EXPERIMENTAL STUDY OF AIR-WATER TWO-PHASE FLOW IN PARALLEL HELICALLY COILED PIPES
Panella, Bruno
2012-01-01
The air-water two-phase flow in a 12 mm inner diameter parallel helically coiled pipes is investigated with three different coils diameters. Void fraction, flow rate distribution and two-phase pressure drops along the pipes in the parallel channels are measured. The test two-phase pressure drops are compared with theoretical ones, in terms of multipliers and friction factors. The instabilities arisen during the experimental tests are investigated and are related to the void fraction and flow ...
Two-phase air-water stratified flow measurement using ultrasonic techniques
Fan, Shiwei; Yan, Tinghu; Yeung, Hoi
2014-04-01
In this paper, a time resolved ultrasound system was developed for investigating two-phase air-water stratified flow. The hardware of the system includes a pulsed wave transducer, a pulser/receiver, and a digital oscilloscope. The time domain cross correlation method is used to calculate the velocity profile along ultrasonic beam. The system is able to provide velocities with spatial resolution of around 1mm and the temporal resolution of 200μs. Experiments were carried out on single phase water flow and two-phase air-water stratified flow. For single phase water flow, the flow rates from ultrasound system were compared with those from electromagnetic flow (EM) meter, which showed good agreement. Then, the experiments were conducted on two-phase air-water stratified flow and the results were given. Compared with liquid height measurement from conductance probe, it indicated that the measured velocities were explainable.
Numerical simulation of air-water two-phase flow over stepped spillways
Institute of Scientific and Technical Information of China (English)
CHENG; Xiangju; CHEN; Yongcan
2006-01-01
Stepped spillways for significant energy dissipation along the chute have gained interest and popularity among researchers and dam engineers. Due to the complexity of air-water two-phase flow over stepped spillways, the finite volume computational fluid dynamics module of the FLUENT software was used to simulate the main characteristics of the flow. Adopting the RNG k-ε turbulence model, the mixture flow model for air-water two-phase flow was used to simulate the flow field over stepped spillway with the PISO arithmetic technique. The numerical result successfully reproduced the complex flow over a stepped spillway of an experiment case, including the interaction between entrained air bubbles and cavity recirculation in the skimming flow regime, velocity distribution and the pressure profiles on the step surface as well. The result is helpful for understanding the detailed information about energy dissipation over stepped spillways.
Developments in the research of air-water two-phase flows in turbomachinery
International Nuclear Information System (INIS)
Recently, engineering problems associated with two-phase flows in turbomachinery have become increasingly important in relation to the safety analysis of nuclear reactors or the usage of low quality energy resources; the research on this subject has been promoted. It is a really knotty problem caused by the multiform flow patterns as well as the variety of its applications. However, the mechanics in two-phase machines may involve similar phenomena. In this paper, developments of the research of air-water mixtures in turbomachinery will be briefly reviewed, and the mechanics of two-phase flows in rotating flow fields and the prediction methods of the performance of turbomachinery based on some analytical models are discussed. (author)
Air-water two-phase flow pressure drop across various components of AHWR fuel bundle
International Nuclear Information System (INIS)
Single-phase (water) and two-phase (air-water) experiments were carried out for the measurement of pressure drops across various components of a prototype full scale 54-rod fuel bundle of proposed AHWR (Advanced Heavy Water Reactor). From the measured values of pressure drops, the friction factor for fuel bundle and the loss coefficients for the tie plates and spacers were estimated. The single-phase experimental data were compared with different existing correlations. Correlations have been proposed based on the data generated with the air-water mixture which can be used for prediction of pressure drop across fuel channel (with 54 rod fuel bundle) of AHWR under normal operating conditions with appropriate correction factor for steam-water flow. Also a heuristic approach to predict the Lockhart-Martinelli parameter has been presented. Further, a new correlation for two-phase friction multiplier applicable to 54-rod cluster geometry has been developed based on two-phase experimental pressure drop data. The effect of mixture mass flux on the two-phase friction multiplier has been probed and the assessment of existing friction multiplier correlations has also been carried out with the test data. (author)
Interfacial structures of confined air-water two-phase bubbly flow
Energy Technology Data Exchange (ETDEWEB)
Kim, S.; Ishii, M.; Wu, Q.; McCreary, D.; Beus, S.G.
2000-08-01
The interfacial structure of the two-phase flows is of great importance in view of theoretical modeling and practical applications. In the present study, the focus is made on obtaining detailed local two-phase parameters in the air-water bubbly flow in a rectangular vertical duct using the double-sensor conductivity probe. The characteristic wall-peak is observed in the profiles of the interracial area concentration and the void fraction. The development of the interfacial area concentration along the axial direction of the flow is studied in view of the interfacial area transport and bubble interactions. The experimental data is compared with the drift flux model with C{sub 0} = 1.35.
Structure of air-water two-phase flow in helically coiled tubes
International Nuclear Information System (INIS)
Air-water two-phase flow in helically coiled tubes is investigated experimentally to elucidate the effects of centrifugal acceleration on the flow regime map and the spatial and the temporal flow structure distribution. Three kinds of test tubes with 20 mm inner diameters including a straight tube are used to compare the turbulent flow structure. Superficial velocities up to 6 m/s are tested so that the centrifugal Froude number covers a range from 0 to 3. The interfacial structure is photographed from two directions by a high-speed video system with synchronized measurement of local pressure fluctuations. The results reveal that the flow transition line alters due to centrifugal force acting on the liquid phase in the tube. In particular, the bubbly flow regime is narrowed significantly. The pressure fluctuation amplitude gets large relatively to the average pressure loss as void fraction increases. The frequency spectra of the pressure fluctuation have plural peaks in the case of strong curvature, implying that the periodicity of slugging two-phase flow is collapsed by an internal secondary flow activated inside the liquid phase. Moreover, under large Froude number conditions, the substantial velocity of the gas phase that biases to the inner side of the helical coil is slower than the total superficial velocity because the liquid flow is allowed to pass through the outer side and so resembles a radial stratified flow
Time-resolved Fast Neutron Radiography of Air-water Two-phase Flows
Zboray, Robert; Dangendorf, Volker; Mor, Ilan; Tittelmeier, Kai; Bromberger, Benjamin; Prasser, Horst-Michael
Neutron imaging, in general, is a useful technique for visualizing low-Z materials (such as water or plastics) obscured by high-Z materials. However, when significant amounts of both materials are present and full-bodied samples have to be examined, cold and thermal neutrons rapidly reach their applicability limit as the samples become opaque. In such cases one can benefit from the high penetrating power of fast neutrons. In this work we demonstrate the feasibility of time-resolved, fast neutron radiography of generic air-water two-phase flows in a 1.5 cm thick flow channel with Aluminum walls and rectangular cross section. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany. Exposure times down to 3.33 ms have been achieved at reasonable image quality and acceptable motion artifacts. Different two-phase flow regimes such as bubbly slug and churn flows have been examined. Two-phase flow parameters like the volumetric gas fraction, bubble size and bubble velocities have been measured.
Experimental study of flow monitoring instruments in air-water, two-phase downflow
International Nuclear Information System (INIS)
The performance of a turbine meter, target flow meter (drag disk), and a gamma densitometer was studied in air-water, two-phase vertical downflow. Air and water were metered into an 0.0889-m-ID (3.5-in.) piping system; air flows ranged from 0.007 to 0.3 m3/sec (16 to 500 scfm) and water flows ranged from 0.0006 to 0.03 m3/sec (10 to 500 gpm). The study included effects of flow rate, quality, flow regime, and flow dispersion on the mean and fluctuating components of the instrument signals. Wire screen flow dispersers located at the inlet to the test section had a significant effect on the readings of the drag disk and gamma densitometer, but had little effect on the turbine. Further, when flow dispersers were used, mass flow rates determined from the three instrument readings and a two-velocity, slip flow model showed good agreement with actual mass flow rate over a three-fold range in quality; mass flows determined with the drag disk and densitometer readings assuming homogeneous flow were nearly as accurate. However, when mass flows were calculated using the turbine and densitometer or turbine and drag disk readings assuming homogeneous flow, results were scattered and relatively inaccurate compared to the actual mass flows. Turbine meter data were used with a two-velocity turbine model and continuity relationships for each phase to determine the void fraction and mean phase velocities in the test section. The void fraction was compared with single beam gamma densitometer results and fluid momentum calculated from a two-velocity model was compared with drag disk readings
International Nuclear Information System (INIS)
An ultrasonic methodology is proposed for the measurement for two phase (air-water) flow parameters. Ultrasonic backscattered signals were used to analyze the following parameters: average number of bubbles, interfacial area and void fraction. The results show a strong correlation between the parameters and the ultrasonic power signal obtained. (author)
Mehta, Hemant B.; Jyotirmay Banerjee
2014-01-01
The experimentally developed flow pattern maps for micro-scale channels reported by various researchers differ significantly. Also, no theoretical models effectively predict the flow regime transition boundaries in micro-scale channel. The present work proposes an empirical model for air-water two-phase flow pattern transition boundaries for minichannel diameters between 2 to 5mm. Moreover, experiments are conducted with 2.5 mm diameter horizontal circular minichannel to develop a flow regime...
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.
Two-phase air-water flows:Scale effects in physical modeling
Institute of Scientific and Technical Information of China (English)
PFISTER Michael; CHANSON Hubert
2014-01-01
Physical modeling represents probably the oldest design tool in hydraulic engineering together with analytical approaches. In free surface flows, the similitude based upon a Froude similarity allows for a correct representation of the dominant forces, namely gravity and inertia. As a result fluid flow properties such as the capillary forces and the viscous forces might be incorrectly reproduced, affecting the air entrainment and transport capacity of a high-speed model flow. Small physical models operating under a Froude similitude systematically underestimate the air entrainment rate and air-water interfacial properties. To limit scale effects, minimal values of Reynolds or Weber number have to be respected. The present article summarizes the physical background of such limitations and their combination in terms of the Morton number. Based upon a literature review, the existing limits are presented and discussed, resulting in a series of more conservative recommendations in terms of air concentration scaling. For other air-water flow parameters, the selection of the criteria to assess scale effects is critical because some parameters (e.g., bubble sizes, turbulent scales) can be affected by scale effects, even in relatively large laboratory models.
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)
Directory of Open Access Journals (Sweden)
Hemant B. Mehta
2014-01-01
Full Text Available The experimentally developed flow pattern maps for micro-scale channels reported by various researchers differ significantly. Also, no theoretical models effectively predict the flow regime transition boundaries in micro-scale channel. The present work proposes an empirical model for air-water two-phase flow pattern transition boundaries for minichannel diameters between 2 to 5mm. Moreover, experiments are conducted with 2.5 mm diameter horizontal circular minichannel to develop a flow regime map. The proposed empirical model is found to provide good agreement with the experimental data. Comparisons are also shown with the work of Mandhane et al. (1974, Taitel and Dukler (1976, Barnea et al. (1983, Damianides and Westwater (1988, Coleman and Garimella (1999, Yang and Shieh (2001, Venkatesan et al. (2010.
Two-phase air-water flows: Scale effects in physical modelling
Pfister, Michael; Chanson, Hubert
2014-01-01
Physical modeling represents probably the oldest design tool in hydraulic engineering together with analytical approaches. In free surface flows, the similitude based upon a Froude similarity allows for a correct representation of the dominant forces, namely gravity and inertia. As a result fluid flow properties such as the capillary forces and the viscous forces might be incorrectly reproduced, affecting the air entrainment and transport capacity of a high-speed model flow. Small physical mo...
Droplet velocity in horizontal two-phase air/water free jet flow in stagnant ambient
Energy Technology Data Exchange (ETDEWEB)
Surma, R.; Friedel, L. [Wissenschaftlicher Arbeitsbereich Stroemungsmechanik, TU Hamburg-Harburg, Eissendorferstr. 38, D-21073 Hamburg (Germany)
2004-08-01
For the case of an isothermal free jet flow the velocity and the size of the drops were measured with a Phase-Doppler-Anemometer. The axial velocity decay downstream from the nozzle outlet and the radial drop velocity profile are reproducible within reasonable limits, if a so-called homogeneous flow mixture density in the nozzle outlet is introduced. In case of low mass flow qualities an adjustment of the entrainment coefficient and a virtual jet origin as well as a reduced exponent for the Gaussian function type radial velocity profile is required. (Abstract Copyright [2004], Wiley Periodicals, Inc.)
International Nuclear Information System (INIS)
The slug flow transitions and related phenomena for horizontal two-phase flows were studied for a better prediction of two-phase flows that typically appear during the reactor loss-of-coolant accidents (LOCAs). For better representation of the flow conditions experimentally, two large-scaled facility: TPTF for high-pressure steam/water two-phase flows and large duct test facility for air/water two-phase flows, were used. The visual observation of the flow using a video-probe was performed in the TPTF experiments for good understanding of the phenomena. The currently-used models and correlations based mostly on the small-scale low-pressure experiments were reviewed and improved based on these experimental results. The modified Taitel-Dukler model for prediction of transition into slug flow from wavy flow and the modified Steen-Wallis correlation for prediction of onset of liquid entrainment from the interfacial waves were obtained. An empirical correlation for the gas-liquid interfacial friction factor was obtained further for prediction of liquid levels at wavy flow. The region of slug flow regime that is generally under influences of the channel height and system pressure was predicted well when these models and correlations were applied together. (author). 90 refs
Numerical simulation of slug flow regime for an air water two-phase flow in horizontal pipes
International Nuclear Information System (INIS)
Slug flow is a quite common multiphase flow regime in horizontal pipelines and channels, which can be potentially hazardous to the structure of the pipe system or to apparatus and processes following the slug flow pipe section due to the strong oscillating pressure levels formed behind liquid slugs. Areas of application are in the chemical and process industry as well as in safety research and thermo-hydraulic engineering for nuclear power plants. The intended paper deals with the feasibility and accuracy of CFD simulations for an air-water slug flow in a horizontal circular pipe of diameter D = 0.054 m and a pipe length of up to 8 m. In the past most investigations of the slug flow regime in horizontal pipelines and channels have been carried out on experimental test rigs. Due to the transient and three-dimensional character of slug flow regime and the resulting numerical effort only a few attempts of numerical simulation have been made. In principal three different computational approaches can be applied for the simulation of horizontal slug flows: - 'frozen slug' in a domain with moving wall boundaries, where the absolute value of the prescribed wall velocity is equal to the slug propagation velocity in the pipe. The slug propagation velocity and the slug length/period has to be known in advance. - Transient 3-D simulation in a short computational domain with periodic boundary conditions. A driving pressure force has to be prescribed to compensate the kinetic energy losses due to wall friction. Furthermore it has to be ensured, that the geometrical dimensions of the computational domain do not affect the computed slug flow length and time scales. - Transient 3. simulation of slug flow in a long pipe segment with inlet/outlet boundary conditions. The later of the three computational approaches provides the highest predictive capability, also it is the most computational intensive approach. The presented paper will discuss the general aspects of feasibility
International Nuclear Information System (INIS)
To predict the behavior of air-water two-phase flows in centrifugal pumps, we have proposed a three-dimensional numerical method on the basis of an inviscid bubbly flow model with slippage between two phases. The void fractions calculated distribute unevenly and their maximum exceeds an applicability of the model. To extend its applicability, a newly modified model is proposed in this paper by assuming that the bubbles in such high void fraction regions coalesce with each other and adhere to the neighboring impeller walls so as to form a fixed cavity. Using this model, the flows in a radial-flow pump are solved. The cavity obtained increases progressively from the shroud to the hub in the section just after the impeller inlet when the inlet void fraction exceeds a critical value and finally fills the section, showing close relation with the experiments when the pump loses its function due to an air-filled blockade. (author)
International Nuclear Information System (INIS)
To predict the behavior of air-water two-phase flows in a centrifugal pump impeller, a three-dimensional numerical method is proposed based on a bubbly flow model. If it is assumed that the mixtures are homogeneous bubbly flow containing fine bubbles compared with the characteristic length of the impeller channel, then the equations of motion of the mixtures are represented by those of liquid phase and its velocity is expressed as a potential for the quasi-harmonic equation. The equations are solved by use of the finite element method to obtain the velocities and pressures, and the equation of motion of an air bubble is integrated numerically on this flow field to obtain the void fraction. These calculations are repeated until the solutions converge. The results obtained show good agreement with experiments within the range of bubbly flow regime. (author)
Image processing analysis on the air-water slug two-phase flow in a horizontal pipe
Dinaryanto, Okto; Widyatama, Arif; Majid, Akmal Irfan; Deendarlianto, Indarto
2016-06-01
Slug flow is a part of intermittent flow which is avoided in industrial application because of its irregularity and high pressure fluctuation. Those characteristics cause some problems such as internal corrosion and the damage of the pipeline construction. In order to understand the slug characteristics, some of the measurement techniques can be applied such as wire-mesh sensors, CECM, and high speed camera. The present study was aimed to determine slug characteristics by using image processing techniques. Experiment has been carried out in 26 mm i.d. acrylic horizontal pipe with 9 m long. Air-water flow was recorded 5 m from the air-water mixer using high speed video camera. Each of image sequence was processed using MATLAB. There are some steps including image complement, background subtraction, and image filtering that used in this algorithm to produce binary images. Special treatments also were applied to reduce the disturbance effect of dispersed bubble around the bubble. Furthermore, binary images were used to describe bubble contour and calculate slug parameter such as gas slug length, gas slug velocity, and slug frequency. As a result the effect of superficial gas velocity and superficial liquid velocity on the fundamental parameters can be understood. After comparing the results to the previous experimental results, the image processing techniques is a useful and potential technique to explain the slug characteristics.
Local gas- and liquid-phase measurements for air-water two-phase flows in a rectangular channel
International Nuclear Information System (INIS)
Local gas- and liquid-phase measurements of various gas-liquid two-phase flows, including bubbly, cap-bubbly, slug, and churn-turbulent flows, were performed in an acrylic vertical channel with a rectangular cross section of 30 mm x 10 mm and height of 3.0 m. All the measurements were carried out at three measurement elevations along the flow channel, with z/Dh = 9, 72, and 136, respectively, to study the flow development. The gas-phase velocity, void fraction, and bubble number frequency were measured using a double-sensor conductivity probe. A high-speed imaging system was utilized to perform the flow regime visualization and to provide additional quantitative information of the two-phase flow structure. An image processing scheme was developed to obtain the gas-phase velocity, void fraction, Sauter mean diameter, bubble number density, and interfacial area concentration. The liquid-phase velocity and turbulence measurements were conducted using a particle image velocimetry-planar laser-induced fluorescence (PIV-PLIF) system, which enables whole-field and high-resolution data acquisition. An optical phase separation method, which uses fluorescent particles and optical filtration technique, is adopted to extract the velocity information of the liquid phase. An image pre-processing scheme is imposed on the raw PIV images acquired to remove noises due to the presence of bubble residuals and optically distorted particles in the images captured by the PIV-PLIF system. Due to the better light access and less bubble distortion in the narrow rectangular channel, the PIV-PLIF system were able to perform reasonably well in flows of even higher void fractions as compared to the situations with circular pipe test sections. The flow conditions being studied covered various flow regime transitions, void fractions, and liquid-phase flow Reynolds numbers. The obtained experimental data can also be used to validate two-phase CFD results. (author)
Zboray, Robert; Dangendorf, Volker; Mor, Ilan; Bromberger, Benjamin; Tittelmeier, Kai
2015-01-01
In a previous work we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify ...
Analysis of Air-Water Two Phase Flow for K-HERMES-HALF Experiment using RELAP5/MOD3
Energy Technology Data Exchange (ETDEWEB)
Park, Rae Joon; Ha, Kwang Soon; Kim, Sang Baik; Hong, Seong Wan [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Heo, Sun [KHNP Nuclear Engineering and Technology Institute, Daejeon (Korea, Republic of)
2011-05-15
The IVR (In-Vessel corium Retention) through the ERVC (External Reactor Vessel Cooling) is known to be an effective means for maintaining the integrity of the reactor pressure vessel during a severe accident in a nuclear power plant. This measure has been adopted in some low-power reactors such as the AP600, AP1000, and the Loviisa nuclear power plants as a design feature, and in the high-power reactor of the APR (Advanced Power Reactor) 1400 as an accident management strategy for severe accident mitigation. As part of a study on two-phase flow in the reactor cavity under external reactor vessel cooling in the APR1400, K-HERMES-HALF experiment (Hydraulic Evaluation of Reactor cooling Mechanism by External Self-induced flow-HALF scale) had performed at KAERI. This large-scale experiment using a half-height and half-sector model of the APR1400 uses the non-heating method of the air injection. In this research, K-HERMES-HALF test results had been evaluated by using RELAP5/MOD3 computer code to observe and evaluate the two-phase natural circulation phenomena through the annulus gap between the outer reactor vessel and the vessel insulation material
Energy Technology Data Exchange (ETDEWEB)
Minemura, Kiyoshi; Kinoshita, Katsuhiko [Nagoya Univ. (Japan). School of Informatics and Sciences; Ihara, Masaru; Furukawa, Hironori; Egashira, Kazuyuki [Japan National Oil Corp., Chiba (Japan). Petroleum Engineering Lab.
1995-12-31
To establish the optimum design parameters of offshore oil well centrifugal pumps, which should deliver crude oil containing a large amount of gas, various shapes of pump impeller with different outlet blade angles, locations of leading-edge and numbers of impeller blades as the design parameters were tested with various rotating speeds and suction pressures under air-water two-phase flow conditions. The greater the outlet blade angle, the less the degradation of the pump performance becomes, showing the optimum blade angle approximately equals to 90{degree}.
Energy Technology Data Exchange (ETDEWEB)
Zboray, Robert [Paul Scherrer Institute, PSI Villigen 5232 (Switzerland); Dangendorf, Volker; Bromberger, Benjamin; Tittelmeier, Kai [Physikalisch-Technische Bundesanstalt (PTB), Braunschweig 38116 (Germany); Mor, Ilan [Soreq NRC, Yavne 81800 (Israel)
2015-07-15
In a previous work, we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify the detector and optimize it for the given application, which is described in the present work. Furthermore, we managed to improve the image post-processing methodology and the noise suppression. Using the tailored detector and the improved post-processing, significant increase in the image quality and an order of magnitude lower exposure times, down to 3.33 ms, have been achieved with minimized motion artifacts. Similar to the previous study, different two-phase flow regimes such as bubbly slug and churn flows have been examined. The enhanced imaging quality enables an improved prediction of two-phase flow parameters like the instantaneous volumetric gas fraction, bubble size, and bubble velocities. Instantaneous velocity fields around the gas enclosures can also be more robustly predicted using optical flow methods as previously.
Zboray, Robert; Dangendorf, Volker; Mor, Ilan; Bromberger, Benjamin; Tittelmeier, Kai
2015-07-01
In a previous work, we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify the detector and optimize it for the given application, which is described in the present work. Furthermore, we managed to improve the image post-processing methodology and the noise suppression. Using the tailored detector and the improved post-processing, significant increase in the image quality and an order of magnitude lower exposure times, down to 3.33 ms, have been achieved with minimized motion artifacts. Similar to the previous study, different two-phase flow regimes such as bubbly slug and churn flows have been examined. The enhanced imaging quality enables an improved prediction of two-phase flow parameters like the instantaneous volumetric gas fraction, bubble size, and bubble velocities. Instantaneous velocity fields around the gas enclosures can also be more robustly predicted using optical flow methods as previously.
International Nuclear Information System (INIS)
In a previous work, we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify the detector and optimize it for the given application, which is described in the present work. Furthermore, we managed to improve the image post-processing methodology and the noise suppression. Using the tailored detector and the improved post-processing, significant increase in the image quality and an order of magnitude lower exposure times, down to 3.33 ms, have been achieved with minimized motion artifacts. Similar to the previous study, different two-phase flow regimes such as bubbly slug and churn flows have been examined. The enhanced imaging quality enables an improved prediction of two-phase flow parameters like the instantaneous volumetric gas fraction, bubble size, and bubble velocities. Instantaneous velocity fields around the gas enclosures can also be more robustly predicted using optical flow methods as previously
International Nuclear Information System (INIS)
An electromagnetic velocity meter has been applied to measure the liquid velocity distribution along a large vertical pipe (Inner diameter: 0.48 m, Length of flow path: 2 m) under air-water two-phase flow. This measurement is performed to examine the flow structure along the large vertical pipe where the flow structure has not been fully understood yet. The experiment was performed under atmospheric pressure and superficial air and water velocities in the test section were 0.02--0.87 m/s and 0.01--0.2 m/s, respectively. The accuracy of the electromagnetic velocity meter was firstly checked and was confirmed to be within the error of ±10% for the local liquid velocity up to about 2 m/s under bubbly two-phase flow. The velocity meter was used to measure the radial distribution of local liquid velocity including flow direction in the large vertical pipe. With increasing air flow rate, the axial liquid velocity at the center of the pipe becomes higher, the direction of axial liquid flow near the wall becomes downward and the degree of anisotropy of liquid velocity fluctuation becomes larger. A developing region exists below about 1 m from the bottom of the test section and the flow structure above the elevation is considered to be almost developed based on the measurement of the radial distribution of axial liquid velocity
Zboray, Robert; Mor, Ilan; Bromberger, Benjamin; Tittelmeier, Kai
2015-01-01
In a previous work we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify the detector and optimize it for the given application, which is described in the present work. Furthermore, we managed to improve the image post-processing methodology and the noise suppression. Using the tailored detector and the improved post-processing significant increase in the image quality and an order of magnitude lower exposure times, down to 3.33 ms, have been achieved with minimized motion artifacts. Similar to the previous study, different two-phase flow regimes such as bubbly slug and churn flows have been e...
The Effect of Sudden Change in Pipe Diameter on Flow Patterns of Air-Water Two-Phase
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Flow patterns upstream and downstream of a sudden-contraction cross-section in a vertical straight pipe were presented. By comparing with flow patterns in uniform croes-section vertical tubes, the effect of the sudden change in pipe diameter on flow patterns was analyzed. Flow pattern transition mechanisms were discussed and transition criteria for flow pattern transitions were deduced accordingly using the dimensional analysis.
International Nuclear Information System (INIS)
Two-phase compressible flow fields of air-water are investigated numerically in the fixed Eulerian grid framework. The phase interface is captured via volume fractions of ech phase. A way to model two phase compressible flows as a single phase one is found based on an equivalent equation of states of Tait's type for a multiphase cell. The equivalent single phase field is discretized using the Roe's approximate Riemann solver. Two approaches are tried to suppress the pressure oscillation phenomena at the phase interface, a passive advection of volume fraction and a direct pressure relaxation with the compressible form of volume fraction equation. The direct pressure equalizing method suppresses pressure oscillation successfully and generates sharp discontinuities, transmitting and reflecting acoustic waves naturally at the phase interface. In discretizing the compressible form of volume fraction equation, phase interfaces are geometrically reconstructed to minimize the numerical diffusion of volume fraction and relevant variables. The motion of a projectile in a water-filled tube which is fired by the release of highly pressurized air is simulated presuming the flow field as a two dimensional one, and several design factors affecting the projectile movement are investigated
International Nuclear Information System (INIS)
Full text of publication follows: Within the framework of the nuclear power plant lifetime issue, the assessment of the French 900 MWe (3-loops) series reactor pressure vessel (RPV) integrity has been performed. A simplified analysis has shown that the most severe loading conditions are given by the small break loss of coolant accidents due to the pressurized injection of cold water (9 deg. C) into the cold leg and down comer of the RPV. During these transient scenarios, single or two-phase (uncovered cold leg) flows have been shown in the cold leg, depending on the crack size and RPV model (900 MWe or 1300 MWe). An experimental study has been carried out, on the one hand, to consolidate the numerical results obtained with CFD home code (Code-Saturne) which mainly showed the stratified flow in the cold leg and the fluid flow separation and its oscillations in the down comer during a single phase scenario. These physical phenomena are important for the thermal RPV loading assessment. On the other hand, the absence of experimental two-phase data necessitated to carry out an experimental study around the mixing area behavior (free surface, stratified flow) during an ECC injection with an uncovered cold leg. The new EDF R and D mock up, called HYBISCUS, is a facility which is made out of Plexiglas (atmosphere pressure) and represents a half scale CP0 geometry with one cold leg and part of the down comer. The mock up modularity allows us to insert representative ECC nozzles and a thermal shield. In reference to the reactor scenarios, the experimental operating conditions are derived from the conservation of the density effects (Froude number). For that, a heated salted water flow is used to represent the ECC injection whereas water represents the cold leg fluid. This mock up has been defined in order to represent single phase flow (cold leg and down comer full of water) or two-phase flow (uncovered cold leg) ECC scenarios. This paper reports experimental results
International Nuclear Information System (INIS)
Experimental investigation about the onset flooding was made on an air-water two-phase flow in inclined pipe. The pipe inclination angles examined were 30deg, 45deg and 60deg from horizontal. The tube diameter was 26 mm I.D., and superficial velocities of air and water ranged from 2.2 - 25 m/sec and from 0.018 - 0.141 m/sec, respectively. As a result, it was found that (1) there were two characteristic regimes before and after the onset of flooding, pre-flooding and post-flooding, (2) unstable movement in the liquid film with roll wave was occurred at the onset of flooding, (3) pressure gradient increased suddenly at the onset of flooding, while it decreased gradually in post-flooding after violent fluctuation, (4) the fluctuation in post-flooding was the biggest among the three regimes, (5) the flooding gas velocity increased with the pipe inclination due to the increment of gravity component which has to be sustained by the gas flow. (author)
International Nuclear Information System (INIS)
To predict the behavior of gas-liquid two-phase flows in a centrifugal pump impeller, a three-dimensional numerical method is proposed on the basis of a bubbly flow model. Under the assumption of homogeneous bubbly flow entraining fine bubbles, the equation of motion of the mixture is represented by that of liquid-phase and the liquid velocity is expressed as a potential for a quasi-harmonic equation. This equation is solved with a finite element method to obtain the velocities, and the equation of motion of an air bubble is integrated numerically in the flow field to obtain the void fraction. These calculations are iterated to obtain a converged solution. The method has been applied to a radial-flow pump, and the results obtained have been confirmed by experiments within the range of bubbly flow regime
Two-phase flow characterisation by nuclear magnetic resonance
International Nuclear Information System (INIS)
The results presented in this paper demonstrate the performance of the PFGSE-NMR to obtain a complete characterisation of two-phase flows. Different methods are proposed to characterise air-water flows in different regimes: stationary two-phase flows and flows in transient condition. Finally a modified PFGSE is proposed to analyse the turbulence of air-water bubbly flow. (author)
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
Flow patterns in upstream and downstream straight tubes of sudden-changedareas in ahorizontal straight pipe were experimentally examined. Both sudden-expansioncross-section (SECS)and sudden-contraction cross-section (SCCS) were investigated. The flow pattern mapsupstream anddownstream were delineated and compared with those in straight tubes with uniformcross-sections.The effects of the SECS and SCCS on flow patterns were discussed and analyzed.Furthermore, flowpattern transition mechanisms resulting in occurrences of different flow patternswere simplydiscussed and some transition criteria for the flow pattern transitions were deduced byusing the non-dimensionlized analysis method.
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
Energy Technology Data Exchange (ETDEWEB)
Sato, S. (Tsuyama National College of Technology, Okayama (Japan)); Furukawa, A. (Kyushu University, Fukuoka (Japan). Faculty of Engineering); Takamatsu, Y. (Ariake National College of Technology, Fukuoka (Japan))
1993-11-25
An air/water two-phase flow experiment was carried out on the impellers of a centrifugal pump to study the lifting performance and the flow aspect of gas phase. In the experiment, pressurized air is fed to the blowing pipe of a vertical-shaft type pump through a compressor. Transparent acryl resin was used to form the side wall, etc. of the casing through which a video picture of the flowing aspect of the gas phase was taken. The results showed the flowing aspect suddenly changes due to the increase of air flow rate in a low flow rate region where the angle of incidence of flow is large, and the negative pressure sides of impellers were covered with gas. At this time, the lift lowers sharply and discontinuously and then gradually with extension of the gas residence region. This effect appeared more clearly as the outlet angle of the impeller increased. The experimental result agrees roughly with that of the air-bubble calculation in the region where the gas-liquid ratio is so low that a fine air-bubble flow is maintained, but not in the region where the lift lowers sharply, approaching the result of separate flow calculation. The lift after the gas residence region occurs decreases gradually with the increase of air flow rate, showing the same tendency as the result of separate-flow calculation. 13 refs., 14 figs., 1 tab.
Directory of Open Access Journals (Sweden)
Francisco García
2009-01-01
Full Text Available Se realizó un estudio experimental de patrones de flujo bifásico aire-agua en tuberías horizontales y ligeramente inclinadas. Se realizaron 493 experimentos de flujo bifásico aire-agua de los cuales 191 corresponden a tubería horizontal y 302 corresponden a flujo ascendente. Las distribuciones espaciales de los experimentos incluyen los patrones de flujo estratificado liso y ondulado, tapón, anular y burbuja dispersa. Se desarrollan mapas de patrones de flujo experimentales para cada ángulo de inclinación y se evalúa la capacidad de predicción de cuatro modelos mecanicistas y dos modelos de correlación utilizados comúnmente en la literatura para determinar patrones de flujo. Comparando con los valores experimentales se encuentra que los modelos seleccionados tienen un porcentaje de acierto mayor al 75 %.An experimental study in horizontal and slightly inclined pipelines was performed. A total of 493 air-water two-phase flow experiments were carried out, of which 191 correspond to horizontal pipelines and 302 correspond to upward flow. The space distributions of the experiments include the smooth and wavy stratified, slug, annular and dispersed bubble flow patterns. Experimental maps of the flow patterns for each inclination angle are developed and the prediction capability of four mechanistic models and two correlating models commonly used in the literature for determining flow patterns are evaluated. Comparison between calculated and experimental values indicates that the selected models have a success percentage greater than 75%.
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
In this companion paper, flow patterns in the upstream and downstream tubes of a sudden-expansion cross-section (SECS) in a vertical straight pipe were presented. The effect of SECS on flow patterns upstream and downstream was analyzed by comparing with flow patterns in uniform cross-section vertical tubes. It is found the effect is great. There exist great instabilities of two-phase flow in the neighboring areas of the SECS both downstream and upstream.
Two-Phase Flow in Heterogeneous Media
Ghaffari, Hamed O
2009-01-01
In this study, we investigate the appeared complexity of two-phase flow (air-water) in a heterogeneous soil where the supposed porous media is non-deformable media which is under the time-dependent gas pressure. After obtaining of governing equations and considering the capillary pressure-saturation and permeability functions, the evolution of the models unknown parameters were obtained. In this way, using COMSOL (FEMLAB) and fluid flow-script Module, the role of heterogeneity in intrinsic permeability was analysed. Also, the evolution of relative permeability of wetting and non-wetting fluid, capillary pressure and other parameters were elicited.
