Thread-annular flow in vertical pipes
Frei, Ch.; Lüscher, P.; Wintermantel, E.
2000-05-01
Thread injection is a promising method for different minimally invasive medical applications. This paper documents an experimental study dealing with an axially moving thread in annular pipe flow. Mass flow and axial force on the thread are measured for a 0.46 mm diameter thread in pipes with diameters between 0.55 and 1.35 mm. The experiments with thread velocities of up to 1.5 ms[minus sign]1 confirm the findings of theoretical studies that for clinical requirements the radius ratio between thread and pipe is crucial for the adjustments of mass ow and force on the thread.
Air entrainment into annular water flows in a vertical pipe
International Nuclear Information System (INIS)
An experimental investigation was carried out on air entrainment into water flowing downward in a vertical pipe. Local flow rates of water and air in a fluid layer of annular flow, formed on the pipe wall, were measured precisely by using a small tube probe. Measurements were also made of local flow rates of water and air in bubbly flow downstream of annular water flow. Distributions of local flow rates in the radial direction of the pipe for annular flow regime indicate that the fluid layer consists of a water layer adjacent to the pipe wall and a water-air (two-phase fluid) layer located inside of the water layer. The water-air layer is formed as a result of air entrainment. The departure of air bubbles from a water pool to air phase was found for bubbly flow regime. (author)
Two-phase flow instabilities in a vertical annular channel
Energy Technology Data Exchange (ETDEWEB)
Babelli, I.; Nair, S.; Ishii, M. [Purdue Univ., West Lafayette, IN (United States)
1995-09-01
An experimental test facility was built to study two-phase flow instabilities in vertical annular channel with emphasis on downward flow under low pressure and low flow conditions. The specific geometry of the test section is similar to the fuel-target sub-channel of the Savannah River Site (SRS) Mark 22 fuel assembly. Critical Heat Flux (CHF) was observed following flow excursion and flow reversal in the test section. Density wave instability was not recorded in this series of experimental runs. The results of this experimental study show that flow excursion is the dominant instability mode under low flow, low pressure, and down flow conditions. The onset of instability data are plotted on the subcooling-Zuber (phase change) numbers stability plane.
Droplet sizes, dynamics and deposition in vertical annular flow
International Nuclear Information System (INIS)
The role of droplets in vertical upwards annular flow is investigated, focusing on the droplet size distributions, dynamics, and deposition phenomena. An experimental program was performed based on a new laser optical technique developed in these laboratories and implemented here for annular flow. This permitted the simultaneous measurement of droplet size, axial and radial velocity. The dependence of droplet size distributions on flow conditions is analyzed. The Upper-Log Normal function proves to be a good model for the size distribution. The mechanism controlling the maximum stable drop size was found to result from the interaction of the pressure fluctuations of the turbulent flow of the gas core with the droplet. The average axial droplet velocity showed a weak dependence on gas rates. This can be explained once the droplet size distribution and droplet size-velocity relationship are analyzed simultaneously. The surprising result from the droplet conditional analysis is that larger droplet travel faster than smaller ones. This dependence cannot be explained if the drag curves used do not take into account the high levels of turbulence present in the gas core in annular flow. If these are considered, then interesting new situations of multiplicity and stability of droplet terminal velocities are encountered. Also, the observed size-velocity relationship can be explained. A droplet deposition is formulated based on the particle inertia control. This permitted the calculation of rates of drop deposition directly from the droplet size and velocities data
Interfacial friction in low flowrate vertical annular flow
International Nuclear Information System (INIS)
During boil-off and reflood transients in nuclear reactors, the core liquid inventory and inlet flowrate are largely determined by the interfacial friction in the reactor core. For these transients, annular flow occurs at relatively modest liquid flowrates and at the low heat fluxes typical of decay heat conditions. The resulting low vapor Reynolds numbers, are out of the data range used to develop the generally accepted interfacial friction relations for annular flow. In addition, most existing annular flow data comes from air/liquid adiabatic experiments with fully developed flows. By contrast, in a reactor core, the flow is continuously developing along the heated length as the vapor flowrate increases and the flow regimes evolve from bubbly to annular flow. Indeed, the entire annular flow regime may exist only over tens of L/D's. Despite these limitations, many of the advanced reactor safety analysis codes employ the Wallis model for interfacial friction in annular flow. Our analyses of the conditions existing at the end-of-reflood in the PERICLES tests have indicated that the Wallis model seriously underestimates the interfacial shear for low vapor velocity cocurrent upflow. To extend the annular flow data base to diabatic low flowrate conditions, the DADINE tests were re-analyzed. In these tests, both pressure drop and local cross-section averaged void fractions were measured. Thus, both the wall and interfacial shear can be deduced. Based on the results of this analysis, a new correlation is proposed for interfacial friction in annular flow. (authors). 5 figs., 12 refs
Entrainment in vertical annular two-phase flow
International Nuclear Information System (INIS)
Prediction of amount of entrained droplets or entrainment fraction in annular two-phase flow is essential for the estimation of dryout condition and analysis of post dryout heat transfer in light water nuclear reactors and steam boilers. In this study, air-water and organic fluid (Freon-113) annular flow entrainment experiments have been carried out in 9.4 and 10.2 mm diameter test sections, respectively. Both the experiments covered three distinct pressure conditions and wide range of liquid and gas flow conditions. The organic fluid experiments simulated high pressure steam-water annular flow conditions. In each of the experiments, measurements of entrainment fraction, droplet entrainment rate and droplet deposition rate have been performed by using a liquid film extraction method. A simple, explicit and non-dimensional correlation developed by Sawant et al. (2008a) for the prediction of entrainment fraction is further improved in this study in order to account for the existence of critical gas and liquid flow rates below which no entrainment is possible. Additionally, a new correlation is proposed for the estimation of minimum liquid film flow rate at the maximum entrainment fraction condition. The improved correlation successfully predicted the newly collected air-water and Freon-113 entrainment fraction data. Furthermore, the correlations satisfactorily compared with the air-water, helium-water and air-genklene experimental data measured by Willetts (1987). (author)
Sun, Shufeng; Wu, Yuyuan; Zhao, Rongyi
2001-04-01
According to a separated phase flow model for vertical annular two-phase flow in an annular channel, the liquid film thickness, distributions of velocities and temperatures in the liquid layer are predicted in the range of heat fluxes: 6000-12000 W/m 2, mass flux: 500-1100 kg/m2 s. The pressure drop along the flow channel and heat transfer coefficient are also calculated. The liquid film thickness is in the order of micrometers and heat transfer coefficient is 2800-7800 W/m2 K of liquid nitrogen boiling in narrow annular channels. The measured heat transfer coefficient is 29% higher than the calculated values. With the mass flux increasing and the gap of the annular channel decreasing, pressure drop and heat transfer coefficient increase.
TWO-PHASE ANNULAR FLOW IN A VERTICALLY MOUNTED VENTURI FLOW METER
Panella, Bruno; Salve, Mario De; Monni, Grazia
2014-01-01
In the present research work, the experimental investigation of a vertical upward annular two-phase flow in a Venturi Flow Meter (VFM) is performed. The pressure drops between the inlet and throat section and between inlet and outlet (irreversible pressure drops) are measured and analyzed. The flow meter is characterized by an inlet diameter of 80 mm and a throat diameter of 40 mm (β=0.5), with equal convergent and divergent angles (θ=21°). The instrument has been tested in a test section, ha...
Annular flow entrainment rate experiment in a small vertical pipe
International Nuclear Information System (INIS)
Two-fluid model predictions of film dryout in annular flow, leading to nuclear reactor fuel failure, are limited by the uncertainties in the constitutive relations for the entrainment rate of droplets from the liquid film. The main cause of these uncertainties is the lack of separate-effects experimental data in the range of the operating conditions in nuclear power reactors. An air-water experiment has been performed to measure the entrainment rate in a small pipe. The current data extend the available database in the literature to higher gas and liquid flows and also to higher pressures. The measurements were made with the film extraction technique. A mechanistic model was obtained based on Kelvin-Helmholtz' instability theory. The dimensionless model includes the Weber number of the gas and the liquid film Reynolds number. Kataoka and Ishii's correlation (Kataoka, I., Ishii, M., (1982)) is modified based on this model and the new data. The new correlation collapses the present air-water data and Cousins and Hewitt's data (Cousins, L.B. (1968)) The effects of pressure and surface tension were considered in the derivation so it may be applied for boiling water reactor operating conditions. (orig.)
Flooding in vertical counter-current annular flow
International Nuclear Information System (INIS)
The hydrodynamic characteristics of falling liquid films inside a vertical tube (50.8 mm ID and 244 cm high) with counter-current interfacial shear at the onset of flooding have been investigated experimentally. High speed video photography and a flow visualization technique were utilized to investigate the mechanisms involved in the initiation of the flooding phenomenon over a wide range of liquid film Reynolds number (ReL=Γ4/μ) from 1391 to 6584 at a distance of 150 cm from the liquid inlet. The present experimental data indicated neither the interfacial wave growth nor reversal in the wave propagation could be responsible for the initiation of flooding. Also the measured velocity profiles indicated only a slight reduction in liquid velocity within a narrow region very close to the gas-liquid interface, and no flow reversal in the liquid film at the measurement location.
Flooding in vertical counter-current annular flow
International Nuclear Information System (INIS)
The hydrodynamic characteristics of falling liquid films inside a vertical tube (50.8 mm ID and 244 cm high) with counter-current interfacial shear at the onset of flooding have been investigated experimentally. High speed video photography and a flow visualization technique were utilized to investigate the mechanisms involved in the initiation of the flooding phenomenon over a wide range of liquid film Reynolds number (ReL = 4Γ/μ) from 1391 to 6584 at a distance of 150 cm from the liquid inlet. The present experimental data indicated neither the interfacial wave growth nor reversal in the wave propagation could be responsible for the initiation of flooding. Also the measured velocity profiles indicated only a slight reduction in liquid velocity within a narrow region very close to the gas-liquid interface, and no flow reversal in the liquid film at the measurement location. (author)
Fully developed MHD natural convection flow in a vertical annular microchannel: An exact solution
Directory of Open Access Journals (Sweden)
Basant K. Jha
2015-07-01
Full Text Available An exact solution of steady fully developed natural convection flow of viscous, incompressible, electrically conducting fluid in a vertical annular micro-channel with the effect of transverse magnetic field in the presence of velocity slip and temperature jump at the annular micro-channel surfaces is obtained. Exact solution is expressed in terms of modified Bessel function of the first and second kind. The solution obtained is graphically represented and the effects of radius ratio (η, Hartmann number (M, rarefaction parameter (βvKn, and fluid–wall interaction parameter (F on the flow are investigated. During the course of numerical computations, it is found that an increase in Hartmann number leads to a decrease in the fluid velocity, volume flow rate and skin friction. Furthermore, it is found that an increase in curvature radius ratio leads to an increase in the volume flow rate.
Detection and analysis of transition from annular to intermittent flow in vertical tubes
International Nuclear Information System (INIS)
In vertical co-current gas-liquid flow, the transition from annular to intermittent flow occurs when gas core becomes interrupted by liquid bridges due to the instability of the interfacial capillary waves. An analytical model is formulated to explain the liquid bridging in terms of the growth of finite amplitude interfacial capillary waves. Experimental results show that the longest wave length, which is associated with the transition, is about eight times the wave length of waves moving with the velocity of the liquid film. (author). 12 refs., 8 figs
Gas-liquid annular flow in vertical circular tubes with liquid penetrated in nucleus
International Nuclear Information System (INIS)
A semi-analytical model is proposed for fully developed upward gas-liquid annular flow inside vertical circular tubes, by utilizing wall-known turbulence algebraic models for single-phase flows, within both streams, combined with empirical correlations for the gas-liquid interface friction factor. Direct integration of the associated momentum equations provide the velocity distribution for each phase, as well as overall quantities of practical interest such as liquid film thickness and pressure gradient. The effects of liquid droplets entrainment in the gas is specialized empirical correlations. Extensive comparisons with experimental results are made in order to demonstrate the consistency of the proposed model. (author)
A two-dimensional parabolic model for vertical annular two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Fernandez, F.M.; Toledo, A. Alvarez; Paladino, E.E. [Graduate Program in Mechanical Engineering, Universidade Federal de Rio Grande do Norte, Natal, RN (Brazil)], e-mail: emilio@ct.ufrn.br
2010-07-01
This work presents a solution algorithm for predicting hydrodynamic parameters for developing and equilibrium, adiabatic, annular, vertical two-phase flow. It solves mass and momentum transport differential equations for both the core and the liquid film across their entire domains. Thus, the velocity and shear stress distributions from the tube center to the wall are obtained, together with the average film thickness and the pressure gradient, making no use of empirical closure relations nor assuming any known velocity profile to solve the triangular relationship in the liquid film. The model was developed using the Finite Volume Method and an iterative procedure is proposed to solve all flow variables for given phase superficial velocities. The procedure is validated against the analytical solution for laminar flow and experimental data for gas-liquid turbulent flow with entrainment. For the last case, an algebraic turbulence model is used for turbulent viscosity calculation for both, liquid film and gas core. (author)
Effect of wall wettability on droplet entrainment in vertical upward annular two-phase flow
International Nuclear Information System (INIS)
To evaluate the effect of wall surface wettability on the characteristics of upward gas-liquid annular two-phase flow in a vertical pipe, an experimental study was performed using two test pipes: an acrylic pipe and a FEP pipe. Measured contact angles on the acrylic and FEP pipe surfaces were 60deg and 80deg, respectively. Basic flow characteristics such as liquid film thickness and liquid entrainment ratio were respectively measured by a laser focus displacement meter and a suction method. At relatively high gas flow rate and low liquid flow rate conditions, a reduction of the surface wettability by the FEP pipe enhanced the interfacial waves on liquid film, and caused an increase in the liquid entrainment ratio and a decrease in the liquid film thickness. (author)
Electrical Capacitance Probe Characterization in Vertical Annular Two-Phase Flow
Directory of Open Access Journals (Sweden)
Grazia Monni
2013-01-01
Full Text Available The paper presents the experimental analysis and the characterization of an electrical capacitance probe (ECP that has been developed at the SIET Italian Company, for the measurement of two-phase flow parameters during the experimental simulation of nuclear accidents, as LOCA. The ECP is used to investigate a vertical air/water flow, characterized by void fraction higher than 95%, with mass flow rates ranging from 0.094 to 0.15 kg/s for air and from 0.002 to 0.021 kg/s for water, corresponding to an annular flow pattern. From the ECP signals, the electrode shape functions (i.e., the signals as a function of electrode distances in single- and two-phase flows are obtained. The dependence of the signal on the void fraction is derived and the liquid film thickness and the phase’s velocity are evaluated by means of rather simple models. The experimental analysis allows one to characterize the ECP, showing the advantages and the drawbacks of this technique for the two-phase flow characterization at high void fraction.
Wall pressure measurements of flooding in vertical countercurrent annular air–water flow
Energy Technology Data Exchange (ETDEWEB)
Choutapalli, I., Vierow, K.
2010-01-01
An experimental study of flooding in countercurrent air-water annular flow in a large diameter vertical tube using wall pressure measurements is described in this paper. Axial pressure profiles along the length of the test section were measured up to and after flooding using fast response pressure transducers for three representative liquid flow rates representing a wide range of liquid Reynolds numbers (ReL = 4Γ/μ; Γ is the liquid mass flow rate per unit perimeter; μ is the dynamic viscosity) from 3341 to 19,048. The results show that flooding in large diameter tubes cannot be initiated near the air outlet and is only initiated near the air inlet. Fourier analysis of the wall pressure measurements shows that up to the point of flooding, there is no dominant wave frequency but rather a band of frequencies encompassing both the low frequency and the broad band that are responsible for flooding. The data indicates that flooding in large diameter vertical tubes may be caused by the constructive superposition of a plurality of waves rather than the action of a single large-amplitude wave.
Wall pressure measurements of flooding in vertical countercurrent annular air-water flow
International Nuclear Information System (INIS)
An experimental study of flooding in countercurrent air-water annular flow in a large diameter vertical tube using wall pressure measurements is described in this paper. Axial pressure profiles along the length of the test section were measured up to and after flooding using fast response pressure transducers for three representative liquid flow rates representing a wide range of liquid Reynolds numbers (ReL = 4Γ/μ; Γ is the liquid mass flow rate per unit perimeter; μ is the dynamic viscosity) from 3341 to 19,048. The results show that flooding in large diameter tubes cannot be initiated near the air outlet and is only initiated near the air inlet. Fourier analysis of the wall pressure measurements shows that up to the point of flooding, there is no dominant wave frequency but rather a band of frequencies encompassing both the low frequency and the broad band that are responsible for flooding. The data indicates that flooding in large diameter vertical tubes may be caused by the constructive superposition of a plurality of waves rather than the action of a single large-amplitude wave.
International Nuclear Information System (INIS)
A model is developed to describe the transition from annular flow to intermittent flow in a vertical two-phase flow system. Since the instability of the disturbance wave, which is a dominant wave shape at the boundary between annular flow and intermittent flow, is considered as a governing mechanism, this instability described by the concept of hyperbolicity breaking in the characteristic equation is included in the model. The developed model is validated by comparing its predictions of gas superficial velocity for the transition with experimental data available in the literature, and comparing those with the predictions of the other correlations. The comparison results show that the model gives better predictions for the transition condition than existing correlations, and the effects of fluid properties, geometry and liquid flow rate on the transition are well considered by the developed model. The average of prediction errors is 3% for the present model. The standard deviation of the prediction errors of the model reaches 28%, which is the smallest among the models compared here. (author)
Annular Flow Distribution test
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This report documents the Babcock and Wilcox (B ampersand W) Annular Flow Distribution testing for the Savannah River Laboratory (SRL). The objective of the Annular Flow Distribution Test Program is to characterize the flow distribution between annular coolant channels for the Mark-22 fuel assembly with the bottom fitting insert (BFI) in place. Flow rate measurements for each annular channel were obtained by establishing ''hydraulic similarity'' between an instrumented fuel assembly with the BFI removed and a ''reference'' fuel assembly with the BFI installed. Empirical correlations of annular flow rates were generated for a range of boundary conditions
Turbulence modification in vertical upward annular flow passing through a throat section
International Nuclear Information System (INIS)
Experimental studies on the turbulence modification in annular two-phase flow passing through a throat section were carried out. The turbulence modification in multi-phase flow due to the interactions between two-phases is one of the most interesting scientific issues and has attracted research attention. In this study, the gas-phase turbulence modification in annular flow due to the gas-liquid phase interaction is experimentally investigated. The annular flow passing through a throat section is under the transient state due to the changing cross sectional area of the channel and resultantly the superficial velocities of both phases are changed compared with a fully developed flow in a straight pipe. The measurements for the gas-phase turbulence were precisely performed by using a constant temperature hot-wire anemometer, and made clear the turbulence structure such as velocity profiles, fluctuation velocity profiles. The behavior of the interfacial waves in the liquid film flow such as the ripple or disturbance waves was also observed. The measurements for the liquid film thickness by the electrode needle method were also performed to measure the base film thickness, mean film thickness, maximum film thickness and wave height of the ripple or the disturbance waves
A self-standing two-fluid CFD model for vertical upward two-phase annular flow
Energy Technology Data Exchange (ETDEWEB)
Liu, Y., E-mail: yang_liu@mail.dlut.edu.c [Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, Dalian University of Technology, Dalian 116024, Liaoning Province (China); Li, W.Z.; Quan, S.L. [Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education, Dalian University of Technology, Dalian 116024, Liaoning Province (China)
2011-05-15
Research highlights: A mathematic model for two-phase annular flow is established in this paper. Pressure loss and wall shear stress increase with inlet gas and liquid flow velocities. Droplet mass fraction distribution exhibits a concave profile radially. - Abstract: In this paper, a new two-fluid CFD (computational fluid dynamics) model is proposed to simulate the vertical upward two-phase annular flow. This model solves the basic mass and momentum equations for the gas core region flow and the liquid film flow, where the basic governing equations are accounted for by the commercial CFD package Fluent6.3.26. The liquid droplet flow and the interfacial inter-phase effects are accounted for by the programmable interface of Fluent, UDF (user defined function). Unlike previous models, the present model includes the effect of liquid roll waves directly determined from the CFD code. It is able to provide more detailed and, the most important, self-standing information for both the gas core flow and the film flow as well as the inner tube wall situations.
Effect of flow obstacle on droplet sizes in vertical annular air-water flow in a small diameter pipe
International Nuclear Information System (INIS)
Droplet size distributions have been measured for air-water annular-mist flow in a vertical 12.0 mm diameter pipe at atmospheric pressure. A laser diffraction technique has been employed using a Malvern Spraytec instrument. The test section was specially designed for meticulous measurement in the present experiment: any optical windows were not used to avoid problems arose from glass contamination by sucking the liquid film through the wall just below the measurement elevation. Sauter mean diameters measured in this work decreased simply with an increase of air superficial velocity, whereas the dependence on water superficial velocity showed complicated dependency on air velocity. The effect of a flow obstacle on droplet size distribution was also investigated. A small tube was placed in the centerline of the test section as an obstacle. Three obstacles having different blockage ratio were tested. It is found through the present experiments that the obstacle effect is not so significant for the blockage ratio of up to 0.3, and the droplet diameter decreases to approximately 80% in average. Based on the data, an empirical correlation to predict Sauter diameter was developed by modifying the existing correlation. A hydraulic equivalent diameter that takes account of the blockage ratio is applied to the characteristic length in the correlation. (author)
The transition from flooding to upwards cocurrent annular flow in a vertical pipe
International Nuclear Information System (INIS)
The limits of countercurrent flow in a vertical pipe are related to the onset of cocurrent upwards annual flow. The results are confirmed by evidence from several sources and lead to the criterion vg=(0.8→0.9)pg-1/2[D g (pf-pg)]1/2 for the minimum gas superficial velocity which will support a liquid film in concurrent flow. (author)
International Nuclear Information System (INIS)
This experimental and computational study is concerned with variable property mixed convection heat transfer to air flowing through a vertical passage of annular cross-section having a uniformly heated core and an unheated and well-insulated outer casing. The aims of the study were to investigate the extent to which established ideas concerning the effects of variable properties and buoyancy in heated tubes apply in the case of such an annular passage and to use the basic data produced to validate a computational formulation designed for simulating flow and heat transfer under such conditions. The experimental results confirm that systematic enhancement of heat transfer occurs with increase of buoyancy influence for downward flow and that impairment of heat transfer followed by recovery and enhancement occurs with upward flow in a passage of the kind considered. However, the onset of such effects is delayed and the magnitude is reduced in comparison with those for a circular tube. The computational simulations of the experiments using a variable property, developing flow formulation which took account of property variations and buoyancy influences and incorporated the low-Reynolds number k-ε turbulence model of Abe-Kondoh-Nagano reproduced the main features of the experimental results
International Nuclear Information System (INIS)
If a flow obstruction such as a spacer is set in a boiling two-phase flow within an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heater tube is severely affected by the existence of the spacer. In some case the spacer has a cooling effect, and in the other case it causes the dryout of the cooling liquid film on the heating surface resulting in the burnout of the tube. But the burnout mechanism near the spacer is not still clear. In the present paper we discus the influence of the flow obstacle on the occurrence of burnout downstream of the flow obstacle in boiling two-phase upward flow within a vertical annular channel. (author)
International Nuclear Information System (INIS)
If a flow obstruction such as a spacer is set in a boiling two-phase flow within an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heater tube is severely affected by the existence of the spacer. In some cases the spacer has a cooling effect, and in the other case it causes the dryout of the cooling liquid film on the heating surface resulting in the burnout of the tube. But the thermo-fluid dynamic mechanism to cause burnout near the spacer is not still clear. In the present paper we discuss the influence of the flow obstacle on the occurrence of burnout downstream of the flow obstacle in boiling two-phase upward flow within a vertical annular channel. (author)
Air--water countercurrent annular flow in vertical tubes. Interim report. [BWR; PWR
Energy Technology Data Exchange (ETDEWEB)
Bharathan, D.
1978-05-01
Air--water countercurrent flow characteristics in 2.5 and 5.1 cm vertical tubes are investigated. Experimental measurements include air and water flow rates, pressure losses, pressure gradients, and liquid fractions. Tube-end geometries are altered to study their influence on the flow characteristics. Liquid-fraction measurements indicate that the countercurrent flow may be divided into three regions based upon the relative magnitudes of interfacial and wall shear stresses. The dependence of interfacial friction factor on the liquid fraction is isolated. The mechanism limiting countercurrent flows within a tube is modelled by a simple theory. Salient features of the theory are demonstrated. Comparisons between the theory and some experimental data are presented.
Air--water countercurrent annular flow in vertical tubes. Interim report
International Nuclear Information System (INIS)
Air--water countercurrent flow characteristics in 2.5 and 5.1 cm vertical tubes are investigated. Experimental measurements include air and water flow rates, pressure losses, pressure gradients, and liquid fractions. Tube-end geometries are altered to study their influence on the flow characteristics. Liquid-fraction measurements indicate that the countercurrent flow may be divided into three regions based upon the relative magnitudes of interfacial and wall shear stresses. The dependence of interfacial friction factor on the liquid fraction is isolated. The mechanism limiting countercurrent flows within a tube is modelled by a simple theory. Salient features of the theory are demonstrated. Comparisons between the theory and some experimental data are presented
Phase flow rate measurements of annular flows
Al-Yarubi, Qahtan
2010-01-01
In the international oil and gas industry multiphase annular flow in pipelines and wells is extremely important, but not well understood. This thesis reports the development of an efficient and cheap method for measuring the phase flow rates in two phase annular and annular mist flow, in which the liquid phase is electrically conducting, using ultrasonic and conductance techniques. The method measures changes in the conductance of the liquid film formed during annular flow and uses these to c...
El Nakla, Meamer A.
An experimental investigation of inverted annular film boiling heat transfer has been performed for vertical up-flow in a round tube. The working fluid was R-134a and the flow conditions covered a pressure range of 640 to 2390 kPa (water equivalent range: 4000 to 14000 kPa) and a mass flux range of 500 to 4000 kgm-2s-1 (water equivalent range: 700 to 5700 kgm-2s-1 ). The inlet qualities of the tests ranged from -0.75 to -0.03. The hot-patch technique is used to obtain the subcooled film boiling measurements. The parametric trends of the heat transfer coefficient with respect to mass flux, inlet quality, heat flux and pressure are examined and compared to reported parametric trends from the literature. The comparison shows agreement between observed effects of flow parameters with those reported by other researchers. The heat transfer vs. quality curve is divided into four different regions. It is shown that these regions are dependent on pressure, mass flux and local quality. A two-fluid one-dimensional model has been developed to predict the wall temperature of an internally-heated tube during IAFB. The model is derived using basic conservation equations of mass, momentum and energy. To simplify the derivation of the constitutive heat transfer relations, flow between two parallel plates is assumed. The model features shear stress and interfacial relations that make it accurately predicts the parametric effects and heat transfer characteristics of IAFB over a wide range of flow conditions. The model predicts wall temperatures of R-134a-cooled tubes with an average error of -1.21% and an RMS error of 6.37%. This corresponds to average and RMS errors in predicted heat transfer coefficients of 1.33% and 10.07%, respectively. Using water data, the model predicts wall temperatures with an average error of -1.76% and an RMS error of 7.78% which corresponds to average and RMS errors in predicted heat transfer coefficients of 4.16% and 15.06%, respectively.
Energy Technology Data Exchange (ETDEWEB)
Mori, Shoji [Yokohama National University, Yokohama 240-8501 (Japan)], E-mail: morisho@ynu.ac.jp; Tominaga, Akira [Ube National College of Technology, Ube 755-8555 (Japan)], E-mail: tominaga@ube-k.ac.jp; Fukano, Tohru [Kurume Institute of University, Fukuoka 830-0052 (Japan)], E-mail: fukanot@cc.kurume-it.ac.jp
2007-12-15
If a flow obstacle, such as a spacer is placed in a boiling two-phase flow within a channel, the temperature on the surface of the heating tube is severely affected by the existence of the spacer. Under certain conditions, a spacer has a cooling effect, and under other conditions, the spacer causes dryout of the cooling water film on the heating surface. The burnout mechanism, which always occurs upstream of a spacer, however, remains unclear. In a previous paper [Fukano, T., Mori, S., Akamatsu, S., Baba, A., 2002. Relation between temperature fluctuation of a heating surface and generation of drypatch caused by a cylindrical spacer in a vertical boiling two-phase upward flow in a narrow annular channel. Nucl. Eng. Des. 217, 81-90], we reported that the disturbance wave has a significant effect on dryout and burnout occurrence and that a spacer greatly affects the behavior of the liquid film downstream of the spacer. In the present study, we examined in detail the influences of a spacer on the heat transfer and film thickness characteristics downstream of the spacer by considering the result in steam-water and air-water systems. The main results are summarized as follows: (1)The spacer averages the liquid film in the disturbance wave flow. As a result, dryout tends not to occur downstream of the spacer. This means that large temperature increases do not occur there. However, traces of disturbance waves remain, even if the disturbance waves are averaged by the spacer. (2)There is a high probability that the location at which burnout occurs is upstream of the downstream spacer, irrespective of the spacer spacing. (3)The newly proposed burnout occurrence model can explain the phenomena that burnout does occur upstream of the downstream spacer, even if the liquid film thickness t{sub Fm} is approximately the same before and behind the spacer.
International Nuclear Information System (INIS)
If a flow obstacle, such as a spacer is placed in a boiling two-phase flow within a channel, the temperature on the surface of the heating tube is severely affected by the existence of the spacer. Under certain conditions, a spacer has a cooling effect, and under other conditions, the spacer causes dryout of the cooling water film on the heating surface. The burnout mechanism, which always occurs upstream of a spacer, however, remains unclear. In a previous paper [Fukano, T., Mori, S., Akamatsu, S., Baba, A., 2002. Relation between temperature fluctuation of a heating surface and generation of drypatch caused by a cylindrical spacer in a vertical boiling two-phase upward flow in a narrow annular channel. Nucl. Eng. Des. 217, 81-90], we reported that the disturbance wave has a significant effect on dryout and burnout occurrence and that a spacer greatly affects the behavior of the liquid film downstream of the spacer. In the present study, we examined in detail the influences of a spacer on the heat transfer and film thickness characteristics downstream of the spacer by considering the result in steam-water and air-water systems. The main results are summarized as follows: (1)The spacer averages the liquid film in the disturbance wave flow. As a result, dryout tends not to occur downstream of the spacer. This means that large temperature increases do not occur there. However, traces of disturbance waves remain, even if the disturbance waves are averaged by the spacer. (2)There is a high probability that the location at which burnout occurs is upstream of the downstream spacer, irrespective of the spacer spacing. (3)The newly proposed burnout occurrence model can explain the phenomena that burnout does occur upstream of the downstream spacer, even if the liquid film thickness tFm is approximately the same before and behind the spacer
International Nuclear Information System (INIS)
Annular gas-liquid two phase flow widely occurs in nuclear industry. Various combinations of techniques have been employed in annular gas-liquid two phase flows to measure the flow parameters (e.g. liquid film thickness, gas volume fraction and the phase flow rates). One of the most useful techniques which has proven attractive for many multiphase flow applications is the electrical conductance technique. This paper presents an advanced conductance multiphase Venturi meter (CMVM) which is capable of measuring the gas volume fractions at the inlet and the throat of the Venturi. A new model was investigated to measure the gas flow rate. This model is based on the measurement of the gas volume fractions at the inlet and the throat of the Venturi meter using a conductance technique rather than relying on prior knowledge of the mass flow quality x. We measure conductance using two ring electrodes flush with the inner surface of the Venturi throat and two ring electrodes flush with the inner surface of the Venturi inlet. The basic operation of the electrical conductance technique in a multiphase flow is that the conductance of the mixture depends on the gas volume fraction in the water. An electronic circuit was built and calibrated to give a dc voltage output which is proportional to the conductance of the mixture which can then be related to the water film thickness in annular flow (and hence to the gas volume fraction). It was inferred from the experimental results that the minimum average percentage error of the predicted gas mass flow rates (i.e. -0.0428%) can be achieved at the optimum gas discharge coefficient of 0.932.
International Nuclear Information System (INIS)
When a flow obstruction such as a cylindrical spacer is set in a boiling two-phase flow with-in an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heating tube is severely affected by its existence. In some cases the cylindrical spacer has a cooling effect, and in the other cases it causes the dryout of the cooling water film on the heating surface resulting in the burnout of the heating tube. In the present paper we have focused our attention on the influence of a flow obstacle on the occurrence of burnout of the heating tube in boiling two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Mori, S.; Fukano, T. [Kyushu Univ., Fukuoka (Japan)
2003-07-01
When a flow obstruction such as a cylindrical spacer is set in a boiling two-phase flow with-in an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heating tube is severely affected by its existence. In some cases the cylindrical spacer has a cooling effect, and in the other cases it causes the dryout of the cooling water film on the heating surface resulting in the burnout of the heating tube. In the present paper we have focused our attention on the influence of a flow obstacle on the occurrence of burnout of the heating tube in boiling two-phase flow.
Adiabatic Steam-Water Annular Flow in an Annular Geometry
DEFF Research Database (Denmark)
Andersen, P. S.; Würtz, J.
1981-01-01
Experimental results for fully developed steam-water annular flow in annular geometries are presented. Rod and tube film flow rates and axial pressure gradients were measured for mass fluxes between 500 and 2000 kg/m2s, steam qualities between 20 and 60 per cent and pressures ranging from 3 to 9...... MPa. It was found that the measured tube film flow rate per unit tube perimeter is always many times greater than the corresponding rod film flow rate. Possible explanations for this asymmetry are discussed....
Energy Technology Data Exchange (ETDEWEB)
Mori, S.; Fukano, T. E-mail: fukanot@mech.kyushu-u.ac.jp
2003-10-01
When a flow obstruction such as a cylindrical spacer is set in a boiling two-phase flow within an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heating tube is severely affected by its existence. In some cases, the cylindrical spacer has a cooling effect, and in the other cases it causes the dryout of the cooling water film on the heating surface resulting in the burnout of the heating tube. In the present paper, we have focused our attention on the influence of a flow obstacle on the occurrence of burnout of the heating tube in boiling two-phase flow. The results are summarized as follows: - When the heat flux approaches the burnout condition, the wall temperature on the heating tube fluctuates with a large amplitude. And once the wall temperature exceeds the Leidenfrost temperature, the burnout occurs without exception. - The trigger of dryout of the water film which causes the burnout is not the nucleate boiling but the evaporation of the base film between disturbance waves. - The burnout never occurs at the downstream side of the spacer. This is because the dryout area downstream of the spacer is rewetted easily by the disturbance waves.
International Nuclear Information System (INIS)
When a flow obstruction such as a cylindrical spacer is set in a boiling two-phase flow within an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heating tube is severely affected by its existence. In some cases, the cylindrical spacer has a cooling effect, and in the other cases it causes the dryout of the cooling water film on the heating surface resulting in the burnout of the heating tube. In the present paper, we have focused our attention on the influence of a flow obstacle on the occurrence of burnout of the heating tube in boiling two-phase flow. The results are summarized as follows: - When the heat flux approaches the burnout condition, the wall temperature on the heating tube fluctuates with a large amplitude. And once the wall temperature exceeds the Leidenfrost temperature, the burnout occurs without exception. - The trigger of dryout of the water film which causes the burnout is not the nucleate boiling but the evaporation of the base film between disturbance waves. - The burnout never occurs at the downstream side of the spacer. This is because the dryout area downstream of the spacer is rewetted easily by the disturbance waves
International Nuclear Information System (INIS)
Gas-liquid two-phase flow is encountered in many industries, including flow near nuclear fuel rods in boiling water reactor (BWR). Especially dryout of water film occurs at the thin base film between two successive disturbance waves. Therefore, it is important to clarify the detailed behavior of the disturbance wave. In previous studies, many experiments were performed under atmospheric condition. However the properties of liquid and gas under atmospheric condition are quite different from those of a BWR operating condition (7 MPa, 285degC). Therefore, in the present study, HFC134a gas and ethanol liquid, whose properties are similar to those of the BWR operating conditions are used as the test fluids at comparatively low pressure and low temperature (0.7 MPa, 40degC). In this paper, the effect of gas-liquid properties on the liquid film thickness is discussed. (author)
Energy Technology Data Exchange (ETDEWEB)
Mori, Shoji; Fukano, Tohru [Kyushu Univ., Graduate School of Engineering, Fukuoka (Japan)
2002-07-01
If a flow obstruction such as a spacer is set in a boiling two-phase flow within an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heater tube is severely affected by the existence of the spacer. In some cases the spacer has a cooling effect, and in the other case it causes the dryout of the cooling liquid film on the heating surface resulting in the burnout of the tube. But the thermo-fluid dynamic mechanism to cause burnout near the spacer is not still clear. In the present paper we discuss temperature fluctuation characteristics in relation to the change of the differential pressure across the spacer caused by the passing of the disturbance waves in case that the burnout generates. (author)
International Nuclear Information System (INIS)
If a flow obstruction such as a spacer is set in a boiling two-phase flow within an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heater tube is severely affected by the existence of the spacer. In some cases the spacer has a cooling effect, and in the other case it causes the dryout of the cooling liquid film on the heating surface resulting in the burnout of the tube. But the thermo-fluid dynamic mechanism to cause burnout near the spacer is not still clear. In the present paper we discuss temperature fluctuation characteristics in relation to the change of the differential pressure across the spacer caused by the passing of the disturbance waves in case that the burnout generates. (author)
Energy Technology Data Exchange (ETDEWEB)
Mori, Shoji [Yokohama National University, Yokohama 240-8501 (Japan)]. E-mail: morisho@ynu.ac.jp; Fukano, Tohru [Kurume Institute of University, Fukuoka 830-0052 (Japan)]. E-mail: fukanot@cc.kurume-it.ac.jp
2006-05-15
If a flow obstacle such as a spacer is placed in a boiling two-phase flow within a channel, the temperature on the surface of the heating tube is severely affected by the existence of the spacer. Under certain conditions the spacer has a cooling effect, and under other conditions the spacer causes dryout of the cooling water film on the heating surface, resulting in burnout of the tube. The burnout mechanism near the spacer, however, remains unclear. In a previous paper (Fukano, T., Mori, S., Akamatsu, S., Baba, A., 2002. Relation between temperature fluctuation of a heating surface and generation of drypatch caused by a cylindrical spacer in a vertical boiling two-phase upward flow in a narrow annular channel. Nucl. Eng. Des. 217, 81-90), we reported that the disturbance wave has a significant effect on dryout occurrence. Therefore, in the present paper, the relation between dryout, burnout occurrence, and interval between two successive disturbance waves obtained from the differential pressure fluctuation caused by the disturbance waves passing by a spacer, is further discussed in detail.
International Nuclear Information System (INIS)
If a flow obstacle such as a spacer is placed in a boiling two-phase flow within a channel, the temperature on the surface of the heating tube is severely affected by the existence of the spacer. Under certain conditions the spacer has a cooling effect, and under other conditions the spacer causes dryout of the cooling water film on the heating surface, resulting in burnout of the tube. The burnout mechanism near the spacer, however, remains unclear. In a previous paper (Fukano, T., Mori, S., Akamatsu, S., Baba, A., 2002. Relation between temperature fluctuation of a heating surface and generation of drypatch caused by a cylindrical spacer in a vertical boiling two-phase upward flow in a narrow annular channel. Nucl. Eng. Des. 217, 81-90), we reported that the disturbance wave has a significant effect on dryout occurrence. Therefore, in the present paper, the relation between dryout, burnout occurrence, and interval between two successive disturbance waves obtained from the differential pressure fluctuation caused by the disturbance waves passing by a spacer, is further discussed in detail
On the Motion of an Annular Film in Microgravity Gas-Liquid Flow
McQuillen, John B.
2002-01-01
Three flow regimes have been identified for gas-liquid flow in a microgravity environment: Bubble, Slug, and Annular. For the slug and annular flow regimes, the behavior observed in vertical upflow in normal gravity is similar to microgravity flow with a thin, symmetrical annular film wetting the tube wall. However, the motion and behavior of this film is significantly different between the normal and low gravity cases. Specifically, the liquid film will slow and come to a stop during low frequency wave motion or slugging. In normal gravity vertical upflow, the film has been observed to slow, stop, and actually reverse direction until it meets the next slug or wave.
Vertical countercurrent flow limitation phenomena under oscillatory gas flow
International Nuclear Information System (INIS)
During the hypothetical loss of coolant accident in a nuclear power plant, the emergency core cooling water could not penetrate to the reactor core when the steam flow rate from the reactor core exceeds CCFL (Countercurrent flow limitation). The criteria of CCFL generated by earlier investigators were developed under steady gas flow. However, the flow instability in the reactor loop could generate oscillatory steam flow, hence their applicability under oscillating flow should be investigated. In this work, an experimental investigation of countercurrent flow in a vertical flow channel has been conducted under oscillatory gas flow condition. In the present flooding loop, flooding occurs from the annular flow regime, annular flooding, or the periodic slug/annular flow regime, slug flooding. The oscillatory gas flow changes the flooding map of the steady gas flow according to its magnitude and oscillating frequency. Further, when its minimum gas flow rate is less than a threshold value, no flooding was observed. When it was annular flow regime, the threshold of no flooding was the deflooding value under the steady gas flow. But when it was the slug or periodic slug/annular flow regime, the threshold of no flooding was in between the deflooding and flooding value under steady gas flow. Also, it was observed that this no flooding threshold is insensitive to the oscillating frequency except for high frequency over 0.3 Hz. Therefore, the flooding condition under oscillatory gas flow is less restrictive than that under steady gas flow
Air-water countercurrent annular flow
Energy Technology Data Exchange (ETDEWEB)
Bharathan, D.
1979-09-01
Countercurrent annular flow of air and water in circular tubes of diameters ranging from 6.4 to 152 mm is investigated. Experimental measurements include liquid fraction, pressure gradients and countercurrent gas and liquid fluxes. Influences of tube end geometries on the countercurrent fluxes are isolated. Analogies between countercurrent flow, open channel flow, and compressible flow are established. Interfacial momentum transfer between the phases are characterized by empirical friction factors. The dependence of interfacial friction factors on tube diameter is shown to yield a basis for extending the present results to larger tubes.
Air-water countercurrent annular flow
International Nuclear Information System (INIS)
Countercurrent annular flow of air and water in circular tubes of diameters ranging from 6.4 to 152 mm is investigated. Experimental measurements include liquid fraction, pressure gradients and countercurrent gas and liquid fluxes. Influences of tube end geometries on the countercurrent fluxes are isolated. Analogies between countercurrent flow, open channel flow, and compressible flow are established. Interfacial momentum transfer between the phases are characterized by empirical friction factors. The dependence of interfacial friction factors on tube diameter is shown to yield a basis for extending the present results to larger tubes
STABILITY OF SWIRLING ANNULAR FLOW
Czech Academy of Sciences Publication Activity Database
Maršík, František; Trávníček, Zdeněk; Novotný, Pavel; Werner, E.
Kaohsiung : National Pingtung University of Science and Technolog, 2009 - (Tai, C.), s. 32-32 ISBN N. [Pacific Symposium on Flow Visualization and Image Processing /7./ (PSFVIP-7 2009). Kaohsiung (TW), 16.11.2009-19.11.2009] R&D Projects: GA AV ČR(CZ) IAA200760801; GA MŠk(CZ) 1M06031 Institutional research plan: CEZ:AV0Z20760514 Keywords : flow stability * swirling jet * thermodynamic stability Subject RIV: BK - Fluid Dynamics
Interfacial friction in cocurrent upward annular flow
Hossfeld, L. M.; Bharathan, D.; Wallis, G. B.; Richter, H. J.
1982-03-01
Cocurrent upward annular flow is investigated, with an emphasis on correlating and predicting pressure drop. Attention is given to the characteristics of the liquid flow in the film, and the interaction of the core with the film. Alternate approaches are discussed for correlating suitably defined interfacial friction factors. Both approaches are dependent on knowledge of the entrainment in order to make predictions. Dimensional analysis is used to define characteristic parameters of the flow and an effort is made to determine, to the extent possible, the influences of these parameters on the interfacial friction factor.
Directory of Open Access Journals (Sweden)
Sharf Abdusalam M.
2014-03-01
Full Text Available In the oil and gas industries, understanding the behaviour of a flow through an annulus gap in a vertical position, whose outer wall is stationary whilst the inner wall rotates, is a significantly important issue in drilling wells. The main emphasis is placed on experimental (using an available rig and computational (employing CFD software investigations into the effects of the rotation speed of the inner pipe on the axial velocity profiles. The measured axial velocity profiles, in the cases of low axial flow, show that the axial velocity is influenced by the rotation speed of the inner pipe in the region of almost 33% of the annulus near the inner pipe, and influenced inversely in the rest of the annulus. The position of the maximum axial velocity is shifted from the centre to be nearer the inner pipe, by increasing the rotation speed. However, in the case of higher flow, as the rotation speed increases, the axial velocity is reduced and the position of the maximum axial velocity is skewed towards the centre of the annulus. There is a reduction of the swirl velocity corresponding to the rise of the volumetric flow rate.
Fully developed laminar mixed convection through a vertical annular duct filled with porous media
Energy Technology Data Exchange (ETDEWEB)
Kou, H.S.; Huang, D.K. [Tatung Inst. of Tech., Taipei (Taiwan, Province of China). Dept. of Mechanical Engineering
1997-01-01
The fully developed laminar mixed convection through a vertical annular duct embedded in a porous medium has been solved by using the non-Darcian flow model, where thermal boundary conditions on inner and outer walls are prescribed as isothermal-isothermal, isothermal-isoflux, and isoflux-isothermal, separately. The analytical solution has been derived to obtain velocity and temperature profiles, mass flow rate, wall friction factor and heat carried out by fluid. Finally, the parametric zones for flow characteristics of velocity distribution with the upward or downward flow are demonstrated.
Natural convection and entropy generation in a vertically concentric annular space
International Nuclear Information System (INIS)
Natural convection in a vertically concentric annular space is of fundamental interest and practical importance. However, available open literature on entropy generation analysis for it is still sparse. In the present work we investigate systematically the effects of Rayleigh number, curvature of annulus and Prandtl number on flow pattern, temperature distribution and entropy generation for natural convection inside a vertically concentric annuli with the aid of the lattice Boltzmann method. The analyzed range is wide, varying from steady laminar convection to unsteady transitional state. Furthermore, we analyse the non-linear branch of irreversible phenomena from a thermodynamics view point. (authors)
Hydrodynamics of annular-dispersed flow
International Nuclear Information System (INIS)
The interfacial drag, droplet entrainment, and droplet size distributions are important for detailed mechanistic modeling of annular dispersed two-phase flow. In view of this, recently developed correlations for these parameters are presented and discussed in this paper. The drag correlations for multiple fluid particle systems have been developed from a similarity hypothesis based on the mixture viscosity model. The results show that the drag coefficient depends on the particle Reynolds number and droplet concentration. The onset on droplet entrainment significantly alters the mechanisms of mass, momentum, and energy transfer between the film and gas core flow as well as the transfer between the two-phase mixture and the wall. By assuming the roll wave entrainment mechanism, the correlations for the amount of entrained droplet as well as for the droplet size distribution have been obtained from a simple model in collaboration with a large number of data
Study on annular mist flow in pipe, 1
International Nuclear Information System (INIS)
An annular mist flow using air and water at room temperature has been studied experimentally in a vertical pipe with a nozzle along the axis of the pipe for supplying liquid. Observations were made of flow patterns of liquid on the inner surface of the pipe, and measurements were made of pressure losses in pipe, profiles of radial distribution of liquid droplets and total flow rates of the liquid droplets. Changes of these four factors along the pipe were measured in the non-equilibrium region. It was found that the non-equilibrium length should be decided by a position where any changes in the four factors mentioned above could not be recognized in the axial direction. For relatively high velocities of air, i.e., for apparent gaseous Reynolds number R sub(ego) >= 9.4 x 104, it was ascertained that the annular mist flow reached equilibrium at a distance of 170 - 190 diameters from the nozzle outlet when apparent liquid Reynolds number R sub(elo) = 62.1 - 183.6. (author)
Stability of cantilevered coaxial shells with internal and annular flow
International Nuclear Information System (INIS)
This paper is a theoretical study of the stability of cantilevered coaxial cylindrical shells conveying incompressible fluid in the annular space in- between and within the inner shell. The viscous effects of the mean flow are taken into account, but the perturbations of the equilibrium state on the basis of which stability is assessed is carried out by means of potential flow theory, thus neglecting unsteady viscous effects which are known to become important for narrow annular flows. Shell displacements are described by Flugge's equations of motion. Solution of the coupled fluid-structure equations is carried out by means of the Fourier Transform Method. The main finding of this research is that stability is lost by flutter for internal flow, according to both the inviscid and viscous variants of the theory; for annular flow, however, whereas inviscid theory predicts loss of stability by flutter, viscous theory (with dissipative effects included) predicts that the shell loses stability by divergence and then, at appreciably higher flow, by flutter. Reduction of the annular gap generally destabilizes the system; while increased steady viscous effects slightly stabilize the system for internal flow, they strongly destabilize it for annular flow. Increasing the length of the shell destabilizes the system for both internal and annular flows. The presence of internal flow in addition to annular flow tends to stabilize the system vis-a-vis the case of annular flow, but only at low flow velocities, having the opposite effect at higher flows; the same effects arise when the main flow is internal and an annular flow added to the system
International Nuclear Information System (INIS)
If a flow obstacle such as a spacer is set in a boiling two-phase flow within an annular channel, where the inner tube is used as a heater, the temperature on the surface of the heater tube is severely affected by the existence of the spacer. In some case the spacer has a cooling effect, and in the other case it causes the dryout of the cooling liquid film on the heating surface resulting in the burnout of the tube. The burnout mechanism near the spacer, however, is not still clear. In the present paper we focus our attention on the occurrence of the burnout near a spacer, and discuss the occurrence location of dryout and burnout and the relation between the occurrence of burnout and differential-pressure fluctuation characteristics caused by the disturbance waves passing by a spacer. (author)
Displacement of one Newtonian fluid by another: density effects in axial annular flow
DEFF Research Database (Denmark)
Szabo, Peter; Hassager, Ole
1997-01-01
The arbitrary Lagrange-Euler (ALE) finite elementtechnique is used to simulate 3D displacement oftwo immiscible Newtonian fluids in vertical annular wells. For equally viscous fluids the effect of distinct fluid densities is investigated in the region of low to intermediate Reynolds numbers. Comp......, the efficiency of the displacement is analysed for various flow situations....
N.Ameer Ahamad; Hasan Ahmed Mohamed Hassan El Arabawy
2014-01-01
In this work, we visualize the effect of varying wall temperature on the heat transfer by supplying the heat at three different positions to the vertical annular cylinder embedded with porous medium. Finite element method has been used to solve the governing equations. Influence of Aspect ratio , Radius ratio on Nusselt number is presented. The effect of power law exponent effect for different values of Rayleigh number is discussed. The fluid flow and heat tr...
Hydrodynamic stability of inverted annular flow in an adiabatic simulation
International Nuclear Information System (INIS)
In experiments, inverted annular flow was simulated adiabatically with turbulent water jets, issuing downward from long aspect nozzles, enclosed in gas annuli. Velocities, diameters, and gas species were varied, and core jet length, shape, break-up mode, and dispersed-core droplet sizes were recorded at approximately 750 data points. Inverted annular flow was observed to develop into inverted slug flow at low relative velocities, and into dispersed droplet flow at high relative velocities. For both of the above transitions from inverted annular flow, a correlation for core jet length was developed by extending work done on free liquid jets to include this new, coaxial, jet disintegration phenomenon. The result, showing length dependence upon diameter, jet Reynolds number, jet Weber number, void fraction, and gas Weber number, correlates the data well, especially at moderate-to-large relative velocities
Rotordynamic Analysis of Textured Annular Seals With Multiphase (Bubbly Flow
Directory of Open Access Journals (Sweden)
Gérard PINEAU
2011-09-01
Full Text Available For some applications it must be considered that the flow in the annular seal contains a mixture of liquid and gas. The multiphase character of the flow is described by the volume fraction of gas (usually air contained in the liquid under the form of bubbles.The fluid is then a homogenous mixture of air and liquid all thru the annular seal. Its local gas volume fraction depends on the pressure field and is calculated by using a simplified form of the Rayleigh-Plesset equation.The influence of such of a multiphase (bubbly flow on the dynamic characteristics of a straight annular seal is minimal because the volume of the fluid is reduced.The situation is quite different for textured annular (damper seals provided with equally spaced deep cavities intended to increase the damping capabilities and to reduce the leakage flow rate.As a by-product, the volume of the fluid in the seal increases drastically and the compressibility effects stemming from the bubbly nature of the flow are largely increased even for a low gas volume fraction. The present work depicts the influence of the gas volume fraction on the dynamic characteristics of a textured annular seal. It is shown that variations of the gas volume fraction between 1% and 0.1% can lead to frequency dependent stiffness, damping and added mass coefficients.
Improvement of image processing algorithms for annular flow
International Nuclear Information System (INIS)
Annular flow occurs in a wide range of industrial heat-transfer equipment, including the top of a BWR core, in the steam generator of a PWR, and in postulated accident scenarios including critical heat flux (CHF) by dryout. The modeling of annular flow often requires information regarding the average thickness of liquid film at the periphery of the flow channel as a measurement of film roughness (film roughness concept). More recently, two-region modeling efforts require wave intermittency as a measurement of disturbance wave (as opposed to base film thickness) contribution to gas-to-liquid momentum transfer and pressure loss. The present work focuses on the characterization of film behaviors in annular flow using quantitative visualization. The data reduction codes for planar laser-induced flourescence (PLIF) imaging and back-lit quartz tube imaging have been further developed to improve measurement accuracy. Film thickness distribution (base film and wave), disturbance wave length, and wave intermittency estimates have been updated and applied to a recent two-region annular flow model. Outputs of average film thickness, pressure gradient, and average wave velocity have been modeled with mean absolute errors of 8.70%, 17.42%, and 19.14%, respectively. (author)
International Nuclear Information System (INIS)
The identification of flow regime transition is very important part for nuclear safety analysis, improvement and design of mechanical system. There have been many theoretical and experimental attempts to demonstrate flow regime transitions in a horizontal and a vertical pipe, on the other hand, research for the inclined pipe has been rare. Taitel and Dukler proposed a theoretical model for predicting flow regime transitions in a horizontal and near-horizontal pipe. Barnea et al. verified the Taitel and Dukler's model for various inclination angles, and observed that Taitel and Dukler's model well predict the flow regime transition up to inclination angles ±10 .deg., but has limitation in classifying the transition boundary between the smooth and wavy stratified flow. Barnea et al. intensively conducted experiment on the flow regime transition for the whole range of inclination angles from the horizontal to the vertical pipe. Barnea later proposed a unified theoretical model predicting the transition between the annular and intermittent flow, and between the bubbly and intermittent which is valid for the whole range of inclination angles. Also, Barnea summarized flow regime transition models and proposed a unified theoretical model applicable from horizontal to vertical flow. This work, as a preparatory research, is motivated to classify the flow regime, in particular, transition between intermittent and annular flow in an inclined pipe which was constructed in order to describe the condensation heat exchanger in APR+ PAFS
Flow Visualisation of Annular Liquid Sheet Instability & Atomisation
Duke, Daniel; Soria, Julio
2012-01-01
Fluid dynamics videos of unstable thin annular liquid sheets are presented in this short paper. These videos are to be presented in the Gallery of Fluid Motion for the American Physical Society 65th Annual Meeting of the Division of Fluid Dynamics in San Diego, CA, 18-20 November 2012. An annular sheet of thickness h=1mm and mean radius R=18.9mm is subjected to aerodynamic axial shear from co-flowing air at various shear rates on both the inner and outer surface at a liquid sheet Reynolds Number of Re=500.
