the initial dune wavelength. Our results compare well to previous theory of dune orientation and to field, experimental and numerical data.

  11. Quantifying downstream impacts of impoundment on flow regime and channel planform, lower Trinity River, Texas

    Science.gov (United States)

    Wellmeyer, Jessica L.; Slattery, Michael C.; Phillips, Jonathan D.

    2005-07-01

    As human population worldwide has grown, so has interest in harnessing and manipulating the flow of water for the benefit of humans. The Trinity River of eastern Texas is one such watershed greatly impacted by engineering and urbanization. Draining the Dallas-Fort Worth metroplex, just under 30 reservoirs are in operation in the basin, regulating flow while containing public supplies, supporting recreation, and providing flood control. Lake Livingston is the lowest, as well as largest, reservoir in the basin, a mere 95 km above the Trinity's outlet near Galveston Bay. This study seeks to describe and quantify channel activity and flow regime, identifying effects of the 1968 closure of Livingston dam. Using historic daily and peak discharge data from USGS gauging stations, flow duration curves are constructed, identifying pre- and post-dam flow conditions. A digital historic photo archive was also constructed using six sets of aerial photographs spanning from 1938 to 1995, and three measures of channel activity applied using a GIS. Results show no changes in high flow conditions following impoundment, while low flows are elevated. However, the entire post-dam period is characterized by significantly higher rainfall, which may be obscuring the full impact of flow regulation. Channel activity rates do not indicate a more stabilized planform following dam closure; rather they suggest that the Trinity River is adjusting itself to the stress of Livingston dam in a slow, gradual process that may not be apparent in a modern time scale.

  12. Rainfall variability and its influence on surface flow regimes. Examples from the central highlands of Ethiopia

    Energy Technology Data Exchange (ETDEWEB)

    Osman, M. [Debre Zeit (Ethiopia); Sauerborn, P. [Seminar fuer Geographie und ihre Didaktik, Univ. zu Koeln, Koeln (Germany)

    2002-07-01

    The article shows results of an international and interdisciplinary project with the title 'Rainfall and its Erosivity in Ethiopia'. Rainfall variability affects the water resource management of Ethiopia. The influence of rainfall variability on flow regimes was investigated using five gauging stations with data availability from 1982-1997. It was confirmed that the variability in rainfall has a direct implication for surface runoff. Surface runoff declined at most of the gauging stations investigated. Therefore, effective water resource management is recommended for the study area. Future research should focus on watershed management which includes land-use and land cover. The question posed here is whether the variability in rainfall significantly affected surface flow in the study area. (orig.)

  13. A dry-spot model for the prediction of critical heat flux in water boiling in bubbly flow regime

    Energy Technology Data Exchange (ETDEWEB)

    Ha, Sang Jun; No, Hee Cheon [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)

    1998-12-31

    This paper presents a prediction of critical heat flux (CHF) in bubbly flow regime using dry-spot model proposed recently by authors for pool and flow boiling CHF and existing correlations for forced convective heat transfer coefficient, active site density and bubble departure diameter in nucleate boiling region. Without any empirical constants always present in earlier models, comparisons of the model predictions with experimental data for upward flow of water in vertical, uniformly-heated round tubes are performed and show a good agreement. The parametric trends of CHF have been explored with respect to variations in pressure, tube diameter and length, mass flux and inlet subcooling. 16 refs., 6 figs., 1 tab. (Author)

  14. A dry-spot model for the prediction of critical heat flux in water boiling in bubbly flow regime

    Energy Technology Data Exchange (ETDEWEB)

    Ha, Sang Jun; No, Hee Cheon [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)

    1997-12-31

    This paper presents a prediction of critical heat flux (CHF) in bubbly flow regime using dry-spot model proposed recently by authors for pool and flow boiling CHF and existing correlations for forced convective heat transfer coefficient, active site density and bubble departure diameter in nucleate boiling region. Without any empirical constants always present in earlier models, comparisons of the model predictions with experimental data for upward flow of water in vertical, uniformly-heated round tubes are performed and show a good agreement. The parametric trends of CHF have been explored with respect to variations in pressure, tube diameter and length, mass flux and inlet subcooling. 16 refs., 6 figs., 1 tab. (Author)

  15. Condensation of refrigerants in horizontal microfin tubes. Numerical analysis of heat transfer for annular flow regime; Reibai no microfin tsuki suihei kannai gyoshuku. Kanjoryu ryoiki ni okeru netsudentatsu no suchi kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Nozu, S [Okayama Prefectural University, Okayama (Japan); Honda, H [Kyushu University, Fukuoka (Japan). Institute of Advanced Material Study

    1998-07-25

    A method for predicting the local heat transfer coefficient is presented for film condensation of vapor in a spirally grooved horizontal microfin-tube. Based on the flow observation study performed by the present authors, film flow model between fins in the annular flow regime is proposed. For the fin surface, laminar condensate film controlled by the combined effects of vapor shear and surface tension forces is analyzed. While, in the groove, thick condensate film driven by the vapor shear force is taken into consideration. A parameter which accounts for the transition from annular- to stratified flow regimes is also derived. The present and previous local heat transfer data for fluorocarbon refrigerants in the annular flow regime are found by the present numerical analysis to have a mean absolute deviation of 15.1 percent. 12 refs., 10 figs., 2 tabs.

  16. I-V curves of Y-Ba-Cu-O microbridges in the flux flow regime

    International Nuclear Information System (INIS)

    Kalisky, B.; Wolfus, Y.; Yeshurun, Y.; Koren, G.; Huebener, R.P.

    2004-01-01

    We report on measurements of I-V curves in microbridges of thin Y-Ba-Cu-O films of different thickness, in the presence of external magnetic fields up to 6 T. A discontinuity is observed at a critical voltage, V*, in the flux flow regime, reflecting an electronic instability, as predicted by Larkin and Ovchinnikov (LO), and in agreement with results reported by Doettinger et al. [Phys. Rev. Let. 73 (1994) 1691]. The critical voltage, V*, and the flux flow resistance, R 0 , in the limit V→0, are calculated by fitting the data to the LO model. We find that the vortex critical velocity, v*, at the instability, derived from V*, decreases with magnetic field and film thickness. These results, not predicted by the LO theory, reflect the dependence of the (spatially averaged) quasiparticle energy relaxation rate on magnetic field and film thickness

  17. Prevalence of xerostomia and the salivary flow rate in diabetic patients.

    Science.gov (United States)

    Malicka, Barbara; Kaczmarek, Urszula; Skośkiewicz-Malinowska, Katarzyna

    2014-01-01

    Diabetes is a metabolic disease characterized by hyperglycemia, which results from relative or absolute insulin deficiency. One of the first oral symptoms of diabetes is xerostomia. The aim of the study was to determine the prevalence of the xerostomia symptoms and salivary flow rate in diabetic patients according to the type of diabetes, the level of metabolic control and the duration of the disease. The study involved 156 adult patients of both sexes including 34 patients with diabetes type 1 (group C1), 59 with diabetes type 2 (group C2), and 63 generally healthy individuals as two control groups, sex- and age-matched to the diabetic group. The patients suffering from both types of diabetes were additionally subdivided according to the level of metabolic control and the duration of the disease. Xerostomia was diagnosed with the use of a specially prepared questionnaire and Fox's test. Moreover, the salivary flow rate of resting mixed saliva was measured. In type 1 diabetics, a significantly lower salivary flow rate in comparison to the age-matched control group (0.38 ± 0.19 mL/min vs. 0.53 ± 0.20 mL/min, p diabetics, a slight lower salivary flow rate was noticed (on average, 20% lower). Dry mouth was far more frequently diagnosed in type 1 diabetics than in the control group. In type 1 diabetics, in comparison to healthy subjects, a significantly lower resting flow rate of saliva and significantly higher prevalence of xerosomia were observed, but in type 2 diabetics, only a trend of such variability was observed.

  18. On intermittent flow characteristics of gas–liquid two-phase flow

    Energy Technology Data Exchange (ETDEWEB)

    Thaker, Jignesh; Banerjee, Jyotirmay, E-mail: jbaner@gmail.com

    2016-12-15

    Highlights: • Unified correlations for intermittent flow characteristics are developed. • Influence of inflow conditions on intermittent flow characteristics is analysed. • Developed correlations can be used for effective design of piping components. - Abstract: Flow visualisation experiments are reported for intermittent regime of gas–liquid two-phase flow. Intermittent flow characteristics, which include plug/slug frequency, liquid plug/slug velocity, liquid plug/slug length, and plug/slug bubble length are determined by image processing of flow patterns captured at a rate of 1600 frames per second (FPS). Flow characteristics are established as a function of inlet superficial velocity of both the phases (in terms of Re{sub SL} and Re{sub SG}). The experimental results are first validated with the existing correlations for slug flow available in literature. It is observed that the correlations proposed in literature for slug flow do not accurately predict the flow characteristics in the plug flow regime. The differences are clearly highlighted in this paper. Based on the measured database for both plug and slug flow regime, modified correlations for the intermittent flow regime are proposed. The correlations reported in the present paper, which also include plug flow characteristics will aid immensely to the effective design and optimization of operating conditions for safer operation of two-phase flow piping systems.

  19. Experimental investigation on single-phase pressure losses in nuclear debris beds: Identification of flow regimes and effective diameter

    Energy Technology Data Exchange (ETDEWEB)

    Clavier, R., E-mail: remi.clavier@irsn.fr [Institut de Radioprotection et de Sûreté Nucléaire (IRSN) – PSN-RES/SEREX/LE2M, Cadarache bât. 327, 13115 St Paul-lez-Durance (France); Chikhi, N., E-mail: nourdine.chikhi@irsn.fr [Institut de Radioprotection et de Sûreté Nucléaire (IRSN) – PSN-RES/SEREX/LE2M, Cadarache bât. 327, 13115 St Paul-lez-Durance (France); Fichot, F. [Institut de Radioprotection et de Sûreté Nucléaire (IRSN) – PSN-RES/SAG/LEPC, Cadarache bât. 700, 13115 St Paul-lez-Durance (France); Quintard, M. [Université de Toulouse – INPT – UPS – Institut de Mécanique des Fluides de Toulouse (IMFT), Allée Camille Soula, F-31400 Toulouse (France); CNRS – IMFT, F-31400 Toulouse (France)

    2015-10-15

    Highlights: • Single-phase pressure drops versus flow rates in particle beds are measured. • Conditions are representative of the reflooding of a nuclear fuel debris bed. • Darcy, weak inertial, strong inertial and weak turbulent regimes are observed. • A Darcy–Forchheimer law is found to be a good approximation in this domain. • A predictive correlation is derived from new experimental data. - Abstract: During a severe nuclear power plant accident, the degradation of the reactor core can lead to the formation of debris beds. The main accident management procedure consists in injecting water inside the reactor vessel. Nevertheless, large uncertainties remain regarding the coolability of such debris beds. Motivated by the reduction of these uncertainties, experiments have been conducted on the CALIDE facility in order to investigate single-phase pressure losses in representative debris beds. In this paper, these results are presented and analyzed in order to identify a simple single-phase flow pressure loss correlation for debris-bed-like particle beds in reflooding conditions, which cover Darcean to Weakly Turbulent flow regimes. The first part of this work is dedicated to study macro-scale pressure losses generated by debris-bed-like particle beds, i.e., high sphericity (>80%) particle beds with relatively small size dispersion (from 1 mm to 10 mm). A Darcy–Forchheimer law, involving the sum of a linear term and a quadratic deviation, with respect to filtration velocity, has been found to be relevant to describe this behavior in Darcy, Strong Inertial and Weak Turbulent regimes. It has also been observed that, in a restricted domain (Re = 15 to Re = 30) between Darcy and Weak Inertial regimes, deviation is better described by a cubic term, which corresponds to the so-called Weak Inertial regime. The second part of this work aims at identifying expressions for coefficients of linear and quadratic terms in Darcy–Forchheimer law, in order to obtain a

  20. Long-Term Downstream Effects of a Dam on a Lowland River Flow Regime: Case Study of the Upper Narew

    Directory of Open Access Journals (Sweden)

    Paweł Marcinkowski

    2017-10-01

    Full Text Available Most European riverine ecosystems suffer from the negative influence of impoundments on flow regime. Downstream effects of dams lead to a number of environmental and socioeconomic risks and, therefore, should be thoroughly examined in specific contexts. Our study aims to quantify the downstream effects of the Siemianówka Reservoir (Upper Narew, Poland, using statistical analysis of key elements of the river’s flow regime, such as the flow duration and recurrence of floods and droughts. In a comparative study on control catchments not influenced by impoundments (the Supraśl and Narewka Rivers, we revealed the following downstream effects of the analyzed dam: significant shortening of spring floods, reduction of the duration and depth of summer droughts, decrease of the maximum discharge, and homogenization of the discharge hydrographs. Although we determined a significant decrease in the duration of summer floods in the “before” and “after” dam function periods, we showed that this issue is regional, climate-related, and replicated in control catchments, rather than an evident downstream effect of the dam. We conclude that significant hydrological downstream effects of the Siemianówka dam–reservoir system could have been the main driver inducing the deterioration of the anastomosing stretch of the Narew River downstream of the dam.

  1. Numerical and experimental study of the slug-flow regime in a mixture of castor and paraffin oils in a T-type microchannel

    Science.gov (United States)

    Minakov, A. V.; Shebeleva, A. A.; Yagodnitsyna, A. A.; Kovalev, A. V.; Bilsky, A. V.

    2017-09-01

    The slow-flug regime in a mixture of castor and paraffin oils in a T-type microchannel with crosssectional dimensions of 200 × 400 μm has been studied by numerical and experimental methods. The domain of existence of the slow-flug regime in this system has been determined. Dependence of the paraffin-oil slug length on the ratio of flow rates of the mixture components is established. Comparison of the calculated and experimental data shows their good agreement.

  2. Flow regimes and heat transfer modes identification in ANGRA 2 core, during small break in the primary loop with area of 100 cm2, simulated with RELAP5 code

    International Nuclear Information System (INIS)

    Borges, Eduardo M.; Sabundjian, Gaiane

    2015-01-01

    Identifying the flow regimes and the heat transfer modes is important for the analysis of accidents such as the Loss-of-Coolant Accident (LOCA). The aim of this paper is to identify the flow regimes, the heat transfer modes, and the correlations used in the RELAP5/MOD3.2.gama code in ANGRA 2 during the Small-Break Loss-of-Coolant Accident (SBLOCA) with a 100cm 2 -rupture area in the cold leg of primary loop. The Chapter 15 of the Final Safety Analysis Report of ANGRA 2 (FSAR - A2) reports this specific kind of accident. The results from this work demonstrated the several flow regimes and heat transfer modes that can be present in the core of ANGRA 2 during the postulated accident. (author)

  3. Investigation of heat transfer and fluid flow in transitional regime inside a channel with staggered plates heated by radiation for PV/T system

    International Nuclear Information System (INIS)

    Ali, Ahmed Hamza H.; Ahmed, Mahmoud; Abdel-Gaied, S.M.

    2013-01-01

    This study investigates experimentally and theoretically the effects of operating and configuration parameters on convection heat transfer process and fluid flow characteristics for air flowing in transitional regimes through parallel plate channels with staggered plates segments heated by radiant heat flux. This configuration is to be utilized in air heater solar collectors and/or in a combined photovoltaic and air heater solar collector systems (PV/T). The operating parameters tested were Reynolds number (Re) values ranging from 2580 to 4650 with a combination of incident radiation heat flux (q inc ) values of 400, 700, and 1000 W/m 2 , respectively. The experimental results show that the local Nusselt number (Nu x ) is not unique function of the axial distance, in addition, a linear relationship between Re and apparent friction factor (f) was observed. Moreover, the model results show that combination of Re values in the laminar flow regime with proper selection of both plate's length and thickness can lead to enhancement in the heat transfer from the plate segments to the air stream. This is due to self-oscillatory flow mixer in wake zone behind each plate segment. Consequently, this will lead to avoid the need of more pumping power for the case of the flow falling within the transitional regime in the channel. - Highlights: • The local heat transfer coefficient is not unique function in the axial distance. • A linear relationship between Reynolds number and apparent friction factor is observed for Re > 3500. • The plate thickness is the dominant parameter affects both values of the heat transfer and friction factor. • Shorter plates' length, at any plate thickness, leads to periodic boundary layers interruption mechanisms

  4. Effect of wall wettability on flow characteristics of gas-liquid two-phase flow

    International Nuclear Information System (INIS)

    Uematsu, Junichi; Abe, Kazuya; Hazuku, Tatsuya; Takamasa, Tomoji; Hibiki, Takashi

    2007-01-01

    To evaluate the effect of surface wettability in pipe wall on flow characteristics in a vertical upward gas-liquid to-phase flow, visualization study was performed using three test pipes, namely an acrylic pipe, a hydrophilic pipe, a hydrophobic pipe. Such basic flow characteristics as flow patterns and void fraction were investigated in these three pipes. In the hydrophilic pipe, the slug flow-to-churn flow transition boundary was shifted to higher gas velocity condition at a given liquid velocity, whereas the churn flow-to-annular flow transition boundary was shifted to lower gas velocity condition at a given liquid velocity. In the hydrophobic pipe, the inverted-churn flow regime was observed in the region where the churn flow regime was observed in the acrylic pipe, whereas the droplet flow regime was observed in the region where the annular flow regime was observed in the acrylic pipe. At high-gas flow rate condition, the mean void fraction in the hydrophobic pipe took relatively higher value to that in the acrylic pipe. (author)

  5. Linking Flow Regime, Floodplain Lake Connectivity and Fish Catch in a Large River-Floodplain System, the Volga–Akhtuba Floodplain (Russian Federation)

    NARCIS (Netherlands)

    Wolfshaar, K.E. van de; Middelkoop, H.; Addink, E.A.; Winter, H.V.; Nagelkerke, L.A.J.

    2011-01-01

    River-floodplain systems are amongst the most productive—but often severely impacted—aquatic systems worldwide. We explored the ecological response of fish to flow regime in a large riverfloodplain system by studying the relationships between (1) discharge and inundated floodplain area, with a

  6. Flow regimes and heat transfer modes identification in ANGRA 2 core, during small break in the primary loop with area of 100 cm{sup 2}, simulated with RELAP5 code

    Energy Technology Data Exchange (ETDEWEB)

    Borges, Eduardo M.; Sabundjian, Gaiane, E-mail: gdgian@ipen.br, E-mail: borges.em@hotmail.com [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2015-07-01

    Identifying the flow regimes and the heat transfer modes is important for the analysis of accidents such as the Loss-of-Coolant Accident (LOCA). The aim of this paper is to identify the flow regimes, the heat transfer modes, and the correlations used in the RELAP5/MOD3.2.gama code in ANGRA 2 during the Small-Break Loss-of-Coolant Accident (SBLOCA) with a 100cm{sup 2}-rupture area in the cold leg of primary loop. The Chapter 15 of the Final Safety Analysis Report of ANGRA 2 (FSAR - A2) reports this specific kind of accident. The results from this work demonstrated the several flow regimes and heat transfer modes that can be present in the core of ANGRA 2 during the postulated accident. (author)

  7. Linking Flow Regime, Floodplain Lake Connectivity and Fish Catch in a Large River-Floodplain System, the Volga-Akhtuba Floodplain (Russian Federation)

    NARCIS (Netherlands)

    Wolfshaar, van de K.E.; Middelkoop, H.; Addink, E.; Winter, H.V.; Nagelkerke, L.A.J.

    2011-01-01

    River-floodplain systems are amongst the most productive—but often severely impacted—aquatic systems worldwide. We explored the ecological response of fish to flow regime in a large river-floodplain system by studying the relationships between (1) discharge and inundated floodplain area, with a

  8. Simulating the transient regime for main condensate system at Cernavoda NPP

    International Nuclear Information System (INIS)

    Nita, Iulian; Gheorghiu, Mihai; Prisecaru, Ilie; Dupleac, Daniel

    2005-01-01

    The purpose of this project is to make a Thermal Hydraulic Analysis of Main Condensate System for getting real-time answer of installation during regimes occurring during normal and abnormal operation. To obtain the analyses the MMS code was used. The boundaries of the systems analysis are extended to Main Feedwater System in order to get a realistic response of Deaerator equipment which are situated between those two systems and have entrances from both systems. In this way we made a complex analysis with main condenser and steam generators as boundaries. We obtained a model for the entire chain of condensate and feedwater preheater with interface just turbine bleed steam. From that we could reduce the number of assumptions necessary to make the analysis. The analyses consist in hydraulics and thermal hydraulics analyses, respectively. For the first case analysed are: - the nominal operation regime with main condensate pumps; - start-up regime with total circulate of condensate to condenser; - 25% MCR (Maximum Continuous Rate) regime (this regime was used in designing the condensate regulating valves at low flow; - 40% MCR regime (with circulate of some condensate flow to condenser); - operating regime of 60% MCR with one main condensate pump operating; - operating regime with auxiliary condensate pump; - operating regime with discharging a condensate flow to condensate storage tank. The thermal hydraulic analyses deal with normal and abnormal operating regimes, respectively. In the first case analysed are the following regimes: - nominal operating regime with main condensate pump operating 100% MCR; - transient regime, 100-80% MCR; - transient regime, 100-80-60% MCR with two pumps in operation and 60 % MCR with one main condensate pump in operation; - transient regime, 100-80-60-60-40 % MCR; - shut-down regime; - start-up regime from Hot zero power to rated power regime. Finally, for the abnormal operating regimes the analyses concerned: - transient regime 100

  9. Role of medium heterogeneity and viscosity contrast in miscible flow regimes and mixing zone growth: A computational pore-scale approach

    Science.gov (United States)

    Afshari, Saied; Hejazi, S. Hossein; Kantzas, Apostolos

    2018-05-01

    Miscible displacement of fluids in porous media is often characterized by the scaling of the mixing zone length with displacement time. Depending on the viscosity contrast of fluids, the scaling law varies between the square root relationship, a sign for dispersive transport regime during stable displacement, and the linear relationship, which represents the viscous fingering regime during an unstable displacement. The presence of heterogeneities in a porous medium significantly affects the scaling behavior of the mixing length as it interacts with the viscosity contrast to control the mixing of fluids in the pore space. In this study, the dynamics of the flow and transport during both unit and adverse viscosity ratio miscible displacements are investigated in heterogeneous packings of circular grains using pore-scale numerical simulations. The pore-scale heterogeneity level is characterized by the variations of the grain diameter and velocity field. The growth of mixing length is employed to identify the nature of the miscible transport regime at different viscosity ratios and heterogeneity levels. It is shown that as the viscosity ratio increases to higher adverse values, the scaling law of mixing length gradually shifts from dispersive to fingering nature up to a certain viscosity ratio and remains almost the same afterwards. In heterogeneous media, the mixing length scaling law is observed to be generally governed by the variations of the velocity field rather than the grain size. Furthermore, the normalization of mixing length temporal plots with respect to the governing parameters of viscosity ratio, heterogeneity, medium length, and medium aspect ratio is performed. The results indicate that mixing length scales exponentially with log-viscosity ratio and grain size standard deviation while the impact of aspect ratio is insignificant. For stable flows, mixing length scales with the square root of medium length, whereas it changes linearly with length during

  10. The effects of human land use on flow regime and water chemistry of headwater streams in the highlands of Chiapas

    Directory of Open Access Journals (Sweden)

    Castillo M.M.

    2013-03-01

    Full Text Available We studied the effects of land use changes on flow regime and water chemistry of headwater streams in the highlands of Chiapas, a region in southern Mexico that has experienced high rates of deforestation in the last decades. Samples for water chemistry were collected and discharge was measured between September 2007 and August 2008 at eight streams that differed in the land uses of their riparian and catchment areas, including streams draining protected forested areas. Streams with high forest cover (>70% in their catchments maintained flow through the year. Streams draining more disturbed catchments exhibited reduced or no flow for 4 − 6 months during the dry season. Nitrate concentrations were lower at streams draining forested catchments while highest concentrations were measured where conventional agriculture covered a high proportion of the catchment and riparian zone. Highest phosphorus concentrations occurred at the catchment where poultry manure was applied as fertilizer. Differences between forest streams and those draining disturbed areas were correlated with the proportion of forest and agriculture in the riparian zone. Variation in stream variables among sampling dates was lower at the forest sites than at the more disturbed study streams. Conversion of forest into agriculture and urban areas is affecting flow regime and increasing nutrient concentrations, although the magnitude of the impacts are influenced by the type of agricultural practices and the alteration of the riparian zone.

  11. Experiment on smooth, circular cylinders in cross-flow in the critical Reynolds number regime

    Science.gov (United States)

    Miau, J. J.; Tsai, H. W.; Lin, Y. J.; Tu, J. K.; Fang, C. H.; Chen, M. C.

    2011-10-01

    Experiments were conducted for 2D circular cylinders at Reynolds numbers in the range of 1.73 × 105-5.86 × 105. In the experiment, two circular cylinder models made of acrylic and stainless steel, respectively, were employed, which have similar dimensions but different surface roughness. Particular attention was paid to the unsteady flow behaviors inferred by the signals obtained from the pressure taps on the cylinder models and by a hot-wire probe in the near-wake region. At Reynolds numbers pertaining to the initial transition from the subcritical to the critical regimes, pronounced pressure fluctuations were measured on the surfaces of both cylinder models, which were attributed to the excursion of unsteady flow separation over a large circumferential region. At the Reynolds numbers almost reaching the one-bubble state, it was noted that the development of separation bubble might switch from one side to the other with time. Wavelet analysis of the pressure signals measured simultaneously at θ = ±90° further revealed that when no separation bubble was developed, the instantaneous vortex-shedding frequencies could be clearly resolved, about 0.2, in terms of the Strouhal number. The results of oil-film flow visualization on the stainless steel cylinder of the one-bubble and two-bubble states showed that the flow reattachment region downstream of a separation bubble appeared not uniform along the span of the model. Thus, the three dimensionality was quite evident.

  12. Transition to ballistic regime for heat transport in helium II

    Energy Technology Data Exchange (ETDEWEB)

    Sciacca, Michele, E-mail: michele.sciacca@unipa.it [Dipartimento Scienze Agrarie e Forestali, Università degli studi di Palermo, Viale delle Scienze, 90128 Palermo (Italy); Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia (Spain); Sellitto, Antonio, E-mail: ant.sellitto@gmail.com [Dipartimento di Matematica, Informatica ed Economia, Università della Basilicata, Campus Macchia Romana, 85100 Potenza (Italy); Jou, David, E-mail: david.jou@uab.cat [Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia (Spain); Institut d' Estudis Catalans, Carme 47, 08001 Barcelona, Catalonia (Spain)

    2014-07-04

    The size-dependent and flux-dependent effective thermal conductivity of narrow capillaries filled with superfluid helium is analyzed from a thermodynamic continuum perspective. The classical Landau evaluation of the effective thermal conductivity of quiescent superfluid, or the Gorter–Mellinck regime of turbulent superfluids, is extended to describe the transition to ballistic regime in narrow channels wherein the radius R is comparable to (or smaller than) the phonon mean-free path ℓ in superfluid helium. To do so, we start from an extended equation for the heat flux incorporating non-local terms, and take into consideration a heat slip flow along the walls of the tube. This leads from an effective thermal conductivity proportional to R{sup 2} (Landau regime) to another one proportional to Rℓ (ballistic regime). We consider two kinds of flows: along cylindrical pipes and along two infinite parallel plates. - Highlights: • Heat transport in counterflow helium in the ballistic regime. • The one-fluid model based on the Extended Thermodynamics is used. • The transition from the Landau regime to the ballistic regime. • The transition from quantum turbulence to ballistic regime.

  13. Phosphorus mobilization in rewetted peat and sand at variable flow rate and redox regimes

    DEFF Research Database (Denmark)

    Kjærgaard, Charlotte; Heiberg, Lisa; Jensen, Henning S.

    2012-01-01

    the upward percolation of groundwater with variable O2 content and flow rate, we investigated the hydro-biogeochemical Fe and P dynamics in intact cores of a carbon rich peat and carbon poor sand. Percolation of deionized water with high, low or no O2 supply at 10 °C caused markedly different in situ redox...... rates from 7.6 to 11 mg P m−2 day−1. Organic or particulate P contributed to 40–45% of total P losses from the peat. In contrast, the high O2 supply during high flow rate kept the peat oxic and lowered TP release rates to 6.7 mg P m−2 day−1. The carbon poor sand demonstrated that this soil type...... regimes in the two soils during 21 or 67 days of continuous percolation at either 1 or 4 mm h−1. Anoxic conditions occurred in the peat soil at both low oxygen supply and anoxic infiltration, causing reductive Fe(III) dissolution with high Fe(II) and P effluent concentrations and total P (TP) release...

  14. Laboratory modeling of flow regimes in a draft tube of Francis hydro-turbine

    Directory of Open Access Journals (Sweden)

    Shtork Sergey

    2017-01-01

    Full Text Available The paper reports on some results of the experimental study of flow and pressure pulsations in a laboratory model of the draft tube (DT of Francis-99 hydro-turbine over a broad range of operating regimes. Velocity distributions at the model inlet varied within 866 modes of the turbine load conditions, including those with maximum coherent pressure pulsations on the model walls. The contact and non-contact methods were used to measure pressure pulsations on the model walls using acoustic sensors and to measure the averaged velocity distribution with a laser Doppler anemometer “LAD-06i”. Analysis of the results have showed that in the model cone there are flow modes with forming of precessing vortex cores, accompanied by a sharp increase in the amplitude of coherent pressure pulsations on the wall and the velocity field rearrangement. It is shown that the vortex core starts forming with an increase in the integral parameter of swirl up to S>0.5. A novelty of the work is the combination of the rapid prototyping (3-d printing of the inflow swirl generators and computerized measurement techniques that makes it possible to acquire rapidly a large amount of experimental data for a variety of designs and operating conditions. The results can provide insight into the effect of various design and operating parameters on the flow physics, as well as serve for verification of the numerical simulations.

  15. Numerical modeling of time-dependent bio-convective stagnation flow of a nanofluid in slip regime

    Directory of Open Access Journals (Sweden)

    Rakesh Kumar

    Full Text Available A numerical investigation of unsteady stagnation point flow of bioconvective nanofluid due to an exponential deforming surface is made in this research. The effects of Brownian diffusion, thermophoresis, slip velocity and thermal jump are incorporated in the nanofluid model. By utilizing similarity transformations, the highly nonlinear partial differential equations governing present nano-bioconvective boundary layer phenomenon are reduced into ordinary differential system. The resultant expressions are solved for numerical solution by employing a well-known implicit finite difference approach termed as Keller-box method (KBM. The influence of involved parameters (unsteadiness, bioconvection Schmidt number, velocity slip, thermal jump, thermophoresis, Schmidt number, Brownian motion, bioconvection Peclet number on the distributions of velocity, temperature, nanoparticle and motile microorganisms concentrations, the coefficient of local skin-friction, rate of heat transport, Sherwood number and local density motile microorganisms are exhibited through graphs and tables. Keywords: Unsteadiness, Bio-convection, Slip regime, Stagnation point flow, Numerical modeling

  16. Flow regime effects on mature Populus fremontii (Fremont cottonwood) productivity on two contrasting dryland river floodplains

    Science.gov (United States)

    Andersen, Douglas C.

    2016-01-01

    I compared riparian cottonwood (Populus fremontii) productivity-discharge relationships in a relictual stand along the highly regulated Green River and in a naturally functioning stand along the unregulated Yampa River in semiarid northwest Colorado. I used multiple regression to model flow effects on annual basal area increment (BAI) from 1982 to 2011, after removing any autocorrelation present. Each BAI series was developed from 20 trees whose mean size (67 cm diameter at breast height [DBH]) was equivalent in the two stands. BAI was larger in the Yampa River stand except in 2 y when defoliating leaf beetles were present there. I found no evidence for a Yampa flood-magnitude threshold above which BAI declined. Flow variables explained ∼45% of residual BAI variability, with most explained by current-year maximum 90-d discharge (QM90) in the Yampa River stand and by a measure of the year-to-year change in QM90 in the Green River stand. The latter reflects a management-imposed ceiling on flood magnitude—Flaming Gorge Dam power plant capacity—infrequently exceeded during the study period. BAI in the relictual stand began to trend upward in 1992 when flows started to mimic a natural flow regime. Mature Fremont cottonwoods appear to be ecologically resilient. Their productivity along regulated rivers might be optimized using multiyear environmental flow designs.

  17. Assessment of climate change impact on river flow regimes in The Red River Delta, Vietnam – A case study of the Nhue-Day River Basin

    Directory of Open Access Journals (Sweden)

    Phan Cao Duong

    2016-09-01

    Full Text Available Global warming has caused dramatic changes in regional climate variability, particularly regarding fluctuations in temperature and rainfall. Thus, it is predicted that river flow regimes will be altered accordingly. The purpose of this paper is to present the results of modeling such changes by simulating discharge using the HEC-HMS model. The precipitation was projected using super-high resolution multiple climate models (20 km resolution with newly updated emission scenarios as the input for the HEC-HMS model for flow analysis at the Red River Basin in the northern area of Vietnam. The findings showed that climate change impact on the river flow regimes tend towards a decrease in the dry season and a longer duration of flood flow. A slight runoff reduction is simulated for November while a considerable runoff increase is modeled for July and August amounting to 30% and 25%, respectively. The discharge scenarios serve as a basis for water managers to develop suitable adaptation methods and responses on the river basin scale.

  18. Contribution to the analysis and the modelling of turbulent flows in mixed convection regime, application to radioactive waste management

    International Nuclear Information System (INIS)

    Lecocq, Y.

    2008-12-01

    In the frame of radioactive waste management, this work aims to study the flow around a heating wall-mounted cylinder in crossflow in URANS approach. Well-known limitations of first order turbulence models lead us to consider second order turbulence modelling. In that frame, a heat transfer model is developed and validated on academic test cases. To begin with, when mixed convection regime is dominant, these simulations, completed by an isotherm one, all performed with low-Reynolds k-w SST model, give prominence to several eddy structures registered by the bibliography. One simulation is also performed with the high-Reynolds Rij-epsilon SSG model. With the k-w SST model, the heat transfer is correctly reproduced compared to the VALIDA experiment lead by the CEA, though with the Rij-epsilon SSG model, it is strongly under-estimated. It is supposed that it comes from the use of wall functions. Subsequently, when natural convection is predominant, flow topology becomes completely different and the heat transfer becomes less accurate to the VALIDA experiment. Following Durbin's approach, the Elliptic Blending-Renolds Stress Model EBRSM, consists in accounting for wall effects, and in wall blockage in particular. Following this formalism, an Elliptic Blending-Algebraic Flux Model is developed, the EBAFM. With this model, a priori tests in the three convection regimes and then simulations on the same test cases show major improvements in flow predictions. This leads to an interesting perspective to an intermediate model between SGDH and transport equations. (author)

  19. Cellular properties of slug flow in vertical co-current gas-liquid flow: slug-churn transition

    International Nuclear Information System (INIS)

    Lusseyran, Francois

    1990-01-01

    This research thesis reports the study and description of the structure of a slug flow regime in a co-current vertical cylindrical duct, and the characterization and prediction of its transition towards a slug-churn (de-structured) regime. Flow physical mechanisms highlighted by the measurement of two important dynamics variables (wall friction and thickness of liquid films) are related to hypotheses of cellular models. The author first proposes an overview of slug flow regimes: theoretical steady and one-dimensional analysis, mass assessment equations of cellular models, application to the assessment of the flow rate and of the thickness of the film surrounding the gas slug. In the second part, the author addresses the slug flow regime transition towards the slug-churn regime: assessment of the evolution of flow dynamic properties, use of average wall friction analysis to obtain a relevant transition criterion. The third part presents experimental conditions, and measurement methods: conductometry for thickness measurement, polarography for wall friction measurement, and gas phase detection by using an optic barrier or optic fibres [fr

  20. Flow visualization study of post-critical heat flux in inverted flow

    International Nuclear Information System (INIS)

    Babelli, I.; Revankar, S.T.; Ishii, M.

    1994-01-01

    A visual study of film boiling was carried out to determine the flow regime transition in the post-CHF region for a transient bottom reflooding of a hot transparent test section. The effect of test liquid subcooling and inlet velocity on flow transition as well as on the quench front propagation was investigated. The respective ranges for liquid velocity and subcooling were 1.8-26.8 cm/s, and 20-45 C, respectively. The test liquid was Freon 113 which was introduced into the bottom of the quartz test section whose walls were maintained well above the film boiling temperature of the test liquid, via a transparent heat transfer fluid. The flow regimes observed down stream of the upward moving quench front were the rough wavy, the agitated, and the dispersed droplet/ligaments in agreement with a steady state, two-phase core injection study carried on recently by one of the authors. A correlation for the flow regime transition between the inverted annular and the dispersed droplet/ligament flow patterns was developed. The correlation showed a marked dependence on the void fraction at the CHF location and hence on the flow regime encountered in the pre-CHF region. (orig.)

  1. Horizontal two phase flow pattern identification by neural networks

    International Nuclear Information System (INIS)

    Crivelaro, Kelen Cristina Oliveira; Seleghim Junior, Paulo; Hervieu, Eric

    1999-01-01

    A multiphase fluid can flow according to several flow regimes. The problem associated with multiphase systems are basically related to the behavior of macroscopic parameters, such as pressure drop, thermal exchanges and so on, and their strong correlation to the flow regime. From the industrial applications point of view, the safety and longevity of equipment and systems can only be assured when they work according to the flow regimes for which they were designed to. This implies in the need to diagnose flow regimes in real time. The automatic diagnosis of flow regimes represents an objective of extreme importance, mainly for applications on nuclear and petrochemical industries. In this work, a neural network is used in association to a probe of direct visualization for the identification of a gas-liquid flow horizontal regimes, developed in an experimental circuit. More specifically, the signals produced by the probe are used to compose a qualitative image of the flow, which is promptly sent to the network for the recognition of the regimes. Results are presented for different transitions among the flow regimes, which demonstrate the extremely satisfactory performance of the diagnosis system. (author)

  2. Residence times and alluvial architecture of a sediment superslug in response to different flow regimes

    Science.gov (United States)

    Moody, John A.

    2017-10-01

    A superslug was deposited in a basin in the Colorado Front Range Mountains as a consequence of an extreme flood following a wildfire disturbance in 1996. The subsequent evolution of this superslug was measured by repeat topographic surveys (31 surveys from 1996 through 2014) of 18 cross sections approximately uniformly spaced over 1500 m immediately above the basin outlet. These surveys allowed the identification within the superslug of chronostratigraphic units deposited and eroded by different geomorphic processes in response to different flow regimes. Over the time period of the study, the superslug went through aggradation, incision, and stabilization phases that were controlled by a shift in geomorphic processes from generally short-duration, episodic, large-magnitude floods that deposited new chronostratigraphic units to long-duration processes that eroded units. These phases were not contemporaneous at each channel cross section, which resulted in a complex response that preserved different chronostratigraphic units at each channel cross section having, in general, two dominant types of alluvial architecture-laminar and fragmented. Age and transit-time distributions for these two alluvial architectures evolved with time since the extreme flood. Because of the complex shape of the distributions they were best modeled by two-parameter Weibull functions. The Weibull scale parameter approximated the median age of the distributions, and the Weibull shape parameter generally had a linear relation that increased with time since the extreme flood. Additional results indicated that deposition of new chronostratigraphic units can be represented by a power-law frequency distribution, and that the erosion of units decreases with depth of burial to a limiting depth. These relations can be used to model other situations with different flow regimes where vertical aggradation and incision are dominant processes, to predict the residence time of possible contaminated

  3. Socioeconomic inequalities in oral health in different European welfare state regimes.

    Science.gov (United States)

    Guarnizo-Herreño, Carol C; Watt, Richard G; Pikhart, Hynek; Sheiham, Aubrey; Tsakos, Georgios

    2013-09-01

    There is very little information about the relationship between welfare regimes and oral health inequalities. We compared socioeconomic inequalities in adults' oral health in five European welfare-state regimes: Scandinavian, Anglo-Saxon, Bismarckian, Southern and Eastern. Using data from the oral health module of the Eurobarometer 72.3 survey, we assessed inequalities in two self-reported oral health measures: no functional dentition (less than 20 natural teeth) and edentulousness (no natural teeth). Occupational social class, education and subjective social status (SSS) were included as socioeconomic position indicators. We estimated age-standardised prevalence rates, ORs, the Relative Index of Inequality (RII) and the Slope Index of Inequality (SII). The Scandinavian regime showed the lowest prevalence rates of the two oral health measures while the Eastern showed the highest. In all welfare regimes there was a general pattern of social gradients by occupational social class and education. Relative educational inequalities in no functional dentition were largest in the Scandinavian welfare regime (RII=3.81; 95% CI 2.68 to 5.42). The Scandinavian and Southern regimes showed the largest relative inequalities in edentulousness by occupation and education, respectively. There were larger absolute inequalities in no functional dentition in the Eastern regime by occupation (SII=42.16; 95% CI 31.42 to 52.89) and in the Southern by SSS (SII=27.92; 95% CI 17.36 to 38.47). Oral health inequalities in adults exist in all welfare-state regimes, but contrary to what may be expected from theory, they are not smaller in the Scandinavian regime. Future work should examine the potential mechanisms linking welfare provision and oral health inequalities.

  4. Biological assessment of environmental flows for Oklahoma

    Science.gov (United States)

    Fisher, William L.; Seilheimer, Titus S.; Taylor, Jason M.

    2012-01-01

    Large-scale patterns in fish assemblage structure and functional groups are influenced by alterations in streamflow regime. In this study, we defined an objective threshold for alteration for Oklahoma streams using a combination of the expected range of 27 flow indices and a discriminant analysis to predict flow regime group. We found that fish functional groups in reference flow conditions had species that were more intolerant to flow alterations and preferences for stream habitat and faster flowing water. In contrast, altered sites had more tolerant species that preferred lentic habitat and slower water velocity. Ordination graphs of the presence and functional groups of species revealed an underlying geographical pattern roughly conforming to ecoregions, although there was separation between reference and altered sites within the larger geographical framework. Additionally, we found that reservoir construction and operation significantly altered fish assemblages in two different systems, Bird Creek in central Oklahoma and the Kiamichi River in southeastern Oklahoma. The Bird Creek flow regime shifted from a historically intermittent stream to one with stable perennial flows, and changes in fish assemblage structure covaried with changes in all five components of the flow regime. In contrast, the Kiamichi River flow regime did not change significantly for most flow components despite shifts in fish assemblage structure; however, most of the species associated with shifts in assemblage structure in the Kiamichi River system were characteristic of lentic environments and were likely related more to proximity of reservoirs in the drainage system than changes in flow. The spatial patterns in fish assemblage response to flow alteration, combined with different temporal responses of hydrology and fish assemblage structure at sites downstream of reservoirs, indicate that interactions between flow regime and aquatic biota vary depending on ecological setting. This

  5. On natural circulation in High Temperature Gas-Cooled Reactors and pebble bed reactors for different flow regimes and various coolant gases

    International Nuclear Information System (INIS)

    Melesed'Hospital, G.

    1983-01-01

    The use of CO 2 or N 2 (heavy gas) instead of helium during natural circulation leads to improved performance in both High Temperature Gas-Cooled Reactors (HTGR) and in Pebble Bed Reactors (PBR). For instance, the coolant temperature rise corresponding to a coolant pressure level and a rate of afterheat removal could be only 18% with CO 2 as compared to He, for laminar flow in HTGR; this value would be 40% in PBR. There is less difference between HTGR and PBR for turbulent flows; CO 2 is found to be always better than N 2 . These types of results derived from relationships between coolant properties, coolant flow, temperature rise, pressure, afterheat levels and core geometry, are obtained for HTGR and PBR for various flow regimes, both within the core and in the primary loop

  6. Experimental study on downward two-phase flow in narrow rectangular channel

    Energy Technology Data Exchange (ETDEWEB)

    Kim, T.H.; Jeong, J.H. [Pusan National Univ., Busan (Korea, Republic of)

    2014-07-01

    Adiabatic vertical two-phase flow of air and water through narrow rectangular channels was investigated. This study involved the observation of flow using a high speed camera and flow regimes were determined by image processing program using a MATLAB. The flows regimes in channel with downward flow are similar to those found by previous studies with upward flow. The flow regimes in downward flow at low liquid velocity are different from the previous studies in upward flow. The flow regimes can be classified into bubbly, cap-bubbly, slug and churn flow. (author)

  7. The simulation of multidimensional multiphase flows

    International Nuclear Information System (INIS)

    Lahey, Richard T.

    2005-01-01

    This paper presents an assessment of various models which can be used for the multidimensional simulation of multiphase flows, such as may occur in nuclear reactors. In particular, a model appropriate for the direct numerical simulation (DNS) of multiphase flows and a mechanistically based, three-dimensional, four-field, turbulent, two-fluid computational multiphase fluid dynamics (CMFD) model are discussed. A two-fluid bubbly flow model, which was derived using potential flow theory, can be extended to other flow regimes, but this will normally involve ensemble-averaging the results from direct numerical simulations (DNS) of various flow regimes to provide the detailed numerical data necessary for the development of flow-regime-specific interfacial and wall closure laws

  8. Prediction of evaporation heat transfer coefficient based on gas-liquid two-phase annular flow regime in horizontal microfin tubes

    International Nuclear Information System (INIS)

    Wang Yueshe; Wang Yanling; Wang, G.-X.; Honda, Hiroshi

    2009-01-01

    A physical model of gas-liquid two-phase annular flow regime is presented for predicting the enhanced evaporation heat transfer characteristics in horizontal microfin tubes. The model is based on the equivalence of a periodical distortion of the disturbance wave in the substrate layer. Corresponding to the stratified flow model proposed previously by authors, the dimensionless quantity Fr 0 = G/[gd e ρ v (ρ l - ρ v )] 0.5 may be used as a measure for determining the applicability of the present theoretical model, which was used to restrict the transition boundary between the stratified-wavy flow and the annular/intermittent flows. Comparison of the prediction of the circumferential average heat transfer coefficient with available experimental data for four tubes and three refrigerants reveals that a good agreement is obtained or the trend is better than that of the previously developed stratified flow model for Fr 0 > 4.0 as long as the partial dry out of tube does not occur. Obviously, the developed annular model is applicable and reliable for evaporation in horizontal microfin tubes under the case of high heat flux and high mass flux.