New concept of analytical method for two-phase flow
International Nuclear Information System (INIS)
The authors are developing a new analytical method for vertical upward two-phase flow based on a concept that two-phase flow with minimum pressure energy consumption rate is the most stable and easily flowable two-phase flow for the given boundary conditions and, thus, such two-phase flow should be realized actually. Although this concept is applied basically one-dimensionally in the analytical method, gravity convection effect due to density difference between liquid film on the channel wall and two-phase flow core in the central region of the channel is taken into account through a two-dimensional turbulent flow analysis. An air-water two-phase flow experiment was performed to verify the proposed analytical method. In the present paper, results of the experimental analysis with the proposed method are reported. (author)
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume IV. Chapters 15-19)
Energy Technology Data Exchange (ETDEWEB)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume II. Chapters 6-10)
Energy Technology Data Exchange (ETDEWEB)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume III. Chapters 11-14)
Energy Technology Data Exchange (ETDEWEB)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume I. Chapters 1-5)
Energy Technology Data Exchange (ETDEWEB)
Guo, T.; Park, J.; Kojasoy, G.
2003-03-15
Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.
Wallis, Graham B.
1989-01-01
Some features of two recent approaches of two-phase potential flow are presented. The first approach is based on a set of progressive examples that can be analyzed using common techniques, such as conservation laws, and taken together appear to lead in the direction of a general theory. The second approach is based on variational methods, a classical approach to conservative mechanical systems that has a respectable history of application to single phase flows. This latter approach, exemplified by several recent papers by Geurst, appears generally to be consistent with the former approach, at least in those cases for which it is possible to obtain comparable results. Each approach has a justifiable theoretical base and is self-consistent. Moreover, both approaches appear to give the right prediction for several well-defined situations.
Development of methods for mass flow measurement of non-stationary two-phase flows
International Nuclear Information System (INIS)
The topics of the present work are: 1) functioning and testing of a True Mass Flow Meter (TMFM), 2) development of an infra-red absorption measuring process to determine the single components and the mass flows in a non-stationary air/water two-phase flow, 3) presentation of a radionuclide measuring method to measure two-phase mass flow, 4) description of a test stand to calibrate various two-phase mass flow measuring methods. (RW/LH)
Flow pattern maps in two phase flow: present panorama
International Nuclear Information System (INIS)
In this work is presented a general panorama on the condition that watch over the related understanding to the pattern maps of flux regimes in the two-phase flow. The revision that has been done no exhaustive treat of flux patterns observed in vertical and horizontal ducts. As resulting of this investigation, it has been to make evident the necessity of lighting up with precision the use of flux pattern maps that they are not framed respect to really two-phase flow, but that they correspond really to the simultaneous flux of a gas and a liquid un miscible flowing in adiabatic conditions. The case more common of late these is the relative to the air-water mixture. The observed necessity has generated in the Thermo fluids Department of National Institute of Nuclear Research the restlessness of realizing experimental studies in this area. This in spite of being motive of research over 40 years and also of counting with a vast reported bibliography, on one the hand it has not conveyed to obtain representations of general character. And on the other hand it has origined a great confusion about the applicability of available information. In the same way it is described the advances developed in the experimental studies in the field of forced convection, as to only phase as one in two phases. (Author)
Flow instabilities in two-phase flow system with and without phase change
International Nuclear Information System (INIS)
The gas-liquid two-phase flow of various types, such as single component or multiple components, and boiling two-phase flow or insulated two-phase flow, exist in piping systems, and the undesirable phenomena for the operation of systems such as the large scale pulsation of flow rate and the uneven distribution of flow may occur according to the condition. Generally these phenomena are called unstable flow. The author has carried out the research on unstable flow with air-water two-phase flow system, but a question arose to what extent the results in air-water system are applicable to boiling system. The unstable flow is explained with some examples. In this study, the similarity of pulsation in boiling system and insulated system was clarified, using the examples of pressure drop oscillation and flow rate distribution, and the theory to treat them in unified way was presented. The range of discussion is limited to the phenomena that do not depend on the microstructure of flow. The experimental setups were Freon boiling system, air-water capillary system and air-water vertical tube system. The characteristics of pressure drop oscillation and the fundamental mechanism, the theoretical analysis of pressure drop oscillation, the uneven distribution of flow rate in parallel tubes, the stability of flow rate distribution, and the numerical simulation are reported. (Kako, I.)
Håland, Gaute
2010-01-01
The use of multiphase flow meters (MPFMs) increase each year. The main reasons for this are the cost benefits connected to the use of such a meter by eliminating exclusive lines to the test separator and the test separator itself and the demand for a meter that can measure the produced fluids in real time without separating the phases. The MPFMs measures the flow rate by use of different measurement principles and techniques, and in combination of these, e.g. by means of Venturi and void frac...
Two-phase flow in refrigeration systems
Gu, Junjie; Gan, Zhongxue
2013-01-01
Two-Phase Flow in Refrigeration Systems presents recent developments from the authors' extensive research programs on two-phase flow in refrigeration systems. This book covers advanced mass and heat transfer and vapor compression refrigeration systems and shows how the performance of an automotive air-conditioning system is affected through results obtained experimentally and theoretically, specifically with consideration of two-phase flow and oil concentration. The book is ideal for university postgraduate students as a textbook, researchers and professors as an academic reference book, and b
Coherent Calculation for Air-Water Flow and Boiling Flow by Using CUPID Code
International Nuclear Information System (INIS)
The Korea Atomic Energy Research Institute has been developing a three-dimensional thermal-hydraulic code, called CUPID, which was motivated from practical needs for the realistic simulation of two-phase flows in nuclear reactor components. This paper presents coherent simulation of an air-water flow test and a sub-cooled boiling flow test, and the model implementation of related to them. The closure relations for the air-water flow and sub-cooled boiling flow are turbulence model, interfacial non-drag force, interfacial condensation, wall evaporation model, interfacial area transport equation, and so on
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)
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
Laser diagnostics in two phase flows
Energy Technology Data Exchange (ETDEWEB)
Krueger, S.
2001-06-01
The existence of a huge lack of experimental data from both technical and fundamental two phase flows was mentioned. The development of laser based non-intrusive measurement techniques to overcome this problem were the task of this work. An optical flow algorithm was adapted for the determination of the velocity fields of continuous and dispersed phase in flow systems. It was used as data reduction method for the newly developed gaseous imaging velocimetry (GIV) technique. The measurement technique including the data reduction has been validated by comparing it to the well-established particle image velocimetry (PIV). Its applicability on scalar data from 2D two-phase flows and reacting gaseous flows was demonstrated. Laser based measurement techniques concerning 3D two-phase flows have also been developed. Solutions for the measurement of the velocity field of the gaseous phase in between the droplets as well as of the liquid phase in an automotive DI spray have been given. (orig.)
Two-phase flow in fractured rock
International Nuclear Information System (INIS)
This report gives the results of a three-day workshop on two-phase flow in fractured rock. The workshop focused on two-phase flow processes that are important in geologic disposal of nuclear waste as experienced in a variety of repository settings. The goals and objectives of the workshop were threefold: exchange information; describe the current state of understanding; and identify research needs. The participants were divided into four subgroups. Each group was asked to address a series of two-phase flow processes. The following groups were defined to address these processes: basic flow processes; fracture/matrix interactions; complex flow processes; and coupled processes. For each process, the groups were asked to address these four issues: (1) describe the two-phase flow processes that are important with respect to repository performance; (2) describe how this process relates to the specific driving programmatic issues given above for nuclear waste storage; (3) evaluate the state of understanding for these processes; and (4) suggest additional research to address poorly understood processes relevant to repository performance. The reports from each of the four working groups are given here
Two-phase flow measurement by pulsed neutron activation techniques
International Nuclear Information System (INIS)
The Pulsed Neutron Activation (PNA) technique for measuring the mass flow velocity and the average density of two-phase mixtures is described. PNA equipment can be easily installed at different loops, and PNA techniques are non-intrusive and independent of flow regimes. These features of the PNA technique make it suitable for in-situ measurement of two-phase flows, and for calibration of more conventional two-phase flow measurement devices. Analytic relations governing the various PNA methods are derived. The equipment and procedures used in the first air-water flow measurement by PNA techniques are discussed, and recommendations are made for improvement of future tests. In the present test, the mass flow velocity was determined with an accuracy of 2%, and average densities were measured down to 0.08 g/cm3 with an accuracy of 0.04 g/cm3. Both the accuracy of the mass flow velocity measurement and the lower limit of the density measurement are functions of the injected activity and of the total number of counts. By using a stronger neutron source and a larger number of detectors, the measurable density can be decreased by a factor of 12 to .007 g/cm3 for 12.5 cm pipes, and to even lower ranges for larger pipes
Study on flooding in two-phase flow
International Nuclear Information System (INIS)
In a countercurrent two-phase flow, where gas phase flows in the upward direction against a gravity-driven liquid downflow, the liquid downflow rate begins to be limited when the gas flow rate exceeds a certain threshold value. This phenomenon, termed 'flooding', may occur during a loss-of-coolant accident (LOCA) at such locations in reactor coolant system as steam generator (SG) U-tubes in a pressurized water reactor (PWR). Flooding generally tends to reduce the amount of water available for core cooling in emergency situations. Flooding has been studied for various flow conditions and geometries, in particular for vertical channels. Most of these studies were concerned with those situations where the lower entry of the channel is exposed to the gas phase or a gas-continuous two-phase flow, and scarcely dealt with such situations where the liquid is the continuous phase at the channel lower entry. However, in a PWR small-break LOCA, where the reactor coolant inventory is depleted only slowly, the latter situations would be encountered more frequently than the former. The present study is concerned with flooding in a vertical channel whose lower entry is facing to a liquid-continuous two-phase flow. Experiments were conducted using Freon R-113 as a simulant of high-pressure steam-water two-phase flow. Experimental results indicate that flooding for this situation initiates when the two-phase mixture swell level in the channel, which indicates large fluctuations with time, reaches the channel top entry at the peaks of level fluctuations. It was also found that the flooding correlation developed formerly by the authors for air-water flows can be applied to the present R-113 case if the difference in fluid properties are considered appropriately. (author)
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)
Development of gas-liquid two-phase flow interfacial structure in a confined bubbly flow
International Nuclear Information System (INIS)
In gas-liquid two-phase flow systems, the interfacial structure specifies the geometric capability of the interfacial transfer of mass, momentum, and energy between the two phases. In view of this, extensive experiments have been carried out in an air-water upward two-phase flow through a test section of 20-cm in width and 1-cm in gap. In it, the local two-phase flow parameters were acquired by the double-sensor conductivity probe at three different elevations in a wide range of the bubbly flow conditions. The acquired local parameters include void fraction ( α), interfacial area concentration (ai), bubble velocity (Ub), bubble Sauter mean diameter (Dsm) and bubble frequency. By taking advantage of the transparent two-dimensional flow path, the flow regime map was constructed through flow visualization. Examination of the measured parameters reveals the development of the interfacial structure due to bubble interactions. (author)
Two-phase flow and heat transfer under low gravity
Frost, W.
1981-11-01
Spacelab experiment to investigate two-phase flow patterns under gravity uses a water-air mixture experiment. Air and water are circulated through the system. The quality or the mixture or air-water is controlled. Photographs of the test section are made and at the same time pressure drop across the test section is measured. The data establishes a flow regime map under reduced gravity conditions with corresponding pressure drop correlations. The test section is also equipped with an electrical resistance heater in order to allow a flow boiling experiment to be carried out using Freon II. High-speed photographs of the test section are used to determine flow patterns. The temperature gradient and pressure drop along the duct can be measured. Thus, quality change can be measured, and heat transfer calculated.
Research on one-dimensional two-phase flow
International Nuclear Information System (INIS)
In the Part I, the author describes about the fundamental form of the hydraulic basic equations for a one-dimensional two-phase flow (two fluid model). Most of the discussions are concentrated on the treatment of phase change inertial force terms in the equations of motion and the author's equations of motion have a strong uniqueness on the following three points in comparison with conventional equations of motion. (1) To express force balance of unit mass two-phase fluid instead of that of unit volume two-phase fluid. (2) To pick up the unit existing mass and the unit flowing mass as the unit mass of two-phase fluid. (3) To apply the kinetic energy principle instead of the momentum low in the evaluation of stational inertia force term. In these three, the item (1) is for excluding a part of momentum change or kinetic energy change due to mass change of the elementary part of fluid, which is independent of force. The item (2) is not to introduce a phenomenological physical model into the evaluation of phase change inertial force term. And the item (3) is for correctly applying the momentum law taking into account the difference of representative velocities between the main flow fluid (vapor phase or liquid phase) and the phase change part of fluid. In the Part II, characteristics of various kinds of high speed two-phase flow are clarified theoretically by using the basic equations derived in the Part I. It is demonstrated that the steam-water two-phase critical flow with violent flashing and the air-water two-phase critical flow without phase change can be described with fundamentally the same basic equations. Furthermore, by comparing the experimental data from the two-phase critical discharge test and the author's theoretical prediction, the two-phase discharge coefficient, CD, for large sharp-edged orifice is determined as the value which is not affected by the experimental facility characteristics, etc.. (J.P.N.)
An introduction to two-phase flows
International Nuclear Information System (INIS)
This course aims at proposing the necessary background for a rational approach to two-phase flows which are notably present in numerous industrial devices and equipment designed to perform energy transfer or mass transfer. The first part proposes a phenomenological approach to main two-phase flow structures and presents their governing variables. The second part presents some proven measurement techniques. The third part focuses on modelling. It recalls the equation elaboration techniques which are based on basic principles of mechanics and thermodynamics and on the application of different averaging operators to these principles. Some useful models are then presented such as models of pressure loss in a duct. The last chapter addresses some fundamental elements of heat transfers in ebullition and condensation
Modeling of two-phase slug flow
International Nuclear Information System (INIS)
When gas and liquid flow in a pipe, over a range of flow rates, a flow pattern results in which sequences of long bubbles, almost filling the pipe cross section, are successively followed by liquid slugs that may contain small bubbles. This flow pattern, usually called slug flow, is encountered in numerous practical situations, such as in the production of hydrocarbons in wells and their transportation in pipelines; the production of steam and water in geothermal power plants; the boiling and condensation in liquid-vapor systems of thermal power plants; emergency core cooling of nuclear reactors; heat and mass transfer between gas and liquid in chemical reactors. This paper provides a review of two phase slug flow modeling
Stability of oscillatory two phase Couette flow
Coward, Adrian V.; Papageorgiou, Demetrios T.
1993-01-01
We investigate the stability of two phase Couette flow of different liquids bounded between plane parallel plates. One of the plates has a time dependent velocity in its own plane, which is composed of a constant steady part and a time harmonic component. In the absence of time harmonic modulations, the flow can be unstable to an interfacial instability if the viscosities are different and the more viscous fluid occupies the thinner of the two layers. Using Floquet theory, we show analytically in the limit of long waves, that time periodic modulations in the basic flow can have a significant influence on flow stability. In particular, flows which are otherwise unstable for extensive ranges of viscosity ratios, can be stabilized completely by the inclusion of background modulations, a finding that can have useful consequences in many practical applications.
Coupling two-phase fluid flow with two-phase darcy flow in anisotropic porous media
Chen, J.
2014-06-03
This paper reports a numerical study of coupling two-phase fluid flow in a free fluid region with two-phase Darcy flow in a homogeneous and anisotropic porous medium region. The model consists of coupled Cahn-Hilliard and Navier-Stokes equations in the free fluid region and the two-phase Darcy law in the anisotropic porous medium region. A Robin-Robin domain decomposition method is used for the coupled Navier-Stokes and Darcy system with the generalized Beavers-Joseph-Saffman condition on the interface between the free flow and the porous media regions. Obtained results have shown the anisotropic properties effect on the velocity and pressure of the two-phase flow. 2014 Jie Chen et al.
Two-Phase Flow Complexity in Heterogeneous Media
Ghaffari, Hamed O
2009-01-01
In this study, we investigate the appeared complexity of two-phase flow (air/water) in a heterogeneous soil where the supposed porous media is non-deformable media which is under the timedependent gas pressure. After obtaining of governing equations and considering the capillary pressuresaturation and permeability functions, the evolution of the model unknown parameters were obtained. In this way, using COMSOL (FEMLAB) and fluid flow/script Module, the role of heterogeneity in intrinsic permeability was analysed. Also, the evolution of relative permeability of wetting and non-wetting fluid, capillary pressure and other parameters were elicited. In the last part, a complex network approach to analysis of emerged patterns will be employed.
Refrigeration. Two-Phase Flow. Flow Regimes and Pressure Drop
DEFF Research Database (Denmark)
Knudsen, Hans-Jørgen Høgaard
2002-01-01
The note gives the basic definitions used in two-phase flow. Flow regimes and flow regimes map are introduced. The different contributions to the pressure drop are stated together with an imperical correlation from the litterature....
Two Phase Flow Simulation Using Cellular Automata
International Nuclear Information System (INIS)
The classical mathematical treatment of two-phase flows is based on the average of the conservation equations for each phase.In this work, a complementary approach to the modeling of these systems based on statistical population balances of aut omata sets is presented.Automata are entities defined by mathematical states that change following iterative rules representing interactions with the neighborhood.A model of automata for two-phase flow simulation is presented.This model consists of fie lds of virtual spheres that change their volumes and move around a certain environment.The model is more general than the classical cellular automata in two respects: the grid of cellular automata is dismissed in favor of a trajectory generator, and the rules of interaction involve parameters representing the actual physical interactions between phases.Automata simulation was used to study unsolved two-phase flow problems involving high heat flux rates. One system described in this work consists of a vertical channel with saturated water at normal pressure heated from the lower surface.The heater causes water to boil and starts the bubble production.We used cellular automata to describe two-phase flows and the interaction with the heater.General rule s for such cellular automata representing bubbles moving in stagnant liquid were used, with special attention to correct modeling of different mechanisms of heat transfer.The results of the model were compared to previous experiments and correlations finding good agreement.One of the most important findings is the confirmation of Kutateladze's idea about a close relation between the start of critical heat flux and a change in the flow's topology.This was analyzed using a control volume located in the upper surface of the heater.A strong decrease in the interfacial surface just before the CHF start was encountered.The automata describe quite well some characteristic parameters such as the shape of the local void fraction in the
MHD Generators Operating with Two-Phase Liquid Metal Flows
International Nuclear Information System (INIS)
with a sequence of tests in which the generator performance will be studied at mixture, qualities up to 50%. The trends of the data accumulated to date have been verified by analysis. A second generator in which the two-phase mixture is passed directly through the generator with no. deliberate attempt to form a film is also being studied. Experimental studies of air-water mixtures have shown that the conductivity of two-phase mixtures does not deteriorate excessively until mixture qualities of 30% are reached. A continuous functional relationship between the quality and conductivity exists even though the flow pattern traverses the gamut of two-phase flow regimes, from bubble to dispersed annular. From these tests, it appears that the electrical conduction is also through an annular film which exists in the various flow regimes. Such a generator has been operated successfully at very low qualities and flow rates, < 5%; currently its performance characteristics in the higher quality regime are being investigated. (author)
Two-phase flow simulation of aeration on stepped spillway
Institute of Scientific and Technical Information of China (English)
CHENG Xiangju; LUO Lin; ZHAO Wenqian; LI Ran
2004-01-01
Stepped spillways have existed as escape works for a very long time. It is found that water can trap a lot of air when passing through steps and then increasing oxygen content in water body, so stepped spillways can be used as a measure of re-aeration and to improve water quality of water body. However, there is no reliable theoretical method on quantitative calculation of re-aeration ability for the stepped spillways. By introducing an air-water two-phase flow model, this paper used k-ε turbulence model to calculate the characteristic variables of free-surface aeration on stepped spillway. The calculated results fit with the experimental results well. It supports that the numerical modeling method is reasonable and offers firm foundation on calculating re-aeration ability of stepped spillways. The simulation approach can provide a possible optimization tool for designing stepped spillways of more efficient aeration capability.
A software technique for flow-rate measurement in horizontal two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Darwich, T.D.; Toral, H.; Archer, J.S. (Imperial Company (EG))
1991-08-01
This paper presents a software technique for measuring individual phase flow rates in two-phase flow. The technique is based on the extraction, classification, and identification of stochastic features from turbulent pressure and void-fraction waveforms. Experiments in a horizontal air/water loop showed that a set of stochastic features is uniquely related to the individual phase flow rates. The software flowmeter is calibrated in situ by compilation of feature sets related to individual phase flow rates in a data base. On-line flow-rate measurement is made by a pattern recognition technique that identifies the best match to the measured feature vector from the calibration data base.
Air-water upward flow in prismatic channel of rectangular base
International Nuclear Information System (INIS)
Experiments had carried out to investigate the two-phase upward air-water flow structure, in a rectangular test section, by using independent measuring techniques, which comprise direct viewing and photography, electrical probes and gamma-ray attenuation. Flow pattern maps and correlations for flow pattern transitions, void fraction profiles, liquid film thickness and superficial average void fraction are proposed and compared to available data. (Author)
Tracer Partitioning in Two-Phase Flow
Sathaye, K.; Hesse, M. A.
2012-12-01
The concentration distributions of geochemical tracers in a subsurface reservoir can be used as an indication of the reservoir flow paths and constituent fluid origin. In this case, we are motivated by the origin of marked geochemical gradients in the Bravo Dome natural CO2 reservoir in northeastern New Mexico. This reservoir contains 99% CO2 with various trace noble gas components and overlies the formation brine in a sloping aquifer. It is thought that magmatic CO2 entered the reservoir, and displaced the brine. This displacement created gradients in the concentrations of the noble gases. Two models to explain noble gas partitioning in two-phase flow are presented here. The first model assumes that the noble gases act as tracers and uses a first order non-linear partial differential equation to compute the volume fraction of each phase along the displament path. A one-way coupled partial differential equation determines the tracer concentration, which has no effect on the overall flow or phase saturations. The second model treats each noble gas as a regular component resulting in a three-component, two-phase system. As the noble gas injection concentration goes to zero, we see the three-component system behave like the one-way coupled system of the first model. Both the analytical and numerical solutions are presented for these models. For the process of a gas displacing a liquid, we see that a noble gas tracer with greater preference for the gas phase, such as Helium, will move more quickly along the flowpath than a heavier tracer that will more easily enter the liquid phase, such as Argon. When we include partial miscibility of both the major and trace components, these differences in speed are shown in a bank of the tracer at the saturation front. In the three component model, the noble gas bank has finite width and concentration. In the limit where the noble gas is treated as a tracer, the width of the bank is zero and the concentration increases linearly
Two-Phase Flow Pressure Drop in Superhydrophobic Channels
Stevens, Kimberly; Crockett, Julie; Maynes, Daniel R.; Iverson, Brian C.
2015-01-01
Superhydrophobic surfaces promote dropwise condensation, which increases the rate of thermal transport, making them desirable for use in condensers. Adiabatic two-phase flow loops have been constructed to gain insight into the hydrodynamics of two-phase systems, laying the groundwork for further study of condensing flow on superhydrophobic surfaces. A two-phase flow loop to measure pressure drop and visualize the flow patterns of two-phase flow in superhydrophobic channels relative to classic...
Numerical calculation of two-phase flows
International Nuclear Information System (INIS)
The theoretical study of time-varying two-phase flow problems in several space dimensions introduces such a complicated set of coupled nonlinear partial differential equations that numerical solution procedures for high-speed computers are required in almost all but the simplest examples. Efficient attainment of realistic solutions for practical problems requires a finite- difference formulation that is simultaneously implicit in the treatment of mass convection, equations of state, and the momentum coupling between phases. Such a method is described, the equations on which it is based are discussed, and its properties are illustrated by means of examples. In particular, the capability for calculating physical instabilities and other time-varying dynamics, at the same time avoiding numerical instability is emphasized. The computer code is applicable to problems in reactor safety analysis, the dynamics of fluidized dust beds, raindrops or aerosol transport, and a variety of similar circumstances, including the effects of phase transitions and the release of latent heat or chemical energy. (U.S.)
Advances in two-phase flow instrumentation
International Nuclear Information System (INIS)
Multiphase flow measurements have become increasingly in a number of process and power systems. However, the need to predict system behavior under transient and accident conditions in nuclear reactors has given impetus to research in this area. Since moving internal interfaces make theoretical predictions difficult, much information for design and supporting analyses is based on experimental observation. The simplest models involving parameters representing mixture density and mixture mass flux, assume thermal equillibrium of the two phases, and are applicable only to a limited number of situations. Most of the parameters, such as interface area and local mixture density, needed for more sophisticated models, are particularly difficult to measure. At present, there are no truly direct methods for measuring local void fraction or mass flux. Local measurements can be taken for a cross-section using, for example, a system of simultaneously quick-closing valves. These valves obtained for the cross section can be integrated, and the result compared with direct measurements for an entire pipeline. Consistent results tend to support the response-model used
Hasan, Abbas; Lucas, Gary
2007-01-01
In two phase flow, differential pressures technique can be used to measure the volume fraction of the gas phase. In the case where no restriction is available in the pipeline, the differential pressure technique can be used only in vertical or inclined pipelines. Two phase air-water pressure drop across a Venturi meter may change its sign from positive to negative due to change in the compressibility of the gas phase. In other words, the inlet of the venturi (upstream section) is not...
Two-phase flow measurements with advanced instrumented spool pieces and local conductivity probes
International Nuclear Information System (INIS)
A series of two-phase, air-water and steam-water tests performed with instrumented spool pieces and with conductivity probes obtained from Atomic Energy of Canada, Ltd. is described. The behavior of the three-beam densitometer, turbine meter, and drag flowmeter is discussed in terms of two-phase models. Application of some two-phase mass flow models to the recorded spool piece data is made and preliminary results are shown. Velocity and void fraction information derived from the conductivity probes is presented and compared to velocities and void fractions obtained using the spool piece instrumentation
Measurements of local two-phase flow parameters in a boiling flow channel
International Nuclear Information System (INIS)
Local two-phase flow parameters were measured lo investigate the internal flow structures of steam-water boiling flow in an annulus channel. Two kinds of measuring methods for local two-phase flow parameters were investigated. These are a two-conductivity probe for local vapor parameters and a Pitot cube for local liquid parameters. Using these probes, the local distribution of phasic velocities, interfacial area concentration (IAC) and void fraction is measured. In this study, the maximum local void fraction in subcooled boiling condition is observed around the heating rod and the local void fraction is smoothly decreased from the surface of a heating rod to the channel center without any wall void peaking, which was observed in air-water experiments. The distributions of local IAC and bubble frequency coincide with those of local void fraction for a given area-averaged void fraction. (author)
Experimental study on flow pattern transitions for inclined two-phase flow
International Nuclear Information System (INIS)
In this paper, experimental data on flow pattern transition of inclination angles from 0-90 are presented. A test section is constructed 2 mm long and I.D 1inch using transparent material. The test section is supported by aluminum frame that can be placed with any arbitrary inclined angles. The air-water two-phase flow is observed at room temperature and atmospheric condition using both high speed camera and void impedance meter. The signal is sampled with sampling rate 1kHz and is analyzed under fully-developed condition. Based on experimental data, flow pattern maps are made for various inclination angles. As increasing the inclination angels from 0 to 90, the flow pattern transitions on the plane jg-jf are changed, such as stratified flow to plug flow or slug flow or plug flow to bubbly flow. The transition lines between pattern regimes are moved or sometimes disappeared due to its inclined angle
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
Flow visualization on flooding phenomena in two phase flow
International Nuclear Information System (INIS)
Flow pattern on flooding phenomena in counter-current two phase flow in vertical tube is experimentally studied by means of dye tracer technique for the following condition: the length -to-diameter ratio L/D=30. Just before flooding, oscillatory motion of the liquid upwards and downwards in the tube is observed. Under flooding conditions, churn flow in the tube is observed. (author)
Chi, Changqing
2016-01-01
Ferrofluids currently are the only type of magnetic liquid materials with wide practical use. The theory on ferrofluids is an example of success to apply statistics to science. Ferrofluids are two-phase liquids consisting of dispersed nanoscale ferromagnetic particles suspended in a carrier fluid. Due to their tiny size, individual ferromagnetic particles clearly exhibit Brownian motions. Only when a large number of randomly-moving particles are subject to an external magnetic field, can they...
Next steps in two-phase flow: executive summary
Energy Technology Data Exchange (ETDEWEB)
DiPippo, R.
1980-09-01
The executive summary includes the following topics of discussion: the state of affairs; the fundamental governing equations; the one-dimensional mixture model; the drift-flux model; the Denver Research Institute two-phase geothermal flow program; two-phase flow pattern transition criteria; a two-fluid model under development; the mixture model as applied to geothermal well flow; DRI downwell instrumentation; two-phase flow instrumentation; the Sperry Research Corporation downhole pump and gravity-head heat exchanger systems; and the Brown University two-phase flow experimental program. (MHR)
Aspects of two-phase gas--liquid flow
International Nuclear Information System (INIS)
A wide range of topics related to current research on liquid-gas flow is reviewed, and the relevance of these topics to the design of heat exchangers is discussed. Information is included on flow patterns; system variables; mathematical models for parallel flow and non-parallel flow; critical two-phase flow; unsteady flow; and types of two-phase flow equipment used in industry. (U.S.)
Two-phase flow dynamics in ECC
International Nuclear Information System (INIS)
The present report summarizes the achievements within the project ''Two-phase Systems and ECC''. The results during 1978 - 1980 are accounted for in brief as they have been documented in earlier reports. The results during the first half of 1981 are accounted for in greater detail. They contain a new model for the Basset force and test runs with this model using the test code RISQUE. Furthermore, test runs have been performed with TRAC-PD2 MOD 1. This code was implemented on Edwards Pipe Blowdown experiment (a standard test case) and UC-Berkeley Reflooding experiment (a non-standard test case.) (Auth.)
Numerical method for two-phase flow discontinuity propagation calculation
International Nuclear Information System (INIS)
In this paper, we present a class of numerical shock-capturing schemes for hyperbolic systems of conservation laws modelling two-phase flow. First, we solve the Riemann problem for a two-phase flow with unequal velocities. Then, we construct two approximate Riemann solvers: an one intermediate-state Riemann solver and a generalized Roe's approximate Riemann solver. We give some numerical results for one-dimensional shock-tube problems and for a standard two-phase flow heat addition problem involving two-phase flow instabilities
Program determines two-phase flow
International Nuclear Information System (INIS)
When a mixture of a gas and a liquid flows along a horizontal pipe, it is possible to have up to seven different flow patterns. These flow patterns are: 1. Dispersed. When nearly all the liquid is entrained as spray by the gas; 2. Annular. The liquid forms a film around the inside wall of the pipe, and the gas flows at a high velocity as a central core; 3. Bubble. Bubbles of gas move along at about the same velocity as the liquid; 4. Stratified. The liquid flows along the bottom of the pipe and the gas flows above over a smooth gas-liquid interface; 5. Wave. Is similar to stratified except the interface is disturbed by waves moving in the direction of flow; 6. Slug. Waves are picked up periodically in the form of frothy slugs that move at a much greater velocity than the average liquid velocity; 7. Plug. Alternate plugs of liquid and gas move along the pipe
Structural developments of turbulent two-phase flow in large pipes
International Nuclear Information System (INIS)
In connection with the thermohydraulic problems of two-phase flow that may be encountered under certain operating conditions in piping systems containing heat sources and sinks such as a CANDU reactor heat transport system, this study investigates some of the turbulent characteristics of both cocurrent air-water two-phase flow and single phase flow in large pipes with horizontal orientation. Pitot tubes together with hot film anemometry have been shown to be an adequate measurement system in turbulent dispersed two-phase flow. A practical semi-empirical formula has been developed to predict local mixture velocity as a function of differential head read by Pitot tube, local void fraction, flow pattern constant, gas-liquid properties, momentum transfer factor and two-phase flow quality. The structural developments of the dispersed mixture velocity was studied along a straight horizontal PVC run and expressed in terms of the radial distance and the pipeline length. A correlation is introduced to determine the local mixture velocity in terms of radial and streamwise distance, two-phase flow quality, gas and liquid densities. A similar correlation is presented to predict the local developments of the void fraction. In addition to those normalized correlations, hypothetical interpretations of the experienced phenonema are presented. It was found that the mixture velocity is significantly influenced by the volumetric mixing ratio of both phases. Conclusions are drawn in the special cases of turbulent single and two-phase flow
Visualization and measurement of two-phase flow in tight rod bundle by neutron tomography
International Nuclear Information System (INIS)
Neutron tomography thermal-hydraulic measurement technique is originally developed based on the neutron radiography, computed tomography and two-phase flow measurement techniques. The purpose of the developing is to measure the void fraction distribution in the Reduced-Moderation Water Reactor which is a water-cooled breeder reactor designed by the JAERI as a future reactor. We have visualized and measured the void distribution of air/water two-phase flow and boiling flow in tight-lattice rod bundles. We used the research reactor JRR-3 as a neutron source. Three-dimensional data can be obtained in order to evaluate the numerical analysis codes. In this manuscript, the neutron tomography system, comparison between the reconstruction methods of computed tomography and examples of the measured two-phase flow data which was taken in the 7 rod bundle with a gap between rods of 1.0 mm. (author)
Acoustics of two-phase pipe flows
van Dijk
2005-01-01
Acoustic signals that are recorded in oil pipelines contain information about the flow. In order to extract this information from the pressure recordings, detailed knowledge about the transmission properties of sound waves in the pipes is required.
INFLUENCE OF SURFACTANT ON TWO-PHASE FLOW REGIME AND PRESSURE DROP IN UPWARD INCLINED PIPES
Institute of Scientific and Technical Information of China (English)
XIA Guo-dong; CHAI Lei
2012-01-01
The influence of a surfactant on the two-phase flow regime and the pressure drop in upward inclined pipes is investigated for various gas/liquid flow rates.The air/water and air/100 ppm sodium dodecyl sulphate aqueous solution are used as the working fluids.The influence of the surfactant on the two-phase flow regime in upward inclined pipes is investigated using the electrical tomographic technique.For 0°,2.5° and 5° pipe inclinations,the surfactant has obvious effect on the transition from the stratified wavy flow to the annular flow,and the range of the stratified smooth flow regime is also extended to higher gas velocities.For 10°pipe inclination,no stratified flow regime is observed in the air/water flow.In the air/surfactant solution system,however,the stratified flow regime can be found in the range of USG =10m/s-28m/s and USL =0.07 m/s-0.2 m/s.For all inclination angles,the changes of the pressure gradient characteristics are accompanied with the flow pattern transitions.Adding surfactant in a two-phase flow would reduce the pressure gradient significantly in the slug flow and annular flow regimes.In the annular flow regime,the pressure gradient gradually becomes free of the influence of the upward inclined angle,and is only dependent on the property of the two-phase flow.