Assessment of TRAC-PF1/MOD1 for countercurrent - annular and stratified flows
International Nuclear Information System (INIS)
I performed an independent assessment of the Transient Reactor Analysis Code, TRAC-PF1/MOD1, using air-water countercurrent-flow limitation data in circular pipes for annular, annular-mist, and stratified flows. Tubes were configurated in the vertical direction with different lengths and diameters and at angles of 60 deg, 40 deg, 20 deg, and 0 deg from the horizontal, respectively. Also, comparisons were made with data from a horizontal tube with an inclined riser at the end that simulated a pressurized water reactor (PWR) hot leg. TRAC-PF1/MOD1 was modified to study the effects of using two different correlations for interfacial shear in the annular-mist flow regime: the Wallis and Bharathan correlations. TRAC-PF1/MOD1 with the Wallis correlation predicts the point of no water penetration (bypass point) in the annular-mist flow regime except for the 40 deg inclined tube. However, for the region of partial water penetration, use of the Bharathan correlation in TRAC-PF1/MOD1 gives better agreement with data. Additional form losses were required at both ends of the tube to predict the flow rate of falling water accurately for the vertical tube. In the stratified-flow regime, TRAC-PF1/MOD1 underpredicts the air velocity which gives the bypass point but gives good agreement for the region of partial penetration. For the case of a simulated PWR hot leg, the code yields similar results to those obtained for the stratified-flow regime. (author)
Experimental Study on Convective Boiling Heat Transfer in Vertical Narrow Gap Annular Tube
Institute of Scientific and Technical Information of China (English)
Li Bin; He Anding; Wang Yueshe; Zhou Fangde
2001-01-01
Experiments are conducted to investigate the characteristics of single-phase forced-flow convection and boiling heat transfer of R113 flowing through annular tube with gap of 1, 1.5 and 2.5 mm, and also the visualization test are carried out to get two-phase flow regime. The data show that the Nusselt numbers for the narrow-gap are higher than those predicted by traditional large channel correlation and boiling heat transfer is enhanced. Based on the data obtained in this investigation, correlations for single-phase, forced convection and flow boiling in annular tube of different gap size has been developed.
Elastic instability in stratified core annular flow
Bonhomme, Oriane; Leng, Jacques; Colin, Annie
2010-01-01
We study experimentally the interfacial instability between a layer of dilute polymer solution and water flowing in a thin capillary. The use of microfluidic devices allows us to observe and quantify in great detail the features of the flow. At low velocities, the flow takes the form of a straight jet, while at high velocities, steady or advected wavy jets are produced. We demonstrate that the transition between these flow regimes is purely elastic -- it is caused by viscoelasticity of the polymer solution only. The linear stability analysis of the flow in the short-wave approximation captures quantitatively the flow diagram. Surprisingly, unstable flows are observed for strong velocities, whereas convected flows are observed for low velocities. We demonstrate that this instability can be used to measure rheological properties of dilute polymer solutions that are difficult to assess otherwise.
Critical heat flux and flow pattern for water flow in annular geometry
International Nuclear Information System (INIS)
An experimental study on critical heat flux (CHF) and two-phase flow visualization has been performed for water flow in internally-heated, vertical, concentric annuli under near atmospheric pressure. Tests have been done under stable forced-circulation, upward and downward flow conditions with three test sections of relatively large gap widths (heated length = 0.6 m, inner diameter 19 mm, outer diameter = 29, 35 and 51 mm). The outer wall of the test section was made up of the transparent Pyrex tube to allow the observation of flow patterns near the CHF occurrence. The CHF mechanism was changed in the order of flooding, churn-to-annular flow transition and local dryout under a large bubble in churn flow as the flow rate was increased from zero to higher values. Observed parametric trends are consistent with the previous understanding except that the CHF for downward flow is considerably lower than that for the upward flow. In addition to the experiment, selected CHF correlations for annuli are assessed based on 1156 experimental data from various sources. The Doerffer et al. (1994); Barnett (1966); Jannsen and Kervinen (1963); Levitan and Lantsman (1977) correlations show reasonable predictions for wide parameter ranges, among which the Doerffer et al. (1994) correlation shows the widest parameter ranges and a possibility of further improvement. However, there is no correlation predicting the low-pressure, low-flow CHF satisfactorily. (orig.)
Directory of Open Access Journals (Sweden)
N.Ameer Ahamad
2014-09-01
Full Text Available In this work, we visualize the effect of varying wall temperature on the heat transfer by supplying the heat at three different positions to the vertical annular cylinder embedded with porous medium. Finite element method has been used to solve the governing equations. Influence of Aspect ratio , Radius ratio on Nusselt number is presented. The effect of power law exponent effect for different values of Rayleigh number is discussed. The fluid flow and heat transfer is presented in terms of streamlines and isotherms.
Slug flooding in air-water countercurrent vertical flow
International Nuclear Information System (INIS)
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)
An investigation of flow characteristics and critical heat flux in vertical upward round tube
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Prediction of critical heat flux (CHF) in annular flow is important for the safety of once- through steam generator and the reactor core under accident conditions. The dryout in annular flow occurs at the point where the film is depleted due to entrainment, deposition, and evaporation. The film thickness, film mass flow rate along axial distribution, and CHF are calculated in vertical upward round tube on the basis of a separated flow model of annular flow. The theoretical CHF values are higher than those derived from experimental data, with error being within 30%.
Heat transfer to liquid sodium flowing through annular channel, (4)
International Nuclear Information System (INIS)
An experimental study was carried out to clarify the heat transfer characteristics of liquid sodium flowing turbulently through an annular channel. For a concentric condition, average psi(=average epsilonH/epsilonM) was found to agree with that proposed by Aoki or Ramm for circular tube. For eccentric conditions, circumferential temperature variations around the inner wall were measured and Nusselt numbers were evaluated. Numerical calculations were also made for temperature fields and compared with the measurements. (author)
Interfacial friction in cocurrent upward annular flow. Final report
International Nuclear Information System (INIS)
Cocurrent upward annular flow is investigated, with an emphasis on correlating and predicting pressure drop. Attention is given to the characteristics of the liquid flow in the film, and the interaction of the core with the film. Alternate approaches are discussed for correlating suitably defined interfacial friction factors. Both approaches are dependent on knowledge of the entrainment in order to make predictions. Dimensional analysis is used to define characteristic parameters of the flow and an effort is made to determine, to the extent possible, the influences of these parameters on the interfacial friction factor
Electroosmotic flow and Joule heating in preparative continuous annular electrochromatography.
Laskowski, René; Bart, Hans-Jörg
2015-09-01
An openFOAM "computational fluid dynamic" simulation model was developed for the description of local interaction of hydrodynamics and Joule heating in annular electrochromatography. A local decline of electrical conductivity of the background eluent is caused by an electrokinetic migration of ions resulting in higher Joule heat generation. The model equations consider the Navier-Stokes equation for incompressible fluids, the energy equation for stationary temperature fields, and the mass transfer equation for the electrokinetic flow. The simulations were embedded in commercial ANSYS Fluent software and in open-source environment openFOAM. The annular gap (1 mm width) contained an inorganic C8 reverse-phase monolith as stationary phase prepared by an in situ sol-gel process. The process temperature generated by Joule heating was determined by thermal camera system. The local hydrodynamics in the prototype was detected by a gravimetric contact-free measurement method and experimental and simulated values matched quite well. PMID:25997390
Entrained liquid fraction prediction in adiabatic and evaporating annular two-phase flow
International Nuclear Information System (INIS)
Highlights: ► New method to predict the entrained liquid fraction in annular two-phase flow. ► Circular and non-circular tubes, adiabatic and evaporating conditions covered. ► Large underlying experimental database (2460 points). ► New method explicit and fully stand-alone. ► New method based on just 1 dimensionless group: the core flow Weber number. - Abstract: A new method to predict the entrained liquid fraction in annular two-phase flow is presented. The underlying experimental database contains 2460 data points collected from 38 different literature studies for 8 different gas–liquid or vapor–liquid combinations (R12, R113, water–steam, water–air, genklene–air, ethanol–air, water–helium, silicon–air), tube diameters from 5.0 mm to 95.3 mm, pressures from 0.1 to 20.0 MPa and covers both adiabatic and evaporating flow conditions, circular and non-circular channels and vertical upflow, vertical downflow and horizontal flow conditions. Annular flows are regarded here as a special form of a liquid atomization process, where a high velocity confined spray, composed by the gas phase and entrained liquid droplets, flows in the center of the channel dragging and atomizing the annular liquid film that streams along the channel wall. Correspondingly, the liquid film flow is assumed to be shear-driven and the energy required to drive the liquid atomization is assumed to be provided in the form of kinetic energy of the droplet-laden gas core flow, so that the liquid film–gas core aerodynamic interaction is ultimately assumed to control the liquid disintegration process. As such, the new prediction method is based on the core flow Weber number, representing the ratio of the disrupting aerodynamic force to the surface tension retaining force, a single and physically plausible dimensionless group. The new prediction method is explicit, fully stand-alone and reproduces the available data better than existing empirical correlations, including in
A research on the mechanisms of transition from annular flow in two-phase pipeline flow
International Nuclear Information System (INIS)
Various kinds mechanisms of transitions from two-phase annular flow in tubes were studied and modelled, and the affection factors on the transitions were also discussed. Some mathematical equations and transition criteria for every mechanisms presented were derived, and an unified general criterion for the annular flow transitions in whole range of pipe inclinations was recommended. The boundaries predicted show good agreement with the air-water two-phase experimental data
Study on natural convection heat transfer in vertical annular space of a double coaxial cylinder
International Nuclear Information System (INIS)
Water cooling panels are adopted as a vessel cooling system of a high temperature-engineering test reactor (HTTR) to cool the reactor core indirectly by natural convection and thermal radiation. In this study, we carried out experiments on natural convection heat transfer coupled with thermal radiation in vertical annular space of a double coaxial cylinder in order to investigate heat transfer characteristics in vertical annular space between the reactor pressure vessel and the cooling panels of the HTTR. In the present experiments, Rayleigh number based on the width of the vertical space was set to be 6.8 x 105 6 for helium and 4.2 x 107 8 for nitrogen. This report described about the heat transfer coefficient of natural convection in the vertical space and the effect of thermal radiation of the transferred heat. As a result, a heat transfer coefficient of natural convection coupled with thermal radiation was obtained as functions of Rayleigh number, aspect ratio of the space, temperature and emissivities on the heated and cooled walls. In addition to the experiments, numerical analyses were performed on the combined phenomena of natural convection and thermal radiation in the space. The numerical results were in good agreement with the experimental ones regarding the temperature on the heated and cooled walls. (author)
Properties of flooding waves in vertical churn flow
International Nuclear Information System (INIS)
It is more accurate to predict the critical heat flux (CHF) from the start of churn flow rather than the start of annular flow. High-speed photography has been employed for qualitative investigation of entrainment in vertical two-phase flow under churn flow condition. This paper mainly focuses on the evolution of the flooding waves close to the water inlet section and liquid distribution in the cross-section of tube. The properties of flooding wave such as frequency and amplitude have been obtained. (author)
International Nuclear Information System (INIS)
Countercurrent flow limitation (CCFL) is the dominant dryout phenomenon in a debris bed that may be formed during a severe accident such as that observed at Three Mile Island unit 2. The actual CCFL situation in a debris bed is very complex, and it is difficult to treat. An annular flow model was developed to predict CCFL in a pipe. If a hypothetical flow channel were assumed, CCFL in a debris bed could be treated in the same manner as CCFL in a pipe. The purpose of this study is to investigate whether the annular flow model developed for CCFL in a pipe is applicable for CCFL in a debris bed
Magnetically guided free surface annular NaK flow experiment
International Nuclear Information System (INIS)
In order to gain basic information on the magnetically guided liquid metal Li waterfall type blanket concept for ICF reactors and liquid metal Li free surface flow for FMIT type accelerator target, an experimental study was conducted by using LINAK (NaK: 50 l, Ar: 0-0.3 MPa) device. A 45 mm O.D. and 25 mm I.D. annular free jet of NaK, which flowed downwards coaxially through a superconducting magnet (2.7 Tmax, B=0.38 T at the nozzle exit), was formed in vacuum chamber and at the nozzle exit where magnetic flux density B was divergent. The experiment covered ranges of U=0.5-2.5 m/s and B=0-0.38 T at the nozzle exit. Photographic and VTR observations were made on the behavior of outer surface of annular flow. The results are summarized as follows. (1) When B=0 T, the downward flow was rather convergent due to the surface tension. (2) By applying B, the flow became divergent like a cone shell and more stable. The divergent half angle increased with intensifying B. (3) The experimental results on the flow divergence agreed fairly well with the numerical analysis which took into account the MHD force, the surface tension and the gravitational force. (4) No growth of outer surface disturbance occurred within an attained maximum divergent half angle of 8deg or less. The results are considered to be encouraging for applying to ICF blanket and FMIT type target. (author)
Entrainment rate of droplets in the ripple-annular regime for small vertical tubes
International Nuclear Information System (INIS)
Two-fluid model predictions of film dryout in annular flow are limited by the uncertainties in the constitutive relations for the entrainment rate of droplets from the liquid film. The main cause of these uncertainties is the lack of separate effects experimental data in the range of the operating conditions in nuclear power reactors. Air/water and Freon-113 entrainment rate data have been obtained in 10 mm tubes using the film extraction technique. These experiments have been scaled to approach high pressure steam-water flow conditions. The effects of surface tension and density ratio, missing from most previous data sets, have been systematically tested. The entrainment rate mechanism is assumed to be a Kelvin-Helmholtz instability. Based on this analysis and two previous correlations, a new correlation is proposed that is valid for low viscosity fluids in small ducts in the ripple annular regime
A magnetorheological valve with both annular and radial fluid flow resistance gaps
International Nuclear Information System (INIS)
In order to increase the efficiency of magnetorheological (MR) valves, Ai et al (2006) proposed an MR valve simultaneously possessing annular and radial fluid flow resistance channels with the assumption that the magnetic flux densities at the annular and radial fluid flow gaps are identical. In this paper, an MR valve simultaneously possessing annular and radial fluid flow resistance channels is designed, fabricated, modeled and tested. A model for the developed MR valve is produced and its performances are theoretically predicted based on the average magnetic flux densities in the annular and radial fluid flow gaps through finite element analysis. The theoretical results for the developed MR valve are compared with the experimental results. In addition, the performances of the developed MR valve are theoretically and experimentally compared with those of the MR valve with only annular fluid flow gaps. It has been shown that the theoretical results match well with the experimental results. Mainly attributed to the radial fluid flow gaps, the pressure drops across the MR valve with both annular and radial fluid flow gaps are larger than those across the MR valve with only annular fluid flow gaps for varying valve parameters. The radial fluid flow gaps in the MR valve can reach a higher efficiency and larger controllable range than those by annular fluid flow gaps to some extent
International Nuclear Information System (INIS)
Highlights: → Knowledge of the interfacial wave structure is essential for making an accurate prediction of the amount of entrained droplets. → A new droplet entrainment model based on the force balance of interfacial waves in vertical annular flow. → An analytic wave shape function was developed. → A new droplet entrainment model was validated using the experimental data reported by Hewitt and Pulling and by Keeys et al. - Abstract: Droplets are generated at the interface of annular flow due to an interaction between a liquid film and gas core flow. Therefore, knowledge of the interfacial wave structure is essential for making an accurate prediction of the amount of entrained droplets. A new droplet entrainment model was proposed based on the force balance of interfacial waves in vertical annular flow. An analytic wave shape function was developed reflecting the detailed experimental findings, and was used in the development of a new model. The model was validated using the experimental data reported by Hewitt and Pulling at low pressures and by Keeys et al. at high pressures, which had been performed in adiabatic vertical tubes. The root-mean-square error of the prediction of the amount of entrainment was approximately 27% when the model was implemented into COBRA-TF code, which is approximately 23% less than that determined by the Wuertz model. The models proposed by Okawa et al. and Stevanovic et al. were also implemented into COBRA-TF and compared with the proposed model.
Core-annular flow through a horizontal pipe: Hydrodynamic counterbalancing of buoyancy force on core
Ooms, G.; Vuik, C.; Poesio, P.
2007-01-01
A theoretical investigation has been made of core-annular flow: the flow of a high-viscosity liquid core surrounded by a low-viscosity liquid annular layer through a horizontal pipe. Special attention is paid to the question of how the buoyancy force on the core, caused by a density difference betwe
Computation of Flow through an Annular Diffuser and Volute Exhaust
Directory of Open Access Journals (Sweden)
M. Arun
2006-04-01
Full Text Available Turbulent flow in a diffuser with swirl occurs in many commonly used fluid mechanicaldevices,eg, diffusers located downstream of a gas turbine, and in certain types of combustionchambers. Diffusers are widely used for converting kinetic energy to pressure, and a reliableprediction method of such flows with the required flow conditions would lead to the design offluid machinery with improved efficiency. As a first step, turbulent swirling flow through a 12oincluded angle conical diffuser for a swirl parameter, m = 0.18 was numerically investigated usingvarious turbulence models like standard k- , RNG-based k- , shear-stress transport (SST kandReynolds stress model (RSM. Though the comparison between the experimental and thepredicted mean velocity profile by RSM is superior to that by RNG kandSST models, the lattertwo models give closer comparison with the experimental pressure distribution. Subsequently,computation of flow inside a complex duct involving axisymmetric annular diffuser, transitionfrom rectangular to circular cross section, and exit pipe have been carried out using RNG kandSST k models.The comparison of computed and experimental results indicates that theSST k modelgives predictions with reasonable accuracy.
Liquid transfer and entrainment correlation for droplet-annular flow
International Nuclear Information System (INIS)
A correlation for the amount of entrained liquid in annular flow has been developed from a simple model and experimental data. There are basically two different regions of entrainment, namely, the entrance and quasi-equilibrium regions. The correlation for the equilibrium region is expressed in terms of the dimensionless gas flux, diameter, cand total liquid Reynolds number. The entrance effect is taken into account by an exponential relaxation function. It has been shown that this new model can satisfactorily correlate wide ranges of experimental data for water. Furthermore, the necessary distance for the development of entrainment is identified. These correlations, therefore, can supply accurate information on entrainment which has not been available previously
International Nuclear Information System (INIS)
A model is developed to describe the transition of annular flow to intermittent flow in a vertical two-phase flow system. The instability of the disturbance wave, which is a dominant wave shape at the boundary between annular flow and intermittent flow, is considered as the governing mechanism and this instability is described by the concept of hyperbolicity breaking in the characteristic equation. The developed model is validated by comparing its predictions of gas superficial velocity for the transition with the experimental data available from the literature, and comparing those with the predictions of the other correlations. The comparison results show that the developed model gives better predictions for the transition condition than the existing correlations and the effects of fluid properties, geometry and liquid flow rate on the transition are well considered by the developed model. It is found that the predictions of the developed model have much smaller bias than those of the other correlations; the average of the prediction error is 3% for the present model. The standard deviation of the prediction errors of the present model reaches 28%, which is the smallest among the models compared here. Through the core uncovery experiments, it has been known that the low power and high power core boil-off patterns are observed in the high pressure core uncovery following a small-break loss-of-coolant accident. The developed model for the annular to intermittent flow regime transition was applied to the classification of low power boil-off and high power boil-off patterns. At first, the applicability of the developed criterion to the rod-bundle geometry is demonstrated using the flow pattern transition data taken by Bergles et al. and Venkateswararao. It is shown that the developed criterion well predicts the boundary between low power boil-off and high power boil-off through the comparisons of the predicted annular to intermittent flow transition conditions with
Characterization and modeling of annular two-phase flows
International Nuclear Information System (INIS)
Three aspects of annular two-phase flow are studied: (a) wave motion on falling films, (b) flow transition from downflow to upflow, and (c) the upflow. For the case of wave motion on falling films, it is shown that the assumption of the Nusselt velocity profile for finite-amplitude waves is solution of the wave profile, wave velocity, and velocity components within the wave is developed. An algorithm based on collocation methods is also detailed and can be applied to extend the model to solve for higher order terms in the velocity profile. Comparisons with experimental studies show good agreement. Flow transition and the upflow experiments are conducted in a 5.08 x 10-2m inner diameter, 6.5m long Plexiglas column. The liquid rates are varied from 0 to 0.126 kg/s and the gas rates from 0 to 0.0524 kg/s. At four measuring stations along the length of the column, an electrical conductance technique which employs two electrodes mounted flush with the wall is utilized to measure film thickness and pressure transducers are used to make the pressure measurements. Flow visualization studies indicate that flooding takes place as a result of entrainment from the crests of large waves. The effect of column length and pore size of the feed device on flooding velocities is studied. No previous correlation or theory is found to be fully adequate. A speculative interaction among system parameters is proposed to form a basis for a physical model for flooding phenomena
Flow Pressure Loss through Straight Annular Corrugated Pipes
Sargent, Joseph R.; Kirk, Daniel R.; Marsell, Brandon; Roth, Jacob; Schallhorn, Paul A.; Pitchford, Brian; Weber, Chris; Bulk, Timothy
2016-01-01
Pressure loss through annular corrugated pipes, using fully developed gaseous nitrogen representing purge pipes in spacecraft fairings, was studied to gain insight into a friction factor coefficient for these pipes. Twelve pipes were tested: four Annuflex, four Masterflex and two Titeflex with ¼”, 3/8”, ½” and ¾” inner diameters. Experimental set-up was validated using smooth-pipe and showed good agreement to the Moody diagram. Nitrogen flow rates between 0-200 standard cubic feet per hour were used, producing approximate Reynolds numbers from 300-23,000. Corrugation depth varied from 0.248 = E/D = 0.349 and relative corrugation pitch of 0.192 = P/D = 0.483. Differential pressure per unit length was measured and calculated using 8-9 equidistant pressure taps. A detailed experimental uncertainty analysis, including correlated bias error terms, is presented. Results show larger differential pressure losses than smooth-pipes with similar inner diameters resulting in larger friction factor coefficients.
Rayleigh-Bénard convection in a vertical annular container near the convection threshold.
Wang, Bo-Fu; Wan, Zhen-Hua; Ma, Dong-Jun; Sun, De-Jun
2014-04-01
The instabilities and transitions of flow in an annular container with a heated bottom, a cooled top, and insulated sidewalls are studied numerically. The instabilities of the static diffusive state and of axisymmetric flows are investigated by linear stability analysis. The onset of convection is independent of the Prandtl number but determined by the geometry of the annulus, i.e., the aspect ratio Γ (outer radius to height) and radius ratio δ (inner radius to outer radius). The stability curves for onset of convection are presented for 0.001≤δ≤0.8 at six fixed aspect ratios: Γ=1, 1.2, 1.6, 1.75, 2.5, and 3.2. The instability of convective flow (secondary instability), which depends on both the annular geometry and the Prandtl number, is studied for axisymmetric convection. Two pairs of geometric control parameters are chosen to perform the secondary instability analysis-Γ=1.2, δ=0.08 and Γ=1.6, δ=0.2-and the Prandtl number ranges from 0.02 to 6.7. The secondary instability exhibits some similarities to that for convection in a cylinder. A hysteresis stability loop is found for Γ=1.2, δ=0.08 and frequent changes of critical mode with Prandtl number are found for Γ=1.6, δ=0.2. The three-dimensional flows beyond the axisymmetry-breaking bifurcations are obtained by direct numerical simulation for Γ=1.2, δ=0.08. PMID:24827339
Direct measurements of liquid film roughness for the prediction of annular flow pressure drop
Energy Technology Data Exchange (ETDEWEB)
Ashwood, Andrea C.; Schubring, DuWayne; Shedd, Timothy A. [University of Wisconsin, Madison, WI (United States)], e-mail: cashwood@wisc.edu, e-mail: dlschubring@wisc.edu, e-mail: shedd@engr.wisc.edu
2009-07-01
A vertical two-phase (air-water) test section has been constructed to allow for detailed visualization of flow phenomena in the annular regime. The total internal reflection (TIR) technique for film thickness estimation, originally developed by Shedd and Newell (1998), has been adapted for use in this test section. This technique uses the pattern of diffuse light reflected from the gas-liquid interface to estimate the base film thickness, i.e., the thickness between large liquid waves. Measurement of base film thickness separately from the average film thickness, which couples base film and wave behavior, allows for consideration of separate effects from each of the two zones. A modified Hurlburt-Newell (2000) correlation that separates the flow into these two zones has been generated. Data regarding the relationship between average base film thickness and wave height, along with verification of the base film thickness measured from the TIR technique, were provided by planar laser-induced fluorescence (PLIF). For the present vertical air-water up flows with liquid superficial velocities ranging from 4 to 34 cm s{sup -1} and gas superficial velocities from 35 to 85 m s{sup -1}, the modified Hurlburt-Newell correlation predicts pressure loss to within 10%. (author)
Direct measurements of liquid film roughness for the prediction of annular flow pressure drop
International Nuclear Information System (INIS)
A vertical two-phase (air-water) test section has been constructed to allow for detailed visualization of flow phenomena in the annular regime. The total internal reflection (TIR) technique for film thickness estimation, originally developed by Shedd and Newell (1998), has been adapted for use in this test section. This technique uses the pattern of diffuse light reflected from the gas-liquid interface to estimate the base film thickness, i.e., the thickness between large liquid waves. Measurement of base film thickness separately from the average film thickness, which couples base film and wave behavior, allows for consideration of separate effects from each of the two zones. A modified Hurlburt-Newell (2000) correlation that separates the flow into these two zones has been generated. Data regarding the relationship between average base film thickness and wave height, along with verification of the base film thickness measured from the TIR technique, were provided by planar laser-induced fluorescence (PLIF). For the present vertical air-water up flows with liquid superficial velocities ranging from 4 to 34 cm s-1 and gas superficial velocities from 35 to 85 m s-1, the modified Hurlburt-Newell correlation predicts pressure loss to within 10%. (author)
Turbulent structure at the midsection of an annular flow
Ghaemi, S.; Rafati, S.; Bizhani, M.; Kuru, E.
2015-10-01
The turbulent flow in the midsection of an annular gap between two concentric tubes at Reynolds number of 59 200-90 800 based on hydraulic diameter (dh = 57 mm) and average velocity is experimentally investigated. Measurements are carried out using particle tracking velocimetry (PTV) and planar particle image velocimetry (PIV) with spatial resolution of 0.0068dh (size of the binning window) and 0.0129dh (size of the interrogation window), respectively. Both PTV and PIV results show that the location of maximum mean streamwise velocity (yU) does not coincide with the locations of zero shear stress (yuv), minimum streamwise velocity fluctuation (yu2), and minimum radial velocity fluctuation (yv2). The separation between yU and yuv is 0.013dh based on PTV while PIV underestimates the separation distance as 0.0063dh. Conditional averages of turbulent fluctuations based on the four quadrants across the annulus demonstrate that the inner and outer wall flows overlap in the midsection. In the midsection, the flow is subject to opposing sweep/ejection events originating from both the inner and outer walls. The opposite quadrant events of the two boundary layers cancel out at yuv while the local minimum of spatial correlation of u (maximum mixing of the two wall flows) occurs at yU. Investigation of the budget of Reynolds shear stress showed that production and advection terms act towards the coincidence of the yU and yuv while the dissipation term works against the coincidence of the two points. The location of max also overlaps with zero dissipation of . The production of turbulent kinetic energy is slightly negative in the narrow region between yU and yuv. This negative production acts towards smoothing the mean velocity profile at the joint of the two wall flows by equalizing its curvature (∂2/∂y2) on the two sides of yU. The small separation distance of the yU and yuv is associated with slight deviation from the fully developed condition.
Flooding Mechanism in Vertical Flow
International Nuclear Information System (INIS)
This research was carried out to investigate the mechanism of flooding ina vertical liquid-gas counter current flow, along two meter length of thetube. The tube use both circular and square tube, a cross section of squaretube was made the same as a cross section of circular tube with one inchdiameter tube. The liquid enters the tube, passes through a porous wall inletand a groove inlet in a distributor and it flows downwards through a liquidoutlet in a collector. The gas is being introduced at the bottom of the tube,it flows upwards through nozzle in the collector. The results of researchshowed that the flooding occurs earlier in the circular tube than in thesquare tube, either uses a porous wall inlet or a groove inlet. In the squaretube , onset of the flooding occurs at the top of the tube, in front ofliquid injection, it is related to the formation of a film wave, just belowthe liquid feed. Whereas in the circular tube, onset of the flooding occursfrom the bottom of the tube, at the liquid outlet, it is related to theexpand of the film wave. However, in the circular tube with the groove inlet,for the higher liquid flow rate, onset of the flooding from the top, like inthe square tube. (author)
Lee, Joon Sang
The compressible filtered Navier-Stokes equations were solved using a second order accurate finite volume method with low Mach number preconditioning. A dynamic subgrid-scale stress model accounted for the subgrid-scale turbulence. The study focused on the effects of buoyancy and rotation on the structure of turbulence and transport processes including heat transfer. Several different physical arrangements were studied as outlined below. The effects of buoyancy were first studied in a vertical channel using large eddy simulation (LES). The walls were maintained at constant temperatures, one heated and the other cooled. Results showed that aiding and opposing buoyancy forces emerge near the heated and cooled walls, respectively. In the aiding flow, the turbulent intensities and heat transfer were suppressed at large values of Grashof number. In the opposing flow, however, turbulence was enhanced with increased velocity fluctuations. Another buoyancy study considered turbulent flow in a vertically oriented annulus. Isoflux wall boundary conditions with low and high heating were imposed on the inner wall while the outer wall was adiabatic. The results showed that the strong heating and buoyancy force caused distortions of the flow structure resulting in reduction of turbulent intensities, shear stress, and turbulent heat flux, particularly near the heated wall. Flow in an annular pipe with and without an outer wall rotation about its axis was first investigated at moderate Reynolds numbers. When the outer pipe wall was rotated, a significant reduction of turbulent kinetic energy was realized near the rotating wall. Secondly, a large eddy simulation has been performed to investigate the effect of swirl on the heat and momentum transfer in an annular pipe flow with a rotating inner wall. The simulations indicated that the Nusselt number and the wall friction coefficient increased with increasing rotation speed of the wall. It was also observed that the axial velocity
Flow visualization study of inverted annular flow of post dryout heat transfer region
International Nuclear Information System (INIS)
The inverted annular flow is important in the area of LWR accident analysis in terms of the maximum cladding temperature and effectiveness of the emergency core cooling. However, the inverted annular flow thermal-hydraulics is not well understood due to its special heat transfer condition of film boiling. In view of this, the inverted flow is studied in detail experimentally. A new experimental apparatus has been constructed in which film boiling heat transfer can be established in a transparent test section. Data on liquid core stability, core break-up mechanism, and dispersed-core liquid slug and droplet sizes are obtained using F 113 as a test fluid. Both high speed movies and flash photographs are used. The inlet section consists of specially designed coaxial nozzles for gas and liquid such that the ideal inverted annular flow can be generated. The roll wave formation, droplet entrainment from wave crests, agitated sections with large interfacial areas, classical sinuous jet instability, jet break-up into multiple liquid ligaments and drop formation from liquid ligaments have been observed in detail. (orig.)
Measurement of Quasi-periodic Oscillating Flow Motion in Simulated Dual-cooled Annular Fuel Bundle
International Nuclear Information System (INIS)
In order to increase a significant amount of reactor power in OPR1000, KAERI (Korea Atomic Energy Research Institute) has been developing a dual-cooled annular fuel. The dual-cooled annular fuel is simultaneously cooled by the water flow through the inner and the outer channels. KAERI proposed the 12x12 dual-cooled annular fuel array which was designed to be structurally compatible with the 16x16 cylindrical solid fuel array by maintaining the same array size and the guide tubes in the same locations, as shown in Fig. 1. In such a case, due to larger outer diameter of dual-cooled annular fuel than conventional solid fuel, a P/D (Pitch-to-Diameter ratio) of dual cooled annular fuel assembly becomes smaller than that of cylindrical solid fuel. A change in P/D of fuel bundle can cause a difference in the flow mixing phenomena between the dual-cooled annular and conventional cylindrical solid fuel assemblies. In this study, the rod bundle flow motion appearing in a small P/D case is investigated preliminarily using PIV (Particle Image Velocimetry) for dual-cooled annular fuel application
Boiling two-phase flow and heat transfer in concentric annular tube
International Nuclear Information System (INIS)
The boiling flow resistance and heat transfer characteristics is experimentally investigated under the outer tube wall heating condition in a concentric annular tube with 2.1 mm gap size. The results show that the flow resistance in the annular tube is greater than that in circular tube, as well as the boiling heat transfer becomes enhanced. The heat transfer coefficient has close relationship with the pressure, thermal equilibrium quality, mass flux, heat flux, gap size of the annular tube, and heat models as well. The physical explanation about the enhancement boiling heat transfer in the annular tube is proposed with both micro-film evaporation mechanics and bubble disturbance mechanics. The correlations to calculate the flow friction coefficient and heat transfer coefficient are proposed based on the experimental data. (authors)
Uninstrumented assembly airflow testing in the Annular Flow Distribution facility
Energy Technology Data Exchange (ETDEWEB)
Kielpinski, A.L.
1992-02-01
During the Emergency Cooling System phase of a postulated large-break loss of coolant accident (ECS-LOCA), air enters the primary loop and is pumped down the reactor assemblies. One of the experiments performed to support the analysis of this accident was the Annular Flow Distribution (AFD) experiment, conducted in a facility built for this purpose at Babcock and Wilcox Alliance Research Center in Alliance, Ohio. As part of this experiment, a large body of airflow data were acquired in a prototypical mockup of the Mark 22 reactor assembly. This assembly was known as the AFD (or the I-AFD here) reference assembly. The I-AFD assembly was fully prototypical, having been manufactured in SRS`s production fabrication facility. Similar Mark 22 mockup assemblies were tested in several test facilities in the SRS Heat Transfer Laboratory (HTL). Discrepancies were found. The present report documents further work done to address the discrepancy in airflow measurements between the AFD facility and HTL facilities. The primary purpose of this report is to disseminate the data from the U-AFD test, and to compare these test results to the I-AFD data and the U-AT data. A summary table of the test data and the B&W data transmittal letter are included as an attachment to this report. The full data transmittal volume from B&W (including time plots of the various instruments) is included as an appendix to this report. These data are further analyzed by comparing them to two other HTL tests, namely, SPRIHTE 1 and the Single Assembly Test Stand (SATS).
International Nuclear Information System (INIS)
The heat transfer characteristics of R134a during downward condensation are investigated experimentally and numerically. While the convective heat transfer coefficient, two-phase multiplier and frictional pressure drop are considered to be the significant variables as output for the analysis, inputs of the computational numerical techniques include the important two-phase flow parameters such as equivalent Reynolds number, Prandtl number, Bond number, Froude number, Lockhart and Martinelli number. Genetic algorithm technique (GA), unconstrained nonlinear minimization algorithm-Nelder-Mead method (NM) and non-linear least squares error method (NLS) are applied for the optimization of these significant variables in this study. Regression analysis gave convincing correlations on the prediction of condensation heat transfer characteristics using ±30% deviation band for practical applications. The most suitable coefficients of the proposed correlations are depicted to be compatible with the large number of experimental data by means of the computational numerical methods. Validation process of the proposed correlations is accomplished by means of the comparison between the various correlations reported in the literature
International Nuclear Information System (INIS)
A method of droplet behavior simulation in an annular dispersed flow has been developed. In this method, both droplet deposition and entrainment from liquid film are considered. The Lagrangian method and stochastic model are used to analyze droplet diffusion and deposition behavior in a turbulent flow, and droplet entrainment from liquid film is calculated by an entrainment correlation. For the verification of this method, Gill's experiment is analyzed, in which the transition from annular flow with no entrainment to equilibrium annular dispersed flow was observed. Analysis results can also show the similar transition tendency. The experimental results of radial distribution of droplet mass flux are compared with analysis results. The agreement is good for low liquid flow rate, but entrainment rate must be adjusted for high liquid flow rate, in which gas turbulence is thought to be modified by high droplet density. In future work the effect of high droplet density on turbulence should be considered. (author)
Numerical modeling of a horizontal annular flow experiment using a droplet entrainment model
International Nuclear Information System (INIS)
Highlights: • A new droplet entrainment model within the AIAD framework is proposed. • The approach was validated against a horizontal annular flow experiment. • Important flow phenomena could be calculated and analyzed. - Abstract: One limitation in current simulating horizontal annular flows is the lack of treatment of droplet formation mechanisms. For self-generating annular flows in horizontal pipes, the interfacial momentum exchange and the turbulence parameters have to be modelled correctly. Furthermore the understanding of the mechanism of droplet entrainment in annular flow regimes for heat and mass transfer processes is of great importance in the chemical and nuclear industry. A new entrainment model is proposed. It assumes that due to liquid turbulence the interface gets rough and wavy and forms droplets. The new approach is validated with HZDR annular flow experiments. Important phenomena like the pressure drop, the wave pumping effect, the droplet entrainment, the liquid film formation and the transient flow behavior could be calculated, analyzed and some of the phenomena compared with the measurement
The numerical solution of flow field of short-annular combustion chamber
Xu, H.; Ning, H.
1986-05-01
The recirculating flow field of a short-annular combustion chamber has been studied. The body-fitting coordinate system and the 'simple' method combined with a constant viscosity model have been employed to solve the Navier-Stokes equations in a regime containing a complicated curved boundary. The result could provide the theoretical reference for the design and improvement of short-annular combustion chambers.
Transition from slug to annular flow in horizontal air-water flow
International Nuclear Information System (INIS)
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.)
International Nuclear Information System (INIS)
Water single-phase and nucleate boiling heat transfer were experimentally investigated in vertical annuli with narrow gaps. The experimental data about water single-phase flow and boiling two-phase flow heat transfer in narrow annular channel were accumulated by two test sections with the narrow gaps of 1.0 mm and 1.5 mm. Empirical correlations to predict the heat transfer of the single-phase flow and boiling two-phase flow in the narrow annular channel were obtained, which were arranged in the forms of the Dittus-Boelter for heat transfer coefficients in a single-phase flow and the Jens-Lottes formula for a boiling two-phase flow in normal tubes, respectively. The mechanism of the difference between the normal channel and narrow annular channel were also explored. From experimental results, it was found that the turbulent heat transfer coefficients in narrow gaps are nearly the same to the normal channel in the experimental range, and the transition Reynolds number from a laminar flow to a turbulent flow in narrow annuli was much lower than that in normal channel, whereas the boiling heat transfer in narrow annular gap was greatly enhanced compared with the normal channel. (authors)
The effects of annular flow on dynamics of AP1000 reactor coolant pump rotor
International Nuclear Information System (INIS)
The feature of AP1000 RCP rotor system is that the whole rotor system is immersed in the annular flow. The rotor in annular flow induces fluctuating fluid forces, thereby causes vibration and noise, even rotor instability. The effects of annular flow on AP1000 RCP rotor system are different from that in bearings and seals and should be considered in a new approach. Based on the turbulent bulk flow theory and perturbation analysis, the rotor-flow coupled linear dynamic model is developed to predict the dynamics of AP1000 RCP immersed rotor. During the analysis, the rotor eccentricity, stator and rotor wall friction effects are emphasized. The analytic results show the rotor eccentricity induces divergence instability and significant decrease of instability speed for system with moderate or large eccentricity; however, stator and rotor wall friction effects distinctly suppress divergence instability and increase instability speed for system with small or moderate eccentricity. Finally, we can have the conclusion that the flow-structure interaction induced by annular flow has great effects on the dynamics of AP1000 RCP immersed rotor, which should be considered in rotor dynamic analysis and design of AP1000 RCP. The method and results in the paper have theoretical significance and practical importance. (author)
THE PERTURBATION SOLUTIONS OF THE FLOW IN A ROTATING CURVED ANNULAR PIPE
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
In this paper, the flow in a rotating curved annular pipe isexamined by a perturbation method. A second order perturbation solution is presented. The characteristics of the secondary flow and the axial flow are studied in detail.The study indicates that the loops of the secondary flow are more complex than those in a curved annular pipe without rotation and its numbers depend on the ratio of the Coriolis force to centrifugal force F. As F ≈- 1 , the secondary flow has eight loops and its intensity reaches the minimum value, and the distribution of the axial flow is like that of the Poiseuille flow. The position of the maximum axial velocity is pushed to either outer bend or inner bend, which is also determined by F.
DNS of forced gas flows in annular flow with strong heating
International Nuclear Information System (INIS)
Full text of publication follows: A direct numerical simulation (DNS) with turbulent transport of annular flow has been carried out with a variable property. In this study, the inlet Reynolds number based on a bulk velocity and a hydraulic diameter was set to be constant; Re=9700. The fluid is Helium gas which is heated wall at inner wall and adiabatic wall at outer wall. The experimental data are provided as a basis of the comparison with the computational results. This condition exactly corresponds to one of some experiments (Fuji et al., 1991). Present DNS code is modified from the pipe one (Satake et al., 2000). The number of computational grids at main region used in this study was 2304 x 128 x 192 in the z-, r- and Φ-directions, respectively. Annular channel with two direction of periodic boundary condition is used as driver unit to provide fully developed turbulence to main region. The turbulent quantities such as the mean flow, temperature fluctuations, turbulent stresses and the turbulent statistics were obtained via present DNS. (authors)
Effect of the Radial Pressure Gradient on the Secondary Flow Generated in an Annular Turbine Cascade
Hesham M. El-Batsh
2012-01-01
This paper introduces an investigation of the effect of radial pressure gradient on the secondary flow generated in turbine cascades. Laboratory measurements were performed using an annular sector cascade which allowed the investigation using relatively small number of blades. The flow was measured upstream and downstream of the cascade using a calibrated five-hole pressure probe. The three-dimensional Reynolds Averaged Navier Stokes equations were solved to understand flow physics. Turbulenc...
Applicability of the limiting cases for axial annular flow of power-law fluids
Czech Academy of Sciences Publication Activity Database
Filip, Petr; David, Jiří
Fukuoka: WSEAS Press, 2013 - ( Fujita , H.; Tuba, M.; Sasaki, J.), s. 45-48 ISBN 978-1-61804-177-7. ISSN 1790-5117. [Recent advances in automatic control, modelling and simulation. Morioka City (JP), 23.04.2013-25.04.2013] R&D Projects: GA ČR GA103/09/2066 Institutional support: RVO:67985874 Keywords : annular flow * power-law fluids * poiseuille flow * flow rate * pressure drop Subject RIV: BK - Fluid Dynamics
Damping of cylindrical structures subject to annular flow
International Nuclear Information System (INIS)
In previous reports theoretical methods have been described for estimating the aerodynamic forces acting on cylinders vibrating laterally when surrounded by an annulus carrying high velocity gas. For a certain restricted set of geometries it is possible to predict whether a particular structure is stable or unstable and to determine the level of aerodynamic damping positive or negative due to the presence of the gas. This report describes experimental work which validates the computer program in which the theoretical methods are embodied; in particular the damping, inertial and decentralising forces acting on a cylinder in an annulus are measured and compared with theory over a range of frequencies from 0 to 25 Hz, and of Reynolds numbers from zero to 104. In addition a summary of simple relationships is provided which can be used to provide credible initial estimates of both the positive and negative damping of cylinders in a range of annular geometries. (author)
Intermittent Flow of Granular Matter in an Annular Geometry
Brzinski, Ted; Daniels, Karen E.
Granular solids can be subjected to a finite stress below which the response is elastic. Above this yield stress, however, the material fails catastrophically, undergoing a rapid plastic deformation. In the case of a monotonically increasing stress the material exhibits a characteristic stick-slip response. We investigate the statistics of this intermittent failure in an annular shear geometry, driven with a linear-ramp torque in order to generate the stick-slip behavior. The apparatus is designed to allow visual access to particle trajectories and inter-particle forces (through the use of photoelastic materials). Additionally, twelve piezoelectric sensors at the outer wall measure acoustic emissions due to the plastic deformation of the material. We vary volume fraction, and use both fixed and deformable boundaries. We measure how the distribution of slip size and duration are related to the bulk properties of the packing, and compare to systems with similar governing statistics.
Laboratory and Numerical Investigations of Residence Time Distribution of Fluids in Laminar Flow Stirred Annular PhotoreactorE. Sahle-Demessie1, Siefu Bekele2, U. R. Pillai11U.S. EPA, National Risk Management Research LaboratorySustainable Technology Division,...
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
1989-12-31
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.
International Nuclear Information System (INIS)
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
International Nuclear Information System (INIS)
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
Modeling Mist to Annular Flow Development in the Discharge of a Compressor
Wujek, Scott S.; Hrnjak, Predrag S.
2012-01-01
A model has been created to describe the development of flow leaving a compressor as it transitions from mist to annular flow. Flow parameters such as the drop size, drop speed, drop concentration, film thickness, and film velocity change as a function of length. Parameters such as refrigerant flow rates, oil in circulation ratios, and fluid properties are accounted for in these models. While some flow development work is found in the open literature for air-water or steam-water flows, little...
CFD model of diabatic annular two-phase flow using the Eulerian–Lagrangian approach
International Nuclear Information System (INIS)
Highlights: • A CFD model of annular two-phase flow with evaporating liquid film has been developed. • A two-dimensional liquid film model is developed assuming that the liquid film is sufficiently thin. • The liquid film model is coupled to the gas core flow, which is represented using the Eulerian–Lagrangian approach. - Abstract: A computational fluid dynamics (CFD) model of annular two-phase flow with evaporating liquid film has been developed based on the Eulerian–Lagrangian approach, with the objective to predict the dryout occurrence. Due to the fact that the liquid film is sufficiently thin in the diabatic annular flow and at the pre-dryout conditions, it is assumed that the flow in the wall normal direction can be neglected, and the spatial gradients of the dependent variables tangential to the wall are negligible compared to those in the wall normal direction. Subsequently the transport equations of mass, momentum and energy for liquid film are integrated in the wall normal direction to obtain two-dimensional equations, with all the liquid film properties depth-averaged. The liquid film model is coupled to the gas core flow, which currently is represented using the Eulerian–Lagrangian technique. The mass, momentum and energy transfers between the liquid film, gas, and entrained droplets have been taken into account. The resultant unified model for annular flow has been applied to the steam–water flow with conditions typical for a Boiling Water Reactor (BWR). The simulation results for the liquid film flow rate show favorable agreement with the experimental data, with the potential to predict the dryout occurrence based on criteria of critical film thickness or critical film flow rate
Investigations of mass transfer in annular gas-liquid flow in a microreactor
Directory of Open Access Journals (Sweden)
Sobieszuk Paweł
2016-03-01
Full Text Available The paper presents an investigation of mass transfer in gas-liquid annular flow in a microreactor. The microreactor had a meandered shape with a square cross-section of the channel (292×292 μm, hydraulic diameter 292 μm and 250 mm in length. The rate of CO2 absorption from the CO2/N2 mixture in NaOH (0.1 M, 0.2 M, 0.7 M, 1.0 M and 1.5 M water solutions was measured. Two velocities of gas flow and two velocities of liquid flow were used. In two cases a fully developed annular flow at the beginning of the channel was observed, whilst in two cases annular flow was formed only in about 2/3 of the microchannel length. Based on the measurements of CO2 absorption rate, the values of volumetric liquid - side mass transfer coefficients with the chemical reaction were determined. Then physical values of coefficients were found. Obtained results were discussed and their values were compared with the values predicted by literature correlations.
Fluid-elastic instability in a confined annular flow: an experimental and analytical approach
International Nuclear Information System (INIS)
Self excitation of slender structures under axial flow have been reported in a large variety of local flow configurations. This paper reports the result of a research program, both experimental and analytical, aimed at the result of the basic phenomena leading to such instabilities. A cylindrical body with a diffuser is put in a confined annular flow of water. A case of flutter is observed and analysed with a classical potential flow method and with a friction based model. Closed-form solutions are proposed and the origin of the flutter instability is discussed. (authors). 25 refs., 6 figs., 5 tabs
Instability patterns in a miscible core annular flow
D'Olce, Marguerite; Martin, Jerome; Rakotomalala, Nicole; Salin, Dominique; Talon, Laurent
2006-11-01
Laboratoire FAST, batiment 502, campus universitaire, 91405 Orsay Cedex (France). Experiments are performed with two miscible fluids of equal density but different viscosities. The fluids are injected co-currently and concentrically into a cylindrical pipe. The so-obtained base state is an axisymmetric parallel flow, for which the ratio of the flow rates of the two fluids monitors the relative amount (and so the radius) of the fluids. Depending on this relative amount and on the total flow rate of the fluids, unstable axisymmetric patterns such as mushrooms and pearls are observed. We delineate the diagram of occurrence of the two patterns and characterize the instabilities.
Three Phase Upward Flow in a Vertical Pipe
International Nuclear Information System (INIS)
Many specialized technologies need to be developed to deal with the mobilization, retrieval, transport and reliable delivery of large amounts of toxic and radioactive waste to pretreatment facilities. At these facilities the waste is prepared for long term, unsupervised storage. At Hanford as well as other DOE nuclear sites, there are many underground storage tanks that are holding many millions of gallons of toxic and radioactive waste. A class of these storage tanks can utilize pneumatic conveying for the retrieval of scarified solids that are occasionally laced with sticky sludge, followed by slurry transport to pretreatment facilities. The formation of a thin liquid film that travels upwards along the internal wall of a vertical retrieval pipe may prevent those particles that are laced with the sticky sludge from adhering to it and eventually causing instability and blockage. In this paper we develop an approach to the design of a three-phase gas-solid-liquid flow system that could transport scarified solid particles, including sticky particles, pneumatically through a vertical pipe. A liquid film is introduced and maintained along the pipe's inner wall to act as a lubricant that ensure that sticky particles will continue to be transported without permanently adhering to the pipe wall. The system's operating conditions are within the boundaries of the annular dispersed region on a typical flow pattern map of vertical flow of a gas-liquid mixture. High gas superficial velocities combined with low liquid superficial velocities, conditions that satisfy the requirement and geometry of our proposed system, characterize such a region
Institute of Scientific and Technical Information of China (English)
Wang Zhiyuan; Sun Baojiang
2009-01-01
It is very important to understand the annular multiphase flow behavior and the effect of hydrate phase transition during deep water drilling. The basic hydrodynamic models, including mass, momentum, and energy conservation equations, were established for annular flow with gas hydrate phase transition during gas kick. The behavior of annular multiphase flow with hydrate phase transition was investigated by analyzing the hydrate-forming region, the gas fraction in the fluid flowing in the annulus, pit gain, bottom hole pressure, and shut-in casing pressure. The simulation shows that it is possible to move the hydrate-forming region away from sea floor by increasing the circulation rate. The decrease in gas volume fraction in the annulus due to hydrate formation reduces pit gain, which can delay the detection of well kick and increase the risk of hydrate plugging in lines. Caution is needed when a well is monitored for gas kick at a relatively low gas production rate, because the possibility of hydrate presence is much greater than that at a relatively high production rate. The shut-in casing pressure cannot reflect the gas kick due to hydrate formation, which increases with time.
Characteristics of low-mass-velocity vertical gas-liquid two-phase flow
International Nuclear Information System (INIS)
Low-mass-velocity two-phase flow in a vertical pipe shows lower void fraction than high-mass-velocity two-phase flow even though their qualities are the same. In order to clarify the flow characteristics of the low-mass-velocity two-phase flow, air-water two-phase flow experiments were conducted under the froth or annular flow conditions. Experimental results show that wall shear stress is positive even though both gas and liquid superficial velocities are positive. Measured water film average velocity is negative under this condition. These results indicate that local flow reversal should exist along the channel wall. This local flow reversal gives to the low void fraction in low-mass-velocity two-phase flow. It is also clarified that the drift flux model can be applied to the low-mass-velocity two-phase flow with local reversal. (author)
Institute of Scientific and Technical Information of China (English)
无
1999-01-01
The mechanism for transporting liquid from the bottom of the pipe to the top still to be established in the prediction of the film thickness distribution in horizontal annular two-phase flow.To resolve this issue,using five parallel-wire conductance probes,time records of local liquid film thickness at five circumferential positions were collected.The characteristics of circumferential liquid film thickness profiles and its variation with gas and liquid velocities were obtained.The basic features of probability distribution function,probability density function,auto-correlation,cross-correlation and power spectrum density function of the disturbance waves in annular flow were studied respectively.The characterstics of circumferential profiles of disturbance waves and its variation with gas and liquid velocities were presented.
Estimation of shear stress in counter-current annular flow
International Nuclear Information System (INIS)
The accuracy to which the friction factor is correlated is important in counter-current flow (CCF) analysis using a two-fluid model. Current two-fluid model codes use correlations of friction factors developed for co-current flow, or correlations developed on the assumption of zero wall shear stress. An assessment of two-fluid model codes with these existing correlations shows that the downward flow rate of water is overestimated. An analytical model is developed to calculate the shear stress profile in a liquid film of the CCF in order to obtain information on the shear stress between the interface and the wall. Both this analysis and Bharathan's CCF data show that the wall shear stress acting on the falling water film is approximately of same order as the interfacial shear stress, and the correlation for co-current flow cannot be applied to CCF. Tentative correlations of interfacial and wall friction factors are developed based on the results of the present study. (author)
Flow characteristics of sweepout and entrainment in the annular downcomer
International Nuclear Information System (INIS)
Sweepout from the water surface by gas (vapor or air) flow plays an important role in analyzing the mass and momentum transfer in the reactor downcomer of multidimensional geometry during a loss-of-coolant accident (LOCA) by decreasing the water level in the downcomer. The core water level will tend to decrease rapidly if a considerable amount of the entrained water stream and droplets bypasses through the break. The amount of entrained water is mostly determined by the interacting gas flow rate, the geometric condition, and the interfacial area between the gas and the water. The sweepout is observed to take place in three regions: the beginning of oscillation, the full wave and the wave peak (droplet separation). The beginning of oscillation normally occurs by the Helmholtz instability, which is defined in terms of the difference between the gas and the liquid velocities. The horizontal water surface is waved greatly before the gas flow reaches the critical point of droplet detachment. In the full-wave region, the droplets from the rough wave are swept into the gas flow and driven to the break. The water stream and droplets near the wave-peak region bypass through the break at extremely high velocities. In view of these observations we investigated the relation between the gas flow rate and the amount of bypass as a function of time. The test facility was constructed in a 1/10 linear scale-down model from the APR1400 (Advanced Power Reactor 1400MWe), which has four DVI (Direct Vessel Injection) lines, four cold legs, and two hot legs. The air was injected through the three intact cold legs and bypassed through the broken cold leg. The sweepout was visualized by using the acrylic test vessel. When the water level was located at the bottom of the break nozzle, the amount of bypass increased at the high Reynolds number of the gas. In the test the downcomer water level rapidly decreased for the initial one minute. Then, given the Reynolds number of the gas, the
Stability of forced-convection subcooled boiling in steady-state and transient annular flow
International Nuclear Information System (INIS)
A semi-analytical model developed by Lee and Bankoff for OFI in round tubes is extended to annular or parallel-plate flows with unequal heat fluxes, and shown to compare well with data by Dougherty, et al. and by Whittle and Forgan. The model is a better fit in the high Peclet number range than the Saha-Zuber model, and is simple to use
DNS for laminarization of turbulent forced gas flows in annular tube with strong heating
International Nuclear Information System (INIS)
A direct numerical simulation (DNS) of annular flow with turbulent transport of a variable property has been carried out to grasp and understand a laminarization phenomena caused by a strong heating. In this study, the inlet Reynolds number based on a bulk velocity and a hydraulic diameter was set to be constant; Reb = 9700. The number of computational grids used in this study was 2304 x 128 x 194 in the z-, r- and φ-directions, respectively. (author)
Heat transfer coefficient for flow boiling in an annular mini gap
Hożejowska Sylwia; Musiał Tomasz; Piasecka Magdalena
2016-01-01
The aim of this paper was to present the concept of mathematical models of heat transfer in flow boiling in an annular mini gap between the metal pipe with enhanced exterior surface and the external glass pipe. The one- and two-dimensional mathematical models were proposed to describe stationary heat transfer in the gap. A set of experimental data governed both the form of energy equations in cylindrical coordinates and the boundary conditions. The models were formulated to minimize the numbe...