  9. Prediction of evaporation heat transfer coefficient based on gas-liquid two-phase annular flow regime in horizontal microfin tubes

    Energy Technology Data Exchange (ETDEWEB)

    Wang Yueshe, E-mail: wangys@mail.xjtu.edu.cn [State Key Laboratory of Multiphase Flow in Power Engineering, Xi' an Jiaotong University, Xi' an 710049 (China); Yanling, Wang [State Key Laboratory of Multiphase Flow in Power Engineering, Xi' an Jiaotong University, Xi' an 710049 (China); Wang, G -X [Mechanical Engineering Department, The University of Akron, Akron, OH 44325-3903 (United States); Honda, Hiroshi [Kyushu University, 337 Kasuya-machi, Kasuya-gun, Kukuoka 811-2307 (Japan)

    2009-10-15

    A physical model of gas-liquid two-phase annular flow regime is presented for predicting the enhanced evaporation heat transfer characteristics in horizontal microfin tubes. The model is based on the equivalence of a periodical distortion of the disturbance wave in the substrate layer. Corresponding to the stratified flow model proposed previously by authors, the dimensionless quantity Fr{sub 0} = G/[gd{sub e}{rho}{sub v}({rho}{sub l} - {rho}{sub v})]{sup 0.5} may be used as a measure for determining the applicability of the present theoretical model, which was used to restrict the transition boundary between the stratified-wavy flow and the annular/intermittent flows. Comparison of the prediction of the circumferential average heat transfer coefficient with available experimental data for four tubes and three refrigerants reveals that a good agreement is obtained or the trend is better than that of the previously developed stratified flow model for Fr{sub 0} > 4.0 as long as the partial dry out of tube does not occur. Obviously, the developed annular model is applicable and reliable for evaporation in horizontal microfin tubes under the case of high heat flux and high mass flux.

  10. Two-phase flow patterns and size distribution of droplets in a microfluidic T-junction: Experimental observations in the squeezing regime

    Science.gov (United States)

    Mahdi, Yassine; Daoud, Kamel; Tadrist, Lounès

    2017-04-01

    Generating micrometer sized droplets has been studied in a microfluidic system with T-junction geometry 250 μm in internal diameter and with PTFE capillary tubing. Several experiments were conducted by varying the flow rate of the dispersed phase from 2.78 ṡ10-11 m3 /s to 5.28 ṡ10-9 m3 /s and that of the continuous phase from 2.78 ṡ10-10 m3 /s to 1.94 ṡ10-9 m3 /s. The visualization of different flow regimes (drop, plug, and annular) was carried out for three configurations (not inverted in a horizontal position, inverted in a horizontal position, and inverted in a vertical position) for low capillary numbers. The model of Gauss was also chosen for a droplet size distribution in the dispersed phase, with the flow quality x varying from 0.016 to 0.44. The evolution of the drop size distribution as a function of the flow quality in the dispersed phase shows that the variation coefficient of the droplet's diameter is inversely proportional to the flow quality.

  11. Life history theory predicts fish assemblage response to hydrologic regimes.

    Science.gov (United States)

    Mims, Meryl C; Olden, Julian D

    2012-01-01

    The hydrologic regime is regarded as the primary driver of freshwater ecosystems, structuring the physical habitat template, providing connectivity, framing biotic interactions, and ultimately selecting for specific life histories of aquatic organisms. In the present study, we tested ecological theory predicting directional relationships between major dimensions of the flow regime and life history composition of fish assemblages in perennial free-flowing rivers throughout the continental United States. Using long-term discharge records and fish trait and survey data for 109 stream locations, we found that 11 out of 18 relationships (61%) tested between the three life history strategies (opportunistic, periodic, and equilibrium) and six hydrologic metrics (two each describing flow variability, predictability, and seasonality) were statistically significant (P history strategies, with 82% of all significant relationships observed supporting predictions from life history theory. Specifically, we found that (1) opportunistic strategists were positively related to measures of flow variability and negatively related to predictability and seasonality, (2) periodic strategists were positively related to high flow seasonality and negatively related to variability, and (3) the equilibrium strategists were negatively related to flow variability and positively related to predictability. Our study provides important empirical evidence illustrating the value of using life history theory to understand both the patterns and processes by which fish assemblage structure is shaped by adaptation to natural regimes of variability, predictability, and seasonality of critical flow events over broad biogeographic scales.

  12. Groundwater Recharge and Flow Regime revealed by multi-tracers approach in a headwater, North China Plain

    Science.gov (United States)

    Sakakibara, Koichi; Tsujimura, Maki; Song, Xianfang; Zhang, Jie

    2014-05-01

    Groundwater recharge is a crucial hydrological process for effective water management especially in arid/ semi-arid regions. However, the insufficient number of specific research regarding groundwater recharge process has been reported previously. Intensive field surveys were conducted during rainy season, mid dry season, and end of dry season, in order to clarify comprehensive groundwater recharge and flow regime of Wangkuai watershed in a headwater, which is a main recharge zone of North China Plain. The groundwater, spring, stream water and lake water were sampled, and inorganic solute constituents and stable isotopes of oxygen 18 and deuterium were determined on all water samples. Also the stream flow rate was observed. The solute ion concentrations and stable isotopic compositions show that the most water of this region can be characterized by Ca-HCO3 type and the main water source is precipitation which is affected by altitude effect of stable isotopes. In addition, the river and reservoir of the area seem to recharge the groundwater during rainy season, whereas interaction between surface water and groundwater does not become dominant gradually after the rainy season. The inversion analysis applied in Wangkuai watershed using simple mixing model represents an existing multi-flow systems which shows a distinctive tracer signal and flow rate. In summary, the groundwater recharged at different locations in the upper stream of Wangkuai reservoir flows downward to alluvial fan with a certain amount of mixing together, also the surface water recharges certainly the groundwater in alluvial plain in the rainy season.

  13. Flow characterization in periodic microchannels containing asymmetric grooves

    Energy Technology Data Exchange (ETDEWEB)

    Osorio-Nesme, A; Delgado, A, E-mail: anuhar.nesme@fau.de [Institute of Fluid Mechanics, Friedrich-Alexander Erlangen-Nuremberg University, Cauerstrasse 4, D-91058 Erlangen (Germany)

    2017-10-15

    Characterization of two-dimensional flows in microchannels with anisotropic periodic grooves is numerically carried out by using the lattice Boltzmann method. Periodically placed microstructures, consisting of novel nozzle-diffuser-like grooves are deliberately designed to introduce a flow-direction dependent resistance. Simulations were conducted for a low-to-moderate Reynolds number in the laminar-transition flow regime. Different channel geometries, defined by the half-angle ϕ of the periodic grooves are considered. The influence of the half-angle on both the flow field and the onset of oscillatory flow regime at different driving body forces is analyzed. At a low Reynolds number, the flow is observed stationary and fully reversible, regardless of the groove geometry. In this regime, higher Reynolds numbers were observed when the geometry acts as a diffuser (negative flow) than as a nozzle (positive flow) for a given driving body force. At sufficiently high Reynolds number the flow turns from a steady state to a time-dependent oscillatory regime through a Hopf bifurcation. Successive flow bifurcations lead the flow structure from a periodic regime to a quasi-chaotic regime with three-dimensional structures. The onset of unsteady flow occurs earlier for positive flows and geometries with small half-angles. For higher driving forces, there is a reduction in the volume flow rate due to the advected material in the transversal direction, causing consequently a decrease in the Reynolds number. (paper)

  14. The natural sediment regime in rivers: broadening the foundation for ecosystem management

    Science.gov (United States)

    Wohl, Ellen E.; Bledsoe, Brian P.; Jacobson, Robert B.; Poff, N. LeRoy; Rathburn, Sara L.; Walters, David M.; Wilcox, Andrew C.

    2015-01-01

    Water and sediment inputs are fundamental drivers of river ecosystems, but river management tends to emphasize flow regime at the expense of sediment regime. In an effort to frame a more inclusive paradigm for river management, we discuss sediment inputs, transport, and storage within river systems; interactions among water, sediment, and valley context; and the need to broaden the natural flow regime concept. Explicitly incorporating sediment is challenging, because sediment is supplied, transported, and stored by nonlinear and episodic processes operating at different temporal and spatial scales than water and because sediment regimes have been highly altered by humans. Nevertheless, managing for a desired balance between sediment supply and transport capacity is not only tractable, given current geomorphic process knowledge, but also essential because of the importance of sediment regimes to aquatic and riparian ecosystems, the physical template of which depends on sediment-driven river structure and function.

  15. Condensation of refrigerants in horizontal, spirally grooved microfin tubes: Numerical analysis of heat transfer in the annular flow regime

    Energy Technology Data Exchange (ETDEWEB)

    Nozu, S; Honda, H

    2000-02-01

    A method is presented for estimating the condensation heat transfer coefficient in a horizontal, spirally grooved microfin tube. Based on the flow observation study performed by the authors, a laminar film condensation model in the annular flow regime is proposed. The model assumes that all the condensate flow occurs through the grooves. The condensate film is segmented into thin and thick film regions. In the thin film region formed on the fin surface, the condensate is assumed to be drained by the combined surface tension and vapor shear forces. In the thick film region formed in the groove, on the other hand, the condensate is assumed to be driven by the vapor shear force. The present and previous local heat transfer data including four fluids (CFC11, HCFC22, HCFC123, and HFCl34a) and three microfin tubes are found to agree with the present predictions to a mean absolute deviation of 15.1%.

  16. Impedance void-meter and neural networks for vertical two-phase flows

    International Nuclear Information System (INIS)

    Mi, Y.; Li, M.; Xiao, Z.; Tsoukalas, L.H.; Ishii, M.

    1998-01-01

    Most two-phase flow measurements, including void fraction measurements, depend on correct flow regime identification. There are two steps towards successful identification of flow regimes: one is to develop a non-intrusive instrument to demonstrate area-averaged void fluctuations, the other to develop a non-linear mapping approach to perform objective identification of flow regimes. A non-intrusive impedance void-meter provides input signals to a neural mapping approach used to identify flow regimes. After training, both supervised and self-organizing neural network learning paradigms performed flow regime identification successfully. The methodology presented holds considerable promise for multiphase flow diagnostic and measurement applications. (author)

  17. Investigation of Different Droplet Formation Regimes in a T-junction Microchannel Using the VOF Technique in OpenFOAM

    Science.gov (United States)

    Malekzadeh, Shima; Roohi, Ehsan

    2015-06-01

    Here we aimed to investigate various droplet formation regimes in a two-dimensional T-junction microchannel geometry using the open source software OpenFOAM. Two incompressible fluids, continuous phase in the main channel and dispersed phase in the lateral channel, have been considered. The interFoam solver was used to simulate laminar flow with two incompressible and isothermal phases. We evaluated the capability of "Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM)" volume of fluid (VOF) technique of the OpenFOAM for modeling of the droplet formation and movement in different regimes. The flow behavior in the T-junction microchannel over a wide range of capillary numbers (0.006 to 0.12), volume flow rate ratio (0.125, 0.25, 0.5), and contact angle (130° to 180°) in the squeezing, dripping and jetting regimes were examined.The importance of parameters such as contact angle, capillary number, flow rate ratio, and Reynolds number at the time of separation, as well as the formation of droplets, was investigated in different regimes. We found that droplet detachment time increases by increasing the contact angle in the squeezing regime while increasing the contact angle in the dripping regime results in a decrease in the droplet detachment time. We compare the role of pressure gradient and shear stress forces in the droplet formation process in both dripping and squeezing regimes in details. We also provide a classification of two-phase flow regimes in the investigated T-junction microchannel in terms of three main parameters of, e.g., flow rate ratio, contact angle, and capillary number.

  18. Heat transfer investigation of molten salts under laminar and turbulent flow regimes

    International Nuclear Information System (INIS)

    Srivastava, A.K.; Vaidya, A.M.; Maheshwari, N.K.; Vijayan, P.K.

    2014-01-01

    High temperature reactor and solar thermal power plants use Molten Salt as a coolant, as it has low melting point and high boiling point, enabling us to operate the system at low pressure. Molten fluoride salt (eutectic mixture of LiF-NaF-KF) and molten nitrate salt (mixture of NaNO 3 and KNO 3 in 60:40 ratios by weight) are proposed as a candidate coolant for High Temperature Reactors (HTR) and solar power plant respectively. BARC is developing a 600 MWth pebble bed high temperature reactor, cooled by natural circulation of fluoride salt and capable of supplying process heat at 1000℃ to facilitate hydrogen production by splitting water. Beside this, BARC is also developing a 2MWe solar power tower system using molten nitrate salt as a primary coolant and storage medium. In order to design this, it is necessary to study the heat transfer characteristics of various molten salts. Most of the previous studies related to molten salts are based on the experimental works. These experiments essentially measured the physical properties of molten salts and their heat transfer characteristics. Ferri et al. introduced the property definitions for molten salts in the RELAP5 code to perform transient simulations at the ProvaCollettoriSolari (PCS) test facility. In this paper, a CFD analysis has been performed to study the heat transfer characteristics of molten fluoride salt and molten nitrate salt flowing in a circular pipe for various regimes of flow. Simulation is performed with the help of in-house developed CFD code, NAFA, acronym for Numerical Analysis of Flows in Axi-symmetric geometries. Uniform velocity and temperature distribution are set as the inlet boundary condition and pressure is employed at the outlet boundary condition. The inlet temperature for all simulation is set as 300℃ for nitrate salt and 500℃ for fluoride salt and the operating pressure is 1 atm in both the cases

  19. Theory, methods and tools for determining environmental flows for riparian vegetation: Riparian vegetation-flow response guilds

    Science.gov (United States)

    Merritt, D.M.; Scott, M.L.; Leroy, Poff N.; Auble, G.T.; Lytle, D.A.

    2010-01-01

    Riparian vegetation composition, structure and abundance are governed to a large degree by river flow regime and flow-mediated fluvial processes. Streamflow regime exerts selective pressures on riparian vegetation, resulting in adaptations (trait syndromes) to specific flow attributes. Widespread modification of flow regimes by humans has resulted in extensive alteration of riparian vegetation communities. Some of the negative effects of altered flow regimes on vegetation may be reversed by restoring components of the natural flow regime. 2. Models have been developed that quantitatively relate components of the flow regime to attributes of riparian vegetation at the individual, population and community levels. Predictive models range from simple statistical relationships, to more complex stochastic matrix population models and dynamic simulation models. Of the dozens of predictive models reviewed here, most treat one or a few species, have many simplifying assumptions such as stable channel form, and do not specify the time-scale of response. In many cases, these models are very effective in developing alternative streamflow management plans for specific river reaches or segments but are not directly transferable to other rivers or other regions. 3. A primary goal in riparian ecology is to develop general frameworks for prediction of vegetation response to changing environmental conditions. The development of riparian vegetation-flow response guilds offers a framework for transferring information from rivers where flow standards have been developed to maintain desirable vegetation attributes, to rivers with little or no existing information. 4. We propose to organise riparian plants into non-phylogenetic groupings of species with shared traits that are related to components of hydrologic regime: life history, reproductive strategy, morphology, adaptations to fluvial disturbance and adaptations to water availability. Plants from any river or region may be grouped

  20. Residence times and alluvial architecture of a sediment superslug in response to different flow regimes

    Science.gov (United States)

    Moody, John A.

    2017-01-01

    A superslug was deposited in a basin in the Colorado Front Range Mountains as a consequence of an extreme flood following a wildfire disturbance in 1996. The subsequent evolution of this superslug was measured by repeat topographic surveys (31 surveys from 1996 through 2014) of 18 cross sections approximately uniformly spaced over 1500 m immediately above the basin outlet. These surveys allowed the identification within the superslug of chronostratigraphic units deposited and eroded by different geomorphic processes in response to different flow regimes.Over the time period of the study, the superslug went through aggradation, incision, and stabilization phases that were controlled by a shift in geomorphic processes from generally short-duration, episodic, large-magnitude floods that deposited new chronostratigraphic units to long-duration processes that eroded units. These phases were not contemporaneous at each channel cross section, which resulted in a complex response that preserved different chronostratigraphic units at each channel cross section having, in general, two dominant types of alluvial architecture—laminar and fragmented. Age and transit-time distributions for these two alluvial architectures evolved with time since the extreme flood. Because of the complex shape of the distributions they were best modeled by two-parameter Weibull functions. The Weibull scale parameter approximated the median age of the distributions, and the Weibull shape parameter generally had a linear relation that increased with time since the extreme flood. Additional results indicated that deposition of new chronostratigraphic units can be represented by a power-law frequency distribution, and that the erosion of units decreases with depth of burial to a limiting depth. These relations can be used to model other situations with different flow regimes where vertical aggradation and incision are dominant processes, to predict the residence time of possible contaminated

  1. Assessment of MELCOR condensation models with the presence of noncondensable gas in natural convection flow regime

    International Nuclear Information System (INIS)

    Yoon, Dhongik S; Jo, HangJin; Corradini, Michael L

    2017-01-01

    Condensation of steam vapor is an important mode of energy removal from the reactor containment. The presence of noncondensable gas complicates the process and makes it difficult to model. MELCOR, one of the more widely used system codes for containment analyses, uses the heat and mass transfer analogy to model condensation heat transfer. To investigate previously reported nodalization-dependence in natural convection flow regime, MELCOR condensation model as well as other models are studied. The nodalization-dependence issue is resolved by using physical length from the actual geometry rather than node size of each control volume as the characteristic length scale for MELCOR containment analyses. At the transition to turbulent natural convection regime, the McAdams correlation for convective heat transfer produces a better prediction compared to the original MELCOR model. The McAdams correlation is implemented in MELCOR and the prediction is validated against a set of experiments on a scaled AP600 containment. The MELCOR with our implemented model produces improved predictions. For steam molar fractions in the gas mixture greater than about 0.58, the predictions are within the uncertainty margin of the measurements. The simulation results still underestimate the heat transfer from the gas-steam mixture, implying that conservative predictions are provided.

  2. Optimal ranking regime analysis of TreeFlow dendrohydrological reconstructions

    Science.gov (United States)

    The Optimal Ranking Regime (ORR) method was used to identify 6-100 year time windows containing significant ranking sequences in 55 western U.S. streamflow reconstructions, and reconstructions of the level of the Great Salt Lake and San Francisco Bay salinity during 1500-2007. The method’s ability t...

  3. Research on regimes of limonite ore hyrdotransport for the conditions of Perdo Soto Alba plant

    Directory of Open Access Journals (Sweden)

    Рауль Искьердо Пупо

    2017-04-01

    Full Text Available The paper examines regular flow patterns of high-concentrated limonite pulp with significant content of finest grains. Engineering procedures have been developed to calculate basic parameters of limonite ore hydrotransport in turbulent and structured regimes. Trustworthiness of scientific statements, conclusions and recommendations is justified by theoretical research, establishment of analytical dependences, results of laboratory and industrial experiments. Practical regularities of behavior have been identified for the coefficient of hydraulic resistance, depending on pulp density in the range 35-45 % in case of pulp flow in structured regime, as well as regularity of pressure losses in case of pulp flow in horizontal and inclined pipelines in turbulent regime.

  4. The effects of viscosity, surface tension, and flow rate on gasoil-water flow pattern in microchannels

    Energy Technology Data Exchange (ETDEWEB)

    Boogar, Rahman Sadeghi; Gheshlaghi, Reza; Mahdavi, Mahmood Akhavan [Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of)

    2013-01-15

    A microchannel was fabricated with glass tubes to investigate the effect of viscosity, surface tension, and flow rate on the liquid-liquid two-phase flow regime. Water and gasoil were selected as aqueous and organic working fluids, respectively. The two fluids were injected into the microchannel and created either slug or parallel profile depending on the applied conditions. The range of Reynolds and capillary numbers was chosen in such a way that neither inertia nor interfacial tension forces were negligible. Xanthan gum was used to increase viscosity and Triton X-100 (TX-100) and Sodium Dodecyl Sulfate (SDS) were used to reduce the interfacial tension. The results demonstrated that higher value of viscosity and flow rate increased interfacial area, but slug flow regime remained unchanged. The two surfactants showed different effects on the flow regime and interfacial area. Addition of TX-100 did not change the slug flow but decreased the interfacial area. In contrast, addition of SDS increased interfacial area by decreasing the slug’s length in the low concentrations and by switching from slug to parallel regime at high concentrations.

  5. Interfacial area concentration in gas–liquid bubbly to churn flow regimes in large diameter pipes

    International Nuclear Information System (INIS)

    Shen, Xiuzhong; Hibiki, Takashi

    2015-01-01

    -developed two-group IAC correlation were compared with the collected experimental data in gas–liquid bubbly to churn flow regimes in large diameter pipes and their mean absolute relative deviations were obtained to be 28.1%, 54.4% and 29.6% for group 1, group 2 and all bubbles respectively

  6. Recent flow regime and sedimentological evolution of a fluvial system as the main factors controlling spatial distribution of arsenic in groundwater (Red River, Vietnam)

    DEFF Research Database (Denmark)

    Kazmierczak, J.; Larsen, F.; Jakobsen, R.

    2016-01-01

    sediments was partially eroded during the Holocene and covered by sand and clay deposited in fluvial environments. Sedimentary processes lead to the development of two flow systems. Shallow groundwater discharges either to the local surface water bodies or, in the areas where low permeable sediments...... isolating Pleistocene and Holocene aquifers were eroded, to the deep groundwater flow system discharging to Red River. Previously reported pattern of arsenic groundwater concentrations decreasing with an increasing sediment age is modified by the observed flow regime. Connection of the younger and older...... river channels resulted in a transport of high arsenic concentrations towards the Pleistocene aquifer, where low arsenic concentrations were expected....

  7. Recent changes (1973-2014 versus 1903-1972) in the flow regime of the Lower Paraná River and current fluvial pollution warnings in its Delta Biosphere Reserve.

    Science.gov (United States)

    Puig, Alba; Olguín Salinas, Héctor F; Borús, Juan A

    2016-06-01

    Alterations in flow regimes of large rivers may originate or increase risks to ecosystems and humans. The Paraná River basin (South America) undergoes human pressures (e.g., heavy damming in the upper basin, deforestation, and mixed pollution) that may affect the water quantity and quality of its terminal Delta (Argentina). In this study, after applying univariate and multivariate change-point detection and trend analyses to the daily data series of flows incoming to the Delta (Paraná-Santa Fe section), flow characteristics were compared by Indicators of Hydrologic Alteration (IHA) and Environmental Flow Components (EFC). Some flood characteristics were also compared from hydrometric levels in the middle Delta (San Pedro station). Chemical and microbiological water variables in the main rivers of the "Paraná Delta" Biosphere Reserve were examined during two extreme hydrologic years (October 2008 to July 2010) to detect potential risk factors in association with hydrologic conditions. In the Lower Paraná River, a historical period (1903-1972) and two more altered periods (1973-1999 wet period and 2000-2014 dry period) were identified. Flow duration curves evidenced different changes in both altered periods, reflecting the joint effect of climatic variability and human influence. The most evident alterations in the flow regime were the lack of record of the extreme-low-flow component, the attenuation of monthly flow seasonality, and the increase in the number of reversals (dry period) and in the variability of maximum and minimum flow dates. These alterations are consistent with the monthly and daily flow regulation by upstream dams evidenced by available data from the current dry period. In the middle Delta, the marked monthly seasonality in flood days decreased only in the wet period. The proportion between the number of flood days exceeding the evacuation level and that of those exceeding the warning level doubled in the wet period but decreased only

  8. Transport processes in magnetically confined plasmas in the nonlinear regime.

    Science.gov (United States)

    Sonnino, Giorgio

    2006-06-01

    A field theory approach to transport phenomena in magnetically confined plasmas is presented. The thermodynamic field theory (TFT), previously developed for treating the generic thermodynamic system out of equilibrium, is applied to plasmas physics. Transport phenomena are treated here as the effect of the field linking the thermodynamic forces with their conjugate flows combined with statistical mechanics. In particular, the Classical and the Pfirsch-Schluter regimes are analyzed by solving the thermodynamic field equations of the TFT in the weak-field approximation. We found that, the TFT does not correct the expressions of the ionic heat fluxes evaluated by the neoclassical theory in these two regimes. On the other hand, the fluxes of matter and electronic energy (heat flow) is further enhanced in the nonlinear Classical and Pfirsch-Schluter regimes. These results seem to be in line with the experimental observations. The complete set of the electronic and ionic transport equations in the nonlinear Banana regime, is also reported. A paper showing the comparison between our theoretic results and the experimental observations in the JET machine is currently in preparation.

  9. On the instability of convective flow in cylinder and possible secondary regimes

    Energy Technology Data Exchange (ETDEWEB)

    Bekezhanova, V B; Andreev, V K, E-mail: bekezhanova@mail.ru, E-mail: andr@icm.krasn.ru [Institute of Computational Modelling SB RAS, Akademgorodok, 50/44, Krasnoyarsk, Institute of Mathematics and Fundamental Informatics, Siberian Federal University, Svobodny, 79, Krasnoyarsk, 660041 (Russian Federation)

    2014-08-01

    A new exact solution of equations of free convection is constructed in the framework of the Oberbeck–Boussinesq approximation. The solution contains an independent parameter and describes the flow of a viscous heat-conducting liquid in the vertical cylinder with large radius. Complex rheology and radiative heating are taken into account. The considered problem reduces to the operator equation with strongly nonlinear operator. The solvability of the operator problem is proved. The iterative procedure for finding the free parameter is suggested. Three different classes of solution are obtained with the help of the procedure. The linear stability of all classes of solutions is studied numerically. Critical thermal mode is isolated. Evolution of oscillatory mode depending on Prandtl number is investigated. It is shown that under small Prandtl numbers oscillatory modes decay. If Prandtl numbers are not small a new instability type appears. This instability is connected with growing thermal disturbances. Another instability mechanism is discovered in the short waves domain. In this case the crisis is attributed to growing hydrodynamical disturbances. Secondary regimes arising in the hydrodynamical mechanism of the stability loss are calculated. (paper)

  10. Apparatus for monitoring two-phase flow

    Science.gov (United States)

    Sheppard, John D.; Tong, Long S.

    1977-03-01

    A method and apparatus for monitoring two-phase flow is provided that is particularly related to the monitoring of transient two-phase (liquid-vapor) flow rates such as may occur during a pressurized water reactor core blow-down. The present invention essentially comprises the use of flanged wire screens or similar devices, such as perforated plates, to produce certain desirable effects in the flow regime for monitoring purposes. One desirable effect is a measurable and reproducible pressure drop across the screen. The pressure drop can be characterized for various known flow rates and then used to monitor nonhomogeneous flow regimes. Another useful effect of the use of screens or plates in nonhomogeneous flow is that such apparatus tends to create a uniformly dispersed flow regime in the immediate downstream vicinity. This is a desirable effect because it usually increases the accuracy of flow rate measurements determined by conventional methods.

  11. Using Flow Regime Lightning and Sounding Climatologies to Initialize Gridded Lightning Threat Forecasts for East Central Florida

    Science.gov (United States)

    Lambert, Winifred; Short, David; Volkmer, Matthew; Sharp, David; Spratt, Scott

    2007-01-01

    Each morning, the forecasters at the National Weather Service in Melbourne, FL (NWS MLB) produce an experimental cloud-to-ground (CG) lightning threat index map for their county warning area (CWA) that is posted to their web site (httl://www.srh.weather.gov/mlb/ghwo/lightning.shtml) . Given the hazardous nature of lightning in East Central Florida, especially during the warm season months of May September, these maps help users factor the threat of lightning, relative to their location, into their daily plans. The maps are color-coded in five levels from Very Low to Extreme, with threat level definitions based on the probability of lightning occurrence and the expected amount of CG activity. On a day in which thunderstorms are expected, there are typically two or more threat levels depicted spatially across the CWA. The locations of relative lightning threat maxima and minima often depend on the position and orientation of the low-level ridge axis, forecast propagation and interaction of sea/lake/outflow boundaries, expected evolution of moisture and stability fields, and other factors that can influence the spatial distribution of thunderstorms over the CWA. The lightning threat index maps are issued for the 24-hour period beginning at 1200 UTC each day with a grid resolution of 5 km x 5 km. Product preparation is performed on the AWIPS Graphical Forecast Editor (GFE), which is the standard NWS platform for graphical editing. Until recently, the forecasters created each map manually, starting with a blank map. To improve efficiency of the forecast process, NWS MLB requested that the Applied Meteorology Unit (AMU) create gridded warm season lightning climatologies that could be used as first-guess inputs to initialize lightning threat index maps. The gridded values requested included CG strike densities and frequency of occurrence stratified by synoptic-scale flow regime. The intent was to improve consistency between forecasters while allowing them to focus on the

  12. Countercurrent two-phase flow

    International Nuclear Information System (INIS)

    Hewitt, G.F.; Imperial Coll. of Science and Technology, London

    1989-01-01

    A survey is presented of counter-current flow with particular reference to the limits of the regime, namely the 'flooding' phenomena. Emphasis is also given to the transiently counter-current type of flow ('churn flow') which is formed on the break-down of falling film counter-current flow. The mechanisms of flooding are reviewed and flooding in systems with heat transfer and in non-vertical channels is discussed. New data on the flooding phenomena and the region of simultaneous downflow and upflow beyond flooding are presented. The onset of churn flow is discussed and new measurements on churn flow are presented. The characteristics of the churn flow regime are shown to be independent of the coexistence of a falling film region below the liquid injection point. (orig.)

  13. Buoyancy-driven chaotic regimes during solute dispersion in pore networks

    International Nuclear Information System (INIS)

    Tsakiroglou, C.D.; Theodoropoulou, M.A.; Karoutsos, V.

    2005-01-01

    In an attempt to investigate gravity effects on solute dispersion at the scale of a pore network, single source-solute transport visualization experiments are performed on glass-etched pore networks of varying morphology and degree of pore-scale heterogeneities. The (lighter) low solute concentration aqueous solution flows steadily through the porous medium and the (heavier) high solute concentration solution is injected at a very low and constant flow rate through an inner port. The transient evolution of the solute concentration distribution over various regions of the pore network is determined at different scales by capturing and video-recording snapshots of the dispersion on PC, measuring automatically the spatial variation of the color intensity of the solution, and transforming the color intensities to solute concentrations. Without the action of gravity, the steady-state dispersion regime changes with Peclet (Pe) number, and the longitudinal and transverse dispersivities are estimated by fitting the experimental datasets to approximate analytic solutions of the advection-dispersion equation. Under the action of gravity, multiple of steady-state solute dispersion regimes is developed at each Pe value, and lobe-shaped instabilities of the solute concentration are observed across the pore network, as the downward flow of the denser (higher solute concentration) fluid is counterbalanced by the upward flow of the less dense (lower solute concentration) fluid. The steady-state dispersion regimes may be periodic, quasi-periodic or chaotic depending on the system parameters. The nature of the transient fluctuations of the average solute concentration is analyzed by identifying the periodicity of the fluctuations, determining the autocorrelation function and the statistical moments of the time series, and inspecting the FFT (fast Fourier transform) power spectra. It is found that the mixing zone tends to be stabilized at higher values of the Peclet (Pe) number

  14. Apparatus for monitoring two-phase flow

    International Nuclear Information System (INIS)

    Sheppard, J.D.; Tong, L.S.

    1977-01-01

    A method and apparatus for monitoring two-phase flow is provided that is particularly related to the monitoring of transient two-phase (liquid-vapor) flow rates such as may occur during a pressurized water reactor core blow-down. The present invention essentially comprises the use of flanged wire screens or similar devices, such as perforated plates, to produce certain desirable effects in the flow regime for monitoring purposes. One desirable effect is a measurable and reproducible pressure drop across the screen. The pressure drop can be characterized for various known flow rates and then used to monitor nonhomogeneous flow regimes. Another useful effect of the use of screens or plates in nonhomogeneous flow is that such apparatus tends to create a uniformly dispersed flow regime in the immediate downstream vicinity. This is a desirable effect because it usually increases the accuracy of flow rate measurements determined by conventional methods. 3 claims, 9 figures

  15. Two-phase flow patterns and their relationship to two-phase heat transfer

    International Nuclear Information System (INIS)

    Hewitt, G.F.

    1977-01-01

    The objective of this lecture was to discuss the general nature of two phase flows, to define the various regimes of flow and to discuss the influence of these regimes on the heat transfer processes taking place. The methods of regime delineation are briefly described and regime descriptions introduced for both vertical and horizontal flows in tubes. ''Flow regime maps'' have been widely used as an aid to determination of the regime which occurs in a given situation. Some of the more widely used maps are described and the limitations of this approach discussed. There have been many attempts to obtain a better phenomenological description of two phase flow patterns. In this lecture, these attempts will be reviewed in the context of the bubble/plug, plug/churn and churn/annular flow transitions in vertical flow. The latter two transitions are related to the flooding/flow reversal phenomena. For horizontal flows, recent work on the onset of slugging will be reviewed. In flows with evaporation or condensation, the situation is influenced by departures from thermodynamic equilibrium and the types of departure observed are discuss briefly. Flow patterns and their relationships with heat transfer regimes are then reviewed for the case of condensation in horizontal tubes and evaporation in vertical tubes

  16. Entropy feature extraction on flow pattern of gas/liquid two-phase flow based on cross-section measurement

    International Nuclear Information System (INIS)

    Han, J; Dong, F; Xu, Y Y

    2009-01-01

    This paper introduces the fundamental of cross-section measurement system based on Electrical Resistance Tomography (ERT). The measured data of four flow regimes of the gas/liquid two-phase flow in horizontal pipe flow are obtained by an ERT system. For the measured data, five entropies are extracted to analyze the experimental data according to the different flow regimes, and the analysis method is examined and compared in three different perspectives. The results indicate that three different perspectives of entropy-based feature extraction are sensitive to the flow pattern transition in gas/liquid two-phase flow. By analyzing the results of three different perspectives with the changes of gas/liquid two-phase flow parameters, the dynamic structures of gas/liquid two-phase flow is obtained, and they also provide an efficient supplementary to reveal the flow pattern transition mechanism of gas/liquid two-phase flow. Comparison of the three different methods of feature extraction shows that the appropriate entropy should be used for the identification and prediction of flow regimes.

  17. Classifying low flow hydrological regimes at a regional scale

    Science.gov (United States)

    Kirkby, M. J.; Gallart, F.; Kjeldsen, T. R.; Irvine, B. J.; Froebrich, J.; Lo Porto, A.; de Girolamo, A.; Mirage Team

    2011-12-01

    The paper uses a simple water balance model that partitions the precipitation between actual evapotranspiration, quick flow and delayed flow, and has sufficient complexity to capture the essence of climate and vegetation controls on this partitioning. Using this model, monthly flow duration curves have been constructed from climate data across Europe to address the relative frequency of ecologically critical low flow stages in semi-arid rivers, when flow commonly persists only in disconnected pools in the river bed. The hydrological model is based on a dynamic partitioning of precipitation to estimate water available for evapotranspiration and plant growth and for residual runoff. The duration curve for monthly flows has then been analysed to give an estimate of bankfull flow based on recurrence interval. Arguing from observed ratios of cross-sectional areas at flood and low flows, hydraulic geometry suggests that disconnected flow under "pool" conditions is approximately 0.1% of bankfull flow. Flow duration curves define a measure of bankfull discharge on the basis of frequency. The corresponding frequency for pools is then read from the duration curve, using this (0.1%) ratio to estimate pool discharge from bank full discharge. The flow duration curve then provides an estimate of the frequency of poorly connected pool conditions, corresponding to this discharge, that constrain survival of river-dwelling arthropods and fish. The methodology has here been applied across Europe at 15 km resolution, and the potential is demonstrated for applying the methodology under alternative climatic scenarios.

  18. Classifying low flow hydrological regimes at a regional scale

    Directory of Open Access Journals (Sweden)

    M. J. Kirkby

    2011-12-01

    Full Text Available The paper uses a simple water balance model that partitions the precipitation between actual evapotranspiration, quick flow and delayed flow, and has sufficient complexity to capture the essence of climate and vegetation controls on this partitioning. Using this model, monthly flow duration curves have been constructed from climate data across Europe to address the relative frequency of ecologically critical low flow stages in semi-arid rivers, when flow commonly persists only in disconnected pools in the river bed. The hydrological model is based on a dynamic partitioning of precipitation to estimate water available for evapotranspiration and plant growth and for residual runoff. The duration curve for monthly flows has then been analysed to give an estimate of bankfull flow based on recurrence interval. Arguing from observed ratios of cross-sectional areas at flood and low flows, hydraulic geometry suggests that disconnected flow under "pool" conditions is approximately 0.1% of bankfull flow. Flow duration curves define a measure of bankfull discharge on the basis of frequency. The corresponding frequency for pools is then read from the duration curve, using this (0.1% ratio to estimate pool discharge from bank full discharge. The flow duration curve then provides an estimate of the frequency of poorly connected pool conditions, corresponding to this discharge, that constrain survival of river-dwelling arthropods and fish. The methodology has here been applied across Europe at 15 km resolution, and the potential is demonstrated for applying the methodology under alternative climatic scenarios.

  19. Seasonal dynamics of trace elements in tidal salt marsh soils as affected by the flow-sediment regulation regime.

    Directory of Open Access Journals (Sweden)

    Junhong Bai

    Full Text Available Soil profiles were collected in three salt marshes with different plant species (i.e. Phragmites australis, Tamarix chinensis and Suaeda salsa in the Yellow River Delta (YRD of China during three seasons (summer and fall of 2007 and the following spring of 2008 after the flow-sediment regulation regime. Total elemental contents of As, Cd, Cu, Pb and Zn were determined using inductively coupled plasma atomic absorption spectrometry to investigate temporal variations in trace elements in soil profiles of the three salt marshes, assess the enrichment levels and ecological risks of these trace elements in three sampling seasons and identify their influencing factors. Trace elements did not change significantly along soil profiles at each site in each sampling season. The highest value for each sampling site was observed in summer and the lowest one in fall. Soils in both P. australis and S. salsa wetlands tended to have higher trace element levels than those in T. chinensis wetland. Compared to other elements, both Cd and As had higher enrichment factors exceeding moderate enrichment levels. However, the toxic unit (TU values of these trace elements did not exceed probable effect levels. Correlation analysis showed that these trace elements were closely linked to soil properties such as moisture, sulfur, salinity, soil organic matter, soil texture and pH values. Principal component analysis showed that the sampling season affected by the flow-sediment regulation regime was the dominant factor influencing the distribution patterns of these trace elements in soils, and plant community type was another important factor. The findings of this study could contribute to wetland conservation and management in coastal regions affected by the hydrological engineering.

  20. Predicting the natural flow regime: Models for assessing hydrological alteration in streams

    Science.gov (United States)

    Carlisle, D.M.; Falcone, J.; Wolock, D.M.; Meador, M.R.; Norris, R.H.

    2009-01-01

    Understanding the extent to which natural streamflow characteristics have been altered is an important consideration for ecological assessments of streams. Assessing hydrologic condition requires that we quantify the attributes of the flow regime that would be expected in the absence of anthropogenic modifications. The objective of this study was to evaluate whether selected streamflow characteristics could be predicted at regional and national scales using geospatial data. Long-term, gaged river basins distributed throughout the contiguous US that had streamflow characteristics representing least disturbed or near pristine conditions were identified. Thirteen metrics of the magnitude, frequency, duration, timing and rate of change of streamflow were calculated using a 20-50 year period of record for each site. We used random forests (RF), a robust statistical modelling approach, to develop models that predicted the value for each streamflow metric using natural watershed characteristics. We compared the performance (i.e. bias and precision) of national- and regional-scale predictive models to that of models based on landscape classifications, including major river basins, ecoregions and hydrologic landscape regions (HLR). For all hydrologic metrics, landscape stratification models produced estimates that were less biased and more precise than a null model that accounted for no natural variability. Predictive models at the national and regional scale performed equally well, and substantially improved predictions of all hydrologic metrics relative to landscape stratification models. Prediction error rates ranged from 15 to 40%, but were 25% for most metrics. We selected three gaged, non-reference sites to illustrate how predictive models could be used to assess hydrologic condition. These examples show how the models accurately estimate predisturbance conditions and are sensitive to changes in streamflow variability associated with long-term land-use change. We also

  1. Analysis of relations for heat transfer at the post-CHF regime

    Energy Technology Data Exchange (ETDEWEB)

    Dorokhovich, S. L. [Obninsk State Techical Univ., Obninsk (Russian Federation); Kirillov, P. L. [Institute of Physics and Power Engineering, Obninsk (Russian Federation)

    2003-07-01

    Information about heat transfer rates in two-fluid flow at the post-CHF regime is important for analysis of accidents of water-cooled nuclear reactors as well as calculations of steam generators (liquid metal-water). It is complicate to create analytical methods because there is a variety of two-fluid flow regimes dictated by channel size, pressure, mass flow rate, heat flux, droplet spectrum, flow quality, other factors and, finally, by crisis type. At crisis in subcooled liquid or low quality two-phase flows Inverted Annular Film Boiling (IAFB) takes place when liquid flow is separated from the wall by a thin superheated vapor film. For dispersed flow crisis is usually related to drying a liquid film moving along the heated surface (wall). In both cases two-phase flow is thermodynamically nonequilibrium since the temperatures of phases (liquid and vapor) are different. The mean (at the rate of heat content) flow temperature is not the determining parameter. Different boundary conditions of experiment s uniform heat fluxes or 'hot' spots, are able to lead to different relations for the heat transfer coefficient. Last years the great number of semiempirical models were elaborated, that become more and more complicate. It is difficult to examine many parameters of the models. An agreement between final results and separate experimental data is not yet the evidence for the verity of extension while prerequisites taken in the models are often doubtful and hardly examined. Thus the correlations obtained from experimental data, for example, are used in practice. The analysis of relations for heat transfer at the Deteriorated Heat Transfer (DHT) regime, the comparison of relations with the data of look up tables made on the basis of the Institute of Physics and Power Engineering and Chalk River Laboratories experimental data banks are the objective of current report.

  2. Analysis of relations for heat transfer at the post-CHF regime

    International Nuclear Information System (INIS)

    Dorokhovich, S. L.; Kirillov, P. L.

    2003-01-01

    Information about heat transfer rates in two-fluid flow at the post-CHF regime is important for analysis of accidents of water-cooled nuclear reactors as well as calculations of steam generators (liquid metal-water). It is complicate to create analytical methods because there is a variety of two-fluid flow regimes dictated by channel size, pressure, mass flow rate, heat flux, droplet spectrum, flow quality, other factors and, finally, by crisis type. At crisis in subcooled liquid or low quality two-phase flows Inverted Annular Film Boiling (IAFB) takes place when liquid flow is separated from the wall by a thin superheated vapor film. For dispersed flow crisis is usually related to drying a liquid film moving along the heated surface (wall). In both cases two-phase flow is thermodynamically nonequilibrium since the temperatures of phases (liquid and vapor) are different. The mean (at the rate of heat content) flow temperature is not the determining parameter. Different boundary conditions of experiment s uniform heat fluxes or 'hot' spots, are able to lead to different relations for the heat transfer coefficient. Last years the great number of semiempirical models were elaborated, that become more and more complicate. It is difficult to examine many parameters of the models. An agreement between final results and separate experimental data is not yet the evidence for the verity of extension while prerequisites taken in the models are often doubtful and hardly examined. Thus the correlations obtained from experimental data, for example, are used in practice. The analysis of relations for heat transfer at the Deteriorated Heat Transfer (DHT) regime, the comparison of relations with the data of look up tables made on the basis of the Institute of Physics and Power Engineering and Chalk River Laboratories experimental data banks are the objective of current report

  3. Two-phase flow operational maps for multi-microchannel evaporators

    International Nuclear Information System (INIS)

    Szczukiewicz, Sylwia; Borhani, Navid; Thome, John Richard

    2013-01-01

    Highlights: • New operational maps for several different micro-evaporators are presented. • Inlet micro-orifices prevented flow instability, back flow, and flow maldistribution. • Eight different operating regimes were distinguished. • The flashing two-phase flow without back flow operating regime is preferred. -- Abstract: The current paper presents new operational maps for several different multi-microchannel evaporators, with and without any inlet restrictions (micro-orifices), for the two-phase flow of refrigerants R245fa, R236fa, and R1234ze(E). The test fluids flowed in 67 parallel channels, each having a cross-sectional area of 100 × 100 μm 2 . In order to emulate the power dissipated by active components in a 3D CMOS CPU chip, two aluminium microheaters were sputtered onto the back-side of the test section providing a 0.5 cm 2 each. Without any inlet restrictions in the micro-evaporator, significant parallel channel flow instabilities, vapor back flow, and flow maldistribution led to high-amplitude and high-frequency temperature and pressure oscillations. Such undesired phenomena were then prevented by placing restrictions at the inlet of each channel. High-speed flow visualization distinguished eight different operating regimes of the two-phase flow depending on the tested operating conditions. Therefore, the preferred operating regimes can be easily traced. In particular, flashing two-phase flow without back flow appeared to be the best operating regime without any flow and temperature instabilities

  4. Development of an electrical sensor for measurement of void fraction and identification of flow regime in a horizontal pipe

    International Nuclear Information System (INIS)

    Won, Woo Yeon; Lee, Yeon Gun; Lee, Bo An; Ko, Min Seok; Kim, Sin

    2015-01-01

    The electrical signals of the electrical impedance sensor depend on the flow structure as well as the void fraction. For this reason, the electrical responses to a given void fraction differ according to the flow pattern. For reliable void fraction measurement, hence, information on the flow pattern should be given. Based on this idea, a new improved conductance sensor is proposed in this study to measure the void fraction and simultaneously determine the flow pattern of the air-water two-phase mixture in a horizontal pipe. The proposed sensor is composed of a 3-electrode set of adjacent and opposite electrodes. The opposite electrodes measures the void fraction, the adjacent electrode serves to determine the flow patterns. Prior to the real applications of the proposed approach, several numerical calculations based on the FEM are performed to optimize the electrode and insulator sizes in terms of the sensor linearity. The numerical results are assessed in comparison with the data from static experiments. The sensor system is applied for a horizontal flow loop with 40 mm in inner diameter and 5 m in length and its measurement performance for the void fraction is compared with that of a wire-mesh sensor system. In this study, an electrical sensor for measuring the void fraction and identifying flow pattern in horizontal pipes has been designed. For optimization of the sensor, numerical analysis have been performed in order to determine the geometry and verified it through static experiments. Also, the loop experiments were conducted for several flow rate conditions covering stratified and intermittent flow regimes and the experimental results for the void fractions measured by the proposed sensor were compared with those of a wire-mesh sensor. The comparison results are in overall good agreements

  5. Aperiodic pressure pulsation under non optimal hydraulic turbine regimes at low swirl number

    Science.gov (United States)

    Skripkin, S. G.; Tsoy, M. A.; Kuibin, P. A.; Shtork, S. I.

    2017-09-01

    Off-design operating conditions of hydraulic turbines is hindered by pressure fluctuations in the draft tube of the turbine. A precessing helical vortex rope develops, which imperils the mechanical structure and limits the operation flexibility of hydropower station. Understanding of the underlying instabilities of precessing vortex rope at low swirl number is incomplete. In this paper flow regimes with different residual swirl is analysed, particular attention is paid to the regime with a small swirl parameter. Study defines upper and low boundaries of regime where aperiodic pressure surge is observed. Flow field at the runner exit is investigated by Laser Doppler Velocimetry and high-speed visualizations, which are complemented draft tube wall pressure measurements.