Stochastic modelling of two-phase flows including phase change
International Nuclear Information System (INIS)
Stochastic modelling has already been developed and applied for single-phase flows and incompressible two-phase flows. In this article, we propose an extension of this modelling approach to two-phase flows including phase change (e.g. for steam-water flows). Two aspects are emphasised: a stochastic model accounting for phase transition and a modelling constraint which arises from volume conservation. To illustrate the whole approach, some remarks are eventually proposed for two-fluid models. (authors)
Thermo-Fluid Dynamics of Two-Phase Flow
Ishii, Mamrou
2011-01-01
"Thermo-fluid Dynamics of Two-Phase Flow, Second Edition" is focused on the fundamental physics of two-phase flow. The authors present the detailed theoretical foundation of multi-phase flow thermo-fluid dynamics as they apply to: Nuclear reactor transient and accident analysis; Energy systems; Power generation systems; Chemical reactors and process systems; Space propulsion; Transport processes. This edition features updates on two-phase flow formulation and constitutive equations and CFD simulation codes such as FLUENT and CFX, new coverage of the lift force model, which is of part
Two-phase-flow models and their limitations
International Nuclear Information System (INIS)
An accurate prediction of transient two-phase flow is essential to safety analyses of nuclear reactors under accident conditions. The fluid flow and heat transfer encountered are often extremely complex due to the reactor geometry and occurrence of transient two-phase flow. Recently considerable progresses in understanding and predicting these phenomena have been made by a combination of rigorous model development, advanced computational techniques, and a number of small and large scale supporting experiments. In view of their essential importance, the foundation of various two-phase-flow models and their limitations are discussed in this paper
Sensitivity study of poisson corruption in tomographic measurements for air-water flows
Energy Technology Data Exchange (ETDEWEB)
Munshi, P. (Fraunhofer Institute for Nondestructive Testing, Saarbrucken (Germany)); Vaidya, M.S. (Indian Institute of Technology, Kanpur (India))
1993-01-01
An application of computerized tomography (CT) for measuring void fraction profiles in two-phase air-water flows was reported earlier. Those attempts involved some special radial methods for tomographic reconstruction and the popular convolution backprojection (CBP) method. The CBP method is capable of reconstructing void profiles for nonsymmetric flows also. In this paper, we investigate the effect of corrupted CT data for gamma-ray sources and aCBP algorithm. The corruption in such a case is due to the statistical (Poisson) nature of the source.
Sensitivity study of poisson corruption in tomographic measurements for air-water flows
International Nuclear Information System (INIS)
An application of computerized tomography (CT) for measuring void fraction profiles in two-phase air-water flows was reported earlier. Those attempts involved some special radial methods for tomographic reconstruction and the popular convolution backprojection (CBP) method. The CBP method is capable of reconstructing void profiles for nonsymmetric flows also. In this paper, we investigate the effect of corrupted CT data for gamma-ray sources and aCBP algorithm. The corruption in such a case is due to the statistical (Poisson) nature of the source
Review on two-phase flow instabilities in narrow spaces
International Nuclear Information System (INIS)
Instabilities in two-phase flow have been studied since the 1950s. These phenomena may appear in power generation and heat transfer systems where two-phase flow is involved. Because of thermal management in small size systems, micro-fluidics plays an important role. Typical processes must be considered when the channel hydraulic diameter becomes very small. In this paper, a brief review of two-phase flow instabilities encountered in channels having hydraulic diameters greater than 10 mm are presented. The main instability types are discussed according to the existing experimental results and models. The second part of the paper examines two-phase flow instabilities in narrow spaces. Pool and flow boiling cases are considered. Experiments as well as theoretical models existing in the literature are examined. It was found that several experimental works evidenced these instabilities meanwhile only limited theoretical developments exist in the literature. In the last part of the paper an interpretation of the two-phase flow instabilities linked to narrow spaces are presented. This approach is based on characteristic time scales of the two-phase flow and bubble growth in the capillaries
Gravity Independence of Microchannel Two-Phase Flow Project
National Aeronautics and Space Administration — Most of the amassed two-phase flow and heat transfer knowledge comes from experiments conducted in Earth’s gravity. Space missions span varying gravity...
Research on one-dimensional two-phase flow
International Nuclear Information System (INIS)
In Part I the fundamental form of the hydrodynamic basic equations for a one-dimensional two-phase flow (two-fluid model) is described. Discussions are concentrated on the treatment of phase change inertial force terms in the equations of motion and the author's equations of motion which have a remarkable uniqueness on the following three points. (1) To express force balance of unit mass two-phase fluid instead of that of unit volume two-phase fluid. (2) To pick up the unit existing mass and the unit flowing mass as the unit mass of two-phase fluid. (3) To apply the kinetic energy principle instead of the momentum low in the evaluation of steady inertial force term. In these three, the item (1) is for excluding a part of momentum change or kinetic energy change due to mass change of the examined part of fluid, which is independent of force. The item (2) is not to introduce a phenomenological physical model into the evaluation of phase change inertial force term. And the item (3) is for correctly applying the momentum law taking into account the difference of representative velocities between the main flow fluid (vapor phase or liquid phase) and the phase change part of fluid. In Part II, characteristics of various kinds of high speed two-phase flow are clarified theoretically by the basic equations derived. It is demonstrated that the steam-water two-phase critical flow with violent flashing and the airwater two-phase critical flow without phase change can be described with fundamentally the same basic equations. Furthermore, by comparing the experimental data from the two-phase critical discharge test and the theoretical prediction, the two-phase discharge coefficient, CD, for large sharp-edged orifice is determined as the value which is not affected by the experimental facility characteristics, etc. (author)
Adiabatic boiling of two-phase coolant in upward flow
International Nuclear Information System (INIS)
A mathematical model of the process of adiabatic boiling (self-condensation) of a two-phase coolant in upward (downward) flow is developed. The model takes account of changes in phase properties with static pressure decrease. The process is investigated numerically. Approximate analytical formulas for design calculations are obtained. It is shown that effects of adiabatic boiling (self-condensation) should be taken into account when calculating two-phase coolant flow in stretched vertical channels
Mechanistic multidimensional analysis of horizontal two-phase flows
International Nuclear Information System (INIS)
The purpose of this paper is to discuss the results of analysis of two-phase flow in horizontal tubes. Two flow situations have been considered: gas/liquid flow in a long straight pipe, and similar flow conditions in a pipe with 90 deg. elbow. The theoretical approach utilizes a multifield modeling concept. A complete three-dimensional two-phase flow model has been implemented in a state-of-the-art computational multiphase fluid dynamics (CMFD) computer code, NPHASE. The overall model has been tested parametrically. Also, the results of NPHASE simulations have been compared against experimental data for a pipe with 90 deg. elbow.
Two-Phase flow instrumentation for nuclear accidents simulation
Monni, G.; De Salve, M.; Panella, B.
2014-11-01
The paper presents the research work performed at the Energy Department of the Politecnico di Torino, concerning the development of two-phase flow instrumentation and of models, based on the analysis of experimental data, that are able to interpret the measurement signals. The study has been performed with particular reference to the design of power plants, such as nuclear water reactors, where the two-phase flow thermal fluid dynamics must be accurately modeled and predicted. In two-phase flow typically a set of different measurement instruments (Spool Piece - SP) must be installed in order to evaluate the mass flow rate of the phases in a large range of flow conditions (flow patterns, pressures and temperatures); moreover, an interpretative model of the SP need to be developed and experimentally verified. The investigated meters are: Turbine, Venturi, Impedance Probes, Concave sensors, Wire mesh sensor, Electrical Capacitance Probe. Different instrument combinations have been tested, and the performance of each one has been analyzed.
Numerical simulation of two phase flows in heat exchangers
International Nuclear Information System (INIS)
The report presents globally the works done by the author in the thermohydraulic applied to nuclear reactors flows. It presents the studies done to the numerical simulation of the two phase flows in the steam generators and a finite element method to compute these flows. (author)
Two phase discharge flow prediction in safety valves
International Nuclear Information System (INIS)
Safety relief valves (SRV) are necessary elements in the protection of any pressurised system and the prediction of the expected discharge flows is an important consideration for the valve sizing to ensure that rupture pressures do not occur. The high speed flows that occur inside the SRV are complex particularly when a two-phase flow is involved and lead to a less capable protection device which result in larger valves compared to single phase flows. In this paper the ability of a CFD based two phase mixture model to predict the critical flows of air and water through a safety valve is examined. An industrial refrigeration safety relief valve of ¼″ inlet bore size has been tested experimentally over a pressure range of 6–15 barg and air mass qualities from 0.1 to 1 when discharging to near atmospheric conditions for a fully open condition. A two-dimensional mixture model consisting of mixture mass, momentum, and energy equations, combined with a liquid mass equation and the standard k–ε turbulence model for mixture turbulent transport has been used to predict the two phase flows through the valve. The mixture model results have been compared with the Homogenous Equilibrium Model (HEM) commonly used for in valve sizing in non flashing two phase flow conditions. The accuracy of the models over the two phase flow range are quantified and discussed
Definition of two-phase flow behaviors for spacecraft design
Reinarts, Thomas R.; Best, Frederick R.; Miller, Katherine M.; Hill, Wayne S.
1991-01-01
Data for complete models of two-phase flow in microgravity are taken from in-flight experiments and applied to an adiabatic flow-regime analysis to study the feasibility of two-phase systems for spacecraft. The data are taken from five in-flight experiments by Hill et al. (1990) in which a two-phase pump circulates a freon mixture and vapor and liquid flow streams are measured. Adiabatic flow regimes are analyzed based on the experimental superficial velocities of liquid and vapor, and comparisons are made with the results of two-phase flow regimes at 1 g. A motion analyzer records the flow characteristics at a rate of 1000 frames/sec, and stratified flow regimes are reported at 1 g. The flow regimes observed under microgravitational conditions are primarily annular and include slug and bubbly-slug regimes. The present data are of interest to the design and analysis of two-phase thermal-management systems for use in space missions.
Multidimensional two-phase flow regime distribution in a PWR downcomer during an LBLOCA refill phase
International Nuclear Information System (INIS)
The multidimensional countercurrent two-phase flow regimes that occur in a pressurized-water reactor (PWR) vessel downcomer during the refill phase of a large-break loss-of-coolant accident are studied using a transparent 1/10 scale model of a PWR vessel. The various flow regimes and their distribution in the downcomer have been identified and mapped for a range of air-water flooding experiments. The two-phase flow patterns that are identified in the downcomer included various types of film flows, droplet flows, countercurrent churn flows and cocurrent flows depending on the flooding condition. Through observation of the two-phase flow dynamics it was deduced that the physical mechanisms associated with the flooding processes could be separated into a liquid entrainment process and a film flow reversal process. In addition to the above exercise, the effect of non-uniform injection of water into the downcomer via different combinations of cold leg was studied similarly by determining flooding curves and flow pattern maps. It was found that differences in the flooding characteristic were noticeable for various water inlet configurations when compared with the uniform injection case. The differences could be explained qualitatively in terms of the flooding mechanisms identified previously by examining the flow patterns in the downcomer for the non-uniform injection tests. ((orig.))
Two-phase flow characteristics analysis code: MINCS
International Nuclear Information System (INIS)
Two-phase flow characteristics analysis code: MINCS (Modularized and INtegrated Code System) has been developed to provide a computational tool for analyzing two-phase flow phenomena in one-dimensional ducts. In MINCS, nine types of two-phase flow models-from a basic two-fluid nonequilibrium (2V2T) model to a simple homogeneous equilibrium (1V1T) model-can be used under the same numerical solution method. The numerical technique is based on the implicit finite difference method to enhance the numerical stability. The code structure is highly modularized, so that new constitutive relations and correlations can be easily implemented into the code and hence evaluated. A flow pattern can be fixed regardless of flow conditions, and state equations or steam tables can be selected. It is, therefore, easy to calculate physical or numerical benchmark problems. (author)
Study of the Gas-Liquid Two-Phase Flow Measuring Method Based on the V-Cone Flow Meter
Dong, Feng; Hu, Jun
2007-06-01
The paper presents a proper correlation for measuring air-water two-phase flow based on the V-Cone flow meter (β=0.65). The calibrating methods of discharge coefficient and the corrective coefficient θ of V-Cone were introduced. On the basis of theoretical and experimental studies, the Lin Zonghu correlation was studied. The relationship between θ and static pressure (P) or gas-liquid density ratio was obtained. The root-square-errows of gas mass flow and that of liquid mass flow were 2.25% and 2.23% respectively according to the modified Lin Zonghu correlation.
Analysis of water hammer in two-component two-phase flows
International Nuclear Information System (INIS)
The water hammer phenomena caused by a sudden valve closure in air-water two-phase flows must be clarified for the safety analysis of LOCA in reactors and further for the safety of boilers, chemical plants, pipe transport of fluids such as petroleum and natural gas. In the present paper water hammer phenomena caused by a sudden valve closure in two-component two-phase flow are investigated theoretically and experimentally. The phenomena are more complicated that in single phase-flow due to the fact of the presence of compressible component. Basic partial differential equations based on a one-dimensional homogeneous flow model are solved by the method of characteristic. The analysis is extended to include friction in a two-phase mixture depending on the local flow pattern. The profiles of the pressure transients, the propagation velocity of pressure waves and the effect of valve closure on the transient pressure are found. Different two-phase flow pattern and frictional pressure drop correlations were used including Baker, Chesholm and Beggs ampersand Bril correlations
Designing piping systems for two-phase flow
International Nuclear Information System (INIS)
A wide range of industrial systems, such as thermosiphon reboilers and chemical reactors, involve two-phase gas-liquid flow in conduits. Design of these systems requires information about the flow regime, pressure drop, slug velocity and length, and heat transfer coefficient. An understanding of two-phase flow is critical for the reliable and cost-effective design of such systems. The successful design of a pipeline in two-phase flow, for example, is a two-step process. The first step is the determination of the flow regime. If an undesirable flow regime, such as slug flow, is not anticipated and adequately designed for, the resulting flow pattern can upset a tower control system or cause mechanical failures of piping components. The second step is the calculation of flow parameters such as pressure drop and density to size lines and equipment. Since the mechanism of fluid flow (and heat transfer) depends on the flow pattern, separate flow models are required for different flow patterns
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
International Nuclear Information System (INIS)
In view of the need to determine void fraction and flow regime of vapor-liquid two-phase flow in the steam generator test model, domestic made optical probe was applied on a small-scale freon two-phase flow test rig. Optical probe signals were collected at a sampling rate up to 500 Hz and converted into digital form. Both the time signal, and the amplitude probability density function and FFT spectrum function calculated thereof were analysed in the time and frequency domains respectively. The threshold characterizing vapor or liquid contact with the probe tip was determined from the air-water two-phase flow pressure drop test results. Then, the boiling freon two-phase flow void fraction was determined by single threshold method, and compared with numerical heat transfer computation. Typical patterns which were revealed by the above-mentioned time signal and the functions were found corresponding to distinct flow regimes, as corroborated by visual observation. The experiment shows that the optical probe was a promising technique for two-phase flow void fraction measurement and flow regime identification (3 refs., 15 figs., 1 tab.)
Two-Phase Slug Flow Experiments with Viscous Liquids
Diaz, Mariana J.C.
2016-01-01
The challenges behind the multiphase transport of oil and gas mixtures are increasing as the oil and gas industry is moving towards production from non-conventional reservoirs and in remote locations. Transport of high viscosity fluids in long multiphase pipelines is a particular challenge. Previous experiments have shown that gas-liquid slug flow is a frequent two-phase flow pattern at high liquid viscosities. The slug flow regime is an unstable flow, which may lead to operati...
Experimental investigation two phase flow in direct methanol fuel cells
International Nuclear Information System (INIS)
Direct methanol fuel cells (DMFC) have received many attentions specifically for portable electronic applications since it utilize methanol which is in liquid form in atmospheric condition and high energy density of the methanol. Thus it eliminates the storage problem of hydrogen. It also eliminates humidification requirement of polymeric membrane which is a problem in PEM fuel cells. Some electronic companies introduced DMFC prototypes for portable electronic applications. Presence of carbon dioxide gases due to electrochemical reactions in anode makes the problem a two phase problem. A two phase flow may occur at cathode specifically at high current densities due to the excess water. Presence of gas phase in anode region and liquid phase in cathode region prevents diffusion of fuel and oxygen to the reaction sites thus reduces the performance of the system. Uncontrolled pressure buildup in anode region increases methanol crossover through membrane and adversely effect the performance. Two phase flow in both anode and cathode region is very effective in the performance of DMYC system and a detailed understanding of two phase flow for high performance DMFC systems. Although there are many theoretical and experimental studies available on the DMFC systems in the literature, only few studies consider problem as a two-phase flow problem. In this study, an experimental set up is developed and species distributions on system are measured with a gas chromatograph. System performance characteristics (V-I curves) is measured depending on the process parameters (temperature, fuel ad oxidant flow rates, methanol concentration etc)
Simulation of Two-Phase Flow in Sloshing Tanks
Luppes, Roel; Veldman, Arthur; Wemmenhove, Rik; Kuzmin, A
2011-01-01
The CFD simulation tool ComFLOW is applied to study the effect of tank motions on two-phase flow phenomena inside a sloshing tank. An improved VOF method is used to assure an accurate description of the fluid displacement. With a novel “gravity-consistent” density averaging method, spurious velociti
Pigging analysis for gas-liquid two phase flow in pipelines
International Nuclear Information System (INIS)
A new method to analyze transient phenomena caused by pigging in gas-liquid two-phase flow is developed. During pigging, a pipeline is divided into three sections by two moving boundaries, namely the pig and the leading edge of the liquid slug in front of the pig. The basic equations are mass, momentum and energy conservation equations. The boundary conditions at the moving boundaries are determined from the mass conservation across the boundaries, etc. A finite difference method is used to solve the equations numerically. The method described above is also capable of analyzing transient two-phase flow caused by pressure and flow rate changes. Thus the over-all analysis of transient two-phase flow in pipelines becomes possible. A series of air-water two-phase flow pigging experiments was conducted using 105.3 mm diameter and 1436.5 m long test pipeline. The agreement between the measured and the calculated results is very good
International Nuclear Information System (INIS)
Full text of publication follows: A new type instrumentation, average bidirectional flow tube, was suggested to apply to the single and two phase flow condition. Its working principle is similar to that of the Pitot tube. The pressure measured at the front of the flow tube is equal to the total pressure, while that measured at the rear tube is slightly less than static pressure of flow field due to the suction effect at the downstream. It gives an amplification effect of measured pressure difference at the flow tube. The proposed instrumentation has the characteristics that it could be applicable to low flow condition and measure bidirectional flow. It was tested in the air-water vertical and horizontal test sections which have 0.08 m inner diameter. The pressure difference across the average bidirectional flow tube, system pressure, average void fraction and injection phasic mass flow rates were measured on the measuring plane. Test was performed primarily in the single phase water and air flow condition to get the amplification factor k of the flow tube. The test was also performed in the air-water two phase flow condition and the covered flow regimes were bubbly, slug, churn turbulent flow in the vertical pipe and stratified flow in the horizontal pipe. In order to calculate the phasic and total mass flow rates from the measured differential pressure, Chexal drift-flux correlation and momentum exchange factor between the two phases were introduced. The test result shows that the suggested instrumentation with the measured void fraction, Chexal drift-flux correlation and Bosio and Malnes' momentum exchange model can predict the phasic mass flow rates within 15% error compared to the true values. A new momentum exchange model was also suggested and it gives up to 5% improvement of the measured mass flow rate compared to combination of Bosio and Malnes' momentum exchange model. (authors)
Multiparticle imaging velocimetry measurements in two-phase flow
International Nuclear Information System (INIS)
The experimental flow visualization tool, Particle Image Velocimetry (PIV), is being extended to determine the velocity fields in two and three-dimensional, two-phase fluid flows. In the past few years, the technique has attracted quite a lot of interest. PIV enables fluid velocities across a region of a flow to be measured at a single instant in time in global domain. This instantaneous velocity profile of a given flow field is determined by digitally recording particle (microspheres or bubbles) images within the flow over multiple successive video frames and then conducting flow pattern identification and analysis of the data. This paper presents instantaneous velocity measurements in various two and three- dimensional, two-phase flow situations. (author)
Advanced Conceptual Models for Unsaturated and Two-Phase Flow in Fractured Rock
Energy Technology Data Exchange (ETDEWEB)
Harihar Rajaram; Robert J. Glass; Michael J. Nicholl; Thomas R. Wood
2007-06-24
The Department of Energy Environmental Management Program is faced with two major issues involving two-phase flow in fractured rock; specifically, transport of dissolved contaminants in the Vadose Zone, and the fate of Dense Nonaqueous Phase Liquids (DNAPLs) below the water table. Conceptual models currently used to address these problems do not correctly include the influence of the fractures, thus leading to erroneous predictions. Recent work has shown that it is crucial to understand the topology, or 'structure' of the fluid phases (air/water or water/DNAPL) within the subsurface.
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)
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)
Mathematical modeling of disperse two-phase flows
Morel, Christophe
2015-01-01
This book develops the theoretical foundations of disperse two-phase flows, which are characterized by the existence of bubbles, droplets or solid particles finely dispersed in a carrier fluid, which can be a liquid or a gas. Chapters clarify many difficult subjects, including modeling of the interfacial area concentration. Basic knowledge of the subjects treated in this book is essential to practitioners of Computational Fluid Dynamics for two-phase flows in a variety of industrial and environmental settings. The author provides a complete derivation of the basic equations, followed by more advanced subjects like turbulence equations for the two phases (continuous and disperse) and multi-size particulate flow modeling. As well as theoretical material, readers will discover chapters concerned with closure relations and numerical issues. Many physical models are presented, covering key subjects including heat and mass transfers between phases, interfacial forces and fluid particles coalescence and breakup, a...
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.
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)
Stability of interfacial waves in two-phase flows
International Nuclear Information System (INIS)
The influence of the interfacial pressure and the flow distribution in the one-dimensional two-fluid model on the stability problems of interfacial waves is discussed. With a proper formulation of the interfacial pressure, the following two-phase phenomena can be predicted from the stability and stationary criteria of the interfacial waves: onset of slug flow, stationary hydraulic jump in a stratified flow, flooding in a vertical pipe, and the critical void fraction of a bubbly flow. It can be concluded that the interfacial pressure plays an important role in the interfacial wave propagation of the two-fluid model. The flow distribution parameter may enhance the flow stability range, but only plays a minor role in the two-phase characteristics. (author). 20 refs., 3 tabs., 4 figs
Safety relief valve performance for two-phase flow
International Nuclear Information System (INIS)
The performance of main steam safety relief valve has been evaluated with respect only to the steam. In the present study, two-phase flow and subcooled water blow-out tests with model valves were performed in order to evaluate the valve's characteristics and performance. From the test results, it was made clear that not only for the steam but also for the two-phase flow the measurement data were hardly affected by scaling and also that the reaction force of the fluid to the valve stem was hardly dependent upon the void fraction. Analytical study was performed using the two-phase flow model in the valve. The results of the analysis showed good agreement with the test data. It was shown from the test and analysis results that the reaction force of the two-phase flow and subcooled water to the valve stem was almost as much as that of the steam flow, and the integrity of the safety relief valve could be maintained. (author)
Wire-mesh sensors for two-phase flow investigations
International Nuclear Information System (INIS)
In the annual report 1996 a new wire-mesh sensor for gas-liquid flows was presented. It was used to visualise the cavitation bubble behind a fast acting shut-off valve in a pipeline with a time resolution of over 1000 frames per second for the first time. In the last two years the sensor was applied to an air-water flow in a vertical pipeline (inner diameter D=51.2 mm) to study the flow structure in a wide range of superficial velocities. Besides the void fraction distributions, the high resolution of the sensor allows to calculate bubble size distributions from the primary measuring data. It was possible to study the evolution of the bubble size distribution along the flow path with growing distance from the gas injection (inlet length, L). (orig.)
Velocity and energy relaxation in two-phase flows
Meyapin, Yannick; Gisclon, Marguerite
2009-01-01
In the present study we investigate analytically the process of velocity and energy relaxation in two-phase flows. We begin our exposition by considering the so-called six equations two-phase model [Ishii1975, Rovarch2006]. This model assumes each phase to possess its own velocity and energy variables. Despite recent advances, the six equations model remains computationally expensive for many practical applications. Moreover, its advection operator may be non-hyperbolic which poses additional theoretical difficulties to construct robust numerical schemes |Ghidaglia et al, 2001]. In order to simplify this system, we complete momentum and energy conservation equations by relaxation terms. When relaxation characteristic time tends to zero, velocities and energies are constrained to tend to common values for both phases. As a result, we obtain a simple two-phase model which was recently proposed for simulation of violent aerated flows [Dias et al, 2010]. The preservation of invariant regions and incompressible li...
Takenaka, N; Fujii, T; Mizubata, M; Yoshii, K
1999-01-01
Three-dimensional void fraction distribution of air-water two-phase flow in a 4x4 rod-bundle near a spacer was visualized by fast neutron radiography using a CT method. One-dimensional cross sectional averaged void fraction distribution was also calculated. The behaviors of low void fraction (thick water) two-phase flow in the rod bundle around the spacer were clearly visualized. It was shown that the void fraction distributions were visualized with a quality similar to those by thermal neutron radiography for low void fraction two-phase flow which is difficult to visualize by thermal neutron radiography. It is concluded that the fast neutron radiography is efficiently applicable to two-phase flow studies.
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.
Controlling two-phase flow in microfluidic systems using electrowetting
Gu, Hao
2011-01-01
Electrowetting (EW)-based digital microfluidic systems (DMF) and droplet-based two-phase flow microfluidic systems (TPF) with closed channels are the most widely used microfluidic platforms. In general, these two approaches have been considered independently. However, integrating the two technologie
Dynamic Modeling of Phase Crossings in Two-Phase Flow
DEFF Research Database (Denmark)
Madsen, Søren; Veje, Christian; Willatzen, Morten
2012-01-01
here a numerical implementation and novel study of a fully distributed dynamic one-dimensional model of two-phase flow in a tube, including pressure drop, heat transfer, and variations in tube cross-section. The model is based on a homogeneous formulation of the governing equations, discretized by a...
Determination of bubble parameters in two-phase flow
International Nuclear Information System (INIS)
A development of a probe-detector system for measurement of bubble parameters like size, rise velocity and void fraction in two-phase flow is presented. The method uses an electro resistivity probe and a compact electronic circuit has been developed for obtain this purpose. (author)
Fluid dynamics of cryogenic two-phase flows
International Nuclear Information System (INIS)
The objective of this study was to examine the flow behavior of a methane hydrate/methane-liquid hydrogen dispersed two-phase fluid through a given design of a moderator chamber for the ESS target system. The calculations under simplified conditions, e.g., taking no account of heat input from outside, have shown that the computer code used, CFX, was able to simulate the behavior of the two-phase flow through the moderator chamber, producing reasonable results up to a certain level of the solid phase fraction, that allowed a continuous flow process through the chamber. Inlet flows with larger solid phase fractions than 40 vol% were found to be a ''problem'' for the computer code. From the computer runs based on fractions between 20 and 40 vol%, it was observed that with increasing solid phase fraction at the inlet, the resulting flow pattern revealed a strong tendency for blockage within the chamber, supported by the ''heavy weight'' of the pellets compared to the carrying liquid. Locations which are prone to the development of such uneven flow behavior are the areas around the turning points in the semispheres and near the exit of the moderator. The considered moderator chamber with horizontal inlet and outlet flow for a solid-liquid two-phase fluid does not seem to be an appropriate design. (orig.)
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
High speed motion neutron radiography of two-phase flow
International Nuclear Information System (INIS)
Current research in the area of two-phase flow utilizes a wide variety of sensing devices, but some limitations exist on the information which can be obtained. Neutron radiography is a feasible alternative to ''see'' the two-phase flow. A system to perform neutron radiographic analysis of dynamic events which occur on the order of several milliseconds has been developed at Oregon State University. Two different methods have been used to radiograph the simulated two-phase flow. These are pulsed, or ''flash'' radiography, and high speed movie neutron radiography. The pulsed method serves as a ''snap-shot'' with an exposure time ranging from 10 to 20 milliseconds. In high speed movie radiography, a scintillator is used to convert neutrons into light which is enhanced by an optical intensifier and then photographed by a high speed camera. Both types of radiography utilize the pulsing capability of the OSU TRIGA reactor. The principle difficulty with this type of neutron radiography is the fogging of the image due to the large amount of scattering in the water. This difficulty can be overcome by using thin regions for the two-phase flow or using heavy water instead of light water. The results obtained in this paper demonstrate the feasibility of using neutron radiography to obtain data in two-phase flow situations. Both movies and flash radiographs have been obtained of air bubbles in water and boiling from a heater element. The neutron radiographs of the boiling element show both nucleate boiling and film boiling. (Auth.)
Two phase flow instabilities in horizontal straight tube evaporator
Liang, Nan; Shuangquan, Shao; Tian, Changqing; Yan, Y. Y.
2010-01-01
Abstract It is essential to ensure the stability of a refrigeration system if the oscillation in evaporation process is the primary cause for the whole system instability. This paper is concerned with an experimental investigation of two phase flow instabilities in a horizontal straight tube evaporator of a refrigeration system. The relationship between pressure drop and mass flow with constant heat flux and evaporation pressure is measured and determined. It is found that there is...
Simulation of two-phase flow with varying surface tension.
Lervåg, Karl Yngve
2008-01-01
This thesis is a study on the effects of varying surface tension along an interface separating two fluids. Varying surface tension leads to tangential forces along the interface. This is often called the Marangoni effect. These forces are discussed in detail, and two test cases are considered to analyse the Marangoni effect, and to verify the present implementation. The first test studies steady-state two-phase flow where the fluids are separated with plane interfaces and the flow is driv...
Two-phase Flow Distribution in Heat Exchanger Manifolds
Vist, Sivert
2004-01-01
The current study has investigated two-phase refrigerant flow distribution in heat exchange manifolds. Experimental data have been acquired in a heat exchanger test rig specially made for measurement of mass flow rate and gas and liquid distribution in the manifolds of compact heat exchangers. Twelve different manifold designs were used in the experiments, and CO2 and HFC-134a were used as refrigerants.
Two-Phase flow instrumentation for nuclear accidents simulation
International Nuclear Information System (INIS)
The paper presents the research work performed at the Energy Department of the Politecnico di Torino, concerning the development of two-phase flow instrumentation and of models, based on the analysis of experimental data, that are able to interpret the measurement signals. The study has been performed with particular reference to the design of power plants, such as nuclear water reactors, where the two-phase flow thermal fluid dynamics must be accurately modeled and predicted. In two-phase flow typically a set of different measurement instruments (Spool Piece – SP) must be installed in order to evaluate the mass flow rate of the phases in a large range of flow conditions (flow patterns, pressures and temperatures); moreover, an interpretative model of the SP need to be developed and experimentally verified. The investigated meters are: Turbine, Venturi, Impedance Probes, Concave sensors, Wire mesh sensor, Electrical Capacitance Probe. Different instrument combinations have been tested, and the performance of each one has been analyzed
Design and construction of two phases flow meter
International Nuclear Information System (INIS)
This paper deals with design of the gamma ray correlometer and flow loop system for measuring the velocity between two parallel cross-sections of a pipeline. In the laboratory, the radioisotope source and detector were collimated by brass with small beam slit respectively. The flow loop system consists of transparent pipeline, adjustable frequency pump and water container. As a result, when the construction of the flow loop and correlometer is completed, the velocity of two phases flow can be measured by the cross-correlation techniques. (Author)
Hydrodynamics of single- and two-phase flow in inclined rod arrays
International Nuclear Information System (INIS)
Required inputs for thermal-hydraulic codes are constitutive relations for fluid-solid flow resistance, in single-phase flow, and interfacial momentum exchange (relative phase motion), in two-phase flow. An inclined rod array air-water experiment was constructed to study the hydrodynamics of multidimensional porous medium flow in rod arrays. Velocities, pressures, and bubble distributions were measured in square rod arrays of P/d = 1.5, at 0, 30, 45, and 90 degree inclinations to the vertical flow direction. Constitutive models for single-phase flow resistance are reviewed, new comprehensive models developed, and an assessment with previously published and new data made. The principle of superimposing one-dimensional correlations proves successful for turbulent single-phase inclined flow. For bubbly two-phase incline flow a new flow separation phenomena was observed and modeled. A two-region liquid velocity model is developed to explain the experimentally observed phenomena. Fundamental data for bubbles rising in rod arrays were also taken
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.
Hydrodynamics of single- and two-phase flow in inclined rod arrays
International Nuclear Information System (INIS)
Required inputs for thermal-hydraulic codes are constitutive relations for fluid-solid flow resistance, in single-phase flow, and interfacial momentum exchange (relative phase motion), in two-phase flow. An inclined rod array air-water experiment was constructed to study the hydrodynamics of multidimensional porous medium flow in rod arrays. Velocities, pressures, bubble distributions, and void fractions were measured in inline and rotational square rod arrays of P/d = 1.5, at 0, 30, 45, and 90 degree inclinations to the vertical flow direction. Constitutive models for single-phase flow resistance are reviewed, new comprehensive models developed, and an assessment with previously published and new data made. The principle of superimposing one-dimensional correlations proves successful for turbulent single-phase inclined flow. For bubbly two-phase yawed flow through incline rod arrays a new flow separation phenomena was observed and modeled. Bubbles of diameters significantly smaller than the rod diameter travel along the rod axis, while larger diameter bubbles move through the rod array gaps. The outcome is a flow separation not predictable with current interfacial momentum exchange models. This phenomenon was not observed in rotated square rod arrays. Current interfacial momentum exchange models were confirmed for this rod arrangement. Models for the two phase flow resistance multiplier for cross flow were reviewed and compared with data from cross and yawed flow rod arrays. Both drag and lift components of the multiplier were well predicted by the homogenous model. Other models reviewed overpredicted the data by a factor of two
International Nuclear Information System (INIS)
The additional force arising from rolling motion causes the change of two phase flow resistance. The characteristics of air-water mixture flow resistance in narrow rectangular channel (40 mm × 1.6 mm) in rolling motions were experimentally studied with the rolling periods of 8 s, 12 s, 16 s and the angles of 10°, 15°, 30°, respectively. The experimental results show that the transient frictional factor changes periodically. The larger the mass quality and the maximum rolling angle and the smaller the rolling period, the larger the fluctuation amplitude of frictional pressure drop. A new correction for predicting the transient frictional factor of two-phase flow in rolling motion is proposed with a good accuracy. (authors)
Analysis of water hammer in two-component two-phase flows
International Nuclear Information System (INIS)
The water hammer phenomena caused by a sudden valve closure in air-water two-phase flows must be clarified for the safety analysis of LOCA in reactors and further for the safety of boilers, chemical plants, pipe transport of fluids such as petroleum and natural gas. In the present work water hammer phenomena caused by sudden valve closure in two-component two-phase flows are investigated theoretically and experimentally. The phenomena are more complicated than in single phase-flows due to the fact of the presence of compressible component. Basic partial differential equations based on a one-dimensional homogeneous flow model are solved by the method of characteristic. The analysis is extended to include friction in a two-phase mixture depending on the local flow pattern. The profiles of the pressure transients, the propagation velocity of pressure waves and the effect of valve closure on the transient pressure are found. Different two-phase flow pattern and frictional pressure drop correlations were used including Baker, Chesholm and Beggs and Bril correlations. The effect of the flow pattern on the characteristic of wave propagation is discussed primarily to indicate the effect of void fraction on the velocity of wave propagation and on the attenuation of pressure waves. Transient pressure in the mixture were recorded at different air void fractions, rates of uniform valve closure and liquid flow velocities with the aid of pressure transducers, transient wave form recorders interfaced with an on-line pc computer. The results are compared with computation, and good agreement was obtained within experimental accuracy
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 <
Dynamic modelling for two-phase flow systems
International Nuclear Information System (INIS)
Several models for two-phase flow have been studied, developing a thermal-hydraulic analysis code with one of these models. The program calculates, for one-dimensional cases with variable flow area, the transient behaviour of system process variables, when the boundary conditions (heat flux, flow rate, enthalpy and pressure) are functions of time. The modular structure of the code, eases the program growth. In fact, the present work is the basis for a general purpose accident and transient analysis code in nuclear reactors. Code verification has been made against RETRAN-02 results. Satisfactory results have been achieved with the present version of the code. (Author)
Two-fluid model for two-phase flow
Ishii, M.