Stability of forced-convection subcooled boiling in steady-state and transient annular flow
Energy Technology Data Exchange (ETDEWEB)
Gehrke, V.; Bankoff, S.G. [SGB Associates, Evanston, IL (United States)
1993-06-01
A semi-analytical model developed by Lee and Bankoff for OFI in round tubes is extended to annular or parallel-plate flows with unequal heat fluxes, and shown to compare well with data by Dougherty, et al. and by Whittle and Forgan. The model is a better fit in the high Peclet number range than the Saha-Zuber model, and is simple to use.
Interfacial friction in cocurrent upward annular flow. Final report. [PWR; BWR
Energy Technology Data Exchange (ETDEWEB)
Hossfeld, L.M.; Bharathan, D.; Wallis, G.B.; Richter, H.J.
1982-03-01
Cocurrent upward annular flow is investigated, with an emphasis on correlating and predicting pressure drop. Attention is given to the characteristics of the liquid flow in the film, and the interaction of the core with the film. Alternate approaches are discussed for correlating suitably defined interfacial friction factors. Both approaches are dependent on knowledge of the entrainment in order to make predictions. Dimensional analysis is used to define characteristic parameters of the flow and an effort is made to determine, to the extent possible, the influences of these parameters on the interfacial friction factor.
Flow Measurement Model of Ultrasonic Flowmeter for Gas-Liquid Two-Phase Stratified and Annular Flows
Lanchang Xing; Chenquan Hua; Hao Zhu; Wolfgang Drahm
2014-01-01
An error correction model for ultrasonic gas flowmeter was proposed to explore the potential of an ultrasonic flowmeter for metering gas-liquid stratified and annular flows. The gas and liquid mass flowrates could be obtained provided that the gas quality and physical prosperities were known. A single-path ultrasonic flowmeter was investigated and the error of the apparent volumetric flowrate was considered as mainly resulting from the shrinkage of the gas flow path due to the presence of a l...
International Nuclear Information System (INIS)
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
Energy Technology Data Exchange (ETDEWEB)
Bottoni, M.; Ajuha, S. [Argonne National Lab., IL (United States). Energy Technology Div.; Sengpiel, W. [Kernforschungszentrum Karlsruhe (Germany). Inst. fur Reaktorsicherheit
1994-12-31
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 makes the rigorously formulated terms useless for computational purposes, modeling of these terms is discussed.
International Nuclear Information System (INIS)
In the present study a new measurement technique has been developed, which uses an ultrasonic transmission signal in order to determine the vertical two phase flow pattern. The ultrasonic measurement system developed in the present study not only provides the measurement functions required for the identification of vertical two phase flow pattern but also makes the real time identification possible. Various vertical two phase flow patterns such as bubbly, slug, churn, annular flow etc have been accurately identified with the present ultrasonic measurement system. In addition to the identification of flow patterns, the qualitative information for each flow pattern can be obtained, which includes void fraction in bubbly flow, length of slug bubble and liquid tail characteristics in slug flow, and stable or transient condition of the flow patterns, etc
Experimental research on dryout point of flow boiling in narrow annular channels
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
An experimental research on the dryout point of flow boiling in narrow annular channels under low mass flux with 1.55 mm and 1.05 mm annular gap, respectively, is conducted. Distilled water is used as working fluid and the range of pressure is limited within 2.0～4.0 MPa and that of mass flux is 26.0～69.0 kg·m-2·s-1. The relation of critical heat flux (CHF) and critical qualities with mass flux and pressure are revealed. It is found that the critical qualities decrease with the increasing mass flux and increase with the increasing inlet qualities in externally heated annuli.Under the same conditions, critical qualities in the outer tube are always larger than those in the inner tube. The appearance of dryout point in bilaterally heated narrow annuli can be judged according to the ratio of qo/qi.
International Nuclear Information System (INIS)
For the visualization of the phase boundary in annular two-phase flows, the electrical resistance tomography (ERT) technique is introduced. In ERT, a set of predetermined electrical currents is injected trough the electrodes placed on the boundary of the flow passage and the induced electrical potentials are measured on the electrode. With the relationship between the injected currents and the induced voltages, the electrical conductivity distribution across the flow domain is estimated through the image reconstruction algorithm. In this, the conductivity distribution corresponds to the phase distribution. In the application of ERT to two-phase flows where there are only two conductivity values, the conductivity distribution estimation problem can be transformed into the boundary estimation problem. This paper considers a bubble boundary estimation with ERT in annular two-phase flows. As the image reconstruction algorithm, the unscented Kalman filter (UKF) is adopted since from the control theory it is reported that the UKF shows better performance than the extended Kalman filter (EKF) that has been commonly used. We formulated the UKF algorithm to be incorporate into the image reconstruction algorithm for the present problem. Also, phantom experiments have been conducted to evaluate the improvement by UKF
Internal (Annular) and Compressible External (Flat Plate) Turbulent Flow Heat Transfer Correlations.
Energy Technology Data Exchange (ETDEWEB)
Dechant, Lawrence [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Smith, Justin [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2016-01-01
Here we provide a discussion regarding the applicability of a family of traditional heat transfer correlation based models for several (unit level) heat transfer problems associated with flight heat transfer estimates and internal flow heat transfer associated with an experimental simulation design (Dobranich 2014). Variability between semi-empirical free-flight models suggests relative differences for heat transfer coefficients on the order of 10%, while the internal annular flow behavior is larger with differences on the order of 20%. We emphasize that these expressions are strictly valid only for the geometries they have been derived for e.g. the fully developed annular flow or simple external flow problems. Though, the application of flat plate skin friction estimate to cylindrical bodies is a traditional procedure to estimate skin friction and heat transfer, an over-prediction bias is often observed using these approximations for missile type bodies. As a correction for this over-estimate trend, we discuss a simple scaling reduction factor for flat plate turbulent skin friction and heat transfer solutions (correlations) applied to blunt bodies of revolution at zero angle of attack. The method estimates the ratio between axisymmetric and 2-d stagnation point heat transfer skin friction and Stanton number solution expressions for sub-turbulent Reynolds numbers %3C1x10 4 . This factor is assumed to also directly influence the flat plate results applied to the cylindrical portion of the flow and the flat plate correlations are modified by
Phase separation of dispersed annular (rivulet or thin film) flow in a TEE
International Nuclear Information System (INIS)
An experimental and analytical investigation of dispersed annular (rivulet or thin film) flow phase separation in a tee is described in this paper. The research is directed at determining flow conditions, following a loss of coolant accident, in the large rectangular passageways leading to vacuum buildings in the containment envelope of some CANDU reactors. The reported research is part of a larger study, sponsored by Ontario Hydro of Canada, which also investigates dispersed mist flow and transient phase separation effects. The primary objective of the research was to develop mechanistic analytical models and incorporate them in a computer code which predicts phase separation from upstream flow and pressure and downstream and side branch pressure boundary conditions
International Nuclear Information System (INIS)
The Supercritical-Water-Cooled Reactor (SCWR) is a high-temperature, high-pressure water cooled reactor that operates above the critical pressure of water. In order to perform efficiently the thermal design of the SCWR, it is important to assess the thermal-hydraulics in rod bundles of the core. The experimental conditions of mockup tests, however, have to be limited because of technical and financial reasons. Therefore, it is required to establish an analytical design technique which can extrapolate experimental data to various design conditions of the reactor. JAEA (Japan Atomic Energy Agency) have been improved the three-dimensional two-fluid model analysis code ACE-3D, which has been developed originally for the two-phase flow thermal hydraulics of light water reactors, to handle the thermal hydraulic properties of water at supercritical region. In the present paper, heat transfer experiments of supercritical water flowing in a vertical annular channel around a heater pin, which simulates the core flow around a fuel rod, were analyzed with the improved ACE-3D to assess the prediction performance of the code. As a result, it was confirmed that the calculated wall surface temperature agreed with the measured results and the code is applicable to prediction of heat transfer of supercritical water in the system that simulates the SCWR core. (author)
Institute of Scientific and Technical Information of China (English)
Xinghua HUANG; Li WANG; Feng JIA
2008-01-01
A wavelet-transform based approach for flow regime identification in horizontal tube bundles under vertical upward cross-flow condition was presented. Tests on two-phase flow pattern of R 134a were conducted under low mass velocity and flow boiling conditions over Time series of differential pressure fluctuations were mea-sured and analyzed with discrete wavelet transform. Different time-scale characteristics in bubbly flow, churn flow and annular flow were analyzed. The wavelet energy distributions over scales were found to be appropriate for flow regime identification. Based on the wavelet energy distribution over characteristic scales, a criterion of flow regime identification was proposed. The comparison with experiment results show that it is feasible to use the dis-crete wavelet transform as the tool of flow regime iden-tification in horizontal tube bundles under vertical upward cross-flow condition.
Effect of entrained liquid on turbulent mixing rate between subchannels in annular two-phase flows
International Nuclear Information System (INIS)
Turbulent mixing rates of gas and liquid phases between the subchannels have been measured for various air-water two-phase annular flows in a multiple channel consisting of the two identical circular subchannels. In order to study effect of entrained liquid in the gas core on the turbulent mixing rates, experiments were conducted for two types of liquid injection method, i.e., a small bore nozzle placed in the subchannel center and a porous wall, at a fixed gas injection method. The result showed that the effect of entrained liquid on the turbulent mixing rates of both phases is negligibly small. (author)
International Nuclear Information System (INIS)
In large pressurized water Nuclear Power Plants of the type exploited by Electricite de France, neutron flux and temperature distributions are monitored by means of miniature sensing devices inserted into the reactor core. Insertion of these measuring devices is made possible through the existence of small diameter hollow steel tubes which enter the reactor through the lower vessel head and pass vertically upward through a rigid circular passage to the upper end of the fuel strings. Pressurized water enters the annular region between the tube and passage near the lower extremity and flows axially through the annulus for about 1.5 meters. It then passes radially outward and flows vertically upward through the fuel strings. These flexible instrument tubes, known in the French Nuclear Industry as doigts de gant (glove fingers) have been found to undergo serious high amplitude vibration because of the liquid flow. The project reported here began with an analytical study conducted with a view toward establishing the mechanism of tube excitation. This study was followed by the construction of a full-scale laboratory model whereby it was confirmed that the annular nozzle utilized in current reactors is the actual source of the vibration excitation. It was demonstrated that the problem can be resolved by means of modifications to the geometry of this nozzle. (author)
Heat-and-mass transfer during a laminar dissociating gas flow in eccentric annular channels
International Nuclear Information System (INIS)
An algorithm to calculate heat-and-mass transfer processes during dissociating gas laminar flow in an eccentric annular channels is considered. Analytical solutions of the heat transfer equations for a rod clodding and gap with boundary conditions of conjugation of temperatures and heat fluxes have been used to determine temperature field. This has made it possible to proceed from slution of the conjugate problem to solution of the equation of energy only for the coolant. The results of calculation of temperature distribution along the cladding for different values of its eccentricity and thermal conductivity coefficient both for the case of frozen flow and in the presence of chemical reactions in the flow are given. When calculating temperatures with conjugation boundary conditions temperature gradients in azimuthal direction are far less and heat transfer in concentration diffusion is carried out mainly in radial direction
Transient two-phase flow of cryogenic fluid in a vertical transfer line during the cooldown process
Hedayatpour, Ali
1990-08-01
The analytical and numerical modeling for prediction of the thermofluid parameters of the cool down process of a vertical tube carrying cryogenic liquid are presented. Formulation of the problem is based on the flow patterns observed in the experimental studies. In this model, the flow field consists of four distinct regions of fully liquid, inverted annular film boiling, dispersed flow film boiling, and fully vapor. For the fully liquid and fully vapor regions, the 1-D two-fluid model conservation equations are applied. In addition, a 1-D energy equation is formulated to determine the tube wall history. The numerical approximations are based on the finite difference technique. Calculation for inverted annular flow are based on a semi-implicit model while computations for the wall, fully liquid, and dispersed flow regions are performed explicitly. Comparison of calculated results with experimental data for water and liquid nitrogen are presented.
Slip Velocities in Mixture Vertical Pipe Flow
Czech Academy of Sciences Publication Activity Database
Sobota, J.; Vlasák, Pavel; Petryka, L.; Zych, M.
Vol. 10. Sczecin: The International Society of Offshore and Polar Engineers, 2013, s. 221-224. ISBN 978-1-880653-92-0. ISSN 1946-0066. [The Tenth (2013) ISOPE Ocean Mining & Gas Hydrates Symposium. Szczecin (PL), 22.09.2013-26.09.2013] R&D Projects: GA ČR GAP105/10/1574 Grant ostatní: Ministry of Science and Higher Education of Poland(PL) 7553/B/T02/2011/40; InterOceanMetal(CZ) 501-4.1.2/1-11 Institutional support: RVO:67985874 Keywords : slip velocities * vertical flow * mixtures * radioisotope * pipeline Subject RIV: BK - Fluid Dynamics
Slip Velocities in Mixture Vertical Pipe Flow
Czech Academy of Sciences Publication Activity Database
Sobota, J.; Vlasák, Pavel; Petryka, L.; Zych, M.
Vol. 10. Sczecin : The International Society of Offshore and Polar Engineers, 2013, s. 221-224. ISBN 978-1-880653-92-0. ISSN 1946-0066. [The Tenth (2013) ISOPE Ocean Mining & Gas Hydrates Symposium. Szczecin (PL), 22.09.2013-26.09.2013] R&D Projects: GA ČR GAP105/10/1574 Grant ostatní: Ministry of Science and Higher Education of Poland(PL) 7553/B/T02/2011/40; InterOceanMetal(CZ) 501-4.1.2/1-11 Institutional support: RVO:67985874 Keywords : slip velocities * vertical flow * mixtures * radioisotope * pipeline Subject RIV: BK - Fluid Dynamics
Flow regime transition criteria for two-phase flow in a vertical annulus
Energy Technology Data Exchange (ETDEWEB)
Julia, J. Enrique, E-mail: bolivar@emc.uji.es [Departamento de Ingenieria Mecanica y Construccion, Universitat Jaume I., Campus de Riu Sec, 12071 Castellon (Spain); Hibiki, Takashi [School of Nuclear Engineering, Purdue University, 400 Central Dr., West Lafayette, IN 47907-2017 (United States)
2011-10-15
Highlights: > Flow regime transition model is presented for two-phase flows in a vertical annulus. > The transition criteria is easy to be implemented in computational codes. > Final equations do not need experimental input. > New developed model shows better predicting capabilities than existing correlations. > New developed model shows good predicting capabilities in boiling flow. - Abstract: In this work, a new flow regime transition model is proposed for two-phase flows in a vertical annulus. Following previous works, the flow regimes considered are bubbly (B), slug (S) or cap-slug (CS), churn (C) and annular (A). The B to CS transition is modeled using the maximum bubble package criteria of small bubbles. The S to C transition takes place for small annulus perimeter flow channels and it is assumed to occur when the mean void fraction over the entire region exceeds that over the slug-bubble section. If the annulus perimeter is larger that the distorted bubble limit the cap-slug flow regime will be considered since in these conditions it is not possible to distinguish between cap and partial-slug bubbles. The CS to C transition is modeled using the maximum bubble package criteria. However, this transition considers the coalescence of cap and spherical bubbles in order to take into account the flow channel geometry. Finally, the C to A transition is modeled assuming two different mechanisms, (a) flow reversal in the liquid film section along large bubbles; (b) destruction on liquid slugs or large waves by entrainment or deformation. In the S to C and C to A flow regime transitions the annulus flow channel is considered as a rectangular flow channel with no side walls. In all the modeled transitions the drift-flux model is used to obtain the final correlations. The final equations for every flow regime transition are easy to be implemented in computational codes and not experimental input is needed. The prediction accuracy of the newly developed model has been
International Nuclear Information System (INIS)
Highlights: • Importance of a closure for initial entrainment fraction (IEF) is highlighted. • A new methodology has been presented to predict IEF in diabatic annular flow. • The predicted IEF is seen to predict dryout better than ad-hoc IEF values. - Abstract: The estimation of dryout power holds a lot of importance in safety of boiling water reactors (BWRs). The basic mechanism of dryout is the depletion of the liquid film adhering to the walls under the combined action of deposition, entrainment and vaporization. In literature, the rate processes of entrainment and deposition have been correlated empirically and woven into a model for dryout prediction. The greatest advantage of this model is that the formulation for tubular geometry can be extrapolated to rod-bundles, with certain modifications and modeling assumptions. An accurate model thus, has the potential to make redundant the numerous dryout correlations which exist for various rod-bundle geometries. This is the reason why this model has gained a lot of popularity. Initial entrainment fraction (IEF), i.e., the fraction of liquid entrained as droplets at the onset of annular flow is an important boundary condition required for the model. However there is very little theoretical or experimental work towards prediction of IEF. In this paper, a new methodology is presented whereby the IEF can be determined. It is seen that predictions are improved upon using the new method
Flow regime development analysis in adiabatic upward two-phase flow in a vertical annulus
Energy Technology Data Exchange (ETDEWEB)
Julia, J. Enrique [Departamento de Ingenieria Mecanica y Construccion, Universitat Jaume I, Campus de Riu Sec, Castellon 12071 (Spain); Ozar, Basar [School of Nuclear Engineering, Purdue University, 400 Central Dr., West Lafayette, IN 47907-2017 (United States); Jeong, Jae-Jun [Korea Atomic Energy Research Institute, 150 Dukjin, Yuseong, Daejeon 305-353 (Korea, Republic of); Hibiki, Takashi [School of Nuclear Engineering, Purdue University, 400 Central Dr., West Lafayette, IN 47907-2017 (United States); Ishii, Mamoru, E-mail: ishii@purdue.ed [School of Nuclear Engineering, Purdue University, 400 Central Dr., West Lafayette, IN 47907-2017 (United States)
2011-02-15
In this work radial and axial flow regime development in adiabatic upward air-water two-phase flow in a vertical annulus has been investigated. Local flow regimes have been identified using conductivity probes and neural networks techniques. The inner and outer diameters of the annulus are 19.1 mm and 38.1 mm, respectively. The equivalent hydraulic diameter of the flow channel, D{sub H}, is 19.0 mm and the total length is 4.37 m. The flow regime map includes 1080 local flow regimes identifications in 72 flow conditions within a range of 0.01 m/s <
Experimental investigation on Heat Transfer Performance of Annular Flow Path Heat Pipe
Energy Technology Data Exchange (ETDEWEB)
Kim, In Guk; Kim, Kyung Mo; Jeong, Yeong Shin; Bang, In Cheol [UNIST, Ulsan (Korea, Republic of)
2015-05-15
Mochizuki et al. was suggested the passive cooling system to spent nuclear fuel pool. Detail analysis of various heat pipe design cases was studied to determine the heat pipes cooling performance. Wang et al. suggested the concept PRHRS of MSR using sodium heat pipes, and the transient performance of high temperature sodium heat pipe was numerically simulated in the case of MSR accident. The meltdown at the Fukushima Daiichi nuclear power plants alarmed to the dangers of station blackout (SBO) accident. After the SBO accident, passive decay heat removal systems have been investigated to prevent the severe accidents. Mochizuki et al. suggested the heat pipes cooling system using loop heat pipes for decay heat removal cooling and analysis of heat pipe thermal resistance for boiling water reactor (BWR). The decay heat removal systems for pressurized water reactor (PWR) were suggested using natural convection mechanisms and modification of PWR design. Our group suggested the concept of a hybrid heat pipe with control rod as Passive IN-core Cooling System (PINCs) for decay heat removal for advanced nuclear power plant. Hybrid heat pipe is the combination of the heat pipe and control rod. In the present research, the main objective is to investigate the effect of the inner structure to the heat transfer performance of heat pipe containing neutron absorber material, B{sub 4}C. The main objective is to investigate the effect of the inner structure in heat pipe to the heat transfer performance with annular flow path. ABS pellet was used instead of B{sub 4}C pellet as cylindrical structures. The thermal performances of each heat pipes were measured experimentally. Among them, concentric heat pipe showed the best performance compared with others. 1. Annular evaporation section heat pipe and annular flow path heat pipe showed heat transfer degradation. 2. AHP also had annular vapor space and contact cooling surface per unit volume of vapor was increased. Heat transfer
Dynamics of face and annular seals with two-phase flow
Hughes, William F.; Basu, Prithwish; Beatty, Paul A.; Beeler, Richard M.; Lau, Stephen
1988-01-01
A detailed study was made of face and annular seals under conditions where boiling, i.e., phase change of the leaking fluid, occurs within the seal. Many seals operate in this mode because of flashing due to pressure drop and/or heat input from frictional heating. Some of the distinctive behavior characteristics of two phase seals are discussed, particularly their axial stability. The main conclusions are that seals with two phase flow may be unstable if improperly balanced. Detailed theoretical analyses of low (laminar) and high (turbulent) leakage seals are presented along with computer codes, parametric studies, and in particular a simplified PC based code that allows for rapid performance prediction: calculations of stiffness coefficients, temperature and pressure distributions, and leakage rates for parallel and coned face seals. A simplified combined computer code for the performance prediction over the laminar and turbulent ranges of a two phase flow is described and documented. The analyses, results, and computer codes are summarized.
Drop deposition in annular two-phase flow calculated with Lagrangian Particle Tracking
International Nuclear Information System (INIS)
Highlights: • A new drop size correlation is proposed. • Increased drop size accounts for increased concentration. • LPT model has capability to predict obstacle effect. - Abstract: Lagrangian Particle Tracking is tested for its capability to predict deposition rates in pipes and pipes with obstacle. The drop size is one of the input parameters, which defines in its major part the deposition process. A new correlation is proposed to estimate the drop size, following a systematic analysis of the experimental drop sizes in annular two-phase flow. The Lagrangian Particle Tracking model showed good capability of prediction in the cases where the drop size is known; however, when the drop size is estimated the inaccuracy in calculated deposition rate is high. If the drop size is known at the inlet of the channel, Lagrangian Particle Tracking shows good capability of predicting the deposition increase downstream of the obstacle for steam-water flows of 5, 10 and 15 bar pressure
Institute of Scientific and Technical Information of China (English)
CAI; Ruixian; GOU; Chenhua
2006-01-01
This paper presents two algebraically explicit analytical solutions for the incompressible unsteady rotational flow of Oldroyd-B type in an annular pipe. The first solution is derived with the common method of separation of variables. The second one is deduced with the method of separation of variables with addition developed in recent years. The first analytical solution is of clear physical meaning and both of them are fairly simple and valuable for the newly developing computational fluid dynamics. They can be used as the benchmark solutions to verify the applicability of the existing numerical computational methods and to inspire new differencing schemes, grid generation ways, etc. Moreover, a steady solution for the generalized second grade rheologic fluid flow is also presented. The correctness of these solutions can be easily proven by substituting them into the original governing equation.
Heat transfer coefficient for flow boiling in an annular mini gap
Hożejowska, Sylwia; Musiał, Tomasz; Piasecka, Magdalena
2016-03-01
The aim of this paper was to present the concept of mathematical models of heat transfer in flow boiling in an annular mini gap between the metal pipe with enhanced exterior surface and the external glass pipe. The one- and two-dimensional mathematical models were proposed to describe stationary heat transfer in the gap. A set of experimental data governed both the form of energy equations in cylindrical coordinates and the boundary conditions. The models were formulated to minimize the number of experimentally determined constants. Known temperature distributions in the enhanced surface and in the fluid helped to determine, from the Robin condition, the local heat transfer coefficients at the enhanced surface - fluid contact. The Trefftz method was used to find two-dimensional temperature distributions for the thermal conductive filler layer, enhanced surface and flowing fluid. The method of temperature calculation depended on whether the area of single-phase convection ended with boiling incipience in the gap or the two-phase flow region prevailed, with either fully developed bubbly flow or bubbly-slug flow. In the two-phase flow, the fluid temperature was calculated by Trefftz method. Trefftz functions for the Laplace equation and for the energy equation were used in the calculations.
Heat transfer coefficient for flow boiling in an annular mini gap
Directory of Open Access Journals (Sweden)
Hożejowska Sylwia
2016-01-01
Full Text Available The aim of this paper was to present the concept of mathematical models of heat transfer in flow boiling in an annular mini gap between the metal pipe with enhanced exterior surface and the external glass pipe. The one- and two-dimensional mathematical models were proposed to describe stationary heat transfer in the gap. A set of experimental data governed both the form of energy equations in cylindrical coordinates and the boundary conditions. The models were formulated to minimize the number of experimentally determined constants. Known temperature distributions in the enhanced surface and in the fluid helped to determine, from the Robin condition, the local heat transfer coefficients at the enhanced surface – fluid contact. The Trefftz method was used to find two-dimensional temperature distributions for the thermal conductive filler layer, enhanced surface and flowing fluid. The method of temperature calculation depended on whether the area of single-phase convection ended with boiling incipience in the gap or the two-phase flow region prevailed, with either fully developed bubbly flow or bubbly-slug flow. In the two–phase flow, the fluid temperature was calculated by Trefftz method. Trefftz functions for the Laplace equation and for the energy equation were used in the calculations.
Gas-solid flow in vertical tubes
International Nuclear Information System (INIS)
This paper reports on a computational study of fully-developed flow of gas-particle suspensions in vertical pipes which was carried out, using the model proposed recently by Sinclair and Jackson, to understand the predicted scale-up characteristics. It was shown that the model can capture the existence of steady-state multiplicity wherein different pressure gradients can be obtained for the same gas and solids fluxes. A pronounced and nonmonotonic variation of the pressure gradient required to achieve desired fluxes of solid and gas with tube diameter was predicted by the model, and this is explained on a physical basis. The computed results were compared with the experimental data. The model manifests an unsatisfactory degree of sensitivity to the inelasticity of the particle-particle collisions and the damping of particle-phase fluctuating motion by the gas
Exact solutions for the flow of non-Newtonian fluid with fractional derivative in an annular pipe
Institute of Scientific and Technical Information of China (English)
TONG; Dengke; WANG; Ruihe; YANG; Heshan
2005-01-01
This paper deals with some unsteady unidirectional transient flows of Oldroyd-B fluid in an annular pipe. The fractional calculus approach in the constitutive relationship model Oldroyd-B fluid is introduced and a generalized Jeffreys model with the fractional calculus has been built. Exact solutions of some unsteady flows of Oldroyd-B fluid in an annular pipe are obtained by using Hankel transform and Laplace transform for fractional calculus. The following four problems have been studied: (1) Poiseuille flow due to a constant pressure gradient; (2) axial Couette flow in an annulus; (3) axial Couette flow in an annulus due to a longitudinal constant shear; (4) Poiseuille flow due to a constant pressure gradient and a longitudinal constant shear. The well-known solutions for Navier-Stokes fluid, as well as those corresponding to a Maxwell fluid and a second grade one, appear as limited cases of our solutions.
Physical understanding of gas-liquid annular flow and its transition to dispersed droplets
Kumar, Parmod; Das, Arup Kumar; Mitra, Sushanta K.
2016-07-01
Transformation from annular to droplet flow is investigated for co-current, upward gas-liquid flow through a cylindrical tube using grid based volume of fluid framework. Three transitional routes, namely, orificing, rolling, and undercutting are observed for flow transformation at different range of relative velocities between the fluids. Physics behind these three exclusive phenomena is described using circulation patterns of gaseous phase in the vicinity of a liquid film which subsequently sheds drop leading towards transition. Orifice amplitude is found to grow exponentially towards the core whereas it propagates in axial direction in a parabolic path. Efforts have been made to fit the sinusoidal profile of wave structure with the numerical interface contour at early stages of orificing. Domination of gas inertia over liquid flow has been studied in detail at the later stages to understand the asymmetric shape of orifice, leading towards lamella formation and droplet generation. Away from comparative velocities, circulations in the dominant phase dislodge the drop by forming either a ligament (rolling) or a bag (undercut) like protrusion in liquid. Study of velocity patterns in the plane of droplet dislodge reveals the underlying physics behind the disintegration and its dynamics at the later stages. Using numerical phase distributions, rejoining of dislodged droplet with liquid film as post-rolling consequences has been also proposed. A flow pattern map showing the transitional boundaries based on the physical mechanism is constructed for air-water combination.
Experimental investigations of heat transfer at dry patch location in annular two-phase flow
International Nuclear Information System (INIS)
New experiments have been performed to investigate heat transfer to water/steam two-phase mixture flowing in annular test section at trans-dryout conditions. The measurements have been carried out in the High-pressure Water Test (HWAT) loop at the Royal Institute of Technology, Stockholm, Sweden. The primary objective of the experiment investigations has been to study heat transfer at conditions typical for Boiling Water Reactors (BWR), when heat transfer regime changes from convective boiling to post-dryout heat transfer. The experiments indicate a significant enhancement of heat transfer just upstream of dryout patch. It has been observed that the measured heat transfer coefficient is in good agreement with the Chen correlation for quality less than 30%, however, increasing discrepancy is noted for near-critical quality. (author)
Vertical structure of Advection dominated Accretion Flows
Zeraatgari, Fateme Zahra
2015-01-01
We solve the set of hydrodynamic (HD) equations for optically thin Advection Dominated Accretion Flows (ADAFs) by assuming radially self-similar in spherical coordinate system $ (r, \\theta, \\phi) $. The disk is considered to be steady state and axi-symmetric. We define the boundary conditions at the pole and the equator of the disk and to avoid singularity at the rotation axis, the disk is taken to be symmetric with respect to this axis. Moreover, only the $ \\tau_{r \\phi} $ component of viscous stress tensor is assumed and we have set $ v_{\\theta} = 0 $. The main purpose of this study is to investigate the variation of dynamical quantities of the flow in the vertical direction by finding an analytical solution. As a consequence, we found that the advection parameter, $ f^{adv} $, varies along the $ \\theta $ direction and reaches to its maximum near the rotation axis. Our results also show that, in terms of no-outflow solution, thermal equilibrium still exists and consequently advection cooling can balance vis...
Entrained liquid fraction calculation in adiabatic disperse-annular flows at low rate in film
Yagov, V. V.; Minko, M. V.
2016-04-01
In this work, we continue our study [1] and extend further an approach to low reduced pressures. An approximate model of droplets entrainment from the laminar film surface and an equation for calculating entrainment intensity are proposed. To carry out direct verification of this equation using experimental data is extremely difficult because the integral effect—liquid flow rate in a film at a dynamic equilibrium between entrainment and deposition—is usually measured in the experiments. The balance between flows of droplets entrainment and deposition corresponds to the dynamic equilibrium because of turbulent diffusion. The transcendental equation, which was obtained on the basis of this balance, contains one unknown numerical factor and allows one to calculate the liquid rate. Comparing calculation results with the experimental data for the water-air and water-helium flows at low reduced pressures (less than 0.03) has shown their good agreement at the universal value of a numerical constant, if an additional dimensionless parameter, a fourth root of vaporliquid densities ratio, is introduced. The criterion that determines the boundary of using methods of this work and that of [1] in calculations and that reflects effect of pressure and state of film surface on distribution of the liquid in the annular flow is proposed; the numerical value of this criterion has been determined.
Flowing catalyst particles in annular stream around a plug in lift pot
Energy Technology Data Exchange (ETDEWEB)
Skraba, F.W.
1987-06-23
A catalytic cracking process is described comprising (a) flowing a stream of hot cracking catalyst particles longitudinally through at least a portion of a lift pot in an annular stream around a plug which is positioned in the lift pot and which has an upstream end; a downstream end and a longitudinal axis; the hot cracking catalyst particles flow generally radially inwardly toward the plug axis past the downstream end of the plug, and then longitudinally into a riser-reactor; (b) introducing an oil feedstock into the stream of hot cracking catalyst particles as it is moving radially inwardly from around the periphery of the downstream end of the plug for the formation of a reaction mixture with the hot cracking catalyst. The hot catalyst particles and the oil feedstock moves at approximately right angles to each other at the point at which the oil feedstock is introduced; and (c) flowing the reaction mixture through the riser-reactor and into a disengagement chamber. The mixture flows into the disengagement chamber comprising cracked oil product and catalyst particles.
Energy Technology Data Exchange (ETDEWEB)
Colombo, Luigi P.M.; Guilizzoni, Manfredo; Sotgia, Giorgio M. [Politecnico di Milano, Department of Energy, Milan (Italy)
2012-11-15
The transition from annular to wavy-stratified oil-water adiabatic flow within horizontal pipes is experimentally analyzed, and a semiempirical model is proposed. The transition is referred to as critical because it occurs suddenly, giving rise to a sharp and strong increase in the pressure drop due to the contact of the high-viscosity oil with the pipe wall. This could lead to a dangerous accident in pipelines. Experimental runs were performed on eight test sections of both Plexiglas {sup registered} and Pyrex {sup registered} pipes with internal diameters ranging from 21.5 to 50 mm, using tap water and oil with viscosity about 880 times higher than that of water. On the basis of pressure drop measurement and flow pattern visualization, the transition boundary between annular and wavy-stratified flow was analytically determined and compared with flow pattern maps. (orig.)
An assessment of the annular flow transition criteria and interphase friction models in RELAP5/MOD2
International Nuclear Information System (INIS)
An assessment of the annular flow transition criteria and interphase friction models for two-phase flow in tubes used in RELAP5/MOD2 code is described. The assessment examines the theoretical bases for the criteria and models and considers the results of comparisons with experimental data. Several deficiencies in the transition criteria are identified and appropriate improvements proposed. The interphase friction models are found to be adequate for PWR analyses. (author)
Measurement of the deposition rate of droplets in a vertical tube containing a flow obstacle
International Nuclear Information System (INIS)
deposition rate of droplets is scarce in literature. In this study, double film extraction technique was used to elucidate the effects of a flow obstacle on the deposition rate of droplets in annular two-phase flow. The test section was a round tube of 5 mm in inside diameter, air and water were used as test fluids and the flow direction was vertical upward; the reference flow obstacle was a short tube that was 2 mm in inside diameter, 3 mm in outside diameter and 20 mm in length. It was shown that the deposition rate of droplets was markedly increased if the present flow obstacle was concentrically placed in the flow channel. The influence of obstacle geometry was also investigated. The cross-sectional area of an obstacle appeared the most important parameter for the enhancement of droplet deposition. (authors)
Vertical flow of a multiphase mixture in a channel
Massoudi Mehrdad; Rao C. Lakshmana
2000-01-01
The flow of a multiphase mixture consisting of a viscous fluid and solid particles between two vertical plates is studied. The theory of interacting continua or mixture theory is used. Constitutive relations for the stress tensor of the granular materials and the interaction force are presented and discussed. The flow of interest is an ideal one where we assume the flow to be steady and fully developed; the mixture is flowing between two long vertical plates. The non-linear boundary value pro...
MHD stability analysis of a liquid sodium flow at the annular gap of an EM pump
International Nuclear Information System (INIS)
Highlights: ► A MHD stability analysis on an electromagnetic pump was carried out. ► Small perturbations for MHD fields were considered in sinusoidal form. ► Critical Reynolds number depends on the Hartman number and perturbed wave number. ► A magnetic field has a significant stabilizing effect on liquid sodium flow. - Abstract: A stability analysis of a viscous, incompressible, and electrically conducting liquid sodium flow in an annular linear induction electromagnetic pump for sodium coolant circulation of a Sodium Fast Reactor (SFR) was carried out when transverse magnetic fields permeate the sodium fluid across the narrow annular gap. Due to a negligible skin effect and the presence of a magnetic core outside the gap, radial magnetic field is assumed to be constant over the narrow channel gap, and the steady state solution of the axial velocity is obtained as a function of radius. Small perturbations for MHD fields were considered in sinusoidal form as a function of the angular frequency and wave number, and the resulting equations were linearized. The solutions of the perturbed equations were sought in the form of a linear combination of independent orthogonal functions in a non-dimensional radial interval (0, 1), and each orthogonal function was chosen to satisfy the boundary conditions of adhesion to the solid walls of the channel. Under the assumption that solutions of the equations were not oscillated rapidly according to the radial coordinate, finite numbers of orthogonal polynomials were considered. As a result, simultaneous equations with coefficients of steady-state solutions were arranged, and dispersion relations between angular frequency and wave number of perturbed state were sought. The imaginary part of the angular frequency was taken into consideration from the condition of existence of a nontrivial solution of the system, which leads to the relation between critical Reynolds number (Recr) and Hartmann number (Ha). In the present study
Institute of Scientific and Technical Information of China (English)
Shigeru MATSUO; Tae-Hun KIM; Toshiaki SETOGUCHI; Heuy Dong KIM; Yeon-Won LEE
2007-01-01
In comparison with previous researches of swirling flow, spiral flow generated in the spiral nozzle has some different flow characteristics. It does not need a forced tangential momentum to generate its velocity and has some different merits from the swirling flow such as long potential core and low tangential velocity. In this study, the effect of nozzle geometry on the flow characteristics in spiral nozzle was investigated by experiment and computation. As a result, the flow characteristics obtained by experiment has a satisfactory agreement with computational results, quantitatively and qualitatively.
Chaotic heat transfer enhancement in rotating eccentric annular-flow systems
International Nuclear Information System (INIS)
Thermal Taylor dispersion theory for time-periodic systems was used to study the extent of chaotic laminar heat transfer enhancement and axial thermal dispersion occurring during combined transverse and axial annular flow between two nonconcentric circular cylinders undergoing alternate rotations. A local Newton's open-quotes law of coolingclose quotes heat transfer boundary condition was used on the outer cylinder; the inner cylinder was supposed insulated. The effective heat transfer coefficient bar H* describing the global rate of heat loss from the system (differing in general from the true microscale Newton's law heat transfer coefficient h on the outer cylinder) was calculated as a function of the system parameters, to quantify the extent of chaotic heat transfer enhancement. The axial thermal Taylor dispersivity provided an independent measure of the effects of chaotic mixing, as did the axial thermal velocity. Calculations were performed for three different cases: (i) concentric cylinder rotation (the resulting circular transverse flow has no effect upon the effective transport properties); (ii) nonconcentric counter-rotating circular cylinders, each undergoing a steady rotation, creating a time-independent transverse flow field; (iii) nonconcentric counter- and co-rotating circular cylinders, each undergoing time-periodic alternate rotation while the other remains at rest. A open-quotes regularclose quotes enhancement of the heat transfer rate over the concentric cylinder case was observed in case (ii), arising from the presence of a secondary-flow recirculation region. Enhancement due to chaotic advection was observed in case (iii) [about 50% more than that of case (ii) and more than double that of case (i), other things equal]. Concomitant values of the axial thermal Taylor dispersivity and axial thermal velocity confirmed the existence of enhanced transverse transport due to chaotic advection. (Abstract Truncated)
International Nuclear Information System (INIS)
Critical Heat Flux is a very important subject of interest due to design, operation and safety analysis of nuclear power plants. Every new design of the core must be thoroughly checked. Experimental studies have been performed using freon as a working fluid. The possibility of transferring of results into water equivalents has been proved. The experimental study covers vertical flow, annular geometry over a wide range of pressure, mass flow and temperature at inlet of test section. Theoretical models of Critical Heat Flux have been presented but only those which cover DNB. Computer programs allowing for numerical calculations using theoretical models have been developed. A validation of the theoretical models has been performed in accordance with experimental results. (author). 83 refs, 32 figs, 4 tabs
Paı¨Doussis, M. P.; Luu, T. P.; Prabhakar, S.
2008-01-01
A theoretical model is developed for the dynamics of a hanging tubular cantilever conveying fluid downwards; the fluid, after exiting from the free end, is pushed upwards in the outer annular region contained by the cantilever and a rigid cylindrical channel. This configuration thus resembles that of a drill-string with a floating fluid-powered drill-bit. The linear equation of motion is solved by means of a hybrid Galerkin Fourier method, as well as by a conventional Galerkin method. Calculations are conducted for a very slender system with parameters appropriate for a drill-string, for different degrees of confinement of the outer annular channel; and also for another, bench-top-size experiment. For wide annuli, the dynamics is dominated by the internal flow and, for low flow velocities, the flow increases the damping associated with the presence of the annular fluid. For narrow annuli, however, the annular flow is dominant, tending to destabilize the system, giving rise to flutter at remarkably low flow velocities. The mechanisms underlying the dynamics are also considered, in terms of energy transfer from the fluid to the cantilever and vice versa, as are possible applications of this work.
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Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (MUltiple-SIze-Group) model implemented in CFX4.4 is extended to account for the wall nucleation and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter diameter and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcoolings. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter and liquid velocity profiles against measurements. However, significant weakness of the model is evidenced in the prediction of the vapour velocity. Work is in progress to overcome the deficiency of the extended MUSIG model by the consideration of an algebraic slip model to account for bubble separation. (author)
Energy Technology Data Exchange (ETDEWEB)
Moon, S.K.; Chun, S.Y.; Choi, K.Y.; Yang, S.K. [Korea Atomic Energy Research Inst., Taejon (Korea, Republic of)
2001-07-01
An experimental study on transient critical heat flux (CHF) under flow coast-down has been performed for water flow in a non-uniformly heated vertical annulus under low flow and a wide range of pressure conditions. The objectives of this study are to systematically investigate the effect of the flow transient on the CHF and to compare the transient CHF with steady state CHF. The transient CHF experiments have been performed for three kinds of flow transient modes based on the coast-down data of the Kori 3/4 nuclear power plant reactor coolant pump. Most of the CHFs occurred in the annular-mist flow regime. Thus, it means that the possible CHF mechanism might be the liquid film dryout in the annular-mist flow regime. For flow transient mode with the smallest flow reduction rate, the time-to-CHF is the largest. At the same inlet subcooling, system pressure and heat flux, the effect of the initial mass flux on the critical mass flux can be negligible. However, the effect of the initial mass flux on the time-to-CHF becomes large as the heat flux decreases. Usually, the critical mass flux is large for slow flow reduction. There is a pressure effect on the ratio of the transient CHF data to steady state CHF data. Some conventional correlations show relatively better CHF prediction results for high system pressure, high quality and slow transient modes than for low system pressure, low quality and fast transient modes. (author)
Non-linear dynamics of annular creeping flow enclosed by an elastic membrane
Elbaz, Shai; Gat, Amir
2015-11-01
This study deals with the fluid-structure-interaction problem of longitudinal annular flow about a varying cross-section centre-body enclosed by an elastic membrane. The gap between the centre-body and membrane wall may be initially filled with a thin fluid layer or devoid of it. We employ elastic shell theory and the lubrication approximation and obtain a forced nonlinear diffusion equation governing the problem. In the case of an advancing liquid front in an initially unpenetrated interface (viscous peeling) the governing equation degenerates into a forced porous medium equation, for which several closed-form solutions can be obtained. Based on self-similarity we define propagation laws for the fluid-elastic interaction which in turn provide the basis for numerical investigation of compound solutions such as pulse trains and other waveforms. The presented interaction between viscosity and elasticity may be applied to fields such as soft-robotics and micro-scale or larger swimmers by allowing for the time-dependent control of a compliant boundary.
International Nuclear Information System (INIS)
By employing stochastic analysis techniques, an experimental study of a large number of annular flows with bubbles in the liquid ring and entrained droplets has been undertaken in the experimental air-water loop FREDLI, in which the information carrier is two visible light beams crossing the diameter of the tube and modulated by the scattering of the photons at the randomly arriving interfaces; also, some earlier neutron noise measurements in the upper part of a commercial BWR core are carefully analyzed. For the BWR measurements, it is shown for the first time that in the upper part of the core, there are usually three peaks in the cross-correlation function and that all noise analytic functions look extraordinarily similar to the corresponding noise analytic functions of some of the investigated annular flows at the FREDLI loop; a plausible explanation of these findings is given. (Auth.)
Xie, Beibei; Yang, Dong; Xie, Haiyan; Nie, Xin; Liu, Wanyu
2016-08-01
In order to expand the study on flow instability of supercritical circulating fluidized bed (CFB) boiler, a new numerical computational model considering the heat storage of the tube wall metal was presented in this paper. The lumped parameter method was proposed for wall temperature calculation and the single channel model was adopted for the analysis of flow instability. Based on the time-domain method, a new numerical computational program suitable for the analysis of flow instability in the water wall of supercritical CFB boiler with annular furnace was established. To verify the code, calculation results were respectively compared with data of commercial software. According to the comparisons, the new code was proved to be reasonable and accurate for practical engineering application in analysis of flow instability. Based on the new program, the flow instability of supercritical CFB boiler with annular furnace was simulated by time-domain method. When 1.2 times heat load disturbance was applied on the loop, results showed that the inlet flow rate, outlet flow rate and wall temperature fluctuated with time eventually remained at constant values, suggesting that the hydrodynamic flow was stable. The results also showed that in the case of considering the heat storage, the flow in the water wall is easier to return to stable state than without considering heat storage.
Correlation-measurements of vertical two-phase flow by means of laser beams
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Vertical annular two-phase flow in a transparent tube with an internal diameter of 10 mm was investigated by means of correlation of the signals induced in two photodiodes by a pair of horizontal, parallel laser beams, modulated by the two-phase water-air mixture. It was proved that there are two different perturbations propagating upwards in the glass tube. The two disturbances are effectively additive at the detectors. The two perturbations were identified as: a) The first comes from water-droplets carried by the air-stream of the annular two-phase flow. b) The second is due to the fluctuations of the water-air interface. The propagation of the two disturbances is reproduced by theoretical models. A method for the determination of the most probable wave length, lambdasub(max), of the interface-fluctuations is also presented. The measurements show a linear dependence of lambdasub(max) on the square of the mean relative velocity between the two phases. A hypothesis on the generation mechanism of the entrained droplets is formulated. (Auth.)
Contribution to the study of helium two-phase vertical flow
International Nuclear Information System (INIS)
This work aims at a better understanding of the dynamics of helium two-phase flow in a vertical duct. The case of bubble flow is particularly investigated. The most descriptive parameter of two-phase flow is the void fraction. A sensor to measure this parameter was specially designed and calibrated, it is made of a radioactive source and a semiconductor detector. Sensors based on light attenuation were used to study the behaviour of this two-phase flow. The experimental set-up is described. The different flow types were photographed and video filmed. This visualization has allowed to measure the diameter of bubbles and to study their movements in the fluid. Bubble flow then churn and annular flows were observed but slug flow seems not to exist with helium. A modelling based on a Zuber model matches better the experimental results than a Levy type model. The detailed analysis of the signals given by the optical sensors has allowed to highlight a bubble appearance frequency directly linked to the flowrate. (A.C.)
International Nuclear Information System (INIS)
The effect of the moderator density distribution of annular flow on the fuel assembly neutronic characteristics in a boiling water nuclear reactor was investigated using the SRAC95 code system. For the investigation, a model of annular flow for fuel assembly calculation was utilized. The results of the assembly calculation with the model (Method 1) and those of the fuel assembly calculation with the uniform void fraction distribution (Method 2) were compared. It was found that Method 2 underestimates the infinite multiplication factor in the fuel assembly including the gadolinia rod (type 1 assembly). This phenomenon is explained by the fact that the capture rate in the thermal energy region in gadolinia fuel is estimated to be smaller when the liquid film of annular flow at the fuel rod surface is considered. A burnup calculation was performed under the condition of a void fraction of 65% and a volumetric fraction of the liquid film in liquid phase of 1. It is found that Method 2 underestimates the infinite multiplication factor in comparison to Method 1 in the early stage of burnup, and that Method 2 becomes to overestimate the factor after a certain degree of burnup. This is because Method 2 overestimates the depletion rate of the gadolinia. (author)
Institute of Scientific and Technical Information of China (English)
LongZhou Xiao; XinPing Long; XueLong Yang
2014-01-01
The performance of an annular jet pump ( AJP ) is determined by its area ratio A ( ratio of cross sectional area of throat and annular nozzle) and flow rate ratio q ( ratio of primary and secondary flow rate, Qs/Qj ) , while the nozzle lip thickness is neglected in the present studies. This paper presents a study on the effect of the thickness on the flow field and performance of an AJP with A = 1�75. With the increasing flow rate ratio and nozzle lip thickness, a small vortex forms at the nozzle lip and keeps on growing. However, as the flow rate ratio or nozzle lip thickness is extremely low, the vortex at the lip vanishes thoroughly. Moreover, the recirculation width varies conversely with the nozzle lip thickness when the flow rate ratio q≤0�13. While the deviation of the recirculation width with different nozzle lip thickness is negligible with q≥0�13. Additionally the existence of nozzle lip hinders the momentum exchange between the primary and secondary flow and leads to a mutation of velocity gradient near the nozzle exit, which shift the recirculation downstream. Finally, based on the numerical results of the streamwise and spanwise vortex distributions in the suction chamber, the characteristics of the mixing process and the main factors accounting for the AJP performance are clarified.
International Nuclear Information System (INIS)
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)
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Ferrofluid flow in cylindrical and annular geometries under the influence of a uniform rotating magnetic field was studied experimentally using aqueous ferrofluids consisting of low concentrations (−8 kg m/s, two orders of magnitude larger than the value estimated earlier for iron oxide based ferrofluids, and 12 orders of magnitude larger than estimated using dimensional arguments valid in the infinite dilution limit. These results provide further evidence of the existence of couple stresses in ferrofluids and their role in driving the spin-up flow phenomenon
Stability of core-annular flow of power-law fluids in the presence of interfacial surfactant
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
The shear-thinning influence on the core-annular flow stability of two immiscible power-law fluids is considered by making a linear stability analysis.The flow is driven by an axial pressure gradient in a straight pipe with the interface between the two fluids occupied by an insoluble surfactant.Given the basic flow for this core-annular arrangement,the analytical solution is obtained with respect to the power-law fluid model.The linearized equations for the evolution of infinitesimal disturbances are derived and the stability problem is formulated as a generalized matrix eigenvalue problem,which is solved by using the software package Matlab based on the QZ algorithm.The shear-thinning property is found to have marked influence on the power-law fluid core-annular flow stability,which is reflected in various aspects.First,the capillary instability is magnified by the shear-thinning property,which may lead to an essential difference between power-law and Newtonian fluid flows.Especially when the interface is close to the pipe wall,the power-law fluid flow may be unstable while the Newtonian fluid flow is stable.Second,under disturbances to the interface a velocity discontinuity at the interface appears which is destabilizing to the flow.The magnitude of this velocity discontinuity is affected by the power-law index and the flow stability is influenced correspondingly.Besides,the shear-thinning property may induce new stability modes which do not appear in the Newtonian fluid flow.The flow stability shows much dependence on the interface location,the role of which was neglected in most previous studies.The shear-thinning fluid flow is more unstable to long wave disturbances when the interface is close to the pipe wall,while the Newtonian fluid flow is more unstable when the interface is close to the pipe centerline.But this trend is changed by the addition of interfacial surfactant,for which the power-law fluid flow is more stable no matter where the interface is
... page: //medlineplus.gov/ency/article/001142.htm Annular pancreas To use the sharing features on this page, please enable JavaScript. An annular pancreas is a ring of pancreatic tissue that encircles ...
International Nuclear Information System (INIS)
Maintaining the PWR components under reliable operating conditions requires a complex design to prevent various damaging processes including wear problems due to flow induced vibration. To improve wear prediction in PWR components, EDF has undertaken a comprehensive program oriented both on experimental and computational studies. The present paper illustrates one aspect of this program, proposing a numerical model for fluid-structure coupling of a cylindrical center body submitted to an axial annular flow. This model has been developed in the case of an incompressible, single phase, viscous fluid, and for a confined geometry with variable section passage. The structural response is expended in terms of the normal modes of the system. Due to the particular geometry of the problem, a specific numerical procedure has been implemented to provide a good approximate solution of the unsteady Navier-Stokes equations. The boundary conditions and dissipative terms taken into account in the modelization are of particular interest and are developed in detail. In the stable operating region, it provides the evolution versus flow velocity, of the modal characteristics of the coupled fluid-structure system. Consequently, the critical flow velocity can be computed as the velocity at which the damping ratio becomes zero. As a final step, an experimental validation is presented: the results obtained with the numerical model are compared to previously published experimental data concerning an oscillating cylinder submitted to an unsteady annular flow. (authors). 5 figs., 15 refs
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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
Lilley, D. G.; Sander, G. F.
1983-01-01
In connection with the desirability of optimizing the design of a gas turbine combustion chamber, there exists a need for a more complete understanding of the fluid dynamics of the flow in such chambers. In order to satisfy this need, experimental and theoretical research is being conducted with the objective to study two-dimensional axisymmetric geometries under low speed, nonreacting, turbulent, swirling flow conditions. The flow enters the test section and proceeds into a larger chamber. Inlet swirl vanes are adjustable to a variety of vane angles. The present investigation concentrates on the time-mean flow characteristics which are generated by the upstream annular swirler. The investigation makes use of a five-hole pitot probe technique. A theoretical analysis of swirl numbers associated with several idealized exit velocity profiles is included, and values of the ratio of maximum swirl velocity to maximum axial velocity at different swirl strengths are given for each case.
Phase Flow Rate Measurements of Annual Flows
Al-Yarubi, O.S.; Lucas, Gary
2009-01-01
The Annular flow regime makes measurement of the total liquid flow rate difficult. It is even more difficult to measure the individual flow rate of either the oil or the water. In a vertical Perspex tube (i.d. = 50 mm) using a newly-designed flow loop in the University of Huddersfield, annular flow was established and different measurements were carried out. One possible on-line measurement technique to achieve the oil volume fraction measurement is an automated bypass...
Bouaichaoui, Y.; Kibboua, R.; Matkovič, M.
2015-05-01
In this paper a convective flow boiling of refrigerant R-11 in a vertical annular channel has been investigated. Measurements were performed under various conditions of mass flux, heat flux, and inlet subcooling, which enabled to study the influence of different boundary conditions on the development of local flow parameters. Also, some measurements have been compared to the predictions by the three-dimensional two-fluid model of subcooled boiling flow carried out with the computer code ANSYS-CFX-13. Simulation results successfully predict the main experimental tendencies associated with the heat flux and Reynolds number variation. A sensitivity analysis of several modelling parameters on the radial distribution of flow quantities has highlighted the importance of correct description of the boiling boundary layer. In general a good quantitative and qualitative agreement with experimental data was obtained.