  6. Comparison of drift-velocity and drag coefficient approaches for one-dimensional two-fluid models in bubbly flow regime and validation with experimental data

    Energy Technology Data Exchange (ETDEWEB)

    Gómez-Zarzuela, C.; Miró, R.; Verdú, G. [Institute for Industrial Safety, Radiology and Environmental (ISIRYM), Universitat Politècnica de València (Spain); Peña-Monferrer, C.; Chiva, S. [Department of Mechanical Engineering and Construction, Universitat Jaume I, Castellón de la Plana (Spain); Muñoz-Cobo, J.L., E-mail: congoque@iqn.upv.es, E-mail: cpena@uji.es [Institute for Energy Engineering, Universitat Politècnica de València (Spain)

    2017-07-01

    Two-phase flow simulation has been an extended research topic over the years due to the importance of predicting with accuracy the flow behavior within different installations, including nuclear power plants. Some of them are low pressure events, like low water pressure injection, nuclear refueling or natural circulation. This work is devoted to investigate the level of accuracy of the results when a two-phase flow experiment, which has been carried out at low pressure, is performed in a one-dimensional simulation code. In particular, the codes that have been selected to represent the experiment are the best-estimate system codes RELAP5/MOD3 and TRACE v5.0 patch4. The experiment consists in a long vertical pipe along which an air-water fluid in bubbly regime moves upwards in adiabatic conditions and atmospheric pressure. The simulations have been first performed in both codes with their original correlations, which are based on the drift flux model for the case of bubbly regime in vertical pipes. Then, a different implementation for the drag force has been undertaken, in order to perform a simulation with equivalent bubble diameter to the experiment. Results show that the calculation obtained from the codes are within the ranges of validity of the experiment with some discrepancies, which leads to the conclusion that the use of a drag correlation approach is more realistic than drift flux model. (author)

  7. Comparison of drift-velocity and drag coefficient approaches for one-dimensional two-fluid models in bubbly flow regime and validation with experimental data

    International Nuclear Information System (INIS)

    Gómez-Zarzuela, C.; Miró, R.; Verdú, G.; Peña-Monferrer, C.; Chiva, S.; Muñoz-Cobo, J.L.

    2017-01-01

    Two-phase flow simulation has been an extended research topic over the years due to the importance of predicting with accuracy the flow behavior within different installations, including nuclear power plants. Some of them are low pressure events, like low water pressure injection, nuclear refueling or natural circulation. This work is devoted to investigate the level of accuracy of the results when a two-phase flow experiment, which has been carried out at low pressure, is performed in a one-dimensional simulation code. In particular, the codes that have been selected to represent the experiment are the best-estimate system codes RELAP5/MOD3 and TRACE v5.0 patch4. The experiment consists in a long vertical pipe along which an air-water fluid in bubbly regime moves upwards in adiabatic conditions and atmospheric pressure. The simulations have been first performed in both codes with their original correlations, which are based on the drift flux model for the case of bubbly regime in vertical pipes. Then, a different implementation for the drag force has been undertaken, in order to perform a simulation with equivalent bubble diameter to the experiment. Results show that the calculation obtained from the codes are within the ranges of validity of the experiment with some discrepancies, which leads to the conclusion that the use of a drag correlation approach is more realistic than drift flux model. (author)

  8. Investigation on the Flow in a Rotor-Stator Cavity with Centripetal Through-Flow

    Directory of Open Access Journals (Sweden)

    Bo Hu

    2017-10-01

    Full Text Available Daily and Nece distinguished four flow regimes in an enclosed rotor-stator cavity, which are dependent on the circumferential Reynolds number and dimensionless axial gap width. A diagram of the different flow regimes including the respective mean profiles for both tangential and radial velocity was developed. The coefficients for the different flow regimes have also been correlated. In centrifugal pumps and turbines, the centripetal through-flow is quite common from the outer radius of the impeller to the impeller eye, which has a strong influence on the radial pressure distribution, axial thrust and frictional torque. The influence of the centripetal through-flow on the cavity flow with different circumferential Reynolds numbers and dimensionless axial gap width is not sufficiently investigated. It is also quite important to convert the 2D Daily and Nece diagram into 3D by introducing the through-flow coefficient. In order to investigate the impact of the centripetal through-flow, a test rig is designed and built up at the University of Duisburg-Essen. The design of the test rig is described. The impact of the above mentioned parameters on the velocity profile, pressure distribution, axial thrust and frictional torque are presented and analyzed in this paper. The 3D Daily and Nece diagram introducing the through-flow coefficient is also organized in this paper.

  9. Determination of the Hall Thruster Operating Regimes

    International Nuclear Information System (INIS)

    L. Dorf; V. Semenov; Y. Raitses; N.J. Fisch

    2002-04-01

    A quasi one-dimensional (1-D) steady-state model of the Hall thruster is presented. For the same discharge voltage two operating regimes are possible -- with and without the anode sheath. For given mass flow rate, magnetic field profile and discharge voltage a unique solution can be constructed, assuming that the thruster operates in one of the regimes. However, we show that for a given temperature profile the applied discharge voltage uniquely determines the operating regime: for discharge voltages greater than a certain value, the sheath disappears. That result is obtained over a wide range of incoming neutral velocities, channel lengths and widths, and cathode plane locations. It is also shown that a good correlation between the quasi 1-D model and experimental results can be achieved by selecting an appropriate electron mobility and temperature profile

  10. Enstrophy transport conditional on local flow topologies in different regimes of premixed turbulent combustion

    KAUST Repository

    Papapostolou, Vassilios; Wacks, Daniel H.; Chakraborty, Nilanjan; Klein, Markus; Im, Hong G.

    2017-01-01

    , enstrophy decreases from the unburned to the burned gas side for the cases representing the TRZ and BRZ regimes, with diminishing influences of dilatation rate and baroclinic torque. The enstrophy transport in the TRZ and BRZ regimes is governed

  11. Absorption of CO2 and H2S in Aqueous Alkanolamine Solutions using a Fixed-Bed Reactor with Cocurrent Downflow Operation in the Pulsing Flow Regime

    NARCIS (Netherlands)

    Versteeg, G.F.; Swaaij, W.P.M. van

    1988-01-01

    Absorption rates of H2S and CO2 in several aqueous alkanolamines in a cocurrent downflow fixed-bed reactor operated in the pulse flow regime have been measured in order to obtain information on the potential selectivity and on the mass transfer parameters. From these experiments it can be concluded

  12. The Thermal Regime Around Buried Submarine High-Voltage Cables

    Science.gov (United States)

    Emeana, C. J.; Dix, J.; Henstock, T.; Gernon, T.; Thompson, C.; Pilgrim, J.

    2015-12-01

    The expansion of offshore renewable energy infrastructure and the desire for "trans-continental shelf" power transmission, all require the use of submarine High Voltage (HV) cables. These cables have maximum operating surface temperatures of up to 70oC and are typically buried at depths of 1-2 m beneath the seabed, within the wide range of substrates found on the continental shelf. However, the thermal properties of near surface shelf sediments are poorly understood and this increases the uncertainty in determining the required cable current ratings, cable reliability and the potential effects on the sedimentary environments. We present temperature measurements from a 2D laboratory experiment, designed to represent a buried, submarine HV cable. We used a large (2.5 m-high) tank, filled with water-saturated ballotini and instrumented with 120 thermocouples, which measured the time-dependent 2D temperature distributions around the heat source. The experiments use a buried heat source to represent a series of realistic cable surface temperatures with the aim for identifying the thermal regimes generated within typical non-cohesive shelf sediments: coarse silt, fine sand and very coarse sand. The steady state heat flow regimes, and normalised and radial temperature distributions were assessed. Our results show that at temperatures up to 60°C above ambient, the thermal regimes are conductive for the coarse silt sediments and convective for the very coarse sand sediments even at 7°C above ambient. However, the heat flow pattern through the fine sand sediment shows a transition from conductive to convective heat flow at a temperature of approximately 20°C above ambient. These findings offer an important new understanding of the thermal regimes associated with submarine HV cables buried in different substrates and has huge impacts on cable ratings as the IEC 60287 standard only considers conductive heat flow as well as other potential near surface impacts.

  13. Valley-scale morphology drives differences in fluvial sediment budgets and incision rates during contrasting flow regimes

    Science.gov (United States)

    Weber, M. D.; Pasternack, G. B.

    2017-07-01

    High-resolution topographic surveys using LiDAR and multibeam sonar can be used to characterize and quantify fluvial change. This study used repeat surveys to explore how topographic change, fluvial processes, sediment budgets, and aggradation and incision rates vary across spatial scales and across two contrasting decadal flow regimes in a regulated gravel/cobble river. A novel method for quantifying digital elevation model uncertainty was developed and applied to a topographic change detection analysis from 2006/2008 to 2014. During this period, which had four modest 3-5 year floods, most sediment was laterally redistributed through bank erosion and channel migration. Erosion primarily occurred in the floodplain (97,000 m3), terraces (80,000 m3), and lateral bars (58,000 m3); while deposition occurred in the adjacent pools (73,000 m3), fast glides (48,000 m3), and runs (36,000 m3). In contrast, significantly higher magnitude and longer duration floods from 1999 to 2006/2008 caused sediment to be displaced longitudinally, with the upstream reaches exporting sediment and the downstream reaches aggrading. The river maintained floodplain connectivity during both periods, despite different processes dominating the type of connectivity. Larger floods promoted overbank scour and avulsion, while smaller floods promoted bank erosion and lateral migration. This study explores and illustrates how the geomorphic response to contrasting flood regimes in a nonuniform river is highly dependent on which landforms are controlling hydraulics.

  14. Spray characteristics and spray cooling heat transfer in the non-boiling regime

    International Nuclear Information System (INIS)

    Cheng, Wen-Long; Han, Feng-Yun; Liu, Qi-Nie; Fan, Han-Lin

    2011-01-01

    Spray cooling is an effective method for dissipating high heat fluxes in the field of electronics thermal control. In this study, experiments were performed with distilled water as a test liquid to study the spray cooling heat transfer in non-boiling regime. A Phase Doppler Anemometry (PDA) was used to study the spray characteristics. The effects of spray flow rate, spray height, and inlet temperature on spray cooling heat transfer were investigated. It was found that the parameters affect heat transfer of spray cooling in non-boiling regime by the spray characteristics and working fluid thermophysical properties. Then the corresponding droplet axial velocity and Sauter mean diameter (SMD) were successfully correlated with mean absolute error of 15%, which were based upon the orifice diameter, the Weber and Reynolds numbers of the orifice flow prior to liquid breakup, dimensionless spray height and spray cross-section radius. The heat transfer in non-boiling regime was correlated with a mean absolute error of 7%, which was mainly associated with the working fluid thermophysical properties, the Weber and Reynolds numbers hitting the heating surface, dimensionless heating surface temperature and diameter. -- Highlights: → The spray flow rate, spray height, and inlet temperature affect heat transfer of spray cooling in non-boiling regime by the spray characteristics and the working fluid thermophysical properties. → Then the corresponding droplet axial velocity and Sauer mean diameter (SMD) were successfully correlated with mean absolute error of 15%. → The heat transfer in non-boiling regime was correlated with a mean absolute error of 7%.

  15. Two-phase flow structure in large diameter pipes

    International Nuclear Information System (INIS)

    Smith, T.R.; Schlegel, J.P.; Hibiki, T.; Ishii, M.

    2012-01-01

    Highlights: ► Local profiles of various quantities measured in large diameter pipe. ► Database for interfacial area in large pipes extended to churn-turbulent flow. ► Flow regime map confirms previous models for flow regime transitions. ► Data will be useful in developing interfacial area transport models for large pipes. - Abstract: Flow in large pipes is important in a wide variety of applications. In the nuclear industry in particular, understanding of flow in large diameter pipes is essential in predicting the behavior of reactor systems. This is especially true of natural circulation Boiling Water Reactor (BWR) designs, where a large-diameter chimney above the core provides the gravity head to drive circulation of the coolant through the reactor. The behavior of such reactors during transients and during normal operation will be predicted using advanced thermal–hydraulics analysis codes utilizing the two-fluid model. Essential to accurate two-fluid model calculations is reliable and accurate computation of the interfacial transfer terms. These interfacial transfer terms can be expressed as the product of one term describing the potential driving the transfer and a second term describing the available surface area for transfer, or interfacial area concentration. Currently, the interfacial area is predicted using flow regime dependent empirical correlations; however the interfacial area concentration is best computed through the use of the one-dimensional interfacial area transport equation (IATE). To facilitate the development of IATE source and sink term models in large-diameter pipes a fundamental understanding of the structure of the two-phase flow is essential. This understanding is improved through measurement of the local void fraction, interfacial area concentration and gas velocity profiles in pipes with diameters of 0.102 m and 0.152 m under a wide variety of flow conditions. Additionally, flow regime identification has been performed to

  16. Characterising the hydrological regime of an ungauged temporary river system: a case study.

    Science.gov (United States)

    D'Ambrosio, Ersilia; De Girolamo, Anna Maria; Barca, Emanuele; Ielpo, Pierina; Rulli, Maria Cristina

    2017-06-01

    Temporary streams are characterised by specific hydrological regimes, which influence ecosystem processes, groundwater and surface water interactions, sediment regime, nutrient delivery, water quality and ecological status. This paper presents a methodology to characterise and classify the regime of a temporary river in Southern Italy based on hydrological indicators (HIs) computed with long-term daily flow records. By using a principal component analysis (PCA), a set of non-redundant indices were identified describing the main characteristics of the hydrological regime in the study area. The indicators identified were the annual maximum 30- and 90-day mean (DH4 and DH5), the number of zero flow days (DL6), flow permanence (MF) and the 6-month seasonal predictability of dry periods (SD6). A methodology was also tested to estimate selected HIs in ungauged river reaches. Watershed characteristics such as catchment area, gauging station elevation, mean watershed slope, mean annual rainfall, land use, soil hydraulic conductivity and available water content were derived for each site. Selected indicators were then linked to the catchment characteristics using a regression analysis. Finally, MF and SD6 were used to classify the river reaches on the basis of their degree of intermittency. The methodology presented in this paper constitutes a useful tool for ecologists and water resource managers in the Water Framework Directive implementation process, which requires a characterisation of the hydrological regime and a 'river type' classification for all water bodies.

  17. The role of the geophysical template and environmental regimes in controlling stream-living trout populations

    Science.gov (United States)

    Penaluna, Brooke E.; Railsback, Steve F.; Dunham, Jason B.; Johnson, S.; Bilby, Richard E.; Skaugset, Arne E.

    2015-01-01

    The importance of multiple processes and instream factors to aquatic biota has been explored extensively, but questions remain about how local spatiotemporal variability of aquatic biota is tied to environmental regimes and the geophysical template of streams. We used an individual-based trout model to explore the relative role of the geophysical template versus environmental regimes on biomass of trout (Oncorhynchus clarkii clarkii). We parameterized the model with observed data from each of the four headwater streams (their local geophysical template and environmental regime) and then ran 12 simulations where we replaced environmental regimes (stream temperature, flow, turbidity) of a given stream with values from each neighboring stream while keeping the geophysical template fixed. We also performed single-parameter sensitivity analyses on the model results from each of the four streams. Although our modeled findings show that trout biomass is most responsive to changes in the geophysical template of streams, they also reveal that biomass is restricted by available habitat during seasonal low flow, which is a product of both the stream’s geophysical template and flow regime. Our modeled results suggest that differences in the geophysical template among streams render trout more or less sensitive to environmental change, emphasizing the importance of local fish–habitat relationships in streams.

  18. Pulse regime in formation of fractal fibers

    Energy Technology Data Exchange (ETDEWEB)

    Smirnov, B. M., E-mail: bmsmirnov@gmail.com [Joint Institute for High Temperatures (Russian Federation)

    2016-11-15

    The pulse regime of vaporization of a bulk metal located in a buffer gas is analyzed as a method of generation of metal atoms under the action of a plasma torch or a laser beam. Subsequently these atoms are transformed into solid nanoclusters, fractal aggregates and then into fractal fibers if the growth process proceeds in an external electric field. We are guided by metals in which transitions between s and d-electrons of their atoms are possible, since these metals are used as catalysts and filters in interaction with gas flows. The resistance of metal fractal structures to a gas flow is evaluated that allows one to find optimal parameters of a fractal structure for gas flow propagation through it. The thermal regime of interaction between a plasma pulse or a laser beam and a metal surface is analyzed. It is shown that the basic energy from an external source is consumed on a bulk metal heating, and the efficiency of atom evaporation from the metal surface, that is the ratio of energy fluxes for vaporization and heating, is 10{sup –3}–10{sup –4} for transient metals under consideration. A typical energy flux (~10{sup 6} W/cm{sup 2}), a typical surface temperature (~3000 K), and a typical pulse duration (~1 μs) provide a sufficient amount of evaporated atoms to generate fractal fibers such that each molecule of a gas flow collides with the skeleton of fractal fibers many times.

  19. Flow map and measurement of void fraction and heat transfer coefficient using an image analysis technique for flow boiling of water in a silicon microchannel

    International Nuclear Information System (INIS)

    Singh, S G; Duttagupta, S P; Jain, A; Sridharan, A; Agrawal, Amit

    2009-01-01

    The present work focuses on the generation of the flow regime map for two-phase water flow in microchannels of a hydraulic diameter of 140 µm. An image analysis algorithm has been developed and utilized to obtain the local void fraction. The image processing technique is also employed to identify and estimate the percentage of different flow regimes and heat transfer coefficient, as a function of position, heat flux and mass flow rate. Both void fraction and heat transfer coefficient are found to increase monotonically along the length of the microchannel. At low heat flux and low flow rates, bubbly, slug and annular flow regimes are apparent. However, the flow is predominately annular at high heat flux and high flow rate. A breakup of the flow frequency suggests that the flow is bistable in the annular regime, in that at a fixed location, the flow periodically switches from single-phase liquid to annular and vice versa. Otherwise, the occurrence of three regimes—single-phase liquid, bubbly and slug are observed. These results provide several useful insights about two-phase flow in microchannels besides being of fundamental interest

  20. Measurement of flow in supercritical flow regime using cutthroat flumes

    Indian Academy of Sciences (India)

    flumes are used to measure flow rates in irrigation chan- nels and water treatment ... and ha can be expressed in unit system, the values of C and N in Eq. (1) will ... presented in a design chart for determining discharge in throat-less flume ...

  1. Tomographic multiphase flow measurement

    Energy Technology Data Exchange (ETDEWEB)

    Saetre, C., E-mail: camilla@ift.uib.no [Department of Physics and Technology, University of Bergen (Norway); Michelsen Centre for Industrial Measurement Science and Technology (Norway); Johansen, G.A. [Department of Physics and Technology, University of Bergen (Norway); Michelsen Centre for Industrial Measurement Science and Technology (Norway); Tjugum, S.A. [Michelsen Centre for Industrial Measurement Science and Technology (Norway); Roxar Flow Measurement, Bergen (Norway)

    2012-07-15

    Measurement of multiphase flow of gas, oil and water is not at all trivial and in spite of considerable achievements over the past two decades, important challenges remain (). These are related to reducing measurement uncertainties arising from variations in the flow regime, improving long term stability and developing new means for calibration, adjustment and verification of the multiphase flow meters. This work focuses on the first two issues using multi gamma beam (MGB) measurements for identification of the type of flow regime. Further gamma ray tomographic measurements are used for reference of the gas/liquid distribution. For the MGB method one Am-241 source with principal emission at 59.5 keV is used because this relatively low energy enables efficient collimation and thereby shaping of the beams, as well as compact detectors. One detector is placed diametrically opposite the source whereas the second is positioned to the side so that this beam is close to the pipe wall. The principle is then straight forward to compare the measured intensities of these detectors and through that identify the flow pattern, i.e. the instantaneous cross-sectional gas-liquid distribution. The measurement setup also includes Compton scattering measurements, which can provide information about the changes in the water salinity for flow segments with high water liquid ratio and low gas fractions. By measuring the transmitted intensity in short time slots (<100ms), rapid regime variations are revealed. From this we can select the time sections suitable for salinity measurements. Since the salinity variations change at the time scale of hours, a running average can be performed to increase the accuracy of the measurements. Recent results of this work will be presented here. - Highlights: Black-Right-Pointing-Pointer Multiphase flow gas-fraction and flow regime measurements by multi gamma ray beams. Black-Right-Pointing-Pointer High-speed gamma ray tomograph as reference for the flow

  2. Tomographic multiphase flow measurement

    International Nuclear Information System (INIS)

    Sætre, C.; Johansen, G.A.; Tjugum, S.A.

    2012-01-01

    Measurement of multiphase flow of gas, oil and water is not at all trivial and in spite of considerable achievements over the past two decades, important challenges remain (). These are related to reducing measurement uncertainties arising from variations in the flow regime, improving long term stability and developing new means for calibration, adjustment and verification of the multiphase flow meters. This work focuses on the first two issues using multi gamma beam (MGB) measurements for identification of the type of flow regime. Further gamma ray tomographic measurements are used for reference of the gas/liquid distribution. For the MGB method one Am-241 source with principal emission at 59.5 keV is used because this relatively low energy enables efficient collimation and thereby shaping of the beams, as well as compact detectors. One detector is placed diametrically opposite the source whereas the second is positioned to the side so that this beam is close to the pipe wall. The principle is then straight forward to compare the measured intensities of these detectors and through that identify the flow pattern, i.e. the instantaneous cross-sectional gas-liquid distribution. The measurement setup also includes Compton scattering measurements, which can provide information about the changes in the water salinity for flow segments with high water liquid ratio and low gas fractions. By measuring the transmitted intensity in short time slots (<100ms), rapid regime variations are revealed. From this we can select the time sections suitable for salinity measurements. Since the salinity variations change at the time scale of hours, a running average can be performed to increase the accuracy of the measurements. Recent results of this work will be presented here. - Highlights: ► Multiphase flow gas-fraction and flow regime measurements by multi gamma ray beams. ► High-speed gamma ray tomograph as reference for the flow pattern and gas fraction. ► Dual modality

  3. Severe aortic stenosis patients with preserved ejection fraction according to flow and gradient classification: Prevalence and outcomes.

    Science.gov (United States)

    González Gómez, Ariana; Fernández-Golfín, Covadonga; Monteagudo, Juan Manuel; Izurieta, Carlos; Hinojar, Rocío; García, Ana; Casas, Eduardo; Jiménez-Nacher, José Julio; Moya, José Luis; Ruiz, Soledad; Zamorano, José Luis

    2017-12-01

    Clinicians often encounter patients with apparently discordant echocardiographic findings, severe aortic stenosis (SAS) defined by aortic valve area (AVA) despite a low mean gradient. A new classification according to flow state and pressure gradient has been proposed. We sought to assess the prevalence, characteristics and outcomes of patients with asymptomatic SAS with preserved left-ventricular ejection fraction (LVEF) according to flow and gradient. In total 442 patients with SAS (AVAigradient (≥ or Gradient (LF/LG): 21.3%(n=94); Normal Flow/Low Gradient (NF/LG): 32.1%(n=142); Low Flow/High Gradient (LF/HG): 6.8%(n=30); Normal Flow/High Gradient (NF/HG): 39,8%(n=176). Mean follow-up time was 20.5months (SD=10.3). Primary combined endpoint was cardiovascular mortality and hospital admission for SAS related symptom, secondary endpoint was aortic valve replacement (AVR), comparing HG group to LF/LG group. During follow-up 17 (18%) of LF/LG patients and 21 (10.2%) of HG patients met the primary endpoint. A lower free of event survival (cardiovascular mortality and hospital admission) was observed in patients with LF/LG AS (Breslow, p=0.002). Significant differences were noted between groups with a lower AVR free survival in the LF/LG group compared to HG groups (Breslow, p=0.002). Our study confirms the high prevalence and worse prognosis of LF/LG SAS. Clinicians must be aware of this entity to ensure appropriate patient management. Copyright © 2017 Elsevier Ireland Ltd. All rights reserved.

  4. Fishy Business: Response of Stream Fish Assemblages to Small Hydro-power Plant Induced Flow Alteration in the Western Ghats, Karnataka

    Science.gov (United States)

    Rao, S. T.; Krishnaswamy, J.; Bhalla, R. S.

    2017-12-01

    Alteration of natural flow regimes is considered as a major threat to freshwater fish assemblages as it disturbs the water quality and micro-habitat features of rivers. Small hydro-power (SHP), which is being promoted as a clean and green substitute for large hydro-power generation, alters the natural flow regime of head-water streams by flow diversion and regulation. The effects of altered flow regime on tropical stream fish assemblages, driven by seasonality induced perturbations to water quality and microhabitat parameters are largely understudied. My study examined the potential consequences of flow alteration by SHPs on fish assemblages in two tributaries of the west-flowing Yettinahole River which flows through the reserved forests of Sakleshpur in the Western Ghats of Karnataka. The flow in one of the tributaries followed natural flow regime while the other comprised three regimes: a near-natural flow regime above the dam, rapidly varying discharge below the dam and a dewatered regime caused by flow diversion. The study found that the altered flow regime differed from natural flow regime in terms of water quality, microhabitat heterogeneity and fish assemblage response, each indicative of the type of flow alteration. Fish assemblage in the natural flow regime was characterized by a higher catch per site, a strong association of endemic and trophic specialist species. The flow regime above the dam was found to mimic some components of the natural flow regime, both ecological and environmental. Non endemic, generalist and pool tolerant species were associated with the dewatered regime. There was a lack of strong species-regime association and an overall low catch per site for the flow regulated regime below the dam. This study highlights the consequences of altered flows on the composition of freshwater fish assemblages and portrays the potential of freshwater fish as indicators of the degree and extent of flow alteration. The study recommends the need for

  5. Slug flooding in air-water countercurrent vertical flow

    International Nuclear Information System (INIS)

    Lee, Jae Young; Raman, Roger; Chang, Jen-Shih

    2000-01-01

    This paper is to study slug flooding in the vertical air-water countercurrent flow loop with a porous liquid injector in the upper plenum. More water penetration into the bottom plenum in slug flooding is observed than the annular flooding because the flow regime changes from the slug flow regime or periodic slug/annular flow regime to annular flow regime due to the hysteresis between the onset of flooding and the bridging film. Experiments were made tubes of 0.995 cm, 2.07 cm, and 5.08 cm in diameter. A mechanistic model for the slug flooding with the solitary wave whose height is four time of the mean film thickness is developed to produce relations of the critical liquid flow rate and the mean film thickness. After fitting the critical liquid flow rate with the experimental data as a function of the Bond number, the gas flow rate for the slug flooding is obtained by substituting the critical liquid flow rate to the annular flooding criteria. The present experimental data evaluate the slug flooding condition developed here by substituting the correlations for mean film thickness models in the literature. The best prediction was made by the correlation for the mean film thickness of the present study which is same as Feind's correlation multiplied by 1.35. (author)

  6. Determination of the Hall Thruster Operating Regimes; TOPICAL

    International Nuclear Information System (INIS)

    L. Dorf; V. Semenov; Y. Raitses; N.J. Fisch

    2002-01-01

    A quasi one-dimensional (1-D) steady-state model of the Hall thruster is presented. For the same discharge voltage two operating regimes are possible - with and without the anode sheath. For given mass flow rate, magnetic field profile and discharge voltage a unique solution can be constructed, assuming that the thruster operates in one of the regimes. However, we show that for a given temperature profile the applied discharge voltage uniquely determines the operating regime: for discharge voltages greater than a certain value, the sheath disappears. That result is obtained over a wide range of incoming neutral velocities, channel lengths and widths, and cathode plane locations. It is also shown that a good correlation between the quasi 1-D model and experimental results can be achieved by selecting an appropriate electron mobility and temperature profile

  7. Method and apparatus for monitoring two-phase flow. [PWR

    Science.gov (United States)

    Sheppard, J.D.; Tong, L.S.

    1975-12-19

    A method and apparatus for monitoring two-phase flow is provided that is particularly related to the monitoring of transient two-phase (liquid-vapor) flow rates such as may occur during a pressurized water reactor core blow-down. The present invention essentially comprises the use of flanged wire screens or similar devices, such as perforated plates, to produce certain desirable effects in the flow regime for monitoring purposes. One desirable effect is a measurable and reproducible pressure drop across the screen. The pressure drop can be characterized for various known flow rates and then used to monitor nonhomogeneous flow regimes. Another useful effect of the use of screens or plates in nonhomogeneous flow is that such apparatus tends to create a uniformly dispersed flow regime in the immediate downstream vicinity. This is a desirable effect because it usually increases the accuracy of flow rate measurements determined by conventional methods.

  8. Micro/Nano-pore Network Analysis of Gas Flow in Shale Matrix.

    Science.gov (United States)

    Zhang, Pengwei; Hu, Liming; Meegoda, Jay N; Gao, Shengyan

    2015-08-27

    The gas flow in shale matrix is of great research interests for optimized shale gas extraction. The gas flow in the nano-scale pore may fall in flow regimes such as viscous flow, slip flow and Knudsen diffusion. A 3-dimensional nano-scale pore network model was developed to simulate dynamic gas flow, and to describe the transient properties of flow regimes. The proposed pore network model accounts for the various size distributions and low connectivity of shale pores. The pore size, pore throat size and coordination number obey normal distribution, and the average values can be obtained from shale reservoir data. The gas flow regimes were simulated using an extracted pore network backbone. The numerical results show that apparent permeability is strongly dependent on pore pressure in the reservoir and pore throat size, which is overestimated by low-pressure laboratory tests. With the decrease of reservoir pressure, viscous flow is weakening, then slip flow and Knudsen diffusion are gradually becoming dominant flow regimes. The fingering phenomenon can be predicted by micro/nano-pore network for gas flow, which provides an effective way to capture heterogeneity of shale gas reservoir.

  9. Flow and axial dispersion in a sinusoidal-walled tube: Effects of inertial and unsteady flows

    Science.gov (United States)

    Richmond, Marshall C.; Perkins, William A.; Scheibe, Timothy D.; Lambert, Adam; Wood, Brian D.

    2013-12-01

    In this work, we consider a sinusoidal-walled tube (a three-dimensional tube with sinusoidally-varying diameter) as a simplified conceptualization of flow in porous media. Direct numerical simulation using computational fluid dynamics (CFD) methods was used to compute velocity fields by solving the Navier-Stokes equations, and also to numerically solve the volume averaging closure problem, for a range of Reynolds numbers (Re) spanning the low-Re to inertial flow regimes, including one simulation at Re=449 for which unsteady flow was observed. The longitudinal dispersion observed for the flow was computed using a random walk particle tracking method, and this was compared to the longitudinal dispersion predicted from a volume-averaged macroscopic mass balance using the method of volume averaging; the results of the two methods were consistent. Our results are compared to experimental measurements of dispersion in porous media and to previous theoretical results for both the low-Re, Stokes flow regime and for values of Re representing the steady inertial regime. In the steady inertial regime, a power-law increase in the effective longitudinal dispersion (DL) with Re was found, and this is consistent with previous results. This rapid rate of increase is caused by trapping of solute in expansions due to flow separation (eddies). One unsteady (but non-turbulent) flow case (Re=449) was also examined. For this case, the rate of increase of DL with Re was smaller than that observed at lower Re. Velocity fluctuations in this regime lead to increased rates of solute mass transfer between the core flow and separated flow regions, thus diminishing the amount of tailing caused by solute trapping in eddies and thereby reducing longitudinal dispersion. The observed tailing was further explored through analysis of concentration skewness (third moment) and its assymptotic convergence to conventional advection-dispersion behavior (skewness = 0). The method of volume averaging was

  10. Exploring the physical controls of regional patterns of flow duration curves – Part 3: A catchment classification system based on regime curve indicators

    Directory of Open Access Journals (Sweden)

    M. Sivapalan

    2012-11-01

    Full Text Available Predictions of hydrological responses in ungauged catchments can benefit from a classification scheme that can organize and pool together catchments that exhibit a level of hydrologic similarity, especially similarity in some key variable or signature of interest. Since catchments are complex systems with a level of self-organization arising from co-evolution of climate and landscape properties, including vegetation, there is much to be gained from developing a classification system based on a comparative study of a population of catchments across climatic and landscape gradients. The focus of this paper is on climate seasonality and seasonal runoff regime, as characterized by the ensemble mean of within-year variation of climate and runoff. The work on regime behavior is part of an overall study of the physical controls on regional patterns of flow duration curves (FDCs, motivated by the fact that regime behavior leaves a major imprint upon the shape of FDCs, especially the slope of the FDCs. As an exercise in comparative hydrology, the paper seeks to assess the regime behavior of 428 catchments from the MOPEX database simultaneously, classifying and regionalizing them into homogeneous or hydrologically similar groups. A decision tree is developed on the basis of a metric chosen to characterize similarity of regime behavior, using a variant of the Iterative Dichotomiser 3 (ID3 algorithm to form a classification tree and associated catchment classes. In this way, several classes of catchments are distinguished, in which the connection between the five catchments' regime behavior and climate and catchment properties becomes clearer. Only four similarity indices are entered into the algorithm, all of which are obtained from smoothed daily regime curves of climatic variables and runoff. Results demonstrate that climate seasonality plays the most significant role in the classification of US catchments, with rainfall timing and climatic aridity index

  11. Spatial adjustments of mountain channels to changes in the sediment supply regime

    Science.gov (United States)

    Elgueta, M. A.; Hassan, M. A.; von Flotow, C. M.

    2012-12-01

    Sediment supply is a key controlling factor in bed morphology and sediment mobility. Under a low supply regime, bed structuring develops and reduces sediment mobility. Under high supply, structuring is suppressed and the bed exhibits patchiness. This study examines the spatial response of a mountain stream channel to changes in the sediment supply regime. To achieve this goal, a flume experiment was conducted in the Mountain Channel Hydraulic Experimental Laboratory at the University of British Columbia. An 18 meter long, one meter wide flume, with a slope of three percent was used. Seven continuous runs were conducted. Each of them lasted 40 hours, under constant flow and different sediment supply regimes, which included no feed, constant feed and episodic supply. In each run, bed elevation, bed grain size distribution, flow resistance, sediment mobility and degree of armoring were determined. Flume results were compared to field data from a 600 meter channel reach that exhibits rapid, riffle-pool and step-pool morphology in UBC Malcolm Knapp Research Forest. The study gave the possibility to analyze in detail the spatial adjustment of a mountain channel to changes in the sediment supply regime, including episodic inputs.

  12. An Analysis of Vehicular Traffic Flow Using Langevin Equation

    Directory of Open Access Journals (Sweden)

    Çağlar Koşun

    2015-08-01

    Full Text Available Traffic flow data are stochastic in nature, and an abundance of literature exists thereof. One way to express stochastic data is the Langevin equation. Langevin equation consists of two parts. The first part is known as the deterministic drift term, the other as the stochastic diffusion term. Langevin equation does not only help derive the deterministic and random terms of the selected portion of the city of Istanbul traffic empirically, but also sheds light on the underlying dynamics of the flow. Drift diagrams have shown that slow lane tends to get congested faster when vehicle speeds attain a value of 25 km/h, and it is 20 km/h for the fast lane. Three or four distinct regimes may be discriminated again from the drift diagrams; congested, intermediate, and free-flow regimes. At places, even the intermediate regime may be divided in two, often with readiness to congestion. This has revealed the fact that for the selected portion of the highway, there are two main states of flow, namely, congestion and free-flow, with an intermediate state where the noise-driven traffic flow forces the flow into either of the distinct regimes.

  13. An objective indicator for two-phase flow pattern transition

    International Nuclear Information System (INIS)

    Hervieu, E.; Seleghim, P. Jr.

    1998-01-01

    This work concerns the development of a methodology which objective is to characterize and diagnose two-phase flow regime transitions. The approach is based on the fundamental assumption that a transition flow is less stationary than a flow with an established regime. In a first time, the efforts focused on: the design and construction of an experimental loop, allowing to reproduce the main horizontal two-phase flow patterns, in a stable and controlled way; the design and construction of an electrical impedance probe, providing an imaged information of the spatial phase distribution in the pipe; the systematic study of the joint time-frequency and time-scale analysis methods, which permitted to define an adequate parameter quantifying the unstationarity degree. In a second time, in order to verify the fundamental assumption, a series of experiments were conducted, which objective was to demonstrate the correlation between unstationarity and regime transition. The unstationarity degree was quantified by calculating the Gabor's transform time-frequency covariance of the impedance probe signals. Furthermore, the phenomenology of each transition was characterized by the joint moments and entropy. The results clearly show that the regime transitions are correlated with local time-frequency covariance peaks, which demonstrates that these regime transitions are characterized by a loss of stationarity. Consequently, the time-frequency covariance constitutes an objective two-phase flow regime transition indicator. (author)

  14. Water regime of steam power plants

    International Nuclear Information System (INIS)

    Oesz, Janos

    2011-01-01

    The water regime of water-steam thermal power plants (secondary side of pressurized water reactors (PWR); fossil-fired thermal power plants - referred to as steam power plants) has changed in the past 30 years, due to a shift from water chemistry to water regime approach. The article summarizes measures (that have been realised by chemists of NPP Paks) on which the secondary side of NPP Paks has become a high purity water-steam power plant and by which the water chemistry stress corrosion risk of heat transfer tubes in the VVER-440 steam generators was minimized. The measures can also be applied to the water regime of fossil-fired thermal power plants with super- and subcritical steam pressure. Based on the reliability analogue of PWR steam generators, water regime can be defined as the harmony of construction, material(s) and water chemistry, which needs to be provided in not only the steam generators (boiler) but in each heat exchanger of steam power plant: - Construction determines the processes of flow, heat and mass transfer and their local inequalities; - Material(s) determines the minimal rate of general corrosion and the sensitivity for local corrosion damage; - Water chemistry influences the general corrosion of material(s) and the corrosion products transport, as well as the formation of local corrosion environment. (orig.)

  15. Random excitation forces in tube bundles subjected to two-phase cross-flow

    International Nuclear Information System (INIS)

    Taylor, C.E.; Pettigrew, M.J.; Currie, I.G.

    1996-01-01

    Data from two experimental programs have been analyzed to determine the characteristics of the random excitation forces associated with two-phase cross-flow in tube bundles. Large-scale air-water flow loops in France and Canada were used to generate the data. Tests were carried out on cantilevered, clamped-pinned, and clamped-clamped tubes in normal-square, parallel-triangular, and normal-triangular configurations. Either strain gages or force transducers were used to measure the vibration response of a centrally located tube as the tue array was subjected to a wide range of void fractions and flow rates. Power spectra were analyzed to determine the effect of parameters such as tube diameter, frequency, flow rate, void fraction, and flow regime on the random excitation forces. Normalized expressions for the excitation force power spectra were found to be flow-regime dependent. In the churn flow regime, flow rate and void fraction had very little effect on the magnitude of the excitation forces. In the bubble-plug flow regime, the excitation forces increased rapidly with flow rate and void fraction

  16. Fluctuating zonal flows in the I-mode regime in Alcator C-Moda)

    Science.gov (United States)

    Cziegler, I.; Diamond, P. H.; Fedorczak, N.; Manz, P.; Tynan, G. R.; Xu, M.; Churchill, R. M.; Hubbard, A. E.; Lipschultz, B.; Sierchio, J. M.; Terry, J. L.; Theiler, C.

    2013-05-01

    Velocity fields and density fluctuations of edge turbulence are studied in I-mode [F. Ryter et al., Plasma Phys. Controlled Fusion 40, 725 (1998)] plasmas of the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] tokamak, which are characterized by a strong thermal transport barrier in the edge while providing little or no barrier to the transport of both bulk and impurity particles. Although previous work showed no clear geodesic-acoustic modes (GAM) on C-Mod, using a newly implemented, gas-puff-imaging based time-delay-estimate velocity inference algorithm, GAM are now shown to be ubiquitous in all I-mode discharges examined to date, with the time histories of the GAM and the I-mode specific [D. Whyte et al., Nucl. Fusion 50, 105005 (2010)] Weakly Coherent Mode (WCM, f = 100-300 kHz, Δf/f≈0.5, and kθ≈1.3 cm-1) closely following each other through the entire duration of the regime. Thus, the I-mode presents an example of a plasma state in which zero frequency zonal flows and GAM continuously coexist. Using two-field (density-velocity and radial-poloidal velocity) bispectral methods, the GAM are shown to be coupled to the WCM and to be responsible for its broad frequency structure. The effective nonlinear growth rate of the GAM is estimated, and its comparison to the collisional damping rate seems to suggest a new view on I-mode threshold physics.

  17. Extending the collisional fluid equations into the long mean-free-path regime in toroidal plasmas. IV. Banana regime

    International Nuclear Information System (INIS)

    Shaing, K. C.

    2007-01-01

    In Part I [Phys. Fluids B 2, 1190 (1990)] and Part II [Phys. Plasmas 12, 082508 (2005)], it was emphasized that the equilibrium plasma viscous forces when applied for the magnetohydrodynamic (MHD) modes are only rigorously valid at the mode rational surface where m-nq=0. Here, m is the poloidal mode number, n is the toroidal mode number, and q is the safety factor. This important fact has been demonstrated explicitly by calculating the viscous forces in the plateau regime in Parts I and II. Here, the effective viscous forces in the banana regime are calculated for MHD modes by solving the linear drift kinetic equation that is driven by the plasma flows first derived in Part I. At the mode rational surface, the equilibrium plasma viscous forces are reproduced. However, it is found that away from the mode rational surface, the viscous forces for MHD modes decrease, a behavior similar to that observed in the viscous forces for the plateau regime. The proper form of the momentum equation that is appropriate for the modeling of the MHD modes is also discussed

  18. Relationship between thermal stratification and flow patterns in steam-quenching suppression pool

    International Nuclear Information System (INIS)

    Song, Daehun; Erkan, Nejdet; Jo, Byeongnam; Okamoto, Koji

    2015-01-01

    Highlights: • Thermal stratification mechanism by direct contact condensation is investigated. • Thermal stratification condition changes according to the flow pattern. • Thermal stratification depends on the force balance between buoyancy and momentum. • Flow pattern change was observed even in the same regime. • Flow pattern is affected by the sensitive force balance. - Abstract: This study aims to examine the relationship between thermal stratification and flow patterns in a steam-quenching suppression pool using particle image velocimetry. Thermal stratification was experimentally evaluated in a depressurized water pool under different steam mass flux conditions. The time evolution of the temperature profile of the suppression pool was presented with the variation of condensation regimes, and steam condensation processes were visualized using a high-speed camera. The thermal stratification condition was classified into full mixing, gradual thermal stratification, and developed thermal stratification. It was found that the condition was determined by the flow patterns depending on the force balance between buoyancy and momentum. The force balance affected both the condensation regime and the flow pattern, and hence, the flow pattern was changed with the condensation regime. However, the force balance had a sensitive influence on the flow in the pool; therefore, distinct flow patterns were observed even in the same condensation regime.

  19. Visualization of large waves in churn and annular two-phase flow

    International Nuclear Information System (INIS)

    Dasgupta, Arnab; Chandraker, D.K.; Nayak, A.K.; Vijayan, P.K.; Kshirasagar, S.; Reddy, B.R.; Walker, S.P.

    2015-01-01

    The study of churn and annular two-phase flow regimes is important for boiling systems like nuclear reactors, U-tube steam generators etc. In this paper, visualization studies on air-water churn and annular two-phase flow regimes are reported. Though there are differences between air-water and boiling steam water systems, the major flow-pattern characteristics are similar (if not same).The specific object of study is the large waves which exist in both churn and annular regimes. These waves are responsible for majority of the momentum and mass dispersion across the phases. The differentiating characteristics of these waves in the chum and annular flow regimes are reported. The visualization also leads to a more quantitative representation of the transition from churn to annular flow. A new interpretation of the criterion for onset of entrainment is also evolved from the studies. (author)

  20. The Prevalence of Yersinia enterocolitica Species in the Flow of Butchering

    Directory of Open Access Journals (Sweden)

    Ciceronis Cumpanasoiu

    2010-10-01

    Full Text Available During the experimental stages, the researches aimed to establish the prevalence of Y. enterocolitica bacteria on swine, in the butchering flow. The experiments developed on a large number of test specimens (800, sampled starting with the moment of animals receiving and until the final product was obtained. For isolation and identification there were used a modified method, proposed by The International Organization for Standardization, and CIN and SSDC isolating cultures as well. Following the effectuated researches, in accordance with the international ones, we can conclude that, in the present, the butchering process allows the strict observance of the hygiene and disinfection conditions with the purpose of limiting the dispersion of Yersinia enterocolitica, which favors the phenomenon of inter-contamination.

  1. Internet Censorship Circumvention Tools: Escaping the Control of the Syrian Regime

    Directory of Open Access Journals (Sweden)

    Walid Al-Saqaf

    2016-02-01

    Full Text Available Studies have shown that authoritarian regimes tend to censor the media to limit potential threats to the status quo. While such censorship practices were traditionally aimed at broadcast and print media, the emergence of the Internet and social media in particular, prompted some authoritarian regimes, such as the Assad regime in Syria, to try and exert a similar level of censorship on the Internet as well. During the Arab Spring, the Syrian regime blocked hundreds of websites that provided social networking, news, and other services. Taking Syria as a case study, this paper examines whether Internet censorship succeeded in preventing Internet users from reaching censored online content during 2010−2012. By analyzing the use of Alkasir, a censorship circumvention tool created by the author, the paper provides empirical evidence demonstrating that users were in fact able to bypass censorship and access blocked websites. The findings demonstrate that censorship circumvention tools constituted a threat to the information control systems of authoritarian regimes, highlighting the potential of such tools to promote online freedom of expression in countries where Internet censorship is prevalent.

  2. Numerical Study of the Inertia Effect on Flow Distribution in Micro-gap Plate Heat Exchanger

    International Nuclear Information System (INIS)

    Park, Jang Min; Yoon, Seok Ho; Lee, Kong Hoon; Song Chan Ho

    2014-01-01

    This paper presents numerical study on flow and heat transfer characteristics in micro-gap plate heat exchanger. In particular, we investigate the effect of flow inertia on the flow distribution from single main channel to multiple parallel micro-gaps. The flow regime of the main channel is varied from laminar regime (Reynolds number of 100) to turbulent regime (Reynolds number of 10000) by changing the flow rate, and non-uniformity of the flow distribution and temperature field is evaluated quantitatively based on the standard deviation. The flow distribution is found to be significantly affected by not only the header design but also the flow rate of the main channel. It is also observed that the non-uniformity of the temperature field has its maximum at the intermediate flow regime

  3. Two-phase flow induced vibrations in CANDU steam generators

    International Nuclear Information System (INIS)

    Gidi, A.