1987-06-01
The two-fluid model formulation is discussed in detail. The emphasis of the paper is on the three-dimensional formulation and the closure issues. The origin of the interfacial and turbulent transfer terms in the averaged formulation is explained and their original mathematical forms are examined. The interfacial transfer of mass, momentum, and energy is proportional to the interfacial area and driving force. This is not a postulate but a result of the careful examination of the mathematical form of the exact interfacial terms. These two effects are considered separately. Since all the interfacial transfer terms involve the interfacial area concentration, the accurate modeling of the local interfacial area concentration is the first step to be taken for a development of a reliable two-fluid model closure relations. The interfacial momentum interaction has been studied in terms of the standard-drag, lift, virtual mass, and Basset forces. Available analytical and semi-empirical correlations and closure relations are reviewed and existing shortcomings are pointed out. The other major area of importance is the modeling of turbulent transfer in two-phase flow. The two-phase flow turbulence problem is coupled with the phase separation problem even in a steady-state fully developed flow. Thus the two-phase turbulence cannot be understood without understanding the interfacial drag and lift forces accurately. There are some indications that the mixing length type model may not be sufficient to describe the three-dimensional turbulent and flow structures. Although it is a very difficult challenge, the two-phase flow turbulence should be investigated both experimentally and analytically with long time-scale research.
Measurement of liquid layer in two-phase flow by neutron radiography
International Nuclear Information System (INIS)
The main objective of applying NRG to heat-transferring flow phenomena is to visualize without external disturbance the phenomena in metal pipes and so on which are difficult to visualize. Besides, from the information on the luminance of images, quantitative physical information can be obtained. In Japan Atomic Energy Research Institute, in fiscal year 1993, the experiment on the measurement of liquid films in gas-liquid two-phase flow was carried out. The steam-water experiment was carried out for the purpose of obtaining the systematic data on the thinning of liquid films by the spacers in the simulated fuel assembly channels. The air-water experiment was carried out for the purpose of obtaining the data on the film thickness of falling water against rising air flow in a rectangular channel. The experimental setup and the results are reported. The achievements so far and the plan for hereafter are described. (K.I.)
Experimental Study on Two-Phase Flow in Horizontal Rectangular Minichannel with Y-Junction
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Agus Santoso
2016-03-01
Full Text Available An experimental study was conducted to investigate two-phase air-water flow characteristics, in horizontal rectangular minichannel with Y-junction. The width (W, the height (H and the hydraulic diameter (DH of the rectangular cross section for the upstream side of the junction are 4.60 mm, 2.50 mm and 3.24 mm, while those for the downstream side are 2.36 mm, 2.50 mm and 2.43 mm. The entire test section was machined from transparent acrylic block, so that the flow structure could be visualized. Liquid single-phase and air-liquid twophase flow experiments were conducted at room temperature. The flow pattern, the bubble velocity, the bubble length, and the void fraction were measured with a high-speed video camera. Pressure profile upstream and downstream from the junction was also measured for the respective flows, and the pressure loss due to the contraction at the junction was determined from the pressure profiles. Two flow patterns, i.e., slug and annular flows, were observed in the fully-developed region apart from the junction. In the analysis, the frictional pressure drop data, the two-phase frictional multiplier data, bubble velocity data, bubble length data and void fraction data were compared with calculations by some correlations in literatures. In addition, new pressure loss coefficient correlations for the pressure drop at the junction has been proposed. Results of such experiment and analysis are described in the present paper.
Assessment of intermittent two-phase flow using a high-speed visualization technique
International Nuclear Information System (INIS)
The intermittent two-phase horizontal flow is recognized by many authors to be one of the most highly complex inherently unsteady flow pattern. Great efforts have been made in recent years to develop theoretical models to predict the intermittent flow interfacial parameters. However, as far as the flow structure itself is concerned, these models are not capable to predicting them yet. The liquid slug and gas bubble velocity, length and evolution along the flow are examples of structural parameters that require experimental specialised work to their evaluation. In this paper, we describe the application of a visualization technique to assess the intermittent two-phase air-water horizontal flow. The technique consists in employing a high-speed digital camera to take a series of pictures of the bubbles moving in the upper side of a horizontal pipe, where a gas-liquid mixture flows. From the images obtained the bubbles can be tracked along. Analyzing frame by frame it is possible to extract the gas bubbles lengths and velocities. This investigation is restricted to liquid superficial velocities ranging from 0.3 to 2.0 m/s and to gas superficial velocities ranging from 0.1 to 1.6 m/s. (author)
Reactor vessel and core two-phase flow ultrasonic densitometer
International Nuclear Information System (INIS)
A local ultrasonic density (LUD) detector has been developed by EG and G Idaho, Inc., at the Idaho National Engineering Laboratory (INEL) for the Loss-of-Fluid Test (LOFT) reactor vessel and core two-phase flow density measurements. The principle of operating the sensor is the change in propagation time of a torsional ultrasonic wave in a metal transmission line as a function of the density of the surrounding media. A theoretical physics model is presented which represents the total propagation time as a function of the sensor modulus of elasticity and polar moment of inertia. Separate effects tests and two-phase flow tests have been conducted to characterize the detector. Tests show the detector can perform in a 3430C pressurized water reactor environment and measure the average density of the media surrounding the sensor
Two-phase flow experiments through intergranular stress corrosion cracks
International Nuclear Information System (INIS)
Experimental studies of critical two-phase water flow, through simulated and actual intergranular stress corrosion cracks, were performed to obtain data to evaluate a leak flow rate model and investigate acoustic transducer effectiveness in detecting and sizing leaks. The experimental program included a parametric study of the effects of crack geometry, fluid stagnation pressure and temperature, and crack surface roughness on leak flow rate. In addition, leak detection, location, and leak size estimation capabilities of several different acoustic transducers were evaluated as functions of leak rate and transducer position. This paper presents flow rate data for several different cracks and fluid conditions. It also presents the minimum flows rate detected with the acoustic sensors and a relationship between acoustic signal strength and leak flow rate
Controlling two-phase flow in microfluidic systems using electrowetting
Gu, Hao
2011-01-01
Electrowetting (EW)-based digital microfluidic systems (DMF) and droplet-based two-phase flow microfluidic systems (TPF) with closed channels are the most widely used microfluidic platforms. In general, these two approaches have been considered independently. However, integrating the two technologies into one allows to combine the advantages of both worlds: (i) high throughput (from TPF) and (ii) precise control over each individual drop (from EW). Thus the aim of this thesis was to investiga...
Phase appearance or disappearance in two-phase flows
Cordier, Floraine; Degond, Pierre; Kumbaro, Anela
2011-01-01
This paper is devoted to the treatment of specific numerical problems which appear when phase appearance or disappearance occurs in models of two-phase flows. Such models have crucial importance in many industrial areas such as nuclear power plant safety studies. In this paper, two outstanding problems are identified: first, the loss of hyperbolicity of the system when a phase appears or disappears and second, the lack of positivity of standard shock capturing schemes such as the Roe scheme. ...
Controllability and observability in two-phase porous media flow
Van Doren, J.F.M.; Van den Hof, P.M.J.; Bosgra, O.H.; Jansen, J. D.
2013-01-01
Reservoir simulation models are frequently used to make decisions on well locations, recovery optimization strategies etc. The success of these applications is, among other aspects, determined by the controllability and observability properties of the reservoir model. In this paper it is shown how the controllability and observability of two-phase flow reservoir models can be analyzed and quantified with aid of generalized empirical Gramians. The empirical controllability Gramian can be inter...
A diffuse interface model for two-phase ferrofluid flows
Nochetto, Ricardo H.; Salgado, Abner J.; Tomas, Ignacio
2016-01-01
We develop a model describing the behavior of two-phase ferrofluid flows using phase field-techniques and present an energy-stable numerical scheme for it. For a simplified, yet physically realistic, version of this model and the corresponding numerical scheme we prove, in addition to stability, convergence and as by-product existence of solutions. With a series of numerical experiments we illustrate the potential of these simple models and their ability to capture basic phenomenological feat...
Fluctuation model of a nonequilibrium two-phase channel flow
International Nuclear Information System (INIS)
An ill-posed Cauchy problem for a model of a nonequilibrium two-phase flow in the barotropic approximation is transformed into a well-posed problem by changing the type of the initial hyperbolic equations. Approximation of fluctuations of the phase velocities by a random delta-correlated process and averaging of the equations over its realizations generate a system of parabolic equations. Results of numerical integration of this system are compared with experiment and calculations by well-known models
Fluctuation model of a nonequilibrium two-phase channel flow
Energy Technology Data Exchange (ETDEWEB)
Krivoshei, F.A. [Inst. of Engineering Thermophysics, Kiev (Ukraine)
1994-12-01
An ill-posed Cauchy problem for a model of a nonequilibrium two-phase flow in the barotropic approximation is transformed into a well-posed problem by changing the type of the initial hyperbolic equations. Approximation of fluctuations of the phase velocities by a random delta-correlated process and averaging of the equations over its realizations generate a system of parabolic equations. Results of numerical integration of this system are compared with experiment and calculations by well-known models.
Recent advances in two-phase flow numerics
International Nuclear Information System (INIS)
The authors review three topics in the broad field of numerical methods that may be of interest to individuals modeling two-phase flow in nuclear power plants. The first topic is iterative solution of linear equations created during the solution of finite volume equations. The second is numerical tracking of macroscopic liquid interfaces. The final area surveyed is the use of higher spatial difference techniques
Recent advances in two-phase flow numerics
Energy Technology Data Exchange (ETDEWEB)
Mahaffy, J.H.; Macian, R. [Pennsylvania State Univ., University Park, PA (United States)
1997-07-01
The authors review three topics in the broad field of numerical methods that may be of interest to individuals modeling two-phase flow in nuclear power plants. The first topic is iterative solution of linear equations created during the solution of finite volume equations. The second is numerical tracking of macroscopic liquid interfaces. The final area surveyed is the use of higher spatial difference techniques.
Two-phase flow induced vibrations in CANDU steam generators
International Nuclear Information System (INIS)
The U-Bend region of nuclear steam generators tube bundles have suffered from two-phase cross flow induced vibrations. Tubes in this region have experienced high amplitude vibrations leading to catastrophic failures. Turbulent buffeting and fluid-elastic instability has been identified as the main causes. Previous investigations have focused on flow regime and two-phase flow damping ratio. However, tube bundles in steam generators have vapour generated on the surface of the tubes, which might affect the flow regime, void fraction distribution, turbulent intensity levels and tube-flow interaction, all of which have the potential to change the tube vibration response. A cantilevered tube bundle made of electric cartridges heaters was built and tested in a Freon-11 flow loop at McMaster University. Tubes were arranged in a parallel triangular configuration. The bundle was exposed to two-phase cross flows consisting of different combinations of void from two sources, void generated upstream of the bundle and void generated at the surface of the tubes. Tube tip vibration response was measured optically and void fraction was measured by gamma densitometry technique. It was found that tube vibration amplitude in the transverse direction was reduced by a factor of eight for void fraction generated at the tube surfaces only, when compared to the upstream only void generation case. The main explanation for this effect is a reduction in the correlation length of the turbulent buffeting forcing function. Theoretical calculations of the tube vibration response due to turbulent buffeting under the same experimental conditions predicted a similar reduction in tube amplitude. The void fraction for the fluid-elastic instability threshold in the presence of tube bundle void fraction generation was higher than that for the upstream void fraction generation case. The first explanation of this difference is the level of turbulent buffeting forces the tube bundle was exposed to
Two-phase boundary layer prediction in upward boiling flow
International Nuclear Information System (INIS)
In the present work, the numerical modelling of the two-phase turbulent boundary layer in upward boiling flow was investigated. First, non-dimensional liquid velocity and temperature profiles in the two-phase boundary layer were validated on the one-dimensional section of a pipe with prescribed radial void fraction profiles. Simulations were performed on a fine grid with a commercial code CFX-5 using the k-ω turbulence model. A significant deviation of results from the analytical single-phase and two-phase wall functions from the literature was observed. Second, a wall boiling model in a vertical heated pipe was simulated (CFX-5) on the coarse grid. Here the prediction of the two-phase thermal boudary layer was compared to the experimental data, k-ω calculation on the fine grid and against the singlephase analytical wall function. Again a major deviation against single-phase temperature wall function was obtained. Presented analyses suggest that the existing analytical velocity and temperature wall functions cannot be valid for the boiling boundary layer with the high void fraction on the wall. (author)
An improved scaling model of buffeting lift forces in air-water flows
International Nuclear Information System (INIS)
This paper presents the results of a series of experiments to study the influence of diameter on the loading of a single rigid cylinder subjected to air-water cross-flow. Five rigid cylinders of same length and different diameters (12.15 * 10-3 m to 31.9 * 10-3 m) were tested over void fractions ranging from 10% to 80%. The fluctuating lift forces on the cylinder are measured and represented in the form of power spectral density. A scaling model of these forces previously developed from one series of experiments with one tube diameter (12.15 * 10-3 m) is tested on these new results by investigating the effect of tube diameter D. Unlike single phase results where the force spectra vary as D(3), it is shown that for two-phase flows, the force spectra vary as D2. The experimental data collapse remarkably well. Both local void fraction and flow regime appear to be sensitive parameters. It confirms the importance of a precise knowledge of the local characteristics of two-phase flows in the study of buffeting forces mechanisms. (authors)
Characteristics of spatiotemporal intermittency in two phase flows
International Nuclear Information System (INIS)
The characteristics of temporal and spatiotemporal intermittent, or slug flow, in two phase flashing flows are analyzed in the context of intermittency transition to chaos. Particularly, the possibility of occurence of generic intermittency routes (Types I, II and III) is investigated in the presence of density wave instability in the system and conclusive evidence for the occurrence of Types I and III is presented. Particularly important is the prediction of the mean slug length and the slug length distribution since the slug flow represents an unfavorable flow regime for gas-liquid transportation in pipes. Identification of two generic intermittency routes automatically gives a quantitative prediction concerning the length distribution of laminar and turbulent (slug) phases. Spatiotemporal analysis, based on the bi-othogonal decoposition and concepts from information theory, provides quantitative characterization and prediction of slug flows and possible mechanism of transition from spatiotemporal intermittency to spatiotemporal chaos (turbulence) is outlined. The analysis of the intermittency in two-phase flows was performed on the experimental data obtained in the study of natural circulation instabilities during small break loss-of-coolant accident. 7 refs., 14 figs
International Nuclear Information System (INIS)
As part of a study on a two-phase natural circulation flow between the outer reactor vessel and the insulation material in the reactor cavity under an external reactor vessel cooling of APR (Advanced Power Reactor) 1400, a K-HERMES-HALF (Hydraulic Evaluation of Reactor cooling Mechanism by External Self-induced flow-HALF scale) experiment was performed at KAERI (Korea Atomic Energy Research Institute) using an air injection method. This experiment was analyzed to verify and evaluate the experimental results using the RELAP5/MOD3 computer code. In addition, the geometry scaling on full height & full sector, and a material scaling between air-water and steam-water two phase natural circulation flow, have been performed for an application of the experimental results to an actual APR1400. The RELAP5/MOD3 results on the water circulation mass flow rate are very similar to the experimental results, in general. The water circulation mass flow rate of the full height & full sector case is approximately 7.6-times higher than that of the K-HERMEL-HALF case. The water circulation mass flow rate of the air injection case is 20-50 % higher than that of the steam injection case at 20 % of the injection rate. (author)
High-frame rate, fast neutron imaging of two-phase flow in a thin rectangular channel
Zboray, R; Dangendorf, V; Stark, M; Tittelmeier, K; Cortesi, M; Adams, R
2015-01-01
We have demonstrated the feasibility of performing high-frame-rate, fast neutron radiography of air-water two-phase flows in a thin channel with rectangular cross section. The experiments have been carried out at the accelerator facility of the Physikalisch-Technische Bundesanstalt. A polychromatic, high-intensity fast neutron beam with average energy of 6 MeV was produced by 11.5 MeV deuterons hitting a thick Be target. Image sequences down to 10 millisecond exposure times were obtained using a fast-neutron imaging detector developed in the context of fast-neutron resonance imaging. Different two-phase flow regimes such as bubbly slug and churn flows have been examined. Two phase flow parameters like the volumetric gas fraction, bubble size and bubble velocities have been measured. The first results are promising, improvements for future experiments are also discussed.
Numerical simulation of two phase flows in heat exchangers
International Nuclear Information System (INIS)
The author gives an overview of his research activity since 1981. He first gives a detailed presentation of properties and equations of two-phase flows in heat exchangers, and of their mathematical and numerical investigation: semi-local equations (mass conservation, momentum conservation and energy conservation), homogenized conservation equations (mass, momentum and enthalpy conservation, boundary conditions), equation closures, discretization, resolution algorithm, computational aspects and applications. Then, he reports the works performed in the field of turbulent flows, hyperbolic methods, low Mach methods, the Neptune project, and parallel computing
Interfacial area measurements in two-phase flow
International Nuclear Information System (INIS)
A thorough understanding of two-phase flow requires the accurate measurement of the time-averaged interfacial area per unit volume (also called the time-averaged integral specific area). The so-called 'specific area' can be estimated by several techniques described in the literature. These different methods are reviewed and the flow conditions which lead to a rigourous determination of the time-averaged integral specific area are clearly established. The probe technique, involving local measurements seems very attractive because of its large range of application
Modelling experimental investigation of two-phase gas-liquid flow patterns in horizontal pipes
International Nuclear Information System (INIS)
In two-phase flow systems the effect of flow patterns on the behavior of the dynamic flow and heat transfer is very important. The study of flow patterns belongs in the fundamental research that have strong practicality. Flow patterns and their transitions in horizontal pipes have been up to now experimentally studied by a number of investigators, and many flow pattern maps and their transition correlations have been proposed. Besides the complexity of flow patterns themselves, the following account for the occurrence of this impracticability: most of these studies were confined to air-water (i.e. two components) systems; most of these studies were confined to normal atmospheric condition; most of these studies were confined to adiabatic condition; there have not common principles on the classification of flow patterns and common definitions of flow patterns yet; and the better coordinate parameters of flow pattern map have not been found as yet. In order to reveal the effect of parameters and components on flow patterns and their transitions thoroughly, in this study the modelling experiment and analysis of horizontal heated channel flow patterns for single component fluid medium (F-12) at higher pressure (the pressures of F-12 were 10-15 bar, corresponding to water system pressures 65-95 bar) were made
Modeling and numerical study of two phase flow
International Nuclear Information System (INIS)
This thesis describes the modelization and the simulation of two-phase systems composed of droplets moving in a gas. The two phases interact with each other and the type of model to consider directly depends on the type of simulations targeted. In the first part, the two phases are considered as fluid and are described using a mixture model with a drift relation (to be able to follow the relative velocity between the two phases and take into account two velocities), the two-phase flows are assumed at the equilibrium in temperature and pressure. This part of the manuscript consists of the derivation of the equations, writing a numerical scheme associated with this set of equations, a study of this scheme and simulations. A mathematical study of this model (hyperbolicity in a simplified framework, linear stability analysis of the system around a steady state) was conducted in a frame where the gas is assumed baro-tropic. The second part is devoted to the modelization of the effect of inelastic collisions on the particles when the time of the simulation is shorter and the droplets can no longer be seen as a fluid. We introduce a model of inelastic collisions for droplets in a spray, leading to a specific Boltzmann kernel. Then, we build caricatures of this kernel of BGK type, in which the behavior of the first moments of the solution of the Boltzmann equation (that is mass, momentum, directional temperatures, variance of the internal energy) are mimicked. The quality of these caricatures is tested numerically at the end. (author)
Development of Interfacial Structure in a Confined Air-Water Cap-Turbulent and Churn-Turbulent Flow
International Nuclear Information System (INIS)
The objective of the present work is to study and model the interfacial structure development of air-water two-phase flow in a confined test section. Experiments of a total of 9 flow conditions in a cap-turbulent and churn-turbulent flow regimes are carried out in a vertical air-water upward two-phase flow experimental loop with a test section of 20-cm in width and 1-cm in gap. The miniaturized four-sensor conductivity probes are used to measure local two-phase parameters at three different elevations for each flow condition. The bubbles captured by the probes are categorized into two groups in view of the two-group interfacial area transport equation, i.e., spherical/distorted bubbles as Group 1 and cap/churn-turbulent bubbles as Group 2. The acquired parameters are time-averaged local void fraction, interfacial velocity, bubble number frequency, interfacial area concentration, and bubble Sauter mean diameter for both groups of bubbles. Also, the line-averaged and area-averaged data are presented and discussed. The comparisons of these parameters at different elevations demonstrate the development of interfacial structure along the flow direction due to bubble interactions
On drag reduction in a two-phase flow
Gatapova, E. Ya.; Ajaev, V. S.; Kabov, O. A.
2015-02-01
Bubbles collected on a local hydrophobic surface with nanocoating in a two-phase flow in a minichannel have been detected experimentally. It has been proposed to use the effect of concentration of gas bubbles on hydrophobic segments of the surface of the channel with contrast wettability for ensuring drag reduction. A two-dimensional flow model with the Navier slip condition in the region of the bubble layer gives criteria of drag reduction, depending on the slip length, dimension of bubbles, and dimension of the segment with nanocoating. The presence of the bubble layer on half of the surface of the channel can increase the flow rate of a liquid flowing through the channel by 40% at a fixed pressure gradient.
Solutal Marangoni instability in layered two-phase flows
Picardo, Jason R; Pushpavanam, S
2015-01-01
In this paper, the instability of layered two-phase flows caused by the presence of a soluble surfactant (or a surface active solute) is studied. The fluids have different viscosities, but are density matched to focus on Marangoni effects. The fluids flow between two flat plates, which are maintained at different solute concentrations. This establishes a constant flux of solute from one fluid to the other in the base state. A linear stability analysis is performed, using a combination of asymptotic and numerical methods. In the creeping flow regime, Marangoni stresses destabilize the flow, provided a concentration gradient is maintained across the fluids. One long wave and two short wave Marangoni instability modes arise, in different regions of parameter space. A well-defined condition for the long wave instability is determined in terms of the viscosity and thickness ratios of the fluids, and the direction of mass transfer. Energy budget calculations show that the Marangoni stresses that drive long and shor...
A real two-phase submarine debris flow and tsunami
Energy Technology Data Exchange (ETDEWEB)
Pudasaini, Shiva P.; Miller, Stephen A. [Department of Geodynamics and Geophysics, Steinmann Institute, University of Bonn Nussallee 8, D-53115, Bonn (Germany)
2012-09-26
The general two-phase debris flow model proposed by Pudasaini is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model, which includes three fundamentally new and dominant physical aspects such as enhanced viscous stress, virtual mass, and generalized drag (in addition to buoyancy), constitutes the most generalized two-phase flow model to date. The advantage of this two-phase debris flow model over classical single-phase, or quasi-two-phase models, is that the initial mass can be divided into several parts by appropriately considering the solid volume fraction. These parts include a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This innovative formulation provides an opportunity, within a single framework, to simultaneously simulate the sliding debris (or landslide), the water lake or ocean, the debris impact at the lake or ocean, the tsunami generation and propagation, the mixing and separation between the solid and fluid phases, and the sediment transport and deposition process in the bathymetric surface. Applications of this model include (a) sediment transport on hill slopes, river streams, hydraulic channels (e.g., hydropower dams and plants); lakes, fjords, coastal lines, and aquatic ecology; and (b) submarine debris impact and the rupture of fiber optic, submarine cables and pipelines along the ocean floor, and damage to offshore drilling platforms. Numerical simulations reveal that the dynamics of debris impact induced tsunamis in mountain lakes or oceans are fundamentally different than the tsunami generated by pure rock avalanches and landslides. The analysis includes the generation, amplification and propagation of super tsunami waves and run-ups along coastlines, debris slide and deposition at the bottom floor, and debris shock waves. It is observed that the
A real two-phase submarine debris flow and tsunami
International Nuclear Information System (INIS)
The general two-phase debris flow model proposed by Pudasaini is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model, which includes three fundamentally new and dominant physical aspects such as enhanced viscous stress, virtual mass, and generalized drag (in addition to buoyancy), constitutes the most generalized two-phase flow model to date. The advantage of this two-phase debris flow model over classical single-phase, or quasi-two-phase models, is that the initial mass can be divided into several parts by appropriately considering the solid volume fraction. These parts include a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This innovative formulation provides an opportunity, within a single framework, to simultaneously simulate the sliding debris (or landslide), the water lake or ocean, the debris impact at the lake or ocean, the tsunami generation and propagation, the mixing and separation between the solid and fluid phases, and the sediment transport and deposition process in the bathymetric surface. Applications of this model include (a) sediment transport on hill slopes, river streams, hydraulic channels (e.g., hydropower dams and plants); lakes, fjords, coastal lines, and aquatic ecology; and (b) submarine debris impact and the rupture of fiber optic, submarine cables and pipelines along the ocean floor, and damage to offshore drilling platforms. Numerical simulations reveal that the dynamics of debris impact induced tsunamis in mountain lakes or oceans are fundamentally different than the tsunami generated by pure rock avalanches and landslides. The analysis includes the generation, amplification and propagation of super tsunami waves and run-ups along coastlines, debris slide and deposition at the bottom floor, and debris shock waves. It is observed that the
A real two-phase submarine debris flow and tsunami
Pudasaini, Shiva P.; Miller, Stephen A.
2012-09-01
The general two-phase debris flow model proposed by Pudasaini [1] is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model, which includes three fundamentally new and dominant physical aspects such as enhanced viscous stress, virtual mass, and generalized drag (in addition to buoyancy), constitutes the most generalized two-phase flow model to date. The advantage of this two-phase debris flow model over classical single-phase, or quasi-two-phase models, is that the initial mass can be divided into several parts by appropriately considering the solid volume fraction. These parts include a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This innovative formulation provides an opportunity, within a single framework, to simultaneously simulate the sliding debris (or landslide), the water lake or ocean, the debris impact at the lake or ocean, the tsunami generation and propagation, the mixing and separation between the solid and fluid phases, and the sediment transport and deposition process in the bathymetric surface. Applications of this model include (a) sediment transport on hill slopes, river streams, hydraulic channels (e.g., hydropower dams and plants); lakes, fjords, coastal lines, and aquatic ecology; and (b) submarine debris impact and the rupture of fiber optic, submarine cables and pipelines along the ocean floor, and damage to offshore drilling platforms. Numerical simulations reveal that the dynamics of debris impact induced tsunamis in mountain lakes or oceans are fundamentally different than the tsunami generated by pure rock avalanches and landslides. The analysis includes the generation, amplification and propagation of super tsunami waves and run-ups along coastlines, debris slide and deposition at the bottom floor, and debris shock waves. It is observed that the
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)
Interfacial area transport equation of gas-liquid two-phase flow across a horizontal tube
International Nuclear Information System (INIS)
It is important to improve accuracy of the two-phase flow simulation codes, since these codes are used for the performance estimation and the safety designs of the industrial products which two-phase flow occur inside. In the governing equations of the two-phase flow simulation model, interfacial area concentration is one of the most important parameters to improve the model. Some researcher developed a transport equation of the interfacial area concentration that include source and sink terms due to bubble coalescence and breakup. However, these equations use numerous parameters to obtain the source and sink terms. In this study, we have successfully expressed the source and sink term as functions of a single variable to simplify and enhance their usefulness. The coalescence of bubbles was expressed as a function of the local void fraction, and the breakup of bubbles was expressed as a function of the time averaged local liquid velocity. Using this model, we can simulate the local void fraction and interfacial area concentration. In order to validate the simulation model, we also carried out experiments to measure a time averaged local interfacial area concentration and a time averaged local void fraction in a vertical upward air-water two-phase flow across horizontal tube with a double sensor electrical conductivity probe. The test section comprised a 50mm × 50 mm square channel partially obstructed by a single horizontal tube inside. The superficial gas velocity and superficial liquid velocity ranged from 0.019 to 0.215 m/s and from 0.133 to 0.533 m/s, respectively. Measurements of the void fraction and the interfacial area concentration were performed at three axial locations of z = 110, 340, and 640 mm and transverse locations from r = 0 to 25 mm. The experimental data set were compared to the result of the numerical simulations. Good agreement is obtained between these results. (author)
Experimental and numerical investigation on two-phase flow instabilities
Energy Technology Data Exchange (ETDEWEB)
Ruspini, Leonardo Carlos
2013-03-01
Two-phase flow instabilities are experimentally and numerically studied within this thesis. In particular, the phenomena called Ledinegg instability, density wave oscillations and pressure drop oscillations are investigated. The most important investigations regarding the occurrence of two-phase flow instabilities are reviewed. An extensive description of the main contributions in the experimental and analytical research is presented. In addition, a critical discussion and recommendations for future investigations are presented. A numerical framework using a hp-adaptive method is developed in order to solve the conservation equations modelling general thermo-hydraulic systems. A natural convection problem is analysed numerically in order to test the numerical solver. Moreover, the description of an adaptive strategy to solve thermo-hydraulic problems is presented. In the second part of this dissertation, a homogeneous model is used to study Ledinegg, density wave and pressure drop oscillations phenomena numerically. The dynamic characteristics of the Ledinegg (flow excursion) phenomenon are analysed through the simulation of several transient examples. In addition, density wave instabilities in boiling and condensing systems are investigated. The effects of several parameters, such as the fluid inertia and compressibility volumes, on the stability limits of Ledinegg and density wave instabilities are studied, showing a strong influence of these parameters. Moreover, the phenomenon called pressure drop oscillations is numerically investigated. A discussion of the physical representation of several models is presented with reference to the obtained numerical results. Finally, the influence of different parameters on these phenomena is analysed. In the last part, an experimental investigation of these phenomena is presented. The designing methodology used for the construction of the experimental facility is described. Several simulations and a non
Flow regimes of adiabatic gas-liquid two-phase under rolling conditions
Yan, Chaoxing; Yan, Changqi; Sun, Licheng; Xing, Dianchuan; Wang, Yang; Tian, Daogui
2013-07-01
Characteristics of adiabatic air/water two-phase flow regimes under vertical and rolling motion conditions were investigated experimentally. Test sections are two rectangular ducts with the gaps of 1.41 and 10 mm, respectively, and a circular tube with 25 mm diameter. Flow regimes were recorded by a high speed CCD-camera and were identified by examining the video images. The experimental results indicate that the characteristics of flow patterns in 10 mm wide rectangular duct under vertical condition are very similar to those in circular tube, but different from the 1.41 mm wide rectangular duct. Channel size has a significant influence on flow pattern transition, boundary of which in rectangular channels tends asymptotically towards that in the circular tube with increasing the width of narrow side. Flow patterns in rolling channels are similar to each other, nevertheless, the effect of rolling motion on flow pattern transition are significantly various. Due to the remarkable influences of the friction shear stress and surface tension in the narrow gap duct, detailed flow pattern maps of which under vertical and rolling conditions are indistinguishable. While for the circular tube with 25 mm diameter, the transition from bubbly to slug flow occurs at a higher superficial liquid velocity and the churn flow covers more area on the flow regime map as the rolling period decreases.