Mathematical model of induced flow on the airplane vertical tail
Rotaru, Constantin; Cîrciu, Ionicǎ; Edu, Raluca Ioana
2016-06-01
In this paper is presented a mathematical model of the flow around the vertical tail of an airplane, based on the general elements of the aerodynamic design, with details leading to the separate formulation of the Fourier coefficients in the series solution of the Prandtl's lifting-line equation. Numerical results are obtained in Maple soft environment, for a standard configuration of an airplane geometry. The results include the discussion of the vortex model for the sidewash gradient on the vertical stabilizer.
International Nuclear Information System (INIS)
Turbulent mixing rates of gas and liquid phases between adjacent subchannels have been measured for various air-water two-phase annular flows in a multiple channel consisting of two identical circular subchannels. In order to study effect of liquid entrainment in the gas core on the turbulent mixing rates, experiments were conducted for two types of liquid injection method, i.e., a small bore nozzle placed in the subchannel center and a porous wall. The result showed that the effect of liquid entrainment on the turbulent mixing rates of both phases is negligibly small. (author)
Thermosyphon circulation inside vertical condenser bundle with through flow
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The tube side intermittent flow in U-tube bundle of vertical condenser is numerically simulated using RELAP5 MOD3.4. The flow rate intermit between a maximum and minimum value. The results of the simulation shows that reverse flow is established inside a group of the tubes from the outlet to the inlet channel -head during the low flow rate period. The reverse flow is seized when the minimum flow rate exceeds certain value. A steady state numerical simulation predicts the minimum inlet flow rate to establish the reverse flow. The effect of temperature difference at the inlet of the tubes and the tube resistance on the limit of the reverse flow inception is also studied. The heat transfer from the condensing steam on the shell side is also taken into consideration. (author)
International Nuclear Information System (INIS)
Dryout of the liquid coolant film on fuel pins at the top of boiling water reactor (BWR) cores constitutes the type of heat transfer crisis relevant for the conditions of high void fractions. It is a limiting factor in the thermal power, and therefore the economy, of BWRs. Ongoing research on multiphase annular flow, specifically the liquid film thickness, is fundamental not only to nuclear reactor safety and operation but also to that of evaporators, condensers, and pipelines in a general industrial context. We have performed cold neutron tomography of adiabatic air water annular flow in a scaled up model of the subchannel geometry found in BWR fuel assemblies today. All imaging has been performed at the ICON beamline at the neutron spallation source SINQ at the Paul Scherrer Institut in Switzerland. Neutron tomography is shown to excel in investigating the interactions of air water two phase flows with spacer vanes of different geometry. The high resolution, high contrast measurements provide spatial distributions of the coolant on top of the surfaces of the spacer, including the vanes, and in the subchannel downstream of the spacers.
Transient two-phase flow of cryogenic fluid in a vertical transfer line during the cooldown process
International Nuclear Information System (INIS)
The analytical and numerical modeling for prediction of the thermo-fluid parameters of the cooldown process of a vertical tube carrying cryogenic liquid are presented. Formulation of the problem is based on flow patterns observed in the experimental studies. In this model, the flow field consists of four distinct regions of fully liquid, inverted annular film boiling, dispersed flow film boiling, and fully vapor. For the fully liquid and fully vapor regions, the one-dimensional form of the mass, momentum, and energy conservation equations are used. For the two-phase regions, the volume-averaged, one-dimensional two-fluid model conservation equations are applied. In addition, a one-dimensional energy equation is formulated to determine the tube-wall history. The numerical approximations are based on the finite-difference technique. Calculations for inverted annular flow are based on a semi-implicit model while computations for the wall, fully liquid, and dispersed flow regions are performed explicitly. Comparison of calculated results with experimental data for water and liquid nitrogen are presented
Energy Technology Data Exchange (ETDEWEB)
Silva, Maria das Gracas Pena; Martins, Andre Leibsohn; Oliveira, Antonio Augusto Junqueira de [PETROBRAS, Rio de Janeiro (Brazil). Centro de Pesquisas. Div. de Explotacao
1988-12-31
The rheological behavior of drilling fluids during annular flow in a physical simulator well (Surface Hydraulic System - SHS)was investigated. Measurement of volumetric flow and pressure drop the 10-meter simulator well was used to assess applicability of the Bingham, power Law, Casson, and Herschell-Bulkley models to the annular flow of water and oil-based fluids under different temperatures. Additionally, under different pre-set deformation ranges, SHS-observed behavior was compared with behavior observed using the traditional Fann VG 35 A viscometer. (author) 8 refs., 21 figs., 15 tabs.
Using LES to Study Reacting Flows and Instabilities in Annular Combustion Chambers
Wolf, Pierre; Balakrishnan, Ramesh; Staffelbach, Gabriel; Gicquel, Laurent Y.M.; Poinsot, Thierry
2012-01-01
Great prominence is put on the design of aeronautical gas turbines due to increasingly stringent regulations and the need to tackle rising fuel prices. This drive towards innovation has resulted sometimes in new concepts being prone to combustion instabilities. In the particular field of annular combustion chambers, these instabilities often take the form of azimuthal modes. To predict these modes, one must compute the full combustion chamber, which remained out of reach until very recently a...
Intermittent dry granular flow in a vertical pipe
Bertho, Yann; Giorgiutti-Dauphiné, Frédérique; Hulin, Jean-Pierre
2005-01-01
The intermittent compact flow of glass beads in a vertical glass pipe of small diameter is studied experimentally by combining particle fraction, pressure, and air and grain flow rates measurements with a spatio-temporal analysis of the flow. At the onset of the flow, a decompaction front is observed to propagate from the bottom to the top of the tube at a velocity much larger than that of the grains. The blockage front also propagates upwards and at a still higher velocity. The decompaction ...
International Nuclear Information System (INIS)
A supercritical-water-cooled reactor (SCWR) is a high-temperature, high-pressure water cooled reactor that operates above the critical pressure of water. In order to perform efficiently the thermal design of the SCWR, it is important to assess the thermal hydraulics in rod bundles of the core. Experimental conditions of mockup tests, however, may be limited because of technical and financial reasons. Therefore, it is required to establish an analytical design technique that can extrapolate experimental data to various design conditions of the reactor. Japan Atomic Energy Agency (JAEA) has improved the three-dimensional two-fluid model analysis code ACE-3D, which was originally developed for the two-phase flow thermal hydraulics of light water reactors, to handle the thermal hydraulic properties of water in the supercritical region. In the present study, heat transfer experiments of supercritical water flowing in a vertical annular channel around a heater pin, which were performed at JAEA, were analyzed with the improved ACE-3D to assess the prediction performance of the code. As a result, it was implied that the ACE-3D code is applicable to the prediction of wall temperatures of a single rod that simulates the fuel bundle geometry of the SCWR core. (author)
International Nuclear Information System (INIS)
Heat transfer enhancement through turbulence augmentation is recognized as a key factor for improving the safety and economic conditions in the development of both critical and subcritical innovative advanced gas cooled fast reactors (GFR) and transmutation systems. The L-STAR (Luft – STab, Abstandshalter, und Rauigkeiten, Air – rod, spacer grid, and roughness) facility has been designed and built at the Karlsruhe Institute of Technology (KIT) to study turbulent flow behavior and its heat transfer enhancement characteristics in gas cooled annular channels under a wide range of conditions. The test section consists of an annular hexagonal cross section channel with an inner electrical heater rod element, placed concentrically within the test section, to model the flow area of a fuel rod element in a fast gas cooled reactor. Tests are being performed in a closed gas loop at various Reynolds numbers with uniform heat release conditions for the further development and validation of different physical models. In this paper, steady state experimental results for a smooth and roughened heater rod are presented. The pressure drops, as well as axial temperature profiles along the heater rod surface have been measured at Reynolds numbers in the range from 4x103 to 3.5x104. The experimental results were compared with empirical correlations. (author)
Coward, Adrian V.; Papageorgiou, Demetrios T.; Smyrlis, Yiorgos S.
1994-01-01
In this paper the nonlinear stability of two-phase core-annular flow in a pipe is examined when the acting pressure gradient is modulated by time harmonic oscillations and viscosity stratification and interfacial tension is present. An exact solution of the Navier-Stokes equations is used as the background state to develop an asymptotic theory valid for thin annular layers, which leads to a novel nonlinear evolution describing the spatio-temporal evolution of the interface. The evolution equation is an extension of the equation found for constant pressure gradients and generalizes the Kuramoto-Sivashinsky equation with dispersive effects found by Papageorgiou, Maldarelli & Rumschitzki, Phys. Fluids A 2(3), 1990, pp. 340-352, to a similar system with time periodic coefficients. The distinct regimes of slow and moderate flow are considered and the corresponding evolution is derived. Certain solutions are described analytically in the neighborhood of the first bifurcation point by use of multiple scales asymptotics. Extensive numerical experiments, using dynamical systems ideas, are carried out in order to evaluate the effect of the oscillatory pressure gradient on the solutions in the presence of a constant pressure gradient.
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Torres-Diaz, I.; Cortes, A.; Rinaldi, C., E-mail: carlos.rinaldi@bme.ufl.edu [Department of Chemical Engineering, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9000 (United States); Cedeño-Mattei, Y. [Department of Chemistry, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9019 (United States); Perales-Perez, O. [Department of Engineering Science and Materials, University of Puerto Rico, Mayagüez, Puerto Rico 00681-9044 (United States)
2014-01-15
Ferrofluid flow in cylindrical and annular geometries under the influence of a uniform rotating magnetic field was studied experimentally using aqueous ferrofluids consisting of low concentrations (<0.01 v/v) of cobalt ferrite nanoparticles with Brownian relaxation to test the ferrohydrodynamic equations, elucidate the existence of couple stresses, and determine the value of the spin viscosity in these fluids. An ultrasound technique was used to measure bulk velocity profiles in the spin-up (cylindrical) and annular geometries, varying the intensity and frequency of the rotating magnetic field generated by a two pole stator winding. Additionally, torque measurements in the cylindrical geometry were made. Results show rigid-body like velocity profiles in the bulk, and no dependence on the axial direction. Experimental velocity profiles were in quantitative agreement with the predictions of the spin diffusion theory, with a value of the spin viscosity of ∼10{sup −8} kg m/s, two orders of magnitude larger than the value estimated earlier for iron oxide based ferrofluids, and 12 orders of magnitude larger than estimated using dimensional arguments valid in the infinite dilution limit. These results provide further evidence of the existence of couple stresses in ferrofluids and their role in driving the spin-up flow phenomenon.
Surface gravity waves in deep fluid at vertical shear flows
Gogoberidze, G.; Samushia, L.; Chagelishvili, G. D.; Lominadze, J. G.; Horton, W
2005-01-01
Special features of surface gravity waves in deep fluid flow with constant vertical shear of velocity is studied. It is found that the mean flow velocity shear leads to non-trivial modification of surface gravity wave modes dispersive characteristics. Moreover, the shear induces generation of surface gravity waves by internal vortex mode perturbations. The performed analytical and numerical study provides, that surface gravity waves are effectively generated by the internal perturbations at h...
Which Hydraulic Model To Use In Vertical Flow Constructed Wetlands?
Morvannou, A.; Forquet, N.; M. Vanclooster; Molle, P.
2012-01-01
International audience Modeling water flow in a VFCW is a prerequisite to model wastewater treatment using process based filtering models. As for soils, when the vertical structure varies in different material types, it has a significant impact on water flow passing through it. The heterogeneous filtering material is composed of a mix of mineral porous material, and organic matter which makes its hydraulic characterization a difficult task. Indeed, the porosity may serve as preferential fl...
viscosity and density stratification in vertical Poiseuille flow
Renardy, Y
1987-01-01
The linear stability of plane three_layer vertical Poiseuille flow is considered. The layers are composed of two immiscible fluids, one next to the walls and one centrally located. The fluids have different viscosities and densities and surface tension effects are included. Intuitively, an analogy with the concentric Hagen-Poiseuille flow is expected and the similarities and differences are investigated. The ability of heuristic reasoning to predict which arrangements are more likely to be ob...
International Nuclear Information System (INIS)
Highlights: ► Two-phase natural circulation flow induced in insulation gap was investigated. ► Half-scaled non-heating experiments were performed to evaluate flow behavior. ► The loop-integrated momentum equation was formulated and solved asymptotically. ► First-order approximate solution was obtained and agreed with experimental data. - Abstract: The process of two-phase natural circulation flow induced in the annular gap between the reactor vessel and the insulation under external reactor vessel cooling conditions was investigated experimentally and analytically in this study. HERMES-HALF experiments were performed to observe and quantify the induced two-phase natural circulation flow in the annular gap. A half-scaled non-heating experimental facility was designed by utilizing the results of a scaling analysis to simulate the APR1400 reactor and its insulation system. The behavior of the boiling-induced two-phase natural circulation flow in the annular gap was observed, and the liquid mass flow rates driven by the natural circulation loop and the void fraction distribution were measured. Direct flow visualization revealed that choking would occur under certain flow conditions in the minimum gap region near the shear keys. Specifically, large recirculation flows were observed in the minimum gap region for large air injection rates and small outlet areas. Under such conditions, the injected air could not pass through the minimum gap region, resulting in the occurrence of choking near the minimum gap with a periodical air back flow being generated. Therefore, a design modification of the minimum gap region needs to be done to facilitate steam venting and to prevent choking from occurring. To complement the HERMES-HALF experimental effort, an analytical study of the dependence of the induced natural circulation mass flow rate on the inlet area and the volumetric air injection rate was performed using a loop integration of the momentum equation. The loop
Vertical Flow Lithography for Fabrication of 3D Anisotropic Particles.
Habasaki, Shohei; Lee, Won Chul; Yoshida, Shotaro; Takeuchi, Shoji
2015-12-22
A microfluidics-based method for the 3D fabrication of anisotropic particles is reported. The method uses a vertical microchannel where tunable light patterns solidify photocurable resins for stacking multiple layers of the resins, thus enabling an application of stereolithography concepts to conventional flow lithography. Multilayered, tapered, and angular compartmental microparticles are demonstrated. PMID:26551590
Hot-film anemometer measurements in adiabatic two-phase flow through a vertical duct
International Nuclear Information System (INIS)
A hot-film anemometer (HFA) probe was used to obtain local measurements of void fraction and bubble frequency in a vertically oriented, high aspect ratio duct containing R-134a under selected adiabatic two-phase flow conditions. Data were obtained along a narrow dimension scan over the range 0.03 ≤ bar Z ≤ 0.80, where bar Z is the distance from the wall normalized with the duct spacing dimension. The void fraction profiles displayed large gradients in the near-wall regions and broad maxima near the duct centerline. The trends in the bubble frequency data generally follow those for the local void fraction data. However, the relatively large number of bubbles at higher pressure implies a larger magnitude of the interfacial area concentration, for the same cross-sectional average void fraction. For the two annular flow conditions tested, analysis of the HFA output voltage signal enabled identification of three distinct regions of the flow field; liquid film with dispersed bubbles, interfacial waves, and continuous vapor with dispersed droplets
Energy Technology Data Exchange (ETDEWEB)
Shin, Chang-Hwan, E-mail: shinch@kaeri.re.kr; Park, Ju-Yong, E-mail: juyong@kaeri.re.kr; In, Wang-Kee, E-mail: wkin@kaeri.re.kr
2013-12-15
Highlights: • A lower end plug with side flow holes is suggested to provide alternative flow paths of the inner channel. • The inlet loss coefficient of the lower end plug is estimated from the experiment. • The flow rate through the side holes is estimated in a complete entrance blockage of inner channel. • The consequence in the reactor core condition is evaluated with a subchannel analysis code. - Abstract: Dual-cooled annular nuclear fuel for a pressurized water reactor (PWR) has been introduced for a significant increase in reactor power. KAERI has been developing a dual-cooled annular fuel for a power uprate of 20% in an optimized PWR in Korea, the OPR1000. This annular fuel can help decrease the fuel temperature substantially relative to conventional cylindrical fuel at a power uprate. Annular fuel has dual flow channels around itself; however, the inner flow channel has a weakness in that it is isolated unlike the outer flow channel, which is open to other neighbouring outer channels for a coolant exchange in the reactor core. If the entrance of the inner channel is, as a hypothetical event, completely blocked by debris, the inner channel will then experience a rapid increase in coolant temperature such that a departure from nucleate boiling (DNB) may occur. Therefore, a remedy to avoid such a postulated accident is indispensable for the safety of annular fuel. A lower end plug with side flow holes was suggested to provide alternative flow paths in addition to the central entrance of the inner channel. In this paper, the inlet loss coefficient of the lower end plug and the flow rate through the side holes were estimated from the experimental results even in a complete entrance blockage of the inner channel. An optimization for the side hole was also performed, and the results are applied to a subchannel analysis to evaluate the consequence in the reactor core condition.
International Nuclear Information System (INIS)
Highlights: • Mass transfer in back to back elbows in an out of plane configuration was measured. • Tests were performed under annular two phase air–water conditions. • Highest mass transfer was on the outer wall of the first elbow. • The mass transfer on the second elbow was always less than that in the first elbow. • The mass transfer increased with an increase in the air superficial velocity. - Abstract: The mass transfer in back-to-back elbows arranged in an out of plane configuration has been measured under annular two phase air–water flow conditions. The measurements were performed using a wall dissolving technique with the elbow sections cast from gypsum. Experiments were performed to study the effect of increasing the water and air superficial velocities, and the effect of separation distance between the elbows. The highest mass transfer for all cases occurs on the outer wall of the first elbow, and the magnitude was not affected by the separation distance between the elbows. The maximum mass transfer in the second elbow was approximately 60 percent of the maximum value in the first elbow. The mass transfer increased with an increase in either the water or air superficial velocity, with the air velocity having a greater effect. The roughness development in the upstream pipe was modest, but was significant in the regions of high mass transfer on the first and second elbow
An Experimental Study on 3—D Flow in an Annular Cascade of High Turning Angle Turbine Blades
Institute of Scientific and Technical Information of China (English)
WangWensheng; LiangXizhi; 等
1994-01-01
This paper presents an experimental study of the three-dimensional turbulent flow fields in a lowspeed annular cascade of high turning angle turbine blades.Detailed measurements were performed on the blade surfaces and mid-streamsurface in the passage and at three axial planes downstream of the cascade by using wall static pressure taps,a five-hole probe and a hot-wire anemometer,The test data include static pressure distribution on blade surfaces,total pressure loss cofeeicient,mean flow velocity components.radial flow angle,turbulence intensity and Reynolds shear stress.Analyses of the three-dimensional cascade flow characteristics were made on the noset location of high loss vortices.the variation of pressure gradient inside the cascade passage and the properties of endwall boundary layers total pressure loss distributions,secondary vortex turbulent dissipation and wake decay downtream of the cascade.These experimental results are valuable for revealing the details of the complex vortex flow structure in modern highly loaded axial turbomachines and validating the three-dimensional flow numerical computation codes.
International Nuclear Information System (INIS)
Several methods to predict the dynamic behavior of a rod subjected to annular flow have been developed. These include the linearized potential flow theory based model by Mateescu, Paidoussis and Sim, and the pressure-loss model by Hobson and Langthjem. Recently, Kang, Mureithi and Pettigrew proposed a theory based on the pressure-loss model with consideration of flow friction. They showed the critical flow velocity of a simply-supported cylinder could go down to a dimensionless velocity of 2.4. The basic dynamics due to annular flow are known by virtue of these models. For heat exchanger tubes, the support causes highly confined annular flow with a divergent or convergent flow at the exit or the entrance of the support, which is due to chamfering of the support hole for manufacturing convenience. Gorman, Goden, and Planchard qualitatively reported that a finite-length diffuser caused a thimble tube in a pressurized water reactor to reach dynamic instability. Yasuo and Paidoussis tried to solve the flow induced instability problem of heat exchanger tubes subjected to axial flow in a diffuser-shaped, loose intermediate support. They suggested critical flow velocity equations either for divergence or flutter. Application of this theory to practical problems is, however, limited because of the inaccurate prediction of the critical flow velocity for flutter. The purpose of this study is to obtain experimentally the critical flow velocity of a cylinder subjected to annular flow in a finite-length narrow-gap support at the middle of the cylinder and to identify instability
Flow regimes and heat transfer in vertical narrow annuli
Energy Technology Data Exchange (ETDEWEB)
Ulke, A.; Goldberg, I.
1993-11-01
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.
Flow regimes and heat transfer in vertical narrow annuli
International Nuclear Information System (INIS)
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
Critical heat-flux experiments under low-flow conditions in a vertical annulus
International Nuclear Information System (INIS)
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
Ageostrophic instability in rotating, stratified interior vertical shear flows
Wang, Peng; Mcwilliams, James C.; Menesguen, Claire
2014-01-01
The linear instability of several rotating, stably stratified, interior vertical shear flows (U) over bar (z) is calculated in Boussinesq equations. Two types of baroclinic, ageostrophic instability, AI1 and AI2, are found in odd-symmetric (U) over bar (z) for intermediate Rossby number (R-0). AI1 has zero frequency; it appears in a continuous transformation of the unstable mode properties between classic baroclinic instability (BCI) and centrifugal instability (CI). It begins to occur at int...
Two-Fluid Mixed Magnetoconvection Flow in a Vertical Enclosure
. Prof. J. Prathap Kumar; J.C. Umavathi; B.M Biradar
2012-01-01
The problem of steady, laminar flow and heat transfer of an electrically conducting fluid through vertical channel in the presence of uniform transverse magnetic field is formulated using a two-fluid continuum model. Combined free and forced convection inside the channel is considered. The effects of viscous and ohmic dissipations are included in the energy equation. Both walls are kept either at the same or different temperatures such as isoflux-isothermal and isothermal-isoflux conditions. ...
Two-phase slug flow in vertical and inclined tubes
Institute of Scientific and Technical Information of China (English)
无
1996-01-01
Gas-liquid slug flow is investigated experimentally in vertical and inclined tubes.The non-invasive measuremnts of the gas-liquid slug flow are taken by using the EKTAPRO 1000 High Speed Motion Analyzer.The information on the velocity of the Talyor bubble,the size distribution of the dispersed bubbles in the liquid slugs and some characteristics of the liquid film around the Taylor bubble are obtained.The experimental results are in good agreement with the available data.
Patterns of convective flow in a vertically vibrated granular bed
International Nuclear Information System (INIS)
When submitted to vertical vibrations for frequencies from 15 to 150 Hz, granular materials show several convective patterns, as symmetric, asymmetric, one single, one pair and multi-pairs of convection rolls. The vibration frequency (f) plays a significant role in the number of rolls and their flow directions, while the vibration acceleration (Γ) mainly affects the size of roll and strength of flow. The Γ–f phase diagram is presented and divided into the global, local, unstable and non-convection regions. Slope of the granular surface decreases with increase of Γ, and the grains at different positions collide with the bottom un-synchronously.
Numerical investigation of mist flow regime in a vertical tube
International Nuclear Information System (INIS)
In this research, the mist flow regime, consisting dispersed water droplets in vapor flow, is simulated numerically in a vertical tube; using a discrete phase model (DPM). In this method, in addition to solving transport equations for continuous phase, a discrete phase is simulated in a Lagrangian approach and the coupling between phases is modeled through interaction terms in the transport equations. The aims of this research are to investigate thermal equilibrium and evaluate the heat transfer coefficient of mist flow regime. The results show, when thermodynamic non-equilibrium takes happen, the rate of heat transfer from the vapor to the droplets is too slow that their presence is ignored, therefore by increasing the water mass flow rate in this case, due to reduction of vapor mass flow rate, the heat transfer coefficient decreases. But when complete thermodynamic equilibrium condition is established, the rate of heat transfer from the vapor to the droplets is too fast that the vapor temperature remains at the saturation temperature until all the droplets have been evaporated and by increasing the water mass flow rate, the heat transfer coefficient will increase. In order to simulate mist flow regime in thermal equilibrium and non-equilibrium conditions, water droplets with two different diameters are injected into steam flow. The numerical results of heat transfer coefficient and wall temperature in four different vapor qualities are investigated in each state, which show good agreement with experimental data and correlations. (authors)
Oscillating annular liquid membranes
International Nuclear Information System (INIS)
The response of annular liquid membranes (e.g. used as protection systems in laser fusion reactors) to sinusoidal mass flow rate fluctuations at the nozzle exit is analyzed as a function of the amplitude and frequency of the axial velocity fluctuations at the nozzle exit and thermodynamic compression of the gas enclosed by the membrane. The pressure of the gases enclosed by the annular membrane and the axial distance at which the annular membrane merges on the symmetry axis are periodic functions of time which have the same period as that of the mass flow rate fluctuations at the nozzle exit. They are also nearly sinusoidal functions of time for small amplitudes of the mass flow rate fluctuations at the nozzle exit, and exhibit delay and lag times with respect to the sinusoidal axial velocity fluctuations at the nozzle exit. The delay and the lag times are functions of the amplitude and frequency of the mass flow rate fluctuations at the nozzle exit and the polytropic exponent. The amplitudes of both the pressure of the gases enclosed by the annular liquid membrane and the convergence length increase and decrease, resp., as the amplitude and frequency of the mass flow rate fluctuations at the nozzle exit, resp., are increased. They also increase as the polytropic exponent is increased. (orig.)
De Biase, C.
2012-01-01
Vertical flow filters (unplanted) and vertical flow constructed wetlands (planted), simple and inexpensive technologies to treat effectively volatile organic compounds (VOCs) contaminated water, consist of containers filled with granular material which is intermittently fed with contaminated water.
Sun, Xue-Wei; Peng, Jie; Zhu, Ke-Qin
2012-02-01
The long wave stability of core-annular flow of power-law fluids with an axial pressure gradient is investigated at low Reynolds number. The interface between the two fluids is populated with an insoluble surfactant. The analytic solution for the growth rate of perturbation is obtained with long wave approximation. We are mainly concerned with the effects of shear-thinning/thickening property and interfacial surfactant on the flow stability. The results show that the influence of shear-thinning/thickening property accounts to the change of the capillary number. For a clean interface, the shear-thinning property enhances the capillary instability when the interface is close to the pipe wall. The converse is true when the interface is close to the pipe centerline. For shear-thickening fluids, the situation is reversed. When the interface is close to the pipe centerline, the capillary instability can be restrained due to the influence of surfactant. A parameter set can be found under which the flow is linearly stable.
International Nuclear Information System (INIS)
This study reports the stability of annular leakage-flow-induced vibrations. The pressure distribution of fluid between a fixed outer cylinder and a vibrating inner cylinder was obtained in the case of a translationally and rotationally coupled motion of the inner cylinder. The unsteady fluid force acting on the inner cylinder in the case of translational and rotational single-degree-of-freedom vibrations was then expressed in terms proportional to the acceleration, velocity, and displacement. Then the critical flow rate (at which stability was lost) was determined for an annular leakage-flow-induced vibration. Finally, the stability was investigated theoretically. It is known that instability will occur in the case of a divergent passage, but the critical flow rate depends on the passage increment in a limited range: the eccentricity of the passage and the pressure loss factor at the inlet of the passage lower the stability. (author)
Flow and cooling in narrow, vertical rectangular channels
International Nuclear Information System (INIS)
Laminar flows and energy transfers in narrow, vertical rectangular channels has gained considerable attention in recent years. the cooling channels of TR-2 reactor of CNAEM research center are same and the width of channels is 2.1 mm. Natural convention cooling in these channels, in case of a loss of forced circulation cooling, as would happen in a accident, has utmost importance. A simple open loop experiment was set up in Nuclear Engineering Dep. for the simulation of TR-2 channels. The dummy fuel plates defining cooling channels were heated electrically and temperature measurements were made by thin wire thermocouples. The fluid used at the moment is air. Constant heat flux case was studied only. For the comparison purposes, simplified forms of Navie-Stokes equations for free convention cooling and incompressible flows were solved also on a variable mesh grid by relaxation technique. Flow and temperature distributions inside the channel nad some integral parameters, such as Nu number, were obtained
Flow Structure Around the Intake of a Vertical Pump
Institute of Scientific and Technical Information of China (English)
Akihiro WADA
2006-01-01
The flow structure around the intake of a vertical pump is investigated experimentally and numerically in order to obtain a guideline in designing the optimum shape of the intake of vertical pumps, in which their installation area is demanded to be minimum without losing the high performance. We concentrate our attention on the expansion ratio of the intake as a representative characteristic of the shape of the pumps and investigate the effect of the expansion ratio on pump performance. It is concluded that the optimum expansion ratio ranges in 1.1～1.2 if we take into consideration that the area needed for the installation of the pump should be minimum.
Zhang, P.; Fu, X.
2009-10-01
Application of liquid nitrogen to cooling is widely employed in many fields, such as cooling of the high temperature superconducting devices, cryosurgery and so on, in which liquid nitrogen is generally forced to flow inside very small passages to maintain good thermal performance and stability. In order to have a full understanding of the flow and heat transfer characteristics of liquid nitrogen in micro-tube, high-speed digital photography was employed to acquire the typical two-phase flow patterns of liquid nitrogen in vertically upward micro-tubes of 0.531 and 1.042 mm inner diameters. It was found from the experimental results that the flow patterns were mainly bubbly flow, slug flow, churn flow and annular flow. And the confined bubble flow, mist flow, bubble condensation and flow oscillation were also observed. These flow patterns were characterized in different types of flow regime maps. The surface tension force and the size of the diameter were revealed to be the major factors affecting the flow pattern transitions. It was found that the transition boundaries of the slug/churn flow and churn/annular flow of the present experiment shifted to lower superficial vapor velocity; while the transition boundary of the bubbly/slug flow shifted to higher superficial vapor velocity compared to the results of the room-temperature fluids in the tubes with the similar hydraulic diameters. The corresponding transition boundaries moved to lower superficial velocity when reducing the inner diameter of the micro-tubes. Time-averaged void fraction and heat transfer characteristics for individual flow patterns were presented and special attention was paid to the effect of the diameter on the variation of void fraction.
ASSERT and COBRA predictions of flow distribution in vertical bundles
International Nuclear Information System (INIS)
COBRA and ASSERT are subchannel codes which compute flow and enthalpy distributions in rod bundles. COBRA is a well known code, ASSERT is under development at CRNL. This paper gives a comparison of the two codes with boiling experiments in vertical seven rod bundles. ASSERT predictions of the void distribution are shown to be in good agreement with reported experimental results, while COBRA predictions are unsatisfactory. The mixing models in both COBRA and ASSERT are briefly discussed. The reasons for the failure of COBRA-IV and the success of ASSERT in simulating the experiments are highlighted
International Nuclear Information System (INIS)
This paper focuses on the optimal design of a compact and high damping force engine mount featuring magnetorheological fluid (MRF). In the mount, a MR valve structure with both annular and radial flows is employed to generate a high damping force. First, the configuration and working principle of the proposed MR mount is introduced. The MRF flows in the mount are then analyzed and the governing equations of the MR mount are derived based on the Bingham plastic behavior of the MRF. An optimal design of the MR mount is then performed to find the optimal structure of the MR valve to generate a maximum damping force with certain design constraints. In addition, the gap size of MRF ducts is empirically chosen considering the ‘lockup’ problem of the mount at high frequency. Performance of the optimized MR mount is then evaluated based on finite element analysis and discussions on performance results of the optimized MR mount are given. The effectiveness of the proposed MR engine mount is demonstrated via computer simulation by presenting damping force and power consumption. (paper)
Institute of Scientific and Technical Information of China (English)
胡志华; 杨燕华; 刘磊; 周芳德
2006-01-01
The upward multiphase cross flow and heat transfer in the vertical tube may occur in oil production and chemical facilities. In this study, the local flow patterns of an upward gas-water two phase cross flow in a vertical tube with a horizontal rod have been investigated with an optical probe and the digital high speed video system. The local flow patterns are defined as the bubble, slug, churn and annular flow patterns. Optical probe signals are analyzed in terms of probability density function, and it is proved that the local flow patterns can be recognized by this method. The transition mechanisms between the different flow patterns have been analyzed and the corresponding transitional models are proposed. Finally, local flow pattern maps of the upward gas-water two-phase flow in the vertical tube with a horizontal rod are constructed.
Energy Technology Data Exchange (ETDEWEB)
Maki, H.; Ogawa, N. (Science University of Tokyo, Tokyo (Japan). Faculty of Engineering); Hisamatsu, S. (Science University of Tokyo, Tokyo (Japan))
1992-10-25
In order to research an angled annular impinging jet, angled annular nozzles with various spreading angles were experimentally fabricated and the research was carried out by focusing the first critical distance. The distance from the downstream end of annular nozzle inner tube to the impinged flat plate is defined as the first critical distance. The flow field characteristic of angled annular impinging jet is the existence of critical angle. This flow field can be classified into 4 kinds by combining the distance H between the annular nozzle and the impinged flat plate with the critical angle [theta][sub c]. That is, when the spreading angle is expressed by [theta] and the first critical distance as Hcl and when [theta]< [theta][sub c], there are 2 kinds, that is, H [gt or lt] H[sub cl]; and when [theta]>[theta][sub c], and H for which Coanda effect to the impinged flat plate is strong, is newly defined as the critical distance Lc, there are other 2 kinds, that is, H [gt or lt] Lc. In the case of [theta]< [theta][sub c], Hcl by which recirculating flow is formed exists surely. On the other hand, in the case of [theta]> [theta][sub c], the recirculating flow can be formed in some cases or cannot be formed in other cases depending on the existence of the Coanda effect. 6 refs., 10 figs., 1 tab.
Modeling of subcooled boiling in the vertical flow
International Nuclear Information System (INIS)
A two-dimensional model of subcooled boiling in a vertical channel was developed. Its basic idea is that the vapor phase generation has a similar effect on the flow field as a hypothetical liquid phase generation. The bubble volume, generated due to evaporation process, was filled with liquid and included as a source term in the continuity equation for the liquid phase. Thus, the single-phase from of transport equations was preserved and bubbles were retained in the boundary layer near the heated surface. Time development of subcooled boiling was simulated and effects of governing physical mechanisms (evaporation, condensation, vapor-phase convection, vapor-phase diffusion) on the flow field and pressure drop were analyzed. The Results of the proposed two-dimensional model were compared with experimental data and RELAP5/MOD3.2 calculations. The presented model represents a contribution to the two-dimensional simulation of the subcooled boiling phenomenon.(author)
Characterisation of microbial biocoenosis in vertical subsurface flow constructed wetlands
International Nuclear Information System (INIS)
In this study a quantitative description of the microbial biocoenosis in subsurface vertical flow constructed wetlands fed with municipal wastewater was carried out. Three different methods (substrate induced respiration, ATP measurement and fumigation-extraction) were applied to measure the microbial biomass at different depths of planted and unplanted systems. Additionally, bacterial biomass was determined by epifluorescence microscopy and productivity was measured via 14C leucine incorporation into bacterial biomass. All methods showed that > 50% of microbial biomass and bacterial activity could be found in the first cm and about 95% in the first 10 cm of the filter layer. Bacterial biomass in the first 10 cm of the filter body accounted only for 16-19% of the total microbial biomass. Whether fungi or methodical uncertainties are mainly responsible for the difference between microbial and bacterial biomass remains to be examined. A comparison between the purification performance of planted and unplanted pilot-scale subsurface vertical flow constructed wetlands (PSCWs) showed no significant difference with the exception of the reduction of enterococci. The microbial biomass in all depths of the filter body was also not different in planted and unplanted systems. Compared with data from soils the microbial biomass in the PSCWs was high, although the specific surface area of the used sandy filter material available for biofilm growth was lower, especially in the beginning of the set-up of the PSCWs, due to missing clay and silt fraction
Directory of Open Access Journals (Sweden)
Nili-Ahmadabadi M.
2012-01-01
Full Text Available This paper will present the results of the experimental investigation of heat transfer in a non-annular channel between rotor and stator similar to a real generator. Numerous experiments and numerical studies have examined flow and heat transfer characteristics of a fluid in an annulus with a rotating inner cylinder. In the current study, turbulent flow region and heat transfer characteristics have been studied in the air gap between the rotor and stator of a generator. The test rig has been built in a way which shows a very good agreement with the geometry of a real generator. The boundary condition supplies a non-homogenous heat flux through the passing air channel. The experimental devices and data acquisition method are carefully described in the paper. Surface-mounted thermocouples are located on the both stator and rotor surfaces and one slip ring transfers the collected temperature from rotor to the instrument display. The rotational speed of rotor is fixed at three under: 300rpm, 900 rpm and 1500 rpm. Based on these speeds and hydraulic diameter of the air gap, the Reynolds number has been considered in the range: 4000
Estimation of shear stress in counter-current gas-liquid annular two-phase flow
International Nuclear Information System (INIS)
The accuracy of the correlations of the friction factor is important for the counter-current flow (CCF) analysis with two-fluid model. However, existing two fluid model codes use the correlations of friction factors for co-current flow or correlation developed based on the assumption of no wall shear stress. The assessment calculation for two fluid model code with those existing correlations of friction factors shows the falling water flow rate is overestimated. Analytical model is developed to calculate the shear stress distribution in water film at CCF in order to get the information on the shear stress at the interface and the wall. The analytical results with the analysis model and Bharathan's CCF data shows that the wall shear stress acting on the falling water film is almost same order as the interfacial shear stress and the correlations for co-current flow cannot be applied to the counter-current flow. Tentative correlations of the interfacial and the wall friction factors are developed based on the results of the present study. (author)
Numerical analysis the influence of the rotating cylinder in transitional flow in annular channels
International Nuclear Information System (INIS)
In this paper, numerical experiments were performed to analyze the effects of the rotating cylinder over transitional flow between two horizontal concentric cylinders. The unstable and oscillatory flow was predicted using the large-eddy simulation methodology with dynamic sub-grid scale model. Three-dimensional aspects of transition to turbulence at Rayleigh number Ra =1.7 x 105 and Froude number range of 0.05 ≤ Fr ≤ ∞ was obtained, as well as the effects of the centrifugal force on the heat transfer process was analyzed. (authors)
International Nuclear Information System (INIS)
Highlights: ► The cooling performance of water and n-heptane is compared during subcooled flow boiling. ► Although n-heptane leaves the heat exchanger warmer it has a lower heat transfer coefficient. ► Flow rate, heat flux and degree of subcooling have direct effect on heat transfer coefficient. ► The predictions of some correlations are evaluated against experimental data. - Abstract: In this research, subcooled flow boiling heat transfer coefficients of pure n-heptane and distilled water at different operating conditions have been experimentally measured and compared. The heat exchanger consisted of vertical annulus which is heated from the inner cylindrical heater with variable heat flux (less than 140 kW/m2). Heat flux is varied so that two different flow regimes from single phase forced convection to nucleate boiling condition are created. Meanwhile, liquid flow rate is changed in the range of 2.5 × 10−5–5.8 × 10−5 m3/s to create laminar up to transition flow regimes. Three subcooling levels including 10, 20 and 30 °C are also considered. Experimental results demonstrated that subcooled flow boiling heat transfer coefficient increases when higher heat flux, higher liquid flow rate and greater subcooling level are applied. Furthermore, influence of the operating conditions on the bubbles generation on the heat transfer surface is also discussed. It is also shown that water is better cooling fluid in comparison with n-heptane
Experimental study of flow patterns and pressure drops of heavy oil-water-gas vertical flow
Institute of Scientific and Technical Information of China (English)
LIU Xi-mao; ZHONG Hai-quan; LI Ying-chuan; LIU Zhong-neng; WANG Qi
2014-01-01
A stainless steel apparatus of 18.5 m high and 0.05 m in inner diameter is developed, with the heavy oil from Lukeqin Xinjiang oil field as the test medium, to carry out the orthogonal experiments for the interactions between heavy oil-water and heavy oil-water-gas. With the aid of observation windows, the pressure drop signal can be collected and the general multiple flow patterns of heavy oil-water-gas can be observed, including the bubble, slug, churn and annular ones. Compared with the conventional oil, the bubble flows are identified in three specific flow patterns which are the dispersed bubble (DB), the bubble gas-bubble heavy oil go(B-B), and the bubble gas-intermittent heavy oilgo(B-I). The slug flows are identified in two specific flow patterns which are the intermittent gas-bubble heavy oilgo(I-B)and the intermittent gas-intermittent heavy oilgo(I-I). Compared with the observa- tions in the heavy oil-water experiment, it is found that the conventional models can not accurately predict the pressure gradient. And it is not water but heavy oil and water mixed phase that is in contact with the tube wall. So, based on the principle of the energy con- servation and the kinematic wave theory, a new method is proposed to calculate the frictional pressure gradient. Furthermore, with the new friction gradient calculation method and a due consideration of the flow characteristics of the heavy oil-water-gas high speed flow, a new model is built to predict the heavy oil-water-gas pressure gradient. The predictions are compared with the experiment data and the field data. The accuracy of the predictions shows the rationality and the applicability of the new model.
Oscillatory and Steady Flows in the Annular Fluid Layer inside a Rotating Cylinder
Directory of Open Access Journals (Sweden)
Veronika Dyakova
2016-01-01
Full Text Available The dynamics of a low-viscosity fluid inside a rapidly rotating horizontal cylinder were experimentally studied. In the rotating frame, the force of gravity induces azimuthal fluid oscillations at a frequency equal to the velocity of the cylinder’s rotation. This flow is responsible for a series of phenomena, such as the onset of centrifugal instability in the Stokes layer and the growth of the relief at the interface between the fluid and the granular medium inside the rotating cylinder. The phase inhomogeneity of the oscillatory fluid flow in the viscous boundary layers near the rigid wall and the free surface generates the azimuthal steady streaming. We studied the relative contribution of the viscous boundary layers in the generation of the steady streaming. It is revealed that the velocity of the steady streaming can be calculated using the velocity of the oscillatory fluid motion.
Oscillatory and Steady Flows in the Annular Fluid Layer inside a Rotating Cylinder
Veronika Dyakova; Denis Polezhaev
2016-01-01
The dynamics of a low-viscosity fluid inside a rapidly rotating horizontal cylinder were experimentally studied. In the rotating frame, the force of gravity induces azimuthal fluid oscillations at a frequency equal to the velocity of the cylinder’s rotation. This flow is responsible for a series of phenomena, such as the onset of centrifugal instability in the Stokes layer and the growth of the relief at the interface between the fluid and the granular medium inside the rotating cylinder. The...
An Improved Linear Model for Rotors Subject to Dissipative Annular Flows
Moreira, Miguel; J. Antunes; Pina, H.
2000-01-01
In a previous paper, Antunes, Axisa and co-workers developed a linearized model for the dynamic of rotors under moderate fluid confinement, based on classical perturbation analysis covering two different cases: (i) dissipative motions of a centered rotor; (ii) motions of an eccentric rotor for a frictionless flow. Following the same procedures and assumptions, we derive here an improved model to cover the more general case of a dissipative linearized motion of an eccentric rotor. Besides the ...
Conjugate natural convection flow over a vertical surface with radiation
Siddiqa, Sadia; Hossain, Md. Anwar; Gorla, Rama Subba Reddy
2016-06-01
Numerical study of conjugate natural convection flow over a finite vertical surface with radiation is reported in this article. Rosseland diffusion approximation is used to express the radiative heat flux term. The governing boundary-layer equations are made dimensionless by means of a suitable form of non-similarity transformation. These equations are obtained in three regimes: (1) upstream (when ξ → 0), (2) downstream (when ξ → ∞ ) and (3) entire regime and are solved numerically. The solutions in the upstream and downstream regimes are obtained via shooting method whereas two-point implicit finite difference method is used to get the solutions for the entire regime. It is seen that asymptotic solutions give accurate results when compared with the numerical solution of the entire regime. The results indicate that the flow field and the temperature distributions are greatly influenced by thermal radiation parameter , R_d, surface temperature parameter, θ _w and Prandtl number Pr. It is established from the analysis that recirculation occurs in the flow specifically for R_d=1.5.
Analysis of transition from bubble flow to slug flow in rolling vertical tubes
International Nuclear Information System (INIS)
The mechanism of the transition from bubble flow to slug flow with co-current gas and liquid flowing through vertical tubes under rolling condition is studied. According to the experimental observation, it is found that the dispersed bubble flow pattern is periodically changed with the rolling motion. When the test section is deviated from the vertical condition, bubbles tend to flow at the upper part of the tube, and the bubble density reaches its maximum while test section rolling to the place with maximum incline angle. Besides, through the analysis of forces acted on moving bubbles under rolling condition, it is also found that the radial components of forces keeping dispersed bubbles at the upper part of the tube reach their maximums at maximum incline angle. Therefore, the transition from bubble flow to slug flow is most likely to take place at this moment. Based on the experimental data, a new correlation for predicting the transition from bubble flow to slug flow is proposed. The results show that the model predictions coincide well with the experimental data when gas superficial velocity is larger than 0.4 m/s. (author)
Two-Fluid Mixed Magnetoconvection Flow in a Vertical Enclosure
Directory of Open Access Journals (Sweden)
. Prof. J. Prathap Kumar
2012-01-01
Full Text Available The problem of steady, laminar flow and heat transfer of an electrically conducting fluid through vertical channel in the presence of uniform transverse magnetic field is formulated using a two-fluid continuum model. Combined free and forced convection inside the channel is considered. The effects of viscous and ohmic dissipations are included in the energy equation. Both walls are kept either at the same or different temperatures such as isoflux-isothermal and isothermal-isoflux conditions. Governing equations in cartesian co-ordinates are solved analytically using regular perturbation technique to develop the expression for velocity and temperature. Velocity, temperature and Nusselt number are presented graphically. Effects of pertinent parameters, such as Hartmann number, electric field load parameter, viscosity ratio, width ratio and conductivity ratio are determined.
Flow-blade interaction in a Vertical Axis Wind Turbine
Dominguez, Roberto; Piedra, Saul; Ramos, Eduardo
2014-11-01
We present an analysis of the interaction between an incoming wind and three airfoils symmetrically located, and free to rotate around a common axis. The geometrical configuration considered is a two dimensional model of Vertical Axis Wind Turbine. The model is based in the conservation equations of the fluid coupled with the Newton-Lagrange equations for the interaction with the airfoils. The presence of the rigid body in the fluid is simulated using immersed boundary conditions. The interaction of the wind with the airfoil located further upstream generates a force on the airfoil and vortices that are swept downstream and collide with the other airfoils. This effect generates a complex interplay of dynamical forces whose resultant is a torque that sets the system in motion. We describe the flow around the airfoils and examine the efficiency of the system as a function of geometric variables. Our conclusions are potentially useful for the design of VAWT's.
Burnout specific features in steam-water mixture annular flow in a tube
International Nuclear Information System (INIS)
Some unexplained burnout specific features in a steam-generating tube are analysed on the basis of experimental data. The following problems are considered: 1) the effect of the tube length and the state of the working medium (single-phase, two-phase) on burnout at the tube inlet; 2) the character of the specific thermal flow dependence at the moment of burnout appearance on the mass steam content q=f(x). It is found that the effect of the tube length on the burnout exists only in a relatively narrow range of the operating parameters. The run of the q=f(x) dependence is also explained
Gupta, Diptesh; Hess, Brian; Bachegowda, Lohith
2010-01-01
We present a case of a 77-year-old, diabetic male with a 20-year history of a migratory erythematous, asymptomatic, generalized, nonscaly, and nonitchy rash that started over the dorsum of his left hand. On examination, there were multiple annular erythematous plaques, distributed symmetrically and diffusely over his torso and arms, with central clearing and no scales. A punch biopsy of the skin helped us to arrive at the diagnosis of a generalized granuloma annulare (GA). GA is a benign, self-limiting skin condition of unknown etiology that is often asymptomatic. The cause of this condition is unknown, but it has been associated with diabetes mellitus, infections such as HIV, and malignancies such as lymphoma. These lesions typically start as a ring of flesh-colored papules that slowly progress with central clearing. Lack of symptoms, scaling, or associated vesicles helps to differentiate GA from other skin conditions such as tinea corporis, pityriasis rosea, psoriasis, or erythema annulare centrifugum. Treatment is often not needed as the majority of these lesions are self-resolving within 2 years. Treatment may be pursued for cosmetic reasons. Available options include high-dose steroid creams, PUVA, cryotherapy, or drugs such as niacinamide, infliximab, Dapsone, and topical calcineurin inhibitors. PMID:20209383
Analysis of Forced Convection Heat Transfer for Axial Annular Flow of Giesekus Viscoelastic Fluid
Energy Technology Data Exchange (ETDEWEB)
Mohseni, Mehdi Moayed; Rashidi, Fariborz; Movagar, Mohammad Reza Khorsand [Amirkabir University of Technology, Tehran (Iran, Islamic Republic of)
2015-02-15
Analytical solutions for the forced convection heat transfer of viscoelastic fluids obeying the Giesekus model are obtained in a concentric annulus under laminar flow for both thermal and hydrodynamic fully developed conditions. Boundary conditions are assumed to be (a) constant fluxes at the walls and (b) constant temperature at the walls. Temperature profiles and Nusselt numbers are derived from dimensionless energy equation. Subsequently, effects of elasticity, mobility parameter and viscous dissipation are discussed. Results show that by increasing elasticity, Nusselt number increases. However, this trend is reversed for constant wall temperature when viscous dissipation is weak. By increasing viscous dissipation, the Nusselt number decreases for the constant flux and increases for the constant wall temperature. For the wall cooling case, when the viscous dissipation exceeds a critical value, the generated heat overcomes the heat which is removed at the walls, and fluid heats up longitudinally.
Flow characteristics of gas-liquid-solid three-phase bubbly flow in vertical pipes
International Nuclear Information System (INIS)
The volumetric fractions of each phase in air-water-particle three-phase bubbly flows were measured in vertical pipes of about 10 m in height, and of 20.9, 30.8 and 50.4 mm inside diameter, respectively. The solid particles used in this experiment were three kinds of spherical particles of 1.15, 2.56 and 4.16 mm mean diameter, made of aluminum ceramics with 2270-2400 kg/m3 density. Characteristics of the volumetric fractions of each phase were discussed in this experimental range, especially on the effects of the volumetric flux of each phase, pipe diameter and mean particle diameter. Then, empirical correlations of the volumetric fractions of each phase were proposed. The present empirical correlations would be useful as constitutive equations required to analyze the gas-liquid-solid three-phase bubbly flow in vertical pipes based on the slip flow model. (author)
Directory of Open Access Journals (Sweden)
Mosdorf Romuald
2015-06-01
Full Text Available The two-phase flow (water-air occurring in square minichannel (3x3 mm has been analysed. In the minichannel it has been observed: bubbly flow, flow of confined bubbles, flow of elongated bubbles, slug flow and semi-annular flow. The time series recorded by laser-phototransistor sensor was analysed using the recurrence quantification analysis. The two coefficients:Recurrence rate (RR and Determinism (DET have been used for identification of differences between the dynamics of two-phase flow patterns. The algorithm which has been used normalizes the analysed time series before calculating the recurrence plots.Therefore in analysis the quantitative signal characteristicswas neglected. Despite of the neglect of quantitative signal characteristics the analysis of its dynamics (chart of DET vs. RR allows to identify the two-phase flow patterns. This confirms that this type of analysis can be used to identify the two-phase flow patterns in minichannels.
Wet gas flow modeling for a vertically mounted Venturi meter
International Nuclear Information System (INIS)
Venturi meters are playing an increasingly important role in wet gas metering in natural gas and oil industries. Due to the effect of liquid in a wet gas, the differential pressure over the converging section of a Venturi meter is higher than that when a pure gas flows through with the same flow rate. This phenomenon is referred to as over-reading. Thus, a correction for the over-reading is required. Most of the existing wet gas models are more suitable for higher pressure (>2 MPa) than lower pressure (0.5) than lower quality (<0.5) in recent years. However, conditions of lower pressure and lower quality also widely exist in the gas and oil industries. By comparing the performances of eight existing wet gas models in low-pressure range of 0.26–0.86 MPa and low-quality range of 0.07–0.36 with a vertically mounted Venturi meter of diameter ratio 0.45, de Leeuw's model was proven to perform best. Derived from de Leeuw's model, a modified model with better performance for the low-pressure and low-quality ranges was obtained. Experimental data showed that the root mean square of the relative errors of the over-reading was 2.30%. (paper)
Institute of Scientific and Technical Information of China (English)
龙桐; 翟志刚; 司廷; 罗喜胜
2014-01-01
设计并加工了一套竖直环形同轴无膜激波管，可用于环形汇聚激波诱导下的Richtmyer-Meshkov 不稳定性实验研究。与前人工作相比，本文在流体界面的形成以及流场的观测方法上做了较大的改进。通过实验和数值方法，对该竖直激波管产生的环形柱状汇聚激波的参数进行测量和分析，验证了同轴激波管形成柱状汇聚激波方法的可行性和可靠性。在界面形成方面，采用细丝约束肥皂膜技术形成正八边形气体界面，并利用数值方法考察了细丝对界面发展的影响。结果表明在界面发展的前期，细丝的影响几乎可以忽略。利用连续激光片光结合高速摄影相机对流场进行观测，获得了正八边形air／SF6气体界面在环形汇聚激波及其反射激波冲击下的演化过程，并与数值结果进行了对比，获得了较好的一致性，进一步验证了汇聚激波的对称性以及细丝约束肥皂膜技术用于形成多边形气体界面的可靠性。%A vertical annular coaxial diaphragm-less shock tube is designed based on the prin-cipal proposed by Hosseini and Takayama and modified in order to conveniently install the initial interface in the test section and visualize the flow field for the investigation of the Richtmyer-Meshkov (RM)instability.Parametric study is carried out both experimentally and numerically to explore the characteristics of the annular coaxial cylindrical converging shock wave.The varia-tion of pressure behind the shock shows the feasibility and reliability of this shock tube to generate the annular coaxial cylindrical converging shock wave.The pressure variations with time at differ-ent positions in the test section are acquired from the experiment and numerical simulation,and the converging effect of the shock wave is emphasized.After the validation of the converging shock wave,the experiment of RM instability induced by this converging shock wave is con
Kraft, R. E.
1996-01-01
The objective of this effort is to develop an analytical model for the coupling of active noise control (ANC) piston-type actuators that are mounted flush to the inner and outer walls of an annular duct to the modes in the duct generated by the actuator motion. The analysis will be used to couple the ANC actuators to the modal analysis propagation computer program for the annular duct, to predict the effects of active suppression of fan-generated engine noise sources. This combined program will then be available to assist in the design or evaluation of ANC systems in fan engine annular exhaust ducts. An analysis has been developed to predict the modes generated in an annular duct due to the coupling of flush-mounted ring actuators on the inner and outer walls of the duct. The analysis has been combined with a previous analysis for the coupling of modes to a cylindrical duct in a FORTRAN computer program to perform the computations. The method includes the effects of uniform mean flow in the duct. The program can be used for design or evaluation purposes for active noise control hardware for turbofan engines. Predictions for some sample cases modeled after the geometry of the NASA Lewis ANC Fan indicate very efficient coupling in both the inlet and exhaust ducts for the m = 6 spinning mode at frequencies where only a single radial mode is cut-on. Radial mode content in higher order cut-off modes at the source plane and the required actuator displacement amplitude to achieve 110 dB SPL levels in the desired mode were predicted. Equivalent cases with and without flow were examined for the cylindrical and annular geometry, and little difference was found for a duct flow Mach number of 0.1. The actuator ring coupling program will be adapted as a subroutine to the cylindrical duct modal analysis and the exhaust duct modal analysis. This will allow the fan source to be defined in terms of characteristic modes at the fan source plane and predict the propagation to the
Bacterial carbon utilization in vertical subsurface flow constructed wetlands.