    2009-01-01

    The U-Bend region of nuclear steam generators tube bundles have suffered from two-phase cross flow induced vibrations. Tubes in this region have experienced high amplitude vibrations leading to catastrophic failures. Turbulent buffeting and fluid-elastic instability has been identified as the main causes. Previous investigations have focused on flow regime and two-phase flow damping ratio. However, tube bundles in steam generators have vapour generated on the surface of the tubes, which might affect the flow regime, void fraction distribution, turbulent intensity levels and tube-flow interaction, all of which have the potential to change the tube vibration response. A cantilevered tube bundle made of electric cartridges heaters was built and tested in a Freon-11 flow loop at McMaster University. Tubes were arranged in a parallel triangular configuration. The bundle was exposed to two-phase cross flows consisting of different combinations of void from two sources, void generated upstream of the bundle and void generated at the surface of the tubes. Tube tip vibration response was measured optically and void fraction was measured by gamma densitometry technique. It was found that tube vibration amplitude in the transverse direction was reduced by a factor of eight for void fraction generated at the tube surfaces only, when compared to the upstream only void generation case. The main explanation for this effect is a reduction in the correlation length of the turbulent buffeting forcing function. Theoretical calculations of the tube vibration response due to turbulent buffeting under the same experimental conditions predicted a similar reduction in tube amplitude. The void fraction for the fluid-elastic instability threshold in the presence of tube bundle void fraction generation was higher than that for the upstream void fraction generation case. The first explanation of this difference is the level of turbulent buffeting forces the tube bundle was exposed to

  4. Geothermal regime of Tarim basin, NW China: insights from borehole temperature logging

    Science.gov (United States)

    Liu, S.; Lei, X.

    2013-12-01

    Geothermal regime of sedimentary basin is vital for understanding basin (de)formation process, hydrocarbon generation status and assessing the resource potential. Located at the Precambrian craton block, the Tarim basin is the largest intermountain basin in China, which is also the ongoing target of oil and gas exploration. Previous knowledge of thermal regime of this basin is from limited oil exploration borehole testing temperature, the inherent deficiency of data of this type makes accurate understanding of its thermal regime impossible. Here we reported our latest steady temperature logging results in this basin and analyze its thermal regime as well. In this study, 10 temperature loggings are conducted in the northern Tarim basin where the major oil and gas fields are discovered. All the boreholes for temperature logging are non-production wells and are shut in at least more than 2~3 years, ensuring the temperature equilibrium after drilling. The derived geothermal gradient varies from 20.2 to 26.1 degree/km, with a mean of 22.0 degree/km. However, some previous reported gradients in this area are obviously lower than our results; for example, the previous gradient of THN2 well is 13.2 degree/km but 23.2 degree/km in this study, and not enough equilibrium time in previous logging accounts for this discrepancy. More important, it is found that high gradients usually occur in the gas field and the gradients of the gas fields are larger than those in other oil fields, indicating higher thermal regime in gas field. The cause of this phenomenon is unclear, and the upward migration of hot fluid along fault conduit is speculated as the possible mechanism for this high geothermal anomaly in the oil and gas fields. Combined with measured thermal conductivity data, 10 new heat flow values are also achieved, and the heat flow of the Tarim basin is between 38mW/m2 and 52mW/m2, with a mean of 43 mW/m2. This relatively low heat flow is coincident with that of typical

  5. Two-phase flow boiling pressure drop in small channels

    International Nuclear Information System (INIS)

    Sardeshpande, Madhavi V.; Shastri, Parikshit; Ranade, Vivek V.

    2016-01-01

    Highlights: • Study of typical 19 mm steam generator tube has been undertaken in detail. • Study of two phase flow boiling pressure drop, flow instability and identification of flow regimes using pressure fluctuations is the main focus of present work. • Effect of heat and mass flux on pressure drop and void fraction was studied. • Flow regimes identified from pressure fluctuations data using FFT plots. • Homogeneous model predicted pressure drop well in agreement. - Abstract: Two-phase flow boiling in small channels finds a variety of applications in power and process industries. Heat transfer, boiling flow regimes, flow instabilities, pressure drop and dry out are some of the key issues related to two-phase flow boiling in channels. In this work, the focus is on pressure drop in two-phase flow boiling in tubes of 19 mm diameter. These tubes are typically used in steam generators. Relatively limited experimental database is available on 19 mm ID tube. Therefore, in the present work, the experimental set-up is designed for studying flow boiling in 19 mm ID tube in such a way that any of the different flow regimes occurring in a steam generator tube (from pre-heating of sub-cooled water to dry-out) can be investigated by varying inlet conditions. The reported results cover a reasonable range of heat and mass flux conditions such as 9–27 kW/m 2 and 2.9–5.9 kg/m 2 s respectively. In this paper, various existing correlations are assessed against experimental data for the pressure drop in a single, vertical channel during flow boiling of water at near-atmospheric pressure. A special feature of these experiments is that time-dependent pressures are measured at four locations along the channel. The steady-state pressure drop is estimated and the identification of boiling flow regimes is done with transient characteristics using time series analysis. Experimental data and corresponding results are compared with the reported correlations. The results will be

  6. An objective indicator for two-phase flow pattern transition

    International Nuclear Information System (INIS)

    Hervieua, E.; Seleghim, P. Jr.

    1998-01-01

    This work concerns the development of a methodology the objective of which is to characterize and diagnose two-phase flow regime transitions. The approach is based on the fundamental assumption that a transition flow is less stationary than a flow with an established regime. During the first time, the efforts focused on: (1) the design and construction of an experimental loop, allowing to reproduce the main horizontal two-phase flow patterns, in a stable and controlled way; (2) the design and construction of an electrical impedance probe, providing an imaged information of the spatial phase distribution in the pipe; and (3) the systematic study of the joint time-frequency and time-scale analysis methods, which permitted to define an adequate parameter quantifying the unstationarity degree. During the second time, in order to verify the fundamental assumption, a series of experiments were conducted, the objective of which was to demonstrate the correlation between unstationarity and regime transition. The unstationarity degree was quantified by calculating the Gabor's transform time-frequency covariance of the impedance probe signals. Furthermore, the phenomenology of each transition was characterized by the joint moments and entropy. The results clearly show that the regime transitions are correlated with local time-frequency covariance peaks, which demonstrates that these regime transitions are characterized by a loss of stationarity. Consequently, the time-frequency covariance constitutes an objective two-phase flow regime transition indicator. (orig.)

  7. Study of gas-liquid flow in model porous media for heterogeneous catalysis

    Science.gov (United States)

    Francois, Marie; Bodiguel, Hugues; Guillot, Pierre; Laboratory of the Future Team

    2015-11-01

    Heterogeneous catalysis of chemical reactions involving a gas and a liquid phase is usually achieved in fixed bed reactors. Four hydrodynamic regimes have been observed. They depend on the total flow rate and the ratio between liquid and gas flow rate. Flow properties in these regimes influence transfer rates. Rather few attempts to access local characterization have been proposed yet, though these seem to be necessary to better describe the physical mechanisms involved. In this work, we propose to mimic slices of reactor by using two-dimensional porous media. We have developed a two-dimensional system that is transparent to allow the direct observation of the flow and the phase distribution. While varying the total flow rate and the gas/liquid flow rate ratio, we observe two hydrodynamic regimes: at low flow rate, the gaseous phase is continuous (trickle flow), while it is discontinuous at higher flow rate (pulsed flow). Thanks to some image analysis techniques, we are able to quantify the local apparent liquid saturation in the system. Its fluctuations in time are characteristic of the transition between the two regimes: at low liquid flow rates, they are negligible since the liquid/gas interface is fixed, whereas at higher flow rates we observe an alternation between liquid and gas. This transition between trickle to pulsed flow is in relative good agreement with the existing state of art. However, we report in the pulsed regime important flow heterogeneities at the scale of a few pores. These heterogeneities are likely to have a strong influence on mass transfers. We acknowledge the support of Solvay.

  8. Design of a naturalized flow regime—An example from the Lower Missouri River, USA

    Science.gov (United States)

    Jacobson, Robert B.; Galat, David L.

    2008-01-01

     group of river managers, stakeholders, and scientists met during summer 2005 to design a more naturalized flow regime for the Lower Missouri River (LMOR). The objective was to comply with requirements under the U.S. Endangered Species Act to support reproduction and survival of threatened and endangered species, with emphasis on the endangered pallid sturgeon (Scaphirhynchus albus), while minimizing negative effects to existing social and economic benefits of prevailing river management. Specific hydrograph requirements for pallid sturgeon reproduction are unknown, hence much of the design process was based on features of the natural flow regime. Environmental flow components (EFCs) extracted from the reference natural flow regime were used to design and assess performance of alternative flow regimes.The design process incorporated a primary stage in which conceptual hydrographs were developed and assessed for their general ecological and social-economic performance. The second stage accounted for hydroclimatic variation by coding the conceptual hydrographs into reservoir release rules, adding constraints for downstream flooding and low-storage precludes, and running the rules through 100 years of hydroclimatic simulation. The output flow regimes were then evaluated for presumed ecological benefits based on how closely they resembled EFCs in the reference natural flow regime. Flow regimes also were assessed for social-economic cost indicators, including days of flooding of low-lying agricultural land, days over flood stage, and storage levels in system reservoirs.Our experience with flow-regime design on the LMOR underscored the lack of confidence the stakeholders place in the value of the natural flow regime as a measure of ecosystem benefit in the absence of fundamental scientific documentation. Stakeholders desired proof of ecological benefits commensurate with the certainty of economic losses. We also gained insight into the processes of integrating science

  9. Multiple Changes in the Hydrologic Regime of the Yangtze River and the Possible Impact of Reservoirs

    Directory of Open Access Journals (Sweden)

    Feng Huang

    2016-09-01

    Full Text Available This paper investigates hydrologic changes in the Yangtze River using long-term daily stream flow records (1955–2013 collected from four flow gauging stations located from the upper to the lower reaches of the river. The hydrologic regime is quantified using the Indicators of Hydrologic Alteration, which statistically characterize hydrologic variation within each year. Scanning t-test is applied to analyze multiple changes in the hydrologic regime at different time scales. Then, coherency analysis is applied to identify common changes among different hydrologic indicators and across different reaches of the Yangtze River. The results point to various change patterns in the five components of hydrologic regime, including the magnitude of monthly water conditions, magnitude and duration of annual extreme water conditions, timing of annual extreme water conditions, frequency and duration of high and low pulses, and rate and frequency of water condition changes. The 32 hydrologic indicators feature multiple temporal-scale changes. Spatial variations can be observed in the hydrologic changes of the upper, middle, and lower reaches of the river. Common changes in different reaches consist of hydrologic indicators including the monthly flow in October and the low-flow indicators. The monthly flow in October is dominated by decreasing trends, while the monthly flows between January and March, the annual minimum 1/3/7/30/90-day flows, and the base flow index are characterized by increasing trends. Low pulse duration and total days of low pulses feature downward trends. The coherency analysis reveals significant relationships between the monthly flow in October and the low-flow indicators, indicating that reservoir regulation is an important factor behind the hydrologic changes.

  10. Visual study of air--water mixtures flowing inside serpentine tubes

    International Nuclear Information System (INIS)

    Farukhi, M.N.; Parker, J.D.

    1974-01-01

    Hydrodynamic behavior of air-water mixtures flowing inside serpentine tubes, with bends in the vertical plane, was investigated. Flow visualization was accomplished by injecting dye into the liquid phase and recording the events on color slides and color movies. For certain combinations of gas and liquid flow rates, in the annular type flow regime, ''film inversion'' was observed in the bend as well as in the straight section immediately downstream of the bend. A new flow regime map particularly applicable to two phase flow inside serpentine tubes is presented. (U.S.)

  11. Identification of two-phase flow regimes by time-series modeling

    International Nuclear Information System (INIS)

    King, C.H.; Ouyang, M.S.; Pei, B.S.

    1987-01-01

    The identification of two-phase flow patterns in pipes or ducts is important to the design and operation of thermal-hydraulic systems, especially in the nuclear reactor cores of boiling water reactors or in the steam generators of pressurized water reactors. Basically, two-phase flow shows some fluctuating characteristics even at steady-state conditions. These fluctuating characteristics can be analyzed by statistical methods for obtaining flow signatures. There have been a number of experimental studies conducted that are concerned with the statistical properties of void fraction or pressure pulsation in two-phase flow. In this study, the authors propose a new technique of identifying the patterns of air-water two-phase flow in a vertical pipe. This technique is based on analyzing the statistic characteristics of the pressure signals of the test loop by time-series modeling

  12. A study on the characteristics of upward air-water two-phase flow in a large pipe

    International Nuclear Information System (INIS)

    Shen, Xiuzhong; Mishima, Kaichiro; Nakamura, Hideo

    2003-01-01

    Adiabatic upward air-water two-phase flow in a vertical large pipe (inner diameter, D: 0.2 m, ratio of pipe length to diameter, L/D: 60.5.) was experimentally investigated under various inlet conditions. Flow regime was observed and void fraction, bubble frequency, Sauter mean diameter, interfacial area concentration (IAC) and interfacial direction were measured with optical four-sensor probe. Characteristics of various flow regimes were analyzed carefully. Both the void fraction and the IAC demonstrated radial wall-peak and core-peak distributions in the undisturbed bubbly flow and the other flow regimes, respectively. The existence of bubbly secondary flow accounts for the core-peak distribution in the agitated bubbly, churn bubbly, churn slug and churn froth flow. The bubble frequency showed a wall-peak radial distribution only when the bubbles were small in diameter and the flow was in the undisturbed bubbly flow. The Sauter mean diameter of bubbles did not change much in the main flow of undisturbed bubbly, agitated bubbly and churn bubbly flow regimes and showed a core peak radial distribution in the churn slug flow. In the latter flow regime, the secondary flow disintegrated the bubbles, resulting in the decrease of the Sauter mean diameter. The measurements of the interfacial direction showed that the bubbly main flow and secondary flow can be displayed by the main flow peak and the secondary flow peak, respectively, in the PDF of the interfacial directional angle between the interfacial direction and the z-axis, η zi . The local average η zi at the bubble front hemispheres reflects the local bubble movement and is in direct connection with the flow regimes. Based on the analysis, the authors classified the flow regimes in the vertical large pipe quantitatively by the local average η zi . Bubbles in the liquid phase moved in a zigzag line with no inclination toward any direction in the plane vertical to z-axis in the pipe core. The axial differential

  13. Fluctuating zonal flows in the I-mode regime in Alcator C-Mod

    Energy Technology Data Exchange (ETDEWEB)

    Cziegler, I.; Diamond, P. H.; Fedorczak, N.; Manz, P.; Tynan, G. R.; Xu, M. [Center for Momentum Transport and Flow Organization, University of California, San Diego, La Jolla, California 92093 (United States); Churchill, R. M.; Hubbard, A. E.; Lipschultz, B.; Sierchio, J. M.; Terry, J. L.; Theiler, C. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02138 (United States)

    2013-05-15

    Velocity fields and density fluctuations of edge turbulence are studied in I-mode [F. Ryter et al., Plasma Phys. Controlled Fusion 40, 725 (1998)] plasmas of the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] tokamak, which are characterized by a strong thermal transport barrier in the edge while providing little or no barrier to the transport of both bulk and impurity particles. Although previous work showed no clear geodesic-acoustic modes (GAM) on C-Mod, using a newly implemented, gas-puff-imaging based time-delay-estimate velocity inference algorithm, GAM are now shown to be ubiquitous in all I-mode discharges examined to date, with the time histories of the GAM and the I-mode specific [D. Whyte et al., Nucl. Fusion 50, 105005 (2010)] Weakly Coherent Mode (WCM, f = 100–300 kHz, Δf/f≈0.5, and k{sub θ}≈1.3 cm{sup −1}) closely following each other through the entire duration of the regime. Thus, the I-mode presents an example of a plasma state in which zero frequency zonal flows and GAM continuously coexist. Using two-field (density-velocity and radial-poloidal velocity) bispectral methods, the GAM are shown to be coupled to the WCM and to be responsible for its broad frequency structure. The effective nonlinear growth rate of the GAM is estimated, and its comparison to the collisional damping rate seems to suggest a new view on I-mode threshold physics.

  14. Potential impacts of climate change on flow regime and fish habitat in mountain rivers of the south-western Balkans.

    Science.gov (United States)

    Papadaki, Christina; Soulis, Konstantinos; Muñoz-Mas, Rafael; Martinez-Capel, Francisco; Zogaris, Stamatis; Ntoanidis, Lazaros; Dimitriou, Elias

    2016-01-01

    The climate change in the Mediterranean area is expected to have significant impacts on the aquatic ecosystems and particular in the mountain rivers and streams that often host important species such as the Salmo farioides, Karaman 1938. These impacts will most possibly affect the habitat availability for various aquatic species resulting to an essential alteration of the water requirements, either for dams or other water abstractions, in order to maintain the essential levels of ecological flow for the rivers. The main scope of this study was to assess potential climate change impacts on the hydrological patterns and typical biota for a south-western Balkan mountain river, the Acheloos. The altered flow regimes under different emission scenarios of the Intergovernmental Panel on Climate Change (IPCC) were estimated using a hydrological model and based on regional climate simulations over the study area. The Indicators of Hydrologic Alteration (IHA) methodology was then used to assess the potential streamflow alterations in the studied river due to predicted climate change conditions. A fish habitat simulation method integrating univariate habitat suitability curves and hydraulic modeling techniques were used to assess the impacts on the relationships between the aquatic biota and hydrological status utilizing a sentinel species, the West Balkan trout. The most prominent effects of the climate change scenarios depict severe flow reductions that are likely to occur especially during the summer flows, changing the duration and depressing the magnitude of the natural low flow conditions. Weighted Usable Area-flow curves indicated the limitation of suitable habitat for the native trout. Finally, this preliminary application highlighted the potential of science-based hydrological and habitat simulation approaches that are relevant to both biological quality elements (fish) and current EU Water policy to serve as efficient tools for the estimation of possible climate

  15. Study on cocurrent downtake gas-liquid flow in a vertical channel

    International Nuclear Information System (INIS)

    Lozovetskij, V.V.

    1978-01-01

    Hydraulic resistance and liquid stall from the film surface at cocurrent film and gas downflow in vertical channel in measurement range of reynolds number from 100 to 1260 for the film and from 1.2x10 4 to 10 5 for gas are studied. For downflow two regimes are characteristic: purely annular, that is separate phase flow regime, and the regime of stall and carrying liquid droplets from the film surface, that is annular dispersed flow regime. The existence boundaries of both regimes are determined and criterial equations for pressure drop calculation are obtained. It is established experimentally that at sufficient range from the liquid input place on the working zone the established two-phase flow takes place. In their nucleus two areas can be singled out, which differ by the flow density values of stalled liquid: central, having the permanent flow density value and area adjacent to the film surface, the liquid in the combs of waves making a significant contribution to the flow density value. At equal flooding density with the relative gas speed increase, the flow density value of stalled liquid in the channel central part increase. A similar result also takes place at flooding density increase at permanent relative speed. Flooding density and relative speed increase leads to levelling stalled liquid distribution about the channel cross section

  16. Vibration characteristics of a vertical round tube according to heat transfer regimes

    International Nuclear Information System (INIS)

    Lee, Yong Ho; Kim, Dae Hun; Chang, Soon Heung; Baek, Won Pil

    2001-01-01

    This paper presents the results of an experimental work on the effects of boiling heat transfer regimes on the vibration. the experiment has been performed using an electrically heated veritcal round tube through which water flows at atmospheric pressure. Vibration characteristics of the heated tube are changed significantly by heat transfer regimes and flow patterns. For single-phase liquid convection, the rod vibrations are negligible. However, On the beginning of subcooled nucleate boiling at tube exit, vibration level becomes very large. As bubble departure is occurred at the nucleation site of heated surface, the vibration decrease to saturated boiling region where thermal equilibrium quality becomes 0.0 at tube exit. In saturated boiling region, vibration amplitude increase with exit quality up to certain maximum value then decreases. At liquid film dryout condition, vibration could be regarded as negligible, however, these results cannot be extended to DNB-type CHF mechanism. Frequency analysis results of vibration signals suggested that excitation sources be different with heat transfer regimes. This study would contribute to improve the understanding of the relationship between boiling heat transfer and FIV

  17. Evaluation and Comparison of Extremal Hypothesis-Based Regime Methods

    Directory of Open Access Journals (Sweden)

    Ishwar Joshi

    2018-03-01

    Full Text Available Regime channels are important for stable canal design and to determine river response to environmental changes, e.g., due to the construction of a dam, land use change, and climate shifts. A plethora of methods is available describing the hydraulic geometry of alluvial rivers in the regime. However, comparison of these methods using the same set of data seems lacking. In this study, we evaluate and compare four different extremal hypothesis-based regime methods, namely minimization of Froude number (MFN, maximum entropy and minimum energy dissipation rate (ME and MEDR, maximum flow efficiency (MFE, and Millar’s method, by dividing regime channel data into sand and gravel beds. The results show that for sand bed channels MFN gives a very high accuracy of prediction for regime channel width and depth. For gravel bed channels we find that MFN and ‘ME and MEDR’ give a very high accuracy of prediction for width and depth. Therefore the notion that extremal hypotheses which do not contain bank stability criteria are inappropriate for use is shown false as both MFN and ‘ME and MEDR’ lack bank stability criteria. Also, we find that bank vegetation has significant influence in the prediction of hydraulic geometry by MFN and ‘ME and MEDR’.

  18. Are erosion regimes in SE Australian forests responding to anthropogenic climate change?

    Science.gov (United States)

    Nyman, P.; Rutherfurd, I.; Lane, P. N. J.; Sheridan, G. J.

    2017-12-01

    In southeast Australia a series of exceptional climate events over the last decade have resulted in widespread debris flow activity across the region. The Millennium Drought (1996-2010), extreme fire-weather and record breaking rainfall in the La Nina year of 2011 have all contributed to an intensification of processes such as runoff production and mass failures that lead to debris flows. Debris flows in landmark locations such as the Grampians and Wilsons Promontory National Parks in 2011 were triggered by mass failure as a result of large volumes of intense summer rainfall. Runoff generated debris flows in burned areas have been occurring regularly and in large numbers along the East Coast Dividing Range from the Warrumbungle Mountains (New South Wales) in the north to Kinglake (Victoria) in the south. In northeast Victoria debris flows have been delivering sediment to the Ovens River following wildfires in 2003, 2007, 2009 and in 2013. The impact of these erosion events on infrastructure, water quality and aquatic ecosystems are considerable and important questions are emerging around i) how frequently events have occurred in the past, ii) the importance of fire as a geomorphic agent, and iii) the effects of climate change on erosion regimes. In this paper we investigate the conditions under which these debris flows occurred, and examine the underlying climatic events in context of historical records. Using data on rainfall distributions and fire history dating back to the 1960s we quantify the frequency with which catchments are primed for extreme erosion events. With these data we begin to speculate on whether or not current catchment conditions (e.g. soil depths, colluvial storage and accumulation rate) is consistent with the erosion regimes we observe. The broader aim of our research is to quantify debris flow thresholds using geophysical response models and use these models to determine the sensitivity of debris flow frequency to climatic forcing. In the

  19. Experimental Observations on a Low Strain Counter-Flow Diffusion Flame: Flow and Bouyancy Effects

    Science.gov (United States)

    Sutula, J. A.; Torero, J. L.; Ezekoye, O. A.

    1999-01-01

    Diffusion flames are of great interest in fire safety and many industrial processes. The counter-flow configuration provides a constant strain flow, and therefore is ideal to study the structure of diffusion flames. Most studies have concentrated on the high velocity, high strain limit, since buoyantly induced instabilities will disintegrate the planar flame as the velocity decreases. Only recently, experimental studies in microgravity conditions have begun to explore the low strain regimes. Numerical work has shown the coupling between gas phase reaction rates, soot reaction rates, and radiation. For these programs, size, geometry and experimental conditions have been chosen to keep the flame unaffected by the physical boundaries. When the physical boundaries can not be considered infinitely far from the reaction zone discrepancies arise. A computational study that includes boundary effects and accounts for the deviations occurring when the major potential flow assumptions are relaxed was presented by Borlik et al. This development properly incorporates all heat loss terms and shows the possibility of extinction in the low strain regime. A major constraint of studying the low strain regime is buoyancy. Buoyant instabilities have been shown to have a significant effect on the nature of reactants and heat transport, and can introduce instabilities on the flow that result in phenomena such as flickering or fingering. The counter-flow configuration has been shown to provide a flame with no symmetry disrupting instabilities for inlet velocities greater than 50 mm/s. As the velocity approaches this limit, the characteristic length of the experiment has to be reduced to a few millimetres so as to keep the Rayleigh number (Ra(sub L) = (Beta)(g(sub 0))(L(exp 3) del T)/(alpha(v))) below 2000. In this work, a rectangular counter-flow burner was used to study a two-dimensional counter-flow diffusion flame. Flow visualisation and Particle Image Velocimetry served to describe

  20. Pressure loss in two-phase flow through a microchannel rod bundle

    International Nuclear Information System (INIS)

    Smith, A.C.; Hamm, L.L.; Qureshi, Z.; Steeper, T.J.

    1998-01-01

    The purpose of the microchannel rod bundle two-phase flow test described here was to provide data for benchmarking safety analyses for the accelerator production of tritium (APT). The objective was to obtain pressure loss data for a typical accelerator target rod bundle over a wide range of two-phase flow conditions. The test rod bundle assembly was fabricated for single-phase pressure drop tests conducted at Los Alamos National Laboratory (LANL) and subsequently used for the two-phase flow testing described here. The results for a typical case are given. These results fall generally in the slug flow regime for the horizontal flow results of Fukano and Kariyasaki for a 1.0-mm circular channel. Fukano and Kariyasaki found that surface tension effects were dominant in the 1-mm channel and report no churn regime. The results were also compared with the flow regime maps given by Triplett et al. for flow in discrete microchannels. Triplett employed both circular and trapezoidal channels, the latter to approximate the rod bundle interstitial flow channel shape. It was found that the rod bundle flow fell across the slug-to-churn flow regime transition reported by Triplett. This is consistent with the expectation that cross flow among channels would result in turbulent mixing and would suppress the formation of large discrete bubbles

  1. Resource Windfalls, Political Regimes, and Political Stability

    OpenAIRE

    Francesco Caselli; Andrea Tesei

    2011-01-01

    We study theoretically and empirically whether natural resource windfalls affect political regimes. We document the following regularities. Natural resource windfalls have no effect on the political system when they occur in democracies. However, windfalls have significant political consequences in autocracies. In particular, when an autocratic country receives a positive shock to its flow of resource rents it responds by becoming even more autocratic. Furthermore, there is heterogeneity in t...

  2. A Case for Intermediate Exchange-Rate Regimes

    OpenAIRE

    Agnès Bénassy-Quéré; Véronique Salins

    2010-01-01

    Despite increasing capital mobility and the subsequent difficulty in controlling exchange rates, intermediate exchange-rate regimes have remained widespread, especially in emerging and developing economies. This piece of evidence hardly fits the "impossible Trinity" theory arguing that it becomes difficult to control the exchange rate without a "hard" device when capital flows are freed. Calvo and Reinhart (2000) have suggested several explanations for such "fear of floating": exchange rate p...

  3. Characterizing snowmelt regime of the river swat - a case study

    International Nuclear Information System (INIS)

    Malik, M.A.

    2015-01-01

    Snowmelt generates 70 to 80% of runoff of Indus River and its tributaries. Forecasting snowmelt generated flow is important for water management, reservoir operation and channel diversion. River Swat being not direct contributor to the existing reservoirs remained out of focus for characterizing its snowmelt regime. Thirty years (1971-2000) data of upper Swat catchment above Kalam gauging station was acquired from WAPDA. Normal monthly values over the period and average monthly values of each year were determined for stream flow, precipitation and temperature together with average monthly values of weighted and maximum temperature. Snowmelt regime was ascertained from plot of normal values of flow, precipitation and temperature. Using temperature index approach, average monthly flow over the snowmelt months (April, May and June) in terms of mm depth over the catchment was regressed on all the temperature indices using exponential, power and third degree polynomial functions. Tmax was found the best index for snowmelt with R2 as 0.902 for the third degree polynomial function. Runoff coefficient (ROC) for the total precipitation was conceptualized and through iteration was found as T max 100. The optimized value of ROC was used to segregate rain induced and snowmelt induced runoff. The segregated snowmelt induced runoff was again regressed on Tmax using the same function which slightly improved R2 to 0.916. The model was tested for four years of data and forecasted flow was found reasonable in the context of simplicity of the approach. (author)

  4. Non-hydrostatic layered flows over a sill

    International Nuclear Information System (INIS)

    Jamali, Mirmosadegh

    2013-01-01

    This work takes a new approach to solving non-hydrostatic equations of layered flows over bottom topography. A perturbation technique is used to find explicit expressions for a flow for different regimes of single- and two-layer flows over a sill. Excellent agreement with previous solutions and experimental data is obtained, and more details of the non-hydrostatic flow over a sill are revealed. The proposed method is simple and compact and removes the need for complex numerical techniques to solve the non-hydrostatic equations. It is shown that in the approach-controlled regime of two-layer flow over a sill, the flow upstream and farther downstream the sill crest can be described by the hydrostatic theory, and the flow is non-hydrostatic over only a short distance on the downstream side of the crest. (paper)

  5. Error estimation for CFD aeroheating prediction under rarefied flow condition

    Science.gov (United States)

    Jiang, Yazhong; Gao, Zhenxun; Jiang, Chongwen; Lee, Chunhian

    2014-12-01

    Both direct simulation Monte Carlo (DSMC) and Computational Fluid Dynamics (CFD) methods have become widely used for aerodynamic prediction when reentry vehicles experience different flow regimes during flight. The implementation of slip boundary conditions in the traditional CFD method under Navier-Stokes-Fourier (NSF) framework can extend the validity of this approach further into transitional regime, with the benefit that much less computational cost is demanded compared to DSMC simulation. Correspondingly, an increasing error arises in aeroheating calculation as the flow becomes more rarefied. To estimate the relative error of heat flux when applying this method for a rarefied flow in transitional regime, theoretical derivation is conducted and a dimensionless parameter ɛ is proposed by approximately analyzing the ratio of the second order term to first order term in the heat flux expression in Burnett equation. DSMC simulation for hypersonic flow over a cylinder in transitional regime is performed to test the performance of parameter ɛ, compared with two other parameters, Knρ and MaṡKnρ.

  6. Experimental Study of gas-liquid two-phase flow affected by wall surface wettability

    International Nuclear Information System (INIS)

    Takamasa, T.; Hazuku, T.; Hibiki, T.

    2008-01-01

    To evaluate the effect of wall surface wettability on the characteristics of upward gas-liquid two-phase flow in a vertical pipe, an experimental study was performed using three test pipes: an acrylic pipe, a hydrophilic pipe and a hydrophobic pipe. Basic flow characteristics such as flow patterns, pressure drop and void fraction were measured in these three pipes. In the hydrophilic pipe, a slug to churn flow transition boundary was shifted to a higher gas velocity at a given liquid velocity, whereas a churn to annular flow transition boundary was shifted to a lower gas velocity at a given liquid velocity. In the hydrophobic pipe, an inverted-churn flow regime was observed in the region where the churn flow regime was observed in the acrylic pipe, while a droplet flow regime was observed in the region where an annular flow regime was observed in the acrylic pipe. At a high gas flow rate, the mean void fraction in the hydrophobic pipe was higher than in the acrylic pipe. The effect of surface wettability on frictional pressure loss was confirmed to be insignificant under the present experimental conditions

  7. Nonlinear Plasma Response to Resonant Magnetic Perturbation in Rutherford Regime

    Science.gov (United States)

    Zhu, Ping; Yan, Xingting; Huang, Wenlong

    2017-10-01

    Recently a common analytic relation for both the locked mode and the nonlinear plasma response in the Rutherford regime has been developed based on the steady-state solution to the coupled dynamic system of magnetic island evolution and torque balance equations. The analytic relation predicts the threshold and the island size for the full penetration of resonant magnetic perturbation (RMP). It also rigorously proves a screening effect of the equilibrium toroidal flow. In this work, we test the theory by solving for the nonlinear plasma response to a single-helicity RMP of a circular-shaped limiter tokamak equilibrium with a constant toroidal flow, using the initial-value, full MHD simulation code NIMROD. Time evolution of the parallel flow or ``slip frequency'' profile and its asymptotic approach to steady state obtained from the NIMROD simulations qualitatively agree with the theory predictions. Further comparisons are carried out for the saturated island size, the threshold for full mode penetration, as well as the screening effects of equilibrium toroidal flow in order to understand the physics of nonlinear plasma response in the Rutherford regime. Supported by National Magnetic Confinement Fusion Science Program of China Grants 2014GB124002 and 2015GB101004, the 100 Talent Program of the Chinese Academy of Sciences, and U.S. Department of Energy Grants DE-FG02-86ER53218 and DE-FC02-08ER54975.

  8. Velocity measurements and identification of the flow pattern of vertical air-water flows with light-beam detectors

    International Nuclear Information System (INIS)

    Luebbesmeyer, D.; Leoni, B.

    1980-07-01

    A new detector for measuring fluid velocities in two-phase flows by means of Noise-Analysis (especially Transient-Cross-Correlation-technique) has been developed. The detector utilizes a light-beam which is modulated by changes in the transparency of the two-phase flow. The results of nine measurements for different flow-regimes of vertical air/water-flows are shown. A main topic of these investigations was to answer the question if it is possible to identify the flow-pattern by looking at the shape of different 'Noise-Analytical-functions' (like APSD, CPSD, CCF etc.). The results prove that light-beam sensors are good detectors for fluid-velocity measurements in different flow regimes and in a wide range of fluid velocities starting with values of about 0.08 m/s up to values of 40 m/s. With respect to flow-pattern identification only the time-signals and the shape of the cross-power-density-function (CPSD) seem to be useful. (Auth.)

  9. Experimental investigation of single-phase flow friction in narrow annuli

    International Nuclear Information System (INIS)

    Sun Zhongning; Sun Licheng; Yan Changqi; Huang Weitang

    2004-01-01

    Experimental investigations of water flow friction in horizontal narrow annuli, with gap sizes of 0.57-3.08 mm, were carried out. The tests involved both laminar and turbulent flow regimes. The critical Reynolds number transited from laminar flow to turbulent flow was examed and observed. The friction factors obtained from experiments were compared with conventional correlations evaluated results, and the influences of channel scale and eccentricity on flow friction characteristics were discussed. It was found that fluid friction in turbulent regime could be predicted by conventional correlations with satisfied degree, but both values and varying trend of that vs. r i /r o in laminar regime were obviously departure from theoretically results when the gap sizes were less than 2.0 mm, and the critical Reynolds number was slightly less then 2300 when the gap sizes were less than 1.0 mm

  10. Informed Decision Making Process for Managing Environmental Flows in Small River Basins

    Science.gov (United States)

    Padikkal, S.; Rema, K. P.

    2013-03-01

    Numerous examples exist worldwide of partial or complete alteration to the natural flow regime of river systems as a consequence of large scale water abstraction from upstream reaches. The effects may not be conspicuous in the case of very large rivers, but the ecosystems of smaller rivers or streams may be completely destroyed over a period of time. While restoration of the natural flow regime may not be possible, at present there is increased effort to implement restoration by regulating environmental flow. This study investigates the development of an environmental flow management model at an icon site in the small river basin of Bharathapuzha, west India. To determine optimal environmental flow regimes, a historic flow model based on data assimilated since 1978 indicated a satisfactory minimum flow depth for river ecosystem sustenance is 0.907 m (28.8 m3/s), a value also obtained from the hydraulic model; however, as three of the reservoirs were already operational at this time a flow depth of 0.922 m is considered a more viable estimate. Analysis of daily stream flow in 1997-2006, indicated adequate flow regimes during the monsoons in June-November, but that sections of the river dried out in December-May with alarming water quality conditions near the river mouth. Furthermore, the preferred minimum `dream' flow regime expressed by stakeholders of the region is a water depth of 1.548 m, which exceeds 50 % of the flood discharge in July. Water could potentially be conserved for environmental flow purposes by (1) the de-siltation of existing reservoirs or (2) reducing water spillage in the transfer between river basins. Ultimately environmental flow management of the region requires the establishment of a co-ordinated management body and the regular assimilation of water flow information from which science based decisions are made, to ensure both economic and environmental concerns are adequately addressed.

  11. Experimental and Computational Study of Multiphase Flow Hydrodynamics in 2D Trickle Bed Reactors

    Science.gov (United States)

    Nadeem, H.; Ben Salem, I.; Kurnia, J. C.; Rabbani, S.; Shamim, T.; Sassi, M.

    2014-12-01

    Trickle bed reactors are largely used in the refining processes. Co-current heavy oil and hydrogen gas flow downward on catalytic particle bed. Fine particles in the heavy oil and/or soot formed by the exothermic catalytic reactions deposit on the bed and clog the flow channels. This work is funded by the refining company of Abu Dhabi and aims at mitigating pressure buildup due to fine deposition in the TBR. In this work, we focus on meso-scale experimental and computational investigations of the interplay between flow regimes and the various parameters that affect them. A 2D experimental apparatus has been built to investigate the flow regimes with an average pore diameter close to the values encountered in trickle beds. A parametric study is done for the development of flow regimes and the transition between them when the geometry and arrangement of the particles within the porous medium are varied. Liquid and gas flow velocities have also been varied to capture the different flow regimes. Real time images of the multiphase flow are captured using a high speed camera, which were then used to characterize the transition between the different flow regimes. A diffused light source was used behind the 2D Trickle Bed Reactor to enhance visualizations. Experimental data shows very good agreement with the published literature. The computational study focuses on the hydrodynamics of multiphase flow and to identify the flow regime developed inside TBRs using the ANSYS Fluent Software package. Multiphase flow inside TBRs is investigated using the "discrete particle" approach together with Volume of Fluid (VoF) multiphase flow modeling. The effect of the bed particle diameter, spacing, and arrangement are presented that may be used to provide guidelines for designing trickle bed reactors.

  12. Assessment of RELAP5-3D copyright using data from two-dimensional RPI flow tests

    International Nuclear Information System (INIS)

    Davis, C.B.

    1998-01-01

    The capability of the RELAP5-3D copyright computer code to perform multi-dimensional thermal-hydraulic analysis was assessed using data from steady-state flow tests conducted at Rensselaer Polytechnic Institute (RPI). The RPI data were taken in a two-dimensional test section in a low-pressure air/water loop. The test section consisted of a thin vertical channel that simulated a two-dimensional slice through the core of a pressurized water reactor. Single-phase and two-phase flows were supplied to the test section in an asymmetric manner to generate a two-dimensional flow field. A traversing gamma densitometer was used to measure void fraction at many locations in the test section. High speed photographs provided information on the flow patterns and flow regimes. The RPI test section was modeled using the multi-dimensional component in RELAP5-3D Version BF06. Calculations of three RPI experiments were performed. The flow regimes predicted by the base code were in poor agreement with those observed in the tests. The two-phase regions were observed to be in the bubbly and slug flow regimes in the test. However, nearly all of the junctions in the horizontal direction were calculated to be in the stratified flow regime because of the relatively low velocities in that direction. As a result, the void fraction predictions were also in poor agreement with the measured values. Significantly improved results were obtained in sensitivity calculations with a modified version of the code that prevented the horizontal junctions from entering the stratified flow regime. These results indicate that the code's logic in the determination of flow regimes in a multi-dimensional component must be improved. The results of the sensitivity calculations also indicate that RELAP5-3D will provide a significant multi-dimensional hydraulic analysis capability once the flow regime prediction is improved

  13. Regime-dependent forecast uncertainty of convective precipitation

    Energy Technology Data Exchange (ETDEWEB)

    Keil, Christian; Craig, George C. [Muenchen Univ. (Germany). Meteorologisches Inst.

    2011-04-15

    Forecast uncertainty of convective precipitation is influenced by all scales, but in different ways in different meteorological situations. Forecasts of the high resolution ensemble prediction system COSMO-DE-EPS of Deutscher Wetterdienst (DWD) are used to examine the dominant sources of uncertainty of convective precipitation. A validation with radar data using traditional as well as spatial verification measures highlights differences in precipitation forecast performance in differing weather regimes. When the forecast uncertainty can primarily be associated with local, small-scale processes individual members run with the same variation of the physical parameterisation driven by different global models outperform all other ensemble members. In contrast when the precipitation is governed by the large-scale flow all ensemble members perform similarly. Application of the convective adjustment time scale confirms this separation and shows a regime-dependent forecast uncertainty of convective precipitation. (orig.)

  14. Evaluation of dynamic loads induced by transient regimes of fluid flows in the pipe systems and devices of reducing the loads and their effects

    International Nuclear Information System (INIS)

    Serban, Viorel; Chirita, Alexandru Mihai; Androne, Marian; Alexandru, Constantin; Ciuca, Camelia; Badara, Janina; Alexandru, Carmen

    1995-01-01

    The paper presents the analytic methods for estimating the dynamic effects induced in pipe systems in transient regimes. They are based on computation programs developed in order to check the behaviour of ECCS and EWS under 'water hammer effect' and the behaviour of the primary circuit system under stresses caused by pipe cracks. Computation examples are presented in order to emphasize the capabilities of the programs to model transient phenomena in complex pipe networks. The overpressure induced by the water hammer effect, as revealed by comparing several transient regimes, depends on the fluid viscosity, the initial speed, the duration of starting the transient regime, the system rigidity, etc. Values several ten times higher that the initial one could be thus reached. An overview of new types of devices designed for damping the effect of water hammer phenomenon, as well as of sustaining supports for pipe systems and equipment able to damp the vibrations produced by the transient regimes of fluid flows and seismic movements is presented. These devices have also to cope with the high shocks produced by pipe breakage as well as high static loads. The paper contains the following sections: 1. Introduction; 2. Evaluating dynamic loads associated to the water hammer phenomenon; 3. Determining loads associated to the water hammer phenomenon for the ECC system of the Cernavoda NPP Unit 1; 4. Device for reducing the water hammer effects; 5. Evaluating dynamic loads associated to pipe cracks; 6. Determining loads associated to pipe cracks in the Cernavoda NPP primary circuit; 7. Devices for absorbing and damping the dynamic loads in pipe systems and equipment; 8. Conclusions. (authors)

  15. Laboratory Investigation of Rheology and Infiltration Process of Non-Newtonian Fluids through Porous Media in a Non-Isothermal Flow Regime for Effective Remediation of Contaminants

    Science.gov (United States)

    Naseer, F.

    2017-12-01

    Contamination of soil and groundwater by adsorbent (persistent) contaminants have been a major concern. Mine tailings, Acid mine drainage, waste disposal areas, active or abandoned surface and underground mines are some major causes of soil and water contamination. It is need of the hour to develop cost effective and efficient remediation techniques for clean-up of soil and aquifers. The objective of this research is to study a methodology of using non-Newtonian fluids for effective remediation of adsorbent contaminants in porous media under non-isothermal flow regimes. The research comprises of three components. Since, non-Newtonian fluid rheology has not been well studied in cold temperatures, the first component of the objective is to expose a non-Newtonian fluid (Guar gum solution) to different temperatures ranging from 30 °C through -5 °C to understand the change in viscosity, shear strength and contact angle of the fluid. Study of the flow characteristic of non-Newtonian fluids in complex porous media has been limited. Hence, the second component of this study will focus on a comparison of flow characteristics of a Newtonian fluid, non-Newtonian fluid and a combination of both fluids in a glass-tube-bundle setup that will act as a synthetic porous media. The study of flow characteristics will also be done for different thermal regimes ranging from -5 °C to 30 °C. The third component of the research will be to compare the effectiveness Guar gum to remediate a surrogate adsorbed contaminant at a certain temperature from the synthetic porous media. Guar gum is biodegradable and hence it is benign to the environment. Through these experiments, the mobility and behavior of Guar gum under varying temperature ranges will be characterized and its effectiveness in removing contaminants from soils will be understood. The impact of temperature change on the fluid and flow stability in the porous medium will be examined in this research. Guar gum is good suspension

  16. Role of a naturally varying flow regime in Everglades restoration

    Science.gov (United States)

    Harvey, Judson; Wetzel, Paul R.; Lodge, Thomas E.; Engel, Victor C.; Ross, Michael S.

    2017-01-01

    The Everglades is a low-gradient floodplain predominantly on organic soil that undergoes seasonally pulsing sheetflow through a network of deepwater sloughs separated by slightly higher elevation ridges. The seasonally pulsing flow permitted the coexistence of ridge and slough vegetation, including the persistence of productive, well-connected sloughs that seasonally concentrated prey and supported wading bird nesting success. Here we review factors contributing to the origin and to degradation of the ridge and slough ecosystem in an attempt to answer “How much flow is needed to restore functionality”? A key restoration objective is to increase sheetflow lost during the past century to reestablish interactions between flow, water depth, vegetation production and decomposition, and transport of flocculent organic sediment that build and maintain ridge and slough distinctions. Our review finds broad agreement that perturbations of water level depth and its fluctuations were primary in the degradation of landscape functions, with critical contributions from perturbed water quality, and flow velocity and direction. Whereas water levels are expected to be improved on average across a range of restoration scenarios that replace between 79 and 91% of predrainage flows, the diminished microtopography substantially decreases the probability of timely improvements in some areas whereas others that retain microtopographic differences are poised for restoration benefits. New advances in predicting restoration outcomes are coming from biophysical modeling of ridge–slough dynamics, system-wide measurements of landscape functionality, and large-scale flow restoration experiments, including active management techniques to kick-start slough regeneration.

  17. A BABCOCK–LEIGHTON SOLAR DYNAMO MODEL WITH MULTI-CELLULAR MERIDIONAL CIRCULATION IN ADVECTION- AND DIFFUSION-DOMINATED REGIMES

    Energy Technology Data Exchange (ETDEWEB)

    Belucz, Bernadett; Forgács-Dajka, Emese [Eötvös University, Department of Astronomy, 1518 Budapest, Pf. 32 (Hungary); Dikpati, Mausumi, E-mail: bbelucz@astro.elte.hu, E-mail: dikpati@ucar.edu [High Altitude Observatory, National Center for Atmospheric Research, 3080 Center Green, Boulder, CO 80307-3000 (United States)

    2015-06-20

    Babcock–Leighton type-solar dynamo models with single-celled meridional circulation are successful in reproducing many solar cycle features. Recent observations and theoretical models of meridional circulation do not indicate a single-celled flow pattern. We examine the role of complex multi-cellular circulation patterns in a Babcock–Leighton solar dynamo in advection- and diffusion-dominated regimes. We show from simulations that the presence of a weak, second, high-latitude reverse cell speeds up the cycle and slightly enhances the poleward branch in the butterfly diagram, whereas the presence of a second cell in depth reverses the tilt of the butterfly wing to an antisolar type. A butterfly diagram constructed from the middle of convection zone yields a solar-like pattern, but this may be difficult to realize in the Sun because of magnetic buoyancy effects. Each of the above cases behaves similarly in higher and lower magnetic diffusivity regimes. However, our dynamo with a meridional circulation containing four cells in latitude behaves distinctly differently in the two regimes, producing solar-like butterfly diagrams with fast cycles in the higher diffusivity regime, and complex branches in butterfly diagrams in the lower diffusivity regime. We also find that dynamo solutions for a four-celled pattern, two in radius and two in latitude, prefer to quickly relax to quadrupolar parity if the bottom flow speed is strong enough, of similar order of magnitude as the surface flow speed.