Objective characterization of interfacial structures in two-phase flow
International Nuclear Information System (INIS)
In view of establishing a detailed and reliable measurement technique for characterizing the interfacial structures and identifying flow regimes in two-phase flow, two objective approaches are presented. First, the state-of-the-art four-sensor conductivity probe technique is presented to obtain the detailed local information. The newly designed four-sensor conductivity probe accommodates the double-sensor probe capability. Hence, it can be applied in a wide range of two-phase flow regimes spanning from bubbly to churn-turbulent flows with a measurement error of approximately ± 10%. The signal processing scheme is developed such that it accounts for the missing bubbles and defective signals. Furthermore, it categorizes the acquired parameters into two groups based on bubble cord length information. Local information on the void fraction, interfacial area concentration, Sauter mean diameter, interface velocity for each group of bubbles was obtained successfully. Second, a global measurement technique using the non-intrusive impedance voidmeter and neural networks is presented. In this method, an advanced non-intrusive impedance voidmeter provides global interfacial structure information to neural networks which are used to identify the flow regimes. Both supervised and self-organizing neural network learning paradigms performed flow regime identification successfully. In the application of this global method, two approaches are presented, namely: One based on the Probability Density Function (PDF input method), and another based on the ordered set of void fraction measurements which were acquired in a very short time period (instantaneous direct signal input method). The direct signal input method minimizes the time required for identifying the flow regime
One-dimensional transient unequal velocity two-phase flow by the method of characteristics
International Nuclear Information System (INIS)
An understanding of two-phase flow is important when one is analyzing the accidental loss of coolant or when analyzing industrial processes. If a pipe in the steam generator of a nuclear reactor breaks, the flow will remain critical (or choked) for almost the entire blowdown. For this reason the knowledge of the two-phase maximum (critical) flow rate is important. A six-equation model--consisting of two continuity equations, two energy equations, a mixture momentum equation, and a constitutive relative velocity equation--is solved numerically by the method of characteristics for one-dimensional, transient, two-phase flow systems. The analysis is also extended to the special case of transient critical flow. The six-equation model is used to study the flow of a nonequilibrium sodium-argon system in a horizontal tube in which the nonequilibrium sodium-argon system in a horizontal tube in which the critical flow condition is at the entrance. A four-equation model is used to study the pressure-pulse propagation rate in an isothermal air-water system, and the results that are found are compared with the experimental data. Proper initial and boundary conditions are obtained for the blowdown problem. The energy and mass exchange relations are evaluated by comparing the model predictions with results of void-fraction and heat-transfer experiments. A simplified two-equation model is obtained for the special case of two incompressible phases. This model is used in the preliminary analysis of batch sedimentation. It is also used to predict the shock formation in the gas-solid fluidized bed
A study on the two-phase flow characteristics of nanofluids
International Nuclear Information System (INIS)
While a considerable body of research exists regarding enhancements of the heat transfer using nanofluids, the basic hydraulic phenomenon of a nanofluid has not been investigated as much. Several studies were reported related to the pressure drop of nanofluid flow and a few researches on the hydraulic characteristics of two-phase nanofluid flow were conducted. Two-phase Flow Analysis in a Helical Wire Inserted Tube using CFD Code An analysis on the two-phase flow in a helical wire inserted tube using commercial CFD code, CFX11.0, was performed in bubbly flow and annular flow regions. The analysis method was validated with the experimental results of Keishi Takeshima. Bubbly and annular flows in a 10 mm inner diameter tube with varying pitch lengths and inserted wire diameters were simulated using the same analysis methods after validation. The geometry range of p/D was 1-4 and e/D was 0.08-0.12. The results show that the inserted wire with a larger diameter increased swirl flow generation. An increasing swirl flow was seen as the pitch length increased. Regarding pressure loss, smaller pitch lengths and inserted wires with larger diameters resulted in larger pressure loss. The average liquid film thickness increased as the pitch length and the diameter of the inserted wire increased in the annular flow region. Both in the bubbly flow and annular flow regions, the effect of pitch length on swirl flow generation and pressure loss was more significant than that of the inserted wire diameters. An Experimental Study on the Two-Phase Flow Characteristics of Nanofluids The main objective of this study is to investigate the basic hydraulic phenomenon of the nanofluid in the two-phase flow region. For the accomplishment of this objective, a series of experiments have been performed. The first one is the pressure drop and pressure fluctuation measurements in a vertically upward air-water two-phase flow. The air and the water based nanofluid were used as working fluids under
Effect of flow direction on two-phase flow distribution of refrigerants at a T-junction
International Nuclear Information System (INIS)
The present study experimentally investigated the effect of flow direction and other flow parameters on two-phase flow distribution of refrigerants at a T-junction, and also suggested a prediction model for refrigerant in a T-junction by modifying previous model for air-water flow. R-22, R-134a, and R-410A were used as test refrigerants. As geometric parameters, the direction of the inlet or branch tube and the tube diameter ratio of branch to inlet tube were chosen. The measured data were compared with the values predicted by the models developed for air-water or steam-water mixture in the literature. We propose a modified model for application to the reduced T-junction and vertical tube orientation. Among the geometric parameters, the branch tube direction showed the biggest sensitivity to the mass flow rate ratio for the gas phase, while the inlet quality showed the biggest sensitivity to the mass flow rate ratio among the inlet flow parameters
Two-phase flow instability in a parallel multichannel system
Institute of Scientific and Technical Information of China (English)
HOU Suxia
2009-01-01
The two-phase flow instabilities observed in through parallel multichannel can be classified into three types, of which only one is intrinsic to parallel multichannel systems. The intrinsic instabilities observed in parallel multichannel system have been studied experimentally. The stable boundary of the flow in such a parallel-channel system are sought, and the nature of inlet flow oscillation in the unstable region has been examined experimentally under various conditions of inlet velocity, heat flux, liquid temperature, cross section of channel and entrance throttling. The results show that parallel multichannel system possess a characteristic oscillation that is quite independent of the magnitude and duration of the initial disturbance, and the stable boundary is influenced by the characteristic frequency of the system as well as by the exit quality when this is low, and upon raising the exit quality and reducing the characteristic frequency, the system increases its instability, and entrance throttling effectively contributes to stabilization of the system.
Mathematical model of two-phase flow in accelerator channel
Directory of Open Access Journals (Sweden)
О.Ф. Нікулін
2010-01-01
Full Text Available The problem of two-phase flow composed of energy-carrier phase (Newtonian liquid and solid fine-dispersed phase (particles in counter jet mill accelerator channel is considered. The mathematical model bases goes on the supposition that the phases interact with each other like independent substances by means of aerodynamics’ forces in conditions of adiabatic flow. The mathematical model in the form of system of differential equations of order 11 is represented. Derivations of equations by base physical principles for cross-section-averaged quantity are produced. The mathematical model can be used for estimation of any kinematic and thermodynamic flow characteristics for purposely parameters optimization problem solving and transfer functions determination, that take place in counter jet mill accelerator channel design.
Particle-fluid two-phase flow modeling
Mortensen, G. A.; Trapp, J. A.
This paper describes a numerical scheme and computer program, DISCON, for the calculation of two-phase flows that does not require the use of flow regime maps. This model is intermediate between-thermal instantaneous and the averaged two-fluid model. It solves the Eulerian continuity, momentum, and energy equations for each liquid control volume, and the Lagrangian mass, momentum, energy, and position equations for each bubble. The bubbles are modeled individually using a large representative number of bubbles, thus, avoiding the numerical diffusion associated with Eulerian models. DISCON has been used to calculate the bubbling of air through a column of water and the subcooled boiling of water in a flow channel. The results of these calculations are presented.
Two phase flow models in DxUNSp code platform
Directory of Open Access Journals (Sweden)
Catalin NAE
2011-09-01
Full Text Available The aim of this work is to find an efficient implementation for a two phase flow model in an existing URANS CFD code platform (DxUNSp, initially based on unsteady URANS equations with a k- turbulence model and various other extensions, ranging from a broad selection of wall laws up to a very efficient LES model. This code has the capability for development for nonreacting/reacting multifluid flows for research applications and is under continuous progress. It is intend to present mainly three aspects of this implementation for unstructured mesh based solvers, for high Reynolds compressible flows: the importance of the 5/7 equation model, performance with respect to a basic test cases and implementation details of the proposed schemes. From a numerical point of view, we propose a new approximation schemes of this system based on the VFRoe-ncv.
Stability of stratified two-phase flows in horizontal channels
Barmak, Ilya; Ullmann, Amos; Brauner, Neima; Vitoshkin, Helen
2016-01-01
Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems the stratified flow with smooth interface is stable only in confined zone of relatively lo...
The PDF method for Lagrangian two-phase flow simulations
International Nuclear Information System (INIS)
A recent turbulence model put forward by Pope (1991) in the context of PDF modelling has been used. In this approach, the one-point joint velocity-dissipation pdf equation is solved by simulating the instantaneous behaviour of a large number of Lagrangian fluid particles. Closure of the evolution equations of these Lagrangian particles is based on stochastic models and more specifically on diffusion processes. Such models are of direct use for two-phase flow modelling where the so-called fluid seen by discrete inclusions has to be modelled. Full Lagrangian simulations have been performed for shear-flows. It is emphasized that this approach gives far more information than traditional turbulence closures (such as the K-ε model) and therefore can be very useful for situations involving complex physics. It is also believed that the present model represents the first step towards a complete Lagrangian-Lagrangian model for dispersed two-phase flow problems. (authors). 21 refs., 6 figs
Modeling transient two-phase stratified flow in pipelines
International Nuclear Information System (INIS)
An isothermal, two-fluid model, comprised of separate mass and linear momentum conservation equations for the gas and liquid phases was formulated. Interfacial mass transfer effects were modeled via the black oil method. Both equal and unequal phase pressure formulations were evaluated. The model was used to investigate transient two-phase stratified flow in pipelines. An explicit numerical scheme was used to solve the system of equations. Experimental data were collected in an existing 425 m long, 76.2 mm diameter horizontal pipeline. Good agreement was observed between experimental and predicted results
Strongly coupled dispersed two-phase flows; Ecoulements diphasiques disperses fortement couples
Energy Technology Data Exchange (ETDEWEB)
Zun, I.; Lance, M.; Ekiel-Jezewska, M.L.; Petrosyan, A.; Lecoq, N.; Anthore, R.; Bostel, F.; Feuillebois, F.; Nott, P.; Zenit, R.; Hunt, M.L.; Brennen, C.E.; Campbell, C.S.; Tong, P.; Lei, X.; Ackerson, B.J.; Asmolov, E.S.; Abade, G.; da Cunha, F.R.; Lhuillier, D.; Cartellier, A.; Ruzicka, M.C.; Drahos, J.; Thomas, N.H.; Talini, L.; Leblond, J.; Leshansky, A.M.; Lavrenteva, O.M.; Nir, A.; Teshukov, V.; Risso, F.; Ellinsen, K.; Crispel, S.; Dahlkild, A.; Vynnycky, M.; Davila, J.; Matas, J.P.; Guazelli, L.; Morris, J.; Ooms, G.; Poelma, C.; van Wijngaarden, L.; de Vries, A.; Elghobashi, S.; Huilier, D.; Peirano, E.; Minier, J.P.; Gavrilyuk, S.; Saurel, R.; Kashinsky, O.; Randin, V.; Colin, C.; Larue de Tournemine, A.; Roig, V.; Suzanne, C.; Bounhoure, C.; Brunet, Y.; Tanaka, A.T.; Noma, K.; Tsuji, Y.; Pascal-Ribot, S.; Le Gall, F.; Aliseda, A.; Hainaux, F.; Lasheras, J.; Didwania, A.; Costa, A.; Vallerin, W.; Mudde, R.F.; Van Den Akker, H.E.A.; Jaumouillie, P.; Larrarte, F.; Burgisser, A.; Bergantz, G.; Necker, F.; Hartel, C.; Kleiser, L.; Meiburg, E.; Michallet, H.; Mory, M.; Hutter, M.; Markov, A.A.; Dumoulin, F.X.; Suard, S.; Borghi, R.; Hong, M.; Hopfinger, E.; Laforgia, A.; Lawrence, C.J.; Hewitt, G.F.; Osiptsov, A.N.; Tsirkunov, Yu. M.; Volkov, A.N.
2003-07-01
flow, current distribution and mass transfer along a vertical gas evolving electrode; a two-way coupled model for dilute multiphase flows. Topic 3: turbulence modulation by particles, droplets or bubbles in dense systems: influence of particles on the transition to turbulence in pipe flow; comparison between a point particle model and a finite-diameter-model for the particle turbulence interaction in a suspension; the effect on turbulence by bubbles rising through it under buoyancy; the physical mechanisms of modifying the structure of turbulent homogeneous shear flows by dispersed particles; influence of hydrodynamic interactions between particles on the turbulent flow in a suspension; review of relationships between Lagrangian and Eulerian scales; a two-point PDF for modelling turbulent dispersed two-phase flows and derivation of a two field model; mathematical and numerical modeling of two-phase compressible flows with micro-inertia. Topic 4: collective effects in dispersed two-phase flows clustering and phase distribution: hydrodynamic structure of downward bubbly flow; influence of gravity on the dynamics of a turbulent bubbly pipe flow; experimental study of two-phase flows; particle clusters formed in dispersed gas-solid flows: simulations and experiments; experimental study of the turbulence in bubbly flows at high void fraction; first step in the study of the correlation between air/water flow fluctuations and random buffering forces; clustering and settling velocity of micro-droplets in a grid turbulence. Topic 5: large scale instabilities and gravity driven dispersed flows: new 'non-isothermal' linear instability modes in fluidized beds and bubbly flows; large scale instability in a confined buoyant shear layer; convective instability in uniform dispersed layers; structures in gravity driven bubbly flows; effects of concentration profiles on velocity profiles in sewer; pyroclastic density currents viewed as mammoth scale two-phase flows; mixing and
Construction of the two-phase critical flow test facility
International Nuclear Information System (INIS)
The two-phase critical test loop facility has been constructed in the KAERI engineering laboratory for the simulation of small break loss of coolant accident entrained with non-condensible gas of SMART. The test facility can operate at 12 MPa of pressure and 0 to 60 C of sub-cooling with 0.5 kg/s of non- condensible gas injection into break flow, and simulate up to 20 mm of pipe break. Main components of the test facility were arranged such that the pressure vessel containing coolant, a test section simulating break and a suppression tank inter-connected with pipings were installed vertically. As quick opening valve opens, high pressure/temperature coolant flows through the test section forming critical two-phase flow into the suppression tank. The pressure vessel was connected to two high pressure N2 gas tanks through a control valve to control pressure in the pressure vessel. Another N2 gas tank was also connected to the test section for the non-condensible gas injection. The test facility operation was performed on computers supported with PLC systems installed in the control room, and test data such as temperature, break flow rate, pressure drop across test section, gas injection flow rate were all together gathered in the data acquisition system for further data analysis. This test facility was classified as a safety related high pressure gas facility in law. Thus the loop design documentation was reviewed, and inspected during construction of the test loop by the regulatory body. And the regulatory body issued permission for the operation of the test facility
Droplets Formation and Merging in Two-Phase Flow Microfluidics
Directory of Open Access Journals (Sweden)
Hao Gu
2011-04-01
Full Text Available Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i the emulsification step should lead to a very well controlled drop size (distribution; and (ii the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed.
Droplets formation and merging in two-phase flow microfluidics.
Gu, Hao; Duits, Michel H G; Mugele, Frieder
2011-01-01
Two-phase flow microfluidics is emerging as a popular technology for a wide range of applications involving high throughput such as encapsulation, chemical synthesis and biochemical assays. Within this platform, the formation and merging of droplets inside an immiscible carrier fluid are two key procedures: (i) the emulsification step should lead to a very well controlled drop size (distribution); and (ii) the use of droplet as micro-reactors requires a reliable merging. A novel trend within this field is the use of additional active means of control besides the commonly used hydrodynamic manipulation. Electric fields are especially suitable for this, due to quantitative control over the amplitude and time dependence of the signals, and the flexibility in designing micro-electrode geometries. With this, the formation and merging of droplets can be achieved on-demand and with high precision. In this review on two-phase flow microfluidics, particular emphasis is given on these aspects. Also recent innovations in microfabrication technologies used for this purpose will be discussed. PMID:21731459
Computer simulation of two-phase flow in nuclear reactors
International Nuclear Information System (INIS)
Two-phase flow models dominate the requirements of economic resources for the development and use of computer codes which serve to analyze thermohydraulic transients in nuclear power plants. An attempt is made to reduce the effort of analyzing reactor transients by combining purpose-oriented modelling with advanced computing techniques. Six principles are presented on mathematical modeling and the selection of numerical methods, along with suggestions on programming and machine selection, all aimed at reducing the cost of analysis. Computer simulation is contrasted with traditional computer calculation. The advantages of run-time interactive access operation in a simulation environment are demonstrated. It is explained that the drift-flux model is better suited than the two-fluid model for the analysis of two-phase flow in nuclear reactors, because of the latter's closure problems. The advantage of analytical over numerical integration is demonstrated. Modeling and programming techniques are presented which minimize the number of needed arithmetical and logical operations and thereby increase the simulation speed, while decreasing the cost. (orig.)
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)
Two-phase counter-current flow limitations in complex piping systems
International Nuclear Information System (INIS)
Experiments have been performed to investigate two-phase air-water counter-current flow limitations in two complex geometry test sections. One of the test sections was chosen to represent the complexity of CANDU feeders, at a 1:4 scale. In the second configuration, the effect of declining the horizontal parts of the test section was investigated. For the tested geometry, the results showed that the onset of flooding occurs at lower gas velocity as compared to those required to initiate flooding in vertical tubes or single 90 deg vertical bends. However, the critical gas velocity at the zero liquid penetration limit was found to be comparable to that of a 90 deg vertical bend. (author) 18 refs., 78 figs
Dynamic and spectroscopic characteristics of atmospheric gliding arc in gas-liquid two-phase flow
International Nuclear Information System (INIS)
In this study, an atmospheric alternating-current gliding arc device in gas-liquid two-phase flow has been developed for the purpose of waste water degradation. The dynamic behavior of the gas-liquid gliding arc is investigated through the oscillations of electrical signals, while the spatial evolution of the arc column is analyzed by high speed photography. Different arc breakdown regimes are reported, and the restrike mode is identified as the typical fluctuation characteristic of the hybrid gliding arc in air-water mixture. Optical emission spectroscopy is employed to investigate the active species generated in the gas-liquid plasma. The axial evolution of the OH (309 nm) intensity is determined, while the rotational and vibrational temperatures of the OH are obtained by a comparison between the experimental and simulated spectra. The significant discrepancy between the rotational and translational temperatures has also been discussed.
Non-equilibrium effects in transient two-phase flow
International Nuclear Information System (INIS)
Depressurisation tests were carried out on Refrigerant 113 liquid flowing in a horizontal pipeline, under conditions where vapour was formed by flash evaporation. The tests covered a range of initial velocities up to 2.1 m/s in a 51 mm diameter glass pipeline at starting pressure around 1.5 bar and with varying rates of depressurisation. Measurements were made of local pressure and temperature, circulation rate, pressure difference and void fraction variation over a test section length of 2m. The local pressure and temperature measurements give a direct indication of non-equilibrium effects. The vapour formed during the flash evaporation process quickly formed a stratified type flow and a theoretical model was developed on this basis. The model includes the transient two phase low conservation equations allied to a heat transfer equation. Satisfactory agreement between theoretical predictions and experimental results was obtained. (author)
Flooding in counter-current two-phase flow
International Nuclear Information System (INIS)
Flooding is a phenomenon which is best described as the transition from counter-current to co-current flow. Early notice was taken of this phenomenon in the chemical engineering industry. Flooding also plays an important role in the field of two-phase heat transfer since it is a limit for many systems involving counter-current flow. Practical applications of flooding limited processes include wickless thermosyphons and the emergency core cooling system (ECCS) of pressurized water nuclear reactors. The phenomenon of flooding also is involved in the behavior of nuclear reactor core materials during severe accident conditions where flooding is one of the mechanisms governing the motion of the molten fuel pin cladding
Geometry and Material Scaling on Two Phase Natural Circulation Flow for K-HERMES-HALF Experiment
Energy Technology Data Exchange (ETDEWEB)
Park, Rae Joon; Ha, Kwang Soon; Kim, Sang Baik; Hong, Seong Wan [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Heo, Sun [KHNP Nuclear Engineering and Technology Institute, Daejeon (Korea, Republic of)
2011-05-15
As part of a study on two-phase natural circulation mass flow rate between the outer reactor vessel and vessel insulation in the reactor cavity under the IVR (In-Vessel corium retention) through the ERVC (External Reactor Vessel Cooling) in APR1400, K-HERMES-HALF experiment (Hydraulic Evaluation of Reactor cooling Mechanism by External Self-induced flow) had performed at KAERI. This large-scale experiment using a half-height and half-sector model of the APR1400 uses the non-heating method of the air injection. For this reason, it is necessary to evaluate the geometry scaling on full height and full sector and a material scaling between air-water and steam-water two phase natural circulation flow for an application of the experimental results to an actual APR1400. In the geometry scaling, two cases, such as a half height and half sector and a full height and full sector, had performed by using RELAP5/MOD3 computer code. In the material scaling, two cases, such as an air injection and a steam injection, had performed to compare the air injection experimental results with the steam injection case
CFD analyses for water / air tests to investigate the RPV exterior two-phase flow behavior
International Nuclear Information System (INIS)
The full text follows. Siemens / KWU develops a new boiling water reactor called SWR 1000. It's safety concept will consist of passive safety equipment combined with active systems, and through this diversity, meets the goal of reducing the probability of core damage compared to existing nuclear plants. Siemens / KWU performs - in co-operation with VTT - tests to quantify the safety margins of the exterior cooling concept for the SWR 1000, which are supposed to be very high, by measuring the critical heat fluxes (CHFs). The following stepwise procedure will be applied for the investigation of the CHFs, whereas the first two steps will be needed to design a model in such a way, that it represents the flow around the RPV: -) Water / air experiments with a 1:10 scaled global model; -) Water / air experiments with a 1:10 section model; -) Water / steam experiments with a 1:1-section model. The CHF will be determined by heating the reproduced reactor pressure vessel wall and measuring wall temperatures. FLUENT4 and CFX -codes have been successfully used for validating the two-phase flow in 1:10 air-water experiments and predicting behavior is 1:10 tests. The results are summarized in the paper. The capability of CFD codes for modeling multidimensional two-phase flow is discussed
Numerical prediction of horizontal two phase flow using an interfacial area density model
International Nuclear Information System (INIS)
During a Lost of Coolant Accident (LOCA) cold Emergency Core Cooling (ECC) water can be injected into the cold leg of the primary loop of PWR. A relevant problem occurring in this situation is the development of wavy stratified flows which can lead to slug generation. Because slug flow cannot be predicted with the required accuracy and spatial resolution by the one-dimensional system codes, the stratified flows are increasingly modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated. The recent improvements of the multiphase flow modelling in the ANSYS CFX code make it now possible to simulate these mechanisms in detail. In order to validate existing and further developed multiphase flow models, high-resolution measurement data is needed in time and also in space. For the experimental investigation of co-current air/water flows, the HAWAC (Horizontal Air/Water Channel) was built. The channel allows in particular the study of air/water slug flow under atmospheric pressure. Parallel to the experiments, CFD calculations were carried out. A picture sequence recorded during slug flow was compared with the equivalent CFD simulation made. The two-fluid model was applied with a special turbulence damping procedure at the free surface. An Algebraic Interfacial Area Density (AIAD) model on the basis of the implemented mixture model was introduced, which allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value. The behaviour of slug generation and propagation at the experimental setup was qualitatively reproduced by the simulation, while local deviations require a continuation of the work. The creation of small instabilities due to pressure surge or an increase of
Studies of Two-Phase Flow Dynamics and Heat Transfer at Reduced Gravity Conditions
Witte, Larry C.; Bousman, W. Scott; Fore, Larry B.
1996-01-01
The ability to predict gas-liquid flow patterns is crucial to the design and operation of two-phase flow systems in the microgravity environment. Flow pattern maps have been developed in this study which show the occurrence of flow patterns as a function of gas and liquid superficial velocities as well as tube diameter, liquid viscosity and surface tension. The results have demonstrated that the location of the bubble-slug transition is affected by the tube diameter for air-water systems and by surface tension, suggesting that turbulence-induced bubble fluctuations and coalescence mechanisms play a role in this transition. The location of the slug-annular transition on the flow pattern maps is largely unaffected by tube diameter, liquid viscosity or surface tension in the ranges tested. Void fraction-based transition criteria were developed which separate the flow patterns on the flow pattern maps with reasonable accuracy. Weber number transition criteria also show promise but further work is needed to improve these models. For annular gas-liquid flows of air-water and air- 50 percent glycerine under reduced gravity conditions, the pressure gradient agrees fairly well with a version of the Lockhart-Martinelli correlation but the measured film thickness deviates from published correlations at lower Reynolds numbers. Nusselt numbers, based on a film thickness obtained from standard normal-gravity correlations, follow the relation, Nu = A Re(sup n) Pr(exp l/3), but more experimental data in a reduced gravity environment are needed to increase the confidence in the estimated constants, A and n. In the slug flow regime, experimental pressure gradient does not correlate well with either the Lockhart-Martinelli or a homogeneous formulation, but does correlate nicely with a formulation based on a two-phase Reynolds number. Comparison with ground-based correlations implies that the heat transfer coefficients are lower at reduced gravity than at normal gravity under the same
The Condensation effect on the two-phase flow stability
International Nuclear Information System (INIS)
considering riser condensation and of correcting the localized friction due to the presence of the two-phase mixture in the two-phase region.These effects are more important for high heating power and high inlet subcooling. CAREM 25 nuclear power reactor is investigated to get the stability boundary map. The flow instability regions are appeared at low and high core power. In the low heat flux range, the trends of the thermal equilibrium - equal velocity (homogeneous) model and the thermal non equilibrium - non equal velocity model are the same because the steam quality is small.In the high heat flux range, for the subcooled boiling number and the phase change number, the marginal stability boundaries are crossed in a point, determining tow different regions, of high and low inlet subcooling.For the first region, the steam quality calculation of the first model is greater and has the effect of stabilizing the system more than the second one.For the second region, the two-phase region length calculation of the first model is smaller and has the effect of stabilizing the system less than the second one. In general, the model predicts a more stable system with an increase in inlet restriction or riser condensation or system pressure or a decrease in exit restriction
Tsunami Generated by a Two-Phase Submarine Debris Flow
Pudasaini, S. P.
2012-04-01
The general two-phase debris flow model proposed by Pudasaini (2011) is employed to study subaerial and submarine debris flows, and the tsunami generated by the debris impact at lakes and oceans. The model includes several essential physical aspects, including Mohr-Coulomb plasticity for the solid stress, while the fluid stress is modelled as a solid volume fraction gradient enhanced non-Newtonian viscous stress. The generalized interfacial momentum transfer includes the viscous drag, buoyancy, and the virtual mass. The generalized drag covers both the solid-like and fluid-like contributions, and can be applied to linear to quadratic drags. Strong couplings exist between the solid and the fluid momentum transfer. The advantage of the real two-phase debris flow model over classical single-phase or quasi-two-phase models is that by considering the solid (and/or the fluid) volume fraction appropriately, the initial mass can be divided into several (even mutually disjoint) parts; a dry (landslide or rock slide), a fluid (water or muddy water; e.g., dams, rivers), and a general debris mixture material as needed in real flow simulations. This offers a unique and innovative opportunity within a single framework to simultaneously simulate (a) the sliding debris (or landslide), (b) the water lake or ocean, (c) the debris impact at the lake or ocean, (d) tsunami generation and propagation, (e) mixing and separation between the solid and the fluid phases, and (f) sediment transport and deposition process in the bathymetric surface. The new model is applied to two-phase subaerial and submarine debris flows. Benchmark numerical simulations reveal that the dynamics of the debris impact induced tsunamis are fundamentally different than the tsunami generated by pure rock avalanche and landslides. Special attention is paid to study the basic features of the debris impact to the mountain lakes or oceans. This includes the generation, amplification and propagation of the multiple
Propagation of density disturbances in air-water flow
Nassos, G. P.
1969-01-01
Study investigated the behavior of density waves propagating vertically in an atmospheric pressure air-water system using a technique based on the correlation between density change and electric resistivity. This information is of interest to industries working with heat transfer systems and fluid power and control systems.
Solutal Marangoni instability in layered two-phase flow
Picardo, Jason; Radhakrishna, T. G.; Pushpavanam, S.
2015-11-01
In this work, the instability of layered two-phase flow caused by the presence of a surface-active solute is studied. The fluids are density matched to focus on surfactant effects. The fluids flow between two flat plates, which are maintained at different solute concentrations. This establishes a constant flux of soluble surfactant from one fluid to the other, in the base state. A linear stability analysis is carried out, supported by energy budget calculations. The flow is first analyzed in the creeping flow regime. Long wave as well as short wave Marangoni instabilities are identified, each with a distinct energy signature. The short wave instability manifests as two distinct modes, characterized by the importance of interfacial deformations or lack thereof. The primary instability switches between these different modes as parameters are varied. The effect of small but finite inertia on these solutal Marangoni modes is then examined. The effect of soluble surfactant on a finte inertia flow is also studied, with focus on the transition from the viscosity-induced instability to solutal Marangoni instability. This analysis is relevant to microfluidic applications, such as solvent extraction, in which mass transfer is carried out between stratified immiscible fluids.
Wall function approach for boiling two-phase flows
International Nuclear Information System (INIS)
One of the important goals of the NURESIM project is to assess and improve the simulation capability of the three-dimensional two-fluid codes for prediction of local boiling flow processes. The boiling flow is strongly affected by local mechanisms in the turbulent boundary layer near the heated wall. Wall-to-fluid transfer models for boiling flow with the emphasis on near-wall treatment are being addressed in the paper. Since the computational grid of the 3D two-fluid models is too coarse to resolve the variable gradients in the near-wall region, the use of wall functions is a common approach to model the liquid velocity and temperature profile adjacent to the heated wall. The wall function model for momentum, based on the surface roughness analogy has been discussed and implemented in the NEPTUNECFD code. The model has been validated on several upward boiling flow experiments, differing in the geometry, working fluid and operating conditions. The simulations with the new wall function model show an improved prediction of flow parameters over the boiling boundary layer. Furthermore, a wall function model for the energy equation, based on enhanced two-phase wall friction has been derived and validated.
Stability of stratified two-phase flows in horizontal channels
Barmak, I.; Gelfgat, A.; Vitoshkin, H.; Ullmann, A.; Brauner, N.
2016-04-01
Linear stability of stratified two-phase flows in horizontal channels to arbitrary wavenumber disturbances is studied. The problem is reduced to Orr-Sommerfeld equations for the stream function disturbances, defined in each sublayer and coupled via boundary conditions that account also for possible interface deformation and capillary forces. Applying the Chebyshev collocation method, the equations and interface boundary conditions are reduced to the generalized eigenvalue problems solved by standard means of numerical linear algebra for the entire spectrum of eigenvalues and the associated eigenvectors. Some additional conclusions concerning the instability nature are derived from the most unstable perturbation patterns. The results are summarized in the form of stability maps showing the operational conditions at which a stratified-smooth flow pattern is stable. It is found that for gas-liquid and liquid-liquid systems, the stratified flow with a smooth interface is stable only in confined zone of relatively low flow rates, which is in agreement with experiments, but is not predicted by long-wave analysis. Depending on the flow conditions, the critical perturbations can originate mainly at the interface (so-called "interfacial modes of instability") or in the bulk of one of the phases (i.e., "shear modes"). The present analysis revealed that there is no definite correlation between the type of instability and the perturbation wavelength.
Local measurement of interfacial area, interfacial velocity and liquid turbulence in two-phase flow
International Nuclear Information System (INIS)
Double sensor probe and hotfilm anemometry methods were developed for measuring local flow characteristics in bubbly flow. The formulation for the interfacial area concentration measurement was obtained by improving the formulation derived by Kataoka and Ishii. The assumptions used in the derivation of the equation were verified experimentally. The interfacial area concentration measured by the double sensor probe agreed well with one by the photographic method. The filter to validate the hotfilm anemometry for measuring the liquid velocity and turbulent intensity in bubbly flow was developed based on removing the signal due to the passing bubbles. The local void fraction, interfacial area concentration, interfacial velocity, Sauter mean diameter, liquid velocity, and turbulent intensity of vertical upward air-water flow in a round tube with an inner diameter of 50.8 mm were measured by using these methods. A total of 54 data sets were acquired consisting of three superficial gas flow rates, 0.015-0.076 m s-1, and three superficial liquid flow rates, 0.600, 1.00, and 1.30 m s-1. The measurements were performed at the three locations: L/D=2, 32, and 62. This data is expected to be used for the development of reliable constitutive relations which reflect the true transfer mechanisms in two-phase flow. (orig.)
Local measurement of interfacial area, interfacial velocity and liquid turbulence in two-phase flow
International Nuclear Information System (INIS)
Double sensor probe and hotfilm anemometry methods were developed for measuring local flow characteristics in bubbly flow. The formulation for the interfacial area concentration measurement was obtained by improving the formulation derived by Kataoka and Ishii. The assumptions used in the derivation of the equation were verified experimentally. The interfacial area concentration measured by the double sensor probe agreed well with one by the photographic method. The filter to validate the hotfilm anemometry for measuring the liquid velocity and turbulent intensity in bubbly flow was developed based on removing the signal due to the passing bubbles. The local void fraction, interfacial area concentration, interfacial velocity, Sauter mean diameter, liquid velocity, and turbulent intensity of vertical upward air-water flow in a round tube with inner diameter of 50.8 mm were measured by using these methods. A total of 54 data sets were acquired consisting of three superficial gas flow rates, 0.039, 0.067, and 0.147 m/s, and three superficial liquid flow rates, 0.60, 1.00, and 1.30 m/s. The measurements were performed at the three locations: L/D=2, 32, and 62. This data is expected to be used for the development of reliable constitutive relations which reflect the true transfer mechanisms in two-phase flow. (author)
Bubble Generation in a Flowing Liquid Medium and Resulting Two-Phase Flow in Microgravity
Pais, S. C.; Kamotani, Y.; Bhunia, A.; Ostrach, S.
1999-01-01
The present investigation reports a study of bubble generation under reduced gravity conditions, using both a co-flow and a cross-flow configuration. This study may be used in the conceptual design of a space-based thermal management system. Ensuing two-phase flow void fraction can be accurately monitored using a single nozzle gas injection system within a continuous liquid flow conduit, as utilized in the present investigation. Accurate monitoring of void fraction leads to precise control of heat and mass transfer coefficients related to a thermal management system; hence providing an efficient and highly effective means of removing heat aboard spacecraft or space stations. Our experiments are performed in parabolic flight aboard the modified DC-9 Reduced Gravity Research Aircraft at NASA Lewis Research Center, using an air-water system. For the purpose of bubble dispersion in a flowing liquid, we use both a co-flow and a cross-flow configuration. In the co-flow geometry, air is introduced through a nozzle in the same direction with the liquid flow. On the other hand, in the cross-flow configuration, air is injected perpendicular to the direction of water flow, via a nozzle protruding inside the two-phase flow conduit. Three different flow conduit (pipe) diameters are used, namely, 1.27 cm, 1.9 cm and 2.54 cm. Two different ratios of nozzle to pipe diameter (D(sub N))sup * are considered, namely (D(sub N))sup * = 0.1 and 0.2, while superficial liquid velocities are varied from 8 to 70 cm/s depending on flow conduit diameter. It is experimentally observed that by holding all other flow conditions and geometry constant, generated bubbles decrease in size with increase in superficial liquid velocity. Detached bubble diameter is shown to increase with air injection nozzle diameter. Likewise, generated bubbles grow in size with increasing pipe diameter. Along the same lines, it is shown that bubble frequency of formation increases and hence the time to detachment of a
International Nuclear Information System (INIS)
The purpose of this project is to investigate how changes in interfacial chemical properties affect two-phase transport relationships. Specifically, the objective is to develop a quantitative means that will enable the prediction of changes in the capillary pressure-saturation relationship, a fundamental constitutive relationship in multiphase flow, from changes in interfacial properties, such as adsorption and electrophoretic mobility, through a knowledge of their effect on wettability. The information presented here summarizes the progress we have made in the past eight months of the second project period. Working with a system composed of air-water-silica-cetyltrimethylammonium bromide (CTAB), we have obtained a relationship between degree of adsorption and the surface charge of silica (as measured by electrophoretic mobility), and the drainage and imbibition capillary pressure relationships of system. The bulk of this report describes the completed set of measurements for the air-water-silica-CTAB system at pH 6. We are currently working on a comparable set of measurements for the xylene-water-silica-CTAB system at pH 6. Described here are the interfacial tension, contact angle and preliminary drainage capillary pressure measurements. Our work to date shows a dependence of surface properties on pH. Consequently, in the coming year, we will also complete a set of measurements at another pH value to show the effect of pH on capillary pressure relationships
Buffeting lift forces and local air-water flow aspects around a rigid cylinder
International Nuclear Information System (INIS)
A new experimental programme is conducted in order to relate the characteristics of two-phase flow around a rigid cylinder with the resulting lift forces. The local characteristics of air-water flow measured in the vicinity of the cylinder provide a useful source of information about the effects of flow on the excitation mechanisms. In particular, a selection of relevant parameters has been identified which, with the help of a standard dimensional analysis, may explain the energetic contents of buffeting forces. Among the parameters effective in reducing the data are the flow regime, bubble frequency and gravity forces. In addition, in the range of bubbly regimes, the magnitude of the random forces is found to be related to the local fluctuations of void fraction. Finally, a new formulation is proposed to collapse the dimensionless spectra of the buffeting lift forces in a single characteristic curve. This analysis shows a marked improvement over the collapse of data in comparison with previous normalized models. (authors)
Final Report - Advanced Conceptual Models for Unsaturated and Two-Phase Flow in Fractured Rock
Energy Technology Data Exchange (ETDEWEB)
Nicholl, Michael J.