Tietz, Alexandra; Langergraber, Günter; Watzinger, Andrea; Haberl, Raimund; Kirschner, Alexander K T
2008-03-01
Subsurface vertical flow constructed wetlands with intermittent loading are considered as state of the art and can comply with stringent effluent requirements. It is usually assumed that microbial activity in the filter body of constructed wetlands, responsible for the removal of carbon and nitrogen, relies mainly on bacterially mediated transformations. However, little quantitative information is available on the distribution of bacterial biomass and production in the "black-box" constructed wetland. The spatial distribution of bacterial carbon utilization, based on bacterial (14)C-leucine incorporation measurements, was investigated for the filter body of planted and unplanted indoor pilot-scale constructed wetlands, as well as for a planted outdoor constructed wetland. A simple mass-balance approach was applied to explain the bacterially catalysed organic matter degradation in this system by comparing estimated bacterial carbon utilization rates with simultaneously measured carbon reduction values. The pilot-scale constructed wetlands proved to be a suitable model system for investigating microbial carbon utilization in constructed wetlands. Under an ideal operating mode, the bulk of bacterial productivity occurred within the first 10cm of the filter body. Plants seemed to have no significant influence on productivity and biomass of bacteria, as well as on wastewater total organic carbon removal. PMID:17991505
International Nuclear Information System (INIS)
Highlights: → Annular flows w/wo functional spacers are investigated by cold neutron imaging. → Liquid film thickness distribution on fuel pins and on spacer vanes is measured. → The influence of the spacers on the liquid film distributions has been quantified. → The cross-sectional averaged liquid hold-up significantly affected by the spacers. → The sapers affect the fraction of the entrained liquid hold up in the gas core. - Abstract: Dryout of the coolant liquid film at the upper part of the fuel pins of a boiling water reactor (BWR) core constitutes the type of heat transfer crisis relevant for the conditions of high void fractions. It is both a safety concern and a limiting factor in the thermal power and thus for the economy of BWRs. We have investigated adiabatic, air-water annular flows in a scaled-up model of two neighboring subchannels as found in BWR fuel assemblies using cold-neutron tomography. The imaging of the double suchannel has been performed at the ICON beamline at the neutron spallation source SINQ at the Paul Scherrer Institute, Switzerland. Cold-neutron tomography is shown here to be an excellent tool for investigating air-water annular flows and the influence of functional spacers of different geometries on such flows. The high-resolution, high-contrast measurements provide the spatial distributions of the coolant liquid film thickness on the fuel pin surfaces as well as on the surfaces of the spacer vanes. The axial variations of the cross-section averaged liquid hold-up and its fraction in the gas core shows the effect of the spacers on the redistribution of the two phases.
International Nuclear Information System (INIS)
As the study of two-phase flows is required to assess or optimize the performance of many industrial systems in chemical, thermal or nuclear engineering, this research thesis in fluid mechanics aims at describing the evolution of a two-phase flow in a dispersed annular configuration when passing a convergent nozzle. The study focused on the elaboration of simple, one-dimensional and permanent flows, and is based on experiments performed in the case of a liquid annular injection. The author discusses the mapping of two-phase flows, proposes an overview of their modelling, and proposes a model with its instantaneous local equations and time- and space-averaged equations. He addresses the issues of closure laws for two-field models (friction laws on the walls and at the interfaces, discussion of published experimental results), and of mass transfer laws for three-field models. He reports the development of a droplet carryover rate law and the analysis of published experiments by using the three-field model
Compartment in vertical flow reactor for ferruginous mine water
Hur, Won; Cheong, Young-Wook; Yim, Gil-Jae; Ji, Sang-Woo; Hong, Ji-Hye
2014-05-01
Mine effluents contain varying concentrations of ferrous ion along with other metal ions. Fe(II) that quickly oxidizes to form precipitates in the presence of oxygen under net alkaline or neutral conditions. Thus, passive treatment methods are designed for the mine water to reside in an open containment area so as to allow simultaneous oxidation and precipitation of Fe(II), such as in a lagoon or an oxidation pond. A vertical flow reactor (VFR) was also suggested to remediate ferruginous mine drainage passing down through an accreting bed of ochre. However, VFR has a limited operation time until the system begins to overflow. It was also demonstrated that two-compartment VFR has a longer operation time than single compartment VFR of same size. In this study, a mathematical model was developed as a part of efforts to explore the operation of VFR, showing dynamic changes in head differences, ochre depth and Fe(II)/Fe(III) concentration in the effluent flow. The analysis shows that Fe(II) oxidation and ochre formation should be balanced with permeability of ochre bed to maximize VFR operation time and minimize residual Fe(II) in the effluent. The model demonstrates that two compartment VFR can have a longer operation time than a single-compartment VFR and that an optimum compartment ratio exists that maximize VFR operation time. Accelerated Fe(II) oxidation significantly affects the optimum ratio of compartment area and reduced residual Fe(II) in the effluent. VFR operation time can be significantly prolonged by increasing the rate of ochre formation not by accelerated Fe(II) oxidation. Taken together, ochre forms largely in the first compartment while overflowed mine water with reduced iron contents is efficiently filtered in the second compartment. These results provide us a better understanding of VFR operation and optimum design criteria for maximum operation time in a two-compartment VFR. Rapid ochre accretion in the first compartment maintains constant hydraulic
Lu, N.; Ge, S.
1996-01-01
By including the constant flow of heat and fluid in the horizontal direction, we develop an analytical solution for the vertical temperature distribution within the semiconfining layer of a typical aquifer system. The solution is an extension of the previous one-dimensional theory by Bredehoeft and Papadopulos [1965]. It provides a quantitative tool for analyzing the uncertainty of the horizontal heat and fluid flow. The analytical results demonstrate that horizontal flow of heat and fluid, if at values much smaller than those of the vertical, has a negligible effect on the vertical temperature distribution but becomes significant when it is comparable to the vertical.
Energy Technology Data Exchange (ETDEWEB)
Toma, P. [Society of Petroleum Engineers, London (United Kingdom)]|[P.R. Toma Consulting Ltd., Bern (Germany); Vargas, E. [Alberta Univ., Edmonton, AB (Canada); Kuru, E. [Society of Petroleum Engineers, Canadian Section, Calgary, AB (Canada)]|[Alberta Univ., Edmonton, AB (Canada)
2006-07-01
It is common for gas, liquid hydrocarbons and water to be produced simultaneously through vertical wells in both onshore and offshore petroleum production systems. Water can be removed using artificial lift. In conventional gas lifting from low-pressure gas or coalbed reservoirs, flow instabilities can occur during the upward gas-liquid well transportation due to the slug to annular flow pattern transition (SAT). Conventional gas lifting involves large-diameter tubing. This paper presented the possibility of replacing gas lifting with gas-liquid flow in small-diameter tubes as a unique field production strategy. In particular, it described the effect of tubing diameter on the liquid production rate in gas lifted wells. Experimental and numerical modeling demonstrated the advantages and limitations of using small-diameter tubes for extreme gas lifting conditions. Replacing large-diameter tubing with small-diameter tubing was found to be better for unloading water and resuming production from gas wells with low reservoir pressure. The concept was proven using a specially designed experimental apparatus. 23 refs., 2 tabs., 12 figs., 1 appendix.
Wastewater Treatment Using Vertical Subsurface Flow Constructed Wetland in Indonesia
Directory of Open Access Journals (Sweden)
Denny Kurniadie
2011-01-01
Full Text Available Problem statement: A constructed wetland to treat wastewater from farm house has been built in Padjadjaran University farming research station in Jatinangor, Indonesia, in July 2009. Approach: Water samples from both influent and effluent were taken every two weeks and analysed for COD, BOD5, NO3-N, NO2-N, NH4-N, total-N, PO4-P, total coliform bacteria, pH, O2 and settleable solids. Results: The objective of this study was to install one constructed wetland with a vertical flow system to treat sewage from farm house by using an aquatic macrophyte (Phragmites karka. The average treatment efficiencies during the period from August 2009 to January 2010 for BOD5, COD, NH4-N, total- N, PO4-P and total coliform bacteria were 76,03, 78,89, 88,18, 71,70, 91,06 and 99,45% respectively. The average concentration in effluent from period of August to January for BOD5 was 21.87 mg L-1, COD (57.66 mg L-1, NH4-N (0.82 mg L-1, NO3-N (1,36 mg L-1, total-N (2.68 mg L-1, PO4-P (0.07 mg L-1 and total coliform bacteria (4880 MPN/100 ml. Conclusion/Recommendations: The overall results show that all effluent concentration from constructed wetlands except BOD5 were still low and fall considerably short of Indonesian effluent standards for irrigation water. These results were very promising to be used in treating wastewater from agricultural industry and produce clean water which then can still be used for other purposes such as irrigation water, fisheries and other necessities.
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.
International Nuclear Information System (INIS)
A suspension of glass fibers in alcohol has been used to investigate a upward vertical developing pipe flow. The refractive index of the alcohol was matched to that of the glass fibers, making the whole suspension transparent. Laser Doppler Anemometry (LDA) was applied, and fluid velocities could then be measured for consistencies up to c = 12 g/l. Radial profiles of axial U-velocity and turbulence spectra have been recorded at various positions (z/D = 2, 5, 36) downstream of an orifice (step) with 64% open area. Measurements were taken for different consistencies (c = 1.2, 12 g/l), fiber lengths (l = 1, 3 mm) and Reynolds numbers (Re = 8.5 ⋅ 103, 6.5 ⋅ 104). The fiber crowding factor (nf) has been used to discuss the observed effects of the present fibers on momentum transfer and turbulence structure. The results show both an increase (l= 1 mm, c= 1.2 g/l) and decrease (l=3 mm, c = 12 g/l) in turbulence levels in the presence of fibers. Suspensions with long fibers at the highest consistency show plug flow in parts of the core. This causes damping of the turbulence mainly at smaller length scales. For short fibers at low consistency, the increased turbulent energy was mainly observed at small length scales in the spectrum. (author)
Bistability and hysteresis of annular impinging jets
Tisovsky, Tomas
2016-06-01
In present study, the bistability and hysteresis of annular impinging jets is investigated. Annular impinging jets are simulated using open source CFD code - OpenFOAM. Both flow field patterns of interest are obtained and hysteresis is found by means of dynamic mesh simulation. Effect of nozzle exit velocity on resulting hysteresis loop is also illustrated.
Energy Technology Data Exchange (ETDEWEB)
Augyrond, L
1998-04-01
This work aims at a better understanding of the dynamics of helium two-phase flow in a vertical duct. The case of bubble flow is particularly investigated. The most descriptive parameter of two-phase flow is the void fraction. A sensor to measure this parameter was specially designed and calibrated, it is made of a radioactive source and a semiconductor detector. Sensors based on light attenuation were used to study the behaviour of this two-phase flow. The experimental set-up is described. The different flow types were photographed and video filmed. This visualization has allowed to measure the diameter of bubbles and to study their movements in the fluid. Bubble flow then churn and annular flows were observed but slug flow seems not to exist with helium. A modelling based on a Zuber model matches better the experimental results than a Levy type model. The detailed analysis of the signals given by the optical sensors has allowed to highlight a bubble appearance frequency directly linked to the flowrate. (A.C.) 83 refs.
Institute of Scientific and Technical Information of China (English)
刘雪敏; 李舟航; 吴玉新; 吕俊复
2012-01-01
The air-water two phase flow pattern in vertical tube was experimentally investigated with different tube inner diameter of 20 mm and 8 mm under atmosphere condition. The bubbly flow, slug flow, annular flow and mist flow are observed for two size tubes. Most of the experimental points agree well with Hewitt and Roberts flow pattern map when putting them on the map. With the experimental results, the range line between the flow patterns is suggested for the tubes of 20 mm inner diameter as well as 8 mm. For the vertical flow up, the air superficial velocity when the annular flow appears is independent of the water superficial velocity. The two phase flow patterns range line is similar in tendency and scope for different tubes. The range line between mist flow and annular flow for different tubes is almost overlapping while that between bubbly flow and slug flow is inconsistent for different tubes. The confusion error between bubbly flow and slug flow is of no great importance for heat transfer because the heat transfer for bubbly flow or for slug flow is same. It is believed that the effect of the tube diameter on the two-phase flow in vertical tubes could be neglected, and the Hewitt and Roberts flow pattern map could be adopted without any consideration of tube diameter.%以空气和水作为介质,在管径分别为20mm与8mm的垂直上升管内进行了常压下气液两相流流型的实验研究,得到了这两种管径下泡状流、弹状流、乳状流和环状流等流型,得到的绝大部分实验点与Hewitt和Roberts流型图相符合,并根据实验结果修正了流型图的转化边界.对于气液两相流垂直上升流动,环状流发生所需的气相折算速度几乎不随液相折算速度的变化而变化.不同管径条件下,各种气液两相流流型发生的范围和转换趋势基本一致,乳状流向环状流的转换界限基本重叠,而泡状流与弹状流的界限变化大一些.由于弹状流的换热与泡状流的换热
Geometric effects of 90-degree vertical elbows on global two-phase flow parameters
International Nuclear Information System (INIS)
Geometric effects of 90-degree vertical elbows on global two-phase flow parameters, in particular pressure drop and flow regime transition are investigated. Pressure measurements are obtained along the test section over a wide range of flow conditions in both single-phase and two-phase flow conditions. A two-phase pressure drop correlation analogous to Lockhart-Martinelli correlation is proposed to predict the minor loss across the elbows. Flow visualization is performed to study the effect of elbows on the two-phase flow regime transition. Modified flow regime maps for horizontal and vertical-downward two-phase flow are obtained which demonstrate that downstream of the elbows flow regime transition boundaries deviate significantly from the conventional flow regime transition boundaries. (author)
Vertical cross-spectral phases in atmospheric flow
DEFF Research Database (Denmark)
Chougule, Abhijit S.; Mann, Jakob; Kelly, Mark C.
2014-01-01
there is no significant change in the phase angle of vertical velocity. The phase angles for all atmospheric stabilities show similar order in phasing. The phase angles from the Høvsøre observations under neutral condition are compared with a rapid distortion theory model which show similar order in......The cross-spectral phases between velocity components at two heights are analyzed from observations at the Høvsøre test site under diabatic conditions. These phases represent the degree to which turbulence sensed at one height leads (or lags) in time the turbulence sensed at the other height. The...... phase angle of the cross-wind component is observed to be significantly greater than the phase for the along-wind component, which in turn is greater than the phase for the vertical component. The cross-wind and along-wind phases increase with stream-wise wavenumber and vertical separation distance, but...
Vertical cross-spectral phases in atmospheric flow
International Nuclear Information System (INIS)
The cross-spectral phases between velocity components at two heights are analyzed from observations at the Høvsøre test site under diabatic conditions. These phases represent the degree to which turbulence sensed at one height leads (or lags) in time the turbulence sensed at the other height. The phase angle of the cross-wind component is observed to be significantly greater than the phase for the along-wind component, which in turn is greater than the phase for the vertical component. The cross-wind and along-wind phases increase with stream-wise wavenumber and vertical separation distance, but there is no significant change in the phase angle of vertical velocity. The phase angles for all atmospheric stabilities show similar order in phasing. The phase angles from the H0vs0re observations under neutral condition are compared with a rapid distortion theory model which show similar order in phase shift
Takagi, M.; Desanctis, G. D.; Stretch, D. D.; Nomura, K. K.; Rottman, J. W.; Keller, K. H.; van Atta, C. W.
2001-11-01
A new technique for very rapidly obtaining vertical profiles of vertical velocity and temperature in a thermally-stratified turbulent shear flow is presented. The main purpose of these experiments is to gain a better understanding of what vertical sampling in the ocean tells us about oceanic turbulence and mixing. The technique consists of a cold wire probe for temperature measurements and a hot wire probe for velocity measurements propelled vertically through a thermally-stratified wind tunnel by a pneumatic piston. Speeds of nearly 15 m/s are reached as it traverses the central part of the tunnel. This speed is sufficient to freeze the flow structure sampled by the sensors, so the measured profiles are effectively instantaneous. The design and construction of the vertical traverse device and data acquisition system are described. Ensemble-averaged measurements of the vertical velocity and temperature profiles are presented and comparisons made with single-point time-averaged measurements.
Fermionic flows and tau function of the N = (1 vertical bar 1) superconformal Toda lattice hierarchy
International Nuclear Information System (INIS)
An infinite class of fermionic flows of the N = (1 vertical bar 1) superconformal Toda lattice hierarchy is constructed and their algebraic structure is studied. We completely solve the semi-infinite N = (1 vertical bar 1) Toda lattice and chain hierarchies and derive their tau functions, which may be relevant for building supersymmetric matrix models. Their bosonic limit is also discussed
Axisymmetric annular curtain stability
International Nuclear Information System (INIS)
A temporal stability analysis was carried out to investigate the stability of an axially moving viscous annular liquid jet subject to axisymmetric disturbances in surrounding co-flowing viscous gas media. We investigated in this study the effects of inertia, surface tension, the gas-to-liquid density ratio, the inner-to-outer radius ratio and the gas-to-liquid viscosity ratio on the stability of the jet. With an increase in inertia, the growth rate of the unstable disturbances is found to increase. The dominant (or most unstable) wavenumber decreases with increasing Reynolds number for larger values of the gas-to-liquid viscosity ratio. However, an opposite tendency for the most unstable wavenumber is predicted for small viscosity ratio in the same inertia range. The surrounding gas density, in the presence of viscosity, always reduces the growth rate, hence stabilizing the flow. There exists a critical value of the density ratio above which the flow becomes stable for very small viscosity ratio, whereas for large viscosity ratio, no stable flow appears in the same range of the density ratio. The curvature has a significant destabilizing effect on the thin annular jet, whereas for a relatively thick jet, the maximum growth rate decreases as the inner radius increases, irrespective of the surrounding gas viscosity. The degree of instability increases with Weber number for a relatively large viscosity ratio. In contrast, for small viscosity ratio, the growth rate exhibits a dramatic dependence on the surface tension. There is a small Weber number range, which depends on the viscosity ratio, where the flow is stable. The viscosity ratio always stabilizes the flow. However, the dominant wavenumber increases with increasing viscosity ratio. The range of unstable wavenumbers is affected only by the curvature effect. (paper)
Directory of Open Access Journals (Sweden)
Suwasa Kantawanichkul
2013-10-01
Full Text Available The study was carried out in 4 concrete beds: two vertical subsurface flow beds (dimension of 1x1.4 x 0.6 m3 and twohorizontal subsurface flow beds (dimension of 0.6 x 2.3x 0.6 m3 planted with Cyperus alternifolius L. Under the averagewastewater temperature of 27°C, the hydraulic loading rates (HLR were varied from 5 to 20 cm/d in order to obtain theoptimum operating conditions and compare the removal efficiency. The wastewater was intermittently fed into the verticalsubsurface flow beds (5 minutes on and 55 minutes off, and continuously into the horizontal subsurface flow beds. Themaximum removal efficiencies were found at the lowest hydraulic loading rate for both systems. The horizontal subsurfaceflow system had a higher removal rate than the vertical subsurface flow system in terms of COD (the removal rates at 5-20cm/d were 9.6-33.9 g/m2.d. The vertical subsurface flow system showed higher removal efficiency for TKN and NH4+-N, inevery hydraulic loading rate and the removal rates for TKN and NH4+-N were 0.4-1.1 g/m2.d, respectively. Furthermore, it wasfound that the uptake of N by plants in the horizontal flow system was higher than in the vertical flow system for everyhydraulic loading rate (HLR but the loss of N via adsorption/denitrification was higher in the vertical flow system than inthe horizontal flow system, at 20 cm/d HLR. The removal rate constants in the horizontal subsurface flow system for COD andNH4+-N were 0.0166 and 0.0188 m/d and 0.0204 and 0.0287 m/d for the vertical subsurface flow system, respectively
Film behaviour of vertical gas-liquid flow in a large diameter pipe
Zangana, Mohammed Haseeb Sedeeq
2011-01-01
Gas-liquid flow commonly occurs in oil and gas production and processing system. Large diameter vertical pipes can reduce pressure drops and so minimize operating costs. However, there is a need for research on two-phase flow in large diameter pipes to provide confidence to designers of equipments such as deep water risers. In this study a number of experimental campaigns were carried out to measure pressure drop, liquid film thickness and wall shear in 127mm vertical pipe. Total pressur...
Institute of Scientific and Technical Information of China (English)
李斌; 何安定; 王跃社; 周芳德
2001-01-01
The friction resistance performance of the single-phase flow and double-phase flow was studied when R-113 rized vertically in tho narrow-gap annular tube with various sizes, both single-phase flow and double-phase flow were different from the common flow in tubes. The transition Re Number of the flow in the narrow-gap was 500-1000,the friction resistance of double-bhase flow was bigger than that of the flow in common cycle tubes.Some important data were described,and the relation was proposed for calculating the friction resistance of the single-phase flow and the double-phase flow in the narrow-gap tube annular, the biggest relative error between the testing value and the calculating value was not more than 7.2％.%主要研究不同尺寸窄缝环形管内R-113垂直向上单相和两相流动沸腾时的摩擦阻力特性。研究发现，无论是单相还是两相流动都不同于普通管内流动，流体在窄缝环形管内流动的转变雷诺数Re为500～1000，两相流动摩擦阻力比普通圆管内的大。研究获取了重要的实验数据，并提出了计算窄缝环形管内单相和两相流动摩擦阻力的关系式，试验值与计算值的最大相对误差不超过7.2％。
International Nuclear Information System (INIS)
Previous flow regime studies have been for horizontal, vertical, and inclined pipe flow. As such, only a few studies have been performed on bundle geometries. The present paper examines the flow regimes for a vertical hexagonal flow channel with and without a finned fuel bundle. This type of a 36 finned rod hexagonal fuel bundle in parallel hexagonal flow channels is used in a MAPLE (Multi- purpose Applied Physics Lattice Experimental) type nuclear reactor. An experiment apparatus was designed consisting of the flow channel, inlet plenum and an air-water separator. The inlet plenum is used to provide a uniform mixture of air and water before entering the hexagonal flow channel. A turbine flow meter is used to determine the water flow rate. The turbine flow meter is calibrated for a low flow range and limits the measurable flow to 50 l/min. Flow pattern observation is determined by a SONY video camera, Real-Time Neutron Radiography, pressure transducer and capacitance transducer. The Sony video camera provides visual observation through a Lucite flow channel. The Real-Time Neutron Radiography system allows for flow visualization through an Aluminum flow channel. The pressure drop is correlated by the Validyne pressure transducer and the capacitance transducer provides the void fraction relationship
Deriving debris-flow characteristics from vertical laser profile scanners
Jacquemart, Mylène; Felix, Morsdorf; Graf, Christoph
2015-04-01
Two well-known debris-flow channels in the Swiss Alps, the Dorfbach, in the community of Randa, canton of Valais and the Spreitgraben (community of Guttannen, BE) were fitted with a setup of two laser profile scanners each. Since 2011 (Randa site) and 2012 (Spreitgraben site), these devices have been scanning the passing debris flows at rates of 50 Hz or 75 Hz, recording several million across bed profiles with point densities of roughly 20 points per meter during debris-flow events. In order to comprehend the vast possibilities this extraordinary data set offers, a preliminary evaluation has been undertaken, writing code that allows for a semi-automatic extraction of the main debris-flow characteristics maximum flow height, peak discharge, total discharge as well as spatially distributed flow velocity. The analysis of 13 events, of which 12 took place at the Dorfbach site, and one took place at the Spreitgraben site, revealed that a large-scale Particle Image Velocimetry (PIV) approach can be used to derive flow velocities, and these in turn can be used to compute discharge curves for all of the recorded events. Total automation has proven to be unrealistic, because the choice of the bed geometry greatly influences discharge results. Also, excluding outlying velocity values is necessary, in order to find reliable peak discharge values. Nevertheless, we find that the laser scanners offer distinct advantages over the 'established' setup consisting of geophones and a radar gauge because the scanners catch the debris flow as it changes its flow path and offer much higher resolution in terms of distributed flow height measurements. Furthermore, the single profiles of the recorded debris flows were analyzed with regard to their surface geometry by fitting fourth order polynomials to find the points of inflection along the profiles. From this, we have been able to estimate the amount of flow height that debris flows gain by building their well-known convex fronts, and
Caballero-Miranda, C. I.; Alva-Valdivia, L. M.; González-Rangel, J. A.; Gogitchaishvili, A.; Urrutia-Fucugauchi, J.; Kontny, A.
2016-02-01
The within-flow vertical variation of anisotropy of the magnetic susceptibility (AMS) of three basaltic flow profiles from the Xitle volcano were investigated in relation to the lava flow-induced shear strain. Rock magnetic properties and opaque microscopy studies have shown that the magnetic mineralogy is dominated by Ti-poor magnetite with subtle vertical variations in grain size distribution: PSD grains dominate in a thin bottommost zone, and from base to top from PSD-MD to PSD-SD grains are found. The vertical variation of AMS principal direction patterns permitted identification of two to three main lava zones, some subdivided into subzones. The lower zone is very similar in all profiles with the magnetic foliation dipping toward the flow source, whereas the upper zone has magnetic foliation dipping toward the flow direction or alternates between dipping against and toward the flow direction. The K1 (maximum AMS axis) directions tend to be mostly parallel to the flow direction in both zones. The middle zone shows AMS axes diverging among profiles. We present heterogeneous strain ellipse distribution models for different flow velocities assuming similar viscosity to explain the AMS directions and related parameters of each zone. Irregular vertical foliations and transverse to flow lineation of a few samples at the bottommost and topmost part of profiles suggest SD inverse fabric, levels of intense friction, or degassing effects in AMS orientations.
Vertical clog flow heat transfer with nucleate boiling
International Nuclear Information System (INIS)
This paper presents a model for slug flow heat transfer which is modified by incorporating the effect of nucleate boiling. This modification has made the slug flow model more useful for practical situations where presence of nucleate boiling is generally a norm rather than an exception. The model is further improved by taking into account the previously ignored effect of vapor bubbles present in the liquid slug. These modifications not only make the slug flow model more realistic but also improve its predictive capabilities. This improvement is demonstrated by comparing the predictions of the current model and the previous model with the published slug flow data. The mean deviation between the prediction and the measured slug flow data for water in the range of 20 to 100 kW/m2 heat flux is 5.87% for a total 171 data points
Water quality sample origin in wells under ambient vertical flow conditions
McMillan, Lindsay; Rivett, Michael; Tellam, John; Dumble, Peter; Sharp, Helen
2013-04-01
Sampling from wells remains the key technique for investigation of groundwater contamination. Research into low-flow (pump rate 0.1-0.5L/min) and passive sampling devices and methodologies has largely been driven by needs to minimise sample bias and reduce costs associated with well-volume purge sampling. Such techniques are primarily suited to short-screen (perceived cost/time savings means their use in longer screen wells is attractive. Ambient vertical flows that may perhaps be insignificant in short-screen wells are, however, likely prove increasingly significant as the screen length increases due to the increased probability of vertical flows in greater thicknesses of (layered) geological sequences monitored. The interpretation of sample results assuming idealised horizontal flow conditions may introduce significant bias and prove unsuitable in these conditions. Numerical modelling has been undertaken to investigate the bias introduced under ambient vertical flow conditions. Sampling scenarios were generated by varying partially penetrating screen length, well diameter, sampling device position, pump rate, aquifer thickness and hydraulic conductivity, and boundary head gradients. In well flow rates were based on literature data for relatively short (2-20m) wells. The degree of sampling bias was quantified by calculating the root mean square error between the simulated scenario under a vertical head gradient and ideal horizontal-flow scenario. Low-flow and passive sampling device position, pump rate and pump duration were all found to be important in determining the sample origin. The sample may not be drawn from the entire saturated screen interval even under ideal conditions. When considering vertical flow scenarios, measurable deviation from the ideal case and bias towards the zone of highest head begins with ambient in-well flow rates as little as 50% of the pump rate used. The sample may not predominately originate from the zones most important to flow
Structure of two-phase slug flow in vertical channels
International Nuclear Information System (INIS)
Based on a suggested model of two-phase slug flow in a wide range of varying regime parameters the available literary data and experimental data obtained by the authors on the intensity of void fraction fluctuations, lengths of slugs and liquid plugs are generalized. It is shown that the magnitude of the void fraction is the determining parameter in the formation of the flow regime and structure. The technique for calculating the characteristic frequency of fluctuations of a two-phase flow is suggested
Flooding velocities for air and water in vertical tubes
International Nuclear Information System (INIS)
An investigation of the limiting, or flooding, velocities for countercurrent annular flow of air and water in vertical tubes is reported. The data are correlated in terms of dimensionless groups which are similar to those already in use for describing flooding in packed towers. The relevance of the results to the problem of burnout in boiling equipment is discussed. (author)
Study on particle deposition in vertical square ventilation duct flows by different models
International Nuclear Information System (INIS)
A proper representation of the air flow in a ventilation duct is crucial for adequate prediction of the deposition velocity of particles. In this paper, the mean turbulent air flow fields are predicted by two different numerical models (the Reynolds stress transport model (RSM) and the realizable k-εmodel). Contours of mean streamwise velocity deduced from the k-ε model are compared with those obtained from the Reynolds stress transport model. Dimensionless deposition velocities of particles in downward and upward ventilation duct flows are also compared based on the flow fields presented by the two different numerical models. Trajectories of the particles are tracked using a one way coupling Lagrangian eddy-particle interaction model. Thousands of individual particles are released in the represented flow, and dimensionless deposition velocities are evaluated for the vertical walls in fully developed smooth vertical downward and upward square duct flows generated by the RSM and realizable k-ε model. The effects of particle diameter, dimensionless relaxation time, flow direction and air speed in vertical upward and downward square duct flows on the particle deposition velocities are discussed. The effects of lift and gravity on the particle deposition velocities are evaluated in vertical flows presented by the RSM. It is shown that the particle deposition velocities based on the RSM and realizable k-εmodel have subtle differences. The flow direction and the lift force significantly affect the particle deposition velocities in vertical duct flows. The simulation results are compared with earlier experimental data and the numerical results for fully developed duct flows. It is shown that the deposition velocities predicted are in agreement with the experimental data and the numerical results
Analysis of the flow structure and heat transfer in a vertical mantle heat exchanger
DEFF Research Database (Denmark)
Knudsen, Søren; Morrison, GL; Behnia, M;
2005-01-01
The flow structure inside the inner tank and inside the mantle of a vertical mantle heat exchanger was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the inner tank and in the mantle were measured using a Particle Image...... Velocimetry (PIV) system. A Computational Fluid Dynamics (CFD) model of the vertical mantle heat exchanger was also developed for a detailed evaluation of the heat flux at the mantle wall and at the tank wall. The flow structure was evaluated for both high and low temperature incoming flows and for both...... initially mixed and initially stratified inner tank and mantle. The analysis of the heat transfer showed that the flow in the mantle near the inlet is mixed convection flow and that the heat transfer is dependent on the mantle inlet temperature relative to the core tank temperature at the mantle level. (C...
Institute of Scientific and Technical Information of China (English)
王一平; 陈为强; 黄群武; 冯加和; 崔勇
2016-01-01
Based on the momentum conservation approach, a theoretical model was developed to predict the su-perficial liquid velocity, and a correlation equation was established to calculate the gas holdup of an annular exter-nal-loop airlift reactor(AELAR)in the bubble flow and developing slug flow pattern. Experiments were performed by using tap-water and silicone oil with the viscosity of 2.0 mm2/s(2cs-SiO)and 5.0 mm2/s(5cs-SiO)as liquid phases. The effects of liquid viscosity and flow pattern on the AELAR performance were investigated. The predic-tions of the proposed model were in good agreement with the experimental results of the AELAR. In addition, the comparison of the experimental results shows that the proposed model has good accuracy and could be used to pre-dict the gas holdup and liquid velocity of an AELAR operating in bubble and developing flow pattern.
Energy Technology Data Exchange (ETDEWEB)
Silva, Maria das Gracas Pena [PETROBRAS, Rio de Janeiro (Brazil). Centro de Pesquisas. Setor de Tecnologia de Perfuracao
1989-12-31
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.
Vertically aligned carbon nanotubes for sensing unidirectional fluid flow
Energy Technology Data Exchange (ETDEWEB)
Kiani, Keivan, E-mail: k_kiani@kntu.ac.ir
2015-05-15
From applied mechanics points of view, potential application of ensembles of single-walled carbon nanotubes (SWCNTs) as fluid flow sensors is aimed to be examined. To this end, useful nonlocal analytical and numerical models are developed. The deflection of the ensemble of SWCNTs at the tip is introduced as a measure of its sensitivity. The influences of the length and radius of the SWCNT, intertube distance, fluid flow velocity, and distance of the ensemble from the leading edge of the rigid base on the deflection field of the ensemble are comprehensively examined. The obtained results display how calibration of an ensemble of SWCNTs can be methodically carried out in accordance with the characteristics of the ensemble and the external fluid flow.
International Nuclear Information System (INIS)
This research work consists of studying CHF in vertical tubes under non uniform angular heating conditions. Different non uniform angular heat flux distributions were obtained by using different angular wall thickness of the test section. Over 1000 CHF data points were obtained for two different non uniform angular heating conditions and three different heated lengths. In addition, CHF experiments under uniform heating conditions were also carried out. The results obtained from these tests were used as reference values. In all the cases studied, the same tube inside diameter (=22.2 mm) was used and the experiments were repeated by covering the following flow conditions: the inlet subcooling was varied from 5 to 40 oC, the mass flux was varied from 300 to 1600 kg/m2s, and the outlet pressure was varied from 10 to 40 bars. The data were used to show that the prediction of CHF can be greatly improved by introducing the heat balance method approach instead of the direct method frequently used to evaluate the CHF. Therefore, the prediction of CHF can be obtained by solving simultaneously both an empirical CHF correlation and the heat balance equation. This approach was then used to correlate the CHF data as function of the critical thermodynamic quality. In addition a completely new CHF representation is also proposed. It consists of correlating the CHF as a function of the length over which the dispersed annular flow occurs. This new representation in conjunction with the heat balance method allows the dispersion of the data to be considerable reduced. In general we have observed that non uniform angular heating conditions may considerable affect CHF. (author)
MHD Stagnation Flow of a Newtonian Fluid towards a Uniformly Heated and Moving Vertical Plate
Directory of Open Access Journals (Sweden)
Mehmet Şirin Demir
2016-01-01
Full Text Available Stagnation flow of an electrically conducting incompressible viscous fluid towards a moving vertical plate in the presence of a constant magnetic field is investigated. By using the appropriate transformations for the velocity components and temperature, the partial differential equations governing flow and heat transfer are reduced to a set of nonlinear ordinary differential equations. These equations are solved approximately using a numerical technique for the following two problems: (i two-dimensional stagnation-point flow on a moving vertical plate, (ii axisymmetric stagnation-point flow on a moving vertical plate. The effects of non-dimensional parameters on the velocity components, wall shear stresses, temperature and heat transfer are examined carefully.
Temporal interfacial instability in vertical gas-liquid flows
Schmidt, Patrick; Ó Náraigh, Lennon; Lucquiaud, Mathieu; Valluri, Prashant
2015-11-01
We consider onset and dynamics of interfacial instability in gas-liquid flows, using two-dimensional channel flow of a thin falling film sheared by counter-current gas as a model. Our methodology consists of linear stability theory together with DNS of the two-phase flow in the case of nonlinear disturbances. We study the influence of three main flow parameters (density contrast between liquid and gas, film thickness, pressure drop applied to drive the gas stream) on the interfacial dynamics. Energy budget analyses based on Orr-Sommerfeld theory reveal coexisting unstable modes (interfacial, shear, internal) in the case of high density contrast, resulting in mode coalescence and mode competition, but only one dynamically relevant unstable interfacial mode for low density contrast. DNS of this scenario shows that linear theory holds up remarkably well upon the onset of large-amplitude waves as well as the existence of weakly nonlinear waves. In comparison, although linear stability theory successfully determines the most-dominant features in the interfacial wave dynamics at early-to-intermediate times in a high-density-contrast case, short waves selected by linear theory undergo secondary instability and the wave train is no longer regular but rather exhibits chaotic.
Low-Flow Film Boiling Heat Transfer on Vertical Surfaces
DEFF Research Database (Denmark)
Munthe Andersen, J. G.; Dix, G. E.; Leonard, J. E.; Sun, K. H.
1976-01-01
The phenomenon of film boiling heat transfer for high wall temperatures has been investigated. Based on the assumption of laminar flow for the film, the continuity, momentum, and energy equations for the vapor film are solved and a Bromley-type analytical expression for the heat transfer...... length, an average film boiling heat transfer coefficient is obtained....
International Nuclear Information System (INIS)
Measuring the volumetric flow rate of each of the flowing components is required to be monitored in production logging applications. Hence it is necessary to measure the flow rates of gas, oil and water in vertical and inclined oil wells. An increasing level of interest has been shown by the researchers in developing system for the flow rate measurement in multiphase flows. This paper describes the experimental methodology using a miniature, local four-sensor probe for the measurement of dispersed flow parameters in bubbly two-phase flow for spherical bubbles. To establish interdependent among different parameters corresponding to dispersed flow, the available model has been used to experimentally obtain different parameters such as volume fraction, velocity and bubble shape of the dispersed phase in the bubbly air-water flow.
EFFECT OF A VERTICAL FRACTURE ON HORIZONTAL UNSATURATED SEEPAGE FLOW
Institute of Scientific and Technical Information of China (English)
HUANG Yong; ZHOU Zhi-fang; YU Zhong-bo; NICHOLL M.J.
2011-01-01
The movement of water flow in unsaturated fractured rock was investigated with the sandstone sample through experimental research and numerical simulation.The experimental results show that the arriving time of wetting front is delayed by the fracture, resulting in the increase of water saturation in the domain on the upstream side of the fracture, which will locally enhance water flow through the matrix.The numerical simulation with the finite volume method captures effectively these characteristics.The comparison between simulated and observed travel time and arriving time of wetting front shows that their difference are very small and the simulated results are in agreement with the observed results, which implies calibrated parameters are reliable and effective.Then according to the calibrated parameters, fractured models were established to examine how the change of large fractured aperture would affect the arriving time of wetting fronts, pressure heads and water saturation on the upstream and downstream sides of fracture.
Characterisation of Churn Flow Coalescers (CFC) in vertical pipes
Kanu, Aimé Uzochukwu
2013-01-01
The Gas-Liquid Cylindrical Cyclone (GLCC) separator is commonly used for the separation of oil and gas mixtures flowing from the well head. Similar to the design used by other separators, it has an inlet and two outlets for gas and liquid respectively. However, the inlet to the separator can either be single or dual type. The pipeline connection from the upstream preconditioning equipment (CFC) is inclined downwards and has a tangential inlet slot. The essence of having a downward inclination...
Dynamics of nuclear fuel assemblies in vertical flow channels
International Nuclear Information System (INIS)
DYNMOD is a computer program designed to predict the dynamic behaviour of nuclear fuel assemblies in axial flow. The calculations performed by DYNMOD and the input data required by the program are described in this report. Examples of DYNMOD usage and a brief assessment of the accuracy of the dynamic model are also presented. It is intended that the report will be used as a reference manual by users of DYNMOD
Pipe-wall friction in vertical sand-slurry flows
Czech Academy of Sciences Publication Activity Database
Matoušek, Václav
2009-01-01
Roč. 27, č. 5 (2009), s. 456-468. ISSN 0272-6351 R&D Projects: GA ČR GA103/06/0428 Institutional research plan: CEZ:AV0Z20600510 Keywords : slurry-flow experiment * off-the-wall lift * collisional stress * solids friction * pressure drop Subject RIV: BK - Fluid Dynamics Impact factor: 0.522, year: 2009
Katsanis, T.
1994-01-01
This computer program was developed for calculating the subsonic or transonic flow on the hub-shroud mid-channel stream surface of a single blade row of a turbomachine. The design and analysis of blades for compressors and turbines ideally requires methods for analyzing unsteady, three-dimensional, turbulent viscous flow through a turbomachine. Since an exact solution is impossible at present, solutions on two-dimensional surfaces are calculated to obtain a quasi-three dimensional solution. When three-dimensional effects are important, significant information can be obtained from a solution on a cross-sectional surface of the passage normal to the flow. With this program, a solution to the equations of flow on the meridional surface can be carried out. This solution is chosen when the turbomachine under consideration has significant variation in flow properties in the hubshroud direction, especially when input is needed for use in blade-to-blade calculations. The program can also perform flow calculations for annular ducts without blades. This program should prove very useful in the design and analysis of any turbomachine. This program calculates a solution for two-dimensional, adiabatic shockfree flow. The flow must be essentially subsonic, but there may be local areas of supersonic flow. To obtain the solution, this program uses both the finite difference and the quasi-orthogonal (velocity gradient) methods combined in a way that takes maximum advantage of both. The finite-difference method solves a finite-difference equation along the meridional stream surface in a very efficient manner but is limited to subsonic velocities. This approach must be used in cases where the blade aspect ratios are above one, cases where the passage is curved, and cases with low hub-tip-ratio blades. The quasi-orthogonal method solves the velocity gradient equation on the meridional surface and is used if it is necessary to extend the range of solutions into the transonic regime. In
Flow behavior and pressure drop of two-phase flow through C-shaped bend in vertical plane, (1)
International Nuclear Information System (INIS)
Experimental results are presented on the flow behavior, average void fraction and pressure drop in air-water two-phase flow mixture flowing upward through a C-shaped bend curved in vertical plane. The curved test section of transparent acrylic resin tubing was varied in four versions of (a) 90 mm, (b) 132.5 mm and (c) 180 mm radii of curvature with 16 mm inside diameter tube, and (d) 135 radius with 24 mm diameter tube. The combined action of gravity and centrifugal force acting on the two-phase flow is expressed in terms of a modified Froude number representing the balance of radial forces between those acting on the liquid and the gaseous phases of the flow passing through the reclined vertical U-bend. The average void fraction in the curved test section was determined, and empirically correlated to the pressure drop, by means of a series of nondimensional numbers. (author)
Energy Technology Data Exchange (ETDEWEB)
Barbosa, Adriana; Bannwart, Antonio C. [Universidade Estadual de Campinas, SP (Brazil). Faculdade de Engenharia Mecanica. Dept. de Engenharia de Petroleo
2004-07-01
The use of water-assisted technologies such as core-annular flow to the pipelines of viscous oils has been proposed as an attractive alternative for production and transportation of heavy crudes in both onshore and offshore scenarios. Usually, core-annular flow can be created by injecting a relatively small water flow rate laterally in the pipe, so as to form a thin water annulus surrounding the viscous oil, which is pumped through the center. The reduction in friction losses obtained thanks to lubrication by water is significant, since the pressure drop in a steady state core flow becomes comparable to water flow only. For a complete assessment of core flow technology, however, unwanted effects associated with possible oil adhesion onto the pipe wall should be investigated, since these may cause severe fouling of the wall and pressure drop increase. It has been observed that oil adhesion on metallic surfaces may occur for certain types of crude and oilphilic pipe materials. In this work we present results of pressure drop monitoring during 35 hour-operation of a heavy oil-water core annular flow in a 26.08 mm. i.d. horizontal steel pipe. The oil used is described in terms of its main components and the results of static wet ability tests are also presented for comparison (author)
Energy Technology Data Exchange (ETDEWEB)
Li, D.W. [Hitachi, Ltd., Tokyo (Japan); Kaneko, S. [The University of Tokyo, Tokyo (Japan); Hayama, S. [Toyama Prefectural University, Toyama (Japan)
1999-07-25
This study reports the stability of annular leakage-flow-induced vibrations. The pressure distribution of fluid between a fixed outer cylinder and a vibrating inner cylinder was obtained in the case of a translationally and rotationally coupled motion of the inner cylinder. The unsteady fluid force acting on the inner cylinder in the case of translational and rotational single-degree-of-freedom vibrations was then expressed in terms proportional to the acceleration, velocity, and displacement. Then the critical flow rate (at which stability was lost) was determined for an annular leakage-flow-induced vibration. Finally, the stability was investigated theoretically. It is known that instability will occur in the case of a divergent passage, but the critical flow rate depends on the passage increment in a limited range: the eccentricity of the passage and the pressure loss factor at the inlet of the passage lower the stability. (author)
Experimental observations of flow boiling of liquid helium I in vertical channels
International Nuclear Information System (INIS)
Results are reported of the flow structure and pressure drop of helium 1 flowing upwards in a vertical heated circular glass tube. The experiments covered heat fluxes from 4.5 to 600 Wm-2, mass fluxes from 2 to 12 kg m-2s-1 and pressures between 1 and 1.2 atm. For the bubble flow regime the shape, size and drag coefficient of the observed bubbles are reported. Slip velocity, void fraction and pressure drop measurements are compared with generally accepted two-phase flow theories. A void fraction correlation for two-phase helium flow is proposed. (author)
Interfacial area transport of steam-water two-phase flow in a vertical annulus at elevated pressures
Ozar, Basar
Analysis of accident scenarios in nuclear reactors are done by using codes such as TRACE and RELAP5. Large oscillations in the core void fraction are observed in calculations of advanced passive light water reactors (ALWRs), especially during the low pressure long-term cooling phase. These oscillations are attributed to be numerical in nature and served to limit the accuracy as well as the credibility of the calculations. One of the root causes of these unphysical oscillations is determined to be flow regime transitions caused by the usage of static flow regime maps. The interfacial area transport equation was proposed earlier in order to address these issues. Previous research successfully developed the foundation of the interfacial area transport equation and the experimental techniques needed for the measurement of interfacial area, bubble diameters and velocities. In the past, an extensive database has been then generated for adiabatic air-water conditions in vertical upward and downward bubbly-churn turbulent flows in pipes. Using this database, mechanistic models for the creation (bubble breakup) and destruction (bubble coalescence) of interfacial area have been developed for the bubblyslug flow regime transition. However, none of these studies investigated the effect of phase change. To address this need, a heated annular test section was designed and constructed. The design relied on a three level scaling approach: geometric scaling; hydrodynamic scaling; thermal scaling. The test section consisted of a heated and unheated section in order to study the sub-cooled boiling and bulk condensation/flashing and evaporation phenomena, respectively. Steam-water two-phase flow tests were conducted under sub-cooled boiling conditions in the heated section and with sub-cooled/super-heated bulk liquid in the unheated section. The modeling of interfacial area transport equation with phase change effects was introduced and discussed. Constitutive relations, which took
Effect of Annular Slit Geometry on Characteristics of Spiral Jet
Institute of Scientific and Technical Information of China (English)
Shigeru Matsuo; Kwon-Hee Lee; Shinsuke Oda; Toshiaki Setoguchi; Heuy-Dong Kim
2003-01-01
A spiral flow using an annular slit connected to a conical cylinder does not need special device to generate a tangential velocity component of the flow and differs from swirling flows. Pressurized fluid is supplied to an annular chamber and injected into the convergent nozzle through the annular slit. The annular jet develops into the spiral flow. In the present study, a spiral jet discharged out of nozzle exit was obtained by using a convergent nozzle and an annular slit set in nozzle inlet, and the effect of annular slit geometry on characteristics of the spiral jet was investigated by using a Laser Doppler Velocimeter (LDV) experimentally. Furthermore, velocity distributions of the spiral jet were compared with those of a normal jet.
Jong, Valerie Siaw Wee; Tang, Fu Ee
2016-01-01
Individual septic tanks are the most common means of on-site sanitation in Malaysia, but they result in a significant volume of septage. A two-staged vertical flow constructed wetlands (VFCWs) system for the treatment of septage was constructed and studied in Sarawak, Malaysia. Raw septage was treated in the first stage wetlands, and the resulting percolate was fed onto the second stage wetlands for further treatment. Here, the effects of a batch loading regime on the contaminant removal efficiency at the second stage wetlands, which included palm kernel shell within their filter substrate, are presented. The batch loading regime with pond:rest (P:R) period of 1:1, 2:2 and 3:3 (day:day) was studied. The improvement of the effluent redox condition was evident with P:R = 3:3, resulting in excellent organic matters (chemical oxygen demand and biochemical oxygen demand) and nitrogen reduction. The bed operated with P:R = 1:1 experienced constant clogging, with a water layer observed on the bed surface. For the P:R = 3:3 regime, the dissolved oxygen profile was not found to decay drastically after 24 hours of ponding, suggesting that the biodegradation mainly occurred during the first day. The study results indicate that a suitable application regime with an adequate rest period is important in VFCWs to ensure efficient operation. PMID:26901735
RESONANCE RESPONSE OF ELECTRORHEOLOGICAL FLUIDS IN VERTICAL OSCILLATION SQUEEZE FLOW
Institute of Scientific and Technical Information of China (English)
Sun Jiu-xun; Cai Ling-cang; Wu Qiang; Jing Fu-qian
2000-01-01
The resonance effect of microcrystalline cellulose/castor oil electrorheological (ER) suspensions was studied in a compressed oscillatory squeeze flow under external electric fields. The resonance frequency first increases linearly with increasing external field, and then shift to high-field plateau. The amplitudes of resonance peak increase sharply with the applied fields in the range of 0.17-1.67kV/mm. The phase difference of the.reduced displacement relative to the excitation force inverses in the case of resonance. A viscoelasticity model of the ER suspensions, which offers both the equivalent stiffness and the viscous damping, should be responsible for the appearance of resonance. The influence of the electric field on the resonance frequency and the resonance hump is consistent qualitatively with the interpretation of our proposed model. Storage modulus G′ was presented for the purpose of investigating this influence.
DEFF Research Database (Denmark)
Konnerup, Dennis; Trang, Ngo Thuy Diem; Brix, Hans
2011-01-01
in the outlets. The ornamental Canna×generalis planted in the CWs grew faster and took up more N and P in the vertical flow CWs. The aquaculture fish had a feed conversion ratio of 1.53 based on feed dry weight, and 31% and 34% of N and P input, respectively, were incorporated into fish biomass. Only minor...... niloticus) and common carp (Cyprinus carpio) was recirculated through horizontal and vertical flow CWs. The CWs were able to keep a good water quality with DO (>1mg/l-1), BOD (fish. There was a good removal...
Olivier, L.
2015-01-01
The aim of this report is to present the work done on the experimental monitoring of vertical flow constructed wetland for combined sewer overflow in order to develop a software to help dimensioning this structure. The goal of my internship at Irstea Lyon-Villeurbanne was to monitor a full-scale site of vertical flow constructed wetland for combined sewer overflow to make a first calibration of the model based on the field data. A sensitivity analysis was realized to identify parameters which...
Two-phase flow regime transition in large diameter vertical pipes
International Nuclear Information System (INIS)
The two-phase flow regime transition in a large diameter (I.D.=200mm) vertical pipe was experimentally investigated using a dual-sensor optical probe. The flow transitions from bubbly to chum without an intermediate slug flow regime as the air flow rate is increased. The transition boundaries developed for bubbly to slug flow in small diameter pipes are compared to the bubbly to chum flow transition of the present experiment. The bubbly to chum transition occurs at a void fraction of about 0.15 compared to 0.25 for bubbly to slug transition in small diameter pipes. The radial distribution of bubble diameter, bubble frequency, bubble velocity and local void fraction were obtained using a dual-sensor optical probe at different flow conditions. The Probability Density Function (PDF) and Cumulative Distribution Function (CDF) of the bubble velocity and size are used to study the flow regime transition in the large diameter pipe. (author)
Critical heat flux for low flow boiling in vertical uniformly heated thin rectangular channels
International Nuclear Information System (INIS)
Steady-state, subcooled, low flow, critical heat flux (CHF) experiments simulating natural convection boiling are performed in a thin rectangular vertical channel. The aluminum channel is heated on one side: the other side of the channel is a Pyrex window allowing visual observation of the CHF event. Both upward and downward flow conditions are tested with exit pressure varying from 20 to 85 kPa, inlet water temperature varying from 295 to 343 K (inlet subcooling 5-72 K), and mass flux varying from 30 to 80 kg s-1 m-2. Measured test results indicate downward flow dryout CHF occurring at 85% of upward flow dryout CHF values. This percentage is believed to result from the flow instability and reduced inlet subcooling induced by the counter-current flow. New dryout CHF correlations for low flow rates, representative of natural convection boiling, are recommended for both upward and downward flow. (Author)
International Nuclear Information System (INIS)
Two-phase annular flow with heat transfer is prevalent in many processes such as industrial and energy reformation processes. Recently, advances in high performance electronic chips and the miniaturisation of electronic circuits in which high heat flux will be created and other compact systems such as Integrated Nuclear Power Device (INPD), the refrigeration/air conditioning, automobile environment control systems have resulted in a great demand for developing efficient heat transfer techniques to accommodate these high heat fluxes. It has been studied by many researchers because of its successful application in many areas, but its influence factor and mechanism of heat transfer remain somewhat unknown yet. In order to understand the heat transfer and flow mechanism in the narrow annular channel, experimental and theoretical study of dryout and post-dryout heat transfer of steam-water two-phase flow in annular channel with narrow gap (1.0 mm and 1.5 mm) have been carried out. The working fluid is deionized water. The range of experimental pressure is 1.0 ∼ 6.OMPa. In correspondence with two different narrow gaps, two kinds of test sections were designed. The test sections were made of specially processed straight stainless steel tubes with linearity error less than 0.01% to form narrow concentric annuli. It also needs a good sealed performance at high pressure and high temperature. The experiments were carried out to investigate the characteristics and occurring conditions of the dryout point. The former Soviet researcher Kutateladse's correlation, based on round tube, was quoted and modified to apply barrow annuli under low flow conditions. At full conditions of the influencing factors, such as geometry of test section, pressure, mass flux, heat flux etc., an empirical correlation was developed to apply to bilaterally heated annuli and it had a good agreement with the experimental data A new analytical model for the dryout point of critical quality in
International Nuclear Information System (INIS)
Subcooled flow boiling in a vertical rectangular channel was experimentally investigated to enhance the understanding of the CHF and the effect of the two-phase flow instability on it under low pressure conditions, especially for downward flow which was adopted for Jordan Research and Training Reactor (JRTR) and Kijang research reactor (KJRR) to achieve easier fuel and irradiation rig loading. In addition, visual observations of subcoold flow boiling was conducted by using high-speed video (HSV) for a clear understanding of both phenomena. We concluded that flow excursion (which is static instability) could be induced due to the OPDF (which is dynamic instability) when a system has no resistibility to the pressure drop perturbation, which is caused by the coalescence of facing bubbles on opposing heated surfaces. In more stable system with throttling applied, flow rate could be maintained and stable CHF could be reached. The static flow instability (FI) and critical heat flux (CHF) for subcooled flow boiling in a vertical narrow channels under low pressure condition are fairly crucial phenomena relative to thermal-hydraulic design and safety analysis for pool-type research reactors. It has been recommended that RRs and MTRs be designed to have sufficient margins for CHF and the onset of FI as well, since unstable flow could leads to premature CHF under very low wall heat flux in comparison to stable CHF. Even the fact and previous studies, however, the understanding of relationship among FI, premature CHF and stable CHF is not sufficient to date
Effect of gravitational and inertial forces on vertical distribution of pulmonary blood flow
Chevalier, P. A.; Reed, J. H., Jr.; Vandenberg, R. A.; Wood, E. H.