  18. A BABCOCK–LEIGHTON SOLAR DYNAMO MODEL WITH MULTI-CELLULAR MERIDIONAL CIRCULATION IN ADVECTION- AND DIFFUSION-DOMINATED REGIMES

    International Nuclear Information System (INIS)

    Belucz, Bernadett; Forgács-Dajka, Emese; Dikpati, Mausumi

    2015-01-01

    Babcock–Leighton type-solar dynamo models with single-celled meridional circulation are successful in reproducing many solar cycle features. Recent observations and theoretical models of meridional circulation do not indicate a single-celled flow pattern. We examine the role of complex multi-cellular circulation patterns in a Babcock–Leighton solar dynamo in advection- and diffusion-dominated regimes. We show from simulations that the presence of a weak, second, high-latitude reverse cell speeds up the cycle and slightly enhances the poleward branch in the butterfly diagram, whereas the presence of a second cell in depth reverses the tilt of the butterfly wing to an antisolar type. A butterfly diagram constructed from the middle of convection zone yields a solar-like pattern, but this may be difficult to realize in the Sun because of magnetic buoyancy effects. Each of the above cases behaves similarly in higher and lower magnetic diffusivity regimes. However, our dynamo with a meridional circulation containing four cells in latitude behaves distinctly differently in the two regimes, producing solar-like butterfly diagrams with fast cycles in the higher diffusivity regime, and complex branches in butterfly diagrams in the lower diffusivity regime. We also find that dynamo solutions for a four-celled pattern, two in radius and two in latitude, prefer to quickly relax to quadrupolar parity if the bottom flow speed is strong enough, of similar order of magnitude as the surface flow speed

  19. Current capabilities of transient two-phase flow instruments

    International Nuclear Information System (INIS)

    Solbrig, C.W.; Kondic, N.N.

    1979-01-01

    The measurement of two phase flow phenomena in transient conditions representative of a Loss-of-Coolant Accident requires the use of sophisticated instruments and the further development of other instruments. Measurements made in large size pipes are often flow regime dependent. The flow regimes encountered depend upon the system geometry, transient effects, heat transfer, etc. The geometries in which these measurements must be made, the instruments which are currently used, new instruments being developed, the facilities used to calibrate these instruments, and the improvements which must be made to measurement capabilities are described

  20. Sedimentological regimes for turbidity currents: Depth-averaged theory

    Science.gov (United States)

    Halsey, Thomas C.; Kumar, Amit; Perillo, Mauricio M.

    2017-07-01

    Turbidity currents are one of the most significant means by which sediment is moved from the continents into the deep ocean; their properties are interesting both as elements of the global sediment cycle and due to their role in contributing to the formation of deep water oil and gas reservoirs. One of the simplest models of the dynamics of turbidity current flow was introduced three decades ago, and is based on depth-averaging of the fluid mechanical equations governing the turbulent gravity-driven flow of relatively dilute turbidity currents. We examine the sedimentological regimes of a simplified version of this model, focusing on the role of the Richardson number Ri [dimensionless inertia] and Rouse number Ro [dimensionless sedimentation velocity] in determining whether a current is net depositional or net erosional. We find that for large Rouse numbers, the currents are strongly net depositional due to the disappearance of local equilibria between erosion and deposition. At lower Rouse numbers, the Richardson number also plays a role in determining the degree of erosion versus deposition. The currents become more erosive at lower values of the product Ro × Ri, due to the effect of clear water entrainment. At higher values of this product, the turbulence becomes insufficient to maintain the sediment in suspension, as first pointed out by Knapp and Bagnold. We speculate on the potential for two-layer solutions in this insufficiently turbulent regime, which would comprise substantial bedload flow with an overlying turbidity current.

  1. Hydrologic Impact of Harvesting and Road Construction in Mountainous Regime of Pacific Northwest

    Science.gov (United States)

    Du, E.; Hubbart, J.; Gravelle, J.; Link, T.

    2006-12-01

    The impact of forest management practices on hydrologic flow regimes have been debated for years. Vegetation removal and forest road construction are two anthropogenic disturbances that may affect watershed hydrology. The Mica Creek Experimental Watershed (MCEW), ID was initiated by Potlatch Corporation in 1990 to evaluate how contemporary forest harvest practices may impact water flows, quality and aquatic health. The study was recently expanded to identify the specific mechanisms producing the observed flow responses. The extensive and long term monitoring program in MCEW enables the validation of simulated internal watershed processes, thereby increasing our confidence in the ability of models to simulate the hydrologic effects of land cover change. The spatially-distributed, physically-based Distributed Hydrology Soil Vegetation Model (DHSVM), will be used to deconvolve the effects of canopy change, forest road construction, and climate variability in MCEW. First, the model performance will be assessed for pre-harvest, post-road, and post-harvest experimental periods. The model will then be used to explore how the flow regime would be expected to differ under historical, alternative management and future scenarios. A retrospective study of fully-harvested and increased forest road density (as opposed to current road density of 3 to 5 percent by surface area) will be compared with contemporary management practices. The impact of harvest patterns on sub-catchment flows will be assessed to understand the degree to which flow synchronization or desynchronization on confluent streams might affect cumulative downstream flow regime. Future scenarios will assess the potential impact of climatic variability that is expected to raise the transient snow zone and increase the wintertime rain to snow ratios in the Pacific Northwest. Variables such as harvest patterns and climate variation will be manipulated to project whether the hydrologic effects of land cover and

  2. Prediction of flow rates through an orifice at pressures corresponding to the transition between molecular and isentropic flow

    International Nuclear Information System (INIS)

    DeMuth, S.F.; Watson, J.S.

    1985-01-01

    A model of compressible flow through an orifice, in the region of transition from free molecular to isentropic expansion flow, has been developed and tested for accuracy. The transitional or slip regime is defined as the conditions where molecular interactions are too many for free molecular flow modeling, yet not great enough for isentropic expansion flow modeling. Due to a lack of literature establishing a well-accepted model for predicting transitional flow, it was felt such work would be beneficial. The model is nonlinear and cannot be satisfactorily linearized for a linear regression analysis. Consequently, a computer routine was developed which minimized the sum of the squares of the residual flow for the nonlinear model. The results indicate an average accuracy within 15% of the measured flow throughout the range of test conditions. Furthermore, the results of the regression analysis indicate that the transitional regime lies between Knudsen numbers of approximately 2 and 45. 4 refs., 3 figs., 1 tab

  3. Modeling of dialogue regimes of distance robot control

    Science.gov (United States)

    Larkin, E. V.; Privalov, A. N.

    2017-02-01

    Process of distance control of mobile robots is investigated. Petri-Markov net for modeling of dialogue regime is worked out. It is shown, that sequence of operations of next subjects: a human operator, a dialogue computer and an onboard computer may be simulated with use the theory of semi-Markov processes. From the semi-Markov process of the general form Markov process was obtained, which includes only states of transaction generation. It is shown, that a real transaction flow is the result of «concurrency» in states of Markov process. Iteration procedure for evaluation of transaction flow parameters, which takes into account effect of «concurrency», is proposed.

  4. Inlet effects on vertical-downward air–water two-phase flow

    Energy Technology Data Exchange (ETDEWEB)

    Qiao, Shouxu; Mena, Daniel; Kim, Seungjin, E-mail: skim@psu.edu

    2017-02-15

    Highlights: • Inlet effects on two-phase flow parameters in vertical-downward flow are studied. • Flow regimes in the vertical-downward two-phase flow are defined. • Vertical-downward flow regime maps for three inlet configurations are developed. • Frictional pressure loss analysis for three different inlets is performed. • Database of local two-phase flow parameters for each inlet configuration. - Abstract: This paper focuses on investigating the geometric effects of inlets on global and local two-phase flow parameters in vertical-downward air–water two-phase flow. Flow visualization, frictional pressure loss analysis, and local experiments are performed in a test facility constructed from 50.8 mm inner diameter acrylic pipes. Three types of inlets of interest are studied: (1) two-phase flow injector without a flow straightener (Type A), (2) two-phase flow injector with a flow straightener (Type B), and (3) injection through a horizontal-to-vertical-downward 90° vertical elbow (Type C). A detailed flow visualization study is performed to characterize flow regimes including bubbly, slug, churn-turbulent, and annular flow. Flow regime maps for each inlet are developed and compared to identify the effects of each inlet. Frictional pressure loss analysis shows that the Lockhart–Martinelli method is capable of correlating the frictional loss data acquired for Type B and Type C inlets with a coefficient value of C = 25, but additional data may be needed to model the Type A inlet. Local two-phase flow parameters measured by a four-sensor conductivity probe in four bubbly and near bubbly flow conditions are analyzed. It is observed that vertical-downward two-phase flow has a characteristic center-peaked void profile as opposed to a wall-peaked profile as seen in vertical-upward flow. Furthermore, it is shown that the Type A inlet results in the most pronounced center-peaked void fraction profile, due to the coring phenomenon. Type B and Type C inlets

  5. Features of two-phase flow in a microchannel of 0.05×20 mm

    Science.gov (United States)

    Ronshin, Fedor

    2017-10-01

    We have studied the two-phase flow in a microchannel with cross-section of 0.05×20 mm2. The following two-phase flow regimes have been registered: jet, bubble, stratified, annular, and churn ones. The main features of flow regimes in this channel such as formation of liquid droplets in all two-phase flows have been distinguished.

  6. Quantifying flooding regime in floodplain forests to guide river restoration

    Science.gov (United States)

    Christian O. Marks; Keith H. Nislow; Francis J. Magilligan

    2014-01-01

    Determining the flooding regime needed to support distinctive floodplain forests is essential for effective river conservation under the ubiquitous human alteration of river flows characteristic of the Anthropocene Era. At over 100 sites throughout the Connecticut River basin, the largest river system in New England, we characterized species composition, valley and...

  7. Interfacial structures in downward two-phase bubbly flow

    International Nuclear Information System (INIS)

    Paranjape, S.S.; Kim, S.; Ishii, M.; Kelly, J.

    2003-01-01

    Downward two-phase flow was studied considering its significance in view of Light Water Reactor Accidents (LWR) such as Loss of Heat Sink (LOHS) by feed water loss or secondary pipe break. The flow studied, was an adiabatic, air-water, co-current, vertically downward two-phase flow. The experimental test sections had internal hydraulic diameters of 25.4 mm and 50.8 mm. Flow regime map was obtained using the characteristic signals obtained from an impedance void meter, employing neural network based identification methodology to minimize the subjective judgment in determining the flow regimes. A four sensor conductivity probe was used to measure the local two phase flow parameters, which characterize the interfacial structures. The local time averaged two-phase flow parameters measured were: void fraction (α), interfacial area concentration (a i ), bubble velocity (v g ), and Sauter mean diameter (D Sm ). The flow conditions were from the bubbly flow regime. The local profiles of these parameters as well as their axial development revealed the nature of the interfacial structures and the bubble interaction mechanisms occurring in the flow. Furthermore, this study provided a good database for the development of the interfacial area transport equation, which dynamically models the changes in the interfacial area along the flow field. An interfacial area transport equation was developed for downward flow based on that developed for the upward flow, with certain modifications in the bubble interaction terms. The area averaged values of the interfacial area concentration were compared with those predicted by the interfacial area transport model. (author)

  8. Decision Support System for Evaluation of Gunnison River Flow Regimes With Respect To Resources of the Black Canyon of the Gunnison National Park

    Science.gov (United States)

    Auble, Gregor T.; Wondzell, Mark; Talbert, Colin

    2009-01-01

    This report describes and documents a decision support system for the Gunnison River in Black Canyon of the Gunnison National Park. It is a macro-embedded EXCEL program that calculates and displays indicators representing valued characteristics or processes in the Black Canyon based on daily flows of the Gunnison River. The program is designed to easily accept input from downloaded stream gage records or output from the RIVERWARE reservoir operations model being used for the upstream Aspinall Unit. The decision support system is structured to compare as many as eight alternative flow regimes, where each alternative is represented by a daily sequence of at least 20 calendar years of streamflow. Indicators include selected flow statistics, riparian plant community distribution, clearing of box elder by inundation and scour, several measures of sediment mobilization, trout fry habitat, and federal reserved water rights. Calculation of variables representing National Park Service federal reserved water rights requires additional secondary input files pertaining to forecast and actual basin inflows and storage levels in Blue Mesa reservoir. Example input files representing a range of situations including historical, reconstructed natural, and simulated alternative reservoir operations are provided with the software.

  9. Characterization of fluidization regime in circulating fluidized bed reactor with high solid particle concentration using computational fluid dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Chalermsinsuwan, Benjapon; Thummakul, Theeranan; Piumsomboon, Pornpote [Chulalongkorn University, Bangkok (Thailand); Gidaspow, Dimitri [Armour College of Engineering, Chicago (United States)

    2014-02-15

    The hydrodynamics inside a high solid particle concentration circulating fluidized bed reactor was investigated using computational fluid dynamics simulation. Compared to a low solid particle reactor, all the conventional fluidization regimes were observed. In addition, two unconventional fluidization regimes, circulating-turbulent and dense suspension bypassing regimes, were found with only primary gas injection. The circulating-turbulent fluidization regime showed uniformly dense solid particle distribution in all the system directions, while the dense suspension bypassing fluidization regime exhibited the flow of solid particles at only one side system wall. Then, comprehensive fluidization regime clarification and mapping were evaluated using in-depth system parameters. In the circulating-turbulent fluidization regime, the total granular temperature was low compared to the adjacent fluidization regimes. In the dense suspension bypassing fluidization regime, the highest total granular temperature was obtained. The circulating-turbulent and dense suspension bypassing fluidization regimes are suitable for sorption and transportation applications, respectively.

  10. Precipitation regimes over central Greenland inferred from 5 years of ICECAPS observations

    Science.gov (United States)

    Pettersen, Claire; Bennartz, Ralf; Merrelli, Aronne J.; Shupe, Matthew D.; Turner, David D.; Walden, Von P.

    2018-04-01

    A novel method for classifying Arctic precipitation using ground based remote sensors is presented. Using differences in the spectral variation of microwave absorption and scattering properties of cloud liquid water and ice, this method can distinguish between different types of snowfall events depending on the presence or absence of condensed liquid water in the clouds that generate the precipitation. The classification reveals two distinct, primary regimes of precipitation over the Greenland Ice Sheet (GIS): one originating from fully glaciated ice clouds and the other from mixed-phase clouds. Five years of co-located, multi-instrument data from the Integrated Characterization of Energy, Clouds, Atmospheric state, and Precipitation at Summit (ICECAPS) are used to examine cloud and meteorological properties and patterns associated with each precipitation regime. The occurrence and accumulation of the precipitation regimes are identified and quantified. Cloud and precipitation observations from additional ICECAPS instruments illustrate distinct characteristics for each regime. Additionally, reanalysis products and back-trajectory analysis show different synoptic-scale forcings associated with each regime. Precipitation over the central GIS exhibits unique microphysical characteristics due to the high surface elevations as well as connections to specific large-scale flow patterns. Snowfall originating from the ice clouds is coupled to deep, frontal cloud systems advecting up and over the southeast Greenland coast to the central GIS. These events appear to be associated with individual storm systems generated by low pressure over Baffin Bay and Greenland lee cyclogenesis. Snowfall originating from mixed-phase clouds is shallower and has characteristics typical of supercooled cloud liquid water layers, and slowly propagates from the south and southwest of Greenland along a quiescent flow above the GIS.

  11. Burnout in subcooled flow boiling of water. A visual experimental study

    Energy Technology Data Exchange (ETDEWEB)

    Celata, G.P.; Mariani, A.; Zummo, G. [ENEA, Engineering Div., National Institute of Thermal Fluid-Dynamics, Rome (Italy); Cumo, M. [University of Rome la Sapienza, Rome (Italy)

    2000-12-01

    The objective of the present work is to perform a photographic study of the burnout in highly subcooled flow boiling, in order to provide a qualitative description of the flow pattern under different conditions of boiling regime: ONB (onset of nucleate boiling), subcooled flow boiling and thermal crisis. In particular, the flow visualisation is focused on the phenomena occurring on the heated wall during the thermal crisis up to the physical burnout of the heater. Vapour bubble parameters are measured from flow images recorded, while the wall temperature is measured with an indirect method, by recording the heater elongation during all flow regimes studied. The combination of bubble parameters and wall temperature measurements as well as direct observations of the flow pattern, for all flow regimes, are collected in graphs which provide a useful global point of view of boiling phenomena, especially during boiling crisis. Under these conditions, a detailed analysis of the mechanisms leading to the critical heat flux is reported, and the so called events sequence, from thermal crisis occurrence up to heater burnout, is illustrated. (authors)

  12. Burnout in subcooled flow boiling of water. A visual experimental study

    International Nuclear Information System (INIS)

    Celata, G.P.; Mariani, A.; Zummo, G.; Cumo, M.

    2000-01-01

    The objective of the present work is to perform a photographic study of the burnout in highly subcooled flow boiling, in order to provide a qualitative description of the flow pattern under different conditions of boiling regime: ONB (onset of nucleate boiling), subcooled flow boiling and thermal crisis. In particular, the flow visualisation is focused on the phenomena occurring on the heated wall during the thermal crisis up to the physical burnout of the heater. Vapour bubble parameters are measured from flow images recorded, while the wall temperature is measured with an indirect method, by recording the heater elongation during all flow regimes studied. The combination of bubble parameters and wall temperature measurements as well as direct observations of the flow pattern, for all flow regimes, are collected in graphs which provide a useful global point of view of boiling phenomena, especially during boiling crisis. Under these conditions, a detailed analysis of the mechanisms leading to the critical heat flux is reported, and the so called events sequence, from thermal crisis occurrence up to heater burnout, is illustrated. (authors)

  13. Global hydrological droughts in the 21st century under a changing hydrological regime

    Directory of Open Access Journals (Sweden)

    N. Wanders

    2015-01-01

    Full Text Available Climate change very likely impacts future hydrological drought characteristics across the world. Here, we quantify the impact of climate change on future low flows and associated hydrological drought characteristics on a global scale using an alternative drought identification approach that considers adaptation to future changes in hydrological regime. The global hydrological model PCR-GLOBWB was used to simulate daily discharge at 0.5° globally for 1971–2099. The model was forced with CMIP5 climate projections taken from five global circulation models (GCMs and four emission scenarios (representative concentration pathways, RCPs, from the Inter-Sectoral Impact Model Intercomparison Project. Drought events occur when discharge is below a threshold. The conventional variable threshold (VTM was calculated by deriving the threshold from the period 1971–2000. The transient variable threshold (VTMt is a non-stationary approach, where the threshold is based on the discharge values of the previous 30 years implying the threshold to vary every year during the 21st century. The VTMt adjusts to gradual changes in the hydrological regime as response to climate change. Results show a significant negative trend in the low flow regime over the 21st century for large parts of South America, southern Africa, Australia and the Mediterranean. In 40–52% of the world reduced low flows are projected, while increased low flows are found in the snow-dominated climates. In 27% of the global area both the drought duration and the deficit volume are expected to increase when applying the VTMt. However, this area will significantly increase to 62% when the VTM is applied. The mean global area in drought, with the VTMt, remains rather constant (11.7 to 13.4%, compared to the substantial increase when the VTM is applied (11.7 to 20%. The study illustrates that an alternative drought identification that considers adaptation to an altered hydrological regime has a

  14. Entropy Production in Pipeline Flow of Dispersions of Water in Oil

    Directory of Open Access Journals (Sweden)

    Rajinder Pal

    2014-08-01

    Full Text Available Entropy production in pipeline adiabatic flow of water-in-oil emulsions is investigated experimentally in three different diameter pipes. The dispersed-phase (water droplets concentration of emulsion is varied from 0 to 41% vol. The entropy production rates in emulsion flow are compared with the values expected in single-phase flow of Newtonian fluids with the same properties (viscosity and density. While in the laminar regime the entropy production rates in emulsion flow can be described adequately by the single-phase Newtonian equations, a significant deviation from single-phase flow behavior is observed in the turbulent regime. In the turbulent regime, the entropy production rates in emulsion flow are found to be substantially smaller than those expected on the basis of single-phase equations. For example, the entropy production rate in water-in-oil emulsion flow at a dispersed-phase volume fraction of 0.41 is only 38.4% of that observed in flow of a single-phase Newtonian fluid with the same viscosity and density, when comparison is made at a Reynolds number of 4000. Thus emulsion flow in pipelines is more efficient thermodynamically than single-phase Newtonian flow.

  15. Features of two-phase flow in a microchannel of 0.05×20 mm

    Directory of Open Access Journals (Sweden)

    Ronshin Fedor

    2017-01-01

    Full Text Available We have studied the two-phase flow in a microchannel with cross-section of 0.05×20 mm2. The following two-phase flow regimes have been registered: jet, bubble, stratified, annular, and churn ones. The main features of flow regimes in this channel such as formation of liquid droplets in all two-phase flows have been distinguished.

  16. Critical slowing down associated with regime shifts in the US housing market

    Science.gov (United States)

    Tan, James Peng Lung; Cheong, Siew Siew Ann

    2014-02-01

    Complex systems are described by a large number of variables with strong and nonlinear interactions. Such systems frequently undergo regime shifts. Combining insights from bifurcation theory in nonlinear dynamics and the theory of critical transitions in statistical physics, we know that critical slowing down and critical fluctuations occur close to such regime shifts. In this paper, we show how universal precursors expected from such critical transitions can be used to forecast regime shifts in the US housing market. In the housing permit, volume of homes sold and percentage of homes sold for gain data, we detected strong early warning signals associated with a sequence of coupled regime shifts, starting from a Subprime Mortgage Loans transition in 2003-2004 and ending with the Subprime Crisis in 2007-2008. Weaker signals of critical slowing down were also detected in the US housing market data during the 1997-1998 Asian Financial Crisis and the 2000-2001 Technology Bubble Crisis. Backed by various macroeconomic data, we propose a scenario whereby hot money flowing back into the US during the Asian Financial Crisis fueled the Technology Bubble. When the Technology Bubble collapsed in 2000-2001, the hot money then flowed into the US housing market, triggering the Subprime Mortgage Loans transition in 2003-2004 and an ensuing sequence of transitions. We showed how this sequence of couple transitions unfolded in space and in time over the whole of US.

  17. Charging and Transport Dynamics of a Flow-Through Electrode Capacitive Deionization System.

    Science.gov (United States)

    Qu, Yatian; Campbell, Patrick G; Hemmatifar, Ali; Knipe, Jennifer M; Loeb, Colin K; Reidy, John J; Hubert, Mckenzie A; Stadermann, Michael; Santiago, Juan G

    2018-01-11

    We present a study of the interplay among electric charging rate, capacitance, salt removal, and mass transport in "flow-through electrode" capacitive deionization (CDI) systems. We develop two models describing coupled transport and electro-adsorption/desorption which capture salt removal dynamics. The first model is a simplified, unsteady zero-dimensional volume-averaged model which identifies dimensionless parameters and figures of merits associated with cell performance. The second model is a higher fidelity area-averaged model which captures both spatial and temporal responses of charging. We further conducted an experimental study of these dynamics and considered two salt transport regimes: (1) advection-limited regime and (2) dispersion-limited regime. We use these data to validate models. The study shows that, in the advection-limited regime, differential charge efficiency determines the salt adsorption at the early stage of the deionization process. Subsequently, charging transitions to a quasi-steady state where salt removal rate is proportional to applied current scaled by the inlet flow rate. In the dispersion-dominated regime, differential charge efficiency, cell volume, and diffusion rates govern adsorption dynamics and flow rate has little effect. In both regimes, the interplay among mass transport rate, differential charge efficiency, cell capacitance, and (electric) charging current governs salt removal in flow-through electrode CDI.

  18. Blurring the boundary between rapid granular flow and dense granular flow regimes: Evidence from DEM simulations

    Science.gov (United States)

    Tripathi, Anurag; Prasad, Mahesh; Kumar, Puneet

    2017-11-01

    The saturation of the effective friction coefficient for granular flows at high inertial numbers has been assumed widely by researchers, despite little simulation/experimental evidence. In contrast, a recent simulation study of plane shear flows by Mandal and Khakhar, suggests that the effective friction coefficient becomes maximum and then starts to decrease with increase in the inertial number for I > 0.5 . In order to investigate whether such a dip at higher inertial numbers is indeed a feature of granular rheology, we perform DEM simulations of chute flow of highly inelastic disks. We show that steady, fully developed flows are possible at inclinations much higher than those normally reported in literature. At such high inclinations, the flow is characterised by a significant slip at the base; the height of the layer increases by more than 300 % and kinetic energy of the layer increases by nearly 5 orders of magnitude. We observe, for the first time, steady chute flows at inertial number I 2 and show that the dip at higher inertial numbers can be observed in case of chute flow as well. The predictions of modified μ - I rheology, however, seem to remain valid in the bulk of the layer for packing fractions as low as 0.2. AT acknowledges the funding obtained from IIT Kanpur through the initiation Grant for this study.

  19. Viscoinertial regime of immersed granular flows

    Science.gov (United States)

    Amarsid, L.; Delenne, J.-Y.; Mutabaruka, P.; Monerie, Y.; Perales, F.; Radjai, F.

    2017-07-01

    By means of extensive coupled molecular dynamics-lattice Boltzmann simulations, accounting for grain dynamics and subparticle resolution of the fluid phase, we analyze steady inertial granular flows sheared by a viscous fluid. We show that, for a broad range of system parameters (shear rate, confining stress, fluid viscosity, and relative fluid-grain density), the frictional strength and packing fraction can be described by a modified inertial number incorporating the fluid effect. In a dual viscous description, the effective viscosity diverges as the inverse square of the difference between the packing fraction and its jamming value, as observed in experiments. We also find that the fabric and force anisotropies extracted from the contact network are well described by the modified inertial number, thus providing clear evidence for the role of these key structural parameters in dense suspensions.

  20. JT-60U high performance regimes

    International Nuclear Information System (INIS)

    Ishida, S.

    1999-01-01

    High performance regimes of JT-60U plasmas are presented with an emphasis upon the results from the use of a semi-closed pumped divertor with W-shaped geometry. Plasma performance in transient and quasi steady states has been significantly improved in reversed shear and high- βp regimes. The reversed shear regime elevated an equivalent Q DT eq transiently up to 1.25 (n D (0)τ E T i (0)=8.6x10 20 m-3·s·keV) in a reactor-relevant thermonuclear dominant regime. Long sustainment of enhanced confinement with internal transport barriers (ITBs) with a fully non-inductive current drive in a reversed shear discharge was successfully demonstrated with LH wave injection. Performance sustainment has been extended in the high- bp regime with a high triangularity achieving a long sustainment of plasma conditions equivalent to Q DT eq ∼0.16 (n D (0)τ E T i (0)∼1.4x10 20 m -3 ·s·keV) for ∼4.5 s with a large non-inductive current drive fraction of 60-70% of the plasma current. Thermal and particle transport analyses show significant reduction of thermal and particle diffusivities around ITB resulting in a strong Er shear in the ITB region. The W-shaped divertor is effective for He ash exhaust demonstrating steady exhaust capability of τ He */τ E ∼3-10 in support of ITER. Suppression of neutral back flow and chemical sputtering effect have been observed while MARFE onset density is rather decreased. Negative-ion based neutral beam injection (N-NBI) experiments have created a clear H-mode transition. Enhanced ionization cross- section due to multi-step ionization processes was confirmed as theoretically predicted. A current density profile driven by N-NBI is measured in a good agreement with theoretical prediction. N-NBI induced TAE modes characterized as persistent and bursting oscillations have been observed from a low hot beta of h >∼0.1-0.2% without a significant loss of fast ions. (author)

  1. Magnetogasdynamic Flow Acceleration in a Scramjet Nozzle

    National Research Council Canada - National Science Library

    Harrington, Brian

    2004-01-01

    .... The parameters of conductivity pattern and load factor are varied in both inviscid and viscous flow regimes with the intent of increasing axial force exerted on the flow through a scramjet accelerator...

  2. Uncertainty contributions to low flow projections in Austria

    Science.gov (United States)

    Parajka, J.; Blaschke, A. P.; Blöschl, G.; Haslinger, K.; Hepp, G.; Laaha, G.; Schöner, W.; Trautvetter, H.; Viglione, A.; Zessner, M.

    2015-11-01

    The main objective of the paper is to understand the contributions to the uncertainty in low flow projections resulting from hydrological model uncertainty and climate projection uncertainty. Model uncertainty is quantified by different parameterizations of a conceptual semi-distributed hydrologic model (TUWmodel) using 11 objective functions in three different decades (1976-1986, 1987-1997, 1998-2008), which allows disentangling the effect of modeling uncertainty and temporal stability of model parameters. Climate projection uncertainty is quantified by four future climate scenarios (ECHAM5-A1B, A2, B1 and HADCM3-A1B) using a delta change approach. The approach is tested for 262 basins in Austria. The results indicate that the seasonality of the low flow regime is an important factor affecting the performance of model calibration in the reference period and the uncertainty of Q95 low flow projections in the future period. In Austria, the calibration uncertainty in terms of Q95 is larger in basins with summer low flow regime than in basins with winter low flow regime. Using different calibration periods may result in a range of up to 60 % in simulated Q95 low flows. The low flow projections show an increase of low flows in the Alps, typically in the range of 10-30 % and a decrease in the south-eastern part of Austria mostly in the range -5 to -20 % for the period 2021-2050 relative the reference period 1976-2008. The change in seasonality varies between scenarios, but there is a tendency for earlier low flows in the Northern Alps and later low flows in Eastern Austria. In 85 % of the basins, the uncertainty in Q95 from model calibration is larger than the uncertainty from different climate scenarios. The total uncertainty of Q95 projections is the largest in basins with winter low flow regime and, in some basins, exceeds 60 %. In basins with summer low flows and the total uncertainty is mostly less than 20 %. While the calibration uncertainty dominates over climate

  3. Homogeneous purely buoyancy driven turbulent flow

    Science.gov (United States)

    Arakeri, Jaywant; Cholemari, Murali; Pawar, Shashikant

    2010-11-01

    An unstable density difference across a long vertical tube open at both ends leads to convection that is axially homogeneous with a linear density gradient. We report results from such tube convection experiments, with driving density caused by salt concentration difference or temperature difference. At high enough Rayleigh numbers (Ra) the convection is turbulent with zero mean flow and zero mean Reynolds shear stresses; thus turbulent production is purely by buoyancy. We observe different regimes of turbulent convection. At very high Ra the Nusselt number scales as the square root of the Rayleigh number, giving the so-called "ultimate regime" of convection predicted for Rayleigh-Benard convection in limit of infinite Ra. Turbulent convection at intermediate Ra, the Nusselt number scales as Ra^0.3. In both regimes, the flux and the Taylor scale Reynolds number are more than order of magnitude larger than those obtained in Rayleigh-Benard convection. Absence of a mean flow makes this an ideal flow to study shear free turbulence near a wall.

  4. Investigation of secondary flows in turbulent pipe flows with three-dimensional sinusoidal walls

    Science.gov (United States)

    Chan, Leon; MacDonald, Michael; Chung, Daniel; Hutchins, Nicholas; Ooi, Andrew

    2017-11-01

    The occurrence of secondary flows is systematically investigated via Direct Numerical Simulations (DNS) of turbulent flow in a rough wall pipe at friction Reynolds numbers of 540. In this study, the peak-to-trough height of the roughness elements, which consist of three-dimensional sinusoidal roughness, is fixed at 120 viscous units while the wavelength of the roughness elements is varied. The solidity or effective slope (ES) of the roughness ranges from the sparse regime (ES = 0.18) to the closely packed roughness/dense regime (ES = 0.72). The time-independent dispersive stresses, which arise due to the stationary features of the flow, are analysed and are found to increase with increasing roughness wavelength. These dispersive stresses are related to the occurrence of secondary flows and are maximum within the roughness canopy. Above the crest of the roughness elements, the dispersive stresses reduce to zero at wall-normal heights greater than half of the roughness wavelength. This study has found that the size and wall-normal extent of the secondary flows scales with the roughness wavelength and can reach wall-normal heights of almost half of the pipe radius.

  5. Big River Benthos: Linking Year Round Biological Response to Altered Hydrological Regimes

    Science.gov (United States)

    2017-04-02

    Sieved material was then placed in Whirl-Pak® bags, preserved with 80% EtOH, and returned to the ERDC Fish Ecology Laboratory in Vicksburg, MS... ecological response to altered flow regimes and help document benefits of restoring connectivity between secondary channels and the Mississippi River main...Modifications of the flow and function of the Mississippi River have only increased since then — markedly so after the Great Flood of 1927, an event that

  6. Improved choked flow model for MARS code

    International Nuclear Information System (INIS)

    Chung, Moon Sun; Lee, Won Jae; Ha, Kwi Seok; Hwang, Moon Kyu

    2002-01-01

    Choked flow calculation is improved by using a new sound speed criterion for bubbly flow that is derived by the characteristic analysis of hyperbolic two-fluid model. This model was based on the notion of surface tension for the interfacial pressure jump terms in the momentum equations. Real eigenvalues obtained as the closed-form solution of characteristic polynomial represent the sound speed in the bubbly flow regime that agrees well with the existing experimental data. The present sound speed shows more reasonable result in the extreme case than the Nguyens did. The present choked flow criterion derived by the present sound speed is employed in the MARS code and assessed by using the Marviken choked flow tests. The assessment results without any adjustment made by some discharge coefficients demonstrate more accurate predictions of choked flow rate in the bubbly flow regime than those of the earlier choked flow calculations. By calculating the Typical PWR (SBLOCA) problem, we make sure that the present model can reproduce the reasonable transients of integral reactor system

  7. Two-phase flow characterisation by nuclear magnetic resonance

    International Nuclear Information System (INIS)

    Leblond, J.; Javelot, S.; Lebrun, D.; Lebon, L.

    1998-01-01

    The results presented in this paper demonstrate the performance of the PFGSE-NMR to obtain a complete characterisation of two-phase flows. Different methods are proposed to characterise air-water flows in different regimes: stationary two-phase flows and flows in transient condition. Finally a modified PFGSE is proposed to analyse the turbulence of air-water bubbly flow. (author)

  8. Physics of zonal flows

    International Nuclear Information System (INIS)

    Itoh, K.; Fujisawa, A.; Itoh, S.-I.; Yagi, M.; Nagashima, Y.; Diamond, P.H.; Tynan, G.R.; Hahm, T.S.

    2006-01-01

    Zonal flows, which means azimuthally symmetric band-like shear flows, are ubiquitous phenomena in nature and the laboratory. It is now widely recognized that zonal flows are a key constituent in virtually all cases and regimes of drift wave turbulence, indeed, so much so that this classic problem is now frequently referred to as ''drift wave-zonal flow turbulence.'' In this review, new viewpoints and unifying concepts are presented, which facilitate understanding of zonal flow physics, via theory, computation and their confrontation with the results of laboratory experiment. Special emphasis is placed on identifying avenues for further progress. (author)

  9. Physics of zonal flows

    International Nuclear Information System (INIS)

    Itoh, K.; Itoh, S.-I.; Diamond, P.H.; Hahm, T.S.; Fujisawa, A.; Tynan, G.R.; Yagi, M.; Nagashima, Y.

    2006-01-01

    Zonal flows, which means azimuthally symmetric band-like shear flows, are ubiquitous phenomena in nature and the laboratory. It is now widely recognized that zonal flows are a key constituent in virtually all cases and regimes of drift wave turbulence, indeed, so much so that this classic problem is now frequently referred to as 'drift wave-zonal flow turbulence'. In this review, new viewpoints and unifying concepts are presented, which facilitate understanding of zonal flow physics, via theory, computation and their confrontation with the results of laboratory experiment. Special emphasis is placed on identifying avenues for further progress

  10. Transition between trickle flow and pulse flow in a cocurrent gas-liquid trickle-bed reactor at elevated pressures

    NARCIS (Netherlands)

    Wammes, W.J.A.; Mechielsen, S.J.; Westerterp, K.R.

    1992-01-01

    The effect of reactor pressure in the range of 0.2–2.0 MPa on the transition between the trickle-flow and the pulse-flow regime has been investigated for the non-foaming water—nitrogen and aqueous 40% ethyleneglycol—nitrogen systems. Most models and flow charts which are all based on atmospheric

  11. Multiple Temperature Model for Near Continuum Flows

    International Nuclear Information System (INIS)

    XU, Kun; Liu, Hongwei; Jiang, Jianzheng

    2007-01-01

    In the near continuum flow regime, the flow may have different translational temperatures in different directions. It is well known that for increasingly rarefied flow fields, the predictions from continuum formulation, such as the Navier-Stokes equations, lose accuracy. These inaccuracies may be partially due to the single temperature assumption in the Navier-Stokes equations. Here, based on the gas-kinetic Bhatnagar-Gross-Krook (BGK) equation, a multitranslational temperature model is proposed and used in the flow calculations. In order to fix all three translational temperatures, two constraints are additionally proposed to model the energy exchange in different directions. Based on the multiple temperature assumption, the Navier-Stokes relation between the stress and strain is replaced by the temperature relaxation term, and the Navier-Stokes assumption is recovered only in the limiting case when the flow is close to the equilibrium with the same temperature in different directions. In order to validate the current model, both the Couette and Poiseuille flows are studied in the transition flow regime

  12. Flow Mode Dependent Partitioning Processes of Preferential Flow Dynamics in Unsaturated Fractures - Findings From Analogue Percolation Experiments

    Science.gov (United States)

    Kordilla, J.; Noffz, T.; Dentz, M.; Sauter, M.

    2017-12-01

    To assess the vulnerability of an aquifer system it is of utmost importance to recognize the high potential for a rapid mass transport offered by ow through unsaturated fracture networks. Numerical models have to reproduce complex effects of gravity-driven flow dynamics to generate accurate predictions of flow and transport. However, the non-linear characteristics of free surface flow dynamics and partitioning behaviour at unsaturated fracture intersections often exceed the capacity of classical volume-effective modelling approaches. Laboratory experiments that manage to isolate single aspects of the mass partitioning process can enhance the understanding of underlying dynamics, which ultimately influence travel time distributions on multiple scales. Our analogue fracture network consists of synthetic cubes with dimensions of 20 x 20 x 20 cm creating simple geometries of a single or a cascade of consecutive horizontal fractures. Gravity-driven free surface flow (droplets; rivulets) is established via a high precision multichannel dispenser at flow rates ranging from 1.5 to 4.5 ml/min. Single-inlet experiments show the influence of variable flow rate, atmospheric pressure and temperature on the stability of flow modes and allow to delineate a droplet and rivulet regime. The transition between these regimes exhibits mixed flow characteristics. In addition, multi-inlet setups with constant total infow rates decrease the variance induced by erratic free-surface flow dynamics. We investigate the impacts of variable aperture widths, horizontal offsets of vertical fracture surfaces, and alternating injection methods for both flow regimes. Normalized fracture inflow rates allow to demonstrate and compare the effects of variable geometric features. Firstly, the fracture filling can be described by plug flow. At later stages it transitions into a Washburn-type flow, which we compare to an analytical solution for the case of rivulet flow. Observations show a considerably

  13. Influence of air flow parameters on nanosecond repetitively pulsed discharges in a pin-annular electrode configuration

    KAUST Repository

    Heitz, Sylvain A

    2016-03-16

    The effect of various air flow parameters on the plasma regimes of nanosecond repetitively pulsed (NRP) discharges is investigated at atmospheric pressure. The two electrodes are in a pin-annular configuration, transverse to the mean flow. The voltage pulses have amplitudes up to 15 kV, a duration of 10 ns and a repetition frequency ranging from 15 to 30 kHz. The NRP corona to NRP spark (C-S) regime transition and the NRP spark to NRP corona (S-C) regime transition are investigated for different steady and harmonically oscillating flows. First, the strong effect of a transverse flow on the C-S and S-C transitions, as reported in previous studies, is verified. Second, it is shown that the azimuthal flow imparted by a swirler does not affect the regime transition voltages. Finally, the influence of low frequency harmonic oscillations of the air flow, generated by a loudspeaker, is studied. A strong effect of frequency and amplitude of the incoming flow modulation on the NRP plasma regime is observed. Results are interpreted based on the cumulative effect of the NRP discharges and an analysis of the residence times of fluid particles in the inter-electrode region. © 2016 IOP Publishing Ltd.

  14. Influence of air flow parameters on nanosecond repetitively pulsed discharges in a pin-annular electrode configuration

    KAUST Repository

    Heitz, Sylvain A; Moeck, Jonas P; Schuller, Thierry; Veynante, Denis; Lacoste, Deanna

    2016-01-01

    The effect of various air flow parameters on the plasma regimes of nanosecond repetitively pulsed (NRP) discharges is investigated at atmospheric pressure. The two electrodes are in a pin-annular configuration, transverse to the mean flow. The voltage pulses have amplitudes up to 15 kV, a duration of 10 ns and a repetition frequency ranging from 15 to 30 kHz. The NRP corona to NRP spark (C-S) regime transition and the NRP spark to NRP corona (S-C) regime transition are investigated for different steady and harmonically oscillating flows. First, the strong effect of a transverse flow on the C-S and S-C transitions, as reported in previous studies, is verified. Second, it is shown that the azimuthal flow imparted by a swirler does not affect the regime transition voltages. Finally, the influence of low frequency harmonic oscillations of the air flow, generated by a loudspeaker, is studied. A strong effect of frequency and amplitude of the incoming flow modulation on the NRP plasma regime is observed. Results are interpreted based on the cumulative effect of the NRP discharges and an analysis of the residence times of fluid particles in the inter-electrode region. © 2016 IOP Publishing Ltd.

  15. Modified distribution parameter for churn-turbulent flows in large diameter channels

    Energy Technology Data Exchange (ETDEWEB)

    Schlegel, J.P., E-mail: jschlege@purdue.edu; Macke, C.J.; Hibiki, T.; Ishii, M.

    2013-10-15

    Highlights: • Void fraction data collected in pipe sizes up to 0.304 m using impedance void meters. • Flow conditions extend to transition between churn-turbulent and annular flow. • Flow regime identification results agree with previous studies. • A new model for the distribution parameter in churn-turbulent flow is proposed. -- Abstract: Two phase flows in large diameter channels are important in a wide range of industrial applications, but especially in analysis of nuclear reactor safety for the prediction of BWR behavior and safety analysis in PWRs. To remedy an inability of current drift-flux models to accurately predict the void fraction in churn-turbulent flows in large diameter pipes, extensive experiments have been performed in pipes with diameters of 0.152 m, 0.203 m and 0.304 m to collect area-averaged void fraction data using electrical impedance void meters. The standard deviation and skewness of the impedance meter signal have been used to characterize the flow regime and confirm previous flow regime transition results. By treating churn-turbulent flow as a transition between cap-bubbly dispersed flow and annular separated flow and using a linear ramp, the distribution parameter has been modified for churn-turbulent flow. The modified distribution parameter has been evaluated through comparison of the void fraction predicted by the drift-flux model and the measured void fraction.

  16. Modified distribution parameter for churn-turbulent flows in large diameter channels

    International Nuclear Information System (INIS)

    Schlegel, J.P.; Macke, C.J.; Hibiki, T.; Ishii, M.

    2013-01-01

    Highlights: • Void fraction data collected in pipe sizes up to 0.304 m using impedance void meters. • Flow conditions extend to transition between churn-turbulent and annular flow. • Flow regime identification results agree with previous studies. • A new model for the distribution parameter in churn-turbulent flow is proposed. -- Abstract: Two phase flows in large diameter channels are important in a wide range of industrial applications, but especially in analysis of nuclear reactor safety for the prediction of BWR behavior and safety analysis in PWRs. To remedy an inability of current drift-flux models to accurately predict the void fraction in churn-turbulent flows in large diameter pipes, extensive experiments have been performed in pipes with diameters of 0.152 m, 0.203 m and 0.304 m to collect area-averaged void fraction data using electrical impedance void meters. The standard deviation and skewness of the impedance meter signal have been used to characterize the flow regime and confirm previous flow regime transition results. By treating churn-turbulent flow as a transition between cap-bubbly dispersed flow and annular separated flow and using a linear ramp, the distribution parameter has been modified for churn-turbulent flow. The modified distribution parameter has been evaluated through comparison of the void fraction predicted by the drift-flux model and the measured void fraction

  17. Assessment of fire prevalence and reduction strategies in Miombo ...

    African Journals Online (AJOL)

    An assessment of the proximate causes, effects and factors contributing to fire prevalence was conducted in three districts covered by miombo woodlands in Eastern Tanzania. Three miombo woodlands under different management regimes and governance structures (central government forest reserve, local government ...

  18. Plasma flow in the DIII-D divertor

    International Nuclear Information System (INIS)

    Boedo, J.A.; Porter, G.D.; Schaffer, M.J.

    1998-07-01

    Indications that flows in the divertor can exhibit complex behavior have been obtained from 2-D modeling but so far remain mostly unconfirmed by experiment. An important feature of flow physics is that of flow reversal. Flow reversal has been predicted analytically and it is expected when the ionization source arising from neutral or impurity ionization in the divertor region is large, creating a high pressure zone. Plasma flows arise to equilibrate the pressure. A radiative divertor regime has been proposed in order to reduce the heat and particle fluxes to the divertor target plates. In this regime, the energy and momentum of the plasma are dissipated into neutral gas introduced in the divertor region, cooling the plasma by collisional, radiative and other atomic processes so that the plasma becomes detached from the target plates. These regimes have been the subject of extensive studies in DIII-D to evaluate their energy and particle transport properties, but only recently it has been proposed that the energy transport over large regions of the divertor must be dominated by convection instead of conduction. It is therefore important to understand the role of the plasma conditions and geometry on determining the region of convection-dominated plasma in order to properly control the heat and particle fluxes to the target plates and hence, divertor performance. The authors have observed complex structures in the deuterium ion flows in the DIII-D divertor. Features observed include reverse flow, convective flow over a large volume of the divertor and stagnant flow. They have measured large gradients in the plasma potential across the separatrix in the divertor and determined that these gradients induce poloidal flows that can potentially affect the particle balance in the divertor

  19. Combined convective heat and airborne pollutant removals in a slot vented enclosure under different flow schemes: Parametric investigations and non unique flow solutions

    International Nuclear Information System (INIS)

    Ren, Xiu-Hong; Hu, Jiang-Tao; Liu, Di; Zhao, Fu-Yun; Li, Xiao-Hong; Wang, Han-Qing

    2016-01-01

    Highlights: • Combined convective heat and airborne transports under different flow schemes. • Natural and forced convection dominated regimes were identified with transition. • Dual solution branches were sustained for the transitional mixing flow scheme. • Rest solutions evolving from motionless flows coincided with other solution branch. • Heat and species lines were presented to delineate heat and mass transport structures. - Abstract: This paper reports a numerical study of mixed convection on a heated and polluted strip within a slot ventilated enclosure in which the displacement and mixing flow schemes are considered. Contours of streamfunction, heatfunction, and massfunction are presented to clearly scrutinize the mechanism of heat and airborne pollutant transports. For the displacement flow scheme, thermal Nusselt and pollutant Sherwood numbers under different Reynolds numbers remain almost constant as the value of Gr/Re 2 decreases down to the regime of forced convection dominated. However, as Ar increases up to the regime of natural convection dominated, both Nu and Sh increase sharply with Ar (Gr/Re 2 ). Similar trends could be observed for the situation of mixing ventilated flow scheme. In the mixing scheme, non unique steady flow solutions could be observed for the range of transitional flow regime. Upward solutions, downward solutions and rest solutions have been exemplified with varying Gr/Re 2 . Dual solution branches could be sustained at the range of 39.0 ≤ Gr/Re 2  ≤ 6.0 × 10 3 , while the rest solutions obtained from rest states were completely coinciding with former continuous solutions. The present work could be significant for the natural optimization and passive control of heat and pollutant removals from the electronic boxes or building enclosures.