2006-07-10
The Department of Energy Environmental Management Program is faced with two major issues involving two-phase flow in fractured rock; specifically, transport of dissolved contaminants in the Vadose Zone, and the fate of Dense Nonaqueous Phase Liquids (DNAPLs) below the water table. Conceptual models currently used to address these problems do not correctly include the influence of the fractures, thus leading to erroneous predictions. Recent work has shown that it is crucial to understand the topology, or ''structure'' of the fluid phases (air/water or water/DNAPL) within the subsurface. It has also been shown that even under steady boundary conditions, the influence of fractures can lead to complex and dynamic phase structure that controls system behavior, with or without the presence of a porous rock matrix. Complicated phase structures within the fracture network can facilitate rapid transport, and lead to a sparsely populated and widespread distribution of concentrated contaminants; these qualities are highly difficult to describe with current conceptual models. The focus of our work is to improve predictive modeling through the development of advanced conceptual models for two-phase flow in fractured rock.
Two-phase flow heat transfer in nuclear reactor systems
International Nuclear Information System (INIS)
Complete text of publication follows: Heat transfer and phase change phenomena in two-phase flows are often encountered in nuclear reactor systems and are therefore of paramount importance for their optimal design and safe operation.The complex phenomena observed especially during transient operation of nuclear reactor systems necessitate extensive theoretical and experimental investigations. This special issue brings seven research articles of high quality. Though small in number, they cover a wide range of topics, presenting high complexity and diversity of heat transfer phenomena in two-phase flow. In the last decades a vast amount of research has been devoted to theoretical work and computational simulations, yet the experimental work remains indispensable for understanding of two-phase flow phenomena and for model validation purposes. This is reflected also in this issue, where only one article is purely experimental, while three of them deal with theoretical modelling and the remaining three with numerical simulations. The experimental investigation of the critical heat flux (CHF) phenomena by means of photographic study is presented in the paper of J. Park et al. They have used a high-speed camera system to observe the transient boiling characteristics on a thin horizontal cylinder submerged in a pool of water or highly wetting liquid. Experiments show that the initial boiling process is strongly affected by the properties and wettability of the liquid. The authors have stressed the importance of the local scale observation leading to better understanding of the transient CHF phenomena. In the article of G. Espinosa-Paredes et al. a theoretical work concerning the derivation of transport equations for two-phase flow is presented. The author proposes a novel approach based on derivation of nonlocal volume averaged equations which contain new terms related to nonlocal transport effects. These non-local terms act as coupling elements between the phenomena
Phase appearance or disappearance in two-phase flows
Cordier, Floraine; Kumbaro, Anela
2011-01-01
This paper is devoted to the treatment of specific numerical problems which appear when phase appearance or disappearance occurs in models of two-phase flows. Such models have crucial importance in many industrial areas such as nuclear power plant safety studies. In this paper, two outstanding problems are identified: first, the loss of hyperbolicity of the system when a phase appears or disappears and second, the lack of positivity of standard shock capturing schemes such as the Roe scheme. After an asymptotic study of the model, this paper proposes accurate and robust numerical methods adapted to the simulation of phase appearance or disappearance. Polynomial solvers are developed to avoid the use of eigenvectors which are needed in usual shock capturing schemes, and a method based on an adaptive numerical diffusion is designed to treat the positivity problems. An alternate method, based on the use of the hyperbolic tangent function instead of a polynomial, is also considered. Numerical results are presente...
Equations of two-phase flow in spray chamber
Institute of Scientific and Technical Information of China (English)
李新禹; 张志红; 金星; 徐杰
2009-01-01
The downstream water-air heat and moisture transfer system in a moving coordinate was studied. The relationship between the diameter of the misted droplets and the spray pressure was determined. Based on the theory of the relative velocity,the two-phase flow mode of the spray chamber and the efficiency equation for heat and moisture exchange were established. Corrections were carried out for the efficiency equation with spray pressure of 157 kPa. The results show that the pressure plays an important part in determining the efficiency of heat and moisture exchange. When the spray pressure is less than 157 kPa,better coincidence is noticed between the theoretical analysis and the test results with the error less than 6%. Greater error will be resulted in the case when the spray pressure is beyond 157 kPa. After the correction treatment,the coincidence between the theoretical and the experimental results is greatly improved.
Unsteady interfacial coupling of two-phase flow models
International Nuclear Information System (INIS)
The primary coolant circuit in a nuclear power plant contains several distinct components (vessel, core, pipes,...). For all components, specific codes based on the discretization of partial differential equations have already been developed. In order to obtain simulations for the whole circuit, the interfacial coupling of these codes is required. The approach examined within this work consists in coupling codes by providing unsteady information through the coupling interface. The numerical technique relies on the use of an interface model, which is combined with the basic strategy that was introduced by Greenberg and Leroux in order to compute approximations of steady solutions of non-homogeneous hyperbolic systems. Three different coupling cases have been examined: (i) the coupling of a one-dimensional Euler system with a two-dimensional Euler system; (ii) the coupling of two distinct homogeneous two-phase flow models; (iii) the coupling of a four-equation homogeneous model with the standard two-fluid model. (author)
Thermo-fluid dynamic theory of two-phase flow
International Nuclear Information System (INIS)
A detailed discussion on the formulation of various mathematical models of two-phase flows based on the conservation laws of mass, momentum and energy is presented. Special emphasises have been put on the local instant formulation and on the time-averaged macroscopic models. Two important models have been presented: 1) the two-fluid model which is formulated by considering each phase separately, and 2) the diffusion model which is formulated by considering the mixture as a whole, thus it is expressed in terms of three mixture conservation equations of mass, momentum and energy with one additional diffusion equation. The present formulation can be used to obtain the wall laws by analyses, i.e., the friction factors and heat transfer coefficients. The high-light of the report is the proposed constitutive laws with special emphasis on the interfacial exchange terms as well as on the turbulent transfer terms
Measurement of two-phase flow momentum with force transducers
International Nuclear Information System (INIS)
This paper reports on two strain-gage-based drag transducers developed to measure two-phase flow in simulated pressurized water reactor (PWR) test facilities. One transducer, a drag body (DB), was designed to measure the bidirectional average momentum flux passing through an end box. The second drag sensor, a break through detector (BTD), was designed to sense liquid downflow from the upper plenum to the core region. After prototype sensors passed numerous acceptance tests, transducers were fabricated and installed in two experimental test facilities, one in Japan and one in West Germany. High-quality data were extracted from both the DBs and BTDs for a variety of loss-of-coolant (LOCA) scenarios. The information collected from these sensors has added to the understanding of the thermohydraulic phenomena that occur during the refill/reflood stage of a LOCA in PWR
Numerical modeling of two-phase transonic flow
Czech Academy of Sciences Publication Activity Database
Halama, Jan; Benkhaldoun, F.; Fořt, Jaroslav
2010-01-01
Roč. 80, č. 88 (2010), s. 1624-1635. ISSN 0378-4754 Grant ostatní: GA ČR(CZ) GA201/08/0012 Institutional research plan: CEZ:AV0Z20760514 Keywords : two-phase flow * condensation * fractional step method Subject RIV: BK - Fluid Dynamics Impact factor: 0.812, year: 2010 http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V0T-4VNK68X-2-R&_cdi=5655&_user=640952&_pii=S0378475409000421&_origin=search&_coverDate=04%2F30%2F2010&_sk=999199991&view=c&wchp=dGLzVlb-zSkWb&md5=5ba607428fac339a3e5f67035d3996d0&ie=/sdarticle.pdf
Test of the EG and G two-phase mass flow rate instrumentation at Kernforschungszentrum Karlsruhe
International Nuclear Information System (INIS)
This report presents the data analyses of experiments designed to understand the behavior of a free field drag disc turbine transducer (DTT) and a three beam γ densitometer in steady-state horizontal steam-water and air-water flow. The pressure was varied between 2 and 75 bars, the experiments were made at a mass flow rate and void fraction range where various quite separated flow regimes occurred. Two different test sections with 103 mm ID (5' pipe) and 66 mm ID (3' pipe) were used. Information on flow regime and phase distribution in the cross section was obtained with local impedance probes, measurements of the axial distribution of phase velocities in the test section piping were made with the radiotracer technique. The best overall accuracy of mass flow rate determined by combining two of the three available instruments is obtained by the combination of γ-densitometer and drag disc. From the experiments, single calibration factors are determined which depend only on the γ-densitometer reading. A time averaged separated two-phase model for the DTT is postulated which shows that the DTT measures the local parameters. To obtain the pipe averaged mass flux, a density correction is proposed. For some experiments the radiotracer technique combined with the γ-densitometer for measuring the mass flow rate was tested. (orig./HP) 891 HP/orig.- 892 HIS
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.)
Unsteady flow analysis of a two-phase hydraulic coupling
Hur, N.; Kwak, M.; Lee, W. J.; Moshfeghi, M.; Chang, C.-S.; Kang, N.-W.
2016-06-01
Hydraulic couplings are being widely used for torque transmitting between separate shafts. A mechanism for controlling the transmitted torque of a hydraulic system is to change the amount of working fluid inside the system. This paper numerically investigates three-dimensional turbulent flow in a real hydraulic coupling with different ratios of charged working fluid. Working fluid is assumed to be water and the Realizable k-ɛ turbulence model together with the VOF method are used to investigate two-phase flow inside the wheels. Unsteady simulations are conducted using the sliding mesh technique. The primary wheel is rotating at a fixed speed of 1780 rpm and the secondary wheel rotates at different speeds for simulating different speed ratios. Results are investigated for different blade angles, speed ratios and also different water volume fractions, and are presented in the form of flow patterns, fluid average velocity and also torques values. According to the results, blade angle severely affects the velocity vector and the transmitted torque. Also in the partially-filled cases, air is accumulated in the center of the wheel forming a toroidal shape wrapped by water and the transmitted torque sensitively depends on the water volume fraction. In addition, in the fully-filled case the transmitted torque decreases as the speed ration increases and the average velocity associated with lower speed ratios are higher.
Particle migration in two-phase, viscoelastic flows
Jaensson, Nick; Hulsen, Martien; Anderson, Patrick
2014-11-01
Particles suspended in creeping, viscoelastic flows can migrate across stream lines due to gradients in normal stresses. This phenomenon has been investigated both numerically and experimentally. However, particle migration in the presence of fluid-fluid interfaces is hardly studied. We present results of simulations in 2D and 3D of rigid spherical particles in two-phase flows, where either one or both of the fluids are viscoelastic. The fluid-fluid interface is assumed to be diffuse and is described using Cahn-Hilliard theory. The particle boundary is assumed to be sharp and is described by a boundary-fitted, moving mesh. The governing equations are solved using the finite element method. We show that differences in normal stresses between the two fluids can induce a migration of the particle towards the interface in a shear flow. Depending on the magnitude of the surface tension and the properties of the fluids, particle migration can be halted due to the induced Laplace pressure, the particle can be adsorbed at the interface, or the particle can cross the interface into the other fluid. Dutch Polymer Institute (DPI), P.O. Box 902, 5600 AX Eindhoven, The Netherlands.
Critical two-phase flow through rough slits
International Nuclear Information System (INIS)
The knowledge of the two-phase mass flow rate through a crack in the wall of nuclear or chemical reactor components is very important under the leak-before-break criterion point of view. For providing a qualified analytical tool for calculating critical mass flow rates through such a crack a detailed test program was carried out using subcooled water up to pressures of 14 MPa. A real crack and several simulated cracks (rough slits) were examined experimentally. The important parameters such as inlet pressure, subcooling temperature of water, slit width, and inner surface roughness were varied in a wide range and the measured data compared with calculated values from different models. The data comparison indicates that the model published by Pana leads to predictions which agree best with the observed data. First calculations were carried out using the friction coefficient ζ, which results from single phase flow measurements. A correlation has been developed to calculate ζ from the geometrical dimensions of the crack and was integrated into an advanced version of the Pana model. The modified Pana model was qualified against some hundreds of test values. The measured data were predicted with a relative standard deviation of less than 20%. (orig.)
Uncertainty analysis of two-phase flow pressure drop calculations
Energy Technology Data Exchange (ETDEWEB)
Siqueira, Cezar A.M.; Costa, Bruno M.P.; Fonseca Junior, Roberto da; Gonalves, Marcelo de A.L. [PETROBRAS, Rio de Janeiro, RJ (Brazil)
2004-07-01
The simulation of multiphase flow in pipes is usually performed by petroleum engineers with two main purposes: design of new pipelines and production systems; diagnosis of flow assurance problems in existing systems. The tools used for this calculation are computer codes that use published pressure drop correlations developed for steady-state two-phase flow, such as Hagedorn-Brown, Beggs and Brill and others. Each one of these correlations is best suited for a given situation and the engineer must find out the best option for each particular case, based on his experience. In order to select the best correlation to use and to analyze the results of the calculation, the engineer must determine the reliability of computed values. The uncertainty of the computation is obtained by considering uncertainties of the correlation adopted, of the calculation algorithm and the input data. This paper proposes a method to evaluate the uncertainties of this type of calculation and presents an analysis of these uncertainties. The uncertainty analysis also allows the identification of the parameters that are more significant for the final uncertainty of the simulation. Therefore it makes possible to determine which are the input parameters that must be determined with higher accuracy and the ones that may have lower accuracy, without reducing the reliability of the results. (author)
Test of the EG and G two-phase mass flow rate instrumentation at Kernforschungszentrum Karlsruhe
International Nuclear Information System (INIS)
For many experiments which investigate the Loss-of-Coolant Accident (LOCA) in nuclear reactors, proper measurement of the two-phase mass flow is of great importance. This report presents the experimental description and the data of experiments designed to understand the behaviour of a free field drag disc turbine transducer (DTT) and a three beam gamma densitometer in steady-state horizontal steam-water and air-water flow. The pressure was varied between 2 and 75 bars, the experiments were made at a mass flow rate and void fraction range where various quite separated flow regimes occurred. Two different test sections with 103 mm ID (5 pipe) and 66 mm ID (3 pipe) were used. Information on flow regime and phase distribution in the cross section was obtained with local impedance probes, measurements of the axial distribution of phase velocities in the test section piping were made with the radiotracer technique. These techniques are of great help for the physical interpretation of the single instrument readings. The results of detailed data analyses are given in another report. (orig.)
Simulation of two-phase flows by domain decomposition
International Nuclear Information System (INIS)
This thesis deals with numerical simulations of compressible fluid flows by implicit finite volume methods. Firstly, we studied and implemented an implicit version of the Roe scheme for compressible single-phase and two-phase flows. Thanks to Newton method for solving nonlinear systems, our schemes are conservative. Unfortunately, the resolution of nonlinear systems is very expensive. It is therefore essential to use an efficient algorithm to solve these systems. For large size matrices, we often use iterative methods whose convergence depends on the spectrum. We have studied the spectrum of the linear system and proposed a strategy, called Scaling, to improve the condition number of the matrix. Combined with the classical ILU pre-conditioner, our strategy has reduced significantly the GMRES iterations for local systems and the computation time. We also show some satisfactory results for low Mach-number flows using the implicit centered scheme. We then studied and implemented a domain decomposition method for compressible fluid flows. We have proposed a new interface variable which makes the Schur complement method easy to build and allows us to treat diffusion terms. Using GMRES iterative solver rather than Richardson for the interface system also provides a better performance compared to other methods. We can also decompose the computational domain into any number of sub-domains. Moreover, the Scaling strategy for the interface system has improved the condition number of the matrix and reduced the number of GMRES iterations. In comparison with the classical distributed computing, we have shown that our method is more robust and efficient. (author)
Development of two-phase Flow Model, 'SOBOIL', for Sodium
International Nuclear Information System (INIS)
The objective of this research is to develop a sodium two-phase flow analysis model, 'SOBOIL', for the assessment of the initial stage of the KALIMER HCDA (Hypotherical Core Disruptive Accident). The 'SOBOIL' is basically similar to the multi-bubble slug ejection model used in SAS2A[1]. When a bubble is formed within the liquid slug, the bubble fills the whole cross section of the coolant channel except for a film left on the cladding or on the structure. Up to nine bubbles, separated by the liquid slugs, are allowed in the channel at any time. Each liquid slug flow rate in the model is performed in 2 steps. In the first step, the preliminary flow rate in the liquid slug is calculated neglecting the effect of changes in the vapor bubble pressures over the time step. The temperature and pressure distributions, and interface velocity at the interface between the liquid slug and vapor bubble are also calculated during this process. The new vapor temperature and pressure are then determined from the balance between the net energy transferred into the vapor and the change of the vapor energy. The liquid flow is finally calculated considering the change of the vapor pressure over a time step and the calculation is repeated until specified elapsed time is met. Continuous effort, therefore, must be made on the examination and improvement for the model to become reliable. To this end, much interest must be concentrated in the relevant international collaborations for access to a reference model or test data for the verification
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
Numerical methods for two-phase flow with contact lines
Energy Technology Data Exchange (ETDEWEB)
Walker, Clauido
2012-07-01
This thesis focuses on numerical methods for two-phase flows, and especially flows with a moving contact line. Moving contact lines occur where the interface between two fluids is in contact with a solid wall. At the location where both fluids and the wall meet, the common continuum descriptions for fluids are not longer valid, since the dynamics around such a contact line are governed by interactions at the molecular level. Therefore the standard numerical continuum models have to be adjusted to handle moving contact lines. In the main part of the thesis a method to manipulate the position and the velocity of a contact line in a two-phase solver, is described. The Navier-Stokes equations are discretized using an explicit finite difference method on a staggered grid. The position of the interface is tracked with the level set method and the discontinuities at the interface are treated in a sharp manner with the ghost fluid method. The contact line is tracked explicitly and its dynamics can be described by an arbitrary function. The key part of the procedure is to enforce a coupling between the contact line and the Navier-Stokes equations as well as the level set method. Results for different contact line models are presented and it is demonstrated that they are in agreement with analytical solutions or results reported in the literature.The presented Navier-Stokes solver is applied as a part in a multiscale method to simulate capillary driven flows. A relation between the contact angle and the contact line velocity is computed by a phase field model resolving the micro scale dynamics in the region around the contact line. The relation of the microscale model is then used to prescribe the dynamics of the contact line in the macro scale solver. This approach allows to exploit the scale separation between the contact line dynamics and the bulk flow. Therefore coarser meshes can be applied for the macro scale flow solver compared to global phase field simulations
CFD code validation against stratified air-water flow experimental data
International Nuclear Information System (INIS)
Pressurized Thermal Shock (PTS) modelling has been identified as one of the most important industrial needs related to nuclear reactor safety. A severe PTS scenario limiting the Reactor Pressure Vessel (RPV) lifetime is the cold water Emergency Core Cooling (ECC) injection into the cold leg during a Loss of Coolant Accident (LOCA). Since it represents a big challenge for numerical simulations, this scenario was selected within the NURESIM (European Platform for Nuclear Reactor Simulations) Integrated Project as a reference two-phase problem for CFD code validation. This paper presents a CFD analysis of a stratified air-water flow experimental investigation performed at the Institut de Mecanique des Fluides de Toulouse in 1985 [1], which shares some common physical features with the ECC injection in PWR cold leg. Numerical simulations have been carried out with two commercial codes (Fluent and Ansys CFX), and a research code NEPTUNECFD (developed by EDF and CEA). The aim of this work, carried out at the University of Pisa within the NURESIM IP, is to validate the free surface flow model implemented in the codes against the available experimental data, and to perform code to code benchmarking. Obtained results suggest the relevance of three-dimensional effects and stress the importance of a suitable interface drag coefficient modelling. A relevant improvement of results has been achieved with 3D simulations, even if the air velocity profile was still significantly underestimated. (author)
Study on two-phase flow dynamics in steam injectors
International Nuclear Information System (INIS)
Analytical and experimental studies have been conducted on large-scale steam injectors for a next-generation reactor. The steam injectors are simple, compact, passive steam jet pumps for a steam-injector-driven passive core injection system (SI-PCIS) or steam-injector-driven primary loop recirculation system (SI-PLR). In order to check the feasibility of such large-scale steam injectors, we developed the separate-two-phase flow models installed in the PHOENICS Code, and scale-model tests were conducted for both SI-PCIS and SI-PLR. A 1/2 scale SI-PCIS model achieved a discharge pressure of almost 8 MPa with 7 MPa steam and 0.4 MPa water, and a 1/5 scale SI-PLR model attained a discharge pressure of 12.5 MPa with 3 MPa steam and 7 MPa water. Both results are in good agreement with the analysis, confirming the feasibility of both systems. The systems will help to simplify the next generation of BWRs. (author)
DNS and LES of two-phase flows with cavitation
Hickel, Stefan
2014-01-01
We report on recent progress in the physical and numerical modeling of compressible two-phase flows that involve phase transition between the liquid and gaseous state of the fluid. The high-speed dynamics of cavitation bubbles is studied in well-resolved simulations (DNS) with a sharp-interface numerical model on a micro scale. The underlying assumption of the employed evaporation/condensation model is that phase change occurs in thermal non-equilibrium and that the associated timescale is larger than that of the wave dynamics. Results for the collapse of a spherical vapor bubble close to a solid wall are discussed for three different bubble-wall configurations. The major challenge for such numerical investigations is to accurately reproduce the dynamics of the interface between liquid and vapor during the entire collapse process, including the high-speed dynamics of the late stages, where compressibility of both phases plays a decisive role. Direct interface resolving simulations are intractable for real wor...
Hybrid dynamic modeling for two phase flow condensers
International Nuclear Information System (INIS)
In this paper, a hybrid modeling approach is proposed to describe the dynamic behavior of the two phase flow condensers used in air-conditioning and refrigeration systems. The model is formulated based on fundamental energy and mass balance governing equations, and thermodynamic principles, while some constants and less important variables that change very little during normal operation, such as cross-sectional areas, mean void fraction, the derivative of the saturation enthalpy with respect to pressure, etc., are lumped into several unknown parameters. These parameters are then obtained by experimental data using least squares identification method. The proposed modeling method takes advantages of both physical and empirical modeling approaches, can accurately predict the transient behaviors in real-time and significantly reduce the computational burden. Other merits of the proposed approach are that the order of the model is very low and all the state variables can be easily measured. These advantages make it easy to be applied to model based control system design. The model validation studies on an experimental system show that the model predicts the system dynamic well. -- Highlights: • A hybrid modeling approach is proposed to describe the dynamic behavior of condensers. • This modeling approach balances the trade-offs between complexity and accuracy. • The model order is very low and all the state variables are available for measurement. • The model validation studies show that the model predicts the system dynamic well. • The model is suitable for dynamic analysis and model-based controller design
Experimental and Theoretical Studies on Two-Phase Flows.
Koh, Christopher James
This thesis, comprised of two parts, deals with the flow of suspensions. Part I concerns specifically with the stability of a single drop translating through a quiescent, unbounded suspending fluid at low Reynolds number. The evolution of the shape of an initially nonspherical drop as it translates is studied numerically and experimentally. For finite capillary numbers, it is shown that the drop reverts to a sphere provided that the initial deformation is small enough. However, beyond certain critical initial deformation, the drop deforms continuously. For initially prolate shapes, the drop elongates with the formation of a tail; for initially oblate shapes, the drop flattens with the formation of a cavity at its rear. Experiments extend the numerical results. It is found that initially unstable prolate drops break up into multiple droplets, while initially unstable oblate drops deform in double-emulsion drops. Part II of this thesis considers the flow of high concentration solid suspensions through a rectangular channel. By adapting the well-known Laser Doppler Anemometry, an experimental technique is developed to measure the velocity as well as particle volume fraction of the suspension. A crucial element in these experiments is the reduction of the optical turbidity of the suspension. To accomplish this goal, a systematic method based on refractive-index-matching of the two phases is employed. Experimental results show that the velocity profile is blunted while the concentration profile has a maximum near the center. The qualitative features of the experimental data compare reasonably well with theoretical predictions based on the shear-induced particle migration theory.
Dynamic modeling strategy for flow regime transition in gas-liquid two-phase flows
International Nuclear Information System (INIS)
In modeling gas-liquid two-phase flows, the concept of flow regime has been widely used to characterize the global interfacial structure of the flows. Nearly all constitutive relations that provide closures to the interfacial transfers in two-phase flow models, such as the two-fluid model, are often flow regime dependent. Currently, the determination of the flow regimes is primarily based on flow regime maps or transition criteria, which were developed for steady-state, fully-developed flows and have been widely applied in nuclear reactor system safety analysis codes. As two-phase flows are dynamic in nature (fully-developed two-phase flows generally do not exist in real applications), it is of importance to model the flow regime transition dynamically to be able to predict two-phase flows more accurately. The present work aims to develop a dynamic modeling strategy to determine flow regimes in gas-liquid two-phase flows through introduction of interfacial area transport equations (IATEs) within the framework of a two-fluid model. The IATE is a transport equation that models the interfacial area concentration by considering the creation and destruction of the interfacial area, such as the fluid particle (bubble or liquid droplet) disintegration, boiling and evaporation; and fluid particle coalescence and condensation, respectively. For the flow regimes beyond bubbly flows, a two-group IATE has been proposed, in which bubbles are divided into two groups based on their size and shapes, namely group-1 and group-2 bubbles. A preliminary approach to dynamically identify the flow regimes is discussed, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration. The flow regime predicted with this method shows good agreement with the experimental observations. (author)
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)
High-frame rate, fast neutron imaging of two-phase flow in a thin rectangular channel
Zboray, R.; Mor, I.; Dangendorf, V.; Stark, M.; Tittelmeier, K.; Cortesi, M.; Adams, R.
2015-01-01
We have demonstrated the feasibility of performing high-frame-rate, fast neutron radiography of air-water two-phase flows in a thin channel with rectangular cross section. The experiments have been carried out at the accelerator facility of the Physikalisch-Technische Bundesanstalt. A polychromatic, high-intensity fast neutron beam with average energy of 6 MeV was produced by 11.5 MeV deuterons hitting a thick Be target. Image sequences down to 10 millisecond exposure times were obtained usin...
Prediction of a subcooled boiling flow with advanced two-phase flow models
International Nuclear Information System (INIS)
Highlights: ► In this study, advanced two-phase flow models were examined to enhance the prediction capability of subcooled boiling flows for the CFD code. ► They consist of Sγ bubbles size, new wall boiling and two-phase logarithmic wall function models. ► The benchmark calculation confirms that advanced two-phase flow models show good prediction results. - Abstract: Prediction of bubble size which governs interfacial transfer terms between the two phases is of importance for an accurate prediction of the subcooled boiling flow. In the present work, a mechanistic bubbles size model, Sγ was examined to enhance the prediction capability of subcooled boiling flows for the CFD (computational fluid dynamics) code. In addition to this, advanced subcooled boiling models such as new wall boiling and two-phase logarithmic wall function models were also applied for an improvement of energy partitioning and two-phase turbulence models, respectively. The benchmark calculation against the DEBORA subcooled boiling data confirms that the Sγ bubble size model with the two advanced subcooled boiling models shows good prediction results and is applicable to the wide range of flow conditions that are expected in the nominal and postulated accidental conditions of a nuclear power plant.
Experimental study on two-phase gas-liquid flow patterns at normal and reduced gravity conditions
Institute of Scientific and Technical Information of China (English)
赵建福; 解京昌; 林海; 胡文瑞
2001-01-01
Experimental studies have been performed for horizontal two-phase air-water flows at nor-mal and reduced gravity conditions in a square cross-section channel. The experiments at reducedgravity are conducted on board the Russian IL-76 reduced gravity airplane. Four flow patterns, namelybubble, slug, slug-annular transition and annular flows, are observed depending on the liquid and gassuperficial velocities at both conditions. Semi-theoretical Weber number model is developed to includethe shape influence on the slug-annular transition. It is shown that its prediction is in reasonable agree-ment with the experimental slug-annular transition under both conditions. For the case of two-phasegas-liquid flow with large value of the Froude number, the drift-flux model can predict well the observedboundary between bubble and slug flows.
CFD Simulation of Polydispersed Bubbly Two-Phase Flow around an Obstacle
Directory of Open Access Journals (Sweden)
E. Krepper
2009-01-01
Full Text Available This paper concerns the model of a polydispersed bubble population in the frame of an ensemble averaged two-phase flow formulation. The ability of the moment density approach to represent bubble population size distribution within a multi-dimensional CFD code based on the two-fluid model is studied. Two different methods describing the polydispersion are presented: (i a moment density method, developed at IRSN, to model the bubble size distribution function and (ii a population balance method considering several different velocity fields of the gaseous phase. The first method is implemented in the Neptune_CFD code, whereas the second method is implemented in the CFD code ANSYS/CFX. Both methods consider coalescence and breakup phenomena and momentum interphase transfers related to drag and lift forces. Air-water bubbly flows in a vertical pipe with obstacle of the TOPFLOW experiments series performed at FZD are then used as simulations test cases. The numerical results, obtained with Neptune_CFD and with ANSYS/CFX, allow attesting the validity of the approaches. Perspectives concerning the improvement of the models, their validation, as well as the extension of their applicability range are discussed.
International Nuclear Information System (INIS)
The characteristics of a circulating pump at the time of LOCA in a nuclear reactor, that is, the pump characteristics when two-phase fluid composed of water and the steam produced by self evaporation is pumped draw attention. In order to correctly understand the pump characteristics at the time of steam-water two phases, it is necessary to grasp in detail the behavior of both phases of steam and water at the entrance of the pump and within the pump. For the purpose, it was attempted to measure the three-dimensional distribution of void fraction in channels by installing point electrodes in the channels of an impeller. Moreover, the slip ratio in each cross section of the impeller channels was calculated from the distribution of void fraction, and the relationship between the characteristic behavior of both steam and water phases and the pump characteristics was discussed. The experimental setup and method, and the experimental results are reported. The void fraction in an impeller distributed three-dimensionally in complex state, and bubbles tended to flow from negative pressure side toward positive pressure side in the impeller in biased state. (Kako, I.)
Zero-G two phase flow regime modeling in adiabatic flow
Reinarts, Thomas R.; Best, Frederick R.; Wheeler, Montgomery; Miller, Katheryn M.
1993-01-01
Two-phase flow, thermal management systems are currently being considered as an alternative to conventional, single phase systems for future space missions because of their potential to reduce overall system mass, size, and pumping power requirements. Knowledge of flow regime transitions, heat transfer characteristics, and pressure drop correlations is necessary to design and develop two-phase systems. This work is concerned with microgravity, two-phase flow regime analysis. The data come from a recent sets of experiments. The experiments were funded by NASA Johnson Space Center (JSC) and conducted by NASA JSC with Texas A&M University. The experiment was on loan to NASA JSC from Foster-Miller, Inc., who constructed it with funding from the Air Force Phillips Laboratory. The experiment used R12 as the working fluid. A Foster-Miller two phase pump was used to circulate the two phase mixture and allow separate measurements of the vapor and liquid flow streams. The experimental package was flown 19 times for 577 parabolas aboard the NASA KC-135 aircraft which simulates zero-G conditions by its parabolic flight trajectory. Test conditions included bubbly, slug and annular flow regimes in 0-G. The superficial velocities of liquid and vapor have been obtained from the measured flow rates and are presented along with the observed flow regimes and several flow regime transition predictions. None of the predictions completely describe the transitions as indicated by the data.
Zero-G two phase flow regime modeling in adiabatic flow
International Nuclear Information System (INIS)
Two-phase flow, thermal management systems are currently being considered as an alternative to conventional, single phase systems for future space missions because of their potential to reduce overall system mass, size, and pumping power requirements. Knowledge of flow regime transitions, heat transfer characteristics, and pressure drop correlations is necessary to design and develop two-phase systems. This work is concerned with microgravity, two-phase flow regime analysis. The data come from a recent sets of experiments. The experiments were funded by NASA Johnson Space Center (JSC) and conducted by NASA JSC with Texas A ampersand M University. The experiment was on loan to NASA JSC from Foster-Miller, Inc., who constructed it with funding from the Air Force Phillips Laboratory. The experiment used R12 as the working fluid. A Foster-Miller two phase pump was used to circulate the two phase mixture and allow separate measurements of the vapor and liquid flow streams. The experimental package was flown 19 times for 577 parabolas aboard the NASA KC-135 aircraft which simulates zero-G conditions by its parabolic flight trajectory. Test conditions included bubbly, slug and annular flow regimes in 0-G. The superficial velocities of liquid and vapor have been obtained from the measured flow rates and are presented along with the observed flow regimes and several flow regime transition predictions. None of the predictions completely describe the transitions as indicated by the data
On the Stable Numerical Approximation of Two-Phase Flow with Insoluble Surfactant
Barrett, John W; Nürnberg, Robert
2013-01-01
We present a parametric finite element approximation of two-phase flow with insoluble surfactant. This free boundary problem is given by the Navier--Stokes equations for the two-phase flow in the bulk, which are coupled to the transport equation for the insoluble surfactant on the interface that separates the two phases. We combine the evolving surface finite element method with an approach previously introduced by the authors for two-phase Navier--Stokes flow, which maintains good mesh properties. The derived finite element approximation of two-phase flow with insoluble surfactant can be shown to be stable. Several numerical simulations demonstrate the practicality of our numerical method.
Wei-Yang Xie; Xiao-Ping Li; Lie-Hui Zhang; Xiao-Hua Tan; Jun-Chao Wang; Hai-Tao Wang
2015-01-01
After multistage fracturing, the flowback of fracturing fluid will cause two-phase flow through hydraulic fractures in shale gas reservoirs. With the consideration of two-phase flow and desorbed gas transient diffusion in shale gas reservoirs, a two-phase transient flow model of multistage fractured horizontal well in shale gas reservoirs was created. Accurate solution to this flow model is obtained by the use of source function theory, Laplace transform, three-dimensional eigenvalue method, ...
Numerical simulation for gas-liquid two-phase flow in pipe networks
International Nuclear Information System (INIS)
The complex pipe network characters can not directly presented in single phase flow, gas-liquid two phase flow pressure drop and void rate change model. Apply fluid network theory and computer numerical simulation technology to phase flow pipe networks carried out simulate and compute. Simulate result shows that flow resistance distribution is non-linear in two phase pipe network
Two parametric flow measurement in gas-liquid two-phase flow
Chen, Z.; Chen, C.; Xu, Y.; Zhao, Z.