1978-01-01
Vertical distribution of pulmonary blood flow (VDPBF) was studied, using radioactive microsphere emboli, in dogs without thoracotomy in the right decubitus position during exposure to lateral accelerations of 1, 2, 4, and 6 G. At all levels of force environment studied, an inverse linear relationship was observed between vertical height in the thorax and pulmonary blood flow (ml/min/ml lung tissue) with a decrease in flow to the most dependent region of the lung despite large increases in intravascular pressures at this site. Changes in blood flow were smallest at the mid-lung level, the hydrostatic 'balance point' for vascular and pleural pressures. These force environment-dependent changes in VDPBF are not readily explainable by the Starling resistor analog. Gravity-dependent regional differences in pleural and associated interstitial pressures, plus possible changes in vascular tone resulting from inadequate aeration of blood in the most dependent regions of the lung, probably also affect VDPBF.
Analytical study on mechanism of countercurrent flow limitation in vertical rectangular channels
International Nuclear Information System (INIS)
A quantitative analysis of countercurrent flow limitation (CCFL) or flooding was successfully carried out using the existing experimental data for the vertical rectangular channels, adopting the criterion that the CCFL condition is determined by maximizing the falling water mass velocity with respect to the thickness of falling water film for the whole flow channel, without any additional conditions. It was found that significant factors were the flow pattern, that is, which walls were wet, interfacial friction factor between liquid and gas based on the relative velocity, wall friction factors for laminar, transition, and turbulent flow of liquid and gas, and aspect ratio of rectangular channels. Thus it was clarified that the analytical results give good predictions of the existing experimental data of air-water system for vertical rectangular channels of 33 and 66 mm in channel width, 2.3 to 12.3 mm in channel gap, and 362 and 782 mm in channel length under atmospheric pressure
International Nuclear Information System (INIS)
The experimental study on the flooding process in tubes by the pressure of P = 0.3-1.6 MPa is carried out. The interaction of the phase discharges by flooding and hydrodynamic characteristics of the annular countercurrent flow (the liquid film thickness, interphase friction coefficient, pressure drop by the channel height) are studied. The physical mechanism of the flooding process development by increase in the vapor discharge and effect of the geometrical and regime parameters are considered
Trávníčková, T. (Tereza); Havlica, J. (Jaromír); Kohout, M.
2016-01-01
Mixing of granular systems is one of the most used chemical engineering unit operations. However, detailed description of the dynamics of granular flows through experiments is difficult. Therefore, usage of mathematical modeling increases. In this paper we deal with DEM (Discreet Element Method) simulations of mixing glass beads in a cylindrical vertical bladed mixer. The aim of this work is to describe the influence of blade rake on the development of granular secondary flows for different s...
Thermal receptivity of free convective flow from a heated vertical surface: linear waves
Paul, M.C.; Rees, D.A.S.; Wilson, M.
2008-01-01
Numerical techniques are used to study the receptivity to small-amplitude thermal disturbances of the boundary layer flow of air which is induced by a heated vertical flat plate. The fully elliptic nonlinear, time-dependent Navier–Stokes and energy equations are first solved to determine the steady state boundary-layer flow, while a linearised version of the same code is used to determine the stability characteristics. In particular we investigate (i) the ultimate fate of a localised thermal ...
Downstream wind flow path diversion and its effects on the performance of vertical axis wind turbine
International Nuclear Information System (INIS)
In the present experimental study efforts have been made to analysis path diversion effect of downstream wind flow on performance of vertical axis wind turbine (VAWT). For the blockage of downstream wind flow path at various linear displaced positions, a normal erected flat wall, semi-circular and cylindrical shapes were tested for path diverting geometries. Performance of VAWT in terms of improved rotor speed up to 45% was achieved. (author)
Turbulent Flow Characteristics and Dynamics Response of a Vertical-Axis Spiral Rotor
Yuli Wang; Xin Yang; Can Kang
2013-01-01
The concept of a vertical-axis spiral wind rotor is proposed and implemented in the interest of adapting it to air flows from all directions and improving the rotorâ€™s performance. A comparative study is performed between the proposed rotor and conventional Savonius rotor. Turbulent flow features near the rotor blades are simulated with Spalart-Allmaras turbulence model. The torque coefficient of the proposed rotor is satisfactory in terms of its magnitude and variation through the rotationa...
Convective MHD Oscillatory Flow past a Uniformly Moving Infinite Vertical Plate
Directory of Open Access Journals (Sweden)
N. Ahmed
1992-01-01
Full Text Available The convective magnetohydrodynamic flow past a uniformly moving infinite vertical plate, with the magnetic field and the suction velocity applied normal to the plate has been analysed. Presence of heat source or sink has also been considered. The findings are expected to throw light on some problems of defence applications in the areas of aeronautical designs and also flow and heat transfer problems of a chemically reacting fluid.
DEFF Research Database (Denmark)
Bohorquez, Eliana; Paredes, Diego; Arias, Carlos Alberto;
Vertical flow constructed wetlands (VFWC) design and operation takes into account several variables which affect performance its performance. These aspects had been evaluated and documented among others in countries like USA, Denmark, Austria. In contrast, VFCW had not been studied in tropical...
Vertical flow constructed wetland (VFCW) is a promising engineering technique for removal of excess nutrients and certain pollutants from wastewater and stormwater. The aim of this study was to develop a STELLA (Structural Thinking, Experiential Learning Laboratory with Animation) model for estimati...
De Biase, C.; Carminati, A.; Oswald, S.E.; Thullner, M.
2013-01-01
Vertical flow systems filled with porous medium have been shown to efficiently remove volatile organic contaminants (VOCs) from contaminated groundwater. To apply this semi-natural remediation strategy it is however necessary to distinguish between removal due to biodegradation and due to volatile l
Dazhuan Wu; Leqin Wang; Qinglei Jiang; Lulu Zhai
2011-01-01
The current paper studies the influence of annular seal flow on the transient response of centrifugal pump rotors during the start-up period. A single rotor system and three states of annular seal flow were modeled. These models were solved using numerical integration and finite difference methods. A fluid-structure interaction method was developed. In each time step one of the three annular seal models was chosen to simulate the annular seal flow according to the state of rotor systems. The ...
Energy Technology Data Exchange (ETDEWEB)
D' Ambros, Alder C.; Vitorassi, Pedro H.; Franco, Admilson T.; Morales, Rigoberto E.M. [Universidade Tecnologica Federal do Parana (UTFPR), Curitiba, PR (Brazil); Matins, Andre Leibsohn [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES). Tecnologia de Engenharia de Perfuracao
2008-07-01
The success of oil well drilling process depends on the correct prediction of the velocities and stresses fields inside the gap between the drill string and the rock formation. Using CFD is possible to predict the behavior of the drilling fluid flow along the annular space, from the bottom to the top of the well. Commonly the drilling fluid is modeled as a Herschel-Bulkley fluid. An alternative is to employ a non-linear viscoelastic model, like the one developed by Phan-Thien-Tanner (PTT). In the present work the PTT constitutive equation is used to model the drilling fluid flow along the annular space. Thus, this work investigates the influence of the Deborah number on the laminar flow pattern through the numerical solution of the equations formed by the coupled velocity-pressure-stress fields. The results are analyzed and validated against the analytical solution for the fully developed annular pipe flow. The relation between the Deborah number (De) and the entry length is investigated, along with the influence of high values of Deborah number on the friction factor, stress and velocity fields. (author)
International Nuclear Information System (INIS)
High-thermal performance PWR (pressurized water reactor) spacer grids require both low pressure loss and high critical heat flux (CHF) properties. Numerical investigations on the effect of angles and position of mixing vanes and to understand in more details the main physical phenomena (wall boiling, entrainment of bubbles in the wakes, recondensation) are required. In the field of fuel assembly analysis or design by means of CFD codes, the overwhelming majority of the studies are carried out using two-equation eddy viscosity models (EVM), especially the standard K-ε model, while the use of Reynolds Stress Transport Models (RSTM) remains exceptional. But extensive testing and application over the past three decades have revealed a number of shortcomings and deficiencies in eddy viscosity models. In fact, the K-ε model is totally blind to rotation effects and the swirling flows can be regarded as a special case of fluid rotation. This aspect is crucial for the simulation of a hot channel in a fuel assembly. In fact, the mixing vanes of the spacer grids generate a swirl in the coolant water, to enhance the heat transfer from the rods to the coolant in the hot channels and to limit boiling. First, we started to evaluate computational fluid dynamics results against the AGATE-mixing experiment: single-phase liquid water tests, with Laser-Doppler liquid velocity measurements upstream and downstream of mixing blades. The comparison of computed and experimental azimuthal (circular component in a horizontal plane) liquid velocity downstream of a mixing vane for the AGATE-mixing test shows that the rotating flow is qualitatively well reproduced by CFD calculations but azimuthal liquid velocity is underestimated with the K-ε model. Before comparing performance of EVM and RSTM models on fuel assembly geometry, we performed calculations with a simpler geometry, the ASU-annular channel case. A wall function model dedicated to boiling flows is also proposed.
International Nuclear Information System (INIS)
To qualify CFD codes for two-phase flows, they have to be equipped with constitutive laws describing the interaction between the gaseous and the liquid phases. In the case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. To obtain detailed experimental data, an electrode wire-mesh sensor was used, which enables the measurement of the phase distribution with a very high resolution in space and in time. Air-water flow at ambient conditions in a vertical pipe (51.2 mm inner diameter) is investigated to have well defined boundary conditions. Local bubble size distributions are calculated from the data. The measurements were done in different distances from the gas injection device. As a result the development of bubble size distributions as well as the development of the radial gas fraction profiles can be studied. It was found, that the bubble size distribution as well as local effects determine the transition from bubble flow to slug flow. The data are used for the development of a model, which predicts the development of the bubble size distribution and the transition from bubble flow to slug flow in case of stationary flow in a vertical pipe. (orig.)
International Nuclear Information System (INIS)
Thermal-hydraulic characteristics of an annular fuel channel with spacer ribs for high temperature gas-cooled reactors were analyzed numerically by three-dimensional heat transfer computations under a fully developed turbulent flow. The two-equations κ-ε turbulence model was applied to the present turbulent analysis. In particular, the κ-ε turbulence model constants and the turbulent Prandtl number were improved from the previous standard values proposed by Jones and Launder in order to obtain heat transfer predictions with higher accuracy. Consequently, heat transfer coefficients and friction factors in the spacer-ribbed fuel channel were predicted with sufficient accuracy in the range of Reynolds number exceeding 3000. It was clarified quantitatively from the present study that main mechanism for the heat transfer augmentation in the spacer-ribbed fuel channel was combined effects of the turbulence promoter effect by the spacer ribs and the velocity acceleration effect by a reduction in the channel cross-section. (author)
Energy Technology Data Exchange (ETDEWEB)
Takase, Kazuyuki; Akino, Norio [Japan Atomic Energy Research Inst., Oarai, Ibaraki (Japan). Oarai Research Establishment
1996-06-01
Thermal-hydraulic characteristics of an annular fuel channel with spacer ribs for high temperature gas-cooled reactors were analyzed numerically by three-dimensional heat transfer computations under a fully developed turbulent flow. The two-equations {kappa}-{epsilon} turbulence model was applied to the present turbulent analysis. In particular, the {kappa}-{epsilon} turbulence model constants and the turbulent Prandtl number were improved from the previous standard values proposed by Jones and Launder in order to obtain heat transfer predictions with higher accuracy. Consequently, heat transfer coefficients and friction factors in the spacer-ribbed fuel channel were predicted with sufficient accuracy in the range of Reynolds number exceeding 3000. It was clarified quantitatively from the present study that main mechanism for the heat transfer augmentation in the spacer-ribbed fuel channel was combined effects of the turbulence promoter effect by the spacer ribs and the velocity acceleration effect by a reduction in the channel cross-section. (author)
Turbulent flow and heat transfer in vertical tubes under strong effects of lifting forces
International Nuclear Information System (INIS)
The problem is studied of the turbulent flow and heat transfer in vertical tubes, considering the lifting forces effect on the averaged flow as well on the turbulent transfer. Expressions for the pulse turbulent transfer coefficient and for the Prandtl turbulent number have been obtained by approximate solution of the turbulence energy balance equations and of the enthalpy pulsation intensity equations. The averaged motion and energy equation system of the boundary layers type is solved numerically. The calculated and experimentally measured profiles of the velocity, of the pulse turbulent transfer coefficient distribution, of the heat emission and resistance coefficients are given. The results of calculations performed for water and air at the lifting and dipping flow in the heated vertical tubes, are in a good agreement with the experimental data
Heat transfer study on supercritical CO2 flow in vertical tube
International Nuclear Information System (INIS)
This paper presents an analysis of a new heat-transfer correlation developed for supercritical carbon dioxide (CO2) flowing in vertical bare tubes. A large set of supercritical CO2 experimental data was obtained from Chalk River Laboratories (CRL) AECL. Data points were obtained for an upward flow of CO2 inside 8-mm ID vertical Inconel-600 tube with a 2.208-m heated length for a wide range of flow conditions: Pressures ranging from 7.4 to 8.8 MPa, mass fluxes from 900 to 3000 kg/m2s, inlet fluid temperatures from 20 to 40°C, and heat fluxes from 15 to 615 kW/m2; and for several combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature. (author)
Flow Analysis of Straight Wing Vertical Axis Type Wind Turbine for Power Generation
Horiuchi, Kenji; Seki, Kazuichi
Researches about the aerodynamics of wind turbine with straight wing vertical axis(SW-VAWT)are very limited, in spite of a number of advantages such as low dependence on wind direction variation and easy constructible straight blades. For these reasons, we are researching the lift type SW-VAWT for many years. The elucidation of the behavior of the flow inside and neighborhood of the wind turbine during the rotation is very important because of the performance improvement of the vertical axis wind turbine. This research examined to the aerofoil characters by using the numerical simulation technique and the precision of the prediction technique was confirmed as this result. Furthermore, we estimated flow behavior during the wind turbine rotation by using this numerical simulation technique, and evaluated the flow around the wind turbine. This paper presents outline and results of these calculations and evaluations.
Suwasa Kantawanichkul; Suparurk Wannasri
2013-01-01
The study was carried out in 4 concrete beds: two vertical subsurface flow beds (dimension of 1x1.4 x 0.6 m3) and twohorizontal subsurface flow beds (dimension of 0.6 x 2.3x 0.6 m3) planted with Cyperus alternifolius L. Under the averagewastewater temperature of 27°C, the hydraulic loading rates (HLR) were varied from 5 to 20 cm/d in order to obtain theoptimum operating conditions and compare the removal efficiency. The wastewater was intermittently fed into the verticalsubsurface flow beds (...
Review of Mixed Convection Flow Regime Map of a Vertical pipe
International Nuclear Information System (INIS)
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
Chen, Jui-Sheng; Jang, Cheng-Shin; Cheng, Chung-Ting; Liu, Chen-Wuing
2010-09-01
SummaryThis study presents a novel mathematical model for describing the transport of the remedial reagent in a vertical circulation flow field in an anisotropic aquifer. To develop the mathematical model, the radial and vertical components of the pore water velocity are calculated first by using an analytical solution for steady-state drawdown distribution near a vertical circulation well. Next, the obtained radial and vertical components of the pore water velocity are then incorporated into a three-dimensional axisymmetrical advection-dispersion equation in cylindrical coordinates from which to build the reagent transport equation. The Laplace transform finite difference technique is applied to solve the three-dimensional axisymmetrical advection-dispersion equation with spatial variable-dependent coefficients. The developed mathematical model is used to investigate the effects of various parameters such as hydraulic conductivity anisotropy, longitudinal and transverse dispersivities, the placement of the extraction and injection screened intervals of the vertical circulation well and the injection modes on the transport regime of the remedial reagent. Results show that those parameters have different degrees of impacts on the distribution of the remedial reagent. The mathematical model provides an effective tool for designing and operating an enhanced groundwater remediation in an anisotropic aquifer using the vertical circulation well technology.
International Nuclear Information System (INIS)
The secondary side of the nuclear power plant steam generator is working in a two-phase convective boiling process in which two-phase flow instability must be avoided in design. The time domain method was used to study the two-phase flow instability in a vertical up-flow tube. One-dimensional model was established and a numerical program was compiled. Two-phase flow density-wave instability was simulated, and transient parameter distribution in the tube during the dynamic process was presented. The program was also used to analyze the effects of mass velocity, system pressure, and inlet sub-cooling on flow instability. The result shows that the transient parameter distribution from the program agree well with the experimental results, and it can predict the instability boundary, which is more accurate than that of the usually used Khabenski nomographic method. (authors)
Energy Technology Data Exchange (ETDEWEB)
Ishak, Anuar [School of Mathematical Sciences, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor (Malaysia); Nazar, Roslinda [School of Mathematical Sciences, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor (Malaysia)], E-mail: rmn72my@yahoo.com; Pop, Ioan [Faculty of Mathematics, University of Cluj, R-3400 Cluj, CP 253 (Romania)
2008-03-31
The mixed convection boundary layer flow through a stable stratified porous medium bounded by a vertical surface is investigated. The external velocity and the surface temperature are assumed to vary as x{sup m}, where x is measured from the leading edge of the vertical surface and m is a constant. Numerical solutions for the governing Darcy and energy equations are obtained. The results indicate that the thermal stratification significantly affects the surface shear stress as well as the surface heat transfer, besides delays the boundary layer separation.
International Nuclear Information System (INIS)
This article investigates the weakly nonlinear stability theory of a thin pseudoplastic liquid film flowing down on a vertical wall. The long-wave perturbation method is employed to solve for generalized nonlinear kinematic equation with free film interface. The normal mode approach is used to compute the linear stability solution for the film flow. The method of multiple scales is then used to obtain the weak nonlinear dynamics of the film flow for stability analysis. It is shown that the necessary condition for the existence of such a solution is governed by the Ginzburg - Landau equation. The modeling results indicate that both subcritical instability and supercritical stability conditions are possible to occur in a pseudoplastic film flow system. The results also reveal that the pseudoplastic liquid film flows are less stable than Newtonian's as traveling down along the vertical wall. The degree of instability in the film flow is further intensified by decreasing the flow index n. [copyright] 2001 American Institute of Physics
Turbulent dispersion of bubbles in poly-dispersed gas-liquid flows in a vertical pipe
International Nuclear Information System (INIS)
Turbulence dispersion has a significant effect on the migration of bubbles in a vertical flow. Based on a double averaging approach and by adopting the Favre averaged velocity, we developed the Favre Averaged Drag (FAD) model for the turbulent dispersion force for Eulerian multiphase flows (Burns et al., 2004). The model formulation was originally derived from the instant Eulerian model equations as a result of the correlation between the inter-phase drag and the volume fractions. In this work, a new model derivation starting from the two-way coupled Lagrangian formulation is provided. This derivation explains the physical mechanism of turbulence dispersion in a clear way and makes the sense of the double averaging approach straightforward. Moreover, the new derivation might also be considered as the theoretical foundation for applying the FAD model to the Lagrangian solver, which will significantly increase the computational efficiency. We also carried out extensive validation and evaluation for this model by numerical and experimental investigations of bubbly flows in a vertical pipe. Various flow regimes including bubbly flows with a wall or core peak of the gas volume fraction, or in the transition region between them, and finely dispersed flows were covered. The emphasis is to examine the model applicability under various flow conditions. Different from our previous studies (Shi et al., 2004; Frank et al., 2004), poly-dispersed models were applied in the computations. The innocence of the drag force model on the turbulent dispersion was also examined. (authors)
Coupling Navier-stokes and Cahn-hilliard Equations in a Two-dimensional Annular flow Configuration
Vignal, Philippe
2015-06-01
In this work, we present a novel isogeometric analysis discretization for the Navier-Stokes- Cahn-Hilliard equation, which uses divergence-conforming spaces. Basis functions generated with this method can have higher-order continuity, and allow to directly discretize the higher- order operators present in the equation. The discretization is implemented in PetIGA-MF, a high-performance framework for discrete differential forms. We present solutions in a two- dimensional annulus, and model spinodal decomposition under shear flow.
Vertical distribution of fluid velocity and suspended sediment in open channel turbulent flow
Pal, Debasish; Ghoshal, Koeli
2016-06-01
To predict the vertical distribution of streamwise fluid velocity and suspended sediment concentration profiles in an open channel turbulent flow, we derive a theoretical model here based on the Reynolds averaged Navier-Stokes equation and the mass conservation equations of solid and fluid phases. The model includes the effects of secondary current in terms of the vertical velocity of fluid, additional vertical velocity of fluid due to the suspended particles, mixing length of sediment-laden flow and settlement of the suspended particles due to gravitational force. We numerically solve our model as coupled differential equations and the obtained solution agrees well with a wide spectrum of experimental data. A detailed error analysis asserts the superior determination accuracy of our model in comparison to the traditional log-law and Rouse equation and other existing theoretical models. The significance of the turbulent features included in the model and the importance of their co-existence to compute velocity and concentration profiles are explained. In sharp contrast to the previous researchers, the present model has significant contribution in unveiling several latent phenomena of particle-turbulence interaction throughout the flow region. The model can also address various crucial phenomena of velocity and concentration profiles that occur during flow in real situation.
Numerical investigation of flow and scour around a vertical circular cylinder.
Baykal, C; Sumer, B M; Fuhrman, D R; Jacobsen, N G; Fredsøe, J
2015-01-28
Flow and scour around a vertical cylinder exposed to current are investigated by using a three-dimensional numerical model based on incompressible Reynolds-averaged Navier-Stokes equations. The model incorporates (i) k-ω turbulence closure, (ii) vortex-shedding processes, (iii) sediment transport (both bed and suspended load), as well as (iv) bed morphology. The influence of vortex shedding and suspended load on the scour are specifically investigated. For the selected geometry and flow conditions, it is found that the equilibrium scour depth is decreased by 50% when the suspended sediment transport is not accounted for. Alternatively, the effects of vortex shedding are found to be limited to the very early stage of the scour process. Flow features such as the horseshoe vortex, as well as lee-wake vortices, including their vertical frequency variation, are discussed. Large-scale counter-rotating streamwise phase-averaged vortices in the lee wake are likewise demonstrated via numerical flow visualization. These features are linked to scour around a vertical pile in a steady current. PMID:25512595
International Nuclear Information System (INIS)
Magnetohydrodynamic (MHD) fully developed flow of a viscous incompressible electrically conducting fluid in a vertical channel during combined convection, with asymmetric heating of the wall, under the influence of a constant pressure gradient and in the presence of an uniform transverse magnetic field, is studied. Exact solution of the governing equation is obtained in a closed form. The solution in a dimensionless form contains two pertinent flow parameters, viz. M (the Hartmann number) and Gr (the Grashof number). The limiting cases of a MHD forced and free convection are analysed, what has not been done earlier in the literature. The occurrence of flow reversal indicates that there arises a flow reversal at the cold wall when rT=1 while, for rT<1, no flow reversal is possible in the absence of magnetic forces. (author)
Flow reversal and heat transfer of fully developed mixed convection in vertical channels
Cheng, Chin-Hsiang; Kou, Hong-Sen; Huang, Wen-Hsiung
1990-07-01
The present analysis is concerned with flow reversal phenomena and heat transfer characteristics of the fully developed laminar combined free and forced convection in the heated vertical channels. Three fundamental combinations of thermal boundary conditions on the respective wall surface (namely isoflux-isoflux, isoflux-isothermal, and isothermal-isothermal) are considered separately so as to investigate extensively their distinct influence on the flow pattern. Results of the velocity distribution and temperature distribution as well as the Nusselt number in terms of bulk mean temperature are carried out. Based on the analytical solutions obtained, flow reversal adjacent to the relatively colder wall is found to exist within the channel as Re/Gr is below a threshold value related to the thermal boundary conditions. Parameter zones for the occurrence of reversed flow are presented. Comparisons and verification are made using the existing numerical solutions at locations far downstream of developing flow.
Performance Enhancement of a Full-Scale Vertical Tail Model Equipped with Active Flow Control
Whalen, Edward A.; Lacy, Douglas; Lin, John C.; Andino, Marlyn Y.; Washburn, Anthony E.; Graff, Emilio; Wygnanski, Israel J.
2015-01-01
This paper describes wind tunnel test results from a joint NASA/Boeing research effort to advance active flow control (AFC) technology to enhance aerodynamic efficiency. A full-scale Boeing 757 vertical tail model equipped with sweeping jet actuators was tested at the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel (40x80) at NASA Ames Research Center. The model was tested at a nominal airspeed of 100 knots and across rudder deflections and sideslip angles that covered the vertical tail flight envelope. A successful demonstration of AFC-enhanced vertical tail technology was achieved. A 31- actuator configuration significantly increased side force (by greater than 20%) at a maximum rudder deflection of 30deg. The successful demonstration of this application has cleared the way for a flight demonstration on the Boeing 757 ecoDemonstrator in 2015.
Experimental and Numerical analysis of impingement flow on a vertical flat plate
International Nuclear Information System (INIS)
The direct Vessel Injection (DVI) into the downcomer is one of the major design features of the Korean Next Generation Reactor (KNGR) Emergency Core Cooling System (ECCS). For this type of the ECCS, however, the patterns and thickness of flow in the downcomer during a loss-of-coolant accident (LOCA) have not yet been fully investigated. Also, the experimental and analytical studies on the hydraulic phenomena are not complete enough to allow for detailed design of the system. One of the important phenomena is the impingement by the ECC injection flow. to investigate the behavior of flow such as the impingement, it was necessary to first understand the injected flow motion on a vertical flat wall with well-defined boundary conditions. The experiment was conducted using two flat acryl plates. The conductance method was used to measure the flow width and thickness. According to the distance between the sensor and the flow film, the resistance changes rapidly. In this experiment, we measured the flow width and the film thickness. Results of the measurements are easily understandable. The flow width increases downstream. As the injection velocity increases, so does the flow width. The outer boundary of the fluid flow is thick. Also, the faster the injection velocity, the larger the flow width and the smaller the average film thickness. In an effort to understand the impingement flow characteristics observed from the test CFX4.2, which is a three-dimensional hydrodynamic analysis code, was utilized to analyze the hydraulic behavior relevant to the flat plate flow pattern. In reactor applications, flows from the four DVI lines may get in touch with one another, and thicken to interfere with upcoming steam to the extent the flooding characteristics in the downcomer may change. Experimental and numerical results shed light on the thickness of the DVI film flow, which is pivotal in determining the amount of ECC bypass due to flooding. (author)
Directory of Open Access Journals (Sweden)
Mahmood A.
2012-01-01
Full Text Available The velocity field and the associated shear stress corresponding to the torsional oscillatory flow of a fractional Oldroyd-B fluid, also called generalized Oldroyd-B fluid (GOF, between two infinite coaxial circular cylinders, are determined by means of the Laplace and Hankel transforms. Initially, the fluid and cylinders are at rest and after some time both cylinders suddenly begin to oscillate around their common axis with different angular frequencies of their velocities. The exact analytic solutions of the velocity field and associated shear stress, that have been obtained, are presented under integral and series forms in terms of generalized G and R functions. Moreover, these solutions satisfy the governing differential equation and all imposed initial and boundary conditions. The respective solutions for the motion between the cylinders, when one of them is at rest, can be obtained from our general solutions. Furthermore, the corresponding solutions for the similar flow of classical Oldroyd-B, generalized Maxwell, classical Maxwell, generalized second grade, classical second grade and Newtonian fluids are also obtained as limiting cases of our general solutions.
A VERTICAL 2D MATHEMATICAL MODEL FOR HYDRODYNAMIC FLOWS WITH FREE SURFACE IN σ COORDINATE
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Numerical models with hydrostatic pressure have been widely utilized in studying flows in rivers, estuaries and coastal areas. The hydrostatic assumption is valid for the large-scale surface flows where the vertical acceleration can be ignored, but for some particular cases the hydrodynamic pressure is important. In this paper, a vertical 2D mathematical model with non-hydrostatic pressure was implemented in the σ coordinate. A fractional step method was used to enable the pressure to be decomposed into hydrostatic and hydrodynamic components and the predictor-corrector approach was applied to integration in time domain. Finally, several computational cases were studied to validate the importance of contributions of the hydrodynamic pressure.
Free convection gas flow near a vertical porous plate with heat sources/sinks
Energy Technology Data Exchange (ETDEWEB)
Toki, C.J. [Technological Educational Inst. of Ionian Islands, Zakynthos (Greece). Dept. of Ecology and Environment
2009-11-15
In this work, we study the two dimensional free-convection boundary-layer gas flow of a viscous and incompressible fluid near a moving porous, infinite and vertical plate (or wall) in the presence of heat sources/sinks. Exact solution of this problem is found with the help of Laplace transform technique. Analytical expressions of this solution for velocity, temperature, skin-friction, and rate of heat transfer have been developed. The corresponding expressions for nonporous plate are discussed. The derived results are also discussed in details with the help of graphs for vertical air flows, in order to observe the effects of various governing parameters, such as the heat source/sink parameter. Furthermore, a comparison between the results obtained for porous plate and nonporous plate is illustrated in these graphs. (orig.)
Counter-current flow limitation at lower ends of vertical pipes
International Nuclear Information System (INIS)
Experiments on counter-current flow limitation (CCFL) in a vertical pipe with a round upper end and a sharp lower end are carried out to understand flow patterns under CCFL conditions and to investigate effects of pipe length and water level in an upper tank on CCFL characteristics. As a result, the following conclusions are obtained: (1) CCFL occurs at the lower end of the vertical pipe when the pipe length is more than 10 times as large as the pipe diameter, D, and the water level in the upper tank is more than 15 times as large as D. (2) CCFL data measured by Bharathan et al. and the correlation proposed by Zapke and Kroger agree rather well with the present data within their experimental ranges. (3) When CCFL occurs at the lower end of the pipe, CCFL characteristics do not depend on pipe length and water level in the upper tank. (author)
An Empirical Method for Fast Prediction of Rarefied Flow Field around a Vertical Plate
He, Tao; Wang, Jiang-Feng
2016-06-01
Numerical study is conducted to investigate the effects of free-stream Knudsen (Kn) number on rarefied flow field around a vertical plate employing an unstructured DSMC method, and an empirical method for fast prediction of flow-field structure at different Kn numbers in a given inflow velocity is proposed. First, the flow at a velocity 7500m/s is simulated using a perfect-gas model with free-stream Kn changing from 0.035 to 13.36. The flow-field characteristics in these cases with varying Kn numbers are analyzed and a linear-expansion phenomenon as a function of the square of Kn is discovered. An empirical method is proposed for fast flow-field prediction at different Kn based on the least-square-fitting method. Further, the effects of chemical reactions on flow field are investigated to verify the applicability of the empirical method in the real gas conditions. Three of the cases in perfect-gas flow are simulated again by introducing five-species air chemical module. The flow properties with and without chemical reactions are compared. In the end, the variation of chemical-reaction flow field as a function of Kn is analyzed and it is shown that the empirical method are also suitable when considering chemical reactions.
KORKUSUZ, E. Asuman
2004-01-01
To foster the practical development of the constructed wetlands used for water quality enhancement in Turkey, 2 vertical subsurface flow pilot-scale constructed wetlands were implemented on the METU campus, Ankara, Turkey. Both of the wetlands were planted with Phragmites australis and operated identically at a flowrate of 3 m3.d-1 and a hydraulic loading rate (HLR) of 0.100 m.d {-1}, intermittently. The main objective of the research was to quantify the effect of different substrate...
Energy Technology Data Exchange (ETDEWEB)
Ishak, Anuar; Nazar, Roslinda [School of Mathematical Sciences, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor (Malaysia); Pop, Ioan [Faculty of Mathematics, University of Cluj, R-3400 Cluj, CP 253 (Romania)
2008-07-01
The steady mixed convection boundary layer flow through a stable stratified medium adjacent to a vertical surface is investigated. The velocity outside the boundary layer and the surface temperature are assumed to vary linearly from the leading edge of the surface. The transformed ordinary differential equations are solved numerically by the Keller-box method. It is found that dual solutions exist, and the thermal stratification delays the boundary layer separation. (author)
Stagnation-Point Flow towards a Stretching Vertical Sheet with Slip Effects
Khairy Zaimi; Anuar Ishak
2016-01-01
The effects of partial slip on stagnation-point flow and heat transfer due to a stretching vertical sheet is investigated. Using a similarity transformation, the governing partial differential equations are reduced into a system of nonlinear ordinary differential equations. The resulting equations are solved numerically using a shooting method. The effect of slip and buoyancy parameters on the velocity, temperature, skin friction coefficient and the local Nusselt number are graphically presen...
Chamkha, AJ; Takhar, HS; G. Nath
2004-01-01
An analysis is carried out to study the effects of localized heating (cooling), suction (injection), buoyancy forces and magnetic field for the mixed convection flow on a heated vertical plate. The localized heating or cooling introduces a finite discontinuity in the mathematical formulation of the problem and increases its complexity. In order to overcome this difficulty, a non-uniform distribution of wall temperature is taken at finite sections of the plate. The nonlinear coupled parabolic ...
Steady free convection MHD flow past a vertical porous moving surface
International Nuclear Information System (INIS)
Steady free convection flow of an electrically conducting fluid past a vertical porous moving surface in the presence of constant suction and a source/sink is investigated. The governing set of coupled differential equations is solved by the regular perturbation technique. Velocity and temperature distributions are derived, discussed numerically and shown through graphs. Skin-friction and Nusselt number at the surface are derived and their values are presented. (author)
International Nuclear Information System (INIS)
The rhizosphere is the most active zone in treatment wetlands where take place physicochemical and biological processes between the substrate, plants, microorganisms, and contaminants. Microorganisms play the key role in the mineralisation of organic matter. substrate respiration and phosphatase activities (acid and alkaline) were chosen as indicators of microbial activities, and studied in a vertical-flow wetland system receiving sewage sludge with high organic loads under the Mediterranean climate. (Author)
Heat transfer coefficient determination for flow boiling in vertical and horizontal minichannels
Piasecka Magdalena; Maciejewska Beata
2014-01-01
The paper presents the results of boiling heat transfer research during FC-72 laminar flow along a minichannel of 1 mm depth, positioned vertically and horizontally, with an enhanced heating surface. One glass pane allows to determine the temperature of the heating wall by liquid crystal thermography. Calculations are aimed at the evaluation of one- and two-dimensional heat transfer approaches to determine the local heat transfer coefficient. In the one-dimensional approach only the direction...
An integrated model of substrate clogging in vertical flow constructed wetlands
Hua, G. F.; Li, L.; Zhao, Y. Q.; et al.
2013-01-01
This paper presents an integrated model of substrate clogging in a vertical flow constructed wetland (VFCW). The model simulates the reduction of pore space in the wetland substrate due to combined influences of various physical, biogeochemical and plant-related processes. A series of experiments based on laboratory-scale VFCWs were conducted to examine and measure key parameters related to clogging of the wetland substrate during operation under different conditions. The model was then valid...
Chandrakala P.; Narayana P.
2014-01-01
The effects of thermal radiation on a flow past an impulsively started infinite vertical plate in the presence of a magnetic field have been studied. The fluid considered is a gray, absorbing-emitting radiation but non-scattering medium. The dimensionless governing equations are solved by an efficient, more accurate, unconditionally stable and fast converging implicit scheme. The effects of velocity and temperature for different parameters such as the thermal radiation, magnetic field, Schmid...
Torrens, A.; Molle, P.; Boutin, B.; Salgot, M.
2007-01-01
Removal of fecal coliforms, E. coli, somatic coliphages and F-specific bacteriophages was monitored over a period of two years in 2 Vertical Flow Constructed Wetlands (VFCWs) and 4 Intermittent Sand Filters (ISFs) treating pond effluent. Tracing tests (NaCl) were performed to estimate the filters Hydraulic Retention Time (HRT). The role of Phragmites australis on the removal of the pathogen indicators was investigated. The influence of media characteristics (depth, type of sand), hydraulic do...
An approximate symbolic solution for convective instability flows in vertical cylindrical tubes
International Nuclear Information System (INIS)
The convective flow in vertical cylindrical tubes is investigated and a new formula for its velocity is derived. The Ostroumov problem is briefly discussed, and the relevant fourth-order ordinary differential equation referring to this problem is solved directly in its complete form and within a frame of an allowed simplification, as well. The result obtained for the velocity function is in good qualitative agreement with earlier simulation calculations
An approximate symbolic solution for convective instability flows in vertical cylindrical tubes
Energy Technology Data Exchange (ETDEWEB)
Kirschner, I [Institute of Physics, Roland Eoetvoes University, Pazmany Peter-setany 1 A, Budapest H-1117 (Hungary); Balint, A [Department of Chemistry and Biochemistry, Szent Istvan University, Pater Ku1, Goedoello H-2103 (Hungary); Csikja, R [Department of Analysis, Institute of Mathematics, Budapest University of Technology and Economics, Egry Ju1, Budapest H -1521 (Hungary); Gyarmati, B [Department of Chemistry and Biochemistry, Szent Istvan University, Pater Ku1, Goedoello H-2103 (Hungary); Balogh, A [Institute of Physics, Roland Eoetvoes University, Pazmany Peter-setany 1 A, Budapest H-1117 (Hungary); Meszaros, Cs [Department of Physics and Process Control, Szent Istvan University, Pater K.u.1., Goedoello H-2103 (Hungary)
2007-08-03
The convective flow in vertical cylindrical tubes is investigated and a new formula for its velocity is derived. The Ostroumov problem is briefly discussed, and the relevant fourth-order ordinary differential equation referring to this problem is solved directly in its complete form and within a frame of an allowed simplification, as well. The result obtained for the velocity function is in good qualitative agreement with earlier simulation calculations.
Indian Academy of Sciences (India)
Rudra Kanta Deka; Ashish Paul
2013-10-01
An analysis is performed to study the unsteady, incompressible, one-dimensional, free convective flow over an infinite moving vertical cylinder under combined buoyancy effects of heat and mass transfer with thermal and mass stratifications. Laplace transform technique is adopted for finding solutions for velocity, temperature and concentration with unit Prandtl and Schmidt numbers. Solutions of unsteady state for larger times are compared with the solutions of steady state. Velocity, temperature and concentration profiles are analysed for various sets of physical parameters. Skin friction, Nusselt number and Sherwood number are shown graphically. It has been found that the thermal as well as mass stratification affects the flow appreciably.
Institute of Scientific and Technical Information of China (English)
Sohail Nadeem; Safia Akram
2011-01-01
In the present paper we discuss the magnetohydrodynamic (MHD) peristaltic flow of a hyperbolic tangent fluid model in a vertical asymmetric channel under a zero Reynolds number and long wavelength approximation. Exact solution of the temperature equation in the absence of dissipation term has been computed and the analytical expression for stream function and axial pressure gradient are established. The flow is analyzed in a wave frame of reference moving with the velocity of wave. The expression for pressure rise has been computed numerically. The physical features of pertinent parameters are analyzed by plotting graphs and discussed in detail.
A mathematical model for flow of gas-liquid mixture in a vertical pipe
Dirdal, Inger Karin
2015-01-01
A one-dimensional mathematical model for the ascend velocity to a Taylor bubble consisting of gas in a two-phase flow of gas and liquid in vertical pipes is derived. This model illustrates different effects of two-phase flow in pipes from a numerical approach. The model is based on the conservation laws of mass and momentum for an initial gas slug located on the closed of bottom in a pipe which is filled with stagnant liquid. The model is investigated at laboratory scale where assumpt...
Radiation and chemical reaction effects on MHD flow along a moving vertical porous plate
Ramana Reddy, G. V.; Bhaskar Reddy, N.; Gorla, R. S. R.
2016-02-01
This paper presents an analysis of the effects of magnetohydrodynamic force and buoyancy on convective heat and mass transfer flow past a moving vertical porous plate in the presence of thermal radiation and chemical reaction. The governing partial differential equations are reduced to a system of self-similar equations using the similarity transformations. The resultant equations are then solved numerically using the fourth order Runge-Kutta method along with the shooting technique. The results are obtained for the velocity, temperature, concentration, skin-friction, Nusselt number and Sherwood number. The effects of various parameters on flow variables are illustrated graphically, and the physical aspects of the problem are discussed.
Numerical investigation of flow and scour around a vertical circular cylinder
DEFF Research Database (Denmark)
Baykal, Cüneyt; Sumer, B. Mutlu; Fuhrman, David R.;
2015-01-01
Flow and scour around a vertical cylinder exposed to current are investigated by using a three-dimensional numerical model based on incompressible Reynoldsaveraged Navier–Stokes equations. The model incorporates (i) k-ω turbulence closure, (ii) vortexshedding processes, (iii) sediment transport...... (both bed and suspended load), as well as (iv) bed morphology. The influence of vortex shedding and suspended load on the scour are specifically investigated. For the selected geometry and flow conditions, it is found that the equilibrium scour depth is decreased by 50% when the suspended sediment...
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
Vertical flow constructed wetlands is a typical ecological sanitation system for sewage treatment. The removal rates for COD, BOD5, SS, TN, and TP were 60%, 80%, 74%, 49% and 79%, respectively, when septic tank effluent was treated by vertical flow filter. So the concentration of COD and BOD5 in the treated effluent could meet the quality standard for irrigation water. After that the treated effluent was used for hydroponic cultivation of water spinach and romaine lettuce, the removal efficiencies of the whole system for COD, BOD5, SS, TN and TP were 71.4%, 97.5%, 96.9%, 86.3%, and 87.4%, respectively. And it could meet the integrated wastewater discharge standard for secondary biological treatment plant. It was found that using treated effluent for hydroponic cultivation of vegetables could reduce the nitrate content in vegetables. The removal rates for total bacteria and coliform index by using vertical flow bed system with cinder substrate were 80%-90% and 85%-96%, respectively.
Research on the hydraulic turbine vertical vibration power flow in the head cover system
International Nuclear Information System (INIS)
On the basis of the prior models about the vertical vibration of the hydraulic vibration source, this research introduced a sub-system—head cover. Head cover is one of the main paths when vibration is transferred from the water vibration source to the stable structure. This essay aims to analyze the hydraulic turbine vertical vibration power flow in the head cover system. The research is based on the power flow theory and the probability perturbation method; meanwhile, it considered on the reciprocal coupling effect of the water machine parts and power house structure, etc. Therefore, the results of can clearly provide the random power flow of the vibration transfer path system, which including the head cover system, in frequency domain by given of some uncertain factors in one project. In conclusions, the research provide an overall analysis on the hydropower station vertical vibration transfer path; and it suggest some simplified and efficient solutions in the analysis on the vibration path with some random parameters.
A formulation for vertically integrated groundwater flow in a stratified coastal aquifer
Strack, O. D. L.; Ausk, B. K.
2015-08-01
We present the comprehensive discharge potential for steady three-dimensional flow in horizontally stratified coastal aquifers with a horizontal base and a vertical coastline. The gradient of this comprehensive potential gives the vertically integrated discharge throughout the aquifer, i.e., the specific discharge vector as a function of three-dimensional space integrated over the saturated portion of the aquifer. The boundary values of the comprehensive potential along the coast can be computed precisely, given the geometry of the aquifer: the hydraulic conductivities of the strata, the elevations of the horizontal planes that separate the strata, and the elevation of the impermeable base of the aquifer relative to sea level. Boundary conditions of the comprehensive potential may either be given in terms of its gradient, or computed from given heads along the boundaries. The governing equation of the comprehensive potential is the Poisson equation in areas of infiltration and the Laplace equation elsewhere. The computation of interface elevations, piezometric heads, and the vertical distribution of flow requires that an assumption be made regarding the relation between the comprehensive potential and piezometric heads. We adopt the Dupuit-Forchheimer approximation for this purpose and make use of the Ghyben-Herzberg equation. We present several applications of the approach and find that the stratification may have a significant effect on the boundary value of the comprehensive potential, and thus on the flow rates in the aquifer.
Weidman, P. D.; Kubitschek, J. P.; Medina, A.
2008-11-01
The stability of viscous rotating liquid columns and their application to rotating viscous liquid jets aligned under gravity is reviewed. Experiments on stable viscous fluid flow discharged from rotating vertical pipes exhibit very weak contraction. We present an elementary liquid jet analysis to understand this phenomenon. Indeed, our inviscid model of a slender rotating inviscid liquid jet shows that rotation suppresses contraction. Next we study the comparable problem for granular flow. Our model for noncohesive granular flow emanating from a vertical pipe rotating about its central axis, valid for sufficiently large rotation rate, shows that the granular profiles blossom rather than contract. The profiles of both the liquid and granular jets depend on the same dimensionless parameters—an exit Froude number Fr0 and an exit swirl parameter χ0. The limitations of both models are discussed. Experimental data for granular jet profiles compare well with the collision-free granular flow model in its range of applicability. A criterion for the rotation rate at which particles adjacent to the inner wall of the rotating pipe cease to flow is also given and compared to experiment.
Jaluria, Yogesh; Tamm, Gunnar Olavi
2014-11-01
An experimental investigation was conducted to study buoyancy and pressure induced flow of hot gases in vertical shafts to model smoke propagation in elevator and ventilation shafts of high rise building fires. Various configurations were tested with regard to natural and forced ventilation imposed at the upper and lower surfaces of the vertical shaft. The aspect ratio was taken at a typical value of 6. From a lower vent, the inlet conditions for smoke and hot gases were varied in terms of the Reynolds and Grashof numbers. The forced ventilation at the upper or lower boundary was of the same order as the bulk shaft flow. Measurements were taken within the shaft to allow a detailed study of the steady state flow and thermal fields established for various shaft configurations and inlet conditions, from which optimal means for smoke alleviation in high rise building fires may be developed. Results indicated a wall plume as the primary transport mechanism for smoke propagating from the inlet towards the exhaust region. Recirculation and entrainment dominated at high inlet Grashof number flows, while increased inlet Reynolds numbers allowed greater mixing in the shaft. The development and stability of these flow patterns and their effects on the smoke behavior were assessed for several shaft configurations with different inlet conditions. The comparisons indicated that the fastest smoke removal and lowest overall shaft temperatures occur for a configuration with natural ventilation at the top surface and forced ventilation up from the shaft bottom.
Two-phase distribution in the vertical flow line of a domestic wet central heating system
Directory of Open Access Journals (Sweden)
Ge Y.T.
2013-04-01
Full Text Available The theoretical and experimental aspects of bubble distribution in bubbly two-phase flow are reviewed in the context of the micro bubbles present in a domestic gas fired wet central heating system. The latter systems are mostly operated through the circulation of heated standard tap water through a closed loop circuit which often results in water supersaturated with dissolved air. This leads to micro bubble nucleation at the primary heat exchanger wall, followed by detachment along the flow. Consequently, a bubbly two-phase flow characterises the flow line of such systems. The two-phase distribution across the vertical and horizontal pipes was measured through a consideration of the volumetric void fraction, quantified through photographic techniques. The bubble distribution in the vertical pipe in down flow conditions was measured to be quasi homogenous across the pipe section with a negligible reduction in the void fraction at close proximity to the pipe wall. Such a reduction was more evident at lower bulk fluid velocities.
Numerical Simulation of Cavitating Flow of Liquid Helium in a Vertical Converging-Diverging Nozzle
Ishimoto, J.; Kamijo, K.
2004-06-01
The basic characteristics of the two-dimensional cavitating flow of liquid helium through a vertical converging-diverging nozzle near the lambda point are numerically investigated to realize the further development and high performance of new multiphase He II cooling systems. First, the governing equations of the cavitating flow of liquid helium based on the unsteady thermal nonequilibrium multi-fluid model with generalized curvilinear coordinates system are presented, and several multiphase flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the cavitating flow of liquid helium though a vertical converging-diverging nozzle is shown in detail, and it is also found that the generation of superfluid counterflow against normal fluid flow based on the thermomechanical effect is conspicuous in the large gas phase volume fraction region where the liquid to gas phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase.
Numerical Simulation of Cavitating Flow of Liquid Helium in a Vertical Converging-Diverging Nozzle
International Nuclear Information System (INIS)
The basic characteristics of the two-dimensional cavitating flow of liquid helium through a vertical converging-diverging nozzle near the lambda point are numerically investigated to realize the further development and high performance of new multiphase He II cooling systems. First, the governing equations of the cavitating flow of liquid helium based on the unsteady thermal nonequilibrium multi-fluid model with generalized curvilinear coordinates system are presented, and several multiphase flow characteristics are numerically calculated, taking into account the effect of superfluidity. Based on the numerical results, the two-dimensional structure of the cavitating flow of liquid helium though a vertical converging-diverging nozzle is shown in detail, and it is also found that the generation of superfluid counterflow against normal fluid flow based on the thermomechanical effect is conspicuous in the large gas phase volume fraction region where the liquid to gas phase change actively occurs. Furthermore, it is clarified that the mechanism of the He I to He II phase transition caused by the temperature decrease is due to the deprivation of latent heat for vaporization from the liquid phase
Chaotic Recurrence Analysis of Oil-Gas-Water Three-phase Flow in Vertical Upward Pipe
Directory of Open Access Journals (Sweden)
Ling-Fu Kong
2011-01-01
Full Text Available In this study, the conductance fluctuating signals of oil/gas/water were analyzed by using nonlinear chaotic recurrence, were obtained four kinds of recurrence quantification indicator, recurrence rate, determinism, average length of diagonal segment, entropy which got the transition law of the oil/gas/water three-phase flow patterns in vertical upward pipe. Specific process was: Firstly the C-C algorithm was used to determine phase space embedding dimension and time delay of nonlinear time series, then the method of using the time series data generated by the Lorenz equation to verify the sensitivity of recurrence quantification analysis was presented, finally the chaotic recurrence analysis method was used to identify three-phase flow patterns. The results show that: the texture of chaotic recurrence plot can reflect the oil/gas/water three-phase flow pattern evolution, the recurrence quantification indicator with the phase flow are more sensitive.
Study on the characteristics of counter-current flow in a vertical pipe
International Nuclear Information System (INIS)
Counter-current flow limitation (CCFL) is one of the most important phenomena in loss of coolant accident of nuclear reactors, because the CCFL restricts the amount of the falling water flow rate for core cooling. On the other hand, 'Concept of minimum pressure energy consumption rate' was proposed to predict the characteristics of two-phase flow. In the present study, the CCFL experiment were performed with air-water in a vertical pipe in order to establish the simultaneous database of flow rates, differential pressure and liquid film thickness at CCFL. The wall and the interfacial friction factors were estimated from the database obtained. The calculations with the concept of the minimum pressure energy consumption rate were used to predict the characteristics of the CCFL in a pipe. The calculated results reasonably agreed with the experimental data. The result indicates that the concept is applicable for the prediction of CCFL in a pipe. (author)
Annular pancreas is an abnormal ring or collar of pancreatic tissue that encircles the duodenum (the part of the ... intestine that connects to stomach). This portion of pancreas can constrict the duodenum and block or impair ...
Energy Technology Data Exchange (ETDEWEB)
Garg, P. [Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee 247 667 (India); Picardo, J. R.; Pushpavanam, S., E-mail: spush@iitm.ac.in [Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai 600 036 (India)
2014-07-15
In this work, we investigate the fully developed flow field of two vertically stratified fluids (one phase flowing above the other) in a curved channel of rectangular cross section. The domain perturbation technique is applied to obtain an analytical solution in the asymptotic limit of low Reynolds numbers and small curvature ratios (the ratio of the width of the channel to its radius of curvature). The accuracy of this solution is verified by comparison with numerical simulations of the nonlinear equations. The flow is characterized by helical vortices within each fluid, which are driven by centrifugal forces. The number of vortices and their direction of circulation varies with the parameters of the system (the volume fraction, viscosity ratio, and Reynolds numbers). We identify nine distinct flow patterns and organize the parameter space into corresponding flow regimes. We show that the fully developed interface between the fluids is not horizontal, in general, but is deformed by normal stresses associated with the circulatory flow. The results are especially significant for flows in microchannels, where the Reynolds numbers are small. The mathematical results in this paper include an analytical solution to two coupled biharmonic partial differential equations; these equations arise in two-phase, two-dimensional Stokes flows.
Turbulence kinetic energy budget in bubbly flows in a vertical duct
Energy Technology Data Exchange (ETDEWEB)
Hosokawa, Shigeo; Suzuki, Takashi; Tomiyama, Akio [Graduate School of Engineering, Kobe University, Department of Mechanical Engineering, Kobe, Hyogo (Japan)
2012-03-15
Understanding turbulence kinetic energy (TKE) budget in gas-liquid two-phase bubbly flows is indispensable to develop and improve turbulence models for the bubbly flows. In this study, a molecular tagging velocimetry based on photobleaching reaction was applied to turbulent bubbly flows with sub-millimeter bubbles in a vertical square duct to examine the applicability of the k-{epsilon} models to the bubbly flows. Effects of bubbles on TKE budget are discussed and a priori tests of the standard and low Reynolds number k-{epsilon} models are carried out to examine the applicability of these models to the bubbly flows. The conclusions obtained are as follows: (1) The photobleaching molecular tagging velocimetry is of use for validating turbulence models. (2) The bubbles increase the liquid velocity gradient in the near wall region, and therefore, enhance the production and dissipation rates of TKE. (3) The k-{epsilon} models can reasonably evaluate the production rate of TKE in the bubbly flows. (4) The modulations of diffusion due to the bubbles have different characteristics from the diffusion enhancement due to shear-induced turbulence. Hence, the k-{epsilon} models fail in evaluating the diffusion rate in the near wall region in the bubbly flows. (5) The k-{epsilon} models represent the trends of the production, dissipation, and diffusion rates of {epsilon} in the bubbly flow, although more accurate experimental data are required for quantitative validation of the {epsilon} equation. (orig.)
Obtention of an empirical equation for annular channels
International Nuclear Information System (INIS)
Using a trial circuit, the experimental heat transfer coefficient is determined, in forced convection at one phase only within an annular channel in which water flows ascendantly and for this reason an empirical equation is determined. This work tries to contribute to the understanding of the forced convection phenomena in non tubular geometries like the annular channels. (Author)
Effects of chemical reactions on MHD micropolar fluid flow past a vertical plate in slip-flow regime
Institute of Scientific and Technical Information of China (English)
R.C.Chaudhary; Abhay Kumar Jha
2008-01-01
Heat and mass transfer effects on the unsteady flow of a micropolar fluid through a porous medium bounded by a semi-infinite vertical plate in a slip-flow regime are studied taking into account a homogeneous chemical reaction of the first order.A uniform magnetic field acts perpendicular to the porous surface absorb micropolar fluid with a suction velocity varying with time.The free stream velocity follows an exponentially increasing or decreasing small perturbation law.Using the approximate method,the expressions for the velocity microrotation,temperature,and concentration are obtained.Futher,the results of the skin friction coefficient,the couple stress coefficient,and the rate of heat and mass transfer at the wall are presented with various values of fluid properties and flow conditions.
Gao, Zhong-Ke; Yang, Yu-Xuan; Zhai, Lu-Sheng; Dang, Wei-Dong; Yu, Jia-Liang; Jin, Ning-De
2016-02-01
High water cut and low velocity vertical upward oil-water two-phase flow is a typical complex system with the features of multiscale, unstable and non-homogenous. We first measure local flow information by using distributed conductance sensor and then develop a multivariate multiscale complex network (MMCN) to reveal the dispersed oil-in-water local flow behavior. Specifically, we infer complex networks at different scales from multi-channel measurements for three typical vertical oil-in-water flow patterns. Then we characterize the generated multiscale complex networks in terms of network clustering measure. The results suggest that the clustering coefficient entropy from the MMCN not only allows indicating the oil-in-water flow pattern transition but also enables to probe the dynamical flow behavior governing the transitions of vertical oil-water two-phase flow.