  20. Organizing Environmental Flow Frameworks to Meet Hydropower Mitigation Needs

    Science.gov (United States)

    McManamay, Ryan A.; Brewer, Shannon K.; Jager, Henriette I.; Troia, Matthew J.

    2016-09-01

    The global recognition of the importance of natural flow regimes to sustain the ecological integrity of river systems has led to increased societal pressure on the hydropower industry to change plant operations to improve downstream aquatic ecosystems. However, a complete reinstatement of natural flow regimes is often unrealistic when balancing water needs for ecosystems, energy production, and other human uses. Thus, stakeholders must identify a prioritized subset of flow prescriptions that meet ecological objectives in light of realistic constraints. Yet, isolating aspects of flow regimes to restore downstream of hydropower facilities is among the greatest challenges of environmental flow science due, in part, to the sheer volume of available environmental flow tools in conjunction with complex negotiation-based regulatory procedures. Herein, we propose an organizational framework that structures information and existing flow paradigms into a staged process that assists stakeholders in implementing environmental flows for hydropower facilities. The framework identifies areas where regulations fall short of the needed scientific process, and provide suggestions for stakeholders to ameliorate those situations through advanced preparation. We highlight the strengths of existing flow paradigms in their application to hydropower settings and suggest when and where tools are most applicable. Our suggested framework increases the effectiveness and efficiency of the e-flow implementation process by rapidly establishing a knowledge base and decreasing uncertainty so more time can be devoted to filling knowledge gaps. Lastly, the framework provides the structure for a coordinated research agenda to further the science of environmental flows related to hydropower environments.

  1. A Regime Diagram for Autoignition of Homogeneous Reactant Mixtures with Turbulent Velocity and Temperature Fluctuations

    KAUST Repository

    Im, Hong G.

    2015-04-02

    A theoretical scaling analysis is conducted to propose a diagram to predict weak and strong ignition regimes for a compositionally homogeneous reactant mixture with turbulent velocity and temperature fluctuations. The diagram provides guidance on expected ignition behavior based on the thermo-chemical properties of the mixture and the flow/scalar field conditions. The analysis is an extension of the original Zeldovich’s analysis by combining the turbulent flow and scalar characteristics in terms of the characteristic Damköhler and Reynolds numbers of the system, thereby providing unified and comprehensive understanding of the physical and chemical mechanisms controlling ignition characteristics. Estimated parameters for existing experimental measurements in a rapid compression facility show that the regime diagram predicts the observed ignition characteristics with good fidelity.

  2. A Regime Diagram for Autoignition of Homogeneous Reactant Mixtures with Turbulent Velocity and Temperature Fluctuations

    KAUST Repository

    Im, Hong G.; Pal, Pinaki; Wooldridge, Margaret S.; Mansfield, Andrew B.

    2015-01-01

    A theoretical scaling analysis is conducted to propose a diagram to predict weak and strong ignition regimes for a compositionally homogeneous reactant mixture with turbulent velocity and temperature fluctuations. The diagram provides guidance on expected ignition behavior based on the thermo-chemical properties of the mixture and the flow/scalar field conditions. The analysis is an extension of the original Zeldovich’s analysis by combining the turbulent flow and scalar characteristics in terms of the characteristic Damköhler and Reynolds numbers of the system, thereby providing unified and comprehensive understanding of the physical and chemical mechanisms controlling ignition characteristics. Estimated parameters for existing experimental measurements in a rapid compression facility show that the regime diagram predicts the observed ignition characteristics with good fidelity.

  3. External Shocks and Banking Crises in Developing Countries: Does the Exchange Rate Regime Matter?

    OpenAIRE

    Chandima Mendis

    2002-01-01

    This paper examines some determinants of banking crises in developing economies. Specifically, the effects of terms of trade shocks and capital flows are analyzed. The choice of the nominal exchange rate regime is found to be a crucial factor in the way various shocks are transmitted through the monetary sector. A logit model is used on panel data and preliminary results indicate that countries with flexible regimes were able to lessen the impact of external shocks on the domestic economy. Th...

  4. Secondary flow structures under stent-induced perturbations for cardiovascular flow in a curved artery model

    International Nuclear Information System (INIS)

    Glenn, Autumn L.; Bulusu, Kartik V.; Shu Fangjun; Plesniak, Michael W.

    2012-01-01

    Secondary flows within curved arteries with unsteady forcing result from amplified centrifugal instabilities and are expected to be driven by the rapid accelerations and decelerations inherent in physiological waveforms. These secondary flows may also affect the function of curved arteries through pro-atherogenic wall shear stresses, platelet residence time and other vascular response mechanisms. Planar PIV measurements were performed under multi-harmonic non-zero-mean and physiological carotid artery waveforms at various locations in a rigid bent-pipe curved artery model. Results revealed symmetric counter-rotating vortex pairs that developed during the acceleration phases of both multi-harmonic and physiological waveforms. An idealized stent model was placed upstream of the bend, which initiated flow perturbations under physiological inflow conditions. Changes in the secondary flow structures were observed during the systolic deceleration phase (t/T ≈ 0.20–0.50). Proper Orthogonal Decomposition (POD) analysis of the flow morphologies under unsteady conditions indicated similarities in the coherent secondary-flow structures and correlation with phase-averaged velocity fields. A regime map was created that characterizes the kaleidoscope of vortical secondary flows with multiple vortex pairs and interesting secondary flow morphologies. This regime map in the curved artery model was created by plotting the secondary Reynolds number against another dimensionless acceleration-based parameter marking numbered regions of vortex pairs.

  5. Secondary flow structures under stent-induced perturbations for cardiovascular flow in a curved artery model

    Energy Technology Data Exchange (ETDEWEB)

    Glenn, Autumn L.; Bulusu, Kartik V. [Department of Mechanical and Aerospace Engineering, George Washington University, 801 22nd Street, NW., Washington, DC 20052 (United States); Shu Fangjun [Department of Mechanical and Aerospace Engineering, New Mexico State University, MSC 3450, P.O. Box 30001, Las Cruces, NM 88003-8001 (United States); Plesniak, Michael W., E-mail: plesniak@gwu.edu [Department of Mechanical and Aerospace Engineering, George Washington University, 801 22nd Street, NW., Washington, DC 20052 (United States)

    2012-06-15

    Secondary flows within curved arteries with unsteady forcing result from amplified centrifugal instabilities and are expected to be driven by the rapid accelerations and decelerations inherent in physiological waveforms. These secondary flows may also affect the function of curved arteries through pro-atherogenic wall shear stresses, platelet residence time and other vascular response mechanisms. Planar PIV measurements were performed under multi-harmonic non-zero-mean and physiological carotid artery waveforms at various locations in a rigid bent-pipe curved artery model. Results revealed symmetric counter-rotating vortex pairs that developed during the acceleration phases of both multi-harmonic and physiological waveforms. An idealized stent model was placed upstream of the bend, which initiated flow perturbations under physiological inflow conditions. Changes in the secondary flow structures were observed during the systolic deceleration phase (t/T Almost-Equal-To 0.20-0.50). Proper Orthogonal Decomposition (POD) analysis of the flow morphologies under unsteady conditions indicated similarities in the coherent secondary-flow structures and correlation with phase-averaged velocity fields. A regime map was created that characterizes the kaleidoscope of vortical secondary flows with multiple vortex pairs and interesting secondary flow morphologies. This regime map in the curved artery model was created by plotting the secondary Reynolds number against another dimensionless acceleration-based parameter marking numbered regions of vortex pairs.

  6. Characterization of bio-inspired hair flow sensors for oscillatory airflows: techniques to measure the response for both flow and pressure

    NARCIS (Netherlands)

    Droogendijk, H.; Dagamseh, A.M.K.; Sanders, Remco G.P.; Yntema, Doekle Reinder; Krijnen, Gijsbertus J.M.

    2014-01-01

    Hair sensors for oscillatory airflow, operating in the regime of bulk flow, particle velocity or both, can be characterized by several methods. In this work, we discuss harmonic measurements on MEMS hair flow sensors. To characterize this type of flow sensor the use of three different types of

  7. From gas dynamics with large friction to gradient flows describing diffusion theories

    KAUST Repository

    Lattanzio, Corrado

    2016-12-09

    We study the emergence of gradient flows in Wasserstein distance as high friction limits of an abstract Euler flow generated by an energy functional. We develop a relative energy calculation that connects the Euler flow to the gradient flow in the diffusive limit regime. We apply this approach to prove convergence from the Euler-Poisson system with friction to the Keller-Segel system in the regime that the latter has smooth solutions. The same methodology is used to establish convergence from the Euler-Korteweg theory with monotone pressure laws to the Cahn-Hilliard equation.

  8. From gas dynamics with large friction to gradient flows describing diffusion theories

    KAUST Repository

    Lattanzio, Corrado; Tzavaras, Athanasios

    2016-01-01

    We study the emergence of gradient flows in Wasserstein distance as high friction limits of an abstract Euler flow generated by an energy functional. We develop a relative energy calculation that connects the Euler flow to the gradient flow in the diffusive limit regime. We apply this approach to prove convergence from the Euler-Poisson system with friction to the Keller-Segel system in the regime that the latter has smooth solutions. The same methodology is used to establish convergence from the Euler-Korteweg theory with monotone pressure laws to the Cahn-Hilliard equation.

  9. Hydrodynamics of multi-sized particles in stable regime of a swirling bed

    Energy Technology Data Exchange (ETDEWEB)

    Miin, Chin Swee; Sulaiman, Shaharin Anwar; Raghavan, Vijay Raj; Heikal, Morgan Raymond; Naz, Muhammad Yasin [Universiti Teknologi PETRONAS, Perak (Malaysia)

    2015-11-15

    Using particle imaging velocimetry (PIV), we observed particle motion within the stable operating regime of a swirling fluidized bed with an annular blade distributor. This paper presents velocity profiles of particle flow in an effort to determine effects from blade angle, particle size and shape and bed weight on characteristics of a swirling fluidized bed. Generally, particle velocity increased with airflow rate and shallow bed height, but decreased with bed weight. A 3 .deg. increase in blade angle reduced particle velocity by approximately 18%. In addition, particle shape, size and bed weight affected various characteristics of the swirling regime. Swirling began soon after incipience in the form of a supra-linear curve, which is the characteristic of a swirling regime. The relationship between particle and gas velocities enabled us to predict heat and mass transfer rates between gas and particles.

  10. Transition from weak wave turbulence regime to solitonic regime

    Science.gov (United States)

    Hassani, Roumaissa; Mordant, Nicolas

    2017-11-01

    The Weak Turbulence Theory (WTT) is a statistical theory describing the interaction of a large ensemble of random waves characterized by very different length scales. For both weak non-linearity and weak dispersion a different regime is predicted where solitons propagate while keeping their shape unchanged. The question under investigation here is which regime between weak turbulence or soliton gas does the system choose ? We report an experimental investigation of wave turbulence at the surface of finite depth water in the gravity-capillary range. We tune the wave dispersion and the level of nonlinearity by modifying the depth of water and the forcing respectively. We use space-time resolved profilometry to reconstruct the deformed surface of water. When decreasing the water depth, we observe a drastic transition between weak turbulence at the weakest forcing and a solitonic regime at stronger forcing. We characterize the transition between both states by studying their Fourier Spectra. We also study the efficiency of energy transfer in the weak turbulence regime. We report a loss of efficiency of angular transfer as the dispersion of the wave is reduced until the system bifurcates into the solitonic regime. This project has recieved funding from the European Research Council (ERC, Grant Agreement No. 647018-WATU).

  11. Characterizing dynamic hysteresis and fractal statistics of chaotic two-phase flow and application to fuel cells

    International Nuclear Information System (INIS)

    Burkholder, Michael B.; Litster, Shawn

    2016-01-01

    In this study, we analyze the stability of two-phase flow regimes and their transitions using chaotic and fractal statistics, and we report new measurements of dynamic two-phase pressure drop hysteresis that is related to flow regime stability and channel water content. Two-phase flow dynamics are relevant to a variety of real-world systems, and quantifying transient two-phase flow phenomena is important for efficient design. We recorded two-phase (air and water) pressure drops and flow images in a microchannel under both steady and transient conditions. Using Lyapunov exponents and Hurst exponents to characterize the steady-state pressure fluctuations, we develop a new, measurable regime identification criteria based on the dynamic stability of the two-phase pressure signal. We also applied a new experimental technique by continuously cycling the air flow rate to study dynamic hysteresis in two-phase pressure drops, which is separate from steady-state hysteresis and can be used to understand two-phase flow development time scales. Using recorded images of the two-phase flow, we show that the capacitive dynamic hysteresis is related to channel water content and flow regime stability. The mixed-wettability microchannel and in-channel water introduction used in this study simulate a polymer electrolyte fuel cell cathode air flow channel.

  12. Characterizing dynamic hysteresis and fractal statistics of chaotic two-phase flow and application to fuel cells

    Energy Technology Data Exchange (ETDEWEB)

    Burkholder, Michael B.; Litster, Shawn, E-mail: litster@andrew.cmu.edu [Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States)

    2016-05-15

    In this study, we analyze the stability of two-phase flow regimes and their transitions using chaotic and fractal statistics, and we report new measurements of dynamic two-phase pressure drop hysteresis that is related to flow regime stability and channel water content. Two-phase flow dynamics are relevant to a variety of real-world systems, and quantifying transient two-phase flow phenomena is important for efficient design. We recorded two-phase (air and water) pressure drops and flow images in a microchannel under both steady and transient conditions. Using Lyapunov exponents and Hurst exponents to characterize the steady-state pressure fluctuations, we develop a new, measurable regime identification criteria based on the dynamic stability of the two-phase pressure signal. We also applied a new experimental technique by continuously cycling the air flow rate to study dynamic hysteresis in two-phase pressure drops, which is separate from steady-state hysteresis and can be used to understand two-phase flow development time scales. Using recorded images of the two-phase flow, we show that the capacitive dynamic hysteresis is related to channel water content and flow regime stability. The mixed-wettability microchannel and in-channel water introduction used in this study simulate a polymer electrolyte fuel cell cathode air flow channel.

  13. Drop coalescence and liquid flow in a single Plateau border

    Science.gov (United States)

    Cohen, Alexandre; Fraysse, Nathalie; Raufaste, Christophe

    2015-05-01

    We report a comprehensive study of the flow of liquid triggered by injecting a droplet into a liquid foam microchannel, also called a Plateau border. This drop-injected experiment reveals an intricate dynamics for the liquid redistribution, with two contrasting regimes observed, ruled either by inertia or viscosity. We devoted a previous study [A. Cohen et al., Phys. Rev. Lett. 112, 218303 (2014), 10.1103/PhysRevLett.112.218303] to the inertial imbibition regime, unexpected at such small length scales. Here we report other features of interest of the drop-injected experiment, related to the coalescence of the droplet with the liquid microchannel, to both the inertial and viscous regimes, and to the occurrence of liquid flow through the soap films as well as effects of the interfacial rheology. The transition between the two regimes is investigated and qualitatively accounted for. The relevance of our results to liquid foam drainage is tackled by considering the flow of liquid at the nodes of the network of interconnected microchannels. Extensions of our study to liquid foams are discussed.

  14. Suitability of an MRMCE (multi-resolution minimum cross entropy) algorithm for online monitoring of a two-phase flow

    International Nuclear Information System (INIS)

    Wang, Qi; Wang, Huaxiang; Xin, Shan

    2011-01-01

    The flow regimes are important characteristics to describe two-phase flows, and measurement of two-phase flow parameters is becoming increasingly important in many industrial processes. Computerized tomography (CT) has been applied to two-phase/multi-phase flow measurement in recent years. Image reconstruction of CT often involves repeatedly solving large-dimensional matrix equations, which are computationally expensive, especially for the case of online flow regime identification. In this paper, minimum cross entropy reconstruction based on multi-resolution processing (MRMCE) is presented for oil–gas two-phase flow regime identification. A regularized MCE solution is obtained using the simultaneous multiplicative algebraic reconstruction technique (SMART) at a coarse resolution level, where important information on the reconstructed image is contained. Then, the solution in the finest resolution is obtained by inverse fast wavelet transformation. Both computer simulation and static/dynamic experiments were carried out for typical flow regimes. Results obtained indicate that the proposed method can dramatically reduce the computational time and improve the quality of the reconstructed image with suitable decomposition levels compared with the single-resolution maximum likelihood expectation maximization (MLEM), alternating minimization (AM), Landweber, iterative least square technique (ILST) and minimum cross entropy (MCE) methods. Therefore, the MRMCE method is suitable for identification of dynamic two-phase flow regimes

  15. Droplet formation in microfluidic T-junction generators operating in the transitional regime. I. Experimental observations.

    Science.gov (United States)

    Glawdel, Tomasz; Elbuken, Caglar; Ren, Carolyn L

    2012-01-01

    This is the first part of a two-part study on the generation of droplets at a microfluidic T-junction operating in the transition regime where confinement of the droplet creates a large squeezing pressure that influences droplet formation. In this regime, the operation of the T-junction depends on the geometry of the intersection (height-to-width ratio, inlet width ratio), capillary number, flow ratio, and viscosity ratio of the two phases. Here in paper I we presented our experimental observations through the analysis of high-speed videos of the droplet formation process. Various parameters are tracked during the formation cycle such as the shape of the droplet (penetration depth and neck), interdroplet spacing, production rate, and flow of both phases across several T-junction designs and flow conditions. Generally, the formation process is defined by a two-stage model consisting of an initial filling stage followed by a necking stage. However, video evidence suggests the inclusion of a third stage, which we term the lag stage, at the beginning of the formation process that accounts for the retraction of the interface back into the injection channel after detachment. Based on the observations made in this paper, a model is developed to describe the formation process in paper II, which can be used to understand the design and operation of T-junction generators in the transition regime.

  16. Computational characterization of ignition regimes in a syngas/air mixture with temperature fluctuations

    KAUST Repository

    Pal, Pinaki

    2016-07-27

    Auto-ignition characteristics of compositionally homogeneous reactant mixtures in the presence of thermal non-uniformities and turbulent velocity fluctuations were computationally investigated. The main objectives were to quantify the observed ignition characteristics and numerically validate the theory of the turbulent ignition regime diagram recently proposed by Im et al. 2015 [29] that provides a framework to predict ignition behavior . a priori based on the thermo-chemical properties of the reactant mixture and initial flow and scalar field conditions. Ignition regimes were classified into three categories: . weak (where deflagration is the dominant mode of fuel consumption), . reaction-dominant strong, and . mixing-dominant strong (where volumetric ignition is the dominant mode of fuel consumption). Two-dimensional (2D) direct numerical simulations (DNS) of auto-ignition in a lean syngas/air mixture with uniform mixture composition at high-pressure, low-temperature conditions were performed in a fixed volume. The initial conditions considered two-dimensional isotropic velocity spectrums, temperature fluctuations and localized thermal hot spots. A number of parametric test cases, by varying the characteristic turbulent Damköhler and Reynolds numbers, were investigated. The evolution of the auto-ignition phenomena, pressure rise, and heat release rate were analyzed. In addition, combustion mode analysis based on front propagation speed and computational singular perturbation (CSP) was applied to characterize the auto-ignition phenomena. All results supported that the observed ignition behaviors were consistent with the expected ignition regimes predicted by the theory of the regime diagram. This work provides new high-fidelity data on syngas ignition characteristics over a broad range of conditions and demonstrates that the regime diagram serves as a predictive guidance in the understanding of various physical and chemical mechanisms controlling auto

  17. Numerical study of flame structure in the mild combustion regime

    Directory of Open Access Journals (Sweden)

    Mardani Amir

    2015-01-01

    Full Text Available In this paper, turbulent non-premixed CH4+H2 jet flame issuing into a hot and diluted co-flow air is studied numerically. This flame is under condition of the moderate or intense low-oxygen dilution (MILD combustion regime and related to published experimental data. The modelling is carried out using the EDC model to describe turbulence-chemistry interaction. The DRM-22 reduced mechanism and the GRI2.11 full mechanism are used to represent the chemical reactions of H2/methane jet flame. The flame structure for various O2 levels and jet Reynolds numbers are investigated. The results show that the flame entrainment increases by a decrease in O2 concentration at air side or jet Reynolds number. Local extinction is seen in the upstream and close to the fuel injection nozzle at the shear layer. It leads to the higher flame entertainment in MILD regime. The turbulence kinetic energy decay at centre line of jet decreases by an increase in O2 concentration at hot Co-flow. Also, increase in jet Reynolds or O2 level increases the mixing rate and rate of reactions.

  18. Identification of flow regimes and heat transfer modes in Angra-2 core during the simulation of the small break loss of coolant accident of 250 cm2 in the cold leg of primary loop using RELAP5 code

    International Nuclear Information System (INIS)

    Borges, Eduardo M.; Sabundjian, Gaiane

    2017-01-01

    The aim of this paper is to identify the flow regimes, the heat transfer modes, and the correlations used by RELAP5/MOD3.2. gamma code in Angra-2 during the Small-Break Loss-of-Coolant Accident (SBLOCA) with a 250cm 2 of rupture area in the cold leg of primary loop. The Chapter 15 of the Final Safety Analysis Report of Angra-2 (FSAR-A2) reports this specific kind of accident. The results from this work demonstrated the several flow regimes and heat transfer modes that can be present in the core of Angra-2 during the postulated accident. The results obtained for Angra-2 nuclear reactor core during the postulated accident were satisfactory when compared with the FSAR-A2. Additionally, the results showed the correct actuation of the ECCS guaranteeing the integrity of the reactor core. (author)

  19. Critical state flow rules for CFD simulations of wet granular flows

    NARCIS (Netherlands)

    Schwarze, R.; Gladkyy, A.; Luding, Stefan; E. Onate M. Bischoff, E. Ramm; P. Wriggers,

    2013-01-01

    First rheological investigation results of weakly wet granular media are presented. The materials have been examined experimentally and numerically in well- defined shear configurations in steady state, in the intermediate flow regime. For the experiments, a Searl-type ring shear cell with rotating

  20. Transition from condensation-induced counter-current flow to dispersed flow

    International Nuclear Information System (INIS)

    Gale, J.; Tiselj, I.

    2004-01-01

    Model of transition from the horizontally stratified condensation-induced counter-current flow to slug flow has been analyzed with computer code WAHA and compared to the experimental data obtained in the steamline of the PMK2 test facility of Hungarian Atomic Energy Institute. The experiment was performed in the steamline initially filled with hot vapor that was gradually flooded with cold liquid. Successful simulation of the condensation-induced water hammer that follows the transition, requires accurate description of the horizontally stratified and slug flow regimes and criteria for transition between both flow regimes. Current version of the WAHA code, not verified for the condensation induced type of the water hammer, predicts the water-hammer pressure peak that exceeds 600 bar, while the measured pressure is p m = 170 ± 50 bar. Sensitivity analysis of the inter-phase exchange terms and transition conditions, pointed to the most important closure relations for heat, mass and momentum transfer. The main conclusion of the analysis is large uncertainty of the simulations: minor modification of the crucial correlations can lead to a severe water-hammer in one case, or to the 'calm' transient without pressure peaks in the other case. Large uncertainty is observed in experiments. The same simulation was performed also with RELAP5 code. However, no water hammer was predicted. (author)

  1. Intermittent Flow Regimes in a Transonic Fan Airfoil Cascade

    Directory of Open Access Journals (Sweden)

    J. Lepicovsky

    2004-01-01

    velocity.To date, this flow behavior has only been observed in a linear transonic cascade. Further research is necessary to confirm this phenomenon occurs in actual transonic fans and is not the by-product of an endwall restricted linear cascade.

  2. Three novel tokamak plasma regimes in TFTR

    International Nuclear Information System (INIS)

    Furth, H.P.

    1985-10-01

    Aside from extending ''standard'' ohmic and neutral beam heating studies to advanced plasma parameters, TFTR has encountered a number of special plasma regimes that have the potential to shed new light on the physics of tokamak confinement and the optimal design of future D-T facilities: (1) High-powered, neutral beam heating at low plasma densities can maintain a highly reactive hot-ion population (with quasi-steady-state beam fueling and current drive) in a tokamak configuration of modest bulk-plasma confinement requirements. (2) Plasma displacement away from limiter contact lends itself to clarification of the role of edge-plasma recycling and radiation cooling within the overall pattern of tokamak heat flow. (3) Noncentral auxiliary heating (with a ''hollow'' power-deposition profile) should serve to raise the central tokamak plasma temperature without deterioration of central region confinement, thus facilitating the study of alpha-heating effects in TFTR. The experimental results of regime (3) support the theory that tokamak profile consistency is related to resistive kink stability and that the global energy confinement time is determined by transport properties of the plasma edge region

  3. Overview of zonal flow physics

    International Nuclear Information System (INIS)

    Diamond, P.H.; Itoh, K.; Itoh, S.-I.; Hahm, T.S.

    2005-01-01

    Zonal flows, by which we mean azimuthally symmetric band-like shear flows, are ubiquitous phenomena in nature and the laboratory. It is now widely recognized that zonal flows are a key constituent in virtually all cases and regimes of drift wave turbulence, indeed, so much so that this classic problem is now frequently referred to as 'drift wave-zonal flow turbulence'. In this theory overview, we present new viewpoints and unifying concepts which facilitate understanding of zonal flow physics, via theory, computation and their confrontation with the results of laboratory experiment. Special emphasis is placed on identifying avenues for further progress. (author)

  4. Two-phase flow in short horizontal rectangular microchannels with a height of 300 μm

    Science.gov (United States)

    Chinnov, E. A.; Ron'shin, F. V.; Kabov, O. A.

    2015-09-01

    The two-phase flow in a narrow short horizontal channel with a rectangular cross section is studied experimentally. The channel has a width of 10, 20, or 30 mm and a height of 300 μm. The specifics of formation of such two-phase flows are investigated. It is demonstrated that the regions of bubble and churn flow regimes grow and constrain the region of jet flow as the channel gets wider. The boundaries of the regions of annular and stratified flow regimes remain almost unaltered.

  5. Gender inequalities in mental wellbeing in 26 European countries: do welfare regimes matter?

    Science.gov (United States)

    Dreger, Stefanie; Gerlinger, Thomas; Bolte, Gabriele

    2016-10-01

    Nature and extent of welfare regimes and social policies are important determinants of health and health inequalities. This study examines the association of gender and mental wellbeing in European countries and investigates whether type of welfare regime plays a role in this association. Data of 19 366 women and 14 338 men of the third round of the European Quality of Life Survey (2011-12) was used to analyse mental wellbeing, assessed by the World Health Organization 5-Mental Wellbeing Index. Multilevel logistic regression analyses were performed to analyse the association between gender and good mental wellbeing first at country-level, and secondly the between country variation was analysed and welfare regimes were included as explanatory variables. We observed cross-national variation in good mental wellbeing. At country levels gender inequalities in good mental wellbeing were observed in 7 out of 26 countries. In analyses considering all countries together gender inequalities in good mental wellbeing were identified independent of further individual socio-demographic variables and independent of the welfare regimes that people lived in [women vs. men: OR = 0.76; (95% CI = 0.71-0.81)]. Gender inequalities in good mental wellbeing were not modified by welfare regimes. There are cross-national differences in good mental wellbeing between European countries. Gender inequalities with a lower prevalence of good mental wellbeing among women are common in European countries. This study suggests that welfare regimes do not modify these gender inequalities in mental wellbeing. © The Author 2016. Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved.

  6. Transition from slug to annular flow in horizontal air-water flow

    International Nuclear Information System (INIS)

    Reismann, J.; John, H.; Seeger, W.

    1981-11-01

    The transition from slug to annular flow in horizontal air-water and steam-water flow was investigated. Test sections of 50; 66.6 and 80 mm ID were used. The system pressure was 0.2 and 0.5 MPa in the air-water experiments and 2.5; 5; 7.5 and 10 MPa in the steam-water experiments. For flow pattern detection local impedance probes were used. This method was compared in a part of the experiments with differential pressure and gamma-beam measurements. The flow regime boundary is shifting strongly to smaller values of the superficial gas velocity with increasing pressure. Correlations from literature fit unsatisfactorily the experimental results. A new correlation is presented. (orig.) [de

  7. Tile drainage as karst: Conduit flow and diffuse flow in a tile-drained watershed

    Science.gov (United States)

    Schilling, K.E.; Helmers, M.

    2008-01-01

    The similarity of tiled-drained watersheds to karst drainage basins can be used to improve understanding of watershed-scale nutrient losses from subsurface tile drainage networks. In this study, short-term variations in discharge and chemistry were examined from a tile outlet collecting subsurface tile flow from a 963 ha agricultural watershed. Study objectives were to apply analytical techniques from karst springs to tile discharge to evaluate water sources and estimate the loads of agricultural pollutants discharged from the tile with conduit, intermediate and diffuse flow regimes. A two-member mixing model using nitrate, chloride and specific conductance was used to distinguish rainwater versus groundwater inputs. Results indicated that groundwater comprised 75% of the discharge for a three-day storm period and rainwater was primarily concentrated during the hydrograph peak. A contrasting pattern of solute concentrations and export loads was observed in tile flow. During base flow periods, tile flow consisted of diffuse flow from groundwater sources and contained elevated levels of nitrate, chloride and specific conductance. During storm events, suspended solids and pollutants adhered to soil surfaces (phosphorus, ammonium and organic nitrogen) were concentrated and discharged during the rapid, conduit flow portion of the hydrograph. During a three-day period, conduit flow occurred for 5.6% of the time but accounted for 16.5% of the total flow. Nitrate and chloride were delivered primarily with diffuse flow (more than 70%), whereas 80-94% of total suspended sediment, phosphorus and ammonium were exported with conduit and intermediate flow regimes. Understanding the water sources contributing to tile drainage and the manner by which pollutant discharge occurs from these systems (conduit, intermediate or diffuse flow) may be useful for designing, implementing and evaluating non-point source reduction strategies in tile-drained landscapes. ?? 2007 Elsevier B.V. All

  8. Experimental study on flow pattern transitions for inclined two-phase flow

    Energy Technology Data Exchange (ETDEWEB)

    Kwak, Nam Yee; Lee, Jae Young [Handong Univ., Pohang (Korea, Republic of); Kim, Man Woong [Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of)

    2007-07-01

    In this paper, experimental data on flow pattern transition of inclination angles from 0-90 are presented. A test section is constructed 2 mm long and I.D 1inch using transparent material. The test section is supported by aluminum frame that can be placed with any arbitrary inclined angles. The air-water two-phase flow is observed at room temperature and atmospheric condition using both high speed camera and void impedance meter. The signal is sampled with sampling rate 1kHz and is analyzed under fully-developed condition. Based on experimental data, flow pattern maps are made for various inclination angles. As increasing the inclination angels from 0 to 90, the flow pattern transitions on the plane jg-jf are changed, such as stratified flow to plug flow or slug flow or plug flow to bubbly flow. The transition lines between pattern regimes are moved or sometimes disappeared due to its inclined angle.

  9. Experimental investigation of the two-phase flow in a short horizontal microchannel with the height of 50 μm and width of 20 mm

    Directory of Open Access Journals (Sweden)

    Ronshin Fedor

    2017-01-01

    Full Text Available The two-phase flow has been studied experimentally in a short horizontal microchannel with the height of 50 μm and width of 20 mm. The following regimes of two-phase flows have been registered: jet, bubble, stratified, annular, and churn. The regime map of two-phase flow has been plotted. This map has been compared with the regime map plotted for the channels of larger cross-section; it is shown that the height and width of a rectangular channel has a significant effect on the boundaries between flow regimes.

  10. CFD simulation of fluid dynamic and biokinetic processes within activated sludge reactors under intermittent aeration regime.

    Science.gov (United States)

    Sánchez, F; Rey, H; Viedma, A; Nicolás-Pérez, F; Kaiser, A S; Martínez, M

    2018-08-01

    Due to the aeration system, biological reactors are the most energy-consuming facilities of convectional WWTPs. Many biological reactors work under intermittent aeration regime; the optimization of the aeration process (air diffuser layout, air flow rate per diffuser, aeration length …) is necessary to ensure an efficient performance; satisfying the effluent requirements with the minimum energy consumption. This work develops a CFD modelling of an activated sludge reactor (ASR) which works under intermittent aeration regime. The model considers the fluid dynamic and biological processes within the ASR. The biological simulation, which is transient, takes into account the intermittent aeration regime. The CFD modelling is employed for the selection of the aeration system of an ASR. Two different aeration configurations are simulated. The model evaluates the aeration power consumption necessary to satisfy the effluent requirements. An improvement of 2.8% in terms of energy consumption is achieved by modifying the air diffuser layout. An analysis of the influence of the air flow rate per diffuser on the ASR performance is carried out. The results show a reduction of 14.5% in the energy consumption of the aeration system when the air flow rate per diffuser is reduced. The model provides an insight into the aeration inefficiencies produced within ASRs. Copyright © 2018 Elsevier Ltd. All rights reserved.

  11. Heat transfer in vapour-liquid flow of carbon dioxide

    International Nuclear Information System (INIS)

    Yagov, V.V.

    2009-01-01

    During the last decade a number of studies of boiling heat transfer in carbon dioxide notably increase. As a field of CO 2 practical using corresponds to high reduced pressures, and a majority of available experimental data on CO 2 flow boiling even in submillimetric channels relate to turbulent liquid flow regimes, a possibility arises to develop sufficiently general method for HTC predicting. Under the above conditions nucleate boiling occurs up to rather high flow quality, even in annular flow regime due to extremely small size of an equilibrium vapour bubble. This conclusion is in agreement with the available experimental data. The predicting equation for nucleate boiling heat transfer developed by the present author in 1988 is valid for any nonmetallic liquid. A contribution of forced convection in heat transfer is calculated according to the Petukhov et al. equation with correction factor, which accounted for an effect of velocity increase due to evaporation. This effect can be essential at relatively small heat fluxes and rather high mass flow rates. The Reynolds analogy and homogeneous model are used in order to account for the convective heat transfer augmentation in two-phase flow. Due to low ratio of liquid and vapour densities at high reduced pressures the homogeneous approximation of two-phase flow seems to be warranted. A total heat transfer coefficient is calculated as an interpolated value of boiling and convective HTCs. The experimental data on CO 2 flow boiling related to regimes before heated wall dryout incipience are in rather good agreement with the calculations. (author)

  12. Regime change?

    International Nuclear Information System (INIS)

    Pilat, Joseph F.; Budlong-Sylvester, K.W.

    2004-01-01

    Following the 1998 nuclear tests in South Asia and later reinforced by revelations about North Korean and Iraqi nuclear activities, there has been growing concern about increasing proliferation dangers. At the same time, the prospects of radiological/nuclear terrorism are seen to be rising - since 9/11, concern over a proliferation/terrorism nexus has never been higher. In the face of this growing danger, there are urgent calls for stronger measures to strengthen the current international nuclear nonproliferation regime, including recommendations to place civilian processing of weapon-useable material under multinational control. As well, there are calls for entirely new tools, including military options. As proliferation and terrorism concerns grow, the regime is under pressure and there is a temptation to consider fundamental changes to the regime. In this context, this paper will address the following: Do we need to change the regime centered on the Treaty on the Nonproliferation of Nuclear Weapons (NPT) and the International Atomic Energy Agency (IAEA)? What improvements could ensure it will be the foundation for the proliferation resistance and physical protection needed if nuclear power grows? What will make it a viable centerpiece of future nonproliferation and counterterrorism approaches?

  13. An evaluation of the relations between flow regime components, stream characteristics, species traits and meta-demographic rates of warmwater stream fishes: Implications for aquatic resource management

    Science.gov (United States)

    Peterson, James T.; Shea, C.P.

    2015-01-01

    Fishery biologists are increasingly recognizing the importance of considering the dynamic nature of streams when developing streamflow policies. Such approaches require information on how flow regimes influence the physical environment and how those factors, in turn, affect species-specific demographic rates. A more cost-effective alternative could be the use of dynamic occupancy models to predict how species are likely to respond to changes in flow. To appraise the efficacy of this approach, we evaluated relative support for hypothesized effects of seasonal streamflow components, stream channel characteristics, and fish species traits on local extinction, colonization, and recruitment (meta-demographic rates) of stream fishes. We used 4 years of seasonal fish collection data from 23 streams to fit multistate, multiseason occupancy models for 42 fish species in the lower Flint River Basin, Georgia. Modelling results suggested that meta-demographic rates were influenced by streamflows, particularly short-term (10-day) flows. Flow effects on meta-demographic rates also varied with stream size, channel morphology, and fish species traits. Small-bodied species with generalized life-history characteristics were more resilient to flow variability than large-bodied species with specialized life-history characteristics. Using this approach, we simplified the modelling framework, thereby facilitating the development of dynamic, spatially explicit evaluations of the ecological consequences of water resource development activities over broad geographic areas. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

  14. Evaluation of steady flow torques and pressure losses in a rotary flow control valve by means of computational fluid dynamics

    International Nuclear Information System (INIS)

    Okhotnikov, Ivan; Noroozi, Siamak; Sewell, Philip; Godfrey, Philip

    2017-01-01

    Highlights: • A novel design of a rotary flow control valve driven by a stepper motor is proposed. • The intended use of the valve in the high flow rate independent metering hydraulic system is suggested. • Pressure drops, steady flow torques of the valve for various flow rates and orifice openings are studied by means of computational fluid dynamics. • The discharge coefficient and flow jet angles dependencies on the orifice opening are obtained. • A design method to decrease the flow forces without reducing the flow rate in single-staged valves is demonstrated. - Abstract: In this paper, a novel design of a rotary hydraulic flow control valve has been presented for high flow rate fluid power systems. High flow rates in these systems account for substantial flow forces acting on the throttling elements of the valves and cause the application of mechanically sophisticated multi-staged servo valves for flow regulation. The suggested design enables utilisation of single-stage valves in power hydraulics operating at high flow rates regimes. A spool driver and auxiliary mechanisms of the proposed valve design were discussed and selection criteria were suggested. Analytical expressions for metering characteristics as well as steady flow torques have been derived. Computational fluid dynamics (CFD) analysis of steady state flow regimes was conducted to evaluate the hydraulic behaviour of the proposed valve. This study represents a special case of an independent metering concept applied to the design of power hydraulic systems with direct proportional valve control operating at flow rates above 150 litres per minute. The result gained using parametric CFD simulations predicted the induced torque and the pressure drops due to a steady flow. Magnitudes of these values prove that by minimising the number of spool's mobile metering surfaces it is possible to reduce the flow-generated forces in the new generation of hydraulic valves proposed in this study

  15. An equation of mean velocity of flow in non uniform regime, its relationship with the dispersion phenomenon as time function and its application to study of water quality

    International Nuclear Information System (INIS)

    Constain Aragon, A.; Lemos Ruiz, R.

    2011-01-01

    It is very well known the basic equation of hydraulics discovered by Antoine de Chezy in 1769, which relates in a quadratic from the mean velocity of flow with the slope of energy line and the hydraulic radius, in a uniform regime. This equation has been the central axis of development of hydro metrics as science that faces the huge challenges of penetrating the knowledge of earths streams every time more contaminated. In virtue of that, its mathematical structure and the relationship with other related formulas have been carefully examined, despite the limitation due to constancy of velocity. Starting from chemical considerations rather than dynamic ones as was used to obtain chezys relationship it is possible to establish a second equation for mean velocity of fluid in a non uniform regime that corresponds to averaged movement of a solute poured to steam. This equation will go to relate in an accurate way several aspects hydraulics and mass transport, sight as a single thing, allowing a vital tool for a depth study of water contaminations. to arrive this equation it was reviewed the foundations of mass transport theory in flows, stating a time dependent nature for coefficient currently used in describing dispersion phenomena allowing to interpret properly certain inconsistencies detected long time ago in this theory. It is presented the detailed results of application of this new approach to a small steam and a larger river in Colombia. (Author) 23 refs.

  16. Analytical flow duration curves for summer streamflow in Switzerland

    Science.gov (United States)

    Santos, Ana Clara; Portela, Maria Manuela; Rinaldo, Andrea; Schaefli, Bettina

    2018-04-01

    This paper proposes a systematic assessment of the performance of an analytical modeling framework for streamflow probability distributions for a set of 25 Swiss catchments. These catchments show a wide range of hydroclimatic regimes, including namely snow-influenced streamflows. The model parameters are calculated from a spatially averaged gridded daily precipitation data set and from observed daily discharge time series, both in a forward estimation mode (direct parameter calculation from observed data) and in an inverse estimation mode (maximum likelihood estimation). The performance of the linear and the nonlinear model versions is assessed in terms of reproducing observed flow duration curves and their natural variability. Overall, the nonlinear model version outperforms the linear model for all regimes, but the linear model shows a notable performance increase with catchment elevation. More importantly, the obtained results demonstrate that the analytical model performs well for summer discharge for all analyzed streamflow regimes, ranging from rainfall-driven regimes with summer low flow to snow and glacier regimes with summer high flow. These results suggest that the model's encoding of discharge-generating events based on stochastic soil moisture dynamics is more flexible than previously thought. As shown in this paper, the presence of snowmelt or ice melt is accommodated by a relative increase in the discharge-generating frequency, a key parameter of the model. Explicit quantification of this frequency increase as a function of mean catchment meteorological conditions is left for future research.

  17. Pain prevalence in hospitalized children

    DEFF Research Database (Denmark)

    Walther-Larsen, S; Pedersen, M T; Friis, S M

    2017-01-01

    admitted the same day. The single most common painful procedure named by the children was needle procedures, such as blood draw and intravenous cannulation. CONCLUSION: This study reveals high pain prevalence in children across all age groups admitted to four Danish university hospitals. The majority......BACKGROUND: Pain management in hospitalized children is often inadequate. The prevalence and main sources of pain in Danish university hospitals is unknown. METHODS: This prospective mixed-method cross-sectional survey took place at four university hospitals in Denmark. We enrolled 570 pediatric...... patients who we asked to report their pain experience and its management during the previous 24 hours. For patients identified as having moderate to severe pain, patient characteristics and analgesia regimes were reviewed. RESULTS: Two hundred and thirteen children (37%) responded that they had experienced...

  18. Pulsatility role in cylinder flow dynamics at low Reynolds number

    KAUST Repository

    Qamar, Adnan; Samtaney, Ravi; Bull, Joseph L.

    2012-01-01

    range of TAL. Two distinct fluid regimes are identified. In both regimes, the size of the separated zone is much greater than the uniform flow case, the onset of separation is function of KC, and the separation vortex collapses rapidly during the last

  19. New modeling and experimental approaches for characterization of two-phase flow interfacial structure

    International Nuclear Information System (INIS)

    Ishii, Mamoru; Sun, Xiaodong

    2004-01-01

    This paper presents new experimental and modeling approaches in characterizing interfacial structures in gas-liquid two-phase flow. For the experiments, two objective approaches are developed to identify flow regimes and to obtain local interfacial structure data. First, a global measurement technique using a non-intrusive ring-type impedance void-meter and a self-organizing neural network is presented to identify the one-dimensional'' flow regimes. In the application of this measurement technique, two methods are discussed, namely, one based on the probability density function of the impedance probe measurement (PDF input method) and the other based on the sorted impedance signals, which is essentially the cumulative probability distribution function of the impedance signals (instantaneous direct signal input method). In the latter method, the identification can be made close to instantaneously since the required signals can be acquired over a very short time period. In addition, a double-sensor conductivity probe can also be used to obtain ''local'' flow regimes by using the instantaneous direct signal input method with the bubble chord length information. Furthermore, a newly designed conductivity probe with multiple double-sensor heads is proposed to obtain ''two-dimensional'' flow regimes across the flow channel. Secondly, a state-of-the-art four-sensor conductivity probe technique has been developed to obtain detailed local interfacial structure information. The four-sensor conductivity probe accommodates the double-sensor probe capability and can be applied in a wide range of flow regimes spanning from bubbly to churn-turbulent flows. The signal processing scheme is developed such that it categorizes the acquired parameters into two groups based on bubble cord length information. Furthermore, for the modeling of the interfacial structure characterization, the interfacial area transport equation proposed earlier has been studied to provide a dynamic and

  20. Wind Regimes in Complex Terrain of the Great Valley of Eastern Tennessee

    Energy Technology Data Exchange (ETDEWEB)

    Birdwell, Kevin R. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2011-05-01

    This research was designed to provide an understanding of physical wind mechanisms within the complex terrain of the Great Valley of Eastern Tennessee to assess the impacts of regional air flow with regard to synoptic and mesoscale weather changes, wind direction shifts, and air quality. Meteorological data from 2008 2009 were analyzed from 13 meteorological sites along with associated upper level data. Up to 15 ancillary sites were used for reference. Two-step complete linkage and K-means cluster analyses, synoptic weather studies, and ambient meteorological comparisons were performed to generate hourly wind classifications. These wind regimes revealed seasonal variations of underlying physical wind mechanisms (forced channeled, vertically coupled, pressure-driven, and thermally-driven winds). Synoptic and ambient meteorological analysis (mixing depth, pressure gradient, pressure gradient ratio, atmospheric and surface stability) suggested up to 93% accuracy for the clustered results. Probabilistic prediction schemes of wind flow and wind class change were developed through characterization of flow change data and wind class succession. Data analysis revealed that wind flow in the Great Valley was dominated by forced channeled winds (45 67%) and vertically coupled flow (22 38%). Down-valley pressure-driven and thermally-driven winds also played significant roles (0 17% and 2 20%, respectively), usually accompanied by convergent wind patterns (15 20%) and large wind direction shifts, especially in the Central/Upper Great Valley. The behavior of most wind regimes was associated with detectable pressure differences between the Lower and Upper Great Valley. Mixing depth and synoptic pressure gradients were significant contributors to wind pattern behavior. Up to 15 wind classes and 10 sub-classes were identified in the Central Great Valley with 67 joined classes for the Great Valley at-large. Two-thirds of Great Valley at-large flow was defined by 12 classes. Winds

  1. Gap Flows through Idealized Topography. Part I: Forcing by Large-Scale Winds in the Nonrotating Limit.

    Science.gov (United States)

    Gabersek, Sasa.; Durran, Dale R.