The importance and current development of two parametric measurement during two-phase flow are briefly reviewed in this paper. Gas-liquid two-phase two parametric metering experiments were conducted by using an oval gear meter and a sharp edged orifice mounted in series in a horizontal pipe. Compressed air and water were used as gas and liquid phases respectively. The correlations, which can be used to predict the total flow rate and volumetric quality of two-phase flow or volumetric flow rate of each phase, have also been proposed in this paper. Comparison of the calculated values of flow rate of each phase from the correlations with the test data showed that the root mean square fractional deviation for gas flow rate is 2.9 percent and for liquid flow rate 4.4 percent. The method proposed in this paper can be used to measure the gas and liquid flow rate in two-phase flow region without having to separate the phases.
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)
Elazhary, Amr Mohamed; Soliman, Hassan M.
2012-10-01
An experimental study was conducted in order to investigate two-phase flow regimes and fully developed pressure drop in a mini-size, horizontal rectangular channel. The test section was machined in the form of an impacting tee junction in an acrylic block (in order to facilitate visualization) with a rectangular cross-section of 1.87-mm height on 20-mm width on the inlet and outlet sides. Pressure drop measurement and flow regime identification were performed on all three sides of the junction. Air-water mixtures at 200 kPa (abs) and room temperature were used as the test fluids. Four flow regimes were identified visually: bubbly, plug, churn, and annular over the ranges of gas and liquid superficial velocities of 0.04 ≤ JG ≤ 10 m/s and 0.02 ≤ JL ≤ 0.7 m/s, respectively, and a flow regime map was developed. Accuracy of the pressure-measurement technique was validated with single-phase, laminar and turbulent, fully developed data. Two-phase experiments were conducted for eight different inlet conditions and various mass splits at the junction. Comparisons were conducted between the present data and former correlations for the fully developed two-phase pressure drop in rectangular channels with similar sizes. Wide deviations were found among these correlations, and the correlations that agreed best with the present data were identified.
Flow pattern and heat transfer behavior of boiling two-phase flow in inclined pipes
Liu, Dezhang; Ning, Ouyang
1992-09-01
Movable Electrical Conducting Probe (MECP), a kind of simple and reliable measuring transducer, used for predicting full-flow-path flow pattern in a boiling vapor/liquid two-phase flow is introduced in this paper. When the test pipe is set at different inclination angles, several kinds of flow patterns, such as bubble, slug, churn, intermittent, and annular flows, may be observed in accordance with the locations of MECP. By means of flow pattern analysis, flow field numerical calculations have been carried out, and heat transfer coefficient correlations along full-flow-path derived. The results show that heat transfer performance of boiling two-phase flow could be significantly augmented as expected in some flow pattern zones. The results of the investigation, measuring techniques and conclusions contained in this paper would be a useful reference in foundational research for prediction of flow pattern and heat transfer behavior in boiling two-phase flow, as well as for turbine vane liquid-cooling design.
Measurement of interfacial structures in horizontal air-water bubbly flows
International Nuclear Information System (INIS)
In order to predict multi-dimensional phenomena in nuclear reactor systems, methods relying on computational fluid dynamics (CFD) codes are essential. However, to be applicable in assessing thermal-hydraulic safety, these codes must be able to accurately predict the development of two-phase flows. Therefore, before practical application these codes must be assessed using experimental databases that capture multi-dimensional phenomena. While a large database exists that can be employed to assess predictions in vertical flows, the available database for horizontal flows is significantly lacking. Therefore, the current work seeks to develop an additional database in air-water horizontal bubbly flow through a 38.1 mm ID test section with a total development length of approximately 250 diameters. The experimental conditions are chosen to cover a wide range of the bubbly flow regime based upon flow visualization using a high-speed video camera. A database of local time-averaged void fraction, bubble velocity, interfacial area concentration, and bubble Sauter mean diameter are acquired throughout the pipe cross-section using a four-sensor conductivity probe. To investigate the evolution of the flow, measurements are made at axial locations of 44, 116, and 244 diameters downstream of the inlet. In the current work, only measurements obtained at L/D = 244 are presented. It is found that increasing the liquid superficial velocity tends to reduce both the bubble size and the degree of bubble packing near the upper wall. However, it is observed that the position of the maximum void fraction value remains nearly constant and is located approximately one bubble diameter away from the upper wall. It is also found that the bubble velocity exhibits a power law behavior resembling a single phase liquid turbulent velocity profile. Moreover, the local bubble velocity tends to decrease as the local void fraction increases. Conversely, increasing the gas superficial velocity is found to
Liang, Fachun; Zheng, Hongfeng; Yu, Hao; Sun, Yuan
2016-03-01
A novel ultrasonic pulse echo method is proposed for flow pattern identification in a horizontal pipe with gas-liquid two-phase flow. A trace of echoes reflected from the pipe’s internal wall rather than the gas-liquid interface is used for flow pattern identification. Experiments were conducted in a horizontal air-water two-phase flow loop. Two ultrasonic transducers with central frequency of 5 MHz were mounted at the top and bottom of the pipe respectively. The experimental results show that the ultrasonic reflection coefficient of the wall-gas interface is much larger than that of the wall-liquid interface due to the large difference in the acoustic impedance of gas and liquid. The stratified flow, annular flow and slug flow can be successfully recognized using the attenuation ratio of the echoes. Compared with the conventional ultrasonic echo measurement method, echoes reflected from the inner surface of a pipe wall are independent of gas-liquid interface fluctuation, sound speed, and gas and liquid superficial velocities, which makes the method presented a promising technique in field practice.
Mass flow rate measurements in two-phase mixtrues with stagnation probes
International Nuclear Information System (INIS)
Applications of stagnation probes to the measurement of mass flow rate in two-phase flows are discussed. Descriptions of several stagnation devices, which have been evaluated at the Idaho National Engineering Laboratory, are presented along with modeling techniques and two-phase flow data
Mass flow rate measurements in two-phase mixtrues with stagnation probes. [PWR
Energy Technology Data Exchange (ETDEWEB)
Fincke, J.R.; Deason, V.A.
1979-01-01
Applications of stagnation probes to the measurement of mass flow rate in two-phase flows are discussed. Descriptions of several stagnation devices, which have been evaluated at the Idaho National Engineering Laboratory, are presented along with modeling techniques and two-phase flow data.
Two-Phase Flow in Circular Secondary Sedimentation Tanks
Matko, T. I. R.
1997-01-01
The main objective of this work was to optimise a numerical model to predict the flow in circular secondary sedimentation tanks. The numerical models in the literature were reviewed and the new opportunities for research were identified. Single-phase flow characteristics of two circular sedimentation tanks were investigated using the CFD program, CFX-F3D. The flow in the circular clarifiers were modelled in two dimensions (axial and radial) and using the standard k-E turbule...
Fluiddynamic critical two-phase (gas/liquid) flow state in non ideal flow geometries
Energy Technology Data Exchange (ETDEWEB)
Friedel, L. [Technische Univ. Hamburg-Harburg, Hamburg (Germany)
2001-07-01
During the emergency venting of pressurized, in most cases partially liquid loaded reactors across safety devices or in the course of the intentionally controlled depressurisation, resp., degassing of such production equipment across a throttle valve a two-phase flow can establish due to the occurring level swell. In the context of the equipment sizing for safety and economical reasons a maximum mass discharge, resp., critical velocity in the transfer piping system or device is an issue. Indeed, analytical methods for the critical two-phase mass flow prediction are only available for ideal nozzle or pipe flow. In principle, they look like simple derivatives of the ideal model used in (compressible) gas dynamics. In contrast to the explanations in text books referring to the case of an ideal nozzle flow such a characteristic flow state does not establish in the device. This is, amongst others, the consequence of wall detachment of the flow, establishment of an inhomogeneous velocity field across the flow controlling cross section, local random cavitation or flashing/condensation incipience, multiple choking in the transfer piping system and corresponding back pressure change. As a consequence, the experimental maximum mass flow will depend, e.g., on the experimenter's pragmatism as well as capability and the metering quality installed in the test rig as well as, strictly speaking, it can only be valid for the individual specimen due to non avoidable manufacturing tolerances. An example for such a pragmatical approach is the recently proposed short-cut safety valve sizing method by T. Lenzing et al. The basis is formed by the isentropic homogeneous two-phase nozzle flow model, leading under all conditions to a discharge coefficient value in two-phase flow of less than unity. The essential features of the method are thermodynamic and fluiddynamic equilibrium between the phases. (orig.)
Stability of stratified two-phase flows in inclined channels
Barmak, Ilya; Ullmann, Amos; Brauner, Neima
2016-01-01
Linear stability of stratified gas-liquid and liquid-liquid plane-parallel flows in inclined channels is studied with respect to all wavenumber perturbations. The main objective is to predict parameter regions in which stable stratified configuration in inclined channels exists. Up to three distinct base states with different holdups exist in inclined flows, so that the stability analysis has to be carried out for each branch separately. Special attention is paid to the multiple solution regions to reveal the feasibility of non-unique stable stratified configurations in inclined channels. The stability boundaries of each branch of steady state solutions are presented on the flow pattern map and are accompanied by critical wavenumbers and spatial profiles of the most unstable perturbations. Instabilities of different nature are visualized by streamlines of the neutrally stable perturbed flows, consisting of the critical perturbation superimposed on the base flow. The present analysis confirms the existence of ...
Local measurements in two-phase flows using a double optical probe technique
International Nuclear Information System (INIS)
Local measurements are of primary importance for the characterization of gas-liquid two-phase flows, both for processes control and numerical modeling validation. It is a very active research field due to the increasing number of applications in the thermohydraulics of heat exchangers, nuclear plants, chemical processes and oil industries. This paper presents the local measurements in a vertical upward air-water flow using the optical fiber double probe technique. The test section was a 80 mm i.d. and 160 cm long Plexiglas tube. Five different gas superficial velocities ranging from 0.02 to 0.10 m/s were used in combination with two liquid superficial velocities of 0 and 0.10 m/s (atmospheric pressure and temperature). A double optical probe was employed for measurements of the radial profiles of void fraction, bubble frequency, bubble interface velocity, interfacial area concentration and Sauter mean diameter. The working principle of the optical probe is based on the refraction law. Liquid-gas interfaces passing by the tip of the probe causes the system to change from a refraction state to a total reflection state. Since the light detecting circuit is active only when the sensor tip is in contact with the gas phase, the probe behaves in principle like a switch, yielding a two-stage signal. However, to obtain a true square wave type signals, a proper threshold voltage has to be used as a triggering criterion. Herein the signal conditioning is discussed and the influence of the threshold level is analyzed. Using a probe with two sensors displaced axially, the bubble interface velocity could be determined from the time delay which gave maximum correlation between the sensors response. These values of gas velocity in conjunction with void fraction could be integrated to give average gas superficial velocities. Values determined in this manner were compared to values from the inlet gas flowrate measurements and showed a good agreement. (author)
A MODEL FOR PREDICTING PHASE INVERSION IN OIL-WATER TWO-PHASE PIPE FLOW
Institute of Scientific and Technical Information of China (English)
GONG Jing; LI Qing-ping; YAO Hai-yuan; YU Da
2006-01-01
Experiments of phase inversion characteristics for horizontal oil-water two-phase flow in a stainless steel pipe loop (25.7 mm inner diameter,52 m long) are conducted. A new viewpoint is brought forward about the process of phase inversion in oil-water two-phase pipe flow. Using the relations between the total free energies of the pre-inversion and post-inversion dispersions, a model for predicting phase inversion in oil-water two-phase pipe flow has been developed that considers the characteristics of pipe flow. This model is compared against other models with relevant data of phase inversion in oil-water two-phase pipe flow. Results indicate that this model is better than other models in terms of calculation precision and applicability. The model is useful for guiding the design for optimal performance and safety in the operation of oil-water two-phase pipe flow in oil fields.
Mathematical models for two-phase stratified pipe flow
Energy Technology Data Exchange (ETDEWEB)
Biberg, Dag
2005-06-01
The simultaneous transport of oil, gas and water in a single multiphase flow pipe line has for economical and practical reasons become common practice in the gas and oil fields operated by the oil industry. The optimal design and safe operation of these pipe lines require reliable estimates of liquid inventory, pressure drop and flow regime. Computer simulations of multiphase pipe flow have thus become an important design tool for field developments. Computer simulations yielding on-line monitoring and look ahead predictions are invaluable in day-to-day field management. Inaccurate predictions may have large consequences. The accuracy and reliability of multiphase pipe flow models are thus important issues. Simulating events in large pipelines or pipeline systems is relatively computer intensive. Pipe-lines carrying e.g. gas and liquefied gas (condensate) may cover distances of several hundred km in which transient phenomena may go on for months. The evaluation times associated with contemporary 3-D CFD models are thus not compatible with field applications. Multiphase flow lines are therefore normally simulated using specially dedicated 1-D models. The closure relations of multiphase pipe flow models are mainly based on lab data. The maximum pipe inner diameter, pressure and temperature in a multiphase pipe flow lab is limited to approximately 0.3 m, 90 bar and 60{sup o}C respectively. The corresponding field values are, however, much higher i.e.: 1 m, 1000 bar and 200{sup o}C respectively. Lab data does thus not cover the actual field conditions. Field predictions are consequently frequently based on model extrapolation. Applying field data or establishing more advanced labs will not solve this problem. It is in fact not practically possible to acquire sufficient data to cover all aspects of multiphase pipe flow. The parameter range involved is simply too large. Liquid levels and pressure drop in three-phase flow are e.g. determined by 13 dimensionless parameters
Mechanisms for two phase flow in porous media
International Nuclear Information System (INIS)
For a better understanding of transport mechanisms in soil for a system with two phases of immiscible liquids the physics of porous media gives again important contributions. In this report, the considerations mainly concentrate on horizontal transport. Our approach is based on the similarity solution of the transport equation which reduces a given nonlinear partial differential equation (PDE) to an ordinary differential equation (ODE). It can be seen, how dimensionless similarity solutions of the ODE depend, in addition to the similarity variable, on two parameters: - the capillary number Nc, giving the ratio of capillary forces and viscous forces, and - the ratio of the viscosities of the two liquid phases. It is shown, under which conditions different mechanisms of transport are to be expected, such as - a completely stable displacement or - an unstable displacement, related to viscous fingering (DLA, Diffusion Limited Aggregation) or to capillary fingering (IP, Invasion Percolation). These mechanisms are also strongly dependent on certain critical exponents (characteristic for DLA or IP). These relations are discussed in our report. Again, for some regions of saturation, mechanisms of displacement are either clearly dominated - by imbibition (e.g. water pushing oil) or - by drain (e.g. oil pushing water). Some of the results are also transformed again from the similarity solution of the ODE to a solution of the PDE (with space- and time coordinates). It is seen, that even with this somewhat simplified approach, we obtain a considerable spectrum of mechanisms. (orig.)
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.
Analysis of free-surface flows through energy considerations: Single-phase versus two-phase modeling
Marrone, Salvatore; Colagrossi, Andrea; Di Mascio, Andrea; Le Touzé, David
2016-05-01
The study of energetic free-surface flows is challenging because of the large range of interface scales involved due to multiple fragmentations and reconnections of the air-water interface with the formation of drops and bubbles. Because of their complexity the investigation of such phenomena through numerical simulation largely increased during recent years. Actually, in the last decades different numerical models have been developed to study these flows, especially in the context of particle methods. In the latter a single-phase approximation is usually adopted to reduce the computational costs and the model complexity. While it is well known that the role of air largely affects the local flow evolution, it is still not clear whether this single-phase approximation is able to predict global flow features like the evolution of the global mechanical energy dissipation. The present work is dedicated to this topic through the study of a selected problem simulated with both single-phase and two-phase models. It is shown that, interestingly, even though flow evolutions are different, energy evolutions can be similar when including or not the presence of air. This is remarkable since, in the problem considered, with the two-phase model about half of the energy is lost in the air phase while in the one-phase model the energy is mainly dissipated by cavity collapses.
Flow patterns and pressure drop in horizontal two-phase pipe flow
International Nuclear Information System (INIS)
A study was made of the relationship between flow patterns and frictional pressure drop during cocurrent gas-liquid flow in horizontal pipelines. On the basis of a revised flow pattern classification, the key flow pattern transitions were (a) onset of homogeneous flow, (b) onset of separated flow and (c) intermittent-annular transition. The available flow pattern transition observations were compared with the existing correlations for these flow patterns transitions. The onset of homogeneous flow could be satisfactorily predicted by a correlation previously developed by Husain. The onset of separated flow could be predicted by an extension of the work of Wallis and Dobson. None of the existing correlations or any simple extension of correlations were found satisfactory for the annular-intermittent transition. Two theoretical approaches to the intermittent-annular transition were considered. The models were developed on the basis (a) a wave mechanism and (b) entrainment-deposition mechanism. The wave model was considered to provide the most satisfactory correlation of the data. On the basis of these correlations an overall flow pattern map is proposed. The available two-phase pressure drop correlations were compared to the world data on two-phase pressure drop. A world data bank, prepared by the University of Houston and the University of Calgary, was used for this purpose. It was found that an appreciably better fit of two-phase pressure drop in horizontal tubes could be obtained when separate correlations were used for the various flow pattern regions. In the intermittent and annular regions, the Lockhart--Martinelli correlation was best while in the separated flow region Hoogendoorn's correlation was superior. In the homogeneous region, a modified homogeneous approach provided the best agreement
Pitch-to-diameter effect on two-phase flow across an in-line tube bundle
International Nuclear Information System (INIS)
This paper reports on void fraction and friction pressure drop measurements that were made for an adiabatic, vertical two-phase flow of air-water across two horizontal, in-line, 5 x 20 rod bundles, one with a pitch-to-diameter ratio, P/D, of 1.3, the other 1.75. For both bundles the average void fraction showed a strong mass velocity effect and values were significantly less than those predicted by a homogeneous flow model. All void fraction data were found to be well correlated, with no P/D effect, using the dimensionless gas velocity, j*g. The two-phase friction multiplier data exhibited a strong effect of P/D and mass velocity, however, the data for both bundles could be well correlated with the Martinelli parameter for G > 200 kg/m2s. The correlations developed for void fraction and two-phase friction multiplier were successfully tested in predicting the total pressure drop in boiling freon experiments
Interchannel stability analysis of oscillatory instable parallel channel two phase flow regimes
International Nuclear Information System (INIS)
Conditions for interchannel hydrodynamic stability of oscillatory unstable parallel channel two-phase flow regimes are being analysed. For experimental determined transfer functions Nyquist diagrams for one-phase and two-phase flow regimes are being considered. The results are presented show interchannel stability oscillatory unstable linear experimental regimes and interchannel instability nonlinear experimental regimes
Modelling of two-phase flow based on separation of the flow according to velocity
International Nuclear Information System (INIS)
The thesis concentrates on the development work of a physical one-dimensional two-fluid model that is based on Separation of the Flow According to Velocity (SFAV). The conventional way to model one-dimensional two-phase flow is to derive conservation equations for mass, momentum and energy over the regions occupied by the phases. In the SFAV approach, the two-phase mixture is divided into two subflows, with as distinct average velocities as possible, and momentum conservation equations are derived over their domains. Mass and energy conservation are treated equally with the conventional model because they are distributed very accurately according to the phases, but momentum fluctuations follow better the flow velocity. Submodels for non-uniform transverse profile of velocity and density, slip between the phases within each subflow and turbulence between the subflows have been derived. The model system is hyperbolic in any sensible flow conditions over the whole range of void fraction. Thus, it can be solved with accurate numerical methods utilizing the characteristics. The characteristics agree well with the used experimental data on two-phase flow wave phenomena Furthermore, the characteristics of the SFAV model are as well in accordance with their physical counterparts as of the best virtual-mass models that are typically optimized for special flow regimes like bubbly flow. The SFAV model has proved to be applicable in describing two-phase flow physically correctly because both the dynamics and steady-state behaviour of the model has been considered and found to agree well with experimental data This makes the SFAV model especially suitable for the calculation of fast transients, taking place in versatile form e.g. in nuclear reactors
Modelling of two-phase flow based on separation of the flow according to velocity
Energy Technology Data Exchange (ETDEWEB)
Narumo, T. [VTT Energy, Espoo (Finland). Nuclear Energy
1997-12-31
The thesis concentrates on the development work of a physical one-dimensional two-fluid model that is based on Separation of the Flow According to Velocity (SFAV). The conventional way to model one-dimensional two-phase flow is to derive conservation equations for mass, momentum and energy over the regions occupied by the phases. In the SFAV approach, the two-phase mixture is divided into two subflows, with as distinct average velocities as possible, and momentum conservation equations are derived over their domains. Mass and energy conservation are treated equally with the conventional model because they are distributed very accurately according to the phases, but momentum fluctuations follow better the flow velocity. Submodels for non-uniform transverse profile of velocity and density, slip between the phases within each subflow and turbulence between the subflows have been derived. The model system is hyperbolic in any sensible flow conditions over the whole range of void fraction. Thus, it can be solved with accurate numerical methods utilizing the characteristics. The characteristics agree well with the used experimental data on two-phase flow wave phenomena Furthermore, the characteristics of the SFAV model are as well in accordance with their physical counterparts as of the best virtual-mass models that are typically optimized for special flow regimes like bubbly flow. The SFAV model has proved to be applicable in describing two-phase flow physically correctly because both the dynamics and steady-state behaviour of the model has been considered and found to agree well with experimental data This makes the SFAV model especially suitable for the calculation of fast transients, taking place in versatile form e.g. in nuclear reactors. 45 refs. The thesis includes also five previous publications by author.
Two-phase flow research using the learjet apparatus
Mcquillen, John B.; Neumann, Eric S.
1995-01-01
Low-gravity, gas-liquid flow research can be conducted aboard the NASA Lewis Learjet, the Lewis DC-9, or the Johnson Space Center KC-135. Air and water solutions serve as the test liquids in cylindrical test sections with an inner diameter of 1.27 cm and lengths up to 1.5 m. Superficial velocities range from 0.1 to 1.1 m/sec for liquids and from 0.1 to 25 m/sec for air. Flow rate, differential pressure, void fraction, film thickness, wall-shear stress, and acceleration data are measured and recorded throughout the 20 sec duration of the experiment. Flow is visualized by photographing at 400 frames with a high-speed, 16-mm camera.
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.
Directory of Open Access Journals (Sweden)
Wei-Yang Xie
2015-01-01
Full Text Available After multistage fracturing, the flowback of fracturing fluid will cause two-phase flow through hydraulic fractures in shale gas reservoirs. With the consideration of two-phase flow and desorbed gas transient diffusion in shale gas reservoirs, a two-phase transient flow model of multistage fractured horizontal well in shale gas reservoirs was created. Accurate solution to this flow model is obtained by the use of source function theory, Laplace transform, three-dimensional eigenvalue method, and orthogonal transformation. According to the model’s solution, the bilogarithmic type curves of the two-phase model are illustrated, and the production decline performance under the effects of hydraulic fractures and shale gas reservoir properties are discussed. The result obtained in this paper has important significance to understand pressure response characteristics and production decline law of two-phase flow in shale gas reservoirs. Moreover, it provides the theoretical basis for exploiting this reservoir efficiently.
Energy Technology Data Exchange (ETDEWEB)
Oliveira, Livia Alves [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil); Nuclear Engineering Institute (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)], E-mail: livia@lasme.coppe.ufrj.br; Cunha Filho, Jurandyr; Su, Jian [Coordenacao dos Programas de Pos-Graduacao de Engenharia (COPPE/UFRJ), RJ (Brazil). Nuclear Engineering Program], Emails: cunhafilho@lasme.coppe.ufrj.br, sujian@lasme.coppe.ufrj.br; Faccini, Jose Luiz Horacio [Nuclear Engineering Institute (IEN/CNEN-RJ), Rio de Janeiro, RJ (Brazil)], E-mail: faccini@ien.gov.br
2010-07-01
In this paper a flow visualization study was performed for two-phase gas-liquid flow in horizontal and slightly inclined tubes. The test section consists of a 2.54 cm inner diameter stainless steel circular tube, followed by a transparent acrylic tube with the same inner diameter. The working fluids were air and water, with liquid superficial velocities ranging from 0:11 to 3:28 m/s and gas superficial velocities ranging from 0:27 to 5:48 m/s. Flow visualization was executed for upward flow at 5 deg and 10 deg and downward flow at 2:5 deg, 5 deg and 10 deg, as well as for horizontal flow. The visualization technique consists of a high-speed digital camera that records images at rates of 125 and 250 frames per second of a concurrent air-water mixture through a transparent part of the tube. From the obtained images, the flow regimes were identified (except for annular flow), observing the effect of inclination angles on flow regime transition boundaries. Finally, the experimental results were compared with empirical and theoretical flow pattern maps available in literature. (author)
Experimental Studies on the Measurement of Oil-water Two-phase Flow
Ma, Longbo; Zhang, Hongjian; Hua, Yuefang; Zhou, Hongliang
2007-06-01
Oil-water two-phase flow measurement was investigated with a Venturi meter and double-U Coriolis meter in this work. Based on the Venturi differential pressure and the quality of two-phase flow, a model for measuring oil-water mass flow rate was developed, in which fluid asymmetry of oil-water two-phase flow was considered. However, measuring the quality of two-phase flow on-line is rather difficult at present. Though double-U Coriolis meter can provide accurate measurement of two-phase flow, it can not provide desired respective mass flow rate. Therefore, a double-parameter measurement method with Venturi meter and double-U Coriolis meter is proposed. According to the flow rate requirement of Venturi, a new flow regime identification method based on Support Vector Machine (SVM) has been developed for the separated flow and the dispersed flow. With the Venturi model developed in this paper and mass flow rate of oil-water mixture measured with double-U Coriolis meter, mixture mass flow rate, oil mass flow rate and water mass flow rate could be obtained by the correlation. Experiments of flow rate measurement of oil-water two-phase flow were carried out in the horizontal tube with 25mm inner diameter. The water fraction range is from 5% to 95%. Experimental results showed that the flow regime could be identified well with SVM, and the relative error of the total mass flow rate and respective mass flow rate of oil-water two-phase flow was less than ±1.5% and ±10%, respectively.
Experimental on two sensors combination used in horizontal pipe gas-water two-phase flow
International Nuclear Information System (INIS)
Gas-water two phase flow phenomenon widely exists in production and living and the measurement of it is meaningful. A new type of long-waist cone flow sensor has been designed to measure two-phase mass flow rate. Six rings structure of conductance probe is used to measure volume fraction and axial velocity. The calibration of them have been made. Two sensors have been combined in horizontal pipeline experiment to measure two-phase flow mass flow rate. Several model of gas-water two-phase flow has been discussed. The calculation errors of total mass flow rate measurement is less than 5% based on the revised homogeneous flow model
Experimental on two sensors combination used in horizontal pipe gas-water two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Wu, Hao; Dong, Feng [Tianjin Key Laboratory of Process Measurement and Control, School of Electrical Engineering and Automation, Tianjin University, Tianjin (China)
2014-04-11
Gas-water two phase flow phenomenon widely exists in production and living and the measurement of it is meaningful. A new type of long-waist cone flow sensor has been designed to measure two-phase mass flow rate. Six rings structure of conductance probe is used to measure volume fraction and axial velocity. The calibration of them have been made. Two sensors have been combined in horizontal pipeline experiment to measure two-phase flow mass flow rate. Several model of gas-water two-phase flow has been discussed. The calculation errors of total mass flow rate measurement is less than 5% based on the revised homogeneous flow model.
Experimental on two sensors combination used in horizontal pipe gas-water two-phase flow
Wu, Hao; Dong, Feng
2014-04-01
Gas-water two phase flow phenomenon widely exists in production and living and the measurement of it is meaningful. A new type of long-waist cone flow sensor has been designed to measure two-phase mass flow rate. Six rings structure of conductance probe is used to measure volume fraction and axial velocity. The calibration of them have been made. Two sensors have been combined in horizontal pipeline experiment to measure two-phase flow mass flow rate. Several model of gas-water two-phase flow has been discussed. The calculation errors of total mass flow rate measurement is less than 5% based on the revised homogeneous flow model.
Two-phase flow measurements at high void fraction by a Venturi meter
Monni, Grazia; Salve, Mario De; Panella, Bruno
2014-01-01
An experimental investigation of a vertical upward annular two-phase flow across a Venturi flow meter has been performed for the measurement of two-phase flow parameters with reference to the experimental simulation of nuclear accidents, as LOCA, characterized by very high void fraction. The pressure drops between the inlet and throat section and between inlet and outlet (irreversible pressure losses) have been measured and analyzed. The Venturi flow meter is characterized by an inlet diamete...
A continuum theory for two-phase flows of particulate solids: application to Poiseuille flows
Monsorno, Davide; Varsakelis, Christos; Papalexandris, Miltiadis V.
2015-11-01
In the first part of this talk, we present a novel two-phase continuum model for incompressible fluid-saturated granular flows. The model accounts for both compaction and shear-induced dilatancy and accommodates correlations for the granular rheology in a thermodynamically consistent way. In the second part of this talk, we exercise this two-phase model in the numerical simulation of a fully-developed Poiseuille flow of a dense suspension. The numerical predictions are shown to compare favorably against experimental measurements and confirm that the model can capture the important characteristics of the flow field, such as segregation and formation of plug zones. Finally, results from parametric studies with respect to the initial concentration, the magnitude of the external forcing and the width of the channel are presented and the role of these physical parameters is quantified. Financial Support has been provided by SEDITRANS, an Initial Training Network of the European Commission's 7th Framework Programme
Dispersed Two-Phase Flow Simulation and Parameters Optimisation
Achou, Yapi Donatien
2016-01-01
The numerical solution of differential equations is an algorithmic process with various parameters controlling the accuracy, stability and computational time of the simulation. In Computational Fluid Mechanics (CFD) there are numerous softwares designed to solve multiphase flow problems. One such software is OpenFoam, an open-source CFD software. In this thesis we use OpenFoam to simulate two special cases: first the rising of a single air bubble in liquid water, and then a turbulent disperse...
Two-Dimensional Numerical Simulation of Boiling Two-Phase Flow of Liquid Nitrogen
Ishimoto, Jun; Oike, Mamoru; Kamijo, Kenjiro
Two-dimensional characteristics of the boiling two-phase flow of liquid nitrogen in a duct flow are numerically investigated to contribute to the further development of new high-performance cryogenic engineering applications. First, the governing equations of the boiling two-phase flow of liquid nitrogen based on the unsteady drift-flux model are presented and several flow characteristics are numerically calculated taking account the effect of cryogenic flow states. Based on the numerical results, a two-dimensional structure of the boiling two-phase flow of liquid nitrogen is shown in detail, and it is found that the phase change of liquid nitrogen occurs in quite a short time interval compared with that of two-phase pressurized water at high temperature. Next, it is clarified that the distributions of pressure and the void fraction in a two-phase flow show a tendency different from those of fluids at room temperature because of the decrease in sound velocity due to large compressibility and the rapid phase change velocity in a cryogenic two-phase mixture flow. According to these numerical results, the fundamental characteristics of the cryogenic two-phase flow are predicted. The numerical results obtained will contribute to advanced cryogenic industrial applications.
Radiogauging to investigate two phase flow. Graduation report
International Nuclear Information System (INIS)
New measuring methods are developed and are tested with the small reactor simulator MIDAS (Mini Dodewaard ASsembly). The purpose of this work is to be able to measure accurately as many different properties of the flow as possible in the coming bigger simulator SIDAS (Simulated Dodewaard ASsembly). In SIDAS the flow around a fuel assembly of the Dutch Dodewaard reactor will be simulated. An extensive evaluation of the gamma detection system showed that the detection system could be simplified strongly. The simplified system is used to measure the radial and axial distribution of the void fraction in the core of MIDAS for three different operating conditions. Two new measuring methods have been developed and tested. A method to estimate the probability density of the void fraction in time. Due to the nonlinear relation between transmission and void fraction the determined average value of the void fraction in general will contain a systematic error. In this investigation it is shown that this error can be maximally 7.5% in MIDAS and maximally 25% in SIDAS. Therefore a new measuring method has been developed in which the true probability density of the void fraction in time is approximated by two different values of the void fraction, each with a certain probability. With this new method firstly the average void fraction can be determined much more precisely and secondly it often can be used to determine the flow pattern. (orig./WL)
Analysis of Developing Gas/liquid Two-Phase Flows
Energy Technology Data Exchange (ETDEWEB)
Elena A. Tselishcheva; Michael Z. Podowski; Steven P. Antal; Donna Post Guillen; Matthias Beyer; Dirk Lucas
2010-06-01
The goal of this work is to develop a mechanistically based CFD model that can be used to simulate process equipment operating in the churn-turbulent regime. The simulations were performed using a state-of-the-art computational multiphase fluid dynamics code, NPHASE–CMFD [Antal et al,2000]. A complete four-field model, including the continuous liquid field and three dispersed gas fields representing bubbles of different sizes, was first carefully tested for numerical convergence and accuracy, and then used to reproduce the experimental results from the TOPFLOW test facility at Forschungszentrum Dresden-Rossendorf e.V. Institute of Safety Research [Prasser et al,2007]. Good progress has been made in simulating the churn-turbulent flows and comparison the NPHASE-CMFD simulations with TOPFLOW experimental data. The main objective of the paper is to demonstrate capability to predict the evolution of adiabatic churn-turbulent gas/liquid flows. The proposed modelling concept uses transport equations for the continuous liquid field and for dispersed bubble fields [Tselishcheva et al, 2009]. Along with closure laws based on interaction between bubbles and continuous liquid, the effect of height on air density has been included in the model. The figure below presents the developing flow results of the study, namely total void fraction at different axial locations along the TOPFLOW facility test section. The complete model description, as well as results of simulations and validation will be presented in the full paper.
Three dimensional, two phases flow simulation around a cylinder
Ducrocq, Thomas; Ludovic, Cassan
2015-04-01
Fishways are facilities build on the obstacles in river, as dams, to allow the free circulation of migratory fishes. This study focuses on "natural fishpasses" which are high slopes channels composed of blocks rows arranged in staggered. The characterization of the flow structure in this kind of fishways is the aim of the study even if the present first approach is achieved on a single block to validate the model. On one hand, three dimensional simulations are carried with several turbulence closure (k-É, k-ω, RNG-k-ɛ). The VOF model is used to track the free surface. The computation run by the software OpenFOAM which enables to do massively parallel computing. On the other hand, experiments are conducted on a flume in the lab in order to compare the results. The tested configurations are, an emerged cylinder, no slope (i.e 0%) and flows of 10 and 20L/s. The objectif is the comparison of the free surface flow between experiments and simulation results at high Froude number. The results show a good agreement between the experiments and the simulations. The perspective is the simulation of a full fishpasse.