International Nuclear Information System (INIS)
In the framework of a substantial improvement on FBR core safety connected to the development of a new Gen IV reactor type, heterogeneous core with innovative features are being carefully analyzed in France since 2009. At EDF R and D, the main goal is to understand whether a strong reduction of the Na-void worth - possibly attempting a negative value - allows a significant improvement of the core behavior during an unprotected loss of flow accident. Also, the physical behavior of such a core is of interest, before and beyond the (possible) onset of Na boiling. Hence, a cutting-edge heterogeneous design, featuring an annular shape, a Na-plena with a B4C plate and a stepwise modulation of fissile core heights, was developed at EDF by means of the SDDS methodology, with a total Na-void worth of -1 $. The behavior of such a core during the primary phase of a severe accident, initiated by an unprotected loss of flow, is analyzed by means of the SAS-SFR code. This study is carried-out at KIT and EDF, in the framework of a scientific collaboration on innovative FBR severe accident analyses. The results show that the reduction of the Na-void worth is very effective, but is not sufficient alone to avoid Na-boiling and, hence, to prevent the core from entering into the primary phase of a severe accident. Nevertheless, the grace time up to boiling onset is greatly enhanced in comparison to a more traditional homogeneous core design, and only an extremely low fraction of the fuel (<0.1%) enters into melting at the end of this phase. A sensitivity analysis shows that, due to the inherent neutronic characteristics of such a core, the gagging scheme plays a major role on the core behavior: indeed, an improved 4-zones gagging scheme, associated with an enhanced control rod drive line expansion feed-back effect, finally prevents the core from entering into sodium boiling. This major conclusion highlights both the progress already accomplished and the need for more detailed future
CFD Simulation of Annular Centrifugal Extractors
Directory of Open Access Journals (Sweden)
S. Vedantam
2012-01-01
Full Text Available Annular centrifugal extractors (ACE, also called annular centrifugal contactors offer several advantages over the other conventional process equipment such as low hold-up, high process throughput, low residence time, low solvent inventory and high turn down ratio. The equipment provides a very high value of mass transfer coefficient and interfacial area in the annular zone because of the high level of power consumption per unit volume and separation inside the rotor due to the high g of centrifugal field. For the development of rational and reliable design procedures, it is important to understand the flow patterns in the mixer and settler zones. Computational Fluid Dynamics (CFD has played a major role in the constant evolution and improvements of this device. During the past thirty years, a large number of investigators have undertaken CFD simulations. All these publications have been carefully and critically analyzed and a coherent picture of the present status has been presented in this review paper. Initially, review of the single phase studies in the annular region has been presented, followed by the separator region. In continuation, the two-phase CFD simulations involving liquid-liquid and gas-liquid flow in the annular as well as separator regions have been reviewed. Suggestions have been made for the future work for bridging the existing knowledge gaps. In particular, emphasis has been given to the application of CFD simulations for the design of this equipment.
a Mixed-Fractal Flow Model for Stimulated Fractured Vertical Wells in Tight Oil Reservoirs
Su, Yuliang; Sheng, Guanglong; Wang, Wendong; Zhang, Qi; Lu, Mingjing; Ren, Long
2016-02-01
Stimulated reservoir volume (SRV) with large fracture networks can be generated near hydraulic fractured vertical wells (HFVWs) in tight oil reservoirs. Statistics show that natural microfractures and fracture networks stimulated by SRV were self-similar in statistical sense. Currently, various analytical models have been presented to study pressure behaviors of HFVWs in tight oil reservoirs. However, most of the existing models did not take the distribution and self-similarity of fractures into consideration. To account for stimulated characteristic and self-similarity of fractures in tight oil reservoirs, a mixed-fractal flow model was presented. In this model, there are two distinct regions, stimulated region and unstimulated region. Dual-porosity model and single porosity model were used to model stimulated and unstimulated regions, respectively. Fractal geometry is employed to describe fractal permeability and porosity relationship (FPPR) in tight oil reservoirs. Solutions for the mixed-fractal flow model were derived in the Laplace domain and were validated among range of the reservoir parameters. The pressure transient behavior and production rate derivative were used to analyze flow regimes. The type curves show that the fluid flow in HFVWs can be divided into six main flow periods. Finally, effect of fractal parameters and SRV size on flow periods were also discussed. The results show that the SRV size and fractal parameters of fracture network have great effect on the former periods and fractal parameters of matrix mainly influence the later flow periods.
Deb, Arnab; Chakrabarti, Sandip K
2016-01-01
We study time evolution of rotating, axisymmetric, two dimensional inviscid accretion flows around black holes using a grid based finite difference method. We do not use reflection symmetry on the equatorial plane in order to inspect if the disk along with the centrifugal barrier oscillated vertically. In the inviscid limit, we find that the CENtrifugal pressure supported BOundary Layer (CENBOL) is oscillating vertically, more so, when the specific angular momentum is higher. As a result, the rate of outflow produced from the CENBOL, also oscillates. Indeed, the outflow rates in the upper half and the lower half are found to be anti-correlated. We repeat the exercise for a series of specific angular momentum {\\lambda} of the flow in order to demonstrate effects of the centrifugal force on this interesting behaviour. We find that, as predicted in theoretical models of disks in vertical equilibrium, the CENBOL is produced only when the centrifugal force is significant and more specifically, when {\\lambda} > 1.5...
Oxygen profile and clogging in vertical flow sand filters for on-site wastewater treatment.
Petitjean, A; Forquet, N; Boutin, C
2016-04-01
13 million people (about 20% of the population) use on-site wastewater treatment in France. Buried vertical sand filters are often built, especially when the soil permeability is not sufficient for septic tank effluent infiltration in undisturbed soil. Clogging is one of the main problems deteriorating the operation of vertical flow filters for wastewater treatment. The extent of clogging is not easily assessed, especially in buried vertical flow sand filters. We suggest examining two possible ways of detecting early clogging: (1) NH4-N/NO3-N outlet concentration ratio, and (2) oxygen measurement within the porous media. Two pilot-scale filters were equipped with probes for oxygen concentration measurements and samples were taken at different depths for pollutant characterization. Influent and effluent grab-samples were taken three times a week. The systems were operated using batch-feeding of septic tank effluent. Qualitative description of oxygen transfer processes under unclogged and clogged conditions is presented. NH4-N outlet concentration appears to be useless for early clogging detection. However, NO3-N outlet concentration and oxygen content allows us to diagnose the early clogging of the system. PMID:26775157
Vertical velocity of mantle flow of East Asia and adjacent areas
Institute of Scientific and Technical Information of China (English)
CHENG Xianqiong; ZHU Jieshou; CAI Xuelin
2007-01-01
Based on the high-resolution body wave tomo- graphic image and relevant geophysical data, we calculated the form and the vertical and tangential velocities of mantle flow. We obtained the pattern of mantle convection for East Asia and the West Pacific. Some important results and under- standings are gained from the images of the vertical velocity of mantle flow for East Asia and the West Pacific. There is an upwelling plume beneath East Asia and West Pacific, which is the earth's deep origin for the huge rift valley there. We have especially outlined the tectonic features of the South China Sea, which is of the "工" type in the upper mantle shield type in the middle and divergent in the lower; the Siberian clod downwelling dives from the surface to near Core and mantle bounary (CMB), which is convergent in the upper mantle and divergent in the lower mantle; the Tethyan subduction region, centered in the Qinghai-Tibet plateau, is visible from 300 to 2 000 km, which is also convergent in the upper mantle and divergent in the lower mantle. The three regions of mantle convection beneath East Asia and the West Pacific are in accordance with the West Pacific, Ancient Asia and the Tethyan structure regions. The mantle upwelling orig- inates from the core-mantle boundary and mostly occurs in the middle mantle and the lower part of the upper mantle. The velocities of the vertical mantle flow are about 1-4 cm per year and the tangential velocities are 1-10 cm per year. The mantle flow has an effect on controlling the movement of plates and the distributions of ocean ridges, subduction zones and collision zones. The mantle upwelling regions are clearly related with the locations ofhotspots on the earth's surface.
Mixed convective magnetohydrodynamic flow in a vertical channel filled with nanofluids
Directory of Open Access Journals (Sweden)
S. Das
2015-06-01
Full Text Available The fully developed mixed convection flow in a vertical channel filled with nanofluids in the presence of a uniform transverse magnetic field has been studied. Closed form solutions for the fluid temperature, velocity and induced magnetic field are obtained for both the buoyancy-aided and -opposed flows. Three different water-based nanofluids containing copper, aluminium oxide and titanium dioxide are taken into consideration. Effects of the pertinent parameters on the nanofluid temperature, velocity, and induced magnetic field as well as the shear stress and the rate of heat transfer at the channel wall are shown in figures and tables followed by a quantitative discussion. It is found that the magnetic field tends to enhance the nanofluid velocity in the channel. The induced magnetic field vanishes in the cental region of the channel. The critical Rayleigh number at onset of instability of flow is strongly dependent on the volume fraction of nanoparticles and the magnetic field.
Air-water two-phase vertical upward flow regime identification with cross-sectional visualization
International Nuclear Information System (INIS)
The paper presents flow regime identification in two-phase vertical pipe with 30 mm diameter using a high-speed camera and a wire-mesh sensor. In experiments, the wire-mesh sensor which consists of 16x16 wires is installed 2800 mm away from the entrance for capturing the local instantaneous phase distribution, and the high-speed camera which can monitor two-phase flow at the maximum 500,000 fps is set up in order to obtain the axial images at that time. The experimental observations for flow regime identification are compared with existing semi-theoretical model. The comparison results show a good agreement between them. (author)
Institute of Scientific and Technical Information of China (English)
H. P. RANI; G. J. REDDY; C. N. KIM
2013-01-01
The unsteady natural convective couple stress fluid flow over a semi-infinite vertical cylinder is analyzed for the homogeneous first-order chemical reaction effect. The couple stress fluid flow model introduces the length dependent effect based on the material constant and dynamic viscosity. Also, it introduces the biharmonic operator in the Navier-Stokes equations, which is absent in the case of Newtonian fluids. The solution to the time-dependent non-linear and coupled governing equations is carried out with an unconditionally stable Crank-Nicolson type of numerical schemes. Numerical results for the transient flow variables, the average wall shear stress, the Nusselt number, and the Sherwood number are shown graphically for both generative and destructive reactions. The time to reach the temporal maximum increases as the reaction constant K increases. The average values of the wall shear stress and the heat transfer rate decrease as K increases, while increase with the increase in the Sherwood number.
Counter-current flow in a vertical to horizontal tube with obstructions
Energy Technology Data Exchange (ETDEWEB)
Tye, P.; Matuszkiewicz, A.; Teyssedou, A. [Institut de Genie Nucleaire, Quebec (Canada)] [and others
1995-09-01
This paper presents experimental results on counter-current flow and flooding in an elbow between a vertical and a horizontal run. The experimental technique used allowed not only the flooding limit to be determined, but also the entire partial delivery region to be studied as well. The influence that various size orifices placed in the horizontal run have on both the delivered liquid flow rates and on the flooding limits is also examined. It is observed that both the flooding limits and the delivered liquid flow rates decrease with decreasing orifice size. Further, it is also observed that the mechanisms that govern the partial delivery of the liquid are significantly different when an orifice is present in the horizontal leg as compared to the case when no orifice is present.
Scrutiny of mixed convection flow of a nanofluid in a vertical channel
Directory of Open Access Journals (Sweden)
M. Fakour
2014-11-01
Full Text Available The laminar fully developed nanofluid flow and heat transfer in a vertical channel are investigated. By means of a new set of similarity variables, the governing equations are reduced to a set of three coupled equations with an unknown constant, which are solved along with the corresponding boundary conditions and the mass flux conservation relation by the homotopy perturbation method (HPM. We have tried to show reliability and performance of the present method compared with the numerical method (Runge–Kutta fourth-rate to solve this problem. The effects of the Grashof number (Gr, Prandtl number (Pr and Reynolds number (Re on the nanofluid flows are then investigated successively. The effects of the Brownian motion parameter (Nb, the thermophoresis parameter (Nt, and the Lewis number (Le on the temperature and nanoparticle concentration distributions are discussed. The current analysis shows that the nanoparticles can improve the heat transfer characteristics significantly for this flow problem.
Subcooled boiling model to simulate upward vertical flow boiling at low pressures
International Nuclear Information System (INIS)
A new model for upward vertical subcooled flow boiling at low pressure is proposed. The model considers the most relevant closure relationships of one-dimensional thermalhydraulic codes that are important for prediction of vapor contents in the channel: wall evaporation model, condensation model, flow regime transition criterion and drift-flux model. The new model was incorporated in the current version of the thermal-hydraulic computer code RELAP5/MOD3.2.2 Gamma. The modified code was validated against a number of published low-pressure subcooled boiling experiments, and in contrast to the current code, shows good agreement with experimental data. The presented analysis also leads to a better understanding of the basic mechanisms of subcooled flow boiling at low pressure.(author)
Visualization study on the static flow field around a straight-bladed vertical axis wind turbine
Li, Yan; Tagawa, Kotaro
2010-03-01
Visual experiments based on the smoke wire way were carried out on a small model of Straight-blade Vertical Axis Wind Turbine (SB-VAWT) to invest the relationship between the static flow field characteristics and the rotor azimuth angle. The test rotor had 3 blades with NACA0018 aerofoil. The rotor diameter and blade chord were 0.3m and 0.07m, respectively. Visual photos of the static flow path lines in and around the rotor were obtained at every 5 degrees of the azimuth angle. Further, numerical computations of the static flow filed were also carried out for comparison with the same situation as the visual tests and the static torques at different azimuth angles were calculated. According to the results of visual tests and computations, the dependence of the starting performance on the azimuth angle was discussed. The solidity is an important factor affecting the starting performance of the SB-VAWT.
MHD natural convection flow along a vertical wavy surface with heat generation and pressure work
Alim, M. A.; Kabir, K. H.; Andallah, L. S.
2016-07-01
In this paper, the influence of pressure work on MHD natural convection flow of viscous incompressible fluid along a uniformly heated vertical wavy surface with heat generation has been investigated. The governing boundary layer equations are first transformed into a non-dimensional form using suitable set of dimensionless variables. The resulting nonlinear system of partial differential equations are mapped into the domain of a vertical flat plate and then solved numerically employing the implicit finite difference method, known as Keller-box scheme. The numerical results for the velocity profiles, temperature profiles, skin friction coefficient, the rate of heat transfers, the streamlines and the isotherms are shown graphically and skin friction coefficient and rate of heat transfer have been shown in tabular form for different values of the selective set of parameters consisting of pressure work parameter Ge, the magnetic parameter M, Prandtl number Pr, heat generation parameter Q and the amplitude of the wavy surface.
Heat Transfer in MHD Mixed Convection Flow of a Ferrofluid along a Vertical Channel.
Directory of Open Access Journals (Sweden)
Aaiza Gul
Full Text Available This study investigated heat transfer in magnetohydrodynamic (MHD mixed convection flow of ferrofluid along a vertical channel. The channel with non-uniform wall temperatures was taken in a vertical direction with transverse magnetic field. Water with nanoparticles of magnetite (Fe3O4 was selected as a conventional base fluid. In addition, non-magnetic (Al2O3 aluminium oxide nanoparticles were also used. Comparison between magnetic and magnetite nanoparticles were also conducted. Fluid motion was originated due to buoyancy force together with applied pressure gradient. The problem was modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions were obtained for velocity and temperature. Graphical results were plotted and discussed. It was found that temperature and velocity of ferrofluids depend strongly on viscosity and thermal conductivity together with magnetic field. The results of the present study when compared concurred with published work.
Heat Transfer in MHD Mixed Convection Flow of a Ferrofluid along a Vertical Channel.
Gul, Aaiza; Khan, Ilyas; Shafie, Sharidan; Khalid, Asma; Khan, Arshad
2015-01-01
This study investigated heat transfer in magnetohydrodynamic (MHD) mixed convection flow of ferrofluid along a vertical channel. The channel with non-uniform wall temperatures was taken in a vertical direction with transverse magnetic field. Water with nanoparticles of magnetite (Fe3O4) was selected as a conventional base fluid. In addition, non-magnetic (Al2O3) aluminium oxide nanoparticles were also used. Comparison between magnetic and magnetite nanoparticles were also conducted. Fluid motion was originated due to buoyancy force together with applied pressure gradient. The problem was modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions were obtained for velocity and temperature. Graphical results were plotted and discussed. It was found that temperature and velocity of ferrofluids depend strongly on viscosity and thermal conductivity together with magnetic field. The results of the present study when compared concurred with published work. PMID:26550837
International Nuclear Information System (INIS)
Highlights: • 3D CFD of vertical calandria vessel. • Spatial distribution of volumetric heat generation. • Effect of Archimedes number. • Non-dimensional analysis. - Abstract: Three dimensional computational fluid dynamics (CFD) analysis has been performed for the moderator flow and temperature fields inside a vertical calandria vessel of nuclear reactor under normal operating condition using OpenFOAM CFD code. OpenFOAM is validated by comparing the predicted results with the experimental data available in literature. CFD model includes the calandria vessel, calandria tubes, inlet header and outlet header. Analysis has been performed for the cases of uniform and spatial distribution of volumetric heat generation. Studies show that the maximum temperature in moderator is lower in the case of spatial distribution of heat generation as compared to that in the uniform heat generation in calandria. In addition, the effect of Archimedes number on maximum and average moderator temperature was investigated
Energy Technology Data Exchange (ETDEWEB)
Kansal, Anuj Kumar, E-mail: akansal@barc.gov.in [Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Joshi, Jyeshtharaj B., E-mail: jbjoshi@gmail.com [Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094 (India); Maheshwari, Naresh Kumar, E-mail: nmahesh@barc.gov.in [Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Vijayan, Pallippattu Krishnan, E-mail: vijayanp@barc.gov.in [Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India)
2015-06-15
Highlights: • 3D CFD of vertical calandria vessel. • Spatial distribution of volumetric heat generation. • Effect of Archimedes number. • Non-dimensional analysis. - Abstract: Three dimensional computational fluid dynamics (CFD) analysis has been performed for the moderator flow and temperature fields inside a vertical calandria vessel of nuclear reactor under normal operating condition using OpenFOAM CFD code. OpenFOAM is validated by comparing the predicted results with the experimental data available in literature. CFD model includes the calandria vessel, calandria tubes, inlet header and outlet header. Analysis has been performed for the cases of uniform and spatial distribution of volumetric heat generation. Studies show that the maximum temperature in moderator is lower in the case of spatial distribution of heat generation as compared to that in the uniform heat generation in calandria. In addition, the effect of Archimedes number on maximum and average moderator temperature was investigated.
International Nuclear Information System (INIS)
By introducing an additional parameter F0, the processes known hitherto for calculating heat transfer are extended to the heat flux distributions following an exponential law qw = exp(mx) which give a heat transfer coefficient, independent of position for laminar and turbulent flow with a linear pressure drop. For laminar flow along a semi-infinite plate, the heat flux distribution in accordance with the law qw = xm leads to the Nusselt number, regardless of the position. Nu is then determined by the thickness of the thermal boundary layer. For the annular space, the equations for explicit calculation of the temperature field will be given, as well as the Nusselt number in laminar flow and constant heat flux. In turbulent flow, the laws of distribution of eddy diffusivity for momentum in a tube, established by H. Reichardt, adapted for the annular space and the tube bundle, give the velocity field and the coefficient of friction and thus permit solution of the heat transfer equations. The results of the numerical calculation are given in the tables and diagrams for an extended range of the various parameters and compared with the experimental results. A simple process to determine the lower limit of the thermal entry length will be described. (author)
Sea Carousel—A benthic, annular flume
Amos, Carl L.; Grant, J.; Daborn, G. R.; Black, K.
1992-06-01
A benthic annular flume (Sea Carousel) has been developed and tested to measure in situ the erodibility of cohesive sediments. The flume is equipped with three optical backscatter sensors, a lid rotation switch, and an electromagnetic (EM) flow meter capable of detecting azimuthal and vertical components of flow. Data are logged at rates up to 10·66 Hz. Erodibility is inferred from the rate of change in suspended sediment concentration detected in the annulus. The energy-density/wave number spectrum of azimuthal flow showed peaks in the energy spectrum at paddle rotation wave numbers (k) of 14 and 7 m -1 (macroturbulent time scales) but were not significant. Friction velocity ( U*), measured (1) at 1 Hz using a flush-mounted hot-film sensor, and (2) derived from measured velocity profiles in the inner part of the logarithmic layer gave comparable results for Ū* 0·32 m s -1. Radial velocity gradients were proportional to ( Ū y - 0·32 m s -1). Maximum radial differences in U* were 10% for Ū y = 0·5 ms -1. Suspended sediment mass concentration ( S) in the annulus resulted in a significant decrease (10·5%) in Ū* derived by method (1) over the range 0calibration with changes in S. Subaerial deployments of Sea Carousel caused severe substrate disturbance, water losses, and aeration of the annulus. Submarine deployments produced stable results, though dispersion of turbid flume water took place. Results clearly demonstrated the existence of 'Type I' and 'Type II' erosion documented from laboratory studies.
Stability of swirling annular flow
Czech Academy of Sciences Publication Activity Database
Maršík, František; Trávníček, Zdeněk; Novotný, Pavel; Werner, E.
2010-01-01
Roč. 17, č. 3 (2010), s. 267-279. ISSN 1065-3090 R&D Projects: GA AV ČR(CZ) IAA200760801; GA MŠk(CZ) 1M06031 Institutional research plan: CEZ:AV0Z20760514 Keywords : swirling jet * hydrodynamic stability * impinging jet Subject RIV: BK - Fluid Dynamics http://www.begellhouse.com/journals/52b74bd3689ab10b,6bfbd93509947e2e,03fca4e77476857d.html
Vertically integrated models for coupled two-phase flow and geomechanics in porous media
Bjørnarâ, Tore I.; Nordbotten, Jan M.; Park, Joonsang
2016-02-01
Models of reduced dimensionality have been found to be particularly attractive in simulating the fate of injected CO2 in supercritical state in the context of carbon capture and storage. This is motivated by the confluence of three aspects: the strong buoyant segregation of the lighter CO2 phase above water, the relatively long time scales associated with storage, and finally the large aspect ratios that characterize the geometry of typical storage aquifers. However, to date, these models have been confined to considering only the flow problem, as the coupling between reduced dimensionality models for flow and models for geomechanical response has previously not been developed. Herein, we develop a fully coupled, reduced dimension, model for multiphase flow and geomechanics. It is characterized by the aquifer(s) being of lower dimension(s), while the surrounding overburden and underburden being of full dimension. The model allows for general constitutive functions for fluid flow (relative permeability and capillary pressure) and uses the standard Biot coupling between the flow and mechanical equations. The coupled model retains all the simplicities of reduced-dimensional models for flow, including less stiff nonlinear systems of equations (since the upscaled constitutive functions are closer to linear), longer time steps (since the high grid resolution in the vertical direction can be avoided), and less degrees of freedom. We illustrate the applicability of the new coupled model through both a validation study and a practical computational example.
Vertical-flow constructed wetlands treating domestic wastewater contaminated by hydrocarbons.
Al-Isawi, R H K; Sani, A; Almuktar, S A A A N; Scholz, M
2015-01-01
The aim was to compare the impact of different design (aggregate size) and operational (contact time, empty time and chemical oxygen demand (COD) loading) variables on the long-term and seasonal performance of vertical-flow constructed wetland filters operated in tidal flow mode before and after a one-off spill of diesel. Ten different vertical-flow wetland systems were planted with Phragmites australis (Cav.) Trin. ex Steud. (common reed). Approximately 130 g of diesel fuel was poured into four wetland filters. Before the spill, compliance with secondary wastewater treatment standards was achieved by all wetlands regarding ammonia-nitrogen (NH4-N), nitrate-nitrogen (NO₃-N) and suspended solids (SS), and non-compliance was recorded for biochemical oxygen demand and ortho-phosphate-phosphorus (PO₄-P). Higher COD inflow concentrations had a significantly positive impact on the treatment performance for COD, PO₄-P and SS. The wetland with the largest aggregate size had the lowest mean NO₃-N outflow concentration. However, the results were similar regardless of aggregate size and resting time for most variables. Clear seasonal outflow concentration trends were recorded for COD, NH4-N and NO₃-N. No filter clogging was observed. The removal efficiencies dropped for those filters impacted by the diesel spill. The wetlands system shows a good performance regarding total petroleum hydrocarbon (TPH) removal. PMID:25812105
Gas suspension flows of a moderately dense binary mixture of solid particles in vertical tubes
Energy Technology Data Exchange (ETDEWEB)
Zamankhan, P.; Huotari, J. [VTT Energy, Jyvaeskylae (Finland). Combustion and Conversion Lab.
1996-12-01
The turbulent, steady, fully-developed flow of a moderately dense (solid volume faction >>0.001) binary mixture of spherical particles in a gaseous carrier is investigated for the case of flow in a vertical riser. The suspended particles are considered to be in turbulent motion, driven by random aerodynamic forces acting between the particle and the gaseous carrier as well as particle-particle interactive forces. A model is constructed based on the combination of the time-averaged after volume-averaged conservation equations of mass, momentum and mechanical energy of the gas phase in the continuum theory and the corresponding equations for the solid particles obtained using the recently developed Enskog theory for dense multi-component mixtures of slightly inelastic spherical particles. The model properly takes into account the contributions of particle-particle collisions, as well as the fluid-dynamic fluctuating forces on individual particles. To demonstrate the validity of this approach, the fully-developed steady-state mean velocity and concentration distributions of a moderately dense binary mixture of solid particles in a turbulent vertical flow calculated by the present model are compared with available experimental measurements. The results provide a qualitative description of the experimentally observed motion of coarse particles in a fast bed of fine solids. (author)
Heat transfer coefficient determination for flow boiling in vertical and horizontal minichannels
Directory of Open Access Journals (Sweden)
Piasecka Magdalena
2014-03-01
Full Text Available The paper presents the results of boiling heat transfer research during FC-72 laminar flow along a minichannel of 1 mm depth, positioned vertically and horizontally, with an enhanced heating surface. One glass pane allows to determine the temperature of the heating wall by liquid crystal thermography. Calculations are aimed at the evaluation of one- and two-dimensional heat transfer approaches to determine the local heat transfer coefficient. In the one-dimensional approach only the direction of the flow in the channel is considered. In the two-dimensional approach the inverse problem in the heating wall and the direct problem in the glass barrier were solved by the finite element method with Trefftz functions as shape functions (FEMT. The developed flow boiling area was studied. Heat transfer coefficient values obtained for the horizontal minichannel were higher than those obtained for the vertical one. When the heat flux supplied to heating wall grows, the share of gas-phase increases leading to the heat transfer coefficient decreases. The same courses of the experiment were observed for the two applied methods, but the results obtained in the one-dimensional approach are considerably higher than in the two-dimensional one. One-dimensional approach seems to be less sensitive to measurement errors.
Axial and radial void fraction profiles of sub-cooled boiling flow in vertically heated annulus
International Nuclear Information System (INIS)
One of the main challenges in operating this kind of a reactor system are in the complexities of two-phase flow around the rods driven by a vertically distributed heat flux in the rods. This is because the void fraction (vapour fraction) distribution significantly affects the reactor power and is one of the important parameters that determine the heat transfer capability and the possible occurrence of critical heat flux. Knowledge of the time averaged void fraction distribution as well as the velocity profiles of the liquid phase are of great relevance in design of these systems, for providing validation data for thermal-hydraulic CFD codes, as well as for design of nuclear safety systems. In this contribution, measurements for radial void fraction distribution will be reported for a vertical upward flowing sub-cooled boiling flows in an internally heated annulus of a cylinder. The annulus channel consists of an inner electrical-heater rod with a diameter of 25 mm and an outer round pipe with an inner diameter of 75 mm. The design of this unit is as per scale-down rules presented by Situ et al. A schematic of the experimental loop, and a photograph of the setup is shown
Predictions of bubbly flows in vertical pipes using two-fluid models in CFDS-FLOW3D code
Energy Technology Data Exchange (ETDEWEB)
Banas, A.O.; Carver, M.B. [Chalk River Laboratories (Canada); Unrau, D. [Univ. of Toronto (Canada)
1995-09-01
This paper reports the results of a preliminary study exploring the performance of two sets of two-fluid closure relationships applied to the simulation of turbulent air-water bubbly upflows through vertical pipes. Predictions obtained with the default CFDS-FLOW3D model for dispersed flows were compared with the predictions of a new model (based on the work of Lee), and with the experimental data of Liu. The new model, implemented in the CFDS-FLOW3D code, included additional source terms in the {open_quotes}standard{close_quotes} {kappa}-{epsilon} transport equations for the liquid phase, as well as modified model coefficients and wall functions. All simulations were carried out in a 2-D axisymmetric format, collapsing the general multifluid framework of CFDS-FLOW3D to the two-fluid (air-water) case. The newly implemented model consistently improved predictions of radial-velocity profiles of both phases, but failed to accurately reproduce the experimental phase-distribution data. This shortcoming was traced to the neglect of anisotropic effects in the modelling of liquid-phase turbulence. In this sense, the present investigation should be considered as the first step toward the ultimate goal of developing a theoretically sound and universal CFD-type two-fluid model for bubbly flows in channels.
Berman, V.
2014-01-01
The paper presents the results of theoretical and experimental investigations of the pressure gradient for flow of a mixture of large solids particles and water in straight vertical pipelines. The mathematical model of vertical two-phase flow was developed. Based on the developed model and experimental data of the solid particles liquid and liquid relative velocity, the functional dependence of the pressure gradient on the corresponding parameters was derived. This method was generalized ...
Institute of Scientific and Technical Information of China (English)
杨美; 臧新; 周云龙
2016-01-01
Numerical simulation for micro-junction of different branch pipe dip angle was carried out by using the CFD method. The phase split characteristic of slug and annular flow in micro-junction was investigated and the phase volume fraction distribution was analyzed. The results show that Phase separation characteristics of micro channel is influenced by two phase flow upstream flow pattern. Slug priority in the branch current in phase extraction,whereas the annular flow of liquid produced in the branch pipe. Comparison mechanism of Phase Split of Slug and annular Flow in Micro-Junction. when the type inlet flow to annular flow,when the branch pipe dip angle is 60°,after a three-way pipes,continuation of annular flow stability has great advanta-ges,the phase split characteristic is uniformity. when the type inlet flow to slug flow,For the branch pipe dip angle of 20 ° and 30 ° , the quality of separation efficiency difference is less than 5%, causing a lowest quality separation efficiency.%采用计算流体动力学方法，通过改变支管倾角，对微小三通管道模型进行了数值模拟，研究了入口流型为弹状流和环状流时，微小三通管道的相分配特性，分析了管道中气相和液相的体积分数分布规律。结果表明，微通道内的相分离特性受上游两相流流型影响。弹状流气相优先在支管中采出，而环状流的液相优先在支管中采出。对比研究微小三通管弹状流与环状流相分配机理，入口流型为环状流时，支管倾角为60°的管内流动，经过三通管道，延续环状流稳定方面有较大优势，可获得最佳的相均匀分配；入口流型为弹状流时，当支管倾角减小为20°和30°时，两者质量分离效率相差小于5%，质量分离效率最低，可获得最佳的相均匀分配。
Experiences with pre-precipitation of phosphorus in a vertical flow constructed wetland in Austria.
Lauschmann, Robert E; Lechner, Markus; Ertl, Thomas; Langergraber, Guenter
2013-01-01
Using constructed wetlands (CWs) with vertical flow and intermittent loading, high organic matter and ammonium removal can be achieved. In the case of additional requirements for phosphorus removal, which in Austria often occurs if the treated wastewater is discharged into small sensitive receiving waters, additional measures have to be taken. The objective of this work was to investigate the applicability of conventional phosphorus pre-precipitation with sodium aluminate for a CW system. The experiment was carried out at a full-scale CW in Oberwindhag in Lower Austria, a two-stage vertical flow CW with intermittent loading designed for a size of 60 person equivalents (PE). The goal was to reach the required value of 1.6 mg/L PO4-P for the effluent of the system. Prior to the experiments the plant was in operation for 3 years without measures for phosphorus removal. After pre-precipitation with sodium aluminate was activated, three different dosages were investigated. Satisfying results in the preliminary treatment chambers were not obtained until a high dosage (ß = 3.5, i.e. 3.5 times the dose required from stoichiometry) was applied. After an adaptation time of several months the required effluent concentration of 1.6 mg PO4-P/L could be reached and maintained. However, the additional phosphorus pre-precipitation increases the yearly operating costs of a vertical flow CW system significantly, e.g. for 60 and 25 PE, by 15 and 38%, respectively, thus indicating the need for optimizing the dosing of the chemical. PMID:23676407
Directory of Open Access Journals (Sweden)
Olayiwola Oni
2010-08-01
Full Text Available This study reports the simulation technique and the visualisation of the temporal vertical mass flow and leakages in waste layers and gravel bed of a municipal solid waste fill. Visual comparison of the cumulative mass leakage with optimal leachate mass flow in each waste layer enables the negative consequence of seepage of any highly toxic leachate to be mentally comprehended. The impact of the mass leakage appears to be influenced not necessarily by the location of the seepage pore but by its volume, and also distance from the source of the solute contamination. The simulation results necessitate the need for an effective leachate monitoring system within and in the vicinity of a waste landfill. The findings will be of utmost usefulness to the stakeholders of solid waste landfill in both developed and developing countries.
Interfacial area transport of subcooled boiling flow in a vertical annulus
International Nuclear Information System (INIS)
Highlights: • Discussion of boiling and wall nucleation dataset obtained in a vertical annulus. • Overview of the interfacial area transport equation modeling in boiling flow. • Comparison of bubble departure diameter and frequency with existing models. • Evaluation of the interfacial area transport equation prediction in boiling flow. - Abstract: In an effort to improve the prediction of void fraction and heat transfer characteristics in two-phase systems, the two-group interfacial area transport equation has been developed for use with the two-group two-fluid model. The two-group approach treats spherical/distorted bubbles as Group-1 and cap/slug/churn-turbulent bubbles as Group-2. Therefore, the interfacial area transport of steam-water two-phase flow in a vertical annulus has been investigated experimentally, including bulk flow parameters and wall nucleation characteristics. The theoretical modeling of interfacial area transport equation with phase change terms is introduced and discussed along with the experimental results. Benchmark of the interfacial area transport equation is performed considering the effects of bubble interaction mechanisms such as bubble break-up and coalescence, as well as, effects of phase change mechanisms such as wall nucleation and condensation for subcooled boiling. From the benchmark, sensitivity in the constitutive relations for Group-1 phase change mechanisms, such as wall nucleation and condensation is clear. The Group-2 interfacial area transport is shown to be dominated by the interfacial heat transfer mechanism causing expansion of Group-1 bubbles into Group-2 bubbles in the boiling flow
Directory of Open Access Journals (Sweden)
Chandrakala P.
2014-02-01
Full Text Available The effects of thermal radiation on a flow past an impulsively started infinite vertical plate in the presence of a magnetic field have been studied. The fluid considered is a gray, absorbing-emitting radiation but non-scattering medium. The dimensionless governing equations are solved by an efficient, more accurate, unconditionally stable and fast converging implicit scheme. The effects of velocity and temperature for different parameters such as the thermal radiation, magnetic field, Schmidt number, thermal Grashof number and mass Grashof number are studied. It is observed that the velocity decreases in the presence of thermal radiation or a magnetic field
Mixed Convection Flow Adjacent to a Stretching Vertical Sheet in a Nanofluid
Directory of Open Access Journals (Sweden)
Nor Azizah Yacob
2013-01-01
Full Text Available The characteristics of fluid flow and heat transfer over a stretching vertical sheet immersed in a nanofluid are investigated numerically in this paper. Three different types of nanoparticles, namely, copper Cu, alumina Al2O3, and titania TiO2, are considered, using water as the base fluid. It is found that nanofluid with titania nanoparticles has better enhancement on the heat transfer rate compared to copper and alumina nanoparticles. For a particular nanoparticle, increasing the nanoparticle fraction is to reduce the skin friction coefficient and the heat transfer rate at the surface.
Stagnation-Point Flow towards a Stretching Vertical Sheet with Slip Effects
Directory of Open Access Journals (Sweden)
Khairy Zaimi
2016-04-01
Full Text Available The effects of partial slip on stagnation-point flow and heat transfer due to a stretching vertical sheet is investigated. Using a similarity transformation, the governing partial differential equations are reduced into a system of nonlinear ordinary differential equations. The resulting equations are solved numerically using a shooting method. The effect of slip and buoyancy parameters on the velocity, temperature, skin friction coefficient and the local Nusselt number are graphically presented and discussed. It is found that dual solutions exist in a certain range of slip and buoyancy parameters. The skin friction coefficient decreases while the Nusselt number increases as the slip parameter increases.
Mixed-flow vertical tubular hydraulic turbine: determination of proper design duty point
Bergant, Anton; Höfler, Edvard; Širok, Brane
2015-01-01
A new vertical single-regulated mixed-flow turbine with conical guide apparatus and without spiral casing is presented in this paper. Runner blades are fixed to the hub and runner band and resemble to the Francis type runner of extremely high specific speed. Due to lack of information and guidelines for the design of a new turbine, a theoretical model was developed in order to determinate the design duty point, i.e. to determine the optimum narrow operation range of the turbine. It is not nec...
Free Convective MHD Flow Past a Vertical Cone with Variable Heat and Mass Flux
Prakash, J.; S. Gouse Mohiddin; S. Vijaya Kumar Varma
2013-01-01
A numerical study of buoyancy-driven unsteady natural convection boundary layer flow past a vertical cone embedded in a non-Darcian isotropic porous regime with transverse magnetic field applied normal to the surface is considered. The heat and mass flux at the surface of the cone is modeled as a power law according to qwx=xm and qw*(x)=xm, respectively, where x denotes the coordinate along the slant face of the cone. Both Darcian drag and Forchheimer quadratic porous impedance are incorpora...
International Nuclear Information System (INIS)
The combined effects of magnetohydrodynamics and thermal radiations on unsteady flow of an electrically conducting fluid past an impulsively started infinite vertical porous plate with variable temperature is investigated. A magnetic field of uniform strength is applied along an axis perpendicular to the plate. The plate temperature is raised linearly with time. An exact solution is obtained by Laplace transformation technique. The dependence of the amplitude of velocity and skin-friction on various parameters are discussed in detail with the help of graphs. (author)
Transport of waste into caverns by vertical flow of concrete suspensions
International Nuclear Information System (INIS)
The vertical transport of a waste-concrete suspension by gravity without pumps is feasible if a suitable composition of the mixture and a convenient pipe diameter are provided. Then the flow velocity of the suspension n the pipe adjusts corresponding to the pipe diameter, it is much lower than the free-fall velocity. A suitable composition of the mixture must ensure sufficient freedom of movement of the solids, which means the portion of coarser granules (> 400 μm) should not exceed about 50%. This figure should be met in order to allow for the remainder - the fine portion of granules, the cement, water and additives - at least 50%
Masuda, Akira
2011-01-01
Quasi-geostrophic current is expanded in terms of vertical modes such as barotropic and baroclinic ones. Then the evolution of quasi-geostrophic motion is understood from the behavior of each vertical mode. There are some subtle issues, however, as regards vertical modes: boundary conditions, difference between a level model and a layer model, and so on. A comprehensive formulation is given of the expansion of the quasi-geostrophic flows in terms of vertical modes both for a level model and f...
Wind tunnel study of a vertical axis wind turbine in a turbulent boundary layer flow
Rolin, Vincent; Porté-Agel, Fernando
2015-04-01
Vertical axis wind turbines (VAWTs) are in a relatively infant state of development when compared to their cousins the horizontal axis wind turbines. Very few studies have been carried out to characterize the wake flow behind VAWTs, and virtually none to observe the influence of the atmospheric boundary layer. Here we present results from an experiment carried out at the EPFL-WIRE boundary-layer wind tunnel and designed to study the interaction between a turbulent boundary layer flow and a VAWT. Specifically we use stereoscopic particle image velocimetry to observe and quantify the influence of the boundary layer flow on the wake generated by a VAWT, as well as the effect the VAWT has on the boundary layer flow profile downstream. We find that the wake behind the VAWT is strongly asymmetric, due to the varying aerodynamic forces on the blades as they change their position around the rotor. We also find that the wake adds strong turbulence levels to the flow, particularly on the periphery of the wake where vortices and strong velocity gradients are present. The boundary layer is also shown to cause greater momentum to be entrained downwards rather than upwards into the wake.
Maryshev, Boris S; Lyubimova, Tatyana P
2016-06-01
In the present paper we consider slow filtration of a mixture through a close porous filter. The heavy solute penetrates slowly into the porous filter due to the external vertical filtration flow and diffusion. This process is accompanied by the formation of the domain with heavy fluid near the upper boundary of the filter. The developed stratification, at which the heavy fluid is located above the light fluid, is unstable. When the mass of the heavy fluid exceeds the critical value, one can observe the onset of the Rayleigh-Taylor instability. Due to the above peculiarities we can distinguish between two regimes of vertical filtration: 1) homogeneous seepage and 2) convective filtration. When considering the filtration process it is necessary to take into account the diffusion accompanied by the immobilization effect (or sorption) of the solute. The immobilization is described by the linear MIM (mobile/immobile media) model. It has been shown that the immobilization slows down the process of forming the unstable stratification. The purpose of the paper is to find the stability conditions for homogeneous vertical seepage of he solute into the close porous filter. The linear stability problem is solved using the quasi-static approach. The critical times of instability are estimated. The stability maps are plotted in the space of system parameters. The applicability of quasi-static approach is substantiated by direct numerical simulation of the full nonlinear equations. PMID:27349555
Modeling of Air Temperature for Heat Exchange due to Vertical Turbulence and Horizontal Air Flow
Institute of Scientific and Technical Information of China (English)
ZHANG Lei; MENG Qing-lin
2009-01-01
In order to calculate the air temperature of the near surface layer in urban environment,the Sur-face layer air was divided into several layers in the vertical direction,and some energy bakmce equations were de-veloped for each air layer,in which the heat exchange due to vertical turbulence and horizontal air flow was tak-en into account.Then,the vertical temperature distribution of the surface layer air was obtained through the coupled calculation using the energy balance equations of underlying surfaces and building walls.Moreover,the measured air temperatures in a small area (with a horizontal scale of less than 500 m) and a large area (with ahorizontal scale of more than 1000 m) in Guangzhou in summer were used to validate the proposed model.The calculated results agree well with the measured ones,with a maximum relative error of 4.18%.It is thus con-cluded that the proposed model is a high-accuracy method to theoretically analyze the urban heat island and the thermal environment.
The Effect of Gas Kinetics on the Gas-Lift Efficiency for Viscous Oil in Vertical Pipe Flow
Steinbakk, Carina Hoddø
2015-01-01
For heavy oil, artificial lift can be applied to increase and stabilise production flow. How the gas kinetics, i.e. the lift-gas composition will influence this increase is the subject of this thesis and will be described in relation to multiphase flow, pressure drop and pressure-temperature-volume (PVT) -theory. A vertical pipe flow was studied, simulating the pressure drop coupled with the accompanying multiphase flow and PVT-information. The simulations were run in MATLAB, supported by...
Optimum wall conductance ratio in magnetoconvective flow in a long vertical rectangular duct
Energy Technology Data Exchange (ETDEWEB)
Ibanez, Guillermo [Universidad Politecnica de Chiapas, Tuxtla Gutierrez, Chiapas 29010 (Mexico); Cuevas, Sergio [Centro de Investigacion en Energia, Universidad Nacional Autonoma de Mexico, A.P. 34, Temixco, Mor. 62580 (Mexico)
2008-08-15
The entropy generation minimization method is applied to the optimization of a buoyancy-driven laminar magnetohydrodynamic flow in a long vertical rectangular duct with thin conducting or insulating walls. The flow takes place under a strong uniform magnetic field applied transversally to one pair of walls and is driven by a known constant temperature gradient aligned with the field. Numerical solutions for the velocity and electric current density in both fluid and walls are calculated using a spectral collocation method. It is shown that an optimum value of the wall conductance ratio (i.e. the ratio of the electrical conductance of the wall to that of the fluid) that minimizes the global entropy generation rate can be found. The analysis of the irreversibilities caused by heat conduction, viscosity and Joule dissipation allows to explain the existence of the optimum value. (author)
Optimum wall conductance ratio in magneto-convective flow in a long vertical rectangular duct
Energy Technology Data Exchange (ETDEWEB)
Ibanez, G. [Chiapas Univ. Politecnica (Mexico); Cuevas, S. [Mexico Univ. Nacional Autonoma, Centro de Investigacion en Energia (Mexico)
2008-08-15
The entropy generation minimization method is applied to the optimization of a buoyancy-driven laminar magnetohydrodynamic flow in a long vertical rectangular duct with thin conducting or insulating walls. The flow takes place under a strong uniform magnetic field applied transversally to one pair of walls and is driven by a known constant temperature gradient aligned with the field. Numerical solutions for the velocity and electric current density in both fluid and walls are calculated using a spectral collocation method. It is shown that an optimum value of the wall conductance ratio (i.e. the ratio of the electrical conductance of the wall to that of the fluid) that minimizes the global entropy generation rate can be found. The analysis of the irreversibilities caused by heat conduction, viscosity and Joule dissipation allows to explain the existence of the optimum value. (authors)
Optimum wall conductance ratio in magneto-convective flow in a long vertical rectangular duct
International Nuclear Information System (INIS)
The entropy generation minimization method is applied to the optimization of a buoyancy-driven laminar magnetohydrodynamic flow in a long vertical rectangular duct with thin conducting or insulating walls. The flow takes place under a strong uniform magnetic field applied transversally to one pair of walls and is driven by a known constant temperature gradient aligned with the field. Numerical solutions for the velocity and electric current density in both fluid and walls are calculated using a spectral collocation method. It is shown that an optimum value of the wall conductance ratio (i.e. the ratio of the electrical conductance of the wall to that of the fluid) that minimizes the global entropy generation rate can be found. The analysis of the irreversibilities caused by heat conduction, viscosity and Joule dissipation allows to explain the existence of the optimum value. (authors)
Effect of segmental heating on mixed convection aiding flow in a vertical porous annulus
Salman, Ahmed N. J.; Al-Rashed, Abdullah A. A. A.; Kamangar, Sarfaraz; Khan, T. M. Yunus; Khaleed, H. M. T.
2016-06-01
Mixed convection flow in a vertical porous annulus embedded with fluid saturated porous medium for aiding is investigated. The annulus is imposed by 20%, 35% and 50% heater length at the bottom, mid and top sections of the annulus respectively. Darcy law with thermal non-equilibrium approach is considered. The governing partial differential equations are converted to simple algebraic equations using Finite Element Method (FEM). The effects of Peclet number Pe and conductivity ratio Kr on heat transfer and fluid flow behaviour are examined and it is found that for lower conductivity ratio, the heat transfer rate was higher with the increase in the Peclet number Pe, whereas this trend reversed when thermal conductivity ratio Kr is increased.
Hydromagnetic flow and heat transfer adjacent to a stretching vertical sheet in a micropolar fluid
Directory of Open Access Journals (Sweden)
Yacob Nor Azizah
2013-01-01
Full Text Available An analysis is carried out for the steady two-dimensional mixed convection flow adjacent to a stretching vertical sheet immersed in an incompressible electrically conducting micropolar fluid. The stretching velocity and the surface temperature are assumed to vary linearly with the distance from the leading edge. The governing partial differential equations are transformed into a system of ordinary differential equations, which is then solved numerically using a finite difference scheme known as the Keller box method. The effects of magnetic and material parameters on the flow and heat transfer characteristics are discussed. It is found that the magnetic field reduces both the skin friction coefficient and the heat transfer rate at the surface for any given K and λ. Conversely, both of them increase as the material parameter increases for fixed values of M and λ.
Mixed convection boundary layer flow over a vertical cylinder with prescribed surface heat flux
Energy Technology Data Exchange (ETDEWEB)
Ishak, Anuar [School of Mathematical Sciences, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor (Malaysia)], E-mail: anuar_mi@ukm.my
2009-05-15
The steady mixed convection boundary layer flow along a vertical cylinder with prescribed surface heat flux is investigated in this study. The free stream velocity and the surface heat flux are assumed to vary linearly with the distance from the leading edge. Both the case of the buoyancy forces assisting and opposing the development of the boundary layer are considered. Similarity equations are derived, their solutions being dependent on the mixed convection parameter, the curvature parameter, as well as of the Prandtl number. Dual solutions are found to exist for both buoyancy assisting and opposing flows. It is also found that the boundary layer separation is delayed for a cylinder compared to a flat plate.
Two-phase gas bubble-liquid boundary layer flow along vertical and inclined surfaces
International Nuclear Information System (INIS)
The behavior of a two-phase gas bubble-liquid boundary layer along vertical and inclined porous surfaces with uniform gas injection is investigated experimentally and analytically. Using argon gas and water as the working fluids, a photographical study of the two-phase boundary layer flow has been performed for various angles of inclination ranging from 450 to 1350 and gas injection rates ranging from 0.01 to 0.1 m/s. An integral method has been employed to solve the system of equations governing the two-phase motion. The effects of the gas injection rate and the angle of inclination on the growth of the boundary layer have been determined. The predicted boundary layer thickness is found to be in good agreement with the experimental results. The calculated axial liquid velocity and the void fraction in the two-phase region are also presented along with the observed flow behavior
De-entrainment on vertical elements in air droplet cross flow
International Nuclear Information System (INIS)
De-entrainment phenomena on vertical elements in air-water droplet cross flow are generated using a horizontal array of water spray nozzles and a draft-induced wind tunnel. These conditions are used to obtain experimental values of the de-entrainment efficiency of isolated elements (25.4-, 63.5-, and 101.6-mm-diam cylinders and a 76.2-mm-square tube), and of an array of 101.6-mm-diam cylinders. A flow model is developed that extrapolates the de-entrainment efficiency of isolated elements through the use of a correlation for the interference effect to predict the efficiency of large arrays of similar elements. This simple model is shown to provide a good prediction of the de-entrainment efficiency of arrays in terms of the efficiency of an isolated element
Measurements of Burnout Conditions for Flow of Boiling Water in Vertical Rod Clusters
International Nuclear Information System (INIS)
The present report deals with the results of the first phase of an experimental investigation of burnout conditions for flow of boiling water in vertical round ducts. Data were obtained in the following ranges of variables. Pressure 2.4sub2; Mass velocity 1442/s; Heated length 1040BO, were plotted against the pressure with the surface heat flux as parameter. The data have been correlated by curves. The scatter of the data around the curves is less than ± 5 per cent. In the ranges investigated the observed steam quality at burnout, xBO generally decreases with increasing heat flux; increases with increasing pressure and decreases with increasing mass velocity. The mass velocity effect has been explained on the basis of climbing film flow theory. Finally we have found that for engineering purposes the effects of inlet subcooling and channel length are negligible
Bubble Lift-off Diameter and frequency in a Vertical Subcooled Boiling Flow
International Nuclear Information System (INIS)
Together with an active nucleation site density and a bubble detachment frequency, the bubble detachment diameter determines the evaporative heat flux in commercial CFD codes. Also, an increase of an interfacial area concentration by a wall boiling nucleation, i.e., the boiling source term in an interfacial area transport equation (IATE), is expressed by the above three terms. Several studies were performed to investigate the bubble diameters in the forced convective boiling flows. However, the database is still insufficient and the applicability of the suggested models was not thoroughly examined against the existing database. In the present study, the bubble behaviors were captured using a highspeed digital video camera for a forced convective subcooled boiling flow in a vertical annulus. Bubble liftoff diameter and bubble nucleation frequency was quantified by analyzing the captured images. Also, the prediction capability of the models for the bubble lift-off diameter was evaluated against the experimental data of the present work and literature
Weakly nonlinear stability analysis of non-isothermal Poiseuille flow in a vertical channel
Khandelwal, Manish K.; Bera, P.
2015-06-01
A weakly nonlinear stability theory in terms of Landau equation is developed to analyze the nonlinear saturation of stably stratified non-isothermal Poiseuille flow in a vertical channel. The results are presented with respect to fluids: mercury, gases, liquids, and heavy oils. The weakly nonlinear stability results predict only the supercritical instability, in agreement with the published result [Y. C. Chen and J. N. Chung, "A direct numerical simulation of K and H-type flow transition in heated vertical channel," Comput. Fluids 32, 795-822 (2003)] based on direct numerical simulation. Apart from this, the influence of nonlinear interaction among different superimposed waves on the heat transfer rate, real part of wavespeed, and friction coefficient on the wall is also investigated. A substantial enhancement (reduction) in heat transfer rate (friction coefficient) is found for liquids and heavy oils from the basic state beyond the critical Rayleigh number. The amplitude analysis indicates that the equilibrium amplitude decreases on increasing the value of Reynolds number. However, in the case of mercury, influence of nonlinear interaction on the variation of equilibrium amplitude, heat transfer rate, wavespeed, as well as friction coefficient is complex and subtle. The analysis of the nonlinear energy spectra for the disturbance also supports the supercritical instability at and beyond the critical point. Finally, the effect of superimposed waves on the pattern of secondary flow, based on linear stability theory, is also studied. It has been found that the impact of nonlinear interaction of waves on the pattern of secondary flow for mercury is weak compared to gases, which is the consequence of negligible modification in the buoyant production of disturbance kinetic energy of the mercury.
Annular linear induction pump with an externally supported duct
International Nuclear Information System (INIS)
An annular linear induction pump of increased efficiency is described, capable of being readily disassembled for repair or replacement of parts, and having one pass flow of the liquid metal through the pump. (U.K.)