    2004-12-01

    Gap winds produced by a uniform airstream flowing over an isolated flat-top ridge cut by a straight narrow gap are investigated by numerical simulation. On the scale of the entire barrier, the proportion of the oncoming flow that passes through the gap is relatively independent of the nondimensional mountain height , even over that range of for which there is the previously documented transition from a “flow over the ridge” regime to a “flow around” regime.The kinematics and dynamics of the gap flow itself were investigated by examining mass and momentum budgets for control volumes at the entrance, central, and exit regions of the gap. These analyses suggest three basic behaviors: the linear regime (small ) in which there is essentially no enhancement of the gap flow; the mountain wave regime ( 1.5) in which vertical mass and momentum fluxes play a crucial role in creating very strong winds near the exit of the gap; and the upstream-blocking regime ( 5) in which lateral convergence generates the strongest winds near the entrance of the gap.Trajectory analysis of the flow in the strongest events, the mountain wave events, confirms the importance of net subsidence in creating high wind speeds. Neglect of vertical motion in applications of Bernoulli's equation to gap flows is shown to lead to unreasonable wind speed predictions whenever the temperature at the gap exit exceeds that at the gap entrance. The distribution of the Bernoulli function on an isentropic surface shows a correspondence between regions of high Bernoulli function and high wind speeds in the gap-exit jet similar to that previously documented for shallow-water flow.

  2. A novel method for flow pattern identification in unstable operational conditions using gamma ray and radial basis function

    International Nuclear Information System (INIS)

    Roshani, G.H.; Nazemi, E.; Roshani, M.M.

    2017-01-01

    Changes of fluid properties (especially density) strongly affect the performance of radiation-based multiphase flow meter and could cause error in recognizing the flow pattern and determining void fraction. In this work, we proposed a methodology based on combination of multi-beam gamma ray attenuation and dual modality densitometry techniques using RBF neural network in order to recognize the flow regime and determine the void fraction in gas-liquid two phase flows independent of the liquid phase changes. The proposed system is consisted of one 137 Cs source, two transmission detectors and one scattering detector. The registered counts in two transmission detectors were used as the inputs of one primary Radial Basis Function (RBF) neural network for recognizing the flow regime independent of liquid phase density. Then, after flow regime identification, three RBF neural networks were utilized for determining the void fraction independent of liquid phase density. Registered count in scattering detector and first transmission detector were used as the inputs of these three RBF neural networks. Using this simple methodology, all the flow patterns were correctly recognized and the void fraction was predicted independent of liquid phase density with mean relative error (MRE) of less than 3.28%. - Highlights: • Flow regime and void fraction were determined in two phase flows independent of the liquid phase density changes. • An experimental structure was set up and the required data was obtained. • 3 detectors and one gamma source were used in detection geometry. • RBF networks were utilized for flow regime and void fraction determination.

  3. Two-phase flow instabilities in a silicon microchannels heat sink

    International Nuclear Information System (INIS)

    Bogojevic, D.; Sefiane, K.; Walton, A.J.; Lin, H.; Cummins, G.

    2009-01-01

    Two-phase flow instabilities are highly undesirable in microchannels-based heat sinks as they can lead to temperature oscillations with high amplitudes, premature critical heat flux and mechanical vibrations. This work is an experimental study of boiling instabilities in a microchannel silicon heat sink with 40 parallel rectangular microchannels, having a length of 15 mm and a hydraulic diameter of 194 μm. A series of experiments have been carried out to investigate pressure and temperature oscillations during the flow boiling instabilities under uniform heating, using water as a cooling liquid. Thin nickel film thermometers, integrated on the back side of a heat sink with microchannels, were used in order to obtain a better insight related to temperature fluctuations caused by two-phase flow instabilities. Flow regime maps are presented for two inlet water temperatures, showing stable and unstable flow regimes. It was observed that boiling leads to asymmetrical flow distribution within microchannels that result in high temperature non-uniformity and the simultaneously existence of different flow regimes along the transverse direction. Two types of two-phase flow instabilities with appreciable pressure and temperature fluctuations were observed, that depended on the heat to mass flux ratio and inlet water temperature. These were high amplitude/low frequency and low amplitude/high frequency instabilities. High speed camera imaging, performed simultaneously with pressure and temperature measurements, showed that inlet/outlet pressure and the temperature fluctuations existed due to alternation between liquid/two-phase/vapour flows. It was also determined that the inlet water subcooling condition affects the magnitudes of the temperature oscillations in two-phase flow instabilities and flow distribution within the microchannels.

  4. Arctic circulation regimes.

    Science.gov (United States)

    Proshutinsky, Andrey; Dukhovskoy, Dmitry; Timmermans, Mary-Louise; Krishfield, Richard; Bamber, Jonathan L

    2015-10-13

    Between 1948 and 1996, mean annual environmental parameters in the Arctic experienced a well-pronounced decadal variability with two basic circulation patterns: cyclonic and anticyclonic alternating at 5 to 7 year intervals. During cyclonic regimes, low sea-level atmospheric pressure (SLP) dominated over the Arctic Ocean driving sea ice and the upper ocean counterclockwise; the Arctic atmosphere was relatively warm and humid, and freshwater flux from the Arctic Ocean towards the subarctic seas was intensified. By contrast, during anticylonic circulation regimes, high SLP dominated driving sea ice and the upper ocean clockwise. Meanwhile, the atmosphere was cold and dry and the freshwater flux from the Arctic to the subarctic seas was reduced. Since 1997, however, the Arctic system has been under the influence of an anticyclonic circulation regime (17 years) with a set of environmental parameters that are atypical for this regime. We discuss a hypothesis explaining the causes and mechanisms regulating the intensity and duration of Arctic circulation regimes, and speculate how changes in freshwater fluxes from the Arctic Ocean and Greenland impact environmental conditions and interrupt their decadal variability. © 2015 The Authors.

  5. Causas estruturais e consequências dos regimes internacionais: regimes como variáveis intervenientes

    Directory of Open Access Journals (Sweden)

    Stephen D. Krasner

    2012-06-01

    Full Text Available Os regimes internacionais são definidos como princípios, normas, regras e procedimentos de tomada de decisões ao redor dos quais as expectativas dos atores convergem em uma dada área-tema. Como ponto de partida, os regimes são conceituados como variáveis intervenientes, estando entre fatores causais básicos e os resultados e comportamentos relacionados. Há três visões a respeito da importância dos regimes: as orientações estruturais convencionais desvalorizam os regimes como sendo, na melhor das hipóteses, ineficazes; as orientações grocianas vêem os regimes como componentes íntimos do sistema internacional; as perspectivas estruturalistas modificadas vêem os regimes como significativos somente em certas condições restritas. Para os argumentos grociano e estruturalista modificado - que concordam com a visão de que os regimes podem influenciar resultados e comportamentos - , o desenvolvimento de regimes é visto como uma função de cinco variáveis causais básicas: auto-interesse egoísta; poder político; normas e princípios difusos; usos e costumes; conhecimento.

  6. Flow mapping of multiphase flows using a novel single stem endoscopic particle image velocimetry instrument

    International Nuclear Information System (INIS)

    Lad, N; Adebayo, D; Aroussi, A

    2011-01-01

    Particle image velocimetry (PIV) is a successful flow mapping technique which can optically quantify large portions of a flow regime. This enables the method to be completely non-intrusive. The ability to be non-intrusive to any flow has allowed PIV to be used in a large range of industrial sectors for many applications. However, a fundamental disadvantage of the conventional PIV technique is that it cannot easily be used with flows which have no or limited optical access. Flows which have limited optical access for PIV measurement have been addressed using endoscopic PIV techniques. This system uses two separate probes which relay a light sheet and imaging optics to a planar position within the desired flow regime. This system is effective in medical and engineering applications. The present study has been involved in the development of a new endoscopic PIV system which integrates the illumination and imaging optics into one rigid probe. This paper focuses on the validation of the images taken from the novel single stem endoscopic PIV system. The probe is used within atomized spray flow and is compared with conventional PIV measurement and also pitot-static data. The endoscopic PIV system provides images which create localized velocity maps that are comparable with the global measurement of the conventional PIV system. The velocity information for both systems clearly show similar results for the spray characterization and are also validated using the pitot-static data

  7. Effective Wall Friction in Wall-Bounded 3D Dense Granular Flows.

    Science.gov (United States)

    Artoni, Riccardo; Richard, Patrick

    2015-10-09

    We report numerical simulations on granular shear flows confined between two flat but frictional sidewalls. Novel regimes differing by their strain localization features are observed. They originate from the competition between dissipation at the sidewalls and dissipation in the bulk of the flow. The effective friction at sidewalls is characterized (effective friction coefficient and orientation of the friction force) for each regime, and its interdependence with slip and force fluctuations is pointed out. We propose a simple scaling law linking the slip velocity to the granular temperature in the main flow direction which leads naturally to another scaling law for the effective friction.

  8. Thermal regime at the Upper Stillwater dam site, Uinta mountains, Utah: Implications for terrain, microclimate and structural corrections in heat flow studies

    Science.gov (United States)

    Bauer, Michael S.; Chapman, David S.

    1986-08-01

    A detailed study of the subsurface thermal regime at the Upper Stillwater dam site, Uinta Mountains, northeast Utah, has been made. Temperature measurements were made in 36 drillholes located within a 1 km 2 area and ranging in depth from 20 to 97 m. Holes less than about 40 m deep were used only to obtain information about spatial variations in mean annual surface temperature. Several holes in or near talus slopes at the sides of the canyons have temperature minima approaching 0°C between 10 and 20 m indicating the presence of year-round ice at the base of the talus. Another set of holes show transient thermal effects of surface warming resulting from clearing of a construction site 3.5 years prior to our measurements. Most of the remaining holes show conductive behavior and have gradients ranging from 13° to 17°C km -1. Measurements made on 44 core samples yield a thermal conductivity of 5.6 (std. dev. 0.35) W m -1 K -1 for the Precambrian quartzite present. Surface heat flow estimates for these holes range from 70 to 100 mW m -2. However, the local disturbance of the thermal field by topography and microclimate is considerable. A finite difference method used to model these effects yielded a locally corrected Upper Stillwater heat flow of about 75 mW m -2. A final correction to account for the effects of refraction of heat from the low conductivity sedimentary rocks in the Uinta Basin into the high conductivity quartzite at the dam site, produced a regionally corrected Upper Stillwater heat flow between 60 and 65 mW m -2. This value is consistent with the observed heat flow of 60 mW m -2 in the Green River Basin to the north and the Uinta Basin to the south.

  9. AN OVERVIEW ON PULSATILE FLOW DYNAMICS

    OpenAIRE

    Çarpinlioğlu, Melda Özdinç

    2015-01-01

    Pulsatile flow dynamics in reference to the relevant experimental research on the manner between the time periods of 1997- 2015 is presented in this paper. The flow field under discussion is generated through a rigid circular cross-sectional pipe as an axial slightly- compressible and sinusoidal one in a controlled range of the oscillation parameters. Laminar and turbulent flow regimes are considered with a particular emphasis devoted to the transitional characteristics of laminar pulsatile f...

  10. Computational fluid dynamics modeling of two-phase flow in a BWR fuel assembly

    International Nuclear Information System (INIS)

    Andrey Ioilev; Maskhud Samigulin; Vasily Ustinenko; Simon Lo; Adrian Tentner

    2005-01-01

    Full text of publication follows: The goal of this project is to develop an advanced Computational Fluid Dynamics (CFD) computer code (CFD-BWR) that allows the detailed analysis of the two-phase flow and heat transfer phenomena in a Boiling Water Reactor (BWR) fuel bundle under various operating conditions. This code will include more fundamental physical models than the current generation of sub-channel codes and advanced numerical algorithms for improved computational accuracy, robustness, and speed. It is highly desirable to understand the detailed two-phase flow phenomena inside a BWR fuel bundle. These phenomena include coolant phase changes and multiple flow regimes which directly influence the coolant interaction with fuel assembly and, ultimately, the reactor performance. Traditionally, the best analysis tools for the analysis of two-phase flow phenomena inside the BWR fuel assembly have been the sub-channel codes. However, the resolution of these codes is still too coarse for analyzing the detailed intra-assembly flow patterns, such as flow around a spacer element. Recent progress in Computational Fluid Dynamics (CFD), coupled with the rapidly increasing computational power of massively parallel computers, shows promising potential for the fine-mesh, detailed simulation of fuel assembly two-phase flow phenomena. However, the phenomenological models available in the commercial CFD programs are not as advanced as those currently being used in the sub-channel codes used in the nuclear industry. In particular, there are no models currently available which are able to reliably predict the nature of the flow regimes, and use the appropriate sub-models for those flow regimes. The CFD-BWR code is being developed as a customized module built on the foundation of the commercial CFD Code STAR-CD which provides general two-phase flow modeling capabilities. The paper describes the model development strategy which has been adopted by the development team for the

  11. Recognition and measurement gas-liquid two-phase flow in a vertical concentric annulus at high pressures

    Science.gov (United States)

    Li, Hao; Sun, Baojiang; Guo, Yanli; Gao, Yonghai; Zhao, Xinxin

    2018-02-01

    The air-water flow characteristics under pressure in the range of 1-6 MPa in a vertical annulus were evaluated in this report. Time-resolved bubble rising velocity and void fraction were also measured using an electrical void fraction meter. The results showed that the pressure has remarkable effect on the density, bubble size and rise velocity of the gas. Four flow patterns (bubble, cap-bubble, cap-slug, and churn) were also observed instead of Taylor bubble at high pressure. Additionally, the transition process from bubble to cap-bubble was investigated at atmospheric and high pressures, respectively. The results revealed that the flow regime transition criteria for atmospheric pressure do not work at high pressure, hence a new flow regime transition model for annular flow channel geometry was developed to predict the flow regime transition, which thereafter exhibited high accuracy at high pressure condition.

  12. Methodology for Identification of the Coolant Thermalhydraulic Regimes in the Core of Nuclear Reactors

    International Nuclear Information System (INIS)

    Sharaevsky, L.G.; Sharaevskaya, E.I.; Domashev, E.D.; Arkhypov, A.P.; Kolochko, V.N.

    2002-01-01

    The paper deals with one of the acute for the nuclear energy problem of accident regimes of NPPs recognition diagnostics using noise signal diagnostics methodology. The methodology intends transformation of the random noise signals of the main technological parameters at the exit of a nuclear facility (neutron flow, dynamic pressure etc.) which contain the important information about the technical status of the equipment. The effective algorithms for identification of random processes wore developed. After proper transformation its were considered as multidimensional random vectors. Automatic classification of these vectors in the developed algorithms is realized on the basis of the probability function in particular Bayes classifier and decision functions. Till now there no mathematical models for thermalhydraulic regimes of fuel assemblies recognition on the acoustic and neutron noises parameters in the core of nuclear facilities. The two mathematical models for analysis of the random processes submitted to the automatic classification is proposed, i.e. statistical (using Bayes classifier of acoustic spectral density diagnosis signals) and geometrical (on the basis of formation in the featured space of dividing hyper-plane). The theoretical basis of the bubble boiling regimes in the fuel assemblies is formulated as identification of these regimes on the basis of random parameters of auto spectral density of acoustic noise (ASD) measured in the fuel assemblies (dynamic pressure in the upper plenum in the paper). The elaborated algorithms allow recognize realistic status of the fuel assemblies. For verification of the proposed mathematical models the analysis of experimental measurements was carried out. The research of the boiling onset and definition of the local values of the flow parameters in the seven-beam fuel assembly (length of 1.3 m, diameter of 6 mm) have shown the correct identification of the bubble boiling regimes. The experimental measurements on

  13. Forced convection flow boiling and two-phase flow phenomena in a microchannel

    Science.gov (United States)

    Na, Yun Whan

    2008-07-01

    ) technique. The effects of different constant heat fluxes and different channel heights on the boiling mechanisms were investigated. The effects of liquid velocity on the bubble departure diameter were analyzed. The obtained results showed that the wall superheats at the position of nucleate boiling are relatively independent of the mass flow rates at the same channel height. The obtained results, however, showed that the heat flux at the onset of nucleate boiling strongly depends on the channel height. With a decrease of the channel height and an increase of the liquid velocity at the channel inlet, the departure diameter of a bubble was smaller. The periodic flow patterns, such as the bubbly flow, elongated slug flow, and churn flow were observed in the microchannel. Flow instabilities of two-phase flow boiling in a trapezoidal microchannel using a three-dimensional model were investigated. Fluctuation behaviors of flow boiling parameters such as wall temperature and inlet pressure caused by periodic flow patterns were studied at different heat fluxes and mass fluxes. The numerical results showed large amplitude and short period oscillations for wall temperature and inlet pressure fluctuations. Stable and unstable flow boiling regime with short period oscillations were investigated. Those flow boiling regimes were not listed in stable and unstable boiling regime map proposed by Wang et al. (2007).

  14. Stochastic Parametrisations and Regime Behaviour of Atmospheric Models

    Science.gov (United States)

    Arnold, Hannah; Moroz, Irene; Palmer, Tim

    2013-04-01

    The presence of regimes is a characteristic of non-linear, chaotic systems (Lorenz, 2006). In the atmosphere, regimes emerge as familiar circulation patterns such as the El-Nino Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO) and Scandinavian Blocking events. In recent years there has been much interest in the problem of identifying and studying atmospheric regimes (Solomon et al, 2007). In particular, how do these regimes respond to an external forcing such as anthropogenic greenhouse gas emissions? The importance of regimes in observed trends over the past 50-100 years indicates that in order to predict anthropogenic climate change, our climate models must be able to represent accurately natural circulation regimes, their statistics and variability. It is well established that representing model uncertainty as well as initial condition uncertainty is important for reliable weather forecasts (Palmer, 2001). In particular, stochastic parametrisation schemes have been shown to improve the skill of weather forecast models (e.g. Berner et al., 2009; Frenkel et al., 2012; Palmer et al., 2009). It is possible that including stochastic physics as a representation of model uncertainty could also be beneficial in climate modelling, enabling the simulator to explore larger regions of the climate attractor including other flow regimes. An alternative representation of model uncertainty is a perturbed parameter scheme, whereby physical parameters in subgrid parametrisation schemes are perturbed about their optimal value. Perturbing parameters gives a greater control over the ensemble than multi-model or multiparametrisation ensembles, and has been used as a representation of model uncertainty in climate prediction (Stainforth et al., 2005; Rougier et al., 2009). We investigate the effect of including representations of model uncertainty on the regime behaviour of a simulator. A simple chaotic model of the atmosphere, the Lorenz '96 system, is used to study

  15. Identification of flow regimes and heat transfer modes in Angra-2 core during the simulation of the small break loss of coolant accident of 250 cm{sup 2} in the cold leg of primary loop using RELAP5 code

    Energy Technology Data Exchange (ETDEWEB)

    Borges, Eduardo M.; Sabundjian, Gaiane, E-mail: borges.em@hotmail.com, E-mail: gdjian@ipen.br [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNE-SP), Sao Paulo, SP (Brazil)

    2017-07-01

    The aim of this paper is to identify the flow regimes, the heat transfer modes, and the correlations used by RELAP5/MOD3.2. gamma code in Angra-2 during the Small-Break Loss-of-Coolant Accident (SBLOCA) with a 250cm{sup 2} of rupture area in the cold leg of primary loop. The Chapter 15 of the Final Safety Analysis Report of Angra-2 (FSAR-A2) reports this specific kind of accident. The results from this work demonstrated the several flow regimes and heat transfer modes that can be present in the core of Angra-2 during the postulated accident. The results obtained for Angra-2 nuclear reactor core during the postulated accident were satisfactory when compared with the FSAR-A2. Additionally, the results showed the correct actuation of the ECCS guaranteeing the integrity of the reactor core. (author)

  16. Modelling of air flow supply in a room at variable regime by using both K - E and spalart - allmaras turbulent model

    Science.gov (United States)

    Korbut, Vadim; Voznyak, Orest; Sukholova, Iryna; Myroniuk, Khrystyna

    2017-12-01

    The abstract is to The article is devoted to the decision of actual task of air distribution efficiency increasing with the help of swirl and spread air jets to provide normative parameters of air in the production apartments. The mathematical model of air supply with swirl and spread air jets in that type of apartments is improved. It is shown that for reachin of air distribution maximal efficiency it is necessary to supply air by air jets, that intensively extinct before entering into a working area. Simulation of air flow performed with the help of CFD FLUENT (Ansys FLUENT). Calculations of the equation by using one-parameter model of turbulence Spalart-Allmaras are presented. The graphical and the analytical dependences on the basis of the conducted experimental researches, which can be used in subsequent engineering calculations, are shown out. Dynamic parameters of air flow that is created due to swirl and spread air jets at their leakage at variable regime and creation of dynamic microclimate in a room has been determined. Results of experimental investigations of air supply into the room by air distribution device which creates swirl air jets for creation more intensive turbulization air flow in the room are presented. Obtained results of these investigations give possibility to realize engineer calculations of air distribution with swirl air jets. The results of theoretical researches of favourable influence of dynamic microclimate to the man are presented. When using dynamic microclimate, it's possible to decrease conditioning and ventilation system expenses. Human organism reacts favourably on short lasting deviations from the rationed parameters of air environment.

  17. Mathematical modeling of swirled flows in industrial applications

    Science.gov (United States)

    Dekterev, A. A.; Gavrilov, A. A.; Sentyabov, A. V.

    2018-03-01

    Swirled flows are widely used in technological devices. Swirling flows are characterized by a wide range of flow regimes. 3D mathematical modeling of flows is widely used in research and design. For correct mathematical modeling of such a flow, it is necessary to use turbulence models, which take into account important features of the flow. Based on the experience of computational modeling of a wide class of problems with swirling flows, recommendations on the use of turbulence models for calculating the applied problems are proposed.

  18. Lattice Boltzmann approach for complex nonequilibrium flows.

    Science.gov (United States)

    Montessori, A; Prestininzi, P; La Rocca, M; Succi, S

    2015-10-01

    We present a lattice Boltzmann realization of Grad's extended hydrodynamic approach to nonequilibrium flows. This is achieved by using higher-order isotropic lattices coupled with a higher-order regularization procedure. The method is assessed for flow across parallel plates and three-dimensional flows in porous media, showing excellent agreement of the mass flow with analytical and numerical solutions of the Boltzmann equation across the full range of Knudsen numbers, from the hydrodynamic regime to ballistic motion.

  19. Static flow instability in subcooled flow boiling in parallel channels

    International Nuclear Information System (INIS)

    Siman-Tov, M.; Felde, D.K.; McDuffee, J.L.; Yoder, G.L. Jr.

    1995-01-01

    A series of tests for static flow instability or flow excursion (FE) at conditions applicable to the proposed Advanced Neutron Source reactor was completed in parallel rectangular channels configuration with light water flowing vertically upward at very high velocities. True critical heat flux experiments under similar conditions were also conducted. The FE data reported in this study considerably extend the velocity range of data presently available worldwide. Out of the three correlations compared, the Saha and Zuber correlation had the best fit with the data. However, a modification was necessary to take into account the demonstrated dependence of the Stanton (St) and Nusselt (Nu) numbers on subcooling levels, especially in the low subcooling regime

  20. A method for identifying gas-liquid two-phase flow patterns on the basis of wavelet packet multi-scale information entropy and HMM

    International Nuclear Information System (INIS)

    Zhou Yunlong; Zhang Xueqing; Gao Yunpeng; Cheng Yue

    2009-01-01

    For studying flow regimes of gas/liquid two-phase in a vertical upward pipe, the conductance fluctuation information of four typical flow regimes was collected by a measuring the system with self-made multiple conductivity probes. Owing to the non-stationarity of conductance fluctuation signals of gas-liquid two-phase flow, a kind of' flow regime identification method based on wavelet packet Multi-scale Information Entropy and Hidden Markov Model (HMM) was put forward. First of all, the collected conductance fluctuation signals were decomposed into eight different frequency bands signals. Secondly, the wavelet packet multi-scale information entropy of different frequency bands signals were regarded as the input characteristic vectors of all states HMM which had been trained. In the end the regime identification of' the gas-liquid two-phase flow could be performed. The study showed that the method that HMM was applied to identify the flow regime was superior to the one that BP neural network was used, and the results proved that the method was efficient and feasible. (authors)

  1. Characterization of horizontal air–water two-phase flow

    Energy Technology Data Exchange (ETDEWEB)

    Kong, Ran; Kim, Seungjin, E-mail: skim@psu.edu

    2017-02-15

    Highlights: • A visualization study is performed to develop flow regime map in horizontal flow. • Database in horizontal bubbly flow is extended using a local conductivity probe. • Frictional pressure drop analysis is performed in horizontal bubbly flow. • Drift flux analysis is performed in horizontal bubbly flow. - Abstract: This paper presents experimental studies performed to characterize horizontal air–water two-phase flow in a round pipe with an inner diameter of 3.81 cm. A detailed flow visualization study is performed using a high-speed video camera in a wide range of two-phase flow conditions to verify previous flow regime maps. Two-phase flows are classified into bubbly, plug, slug, stratified, stratified-wavy, and annular flow regimes. While the transition boundaries identified in the present study compare well with the existing ones (Mandhane et al., 1974) in general, some discrepancies are observed for bubbly-to-plug/slug, and plug-to-slug transition boundaries. Based on the new transition boundaries, three additional test conditions are determined in horizontal bubbly flow to extend the database by Talley et al. (2015a). Various local two-phase flow parameters including void fraction, interfacial area concentration, bubble velocity, and bubble Sauter mean diameter are obtained. The effects of increasing gas flow rate on void fraction, bubble Sauter mean diameter, and bubble velocity are discussed. Bubbles begin to coalesce near the gas–liquid layer instead of in the highly packed region when gas flow rate increases. Using all the current experimental data, two-phase frictional pressure loss analysis is performed using the Lockhart–Martinelli method. It is found that the coefficient C = 24 yields the best agreement with the data with the minimum average difference. Moreover, drift flux analysis is performed to predict void-weighted area-averaged bubble velocity and area-averaged void fraction. Based on the current database, functional

  2. Kolmogorov flow in two dimensional strongly coupled dusty plasma

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Akanksha; Ganesh, R., E-mail: ganesh@ipr.res.in; Joy, Ashwin [Institute for Plasma Research, Bhat Gandhinagar, Gujarat 382 428 (India)

    2014-07-15

    Undriven, incompressible Kolmogorov flow in two dimensional doubly periodic strongly coupled dusty plasma is modelled using generalised hydrodynamics, both in linear and nonlinear regime. A complete stability diagram is obtained for low Reynolds numbers R and for a range of viscoelastic relaxation time τ{sub m} [0 < τ{sub m} < 10]. For the system size considered, using a linear stability analysis, similar to Navier Stokes fluid (τ{sub m} = 0), it is found that for Reynolds number beyond a critical R, say R{sub c}, the Kolmogorov flow becomes unstable. Importantly, it is found that R{sub c} is strongly reduced for increasing values of τ{sub m}. A critical τ{sub m}{sup c} is found above which Kolmogorov flow is unconditionally unstable and becomes independent of Reynolds number. For R < R{sub c}, the neutral stability regime found in Navier Stokes fluid (τ{sub m} = 0) is now found to be a damped regime in viscoelastic fluids, thus changing the fundamental nature of transition of Kolmogorov flow as function of Reynolds number R. A new parallelized nonlinear pseudo spectral code has been developed and is benchmarked against eigen values for Kolmogorov flow obtained from linear analysis. Nonlinear states obtained from the pseudo spectral code exhibit cyclicity and pattern formation in vorticity and viscoelastic oscillations in energy.

  3. Developing a novel approach to analyse the regimes of temporary streams and their controls on aquatic biota

    Science.gov (United States)

    Gallart, F.; Prat, N.; García-Roger, E. M.; Latron, J.; Rieradevall, M.; Llorens, P.; Barberá, G. G.; Brito, D.; de Girolamo, A. M.; Lo Porto, A.; Neves, R.; Nikolaidis, N. P.; Perrin, J. L.; Querner, E. P.; Quiñonero, J. M.; Tournoud, M. G.; Tzoraki, O.; Froebrich, J.

    2011-10-01

    Temporary streams are those water courses that undergo the recurrent cessation of flow or the complete drying of their channel. The biological communities in temporary stream reaches are strongly dependent on the temporal changes of the aquatic habitats determined by the hydrological conditions. The use of the aquatic fauna structural and functional characteristics to assess the ecological quality of a temporary stream reach can not therefore be made without taking into account the controls imposed by the hydrological regime. This paper develops some methods for analysing temporary streams' aquatic regimes, based on the definition of six aquatic states that summarize the sets of mesohabitats occurring on a given reach at a particular moment, depending on the hydrological conditions: flood, riffles, connected, pools, dry and arid. We used the water discharge records from gauging stations or simulations using rainfall-runoff models to infer the temporal patterns of occurrence of these states using the developed aquatic states frequency graph. The visual analysis of this graph is complemented by the development of two metrics based on the permanence of flow and the seasonal predictability of zero flow periods. Finally, a classification of the aquatic regimes of temporary streams in terms of their influence over the development of aquatic life is put forward, defining Permanent, Temporary-pools, Temporary-dry and Episodic regime types. All these methods were tested with data from eight temporary streams around the Mediterranean from MIRAGE project and its application was a precondition to assess the ecological quality of these streams using the current methods prescribed in the European Water Framework Directive for macroinvertebrate communities.

  4. Post-dryout heat transfer and entrained droplet sizes at low pressure and low flow conditions

    International Nuclear Information System (INIS)

    Jeong, H.Y.; No, H.C.

    1997-01-01

    The entrainment mechanisms and the entrained droplet sizes with relation to the flow regimes are investigated. Through the analysis of many experimental post-dryout data, it is shown that the most probable flow regime near dryout or quench front is not annular flow but churn-turbulent flow when the mass flux is low. A correlation describing the initial droplet size just after the CHF position at low mass flux is suggested through regression analysis. The history-dependent post-dryout model of Varone and Rohsenow replaced by the Webb-Chen model for wall-vapor heat transfer is used as a reference model in the analysis. In the post-dryout region at low pressure and low flow, it is found that the suggested one-dimensional mechanistic model is not applicable when the vapor superficial velocity is very low. This is explained by the change of main entrainment mechanism with the change of flow regime. In bubbly or slug flow a number of tiny droplets generated from bubble burst become important in the heat transfer after dryout. Therefore, the suggested correlation is valid only in the churn-turbulent flow regime (j g * = 0.5∼4.5). It is also suggested that the droplet size generated from the churn-turbulent surface is dependent not only on the pressure but also on the vapor velocity. It turns out that the present model can predict the measured cladding and vapor temperatures within 20% and 25%, respectively

  5. Study of turbulent flow using Half-Fourier Echo-Planar imaging

    International Nuclear Information System (INIS)

    Rodriguez, A.O.

    2006-01-01

    The Echo-Planar Imaging technique combined with a partial Fourier acquisition method was used to obtain velocity images for liquid flows in a circular cross-section pipe at Reynolds number of up to 8000. This partial-Fourier imaging scheme is able to generate shorter echo times than the full-Fourier Echo-Planar Imaging methods, reducing the signal attenuation due to T2 * and flow. Velocity images along the z axis were acquired with a time-scale of 80 ms thus obtaining a real-time description of flow in both the laminar and turbulent regimes. Velocity values and velocity fluctuations were computed with the flow image data. A comparison plot of NMR velocity and bulk velocity and a plot of velocity fluctuations were calculated to investigate the feasibility of this imaging technique. Flow encoded Echo-Planar Imaging together with a reduced data acquisition method can provide us with a real-time technique to capture instantaneous images of the flow field for both laminar and turbulent regimes. (author)

  6. Assessing water quality trends in catchments with contrasting hydrological regimes

    Science.gov (United States)

    Sherriff, Sophie C.; Shore, Mairead; Mellander, Per-Erik

    2016-04-01

    Environmental resources are under increasing pressure to simultaneously achieve social, economic and ecological aims. Increasing demand for food production, for example, has expanded and intensified agricultural systems globally. In turn, greater risks of diffuse pollutant delivery (suspended sediment (SS) and Phosphorus (P)) from land to water due to higher stocking densities, fertilisation rates and soil erodibility has been attributed to deterioration of chemical and ecological quality of aquatic ecosystems. Development of sustainable and resilient management strategies for agro-ecosystems must detect and consider the impact of land use disturbance on water quality over time. However, assessment of multiple monitoring sites over a region is challenged by hydro-climatic fluctuations and the propagation of events through catchments with contrasting hydrological regimes. Simple water quality metrics, for example, flow-weighted pollutant exports have potential to normalise the impact of catchment hydrology and better identify water quality fluctuations due to land use and short-term climate fluctuations. This paper assesses the utility of flow-weighted water quality metrics to evaluate periods and causes of critical pollutant transfer. Sub-hourly water quality (SS and P) and discharge data were collected from hydrometric monitoring stations at the outlets of five small (~10 km2) agricultural catchments in Ireland. Catchments possess contrasting land uses (predominantly grassland or arable) and soil drainage (poorly, moderately or well drained) characteristics. Flow-weighted water quality metrics were calculated and evaluated according to fluctuations in source pressure and rainfall. Flow-weighted water quality metrics successfully identified fluctuations in pollutant export which could be attributed to land use changes through the agricultural calendar, i.e., groundcover fluctuations. In particular, catchments with predominantly poor or moderate soil drainage

  7. Investigation of Two-Phase Flow in Short Horizontal Mini Channel Height of 1 MM

    Directory of Open Access Journals (Sweden)

    Ron’shin Fedor

    2016-01-01

    Full Text Available The experiments with two-phase flow in the short horizontal rectangular minichannel with the height of 1 mm and width of 29 mm have been carried out using water and gas nitrogen. The five two-phase flow patterns have been recognized in the minichannel: churn, stratified, annular, bubble, and jet. These regimes are plotted on a graph and the boundaries between them determine precisely. The height of a horizontal minichannels has a significant role on boundaries between the flow regimes.

  8. Calculated viscosity-distance dependence for some actively flowing lavas

    International Nuclear Information System (INIS)

    Pieri, D.

    1987-01-01

    The importance of viscosity as a gauge of the various energy and momentum dissipation regimes of lava flows has been realized for a long time. Nevertheless, despite its central role in lava dynamics and kinematics, it remains among the most difficult of flow physical properties to measure in situ during an eruption. Attempts at reconstructing the actual emplacement viscosities of lava flows from their solidified topographic form are difficult. Where data are available on the position of an advancing flow front as a function of time, it is possible to calculate the effective viscosity of the front as a function of distance from the vent, under the assumptions of a steady state regime. As an application and test of an equation given, relevant parameters from five recent flows on Mauna Loa and Kilauea were utilized to infer the dynamic structure of their aggregate flow front viscosity as they advanced, up to cessation. The observed form of the viscosity-distance relation for the five active Hawaiian flows examined appears to be exponential, with a rapid increase just before the flows stopped as one would expect

  9. Volume-heated boiling pool flow behavior and application to transition phase accident conditions

    International Nuclear Information System (INIS)

    Ginsberg, T.; Jones, O.C. Jr.; Chen, J.C.

    1978-01-01

    Observations of two-phase flow fields in volume-heated boiling pools are reported. Photographic observations, together with pool-average void fraction measurements are presented. Flow regime transition criteria derived from the measurements are discussed. The churn-turbulent flow regime was the dominant regime for superficial vapor velocities up to nearly five times the Kutateladze dispersal velocity. Within this range of conditions, a churn-turbulent drift flux model provides a reasonable prediction of the pool-average void fraction data. The results of the experiment and analyses are extrapolated to transition phase conditions. It is shown that intense pool boil-up could occur where the pool-average void fraction would be greater than 0.6 for steel vaporization rates equivalent to power levels greater than one percent of nominal LMFBR power density

  10. Numerical simulation of fluid flow in microporous media

    International Nuclear Information System (INIS)

    Xu Ruina; Jiang Peixue

    2008-01-01

    The flow characteristics of water and air in microporous media with average diameters of 200 μm, 125 μm, 90 μm, 40 μm, 20 μm, and 10 μm were studied numerically. The calculated friction factors for water and air in the non-slip-flow regime in the microporous media agree well with the known correlation suitable for normal size porous media. The numerically predicted friction factors for air in the slip-flow regime in the microporous media with 90 μm, 40 μm, 20 μm, and 10 μm diameter particles were less than the correlation for normal size porous media but close to experimental data and a modified correlation that accounts for rarefaction. Comparisons of the numerical results with the experimental data and the modified correlations show that rarefaction effects occur in air flows in the microporous media with particle diameters less than 90 μm and that the numerical calculations with velocity slip on the boundary can properly simulate the fluid flow in microporous media

  11. 3-dimensional Simulation of an Air-lift Pump from Bubbly to Slug Flow

    Energy Technology Data Exchange (ETDEWEB)

    Jo, Hongrae; Jo, Daeseong [Kyungpook National Univ, Daegu (Korea, Republic of)

    2015-10-15

    The air-lift pump has been used in various applications with its merit that it can pump up without any moving parts. E.g. coffee percolator, petroleum industry, suction dredge, OTEC i.e. ocean thermal energy conversion and so on. By the merit, it has high durability for high temperature water or vapor, and fluid-solid mixture like waste water, muddy water and crude, which cause problems when it's pumped up with general pumps. In this regard, the air-lift pump has been one of the most desirable technology. A typical air-lift pump configuration is illustrated in Figure 01. The principle of this pump is very simple. When air is injected from the injector at bottom of a submerged tube, i.e., air bubbles are suspended in the liquid, the average density of the mixture in the tube is less than that of the surrounding fluid in the reservoir. Then hydrostatic pressure over the length of the tube is decreased. This buoyancy force causes a pumping action. The comparison of the simulated results, experimental result, and theoretical result is been able by data shown as Figure 04. They have similar trends but they also have a little differences because there are some limits of simulating the flow regimes. At the different flow condition, different coefficients for friction factor or pressure drop should be used, but this simulation uses a laminar condition and the theoretical equations are valid only for slug regime where the air flow rate is lower than the other regimes. From these causes, the differences has arisen, and difference comes bigger as the air flow rate increases, i.e., becoming annular flow regime or churn flow regime.

  12. A Review of Critical Conditions for the Onset of Nonlinear Fluid Flow in Rock Fractures

    Directory of Open Access Journals (Sweden)

    Liyuan Yu

    2017-01-01

    Full Text Available Selecting appropriate governing equations for fluid flow in fractured rock masses is of special importance for estimating the permeability of rock fracture networks. When the flow velocity is small, the flow is in the linear regime and obeys the cubic law, whereas when the flow velocity is large, the flow is in the nonlinear regime and should be simulated by solving the complex Navier-Stokes equations. The critical conditions such as critical Reynolds number and critical hydraulic gradient are commonly defined in the previous works to quantify the onset of nonlinear fluid flow. This study reviews the simplifications of governing equations from the Navier-Stokes equations, Stokes equation, and Reynold equation to the cubic law and reviews the evolutions of critical Reynolds number and critical hydraulic gradient for fluid flow in rock fractures and fracture networks, considering the influences of shear displacement, normal stress and/or confining pressure, fracture surface roughness, aperture, and number of intersections. This review provides a reference for the engineers and hydrogeologists especially the beginners to thoroughly understand the nonlinear flow regimes/mechanisms within complex fractured rock masses.

  13. Hydrodynamical and magnetohydrodynamic global bifurcations in a highly turbulent von Karman flow

    International Nuclear Information System (INIS)

    Ravelet, F.

    2005-09-01

    We report experimental studies of the turbulent von Karman flow, inertially stirred between counter-rotating impellers. We first study the flow and its transition from laminar to turbulent regime. We highlight the role of slowly varying large scales, due to the presence of an azimuthal mixing layer. The large scales of this flow can be unstable in turbulent regime. We study the statistics of the transitions between the different mean states. The second part is dedicated to an experiment in liquid sodium, called VKS2. We optimize the time-averaged flow in order to allow kinematic dynamo action. We report the very first results of the experiment, and discuss the role of the large scales temporal non-stationariness. (author)

  14. Computations of incompressible fluid flow around a long square ...

    Indian Academy of Sciences (India)

    DEEPAK KUMAR

    The steady-flow regime is observed up to Re = 121 for G = 0.5, and beyond this Re, time-periodic regime is observed. The shift to a time-periodic .... variations of wake dynamics and turbulence characteristics .... ponents of momentum (Eqs. 2 and 3) and the energy ... constructed by making use of Ansys workbench. More.

  15. Exchange rate regimes and monetary arrangements

    Directory of Open Access Journals (Sweden)

    Ivan Ribnikar

    2005-06-01

    Full Text Available There is a close relationship between a country’s exchange rate regime and monetary arrangement and if we are to examine monetary arrangements then exchange rate regimes must first be analysed. Within the conventional and most widely used classification of exchange rate regimes into rigid and flexible or into polar regimes (hard peg and float on one side, and intermediate regimes on the other there, is a much greater variety among intermediate regimes. A more precise and, as will be seen, more useful classification of exchange rate regimes is the first topic of the paper. The second topic is how exchange rate regimes influence or determine monetary arrangements and monetary policy or monetary policy regimes: monetary autonomy versus monetary nonautonomy and discretion in monetary policy versus commitment in monetary policy. Both topics are important for countries on their path to the EU and the euro area

  16. Getting into the flow: Red cells go on a roll, two-component vesicles swing

    Science.gov (United States)

    Viallat, Annie; Dupire, Jules; Khelloufi, Kamel; Al Halifa, Al Hair; Adhesion and Inflammation Team

    2013-11-01

    Red blood cells are soft capsules. Under shear flow, their two known motions were ``tumbling'' and ``swinging-tank treading,'' depending on cell mechanics and flow conditions. We reveal new wobbling regimes, among which the ``rolling'' regime, where red cells move as wheels on a road. We show, by coupling two video-microscopy approaches providing multi-directional cell pictures that the orientation of cells flipping into the flow is determined by the shear rate. Rolling permits to avoid energetically costly cellular deformations and is a true signature of the cytoskeleton elasticity. We highlight two transient dynamics: an intermittent regime during the ``tank-treading-to-flipping'' transition and a Frisbee-like ``spinning'' regime during the ``rolling-to-tank-treading'' transition. We find that the biconcave red cell shape is very stable under moderate shear stresses, and we interpret this result in terms of shape memory and elastic buckling. Finally, we generate lipid vesicles with a shape memory by using two lipids with different bending rigidities. These vesicles swing in shear flow similarly to red blood cells but their non-axisymmetric stress-free shape changes the periodicity of the motion and induces specific features.

  17. Flow and fracture in water-saturated, unconstrained granular beds

    Directory of Open Access Journals (Sweden)

    Germán eVaras

    2015-06-01

    Full Text Available The injection of gas in a liquid-saturated granular bed gives rise to a wide variety of invasion patterns. Many studies have focused on constrained porous media, in which the grains are fixed in the bed and only the interstitial fluid flows when the gas invades the system. With a free upper boundary, however, the grains can be entrained by the ascending gas or fluid motion, and the competition between the upward motion of grains and sedimentation leads to new patterns. We propose a brief review of the experimental investigation of the dynamics of air rising through a water-saturated, unconstrained granular bed, in both two and three dimensions. After describing the invasion pattern at short and long time, a tentative regime-diagram is proposed. We report original results showing a dependence of the fluidized zone shape, at long times, on the injection flow rate and grain size. A method based on image analysis makes it possible to detect not only the fluidized zone profile in the stationary regime, but also to follow the transient dynamics of its formation. Finally, we describe the degassing dynamics inside the fluidized zone, in the stationary regime. Depending on the experimental conditions, regular bubbling, continuous degassing, intermittent regime or even spontaneous flow-to-fracture transition are observed.

  18. Electricity vs Ecosystems – understanding and predicting hydropower impact on Swedish river flow

    Directory of Open Access Journals (Sweden)

    B. Arheimer

    2014-09-01

    Full Text Available The most radical anthropogenic impact on water systems in Sweden originates from the years 1900–1970, when the electricity network was developed in the country and almost all rivers were regulated. The construction of dams and changes in water flow caused problems for ecosystems. Therefore, when implementing the EU Water Framework Directive (WFD hydro-morphological indicators and targets were developed for rivers and lakes to achieve good ecological potential. The hydrological regime is one such indicator. To understand the change in flow regime we quantified the hydropower impact on river flow across Sweden by using the S-HYPE model and observations. The results show that the average redistribution of water during a year due to regulation is 19 % for the total discharge from Sweden. A distinct impact was found in seasonal flow patterns and flow duration curves. Moreover, we quantified the model skills in predicting hydropower impact on flow. The median NSE for simulating change in flow regime was 0.71 for eight dams studied. Results from the spatially distributed model are available for 37 000 sub-basins across the country, and will be used by the Swedish water authorities for reporting hydro-morphological indicators to the EU and for guiding the allocation of river restoration measures.

  19. Annular flow of cement slurries; Escoamento anular de pastas de cimento

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Maria das Gracas Pena; Martins, Andre Leibsohn; Oliveira, Antonio Augusto J. de [PETROBRAS, Rio de Janeiro (Brazil). Centro de Pesquisas. Setor de Tecnologia de Perfuracao

    1990-12-31

    This paper considers the analysis of laminar, transitory and turbulent flow regimes of cement slurries of various compositions flowing in annular sections. It is an experimental study to evaluate the performance of dozens of equations found in the literature that reflect the rheological behavior of non-Newtonian fluids, the dimensioning of annular sections, the delimitation of the transitory zone and the estimative of friction losses in the turbulent flow regime. A large-scale physical simulator (SHS-Surface Hydraulic Simulator), was designed and constructed at the PETROBRAS Research Center in order to obtain flow parameters. A computer program capable of analysing and drawing conclusions from the behavior of non-Newtonian fluids flowing in different geometries and energetic conditions was also developed. These were considered as essential stages for the development of the project. (author) 17 refs., 9 figs., 18 tabs.

  20. Thermal radiation effects on magnetohydrodynamic free convection heat and mass transfer from a sphere in a variable porosity regime

    KAUST Repository

    Prasad, Vallampati Ramachandra Ramachandra

    2012-02-01

    A mathematical model is presented for multiphysical transport of an optically-dense, electrically-conducting fluid along a permeable isothermal sphere embedded in a variable-porosity medium. A constant, static, magnetic field is applied transverse to the cylinder surface. The non-Darcy effects are simulated via second order Forchheimer drag force term in the momentum boundary layer equation. The surface of the sphere is maintained at a constant temperature and concentration and is permeable, i.e. transpiration into and from the boundary layer regime is possible. The boundary layer conservation equations, which are parabolic in nature, are normalized into non-similar form and then solved numerically with the well-tested, efficient, implicit, stable Keller-box finite difference scheme. Increasing porosity (ε) is found to elevate velocities, i.e. accelerate the flow but decrease temperatures, i.e. cool the boundary layer regime. Increasing Forchheimer inertial drag parameter (Λ) retards the flow considerably but enhances temperatures. Increasing Darcy number accelerates the flow due to a corresponding rise in permeability of the regime and concomitant decrease in Darcian impedance. Thermal radiation is seen to reduce both velocity and temperature in the boundary layer. Local Nusselt number is also found to be enhanced with increasing both porosity and radiation parameters. © 2011 Elsevier B.V.

  1. Critical heat-flux experiments under low-flow conditions in a vertical annulus

    International Nuclear Information System (INIS)

    Mishima, K.; Ishii, M.

    1982-03-01

    An experimental study was performed on critical heat flux (CHF) at low flow conditions for low pressure steam-water upward flow in an annulus. The test section was transparent, therefore, visual observations of dryout as well as various instrumentations were made. The data indicated that a premature CHF occurred due to flow regime transition from churn-turbulent to annular flow. It is shown that the critical heat flux observed in the experiment is essentially similar to a flooding-limited burnout and the critical heat flux can be well reproduced by a nondimensional correlation derived from the previously obtained criterion for flow regime transition. The observed CHF values are much smaller than the standard high quality CHF criteria at low flow, corresponding to the annular flow film dryout. This result is very significant, because the coolability of a heater surface at low flow rates can be drastically reduced by the occurrence of this mode of CHF

  2. Confined dense particle-gas flow, application to nuclear fuel relocation

    International Nuclear Information System (INIS)

    Martin, A.

    2010-02-01

    In this work, we investigate particle-gas two-phase flows in the jamming regime where the flow stops in finite time. In this regime, which occurs quite often in nature and industrial applications, the flow is stochastic and needs therefore to be characterized by the jamming probability as well as the flow rate and its fluctuations that depend on the confining geometry, granular microstructure and gas properties. We developed a numerical approach based on the coupling of the Non Smooth Contact Dynamics for the solid phase and a mesoscopic method for the gas phase. We find that the flow rate as a function of the opening is well fit by a power law in agreement with reported experimental data. The presence of a gas affects only the mean flow rate, the flow statistics being sensibly the same as in the absence of the gas. We apply our quantitative statistical results in order to estimate the relocation rate of fragmented nuclear fuel inside its cladding tube as a result of a local balloon caused by an accident (loss-of-coolant accident). (author)

  3. Actual evapotranspiration, root extraction, water regime and productivity in the case of lucerne

    International Nuclear Information System (INIS)

    Rambal, S.; Berger, A.; Parisot, J.M.

    1983-01-01

    Measurements were made of the actual evaportranspiration, root extraction and above-ground yield in the case of two varieties of lucerne Medicago sativa L. - Du Puits and Polder - and mixtures of them in equal parts. The daily kinetics of the water potential of the leaves and the collar show that the water regimes of the two varieties are identical in a first approximation. The root systems are different. Polder has the deeper system. The regime of the binary mixture is not simply a juxtaposition of the regimes of the constitutents. Two types of non-linearity were found. The first relates to water flow and the second to productivity. It is postulated that the root systems of the two varieties constituting the mixture undergo plastic deformation, leading to a more efficient resultant system. A system of this type needs, on the other hand, an allocation of photosynthates that would affect its productivity. (author)

  4. Effects of flow dynamics on the aquatic-terrestrial transition zone (ATTZ) of lower Missouri river sandbars with implications for selected biota

    Science.gov (United States)

    Tracy-Smith, Emily; Galat, David L.; Jacobson, Robert B.

    2012-01-01

    Sandbars are an important aquatic terrestrial transition zone (ATTZ) in the active channel of rivers that provide a variety of habitat conditions for riverine biota. Channelization and flow regulation in many large rivers have diminished sandbar habitats and their rehabilitation is a priority. We developed sandbar-specific models of discharge-area relationships to determine how changes in flow regime affect the area of different habitat types within the submerged sandbar ATTZ (depth) and exposed sandbar ATTZ (elevation) for a representative sample of Lower Missouri River sandbars. We defined six different structural habitat types within the sandbar ATTZ based on depth or exposed elevation ranges that are important to different biota during at least part of their annual cycle for either survival or reproduction. Scenarios included the modelled natural flow regime, current managed flow regime and two environmental flow options, all modelled within the contemporary river active channel. Thirteen point and wing-dike sandbars were evaluated under four different flow scenarios to explore the effects of flow regime on seasonal habitat availability for foraging of migratory shorebirds and wading birds, nesting of softshell turtles and nursery of riverine fishes. Managed flows provided more foraging habitat for shorebirds and wading birds and more nursery habitat for riverine fishes within the channelized reach sandbar ATTZ than the natural flow regime or modelled environmental flows. Reduced summer flows occurring under natural and environmental flow alternatives increased exposed sandbar nesting habitat for softshell turtle hatchling emergence. Results reveal how management of channelized and flow regulated large rivers could benefit from a modelling framework that couples hydrologic and geomorphic characteristics to predict habitat conditions for a variety of biota.

  5. Causas estruturais e consequências dos regimes internacionais: regimes como variáveis intervenientes

    OpenAIRE

    Krasner, Stephen D.

    2012-01-01

    Os regimes internacionais são definidos como princípios, normas, regras e procedimentos de tomada de decisões ao redor dos quais as expectativas dos atores convergem em uma dada área-tema. Como ponto de partida, os regimes são conceituados como variáveis intervenientes, estando entre fatores causais básicos e os resultados e comportamentos relacionados. Há três visões a respeito da importância dos regimes: as orientações estruturais convencionais desvalorizam os regimes como sendo, na melhor ...

  6. Flow boiling in microgap channels experiment, visualization and analysis

    CERN Document Server

    Alam, Tamanna; Jin, Li-Wen

    2013-01-01

    Flow Boiling in Microgap Channels: Experiment, Visualization and Analysis presents an up-to-date summary of the details of the confined to unconfined flow boiling transition criteria, flow boiling heat transfer and pressure drop characteristics, instability characteristics, two phase flow pattern and flow regime map and the parametric study of microgap dimension. Advantages of flow boiling in microgaps over microchannels are also highlighted. The objective of this Brief is to obtain a better fundamental understanding of the flow boiling processes, compare the performance between microgap and c

  7. Another look at zonal flows: Resonance, shearing, and frictionless saturation

    Science.gov (United States)

    Li, J. C.; Diamond, P. H.

    2018-04-01

    We show that shear is not the exclusive parameter that represents all aspects of flow structure effects on turbulence. Rather, wave-flow resonance enters turbulence regulation, both linearly and nonlinearly. Resonance suppresses the linear instability by wave absorption. Flow shear can weaken the resonance, and thus destabilize drift waves, in contrast to the near-universal conventional shear suppression paradigm. Furthermore, consideration of wave-flow resonance resolves the long-standing problem of how zonal flows (ZFs) saturate in the limit of weak or zero frictional drag, and also determines the ZF scale. We show that resonant vorticity mixing, which conserves potential enstrophy, enables ZF saturation in the absence of drag, and so is effective at regulating the Dimits up-shift regime. Vorticity mixing is incorporated as a nonlinear, self-regulation effect in an extended 0D predator-prey model of drift-ZF turbulence. This analysis determines the saturated ZF shear and shows that the mesoscopic ZF width scales as LZ F˜f3 /16(1-f ) 1 /8ρs5/8l03 /8 in the (relevant) adiabatic limit (i.e., τckk‖2D‖≫1 ). f is the fraction of turbulence energy coupled to ZF and l0 is the base state mixing length, absent ZF shears. We calculate and compare the stationary flow and turbulence level in frictionless, weakly frictional, and strongly frictional regimes. In the frictionless limit, the results differ significantly from conventionally quoted scalings derived for frictional regimes. To leading order, the flow is independent of turbulence intensity. The turbulence level scales as E ˜(γL/εc) 2 , which indicates the extent of the "near-marginal" regime to be γLcase of avalanche-induced profile variability. Here, εc is the rate of dissipation of potential enstrophy and γL is the characteristic linear growth rate of fluctuations. The implications for dynamics near marginality of the strong scaling of saturated E with γL are discussed.

  8. Variations of Hydrological Regime in the Jingjiang Reach of the Yangtze River after Operation of the Three Gorges Project

    Science.gov (United States)

    Zhu, Y.-H.; Guo, X.-H.; Hu, W.; Qu, G.; He, G.-S.

    2012-04-01

    The Three Gorges Project (TGP) of China has been in operation since 2003. In October 2010 the water level at the Three Gorges Dam (TGD) rose to the normal storage water level of 175 m, indicting the realization of the integrated targets of the TGP in terms of flood protection, electricity generation, navigation, etc. The operation of the TGP has changed the flow and sediment conditions (i.e. the hydrological regime) of the river channel downstream. The 347.2 km Jingjiang Reach, part of the middle reach of the Yangtze River, is very closely dowstream of the TGD and is affected relatively earlier and significant by the project operation. Based on the measured prototype hydrological data from 1950 to 2010, variations of the hydrological regime in the Jingjiang Reach after operation of the TGP are analyzed. The results showing that the runoff of the river is of no clear variation tendency during the last 60 years. However, after the operation of the TGP, the sediment concentration of the flow in the Jingjiang Reach decreased by 75%; coarsening of the suspended load and bed load in the river is evident; the water level at the same flow rate has a tendency to decline, with the margin of decline of the upper Jingjiang Reach being larger than that of the lower Reach, and that at smaller flow rate being larger than at larger flow rate. The flow and sediment diversion from the Yangtze River to the Dongting Lake via the three outlets also has a tendency to decrease; the degree of dcrease of the sediment diversion is much larger than that of the flow diversion. After the operation of the TGP, except the 2006 is a special low flow year, in which the decrease of the ratios of flow and sediment diversion are relatively large, the ratios are of no clear unidirectional variation tendency in the other years. Due to the operation of the TGP, within one year, the flow diversion in October is decreased comparing with that before the operation. Keywords: The Three Gorges Project, the

  9. Statistical Mechanics of the Geometric Control of Flow Topology in Two-Dimensional Turbulence

    Science.gov (United States)

    Nadiga, Balasubramanya; Loxley, Peter

    2013-04-01

    We apply the principle of maximum entropy to two dimensional turbulence in a new fashion to predict the effect of geometry on flow topology. We consider two prototypical regimes of turbulence that lead to frequently observed self-organized coherent structures. Our theory predicts bistable behavior that exhibits hysteresis and large abrupt changes in flow topology in one regime; the other regime is predicted to exhibit monstable behavior with a continuous change of flow topology. The predictions are confirmed in fully nonlinear numerical simulations of the two-dimensional Navier-Stokes equation. These results suggest an explanation of the low frequency regime transitions that have been observed in the non-equilibrium setting of this problem. Following further development in the non-equilibrium context, we expect that insights developed in this problem should be useful in developing a better understanding of the phenomenon of low frequency regime transitions that is a pervasive feature of the weather and climate systems. Familiar occurrences of this phenomenon---wherein extreme and abrupt qualitative changes occur, seemingly randomly, after very long periods of apparent stability---include blocking in the extra-tropical winter atmosphere, the bimodality of the Kuroshio extension system, the Dansgaard-Oeschger events, and the glacial-interglacial transitions.

  10. A constitutive law for dense granular flows.

    Science.gov (United States)

    Jop, Pierre; Forterre, Yoël; Pouliquen, Olivier

    2006-06-08

    A continuum description of granular flows would be of considerable help in predicting natural geophysical hazards or in designing industrial processes. However, the constitutive equations for dry granular flows, which govern how the material moves under shear, are still a matter of debate. One difficulty is that grains can behave like a solid (in a sand pile), a liquid (when poured from a silo) or a gas (when strongly agitated). For the two extreme regimes, constitutive equations have been proposed based on kinetic theory for collisional rapid flows, and soil mechanics for slow plastic flows. However, the intermediate dense regime, where the granular material flows like a liquid, still lacks a unified view and has motivated many studies over the past decade. The main characteristics of granular liquids are: a yield criterion (a critical shear stress below which flow is not possible) and a complex dependence on shear rate when flowing. In this sense, granular matter shares similarities with classical visco-plastic fluids such as Bingham fluids. Here we propose a new constitutive relation for dense granular flows, inspired by this analogy and recent numerical and experimental work. We then test our three-dimensional (3D) model through experiments on granular flows on a pile between rough sidewalls, in which a complex 3D flow pattern develops. We show that, without any fitting parameter, the model gives quantitative predictions for the flow shape and velocity profiles. Our results support the idea that a simple visco-plastic approach can quantitatively capture granular flow properties, and could serve as a basic tool for modelling more complex flows in geophysical or industrial applications.

  11. Two-phase flow measurements using a photochromic dye activation technique

    International Nuclear Information System (INIS)

    Kawaji, M.

    1998-01-01

    A novel flow visualization method called photochromic dye activation (PDA) technique has been used to investigate flow structures and mechanisms in various two-phase flow regimes. This non-intrusive flow visualization technique utilizes light activation of a photochromic dye material dissolved in a clear liquid and is a molecular tagging technique, requiring no seed particles. It has been used to yield both quantitative and qualitative flow data in the liquid phase in annular flow, slug flow and stratified-wavy flows. (author)

  12. Assessment of acid mine drainage remediation schemes on ground water flow regimes at a reclaimed mine site

    International Nuclear Information System (INIS)

    Gabr, M.A.; Bowders, J.J.

    1994-01-01

    Ground water modeling and a field monitoring program were conducted for a 35-acre reclaimed surface mine site that continues to produce acid mine drainage (AMD). The modeling effort was focused on predicting the effectiveness of various remedial measures implemented at the site for the abatement of AMD on predicting the effectiveness of various remedial measures implemented at the site for the abatement of AMD production. The field work included surface surveys and monitoring of ground water levels with time, seepage areas, and sedimentation ponds located on the site. The surveys provided the physical and topographic characteristics of the site. Pump tests conducted at the site provided general hydraulic conductivities (k) for two major areas of the site; undisturbed area (k ≅ 2.9 x 10 -5 ft/s) and disturbed area (k ≅ 3.3 x 10 -4 ft/s to 2.0 x 10 -3 ft/s). The monitored ground water data indicated rapid change in ground water levels during recharge events. Such behavior is indicative of flow regime that is dominated by fracture flow. Modeling of an approximately 700 ft by 1,500 ft area of the site was achieved using the US GS code MODFLOW, and ground water field measurements were used to calibrate the model. A hydraulic conductivity of about 1.15 x 10 -3 ft/s was estimated for the undisturbed area and 1.15 x 10 -2 ft/s for the reclaimed area. Remedial measures for diverting the ground water away from the areas of spoil included the use of a subsurface seepage cutoff wall and discrete sealing techniques. Modeling results indicated that the most effective remedial technique for this site is the use of a subsurface seepage cutoff wall installed at the interface (highwall) between the disturbed and undisturbed zones. Using this scheme caused a dewatering effect in the reclaimed area and therefore reduction in the volume of the AMD generated at the site

  13. Scaling properties reveal regulation of river flows in the Amazon through a forest reservoir

    Science.gov (United States)

    Salazar, Juan Fernando; Villegas, Juan Camilo; María Rendón, Angela; Rodríguez, Estiven; Hoyos, Isabel; Mercado-Bettín, Daniel; Poveda, Germán

    2018-03-01

    Many natural and social phenomena depend on river flow regimes that are being altered by global change. Understanding the mechanisms behind such alterations is crucial for predicting river flow regimes in a changing environment. Here we introduce a novel physical interpretation of the scaling properties of river flows and show that it leads to a parsimonious characterization of the flow regime of any river basin. This allows river basins to be classified as regulated or unregulated, and to identify a critical threshold between these states. We applied this framework to the Amazon river basin and found both states among its main tributaries. Then we introduce the forest reservoir hypothesis to describe the natural capacity of river basins to regulate river flows through land-atmosphere interactions (mainly precipitation recycling) that depend strongly on the presence of forests. A critical implication is that forest loss can force the Amazonian river basins from regulated to unregulated states. Our results provide theoretical and applied foundations for predicting hydrological impacts of global change, including the detection of early-warning signals for critical transitions in river basins.

  14. Study of gas-water flow in horizontal rectangular channels

    Science.gov (United States)

    Chinnov, E. A.; Ron'shin, F. V.; Kabov, O. A.

    2015-09-01

    The two-phase flow in the narrow short horizontal rectangular channels 1 millimeter in height was studied experimentally. The features of formation of the two-phase flow were studied in detail. It is shown that with an increase in the channel width, the region of the churn and bubble regimes increases, compressing the area of the jet flow. The areas of the annular and stratified flow patterns vary insignificantly.

  15. Nature and characteristics of pulsing flow in trickle-bed reactors

    NARCIS (Netherlands)

    Boelhouwer, J.G.; Piepers, H.W.; Drinkenburg, A.A.H.

    2002-01-01

    Pulsing flow is well known for its advantages in terms of an increase in mass and heat transfer rates, complete catalyst wetting and a decrease in axial dispersion compared to trickle flow. The operation of a trickle-bed reactor in the pulsing flow regime is favorable in terms of a capacity increase

  16. Helium transport and exhaust studies in enhanced confinement regimes in DIII-D

    International Nuclear Information System (INIS)

    Wade, M.R.; Hillis, D.L.; Hogan, J.T.; Mahdavi, M.A.; Maingi, R.; West, W.P.; Burrell, K.H.; Finkenthal, D.F.; Gohil, P.; Groebner, R.J.

    1995-02-01

    A better understanding of helium transport in the plasma core and edge in enhanced confinement regimes is now emerging from recent experimental studies on DIII-D. Overall, the results are encouraging. Significant helium exhaust (τ* He /τ E ∼ 11) has been obtained in a diverted, ELMing H-mode plasma simultaneous with a central source of helium. Detailed analysis of the helium profile evolution indicates that the exhaust rate is limited by the exhaust efficiency of the pump (∼5%) and not by the intrinsic helium transport properties of the plasma. Perturbative helium transport studies using gas puffing have shown that D He /X eff ∼1 in all confinement regimes studied to date (including H-mode and VH-mode). Furthermore, there is no evidence of preferential accumulation of helium in any of these regimes. However, measurements in the core and pumping plenum show a significant dilution of helium as it flows from the plasma core to the pumping plenum. Such dilution could be the limiting factor in the overall removal rate of helium in a reactor system

  17. Sensitivity to spatial and temporal scale and fire regime inputs in deriving fire regime condition class

    Science.gov (United States)

    Linda Tedrow; Wendel J. Hann

    2015-01-01

    The Fire Regime Condition Class (FRCC) is a composite departure measure that compares current vegetation structure and fire regime to historical reference conditions. FRCC is computed as the average of: 1) Vegetation departure (VDEP) and 2) Regime (frequency and severity) departure (RDEP). In addition to the FRCC rating, the Vegetation Condition Class (VCC) and Regime...

  18. Effects of curvature on rarefied gas flows between rotating concentric cylinders

    Science.gov (United States)

    Dongari, Nishanth; White, Craig; Scanlon, Thomas J.; Zhang, Yonghao; Reese, Jason M.

    2013-05-01

    The gas flow between two concentric rotating cylinders is considered in order to investigate non-equilibrium effects associated with the Knudsen layers over curved surfaces. We investigate the nonlinear flow physics in the near-wall regions using a new power-law (PL) wall-scaling approach. This PL model incorporates Knudsen layer effects in near-wall regions by taking into account the boundary limiting effects on the molecular free paths. We also report new direct simulation Monte Carlo results covering a wide range of Knudsen numbers and accommodation coefficients, and for various outer-to-inner cylinder radius ratios. Our simulation data are compared with both the classical slip flow theory and the PL model, and we find that non-equilibrium effects are not only dependent on Knudsen number and accommodation coefficient but are also significantly affected by the surface curvature. The relative merits and limitations of both theoretical models are explored with respect to rarefaction and curvature effects. The PL model is able to capture some of the nonlinear trends associated with Knudsen layers up to the early transition flow regime. The present study also illuminates the limitations of classical slip flow theory even in the early slip flow regime for higher curvature test cases, although the model does exhibit good agreement throughout the slip flow regime for lower curvature cases. Torque and velocity profile comparisons also convey that a good prediction of integral flow properties does not necessarily guarantee the accuracy of the theoretical model used, and it is important to demonstrate that field variables are also predicted satisfactorily.

  19. Design of Environmental Flows Below Diversion Hydropower Dams: Is There Benefit to Advanced Streamflow Prediction in Sparse Data Landscapes?

    Science.gov (United States)

    Kibler, K. M.; Alipour, M.

    2017-12-01

    Diversion hydropower has been shown to significantly alter river flow regimes by dewatering diversion bypass reaches. Data scarcity is one of the foremost challenges to establishing environmental flow regimes below diversion hydropower dams, especially in regions of sparse hydro-meteorological observation. Herein, we test two prediction strategies for generating daily flows in rivers developed with diversion hydropower: a catchment similarity model, and a rainfall-runoff model selected by multi-objective optimization based on soft data. While both methods are designed for ungauged rivers embedded within large regions of sparse hydrologic observation, one is more complex and computationally-intensive. The objective of this study is to assess the benefit of using complex modeling tools in data-sparse landscapes to support design of environmental flow regimes. Models were tested in gauged catchments and then used to simulate a 28-year record of daily flows in 32 ungauged rivers. After perturbing flows with the hydropower diversion, we detect alteration using Indicators of Hydrologic Alteration (IHA) metrics and compare outcomes of the two modeling approaches. The catchment similarity model simulates low flows well (Nash-Sutcliff efficiency (NSE) = 0.91), but poorly represents moderate to high flows (overall NSE = 0.25). The multi-objective rainfall-runoff model performs well overall (NSE = 0.72). Both models agree that flow magnitudes and variability consistently decrease following diversion as temporally-dynamic flows are replaced by static minimal flows. Mean duration of events sustained below the pre-diversion Q75 and mean hydrograph rise and fall rates increase. While we see broad areas of agreement, significant effects and thresholds vary between models, particularly in the representation of moderate flows. Thus, use of simplified streamflow models may bias detected alterations or inadequately characterize pre-regulation flow regimes, providing inaccurate

  20. The stability of Z-pinches with equilibrium flows

    International Nuclear Information System (INIS)

    Howell, D.F.

    1999-01-01

    According to Ideal Magnetohydrodynamic (MHD) theory the Z-pinch is an inherently unstable magnetic configuration. However it is possible that there exist regimes of operation whereby the predicted instabilities may be reduced or even eliminated. We must look to effects normally ignored in the Ideal MHD model in order to predict such regimes. In this thesis various non-ideal effects will be studied, namely the inclusion of equilibrium flow and finite Larmor radius effects. Astrophysical jets, for example those seen to be emitted from active galactic nuclei, are seen to persist for a greater time than suggested by Ideal MHD before the onset of instabilities. It is postulated that one of the contributing factors to this enhanced stability is the presence of a sheared axial flow. In this thesis we study the stability properties of the Z-pinch where flow is present in the equilibrium. It is found that a sheared axial flow generally has a stabilising effect, the degree of which is determined by the equilibrium and flow profiles, but that absolute stability cannot be achieved due to the onset of the Kelvin-Helmholtz instability. The effect of adding rotation has also been studied. It is found that adding rotation changes the equilibrium density profiles from the static case, and that it always has a destabilising effect. Another postulated method of stabilising the Z-pinch is by increasing the ratio of the ion Larmor radius to the pinch radius, and it is seen to have a stabilising effect for some equilibria in the collisionless regime. In this thesis we study the effects of increasing the Larmor radius in the collisional regime using the Hall fluid model. It is found that for free boundary modes the stability properties are unchanged for experimentally realistic values of the Larmor radius, but for fixed boundary modes a small stabilising effect is noted for some equilibria. (author)

  1. Assessment of dam construction impact on hydrological regime changes in lowland river – A case of study: the Stare Miasto reservoir located on the Powa River

    Directory of Open Access Journals (Sweden)

    Sojka Mariusz

    2016-09-01

    Full Text Available The purpose of the presented research is analysis and assessment of the Stare Miasto reservoir impact on the hydrological regime changes of the Powa River. The reservoir was built in 2006 and is located in the central part of Poland. The total area of inundation in normal conditions is 90.68 ha and its capacity is 2.159 mln m3. Hydrological regime alteration of the Powa River is analysed on the basis of daily flows from the Posoka gauge station observed during period 1974–2014. Assessment of hydrological regime changes is carried out on the basis of Range of Variability Approach (RVA method. All calculations are made by means of Indicators of Hydrologic Alteration (IHA software version 7.1.0.10. The analysis shows that the Stare Miasto reservoir has a moderate impact on hydrological regime of the Powa River. Construction of the reservoir has positive effect on stability of minimal flows, which are important for protection of river ecosystems. The results obtained indicate that the Stare Miasto reservoir reduces a spring peak flow and enables to moderate control of floods.

  2. Heat and fluid flow during rapid solidification of non-equilibrium materials

    International Nuclear Information System (INIS)

    Negli, S.C.; Eddingfield, D.L.; Brower, W.E. Jr.

    1990-01-01

    Rapid solidification technology (RST) is an advanced solidification process which is being utilized to produce non-equilibrium structures with properties not previously available with conventionally cast materials. An iron based alloy rapidly quenched to form a metallic glass is being installed on a large scale in electric power transformers where it cuts heat losses dramatically. The formation of a non-equilibrium structure usually requires a cooling rate of at least a million degrees per second. Achieving this high a cooling rate depends not only on the heat transfer conditions during the quenching process, but also on the fluid flow conditions in the molten metal before and during solidification. This paper presents a model of both heat and fluid flow during RST by the hammer and anvil method. The symmetry of two sided cooling permits analysis which is still applicable to the one sided cooling that occurs during melt spinning, the prevalent method of RST. The heat flow is modeled as one dimensional, normal to the quench surface. Previous models have shown the heat flow in the plane of the quench surface not to be significant. The fluid flow portion of the model utilizes the squeeze film solution for flow between two parallel flat plates. The model predicts the effects of superheat of the melt and of the quench hammer speed upon cooling rate during the formation of nonequilibrium phases. An unexpected result is that increased superheat results in much higher cooling rates, due to fluid flow before a potential transformation would take place; this enhanced liquid metal flow results in a thinner section casting which in turn has a dominant effect on the cooling rate. The model also predicts an expanded regime of Newtonian (interface controlled) cooling by about a factor of ten as compared to previous model of RST

  3. Urban base flow with low impact development

    Science.gov (United States)

    Bhaskar, Aditi; Hogan, Dianna M.; Archfield, Stacey A.

    2016-01-01

    A novel form of urbanization, low impact development (LID), aims to engineer systems that replicate natural hydrologic functioning, in part by infiltrating stormwater close to the impervious surfaces that generate it. We sought to statistically evaluate changes in a base flow regime because of urbanization with LID, specifically changes in base flow magnitude, seasonality, and rate of change. We used a case study watershed in Clarksburg, Maryland, in which streamflow was monitored during whole-watershed urbanization from forest and agricultural to suburban residential development using LID. The 1.11-km2 watershed contains 73 infiltration-focused stormwater facilities, including bioretention facilities, dry wells, and dry swales. We examined annual and monthly flow during and after urbanization (2004–2014) and compared alterations to nearby forested and urban control watersheds. We show that total streamflow and base flow increased in the LID watershed during urbanization as compared with control watersheds. The LID watershed had more gradual storm recessions after urbanization and attenuated seasonality in base flow. These flow regime changes may be because of a reduction in evapotranspiration because of the overall decrease in vegetative cover with urbanization and the increase in point sources of recharge. Precipitation that may once have infiltrated soil, been stored in soil moisture to be eventually transpired in a forested landscape, may now be recharged and become base flow. The transfer of evapotranspiration to base flow is an unintended consequence to the water balance of LID.

  4. Double helix vortex breakdown in a turbulent swirling annular jet flow

    NARCIS (Netherlands)

    Vanierschot, M.; Perçin, M.; van Oudheusden, B.W.

    2018-01-01

    In this paper, we report on the structure and dynamics of double helix vortex breakdown in a turbulent annular swirling jet. Double helix breakdown has been reported previously for the laminar flow regime, but this structure has rarely been observed in turbulent flow. The flow field is

  5. Flux flow and flux creep in thick films of YBCO. [Y-Ba-Cu-O

    Energy Technology Data Exchange (ETDEWEB)

    Rickets, J.; Vinen, W.F.; Abell, J.S.; Shields, T.C. (Superconductivity Research Group, Univ. of Birmingham (United Kingdom))

    1991-12-01

    The results are described of new experiments designed to study flux creep and flux flow along a single flux percolation path in thick films of YBCO. The flux flow regime is studied by a four-point resistive technique using pulsed currents, and the flux creep regime by observing the rate at which flux enters a superconducting loop in parallel with the resistance that is associated with the flux percolation path. (orig.).

  6. Unifying Suspension and Granular flows near Jamming

    Directory of Open Access Journals (Sweden)

    DeGiuli Eric

    2017-01-01

    Full Text Available Rheological properties of dense flows of hard particles are singular as one approaches the jamming threshold where flow ceases, both for granular flows dominated by inertia, and for over-damped suspensions. Concomitantly, the lengthscale characterizing velocity correlations appears to diverge at jamming. Here we review a theoretical framework that gives a scaling description of stationary flows of frictionless particles. Our analysis applies both to suspensions and inertial flows of hard particles. We report numerical results in support of the theory, and show the phase diagram that results when friction is added, delineating the regime of validity of the frictionless theory.

  7. Experimental investigation of two-phase gas-liquid flow in microchannel with T-junction

    Science.gov (United States)

    Bartkus, German; Kozulin, Igor; Kuznetsov, Vladimir

    2017-10-01

    Using high-speed video recording and the method of dual laser scanning the gas-liquid flow was investigated in rectangular microchannels with an aspect ratio of 2.35 and 1.26. Experiments were earned out for the vertical flow of ethanol-nitrogen mixture in a microchannel with a cross section of 553×235 µm and for the horizontal flow of water-nitrogen mixture in a microchannel with a cross section of 315×250 µm. The T-mixer was used at the channel's inlet for gas-liquid flow formation. It was observed that elongated bubble, transition, and annular flows are the main regimes for a microchannel with a hydraulic diameter substantially less than the capillary constant. Using laser scanning, the maps of flow regimes for ethanol-nitrogen and water-nitrogen mixtures were obtained and discussed.

  8. Boomerang RG flows in M-theory with intermediate scaling

    Science.gov (United States)

    Donos, Aristomenis; Gauntlett, Jerome P.; Rosen, Christopher; Sosa-Rodriguez, Omar

    2017-07-01

    We construct novel RG flows of D=11 supergravity that asymptotically approach AdS 4 × S 7 in the UV with deformations that break spatial translations in the dual field theory. In the IR the solutions return to exactly the same AdS 4 × S 7 vacuum, with a renormalisation of relative length scales, and hence we refer to the flows as `boomerang RG flows'. For sufficiently large deformations, on the way to the IR the solutions also approach two distinct intermediate scaling regimes, each with hyperscaling violation. The first regime is Lorentz invariant with dynamical exponent z = 1 while the second has z = 5/2. Neither ofthe two intermediatescaling regimesare associatedwith exact hyperscaling violation solutions of D = 11 supergravity. The RG flow solutions are constructed using the four dimensional N = 2 STU gauged supergravity theory with vanishing gauge fields, but non-vanishing scalar and pseudoscalar fields. In the ABJM dual field theory the flows are driven by spatially modulated deformation parameters for scalar and fermion bilinear operators.

  9. A modeling approach to establish environmental flow threshold in ungauged semidiurnal tidal river

    Science.gov (United States)

    Akter, A.; Tanim, A. H.

    2018-03-01

    Due to shortage of flow monitoring data in ungauged semidiurnal river, 'environmental flow' (EF) determination based on its key component 'minimum low flow' is always difficult. For EF assessment this study selected a reach immediately after the Halda-Karnafuli confluence, a unique breeding ground for Indian Carp fishes of Bangladesh. As part of an ungauged tidal river, EF threshold establishment faces challenges in changing ecological paradigms with periodic change of tides and hydrologic alterations. This study describes a novel approach through modeling framework comprising hydrological, hydrodynamic and habitat simulation model. The EF establishment was conceptualized according to the hydrologic process of an ungauged semi-diurnal tidal regime in four steps. Initially, a hydrologic model coupled with a hydrodynamic model to simulate flow considering land use changes effect on streamflow, seepage loss of channel, friction dominated tidal decay as well as lack of long term flow characteristics. Secondly, to define hydraulic habitat feature, a statistical analysis on derived flow data was performed to identify 'habitat suitability'. Thirdly, to observe the ecological habitat behavior based on the identified hydrologic alteration, hydraulic habitat features were investigated. Finally, based on the combined habitat suitability index flow alteration and ecological response relationship was established. Then, the obtained EF provides a set of low flow indices of desired regime and thus the obtained discharge against maximum Weighted Usable Area (WUA) was defined as EF threshold for the selected reach. A suitable EF regime condition was obtained within flow range 25-30.1 m3/s i.e., around 10-12% of the mean annual runoff of 245 m3/s and these findings are within researchers' recommendation of minimum flow requirement. Additionally it was observed that tidal characteristics are dominant process in semi-diurnal regime. However, during the study period (2010-2015) the

  10. Two-phase flow characteristic of inverted bubbly, slug and annular flow in post-critical heat flux region

    International Nuclear Information System (INIS)

    Ishii, M.; Denten, J.P.

    1988-01-01

    Inverted annular flow can be visualized as a liquid jet-like core surrounded by a vapor annulus. While many analytical and experimental studies of heat transfer in this regime have been performed, there is very little understanding of the basic hydrodynamics of the post-CHF flow field. However, a recent experimental study was done that was able to successfully investigate the effects of various steady-state inlet flow parameters on the post-CHF hydrodynamics of the film boiling of a single phase liquid jet. This study was carried out by means of a visual photographic analysis of an idealized single phase core inverted annular flow initial geometry (single phase liquid jet core surrounded by a coaxial annulus of gas). In order to extend this study, a subsequent flow visualization of an idealized two-phase core inverted annular flow geometry (two-phase central jet core, surrounded by a coaxial annulus of gas) was carried out. The objective of this second experimental study was to investigate the effect of steady-state inlet, pre-CHF two-phase jet core parameters on the hydrodynamics of the post-CHF flow field. In actual film boiling situations, two-phase flows with net positive qualities at the CHF point are encountered. Thus, the focus of the present experimental study was on the inverted bubbly, slug, and annular flow fields in the post dryout film boiling region. Observed post dryout hydrodynamic behavior is reported. A correlation for the axial extent of the transition flow pattern between inverted annular and dispersed droplet flow (the agitated regime) is developed. It is shown to depend strongly on inlet jet core parameters and jet void fraction at the dryout point. 45 refs., 9 figs., 4 tabs

  11. Two-phase flow characteristic of inverted bubbly, slug, and annular flow in post-critical heat flux region

    International Nuclear Information System (INIS)

    Ishii, M.; Denten, J.P.

    1989-01-01

    Inverted annular flow can be visualized as a liquid jet-like core surrounded by a vapor annulus. While many analytical and experimental studies of heat transfer in this regime have been performed, there is very little understanding of the basic hydrodynamics of the post-critical heat flux (CHF) flow field. However, a recent experimental study was done that was able to successfully investigate the effects of various steady-state inlet flow parameters on the post-CHF hydrodynamics of the film boiling of a single phase liquid jet. This study was carried out by means of a visual photographic analysis of an idealized single phase core inverted annular flow initial geometry (single phase liquid jet core surrounded by a coaxial annulus of gas). In order to extend this study, a subsequent flow visualization of an idealized two-phase core inverted annular flow geometry (two-phase central jet core, surrounded by a coaxial annulus of gas) was carried out. The objective of this second experimental study was to investigate the effect of steady-state inlet, pre-CHF two-phase jet core parameters on the hydrodynamics of the post-CHF flow field. In actual film boiling situations, two-phase flows with net positive qualities at the CHF point are encountered. Thus, the focus of the present experimental study was on the inverted bubbly, slug, and annular flow fields in the post dryout film boiling region. Observed post dryout hydrodynamic behavior is reported. A correlation for the axial extent of the transition flow pattern between inverted annular and dispersed droplet flow (the agitated regime) is developed. It is shown to depend strongly on inlet jet core parameters and jet void fraction at the dryout point

  12. Investigation of high frequency external perturbation effects on flow in a T-shape microchannel by μLIF technique

    Science.gov (United States)

    Kravtsova, A. Yu; Meshalkin, Yu E.; Bilsky, A. V.

    2017-11-01

    Investigation of high frequency external perturbation effect on flow inside T-shape microchannel was examined. In-phase pulsations of different frequencies were added to both inlets of the T-shaped microchannel to study mixing by means of Micro Laser Induced Fluorescence (μLIF) technique. For all flow regimes studied, mixing enhancement was obtained. Significant enhancement can be achieved at the beginning of the outlet channel operating in steady asymmetric regime (Re=186) by forcing at certain frequency ranges (f = 500Hz, f = 800Hz). Mixing suppression was also observed for two flow regimes (Re = 400, f = 1000Hz) and (Re = 120, f = 700Hz).

  13. Probabilistic description of traffic flow

    International Nuclear Information System (INIS)

    Mahnke, R.; Kaupuzs, J.; Lubashevsky, I.

    2005-01-01

    A stochastic description of traffic flow, called probabilistic traffic flow theory, is developed. The general master equation is applied to relatively simple models to describe the formation and dissolution of traffic congestions. Our approach is mainly based on spatially homogeneous systems like periodically closed circular rings without on- and off-ramps. We consider a stochastic one-step process of growth or shrinkage of a car cluster (jam). As generalization we discuss the coexistence of several car clusters of different sizes. The basic problem is to find a physically motivated ansatz for the transition rates of the attachment and detachment of individual cars to a car cluster consistent with the empirical observations in real traffic. The emphasis is put on the analogy with first-order phase transitions and nucleation phenomena in physical systems like supersaturated vapour. The results are summarized in the flux-density relation, the so-called fundamental diagram of traffic flow, and compared with empirical data. Different regimes of traffic flow are discussed: free flow, congested mode as stop-and-go regime, and heavy viscous traffic. The traffic breakdown is studied based on the master equation as well as the Fokker-Planck approximation to calculate mean first passage times or escape rates. Generalizations are developed to allow for on-ramp effects. The calculated flux-density relation and characteristic breakdown times coincide with empirical data measured on highways. Finally, a brief summary of the stochastic cellular automata approach is given

  14. Experimental study of two-phase flow in a proton exchange membrane fuel cell in short-term microgravity condition

    International Nuclear Information System (INIS)

    Guo, Hang; Liu, Xuan; Zhao, Jian Fu; Ye, Fang; Ma, Chong Fang

    2014-01-01

    Highlights: • Two-phase flow in PEMFC cathode channels is observed in different gravity environments. • The PEMFC shows different operating behavior in normal and microgravity conditions. • Water tends can be removed in microgravity conditions at high water production regime. • Liquid aggregation occurs in microgravity conditions at low water production regime. • Effect of gravity on performance and two-phase flow at two operating regimes is studied. - Abstract: Water management is important for improving the performance and stability of proton exchange membrane fuel cells (PEMFCs) for space applications. An in situ visual observation was conducted on the gas–liquid two-phase flow in the cathode channels of a PEMFC in short-term microgravity condition. The microgravity environment was supplied by a drop tower. A single serpentine flow channel with a depth of 2 mm and a width of 2 mm was applied as the cathode flow field. A membrane electrode assembly comprising of a Nafion 112 membrane sandwiched between gas diffusion layers was used. The anode and cathode were loaded with 1 mg cm −2 platinum. The PEMFC shows a distinct operating behavior in microgravity because of the effect of gravity on the two-phase flow. At a high water production regime, cell performance is enhanced by 4.6% and the accumulated liquid water in the flow channel tends can be removed in microgravity conditions to alleviate flooding. At a low water production regime, cell performance deteriorates by 6.6% and liquid aggregation occurs in the flow channel because of the coalescence of dispersed water droplets in microgravity conditions, thus squeezing the flow channel. The operating behavior of PEMFC in microgravity conditions is different from that in normal gravity conditions. Further studies are needed on PEMFC operating characteristics and liquid management for space applications

  15. An Experimental and analytical study on the bubble-to-slug flow regime transition based on the void wave instability

    International Nuclear Information System (INIS)

    Song, Chul Hwa

    1995-02-01

    An experimental and analytical work is performed to investigate the relation between the developing phenomena in bubble flow and the propagation phenomena of void waves. For this purpose, the structural developments in bubble flow and the propagation property of void waves are measured over a broad range of flow conditions including the bubble-to-slug flow regime transition (BSFRT) region. And a linear stability analysis is performed, based on the two-fluid model, to establish the analytical model on the wave propagation parameters, and the predictability of the model is validated by comparing analytical results with experimental observations. In the experimental work, an impedance void meter is developed to measure the void fraction, and a series of test are performed by varying the bubble size in order to investigate the bubble size effect on the bubble flow structures for various flow conditions. Statistical signal processing techniques are applied to void signals in order to objectively identify the changing modes of bubble flow structures and to estimate the wave propagation properties. The impedance void meter developed in this study showed very good temporal and spatial resolutions enough to identify the developing phenomena in bubble flow structures and to investigate the void wave propagations, and the void distribution effect could be minimized by electrically shielding the guard electrodes. It was also designed so that the inherent errors due to the phase shifts between channels be negligible. Various features occurred in the transitional process of bubble flow could be objectively identified by introducing some statistical parameters evaluated from void signals. Two distinct modes of structural development in bubble flow were observed in the transitional process, and they are found to be much influenced by the initial bubble size. And the mechanism to govern BSFRT could be characterized by two ways depending on the developing modes of bubble flow

  16. Effects of dam operation on the endangered Júcar nase, Parachondrostoma arrigonis, related to mesohabitats, microhabitat availability and water temperature regime, in the river Cabriel (Spain)

    Science.gov (United States)

    Martinez-Capel, Francisco; Costa, Rui; Muñoz-Mas, Rafael; Diego Alcaraz-Hernandez, Juan; Hernandez-Mascarell, Aina

    2010-05-01

    The presence of large dams affects habitat availability, often regarded as the primary factor that limits population and community recovery in rivers. Physical habitat is often targeted in restoration, but there is often a paucity of useful information. Habitat degradation has reduced the complexity and connectivity of the Mediterranean streams in Spain. These changes have diminished the historical range of the endangered Júcar nase, Parachondrostoma arrigonis (Steindachner, 1866), isolated the populations of this species, and probably contributed to its risk of extinction. In the Júcar River basin (Spain), where this fish is endemic, the populations are mainly restricted to the river Cabriel, which is fragmented in two segments by the large dam of Contreras. In this river, 3 main lines of research were developed from 2006 to 2008, i.e., microhabitat suitability, mesohabitat suitability, and water temperature, in order to relate such kind of variables with the flow regime. The main goal of the research project, funded by the Spanish Ministry of Environment, was to detect the main reasons of the species decline, and to propose dam operation improvements to contribute to the recovery of the species. The flow and water temperature regimes were also studied in the river Cabriel, upstream and downstream the large dam of Contreras. During the three years of study, below the dam it was observed a small and not significant variation in the proportions of slow and fast habitats; the regulated flow regime was pointed out as the main reason of such variations. At the microhabitat scale, optimal ranges for average depth and velocity were defined; these data allowed us to develop an estimation of weighted useable area under natural and regulated conditions. The Júcar nase were found majorly at depths no greater than 1,15 meters with slow water velocities. It was possible to observe a clear alteration of the flow and water temperature regime below the dam, due to the cold

  17. Sliding friction in the hydrodynamic lubrication regime for a power-law fluid

    International Nuclear Information System (INIS)

    Warren, P B

    2017-01-01

    A scaling analysis is undertaken for the load balance in sliding friction in the hydrodynamic lubrication regime, with a particular emphasis on power-law shear-thinning typical of a structured liquid. It is argued that the shear-thinning regime is mechanically unstable if the power-law index n   <  1/2, where n is the exponent that relates the shear stress to the shear rate. Consequently the Stribeck (friction) curve should be discontinuous, with possible hysteresis. Further analysis suggests that normal stress and flow transience (stress overshoot) do not destroy this basic picture, although they may provide stabilising mechanisms at higher shear rates. Extensional viscosity is also expected to be insignificant unless the Trouton ratio is large. A possible application to shear thickening in non-Brownian particulate suspensions is indicated. (paper)

  18. Impacts of changing climate and snow cover on the flow regime of Jhelum River, Western Himalayas

    KAUST Repository

    Azmat, Muhammad; Liaqat, Umar Waqas; Qamar, Muhammad Uzair; Awan, Usman Khalid

    2016-01-01

    This study examines the change in climate variables and snow cover dynamics and their impact on the hydrological regime of the Jhelum River basin in Western Himalayas. This study utilized daily streamflow records from Mangla dam, spanning a time

  19. A spatial assessment of stream-flow characteristics and hydrologic ...

    African Journals Online (AJOL)

    The global hydrologic regime has been intensively altered through activities such as dam construction, water abstraction, and inter-basin transfers. This paper uses the Range of Variability Approach (RVA) and daily stream flow records from nine gauging stations to characterize stream-flow post dam construction in the ...

  20. Economic interpretation of environmental flow regime downstream diverted river reaches.

    Science.gov (United States)

    Gorla, Lorenzo; Perona, Paolo

    2013-04-01

    Water demand for hydropower production is increasing together with the consciousness of the importance of riparian ecosystems and biodiversity. Some Cantons in Switzerland and other alpine regions in Austria and in Sud Tirol (Italy) started replacing the inadequate concept of Minimum Flow Requirement (MFR) with a dynamic one, by releasing a fix percentage of the total inflow (e.g. 25 %) to the environment. In the same direction Perona et al. (in revision) mathematically formulated a method particularly suitable for small hydropower plants, handling the environment as a non-traditional water use, which competes with exploitators. This model uses the Principle of Equal Marginal Utility (PEMU) as optimal water allocation rule for generating like-natural flow releases while maximizing the aggregate economic benefit of all uses (Gorla and Perona, in revision). In this paper we show how redistribution policies can be interpreted in terms of PEMU, particularly we focus at traditional water repartition rules, such as the MFR, but also to dynamic ones like proportional redistribution. For the first case we show both ecological and economical arguments suggesting its inappropriateness; in the second case we highlight explicit points of strength and weakness, and suggest ways of improvement. For example the flow release allocation rule can be changed from inflow-independent ones (e.g., proportional redistribution), to inflow-dependent ones (e.g., non-proportional). The latters, having fewer constraints, can generally lead to better both ecological and economical performances. A class of simple functions, based on the PEMU, is then proposed as a suitable solution in run-of-river or small hydropower plants. Each water repartition policy underlies an ecosystem monetization. We explicit the value of the ecosystem health underlying each policy by means of the PEMU under a few assumptions, and discuss how the theoretic efficient redistribution law obtained by our approach is