Experimental database on steam–water flow with phase transfer in a vertical pipe
International Nuclear Information System (INIS)
Highlights: • Steam was injected into sub-cooled water for upward vertical pipe flow. • Evolution of the flow along the pipe was measured using wire-mesh sensors. • 4 pressure levels were investigated (1, 2, 4 and 6.5 MPa). • Data include void and gas velocity profiles, bubble size distributions among others. • CFD-grade database was obtained. - Abstract: The evolution of steam–water flow with an initial sub-cooling along an 8 m long pipe with an inner diameter of about 200 mm was measured to obtain a database suitable for the qualification of CFD-codes on poly-dispersed flows with phase transfer. Phase transfer has to be considered in Nuclear Reactor Safety Research, e.g. in case of sub-cooled boiling or bubble entrainment caused by Emergency Core Cooling (ECC) injection. Bubble size distributions are important, since the phase transfer rate is proportional to the interfacial area density. To develop and validate closure models for CFD codes experimental data with high resolution in space and time are required. The experiments were conducted at the TOPFLOW facility of the Helmholtz–Zentrum Dresden–Rossendorf. Steam was injected into upwards flowing sub-cooled water via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices are used to vary the initial bubble size distribution. The variation of the distance between the location of the gas injection and the measuring plane allows investigating the evolution of the flow along the pipe. Pressure, steam and water flow rates and the sub-cooling were also varied. Measurements are done using wire-mesh sensors and thermocouples. Data on averaged void fraction, radial gas volume fraction profiles, profiles of the gas velocity and bubble size distributions in dependency of the L/D ratio are available
Review of Critical Heat Flux Correlations for Upward Flow in a Vertical Thin Rectangular Channel
International Nuclear Information System (INIS)
From the view point of safety, this type of fuel has higher resistance to earthquake and external impact. The cross section of coolant flow channel in the reactor core composed with the plate fuel is a thin rectangular shape. Thermal-hydraulic characteristics of this thin rectangular channel are different with those of general circular rod fuel bundle flow channel. Accordingly it could be thought that the CHF correlation in a thin rectangular channel is different with that in a circular channel, for which a large number of researches on CHF prediction have been carried out. The objective of this paper is to review previous researches on CHF in a thin rectangular channel, summarize the important conclusion and propose the new simple CHF correlation, which is based on the data set under high pressure and high flow rate condition. The researches on CHF in rectangular channel have been partially carried out according to the pressure, heated surface number, heated surface wettability effect, flow driving force and flow direction conditions. From the literature researches on CHF for upward flow in a vertical thin rectangular channel, some CHF prediction methods were reviewed and compared. There is no universal correlation which can predict CHF at all conditions, but generally, Katto empirical correlation is known to be useful at high pressure and high flow rate. The new simple correlation was developed from the restricted data set, the CHF prediction capacity of which is better than that of Katto. Even though the prediction consistency of the new simple correlation is lower, MAE and RMS error decreased quite. For the more development of the new simple CHF correlation, the more advanced regression analysis method and theoretical analysis should be studied in future
RULE OF TRANSIENT PHREATIC FLOW SUBJECTED TO VERTICAL AND HORIZONTAL SEEPAGE
Institute of Scientific and Technical Information of China (English)
TAO Yue-zan; XI Dao-ying
2006-01-01
In a semi-infinite aquifer bounded by a channel, a transient flow model is constructed for phreatic water subjected to vertical and horizontal seepage. Based on the first linearized Boussinesq equation, the analytical solution of the model is obtained by Laplace transform. Having proven the transformation between the analytical solution and some relevant classic formulas, suitable condition for each of these formulas is demonstrated. On the base of the solution, the variation of transient flow process caused by the variables, such as vertical infiltration intensity, fluctuation range of river stage, aquifer parameters such as transmissivity and specific yield, and the distance from calculating point to channel boundary, are analyzed quantitatively one by one. Lagging effect will happen to the time, when phreatic water gets its maximum fluctuation velocity, response to the varying of the variables stated above. The condition for some variables to form equivalent lagging effect is demonstrated. Corresponding to the mathematical characteristics of the analytical solution, the physical implication and the fluctuation rule of groundwater level are discussed.
Directory of Open Access Journals (Sweden)
Gražina Žibienė
2015-12-01
Full Text Available Different kinds of natural and artificial filter media are able to retain phosphorus in the constructed wetlands. Due to the fact that the constructed wetland needs huge amounts of the filter media, it is very important to find locally available material which distinguishes itself by its ability to retain phosphorus. The materials found in Lithuania were considered and dolomite was chosen. Two dolomite fractions, dolomite powder (1–2 mm and dolomite chippings (2–5 mm, and sand media were used in the laboratory- scale installed for the comparative experiments. The laboratory-scale with dolomite as the filter media was on average by 21% more efficient in total phosphorus removal in comparison with the sand media. Based on the laboratory research pilot–scale vertical flow constructed wetland of 160 m2 was installed and planted with reed Phragmites australis. The dolomite chippings as filter media were chosen in order to avoid the danger of the clogging of constructed wetland. Efficiency of total phosphorus removal in the pilot-scale vertical flow constructed wetland was on average 95.7%, phosphates removal – 94.8% within one year.
International Nuclear Information System (INIS)
An experimental study on the critical heat flux (CHF) has been accomplished for stable low flow of water in a vertical round tube and an annulus near atmospheric pressure (110 kPa) under forced and natural circulation flow condition. CHF data were obtained for water flow in a 0.01m-diameter vertical round tube of variable heated length (Lh = 0.6 m or 0.9m), varying mass flux (0 - 258 kg/m2s), inlet subcooling (135.8 - 344.8 kJ/kg), inlet throttling (large and no), and flow direction (upward and downdard). The CHF values varied from 21 kW/m2 for complete bottom blockage to a maximum of 1130 kW/m2 for a maximum inlet water mass flux of 258 kg/m2s in the experiments. The following parametric effects were observed during the round tube experiments : (1) The CHF increased with the decrease of heated length at the same tube diameter and inlet condition (L/D Effect). (2) The CHF was somewhat weakly affected by the flow instabilities for upward flow while much more susceptible in case of downward flow. The inlet throttling effect was significant in downward flow experiments.(Instability Effect). (3) In the natural circulation experiment, the lower CHF values were observed than those of the forced circulation experiment contrary to the findings of Mishima. It seems to be related to the flow instability.(Natural Circulation Effect). Experiments for annulus geometry were performed to assess the possibility of the following rod-bundle experiment and to visualize the flow pattern transition before and at the occurrence of CHF. Finally, the measured CHF data were compared with predictions by available low pressure and low velocity CHF correlations
Microbial nitrogen removal pathways in integrated vertical-flow constructed wetland systems.
Hu, Yun; He, Feng; Ma, Lin; Zhang, Yi; Wu, Zhenbin
2016-05-01
Microbial nitrogen (N) removal pathways in planted (Canna indica L.) and unplanted integrated vertical-flow constructed wetland systems (IVCWs) were investigated. Results of, molecular biological and isotope pairing experiments showed that nitrifying, anammox, and denitrifying bacteria were distributed in both down-flow and up-flow columns of the IVCWs. Further, the N transforming bacteria in the planted IVCWs were significantly higher than that in the unplanted ones (p<0.05). Moreover, the potential nitrification, anammox, and denitrification rates were highest (18.90, 11.75, and 7.84nmolNg(-1)h(-1), respectively) in the down-flow column of the planted IVCWs. Significant correlations between these potential rates and the absolute abundance of N transformation genes further confirmed the existence of simultaneous nitrification, anammox, and denitrification (SNAD) processes in the IVCWs. The anammox process was the major N removal pathway (55.6-60.0%) in the IVCWs. The results will further our understanding of the microbial N removal mechanisms in IVCWs. PMID:26897412
Study on intermittent flow behavior in a vertical channel under low-pressure condition
International Nuclear Information System (INIS)
The intermittent flow behavior in a vertical annulus under a low-pressure condition was experimentally studied using a scaling experiment facility. The temperature and pressure variations in the channel had been obtained under the heat load ranging from 0 to 2.0 kW, initial subcooled water temperature ranging from 50 to 90°C and length–diameter ratio ranging from 1.6 to 50. The effects of the heat load and length–diameter ratio of channel on the flow characteristics were investigated in detail. The experimental results showed that the steam bubbles erupted more frequently and regularly at a high heat load. The intermittent flow period decreased with increase of the heat load and aspect ratio. Based on the mechanism analysis, an empirical model considering the steam oscillation and the vapor–liquid interface rupture based on the experimental data was proposed. It was found that the accumulated steam basically increased linearly. The oscillation of the pressure and velocity decreased gradually with continuous steam accumulation. The Reynolds number of the liquid within the rising section was very small at the stagnation state since there was no forced circulation flow. Finally, a blockage was engendered in the pipeline with the steam accumulated. (author)
Turbulent Flow Characteristics and Dynamics Response of a Vertical-Axis Spiral Rotor
Directory of Open Access Journals (Sweden)
Yuli Wang
2013-05-01
Full Text Available The concept of a vertical-axis spiral wind rotor is proposed and implemented in the interest of adapting it to air flows from all directions and improving the rotor’s performance. A comparative study is performed between the proposed rotor and conventional Savonius rotor. Turbulent flow features near the rotor blades are simulated with Spalart-Allmaras turbulence model. The torque coefficient of the proposed rotor is satisfactory in terms of its magnitude and variation through the rotational cycle. Along the height of the rotor, distinct spatial turbulent flow patterns vary with the upstream air velocity. Subsequent experiments involving a disk generator gives an in-depth understanding of the dynamic response of the proposed rotor under different operation conditions. The optimal tip-speed ratio of the spiral rotor is 0.4–0.5, as is shown in both simulation and experiment. Under normal and relative-motion flow conditions, and within the range of upstream air velocity from 1 to 12 m/s, the output voltage of the generator was monitored and statistically analyzed. It was found that normal air velocity fluctuations lead to a non-synchronous correspondence between upstream air velocity and output voltage. In contrast, the spiral rotor’s performance when operating from the back of a moving truck was significantly different to its performance under the natural conditions.
Generalized granuloma annulare
Directory of Open Access Journals (Sweden)
Khatri M
1995-01-01
Full Text Available A 35-years-old female patient had generalized pruritic papular lesions, distributed like dermatitis herpetiformis for last 4 years. Histopathologic changes were typical of granuloma annulare with negative results of direct immunofluorescence. The patient did not have association of diabetes mellitus or any other systemic disease. She failed to respond to dapsone therapy and 13-cis-retinoic acid.
Annular Planar Monopole Antennas
Chen, Z. N.; Ammann, Max; Chia, W.Y. W.; See, T.S. P.
2002-01-01
A type of annular planar monopole antenna is presented. The impedance and radiation characteristics of the monopole with different holes and feed gaps are experimentally examined. The measured results demonstrate that the proposed antenna is capable of providing significantly broad impedance bandwidth with acceptable radiation performance.
International Nuclear Information System (INIS)
ASSERT-4 is a subchannel code based on the non-equilibrium equations of two-fluid flow. The paper briefly describes the equations and constitutive models used in the code, and reviews a number of validation exercises in which code results were compared to measurements in vertical and horizontal two-phase flows. (orig.)
Initial dilution of a vertical round non-buoyant jet in wavy cross-flow environment
Wang, Ya-na; Chen, Yong-ping; Xu, Zhen-shan; Pan, Yi; Zhang, Chang-kuan; Li, Chi-wai
2015-12-01
The phenomenon of wastewater discharged into coastal waters can be simplified as a turbulent jet under the effect of waves and currents. Previous studies have been carried out to investigate the jet behaviors under the current only or the wave only environment. To obtain better understanding of the jet behaviors in a realistic situation, a series of physical experiments on the initial dilution of a vertical round jet in the wavy cross-flow environment are conducted. The diluted processes of the jet are recorded by a high-resolution camcorder and the concentration fields of the jet are measured with a peristaltic suction pumping system. When the jet is discharged into the wavy cross-flow environment, a distinctive phenomenon, namely "effluent clouds", is observed. According to the quantitative measurements, the jet width in the wavy cross-flow environment increases more significantly than that does in the cross-flow only environment, indicating that the waves impose a positive effect on the enhancement of jet initial dilution. In order to generalize the experimental findings, a comprehensive velocity scale u a and a characteristic length scale l are introduced. Through dimensional analysis, it is found that the dimensionless centerline concentration trajectories y c/ l is in proportion to 1/3 power of the dimensionless downstream distance x/ l, and the dimensionless centerline dilution S c Q/( u a l 2) is proportional to the square of the dimensionless centerline trajectory y c/ l. Several empirical equations are then derived by using the Froude number of cross-flow Fr c as a reference coefficient. This paper provides a better understanding and new estimations of the jet initial dilution under the combined effect of waves and cross-flow current.
Li, Jing; Ghoshal, Subhasis
2016-02-01
Direct injection of nanoscale zerovalent iron (NZVI) particles is being considered for remediation of contaminated sites. However, the transport characteristics of NZVI under horizontal flow conditions are not fully understood. In this study, NZVI particles were stabilized with carboxymethyl cellulose (CMC) and injected in vertical and horizontal columns to compare the effects of the flow direction on the transport. Columns were packed with sand of mean grain diameters of 180, 340 or 1140 µm (referred to as fine, intermediate and coarse sand, respectively), and were injected with CMC-NZVI suspensions of 0.3, 1 or 3 g Fe L(-1). Experimental breakthrough curves showed that with the coarse and intermediate sands, the steady-state effluent concentration in the horizontal column were up to 84% lower than those in the vertical column regardless of the initial NZVI concentration. However, in the fine sand the differences were insignificant, except at the highest NZVI particle concentration. Additionally, in the horizontally-oriented columns containing the coarse or intermediated sand, NZVI aggregates particles were non-uniformly distributed in the cross-section of the columns and there higher deposition in the bottom-half of the cross-section due to gravity effects. These deposition patterns can be accounted for, in part, by the gravitational settling of the large aggregates of NZVI, especially at high NZVI concentrations. A particle trajectory analysis in three dimensions demonstrated that under horizontal flow, gravity forces resulted in lower deposition of NZVI on the bottom-half of a single collector, as particles approaching the bottom-half of the collector were deflected by gravity to collectors below. PMID:26498094
International Nuclear Information System (INIS)
Highlights: ► Performed experiment for the upward SCO2 flow surrounded by highly conducting metal. ► Selected dimensionless groups representing the property variations and buoyancy. ► Developed the heat transfer correlation for the mixed thermal boundary condition. ► Wrote a finite element heat transfer code to find the appropriate correlation. ► Coupled the 1D convection and 2D heat conduction via heat transfer coefficient. - Abstract: This paper presents heat transfer characteristics of supercritical carbon dioxide flow inside vertical circular pipe surrounded by highly conducting material, and develops an adequate tool to test the performance of available heat transfer correlations with. The possible situations are illustrated for the nuclear power plant to which the above-mentioned geometric configuration might be applicable. An experimental loop with vertical circular geometry is designed and constructed to test the upward flow in supercritical state when the axial heat transfer is enhanced by the surrounding metals, resulting in a wall boundary condition between the constant heat flux and temperature. The set of correlations and important findings are critically reviewed from extensive literature survey. Incorporating nondimensional groups resorting to past insights from the available literature, a convective heat transfer correlation is proposed. The optimization procedure is described which utilizes a random walk method along with the in-house finite element heat transfer code to determine the coefficients of the proposed heat transfer correlation. The proposed methodology can be applied to evaluation of heat transfer when the heat transfer coefficient data cannot directly be determined from the experiment.
International Nuclear Information System (INIS)
Numerical solutions on the influence of surface radiation on the laminar air flow induced by natural convection in vertical, asymmetrically-heated channels are discussed. Variable property effects are accounted for in a full-elliptic mathematical formulation. The density variation is determined from the state equation for ideal gas. The experimental design and data reported in Webb and Hill [1] are taken as the base cases for carrying out the computations. The occurrence of flow reversals is first considered and revisited for pure natural convection, and the Nusselt number correlations derived from the numerical results are favorably compared with those reported in [1]. It is shown that the general effect of surface radiation is to delete the onset of pocket-like re-circulations at the top part of the channel, to reduce the heated wall temperatures, and to increase the facing wall temperatures. Comparisons with usual methods used for decoupling the surface radiation effects are discussed. In the range of parameters investigated, increases in differences between inlet and maximum wall temperatures up to 200 K are shown to have small influences on the flow field and negligible effects on heat transfer performances. (authors)
Directory of Open Access Journals (Sweden)
Norfifah Bachok
Full Text Available The steady boundary layer flow of a viscous and incompressible fluid over a moving vertical flat plate in an external moving fluid with viscous dissipation is theoretically investigated. Using appropriate similarity variables, the governing system of partial differential equations is transformed into a system of ordinary (similarity differential equations, which is then solved numerically using a Maple software. Results for the skin friction or shear stress coefficient, local Nusselt number, velocity and temperature profiles are presented for different values of the governing parameters. It is found that the set of the similarity equations has unique solutions, dual solutions or no solutions, depending on the values of the mixed convection parameter, the velocity ratio parameter and the Eckert number. The Eckert number significantly affects the surface shear stress as well as the heat transfer rate at the surface.
Bubble motion through a generalized power-law fluid flowing in a vertical tube.
Mukundakrishnan, Karthik; Eckmann, David M; Ayyaswamy, P S
2009-04-01
Intravascular gas embolism may occur with decompression in space flight, as well as during cardiac and vascular surgery. Intravascular bubbles may be deposited into any end organ, such as the heart or the brain. Surface interactions between the bubble and the endothelial cells lining the vasculature result in serious impairment of blood flow and can lead to heart attack, stroke, or even death. To develop effective therapeutic strategies, there is a need for understanding the dynamics of bubble motion through blood and its interaction with the vessel wall through which it moves. Toward this goal, we numerically investigate the axisymmetric motion of a bubble moving through a vertical circular tube in a shear-thinning generalized power-law fluid, using a front-tracking method. The formulation is characterized by the inlet Reynolds number, capillary number, Weber number, and Froude number. The flow dynamics and the associated wall shear stresses are documented for a combination of two different inlet flow conditions (inlet Reynolds numbers) and three different effective bubble radii (ratio of the undeformed bubble radii to the tube radii). The results of the non-Newtonian model are then compared with that of the model assuming a Newtonian blood viscosity. Specifically, for an almost occluding bubble (effective bubble radius = 0.9), the wall shear stress and the bubble residence time are compared for both Newtonian and non-Newtonian cases. Results show that at low shear rates, for a given pressure gradient the residence time for a non-Newtonian flow is higher than that for a Newtonian flow. PMID:19426324
Y. Bindar; N.A. Sutrisniningrum; D. Santiani
2009-01-01
More general correlations between pressure drop and gas-solid flow variables are developed from the present experimental data. The correlation was modeled for a pneumatic conveying system in a vertical pipe. The transition boundary between dense and dilute regimes is constructed from the pressure drop correlations. The gas-solid particle flow variables are quantified by the gas Reynold (Nref) and the solid Froude (Frp) numbers. The dense flow regime is indicated by the decrease of the pressur...
Institute of Scientific and Technical Information of China (English)
王斯民; 文键; 李亚梅; 杨辉著; 厉彦忠
2013-01-01
Multiple size group (MUSIG) model combined with a three-dimensional two-fluid model were em-ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat transfer, some important bubble model parameters were amended to be applicable to the modeling of liquid nitrogen. The distribution of different discrete bubble classes was demonstrated numerically and the distribu-tion patterns of void fraction in the wall-heated tube were analyzed. It was found that the average void fraction in-creases nonlinearly along the axial direction with wall heat flux and it decreases with inlet mass flow rate and sub-cooled temperature. The local void fraction exhibited a U-shape distribution in the radial direction. The partition of the wall heat flux along the tube was obtained. The results showed that heat flux consumed on evaporation is the leading part of surface heat transfer at the rear region of subcooled boiling. The turning point in the pressure drop curve reflects the instability of bubbly flow. Good agreement was achieved on the local heat transfer coefficient against experimental measurements, which demonstrated the accuracy of the numerical model.
Simulation of two-phase flows in vertical tubes with the CFD code FLUBOX
International Nuclear Information System (INIS)
The Computational Fluid Dynamics (CFD) code FLUBOX is developed at GRS for the multidimensional simulation of two-phase flows. The single-pressure two-fluid model is used as basis of the simulation. A basic mathematical property of the two-fluid model of FLUBOX is the hyperbolic character of the convection. The numerical solution methods of FLUBOX make explicit use of the hyperbolic structure of the coefficient matrices. The simulation of two-phase flow phenomena needs, apart from the conservation equations for each phase, an additional transport equation for the interfacial area concentration. The concentration of the interfacial area is one of the key parameters for the modelling of interfacial friction forces and interfacial transfer terms. A new transport equation for the interfacial area concentration is in development. It describes the dynamic change of the interfacial area concentration due to mass exchange and a force balance at the phase boundary. Results from FLUBOX calculations for different experiments of two-phase flows in vertical tubes are presented as part of the validation. (authors)
Film stability in a vertical rotating tube with a core-gas flow.
Sarma, G. S. R.; Lu, P. C.; Ostrach, S.
1971-01-01
The linear hydrodynamic stability of a thin-liquid layer flowing along the inside wall of a vertical tube rotating about its axis in the presence of a core-gas flow is examined. The stability problem is formulated under the conditions that the liquid film is thin, the density and viscosity ratios of gas to liquid are small and the relative (axial) pressure gradient in the gas is of the same order as gravity. The resulting eigenvalue problem is first solved by a perturbation method appropriate to axisymmetric long-wave disturbances. The damped nature (to within the thin-film and other approximations made) of the nonaxisymmetric and short-wave disturbances is noted. In view of the limitations on a truncated perturbation solution when the disturbance wavenumber is not small, an initial value method using digital computer is presented. Stability characteristics of neutral, growing, and damped modes are presented showing the influences of rotation, surface tension, and the core-gas flow. Energy balance in a neutral mode is also illustrated.
Simulation of Sweep-Jet Flow Control, Single Jet and Full Vertical Tail
Childs, Robert E.; Stremel, Paul M.; Garcia, Joseph A.; Heineck, James T.; Kushner, Laura K.; Storms, Bruce L.
2016-01-01
This work is a simulation technology demonstrator, of sweep jet flow control used to suppress boundary layer separation and increase the maximum achievable load coefficients. A sweep jet is a discrete Coanda jet that oscillates in the plane parallel to an aerodynamic surface. It injects mass and momentum in the approximate streamwise direction. It also generates turbulent eddies at the oscillation frequency, which are typically large relative to the scales of boundary layer turbulence, and which augment mixing across the boundary layer to attack flow separation. Simulations of a fluidic oscillator, the sweep jet emerging from a nozzle downstream of the oscillator, and an array of sweep jets which suppresses boundary layer separation are performed. Simulation results are compared to data from a dedicated validation experiment of a single oscillator and its sweep jet, and from a wind tunnel test of a full-scale Boeing 757 vertical tail augmented with an array of sweep jets. A critical step in the work is the development of realistic time-dependent sweep jet inflow boundary conditions, derived from the results of the single-oscillator simulations, which create the sweep jets in the full-tail simulations. Simulations were performed using the computational fluid dynamics (CFD) solver Overow, with high-order spatial discretization and a range of turbulence modeling. Good results were obtained for all flows simulated, when suitable turbulence modeling was used.
Efficiency assessment of vertical barriers on the basis of flow and transport numerical modeling
Koda, Eugeniusz; Kołanka, Tomasz; Osiński, Piotr
2012-10-01
The construction of cut-off walls is a common solution applied in such disciplines as land reclamation and landfill containment. Most commonly the construction of vertical barriers is based on cut-off wall mono or diphase technology with the use of bentonite-cement mixture as a filling material. The content of the paper is focused on groundwater flow and transport numerical modeling conducted on landfill areas where vertical bentonite barriers were constructed. The modeling process was conducted with the use of FEMWATER software which employs analysis based on finite element method. There are two examples of the software application presented in the paper which concern such case studies, i.e., reclamation of Radiowo and Łubna landfill sites. These examples are provided to prove that the appropriate investigation of ground conditions as well as definition of initial and boundary conditions and correct selection of material parameters to be fed into the software, are crucial for the overall modeling process. Moreover, the comparison of results obtained from the numerical modeling and the groundwater monitoring on site is presented for one of the case studies.
Unsteady MHD free convective flow past a permeable stretching vertical surface in a nano-fluid
International Nuclear Information System (INIS)
In this paper we investigate the transient MHD laminar free convection flow of nano-fluid past a vertical surface. The vertical surface is considered porous and stretched under acceleration. Four different types of water based nano-fluid are considered in this investigation where copper (Cu), copper oxide (CuO), aluminum oxide (Al2O3), and titanium dioxide (TiO2) are the nano-particles. The boundary-layer forms of the governing partial differential equations (momentum and energy equations) are transformed into highly nonlinear coupled ordinary differential equations (ODEs) using similarity technique. The ordinary differential equations are solved numerically using a fourth order Runge-Kutta method based shooting technique. For some special cases, an excellent agreement is observed between the current results and the results available in the existing literature. The effects of different parameters: the nanoparticle volume fraction (φ), unsteadiness parameter (A), magnetic parameter (M), buoyancy parameter (λ), suction parameter (fw) and different types of nanoparticles on the fluid velocity component (f'(η), temperature distribution (θ(η)), the skin friction coefficient (Cf Rex1/2), and the local Nusselt number (Nux Rex-1/2) are presented graphically and discussed in details. The results illustrate that selecting Al2O3 and Cu as the nanoparticle leads to the minimum and maximum amounts of skin friction coefficient absolute value, and also Cu and TiO2 nanoparticles have the largest and lowest local Nusselt number
The effect of surface tension on flow condensation in vertical small-diameter tube
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The effect of surface tension on flow condensation in vertical small tube with inside diameter of 1-5 mm is compared with that of gravity and shear stress in different gravity environments at low Reynolds number, whichis less concerned in former studies. The present study indicates that surface tension is the most important factor affectingflow condensation, but it is weakened by shear stress as decreasing tube diameter in a microgravity environment. In anormal gravity environment, body force is the dominant effect that is weakened by shear stress as decreasing tube diame-ter, while the effect of capillary pressure drop due to surface tension is enhanced. The work will be helpful in under-standing the characteristics of heat pipe or capillary pumped loop (CPL) at low Reynolds number.
Study on interfacial area transport of two-phase flow in vertical and large circular pipe
International Nuclear Information System (INIS)
Local distribution of the interfacial area concentration (IAC) and void fraction of air-water two-phase flow in a vertical pipe were investigated by using the measurement of optical fiber probe. The inner diameter of the circular pipe was 100 mm, and superficial gas and liquid velocities ranged from 0 to 0.1 m/s and from 0 to 1.0 m/s. accordingly. It is found that the bubble passing through frequency dominates the radial distribution profile of IAC. The axial interfacial area concentration was calculated based on the interfacial area transport model of Ishii-Kim. In the mean time, the analysis of four bubble interaction mechanisms determining the change of IAC shows that it is the local pressure inside the pipe that dominates the value of IAC in the axial direction. A new correlation including the effect of pressure was given for calculating the axial IAC. (authors)
UNSTEADY FREE CONVECTIVE FLOW PAST A MOVING VERTICAL POROUS PLATE WITH NEWTONIAN HEATING
Directory of Open Access Journals (Sweden)
SANKAR KUMAR GUCHHAIT
2012-07-01
Full Text Available The unsteady free convective flow past a vertical porous plate with Newtonian heating has been studied. The governing equations have been solved numerically by Crank-Nicolson implicit finite-difference scheme. The variations of velocity and fluid temperature are presented graphically. It is found that the fluid velocity decreases with an increase in Prandtl number. Both the fluid velocity and the fluid temperature increase with an increase in suction parameter. An increase in Grashof number leads to rise in the fluid velocity. Further, it is observed that the shear stress and the rate of heat transfer at the plate increase with an increase in either Prandtlnumber or suction parameter or time.
Modeling of Kinetics of Air Entrainment in Water Produced by Vertically Falling Water Flow
Directory of Open Access Journals (Sweden)
Adelė VAIDELIENĖ
2014-09-01
Full Text Available This study analyzes the process of air entrainment in water caused by vertically falling water flow in the free water surface. The new kinetic model of air entrainment in water was developed. This model includes the process of air entrapment, as well as air removal, water sputtering and resorption. For the experimental part of this study a new method based on digital image processing was developed. Theoretical and experimental methods were used for determining air concentration and its distribution in water below the air-water interface. A new presented mathematical model of air entrainment process allows determining of air bubbles and water droplets concentrations distribution. The obtained theoretical and experimental results were in good agreement. DOI: http://dx.doi.org/10.5755/j01.ms.20.3.4871
Developing Buoyancy Driven Flow of a Nanofluid in a Vertical Channel Subject to Heat Flux
Directory of Open Access Journals (Sweden)
Nirmal C. Sacheti
2014-01-01
Full Text Available The developing natural convective flow of a nanofluid in an infinite vertical channel with impermeable bounding walls has been investigated. It is assumed that the nanofluid is dominated by two specific slip mechanisms and that the channel walls are subject to constant heat flux and isothermal temperature, respectively. The governing nonlinear partial differential equations coupling different transport processes have been solved numerically. The variations of velocity, temperature, and nanoparticles concentration have been discussed in relation to a number of physical parameters. It is seen that the approach to the steady-state profiles of velocity and temperature in the present work is different from the ones reported in a previous study corresponding to isothermal wall conditions.
Energy Technology Data Exchange (ETDEWEB)
Ge, Ying; Jiang, Yueping; Jiang, Qinsu; Min, Hang; Fan, Haitian; Zeng, Qiang; Chang, Jie [College of Life Sciences, Zhejiang University, Hangzhou (China); Zhang, Chongbang [School of Life Sciences, Taizhou University, Linhai (China); Yue, Chunlei [Zhejiang Forestry Academy, Hangzhou (China)
2011-03-15
Rhizosphere microorganism is an important bio-component for wastewater treatment in constructed wetlands (CWs). Microbial abundance and enzyme activities in the rhizospheres of nine plant species were investigated in an integrated vertical-flow CW. The abundance of denitrifiers, as well as urease, acid, and alkaline phosphatase activities were positively correlated to plant root biomass. The abundance of bacteria, fungi, actinomycetes, ammonifiers, denitrifiers, and phosphorus decomposers, related to nutrient removal efficiencies in CWs, greatly varied among rhizospheres of different plant species (p < 0.05). Significant differences in rhizosphere enzyme activity among plant species were also observed (p < 0.05), with the exception of catalase activity. The principal component analysis using the data of microbial abundance and enzyme activity showed that Miscanthus floridulus, Acorus calamus, and Reineckia carnea were candidates to be used in CWs to effectively remove nitrogen and phosphorus from wastewater. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Free convective flow of a stratified fluid through a porous medium bounded by a vertical plane
Directory of Open Access Journals (Sweden)
H. K. Mondal
1994-01-01
Full Text Available Steady two-dimensional free convection flow of a thermally stratified viscous fluid through a highly porous medium bounded by a vertical plane surface of varying temperature, is considered. Analytical expressions for the velocity, temperature and the rate of heat transfer are obtained by perturbation method. Velocity distribution and rate of heat transfer for different values of parameters are shown in graphs. Velocity distribution is also obtained for certain values of the parameters by integrating the coupled differential equations by Runge-Kutta method and compared with the analytical solution. The chief concern of the paper is to study the effect of equilibrium temperature gradient on the velocity and the rate of heat transfer.
A parametric investigation of two-phase flow instability in a vertical boiling channel
International Nuclear Information System (INIS)
The characteristics of the density wave oscillation in a vertical boiling channel were investigated by a linear model. A classical approach to the frequency response method was adopted in the analysis. Comparing with Saha's experimental data at high quality conditions, it revealed that Ishii's flow-regime-dependent drift velocity model improved the prediction accuracy of the linear model. The homogeneous equilibrium model showed the most conservative predictions. On the basis of the linear model, a simple model has been developed for the analysis of oscillation at low quality conditions (type-I oscillation) by taking into account the gravitational and frictional pressure losses of the channel. The characteristic equation of the system was analyzed by the one-dimensional D-partition method. The necessary condition for the occurrence of type-I oscillation has been deduced from the analysis. The parametric behavior of the stability condition was investigated. (author)
Heat and mass transfer effect on hydromagnetic flow of a moving permeable vertical surface
International Nuclear Information System (INIS)
Numerical results are presented for the effects of heat and mass transfer on hydromagnetic flow of a moving permeable vertical surface. The surface is maintained at linear temperature and concentration variations. The nonlinear-coupled boundary layer equations were transformed and the resulting ordinary differential equations were solved by perturbation technique. Numerical results for the dimensionless velocity profiles, the temperature profiles, the local friction coefficient and the local Nusselt number are presented for various values of Prandtl number, suction/blowing parameter, Schrnidt number, buoyancy ratio and Hartmann number. The effects of the different parameters on the velocity and temperature profiles as well as skin friction and wall heat transfer are evaluated. Favorable comparisons with previously published work confirm the correctness of numerical results
Comparative analysis of turbulence models for flow simulation around a vertical axis wind turbine
Energy Technology Data Exchange (ETDEWEB)
Roy, S.; Saha, U.K. [Indian Institute of Technology Guwahati, Dept. of Mechanical Engineering, Guwahati (India)
2012-07-01
An unsteady computational investigation of the static torque characteristics of a drag based vertical axis wind turbine (VAWT) has been carried out using the finite volume based computational fluid dynamics (CFD) software package Fluent 6.3. A comparative study among the various turbulence models was conducted in order to predict the flow over the turbine at static condition and the results are validated with the available experimental results. CFD simulations were carried out at different turbine angular positions between 0 deg.-360 deg. in steps of 15 deg.. Results have shown that due to high static pressure on the returning blade of the turbine, the net static torque is negative at angular positions of 105 deg.-150 deg.. The realizable k-{epsilon} turbulent model has shown a better simulation capability over the other turbulent models for the analysis of static torque characteristics of the drag based VAWT. (Author)
Critical heat flux experiments for low flow of water in vertical annuli near atmospheric pressure
International Nuclear Information System (INIS)
Critical Heat Flux (CHF) experiments were performed to measure the CHF limits for low water flow in vertical annuli near atmospheric pressure (0.118 MPa) as functions of the annulus ratio, inlet subcooling, and water flow rate. Each of the test sections consisted of a uniformly heated 304 stainless steel inner tube (1.27 cm OD, 49 cm long, and 0.889 mm wall thickness) and an outer pyrex tube, resulting in annulus ratios of 1.575, 1.72 and 2.0. The temperatures at the inner surface of the heated section were measured at eight locations (1, 3, 5, 10, 20, 30, 40, and 45 cm from the top of the test section) using a specially designed temperature probe. The water temperature was also measured at the inlet and the exit of the test section. All temperature measurements were performed using grounded type-K stainless steel sheathed thermocouples. During the experiments, the water flow to the test section was stabilized by using a control valve located upstream of the test section. The electric power to the test section was increased in small increments and at each increment, the inlet water flow and subcooling were kept constant. The CHF limit was determined when a sudden temperature ramp, up to a present limit of 470 K, occurred and/or a bright glow was observed at the top of the heated section. More than 380 CHF data points were collected for water inlet subcoolings ranging from 182 kJ/kg to 312 kJ/kg, and mass flow rates from zero to 0.841 kg/sec. The CHF values varied from 160 kW/m/sup 2/ for zero inlet flow to a maximum of 1560 kW/m/sup 2/ for a water flow rate of 0.841 kg/sec. For the same water inlet mass flux, increasing the coolant inlet subcooling and/or the annulus ratio generally increased the CHF limit
Maréchal, Jean-Christophe
2010-01-01
A steady-state analytical solution is given describing the temperature distribution in a homogeneous massif perturbed by cold water flow through a discrete vertical fracture. A relation is derived to express the flow rate in the fracture as a function of the temperature measured in the surrounding rock. These mathematical results can be useful for tunnel drilling as it approaches a vertical cold water bearing structure that induces a thermal anomaly in the surrounding massif. During the tunnel drilling, by monitoring this anomaly along the tunnel axis one can quantify the flow rate in the discontinuity ahead before intersecting the fracture. The cases of the Simplon, Mont Blanc and Gotthard tunnels (Alps) are handled with this approach which shows very good agreement between observed temperatures and the theoretical trend. The flow rates before drilling of the tunnel predicted with the theoretical solution are similar in the Mont Blanc and Simplon cases, as well as the flow rates observed during the drilling....
International Nuclear Information System (INIS)
This work demonstrates a continuous flow plasma/blood separator using a vertical submicron pillar gap structure. The working principle of the proposed separator is based on size exclusion of cells through cross-flow filtration, in which only plasma is allowed to pass through submicron vertical pillars located tangential to the main flow path of the blood sample. The maximum filtration efficiency of 99.9% was recorded with a plasma collection rate of 0.67 µl min−1 for an input blood flow rate of 12.5 µl min−1. The hemolysis phenomenon was observed for an input blood flow rate above 30 µl min−1. Based on the experimental results, we can conclude that the proposed device shows potential for the application of on-chip plasma/blood separation as a part of integrated point-of-care (POC) diagnostics systems. (technical note)
International Nuclear Information System (INIS)
The present report deals with measurements of the effects of spacers on the burnout conditions in a vertical annulus and a vertical 7-rod cluster. The following ranges of variables were studied and 162 burnout measurements were obtained. Pressure p = 31 kg/cm; Inlet sub-cooling 35 sub 2; Mass velocity 94 2/s; Burnout steam quality 0.10 BO < 0.56. The experimental results showed that the type of spacers employed during the present investigation had negligible effects on the burnout conditions and that the measured burnout heat fluxes could be predicted within ± 5 per cent by means of the correlation by Becker et al for flow in smooth channels
Linear and nonlinear instability in vertical counter-current laminar gas-liquid flows
Schmidt, Patrick; Ó Náraigh, Lennon; Lucquiaud, Mathieu; Valluri, Prashant
2016-04-01
We consider the genesis and dynamics of interfacial instability in vertical gas-liquid flows, using as a model the two-dimensional channel flow of a thin falling film sheared by counter-current gas. The methodology is linear stability theory (Orr-Sommerfeld analysis) together with direct numerical simulation of the two-phase flow in the case of nonlinear disturbances. We investigate the influence of two main flow parameters on the interfacial dynamics, namely the film thickness and pressure drop applied to drive the gas stream. To make contact with existing studies in the literature, the effect of various density contrasts is also examined. Energy budget analyses based on the Orr-Sommerfeld theory reveal various coexisting unstable modes (interfacial, shear, internal) in the case of high density contrasts, which results in mode coalescence and mode competition, but only one dynamically relevant unstable interfacial mode for low density contrast. A study of absolute and convective instability for low density contrast shows that the system is absolutely unstable for all but two narrow regions of the investigated parameter space. Direct numerical simulations of the same system (low density contrast) show that linear theory holds up remarkably well upon the onset of large-amplitude waves as well as the existence of weakly nonlinear waves. For high density contrasts, corresponding more closely to an air-water-type system, linear stability theory is also successful at determining the most-dominant features in the interfacial wave dynamics at early-to-intermediate times. Nevertheless, the short waves selected by the linear theory undergo secondary instability and the wave train is no longer regular but rather exhibits chaotic motion. The same linear stability theory predicts when the direction of travel of the waves changes — from downwards to upwards. We outline the practical implications of this change in terms of loading and flooding. The change in direction of the
Unsteady Hydromagnetic Flow past a Moving Vertical Plate with Convective Surface Boundary Condition
Directory of Open Access Journals (Sweden)
Gauri Shanker Seth
2016-01-01
Full Text Available Investigation of unsteady MHD natural convection flow through a fluid-saturated porous medium of a viscous, incompressible, electrically-conducting and optically-thin radiating fluid past an impulsively moving semi-infinite vertical plate with convective surface boundary condition is carried out. With the aim to replicate practical situations, the heat transfer and thermal expansion coefficients are chosen to be constant and a new set of non-dimensional quantities and parameters are introduced to represent the governing equations along with initial and boundary conditions in dimensionless form. Solution of the initial boundary-value problem (IBVP is obtained by an efficient implicit finite-difference scheme of the Crank-Nicolson type which is one of the most popular schemes to solve IBVPs. The numerical values of fluid velocity and fluid temperature are depicted graphically whereas those of the shear stress at the wall, wall temperature and the wall heat transfer are presented in tabular form for various values of the pertinent flow parameters. A comparison with previously published papers is made for validation of the numerical code and the results are found to be in good agreement.
Free Convective MHD Flow Past a Vertical Cone with Variable Heat and Mass Flux
Directory of Open Access Journals (Sweden)
J. Prakash
2013-01-01
Full Text Available A numerical study of buoyancy-driven unsteady natural convection boundary layer flow past a vertical cone embedded in a non-Darcian isotropic porous regime with transverse magnetic field applied normal to the surface is considered. The heat and mass flux at the surface of the cone is modeled as a power law according to qwx=xm and qw*(x=xm, respectively, where x denotes the coordinate along the slant face of the cone. Both Darcian drag and Forchheimer quadratic porous impedance are incorporated into the two-dimensional viscous flow model. The transient boundary layer equations are then nondimensionalized and solved by the Crank-Nicolson implicit difference method. The velocity, temperature, and concentration fields have been studied for the effect of Grashof number, Darcy number, Forchheimer number, Prandtl number, surface heat flux power-law exponent (m, surface mass flux power-law exponent (n, Schmidt number, buoyancy ratio parameter, and semivertical angle of the cone. Present results for selected variables for the purely fluid regime are compared with the published results and are found to be in excellent agreement. The local skin friction, Nusselt number, and Sherwood number are also analyzed graphically. The study finds important applications in geophysical heat transfer, industrial manufacturing processes, and hybrid solar energy systems.
An Investigation on the Void Fraction for upward Gas-Liquid Slug Flow in Vertical Pipe
Institute of Scientific and Technical Information of China (English)
夏国栋; 周芳德; 胡明胜
2001-01-01
In order to investigate the influence of the entrance effect on the spatial distribution of phases, the experiments on gas-liquid two-phase slug flow in a vertical pipe of 0.03m ID were carried out by using optical probes and an EKTAPRO 1000 high speed motion analyzer. It demonstrates that the radial profile of slug flow void fraction is parabolic. Influenced by the falling liquid film, the radial profile curve of liquid slug void fraction in the wake region is also parabolic. Since fully turbulent velocity distribution is built up in the developed region,the void fraction profile in this region is the saddle type. At given superficial liquid velocity, the liquid slug void fraction increases with gas velocity. The radial profiles of liquid slug void fraction at different axial locations are all saddle curves, but void fraction is obviously high around the centerline in the entrance region. The nearer the measuring station is from the entrance, the farther the peak location is away from the wall.
Energy Technology Data Exchange (ETDEWEB)
John, K.; Purschke, A.; Schuessler, I. [Mannesmann Seiffert GmbH, Berlin (Germany)
1999-07-01
Because of scarcity of space, the last extension stage of the Berlin-Ruhleben sewage treatment plant was executed with vertical-flow final sedimentation tanks with a square surface. The sedimentation efficiency of these tanks in permanent operation is excellent. In the year past, the operation of such a tank at the limits of its capacity was tested under long-term conditions as a master thesis project with a view to further optimization. Subsequently, this Berlin-type tank was developed further into a multi-cell final sedimentation tank, whose effectiveness was verified by means of flow-technical simulation. (orig.) [German] Im KW Berlin-Ruhleben kamen in der letzten Ausbaustufe infolge sehr begrenzter Bauflaeche vertikal durchstroemte Nachklaerbecken mit quadratischer Oberflaeche zum Einsatz. Diese Becken zeigen im Dauerbetrieb eine hervorragende Klaerwirkung, und im vorigen Jahr wurde im Rahmen einer Diplomarbeit zwecks weiterer Optimierung langfristig unter Betriebsbedingungen die Fahrweise eines solchen Beckens an der Auslegungsgrenze getestet. Unter dem Gesichtspunkt der Kostenreduzierung wurde anschliessend der Typ Berliner Becken zum Mehrzellen-Nachklaerbecken weiterentwickelt und seine Wirksamkeit mittels stroemungstechnischer Simulation ueberprueft. (orig.)
Radiation effects on an unsteady MHD natural convective flow of a nanofluid past a vertical plate
Directory of Open Access Journals (Sweden)
Parasuraman Loganathan
2015-01-01
Full Text Available Numerical analysis is carried out on an unsteady MHD natural convective boundary layer flow of a nanofluid past an isothermal vertical plate in the presence of thermal radiation. The governing partial differential equations are solved numerically by an efficient, iterative, tri-diagonal, semi-implicit finite-difference method. In particular, we investigate the effects of radiation, magnetic field and nanoparticle volume fraction on the flow and heat transfer characteristics. The nanofluids containing nanoparticles of aluminium oxide, copper, titanium oxide and silver with nanoparticle volume fraction range less than or equal to 0.04 are considered. The numerical results indicate that in the presence of radiation and magnetic field, an increase in the nanoparticle volume fraction will decrease the velocity boundary layer thickness while increasing the thickness of the thermal boundary layer. Meanwhile, an increase in the magnetic field or nanoparticle volume fraction decreases the average skin-friction at the plate. Excellent validation of the present results has been achieved with the published results in the literature in the absence of the nanoparticle volume fraction.
Bubble Lift-off Diameter and Nucleation Frequency in Vertical Subcooled Boiling Flow
International Nuclear Information System (INIS)
A series of experiments was carried out to investigate the bubble nucleation to lift-off phenomena for subcooled boiling flow in a vertical annulus channel. A high speed digital video camera was used to capture the dynamics of bubbles. The bubble lift-off diameter and the bubble nucleation frequency were evaluated in terms of heat flux, mass flux, and degree of subcooling. The fundamental features of the lift-off diameter and the nucleation frequency (i.e., the variations across nucleation sites and the dependence on the flow and heat flux conditions) were addressed based on the present observation. A database for the bubble lift-off diameter was built by gathering and summarizing the data of Prodanovic et al., Situ et al., and the present experiments. We evaluated the predictive capabilities of Unal's model, Situ et al.'s model, and Prodanovic et al.'s correlation against the database. We obtained the best prediction results through modifying the wall superheat correlation in Unal's model. In addition, we suggested a new correlation for a combined parameter of the bubble nucleation frequency and the bubble lift-off diameter
Mass flow and particle size monitoring of pulverised fuel vertical spindle mills
Directory of Open Access Journals (Sweden)
Archary Hamresin
2016-06-01
Full Text Available The first step towards condition based maintenance of the milling plant is the implementation of online condition monitoring of the mill. The following paper presents and analyses methods of monitoring the key performance factors of a vertical spindle mill that is suited for implementation on older power stations, i.e. the quantity (mass flow rate and quality (particle fineness of the pulverised fuel produced by the mill. It is shown herein that the mill throughput can be monitored on-line using a simple mill energy balance that successfully predicts the coal throughput within 2.33% as compared to a calibrated coal feeder. A sensitivity analysis reveals that the coal moisture is a critical measurement for this method to be adopted as an on-line mass flow monitoring tool. A laser based particle size analyser tool was tested for use in the power plant environment as an online monitoring solution to measure pulverised fuel fineness. It was revealed that several factors around the set-up and operation of the instrument have an influence on the perceived results. Although the instrument showed good precision and repeatability of results, these factors must be taken into account in order to improve the accuracy of the reported results before the instrument can be commissioned as an on-line monitoring solution.
Bubble lift-off diameter and nucleation frequency in vertical subcooled boiling flow
International Nuclear Information System (INIS)
A series of experiments were carried out to investigate phenomena from bubble nucleation to lift-off for a subcooled boiling flow in a vertical annulus channel. A high-speed digital video camera was used to capture the bubble dynamics. The bubble lift-off diameter and bubble nucleation frequency were evaluated in terms of heat flux, mass flux, and degree of subcooling. The fundamental features of the lift-off diameter and nucleation frequency (i.e., the variations across nucleation sites and the dependence on the flow and heat flux conditions) were addressed based on the present observation. A database for the bubble lift-off diameter was built by gathering and summarizing the data of Prodanovic et al., Situ et al., and the present experiments. We evaluated the predictive capabilities of Unal's model, Situ et al.'s model, and Prodanovic et al.'s correlation against the database. We obtained the best prediction results by modifying the wall superheat correlation in Unal's model. In addition, we suggested a new correlation for a combined parameter of the bubble nucleation frequency and bubble lift-off diameter. (author)
International Nuclear Information System (INIS)
The objective of this work is to study the flow and heat transfer for water under super-critical conditions. Two dimensional (axi-symmetric) CFD simulation is performed for this purpose using an in-house developed code named NAFA. The flow is computed for vertically upward as well as downward orientations. Further, for each orientation, wide range of heat flux is considered. It is found that for downward flow, heat transfer coefficient is higher than that for upward flow, other conditions remaining same. The heat transfer characteristics are found to be dependent on the pipe outlet temperature with reference to pseudo-critical temperature. (author)
International Nuclear Information System (INIS)
Countercurrent flow of steam and water occurs in the horizontal and vertical lines of a PWR in case of a LOCA. In order to predict the emergency core cooling behaviour in case of a large or small break LOCA it is important to calculate the volumetric flow rate of water which will get to the reactor core. Theoretical and experimental results of countercurrent flow in horizontal and vertical channels given by publication and reports are critically reviewed for the purpose of a more physical understanding of the flow phenomena. The influence of geometry, pressure and other boundary conditions are emphasized. The existing models which are developed to calculate the onset of flooding are based on experimental results of small test facilities. The applicability of these models to large geometries and high pressures as well as the consideration of condensation and entrainment are investigated. (orig./HP)
Diffractive analysis of annular resonators.
Morin, M; Bélanger, P A
1992-04-20
The modal properties of annular resonators are investigated by using an approximate version of the Kirchhoff-Fresnel integral. It is shown that the radial diffraction of a thin annular beam with a large inside radius is similar to that of a cylindrical field distribution. This permits the formal demonstration of the equivalence that exists between large Fresnel number annular resonators and infinite strip resonators. The model explains the properties of annular resonators that have been observed either experimentally or numerically by others, such as the lack of azimuthal discrimination. PMID:20720842
Institute of Scientific and Technical Information of China (English)
GU Hanyang; YU Yiqi; CHENG Xu; LIU Xiaojing
2008-01-01
Investigations on the thermal-hydraulic behavior in the SCWR fuel assembly have obtained a significant attention in the international SCWR community. However, there is still a lack of understanding of the heat transfer behavior of supercritical fluids. In this paper, the numerical analysis is carried out to study the thermal-hydraulic behaviour in vertical sub-channels cooled by supercritical water. Remarkable differences in characteristics of secondary flow are found, especially in square lattice, between the upward flow and downward flow. The turbulence mixing across sub-channel gap for downward flow is much stronger than that for upward flow in wide lattice when the bulk temperature is lower than pseudo-critical point temperature. For downward flow, heat transfer deterioration phenomenon is suppressed with respect to the case of upward flow at the same conditions.
Jaromin, Maria; Anglart, Henryk
2013-01-01
A numerical study of heat transfer to supercritical water in vertical tubes is carried out using the ANSYS-CFX code and employing the k-omega SST turbulence model. The numerical results on wall temperature distributions under normal and deteriorated heat transfer conditions are compared with experimental data and a good agreement is obtained. The onset of deterioration is captured for both low-flow and high-flow conditions. Sensitivity of numerical results to operational conditions and the tu...
Field, Parker Lawrence
2013-01-01
The commercial CFD software STAR-CCM+ is applied as a RANS solver for comparison with potential flow methods in the calculation of vertical plane radiation and diffraction problems. A two-dimensional rectangular cylinder oscillating in an unbounded fluid is first considered, and the added mass result shown to agree well with the analytical potential flow solution. Hydrodynamic coefficients are then determined for the cylinder oscillating in heave and sway about a calm free surface. Predict...
Dinarvand Saeed; Abbassi Abbas; Hosseini Reza; Pop Ioan
2015-01-01
This article deals with the study of the steady axisymmetric mixed convective boundary layer flow of a nanofluid over a vertical circular cylinder with prescribed external flow and surface temperature. By means of similarity transformation, the governing partial differential equations are reduced into highly non-linear ordinary differential equations. The resulting non-linear system has been solved analytically using an efficient technique namely homotopy a...
Patil Mallikarjun B; Chandrali Baishya
2016-01-01
Analytical solutions for fully developed mixed convection flow of a micro polar fluid with heat generation or heat absorption in a parallel plate vertical channel with symmetric and asymmetric wall temperature distribution has been presented. The two boundaries of the channel are kept either at equal or at different temperatures as isothermal-isothermal, isoflux-isothermal and isothermal-isoflux cases. Reverse flow conditions are observed with increase in micro vortex viscosity. M...
Dunne, R; McKeon, B. J.
2014-01-01
Vertical axis wind turbine (VAWT) blades undergo dynamic separation due to the large angle of attack variation they experience during a turbine rotation. The flow over a single blade was modeled using a sinusoidally pitching and surging airfoil in a constant free stream flow at a mean chord Reynolds number of 10^5. Two-dimensional, time resolved velocity fields were acquired using particle image velocimetry (PIV). Vorticity contours were used to visualize shear layer and vortex activity. A...
Characteristics of gas-liquid two-phase flow in a vertical small diameter tube at a medium pressure
International Nuclear Information System (INIS)
Most of correlations for calculating two-phase flow parameters, such as flow pattern transitions, void fraction and pressure drop, have been developed based on the experimental data on tubes greater than 10 mm in diameter at near atmospheric pressures. For that, the applicability of such correlations is doubtful to the flow in small diameter tubes at a medium pressure as seen in compact heat exchangers like residential room conditioners. In this connection, the purpose of this study is to provide experimental data for gas-liquid two-phase vertical flows in a small diameter tube at medium pressures since the published data for such flows is limited to examine existing correlations and/or develop a new one. Experiments have been conducted on air-water two-phase flows in a vertical circular tube of 9.48 mm internal diameter. In the experiment, system pressure in the channel has been systematically changed from 0.2 to 0.7 MPa (absolute) to study the effect of the pressure on two-phase flow parameters, i.e., two-phase flow pattern transitions, bubble size in bubble flow, void fraction, interfacial shear force, frictional pressure drop and static pressure fluctuations. Furthermore, the respective data obtained have been compared with existing correlations. (author)
Energy Technology Data Exchange (ETDEWEB)
Bouafia, M. [Cemif, Centre d`Etudes mecanique d`ile-de-France, 91 - Evry (France); Ziouchi, A. [IAP de Boumerdes (Algeria); Bertin, Y.; Saulnier, J.B. [Centre National de la Recherche Scientifique (CNRS), 86 - Poitiers (France). Laboratoire d`etudes thermiques, UMR 6608
1999-07-01
The convective heat transfer between the walls of an annular gap with a rotating inner cylinder are studied experimentally and numerically. Two geometrical configurations are analysed: the surfaces of the cylinders are either smooth, or the moving wall is smooth and the other is axially grooved. The experimental study allowed us to appreciate the increase of heat transfer in the presence of grooves for values of Taylor number up to 2.10{sup 7}. The study of the flow and of the heat transfer has also been conducted by numerical simulation by means of three-dimensional laminar model for the grooved gap, and of an axisymmetric model for the smooth gap; the comparison of numerical and experimental data have shown a good agreement of the Nusselt number for values of Taylor number up to 4.10{sup 5}. (authors) 16 refs.
DEFF Research Database (Denmark)
Dan, Truong Hoang; Quang, Le Nhat; Chiem, Nguyen Huu;
2011-01-01
subsurface flow system and a saturated vertical downflow system was established with planted and unplanted beds to assess the effects of system design and presence of plants on treatment performance. The systems were loaded with a mixture of domestic and pig farm wastewater at three hydraulic loading rates...
Experimental data on steam bubble condensation in poly-dispersed upward vertical pipe flow
International Nuclear Information System (INIS)
Experiments were done at the TOPFLOW facility of the Forschungszentrum Dresden-Rossendorf to establish a CFD-grade database on the condensation of steam bubbles injected into sub-cooled upwards vertical pipe flow. Bubble condensation plays an important role e.g. in sub-cooled boiling or steam injection into pools. Since the condensation rate is proportional to the interfacial area density, bubble size distributions have to be considered in an adequate modelling of the condensation process. To develop and validate closure models for CFD codes new experimental data with high resolution in space and time are required. The Variable Gas Injection device of the TOPFLOW facility was used for the experiments. Some extensions were implemented for the condensation experiments. The test section consists of a 195.3 mm inner diameter pipe with a length of about 8 m. Gas is injected symmetrically through orifices in the pipe wall. In total there are 19 injection chambers distributed over the length of the pipe. 1 mm and 4 mm injection orifices are used to vary the initial bubble size distribution. The measuring plane is always at the top of the test section. The variation of the distance between the location of the gas injection and the measuring plane allows investigating the evolution of the flow along the pipe. Measurements are done using wire-mesh sensors and thermocouples. Experimental data were obtained for two-phase flows at 1, 2, 4 and 6.5 MPa. The pressure boundary conditions were set at the position of the respectively activated gas injection chamber. The sub-cooling of the water was obtained by mixing cold water into the water flow from the circulation loop at the lower end of the pipe. The sub-cooling was obtained as the difference between the measured water temperature below the steam injection and the saturation temperature related to the set pressure. Due to this experimental procedure the experiments reflect the same situation as in case of a gas injection at a