The kinematics of moving flow regime interfaces in two-phase flow
International Nuclear Information System (INIS)
Flow regimes are important in two-phase flow modeling for the selection of two-phase flow models and constitutive relations. This paper deals with the time-dependent location of flow regime transition zones or interfaces, notably the locations of boiling incipience and mixture levels. Regime interfaces in one-dimensional transient two-phase flow are classified and their equations of motion are presented. Kinematic or density jump propagation velocities are contrasted with kinematic wave velocities. An algorithm is presented for the numerical integration of the general equations for mixture level tracking in an Eulerian mesh of finite differences. The algorithm is free of numerical diffusion at the position of sharp discontinuities in void fraction and density. Solutions are presented in graphical form for oscillatory inlet velocity and time-invariant uniform wall heating and for the case of no liquid carryover. The method is useful for modeling thermohydraulic transients in nuclear reactor components under conditions of smallbreak loss of coolant accidents
Parallel Instabilities in Two-Phase Flow in Porous Media
Vassvik, Morten
2014-01-01
Two immiscible fluids flowing in parallel with respect to the interface separating them in a two-dimensional porous medium has been studied using a dynamic network model. Two immiscible fluids, one wetting and the other non-wetting moving in parallel is a complicated process that haven't gotten much attention. It is found that there is a competition between imbibition and drainage displacements at the pore-scale along the front separating the two fluids due to an external force driving b...
Enhanced two phase flow in heat transfer systems
Energy Technology Data Exchange (ETDEWEB)
Tegrotenhuis, Ward E; Humble, Paul H; Lavender, Curt A; Caldwell, Dustin D
2013-12-03
A family of structures and designs for use in devices such as heat exchangers so as to allow for enhanced performance in heat exchangers smaller and lighter weight than other existing devices. These structures provide flow paths for liquid and vapor and are generally open. In some embodiments of the invention, these structures can also provide secondary heat transfer as well. In an evaporate heat exchanger, the inclusion of these structures and devices enhance the heat transfer coefficient of the evaporation phase change process with comparable or lower pressure drop.
Experimental Investigation of Two-Phase Flow in Rock Salt
Energy Technology Data Exchange (ETDEWEB)
Malama, Bwalya; Howard, Clifford L.
2014-07-01
This Test Plan describes procedures for conducting laboratory scale flow tests on intact, damaged, crushed, and consolidated crushed salt to measure the capillary pressure and relative permeability functions. The primary focus of the tests will be on samples of bedded geologic salt from the WIPP underground. However, the tests described herein are directly applicable to domal salt. Samples being tested will be confined by a range of triaxial stress states ranging from atmospheric pressure up to those approximating lithostatic. Initially these tests will be conducted at room temperature, but testing procedures and equipment will be evaluated to determine adaptability to conducting similar tests under elevated temperatures.
Two-phase flow through small branches in a horizontal pipe with stratified flow
International Nuclear Information System (INIS)
This report presents the description and results of experiments designed to determine the mass flow rate and quality through a small break at the bottom, the top or the side of a main pipe with stratified gas-liquid flow. If the interface level is far below (above) the branch, only single-phase gas (liquid) flow enters the branch. For smaller distances the interface is locally deformed because of the pressure decrease due to the fluid acceleration near the branch inlet (Bernoulli effect) and liquid (gas) can be entrained. This report contains photographs illustrating the flow phenomena as well as a general correlation to determine the beginning of entrainment. Results are presented on the branch mass flow rate and quality as a function of a normalized distance between the interface and the branch inlet. A model was developed which enables to predict the branch quality and mass flux. Results from air-water flow through horizontal branches, were extrapolated for steam water flow at high pressure with critical branch mass flux. (orig./HP)
Two-phase flow patterns for flow condensation in small-diameter tubes
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
Two-phase flow patterns have been observed visually to investigate the effects of tube diameter, mass flux and tube inclination on flow condensation in small-diameter tubes. For horizontal or inclined small-diameter tubes, gravity-domination is decreased by shear stress and surface tension on phase change interface, which weakens the stratification of condensate and vapor flow due to the action of gravity perpendicular to flow direction. As decreasing the tube diameter from 5.79 mm to 2.18 mm, the annular or sub-annular flows become prevailing in flow regime map. The existing flow regime maps for macro scale cannot predict the experimental data in the present study.
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...
SIMULATION OF LOW-CONCENTRATION SEDIMENT-LADEN FLOW BASED ON TWO-PHASE FLOW THEORY
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Low concentration sediment-laden flow is usually involved in water conservancy, environmental protection, navigation and so on. In this article, a mathematical model for low-concentration sediment-laden flow was suggested based on the two-phase flow theory, and a solving scheme for the mathematical model in curvilinear grids was worked out. The observed data in the Zhang River in China was used for the verification of the model, and the calculated results of the water level, velocity and river bed deformation are in agreement with the observed ones.
Physical modelling and scale effects of air-water flows on stepped spillways
Institute of Scientific and Technical Information of China (English)
CHANSON Hubert; GONZALEZ Carlos A.
2005-01-01
During the last three decades, the introduction of new construction materials (e.g. RCC (Roller Compacted Concrete),strengthened gabions) has increased the interest for stepped channels and spillways. However stepped chute hydraulics is not simple, because of different flow regimes and importantly because of very-strong interactions between entrained air and turbulence. In this study, new air-water flow measurements were conducted in two large-size stepped chute facilities with two step heights in each facility to study experimental distortion caused by scale effects and the soundness of result extrapolation to prototypes. Experimental data included distributions of air concentration, air-water flow velocity, bubble frequency, bubble chord length and air-water flow turbulence intensity. For a Froude similitude, the results implied that scale effects were observed in both facilities, although the geometric scaling ratio was only Lr=2 in each case. The selection of the criterion for scale effects is a critical issue. For example, major differences (i.e. scale effects) were observed in terms of bubble chord sizes and turbulence levels although little scale effects were seen in terms of void fraction and velocity distributions. Overall the findings emphasize that physical modelling of stepped chutes based upon a Froude similitude is more sensitive to scale effects than classical smooth-invert chute studies, and this is consistent with basic dimensional analysis developed herein.
International Nuclear Information System (INIS)
Highlights: • Analysis of the two-phase flow structure in minichannel. • Innovative use of stereology methods and hi-speed photography. • Application of stereological parameters to flow monitoring. - Abstract: The paper describes a method of two-phase flow structure evaluation for minichannels. The two-phase flow structure appears in gas–liquid mixture. The research is based on innovative approach, with the use of stereology methods. Evaluation of the flow structure is made by image analysis. The images are obtained with high-speed visualization technique. The applied stereological analysis is based on the linear methods – the random secants method and directed secants method. Development of mini heat exchangers requires knowledge of the two-phase flow phenomena. The major result of conducted research is that for each flow structure there is a set of stereological parameters, enabling the quantitative estimation of the two-phase flow. It has been found that the interrelation of stereological parameters, during the change of the flow structure, can be used for controlling the operating conditions. The basic conclusion is that the knowledge about the character of the changes taking place in the flow structure may be used for constant process adjustment for various two-phase gas–liquid or gas–solid systems
Two-phase fluid flow in geometric packing.
Paiva, Aureliano Sancho S; Oliveira, Rafael S; Andrade, Roberto F S
2015-12-13
We investigate how a plug of obstacles inside a two-dimensional channel affects the drainage of high viscous fluid (oil) when the channel is invaded by a less viscous fluid (water). The plug consists of an Apollonian packing with, at most, 17 circles of different sizes, which is intended to model an inhomogeneous porous region. The work aims to quantify the amount of retained oil in the region where the flow is influenced by the packing. The investigation, carried out with the help of the computational fluid dynamics package ANSYS-FLUENT, is based on the integration of the complete set of equations of motion. The study considers the effect of both the injection speed and the number and size of obstacles, which directly affects the porosity of the system. The results indicate a complex dependence in the fraction of retained oil on the velocity and geometric parameters. The regions where the oil remains trapped is very sensitive to the number of circles and their size, which influence in different ways the porosity of the system. Nevertheless, at low values of Reynolds and capillary numbers Re<4 and n(c)≃10(-5), the overall expected result that the volume fraction of oil retained decreases with increasing porosity is recovered. A direct relationship between the injection speed and the fraction of oil is also obtained. PMID:26527816
Development of high pressure two-phase choked flow analysis methodology in complex piping system
International Nuclear Information System (INIS)
Choked flow mechanism, characteristics of two-phase flow sound velocity and compressibility effects on flow through various piping system components are studied to develop analysis methodology for high pressure two-phase choked flow in complex piping system which allows choking flow rate evaluation and piping system design related analysis. Piping flow can be said choked if Mach number is equal to 1 and compressibility effects can be accounted through modified incompressible formula in momentum equation. Based on these findings, overall analysis system is developed to study thermal-hydraulic effects on steady-state piping system flow and future research items are presented. (Author)
Energy Technology Data Exchange (ETDEWEB)
Toelke, J.
2001-07-01
The first part of this work is concerned with the development of methodological foundations for the computer simulation of two-phase flows like gas-liquid-mixtures in complex, three-dimensional structures. The basic numerical approach is the Lattice-Boltzmann scheme which is very suitable for this class of problems. After the approach is verified using standard test cases, the method is applied to complex engineering problems. The most important application is the simulation of the two-phase flow (air/water) in a laboratory-scale biofilm reactor for wastewater treatment. The second part of the work deals with the development of efficient numerical methods for the stationary discrete Boltzmann equations. They are discretized by finite differences on uniform and non-uniform grids and fast solvers are applied to the resulting algebraic system of equations. Also a multigrid approach is developed and examined. For typical problems like boundary-layer and driven cavity flow a considerable gain in computing time is achieved. (orig.)
Two-phase bounded acceleration traffic flow model: Analytical solutions and applications
LEBACQUE, JP
2003-01-01
The present paper describes a two phase traffic flow model. One phase is traffic equilibrium: flow and speed are functions of density, and traffic acceleration is low. The second phase is characterized by constant acceleration. This model extends first order traffic flow models and recaptures the fact that traffic acceleration is bounded. The paper show how to calculate analytical solutions of the two-phase model for dynamic traffic situations, provides a set of calculation rules, and analyze...
Flow visualization study of inverted U-bend two-phase flow
International Nuclear Information System (INIS)
A hot-leg U-bend experiment was performed. The experimental condition simulated the two-phase flow in a B and W primary loop during a small break loss of coolant accident or during some other abnormal transients. The loop design was based on the scaling criteria developed previously and the loop was operated either in a natural circulation mode or in a forced circulation mode using nitrogen gas and water. The two-phase flow regimes at the hot-leg were identified on the basis of visual observation. The phase separation at the top of the inverted U-bend was observed at low gas flow rate. The void fractions were measured using differential pressure transducers and compared with the prediction from the drift-flux model. The natural circulation flow interruption occurred in two different modes, namely, quasi-periodic and semi-permanent modes. This phenomenon is mainly dependent on the difference in the hydrostatic head in the riser and downcomer, and the flow regime at hot-leg. Besides this flow interruption phenomenon, dynamic flow instabilities of considerable amplitudes have been observed
Liquid mean velocity and turbulence in a horizontal air-water bubbly flow
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
The liquid phase turbulent structure of an air-water bubbly horizontal flow in a circular pipe has been investigated experimentally. Three-dimensional measurements were implemented with two "X" type probes oriented in different planes, and local liquid-phase velocities and turbulent stresses were simultaneously obtained. Systematic measurements were conducted covering a range of local void fraction from 0 to 11.7%. The important experiment results and parametric trends are summarized and discussed.
Single and two-phase flow fluid dynamics in parallel helical coils
De Salve, M.; Orio, M.; Panella, B.
2014-04-01
The design of helical coiled steam generators requires the knowledge of the single and two-phase fluid dynamics. The present work reports the results of an experimental campaign on single-phase and two phase pressure drops and void fraction in three parallel helicoidal pipes, in which the total water flow rate is splitted by means of a branch. With this test configuration the distribution of the water flow rate in the helicoidal pipes and the phenomena of the instability of the two-phase flow have been experimentally investigated.
Development of One Dimensional Hyperbolic Coupled Solver for Two-Phase Flows
Energy Technology Data Exchange (ETDEWEB)
Kim, Eoi Jin; Kim, Jong Tae; Jeong, Jae June
2008-08-15
The purpose of this study is a code development for one dimensional two-phase two-fluid flows. In this study, the computations of two-phase flow were performed by using the Roe scheme which is one of the upwind schemes. The upwind scheme is widely used in the computational fluid dynamics because it can capture discontinuities clearly such as a shock. And this scheme is applicable to multi-phase flows by the extension methods which were developed by Toumi, Stadtke, etc. In this study, the extended Roe upwind scheme by Toumi for two-phase flow was implemented in the one-dimensional code. The scheme was applied to a shock tube problem and a water faucet problem. This numerical method seems efficient for non oscillating solutions of two phase flow problems, and also capable for capturing discontinuities.
Critical Regimes of Two-Phase Flows with a Polydisperse Solid Phase
Barsky, Eugene
2010-01-01
This book brings to light peculiarities of the formation of critical regimes of two-phase flows with a polydisperse solid phase. A definition of entropy is formulated on the basis of statistical analysis of these peculiarities. The physical meaning of entropy and its correlation with other parameters determining two-phase flows are clearly defined. The interrelations and main differences between this entropy and the thermodynamic one are revealed. The main regularities of two-phase flows both in critical and in other regimes are established using the notion of entropy. This parameter serves as a basis for a deeper insight into the physics of the process and for the development of exhaustive techniques of mass exchange estimation in such flows. The book is intended for graduate and postgraduate students of engineering studying two-phase flows, and to scientists and engineers engaged in specific problems of such fields as chemical technology, mineral dressing, modern ceramics, microelectronics, pharmacology, po...
Numerical simulation of multi-dimensional two-phase flow based on flux vector splitting
Energy Technology Data Exchange (ETDEWEB)
Staedtke, H.; Franchello, G.; Worth, B. [Joint Research Centre - Ispra Establishment (Italy)
1995-09-01
This paper describes a new approach to the numerical simulation of transient, multidimensional two-phase flow. The development is based on a fully hyperbolic two-fluid model of two-phase flow using separated conservation equations for the two phases. Features of the new model include the existence of real eigenvalues, and a complete set of independent eigenvectors which can be expressed algebraically in terms of the major dependent flow parameters. This facilitates the application of numerical techniques specifically developed for high speed single-phase gas flows which combine signal propagation along characteristic lines with the conservation property with respect to mass, momentum and energy. Advantages of the new model for the numerical simulation of one- and two- dimensional two-phase flow are discussed.
Turbulence, aeration and bubble features of air-water flows over macro- and intermediate roughness
Directory of Open Access Journals (Sweden)
Stefano PAGLIARA
2011-06-01
Full Text Available Free surface flows in macro- and intermediate roughness conditions have a high aeration potential in which the flow characteristics vary with slopes and discharges. The underlying phenomenon of two phase flow characteristics in the macro and intermediate roughness conditions were analyzed in a setup assembled at the PITLAB center of the University of Pisa, Italy. Crushed angular rocks and hemispherical boulders were used to intensify the roughness nature of the bed. Flow discharges per unit width ranging between 0.03 m2/s and 0.09 m2/s and slopes between 0.26 and 0.46 were tested over different arrangements of rough bed. Analyses were mainly concentrated in the inner flow region which constitutes both bubbly and intermediate flow region. The findings revealed that two phase flow properties over rough bed were very much affected by the different rough bed arrangement. Turbulence features of two phase flows over rough beds were compared with that of the stepped chute data under similar flow conditions. Overall the results highlighted the flow features in the inner layers of the two phase flow.
Branch Quality Control of Gas-Liquid Two-Phase Flow Using a Novel T-Junction Type Distributor
Institute of Scientific and Technical Information of China (English)
FaChun Liang; Jing Chen; JinLong Wang; Hao Yu
2014-01-01
In order to eliminate mal-distribution and ensure the side arm to produce desirable gas quality a special distributor is proposed. The experimental distributor mainly consists of a straight through section, a gas extraction line, a liquid extraction line and a side arm branch. A gas orifice and a liquid orifice are mounted at the gas and liquid extraction line respectively to control the outlet gas quality. The diameter of the liquid orifice was set to 2�50 mm and three gas orifices with different size ( dG = 2�65, 5�00, 10�00 mm) were tested. The experiments were carried out at an air-water two-phase flow loop. The gas superficial velocity ranged from 6�0 to 20�0 m/s and the liquid superficial velocity was in the range of 0�02-0�18 m/s. Flow patterns such as wave flow, slug flow and annular flow were observed. The gas quality of the side arm branch was found mainly determined by the flow area ratio of the gas orifice to the liquid orifice and independent of gas and liquid superficial velocity, flow patterns and extraction flux.
Some asymmetric thermohydraulic behaviors of liquid metal-gas two-phase MHD flows
International Nuclear Information System (INIS)
In this paper magnetohydrodynamic effect on liquid-metal two-phase flow and heat transfer are summarized based on the measurements made by the present author in NaK-nitrogen flow in a vertical round tube in the presence of a transverse magnetic field. This study covered a wide range of two-phase flow patterns from bubbly flow to annular-dispersed flow, including flow pattern observation, measurements of phase distributions, liquid film behavior, and heat transfer coefficient. Particular emphases are directed towards describing asymmetric thermohydraulic structures induced by the applied magnetic field
International Nuclear Information System (INIS)
It is a classical method by using analysis of differential pressure fluctuation signal to identify two-phase flow pattern. The method which uses trait peak in the frequency-domain will result confusion between bubble flow and intermittent flow due to the influence of gas speed. Considering the spatial geometric significance of two-phase slow patterns and using the differential pressure gauge as a sensor, the Strouhal number 'Sr' is taken as the basis for distinguishing flow patterns. Using Strouhal number 'Sr' to identify flow pattern has clear physical meaning. The experimental results using the spatial analytical technique to measure the flow pattern are also given
The effects of surface tension on flooding in counter-current two-phase flow in an inclined tube
Energy Technology Data Exchange (ETDEWEB)
Deendarlianto [Department of Mechanical and Industrial Engineering, Faculty of Engineering, Gadjah Mada University, Jalan Grafika No.2 Yogyakarta 55281 (Indonesia); Forschungszentrum Dresden-Rossendorf e.V., Institute of Safety Research, P.O. Box 510 119, D-01314 Dresden (Germany); Ousaka, Akiharu [Department of Mechanical Engineering, The University of Tokushima, 2-1 Minami Josanjima, Tokushima 770-8506 (Japan); Indarto [Department of Mechanical and Industrial Engineering, Faculty of Engineering, Gadjah Mada University, Jalan Grafika No.2 Yogyakarta 55281 (Indonesia); Kariyasaki, Akira [Department of Chemical Engineering, Fukuoka University, 8-19-1, Jyonan-ku, Fukuoka 814-0180 (Japan); Lucas, Dirk; Vallee, Christophe [Forschungszentrum Dresden-Rossendorf e.V., Institute of Safety Research, P.O. Box 510 119, D-01314 Dresden (Germany); Vierow, Karen; Hogan, Kevin [Department of Nuclear Engineering Texas A and M University, 129 Zachry Engineering Center, 3133 TAMU College Station, TX 77843-3133 (United States)
2010-10-15
The purpose of the present study is to investigate the effects of surface tension on flooding phenomena in counter-current two-phase flow in an inclined tube. Previous studies by other researchers have shown that surface tension has a stabilizing effect on the falling liquid film under certain conditions and a destabilizing or unclear trend under other conditions. Experimental results are reported herein for air-water systems in which a surfactant has been added to vary the liquid surface tension without altering other liquid properties. The flooding section is a tube of 16 mm in inner diameter and 1.1 m length, inclined at 30-60 from horizontal. The flooding mechanisms were observed by using two high-speed video cameras and by measuring the time variation of liquid hold-up along the test tube. The results show that effects of surface tension are significant. The gas velocity needed to induce flooding is lower for a lower surface tension. There was no upward motion of the air-water interfacial waves upon flooding occurrence, even for lower a surface tension. Observations on the liquid film behavior after flooding occurred suggest that the entrainment of liquid droplets plays an important role in the upward transport of liquid. Finally, an empirical correlation for flooding velocities is proposed that includes functional dependencies on surface tension and tube inclination. (author)
International Nuclear Information System (INIS)
Ultrasonic methods have the advantage, compared to other water layer thickness measurement techniques, of applicability to large volume objects, since most radiation techniques are limited by the thickness of the pipe and plate walls. The ultrasonic experiment was performed to do an analysis for cooling performance in a complete test channel by the investigation of the two phase flow that develops in an inclined gap with heating from the top. This ultrasonic technique for measuring water layer thickness measurement employ the higher relative acoustic impedance of air with respect to that of liquids. By this method it is possible to determine both liquid water distance, void fraction in a gas-liquid two-phase flow. Instantaneous measurement of the water layer thickness is useful in understanding heat and mass transfer characteristics in a two-phase separated flow. An ultrasonic measurement technique for determining water layer thickness in the wavy and slug flow regime of horizontal tube flow has been produced
Two-phase flow operational maps for multi-microchannel evaporators
International Nuclear Information System (INIS)
Highlights: • New operational maps for several different micro-evaporators are presented. • Inlet micro-orifices prevented flow instability, back flow, and flow maldistribution. • Eight different operating regimes were distinguished. • The flashing two-phase flow without back flow operating regime is preferred. -- Abstract: The current paper presents new operational maps for several different multi-microchannel evaporators, with and without any inlet restrictions (micro-orifices), for the two-phase flow of refrigerants R245fa, R236fa, and R1234ze(E). The test fluids flowed in 67 parallel channels, each having a cross-sectional area of 100 × 100 μm2. In order to emulate the power dissipated by active components in a 3D CMOS CPU chip, two aluminium microheaters were sputtered onto the back-side of the test section providing a 0.5 cm2 each. Without any inlet restrictions in the micro-evaporator, significant parallel channel flow instabilities, vapor back flow, and flow maldistribution led to high-amplitude and high-frequency temperature and pressure oscillations. Such undesired phenomena were then prevented by placing restrictions at the inlet of each channel. High-speed flow visualization distinguished eight different operating regimes of the two-phase flow depending on the tested operating conditions. Therefore, the preferred operating regimes can be easily traced. In particular, flashing two-phase flow without back flow appeared to be the best operating regime without any flow and temperature instabilities
Mixed Model for Silt-Laden Solid-Liquid Two-Phase Flows
Institute of Scientific and Technical Information of China (English)
唐学林; 徐宇; 吴玉林
2003-01-01
The kinetic theory of molecular gases was used to derive the governing equations for dense solid-liquid two-phase flows from a microscopic flow characteristics viewpoint by multiplying the Boltzmann equation for each phase by property parameters and integrating over the velocity space. The particle collision term was derived from microscopic terms by comparison with dilute two-phase flow but with consideration of the collisions between particles for dense two-phase flow conditions and by assuming that the particle-phase velocity distribution obeys the Maxwell equations. Appropriate terms from the dilute two-phase governing equations were combined with the dense particle collision term to develop the governing equations for dense solid-liquid turbulent flows. The SIMPLEC algorithm and a staggered grid system were used to solve the discretized two-phase governing equations with a Reynolds averaged turbulence model. Dense solid-liquid turbulent two-phase flows were simulated for flow in a duct. The simulation results agree well with experimental data.
Numerical study for two phase flow in the near nozzle region of turbine combustors
International Nuclear Information System (INIS)
In the present study flow conditions in the near nozzle region of the combustion chamber have been investigated. There exists two-phase flow in this region. The overall performance and pollutant formation in the combustion chamber have been investigated. There exists two-phase flow in this region. The overall performance and pollutant formation in the combustion zone largely depends on the spray field in the near nozzle region the studies are conducted to determined the effects of multi jets on the flow pattern in the near nozzle region The phase doppler particle analyzer (PDPA) has been used to measure the velocities and sizes of the droplets. The flow field of two-phase liquid drop-air jets is formed from three injectors arranged in t line. Furthermore the two-phase flow field has been analyzed numerically also. The numerical analysis consists of two computational models, namely (i) 3 non-evaporating two-phase jets, (II) 3 evaporating two phase jets. The Eulerian-Eulerian approach in incorporated in both the numerical models. Since the flow is turbulent, a two-equation model (k-Epsilon) is implemented in the numerical analysis. Numerical solution of the conservation equation is obtained using PHOENICS computer code. Boundary conditions are provided from the experimental measurements. Numerical domain for the two models of the analysis starts at some distance (about 10 diameters of the injector orifice) where the atomization process is complete and droplet size and velocity could be measured experimentally. (author)
Non-local two phase flow momentum transport in S BWR
International Nuclear Information System (INIS)
The non-local momentum transport equations derived in this work contain new terms related with non-local transport effects due to accumulation, convection, diffusion and transport properties for two-phase flow. For instance, they can be applied in the boundary between a two-phase flow and a solid phase, or in the boundary of the transition region of two-phase flows where the local volume averaging equations fail. The S BWR was considered to study the non-local effects on the two-phase flow thermal-hydraulic core performance in steady-state, and the results were compared with the classical local averaging volume conservation equations. (Author)
Modified Diffusion Flux Model for Analysis of Turbulent Gas-Particle Two-Phase Flows
Institute of Scientific and Technical Information of China (English)
YANG Ruichang; ZHOU Weiduo; FUKUDA Kenji; JU Zejian; SHANG Zhi
2005-01-01
A modified diffusion flux model (DFM) was developed to analyze turbulent multi-dimensional gas-particle two-phase flows. In the model, the solid particles move in a modified acceleration field, , which includes the effects of various forces on the particles as if all the forces have the same effect on the particles as the gravity. The accelerations due to various forces are then taken into account in the calculation of the diffusion velocities of the solid particles in the gas-particle two-phase flow. The DFM was used to numerically simulate the gas-solid two-phase flow behind a vertical backward-facing step. The numerical simulation compared well with experimental data and numerical results using both the k-ε-Ap and k-ε-kp two-fluid models available in the literature. The comparison shows that the modified diffusion flux model correctly simulates the turbulent gas-particle two-phase flow.
Non-local two phase flow momentum transport in S BWR
Energy Technology Data Exchange (ETDEWEB)
Espinosa P, G.; Salinas M, L.; Vazquez R, A., E-mail: gepe@xanum.uam.mx [Universidad Autonoma Metropolitana, Unidad Iztapalapa, Area de Ingenieria en Recursos Energeticos, Apdo. Postal 55-535, 09340 Ciudad de Mexico (Mexico)
2015-09-15
The non-local momentum transport equations derived in this work contain new terms related with non-local transport effects due to accumulation, convection, diffusion and transport properties for two-phase flow. For instance, they can be applied in the boundary between a two-phase flow and a solid phase, or in the boundary of the transition region of two-phase flows where the local volume averaging equations fail. The S BWR was considered to study the non-local effects on the two-phase flow thermal-hydraulic core performance in steady-state, and the results were compared with the classical local averaging volume conservation equations. (Author)
Programs and calculations of heat transfer in two-phase flow
International Nuclear Information System (INIS)
Problems of physical simulation of hydrodynamics and heat exchange processes in two-phase flows of coolants in nuclear reactors are discussed. Programs RELAP-4 and TRAC, used for the analysis of reactor safety, are described
International Nuclear Information System (INIS)
In order to evaluate an influence of earthquake acceleration to the boiling two-phase flow behavior in nuclear reactors, numerical simulations were performed under the simulated earthquake condition. The two-phase flow analysis code, ACE-3D, was modified as the influence of the earth quake acceleration can calculate. To check out if the modification is adequate, a series of calculations were carried out and the following summaries were derived; 1) the void fraction in the fuel bundle receives the influence of the earthquake, 2) the liquid-phase in the two-phase flow moves in the same direction as the direction of oscillation due to the inputted earthquake acceleration, and 3) due to the density difference in comparison with the liquid phase, the gas phase of that moves in the direction opposite to the oscillating direction. This study enabled visualized evaluation of the boiling two-phase flow behavior in the nuclear reactors at the earthquake condition. (author)
Numerical simulation of the two-phase flows in a hydraulic coupling by solving VOF model
Luo, Y.; Zuo, Z. G.; Liu, S. H.; Fan, H. G.; Zhuge, W. L.
2013-12-01
The flow in a partially filled hydraulic coupling is essentially a gas-liquid two-phase flow, in which the distribution of two phases has significant influence on its characteristics. The interfaces between the air and the liquid, and the circulating flows inside the hydraulic coupling can be simulated by solving the VOF two-phase model. In this paper, PISO algorithm and RNG k-ɛ turbulence model were employed to simulate the phase distribution and the flow field in a hydraulic coupling with 80% liquid fill. The results indicate that the flow forms a circulating movement on the torus section with decreasing speed ratio. In the pump impeller, the air phase mostly accumulates on the suction side of the blades, while liquid on the pressure side; in turbine runner, air locates in the middle of the flow passage. Flow separations appear near the blades and the enclosing boundaries of the hydraulic coupling.
Numerical simulation of the two-phase flows in a hydraulic coupling by solving VOF model
International Nuclear Information System (INIS)
The flow in a partially filled hydraulic coupling is essentially a gas-liquid two-phase flow, in which the distribution of two phases has significant influence on its characteristics. The interfaces between the air and the liquid, and the circulating flows inside the hydraulic coupling can be simulated by solving the VOF two-phase model. In this paper, PISO algorithm and RNG k–ε turbulence model were employed to simulate the phase distribution and the flow field in a hydraulic coupling with 80% liquid fill. The results indicate that the flow forms a circulating movement on the torus section with decreasing speed ratio. In the pump impeller, the air phase mostly accumulates on the suction side of the blades, while liquid on the pressure side; in turbine runner, air locates in the middle of the flow passage. Flow separations appear near the blades and the enclosing boundaries of the hydraulic coupling
Personal view of educating two-phase flow and human resource development as a nuclear engineer
International Nuclear Information System (INIS)
As an engineer who has devoted himself in the nuclear industry for almost three decades, the author gave a personal view on educating two-phase flow and developing human resources. An expected role of universities in on-going discussions of collaboration among industry-government-academia is introduced. Reformation of two-phase flow education is discussed from two extreme viewpoints, the basic structure of physics and the practical system analysis. (author)
Two-phase flow and heat transfer symposium-workshop. Proceedings of condensed papers
International Nuclear Information System (INIS)
Two-phase flow applications are found in a wide range of engineering systems, such as boiling water reactors, conventional steam boilers, evaporators of refrigeration systems, and evaporative and condensive heat exchangers in chemical and petroleum industries. Over the past two decades, two-phase flow instability problems have been a challenge to many investigators. Such instabilities could induce boiling crisis, disturb control systems and/or cause mechanical damage. It is important to be able to predict the conditions under which a two-phase flow system will perform without instability. Therefore, the understanding of two-phase flow phenomena is extremely important for the design, control and performance prediction of such systems. Because of the recent energy crisis, many other two-phase flow problems have also become important. Some of them are the modeling of the loss of coolant accident in pressurized water nuclear reactors, scaling up of fluidized bed reactors for converting coal to clean gaseous and liquid fuels, and design of heat exchangers for liquified natural gas, and design of heat exchangers for liquified natural gas. There is a need to provide researchers and engineers in this field with an opportunity to exchange their experience and ideas in order to assess the state-of-the-art of two-phase flow and heat transfer studies, and to establish a basis for identification of areas of future research and application. This symposium provides the latest information on the status of two-phase flow and heat transfer research, development and applications. It also establish a rational basis for identification of areas of two-phase flow and heat transfer for further research and application
Numerical simulation of two-phase gas-liquid flows in inclined and vertical pipelines
Loilier, P.
2006-01-01
The present thesis describes the advances made in modelling two-phase flows in inclined pipes using a transient one-dimensional approach. The research is a developement of an existing numerical methodology, capable of simulating stratified and slugging two-phase flows in horizontal or inclined single pipes. The aim of the present work is to extend the capabilities of the approach in order (i) to account for the effect of the pipe topography in the numerical solution of the two-...
Two-phase flow modeling of cirtical heat flux for subcooled and low quality flow boiling
International Nuclear Information System (INIS)
A two-phase flow model developed to predict a critical heat flux (CHF) in the subcooled and low quality flow boiling. The CHF formula was derived from the local conservation equations of mass, energy and momentum, together with appropriate constitutive relations. The limiting transverse interchange of mass flux crossing the interface of the bubbly layer and core region is represented, in the local momentum conservation equation, by taking account of the convective shear effects due to the drag force on the wallattaced bubbles. Comparison between the predictions by the proposed model and the experimental CHF data from several sources shows good agrrement over a wide range of flow conditions ( 2≤P≤20 MPa, 1≤D≤37.5 mm, 0.035 ≤L≤6 m, 450 ≤G≤7500 kg/m2s, αexit≤0.8). Also the model correctly accounts for the effects of flow variables
Two-phase flow void fraction measurement using gamma ray attenuation technique
International Nuclear Information System (INIS)
The present work deals with experimental void fraction measurements in two-phase water-nitrogen flow, by using a gamma ray attenuation technique. Several upward two-phase flow regimes in a vertical tube were simulated. The water flow was varied from 0.13 to 0.44 m3/h while the nitrogen flow was varied between 0.01 and 0.1 m3/h. The mean volumetric void fraction was determined based on the measured linear void fraction for each flow condition. The results were compared with other authors data and showed a good agreement. (author)
Simulation of throttle flow with two phase and single phase homogenous equilibrium model
Koukouvinis, P.; Gavaises, M.
2015-12-01
This paper aims to compare the results of two commonly used methods for the simulation of cavitating flows; one is the two phase mass transfer approach and the other is a homogenous equilibrium model. Both methodologies are compared in a shock tube and a throttle flow, which resembles the constrictions in Diesel injector passages. The mass transfer rate in the two phase model plays the fundamental role in affecting how close to equilibrium the model is; by increasing the mass transfer the two phase model comes close to the homogenous equilibrium model.
Measurement of local two-phase flow parameters of nanofluids using conductivity double-sensor probe
Park Yu sun; Chang Soon
2011-01-01
Abstract A two-phase flow experiment using air and water-based γ-Al2O3 nanofluid was conducted to observe the basic hydraulic phenomenon of nanofluids. The local two-phase flow parameters were measured with a conductivity double-sensor two-phase void meter. The void fraction, interfacial velocity, interfacial area concentration, and mean bubble diameter were evaluated, and all of those results using the nanofluid were compared with the corresponding results for pure water. The void fract...
Dynamic behavior of pipes conveying gas–liquid two-phase flow
International Nuclear Information System (INIS)
Highlights: • Dynamic behavior of pipes conveying gas–liquid two-phase flow was analyzed. • The generalized integral transform technique (GITT) was applied. • Excellent convergence behavior and long-time stability were shown. • Effects of volumetric quality and volumetric flow rate on dynamic behavior were studied. • Normalized volumetric-flow-rate stability envelope of dynamic system was determined. - Abstract: In this paper, the dynamic behavior of pipes conveying gas–liquid two-phase flow was analytically and numerically investigated on the basis of the generalized integral transform technique (GITT). The use of the GITT approach in the analysis of the transverse vibration equation lead to a coupled system of second order differential equations in the dimensionless temporal variable. The Mathematica's built-in function, NDSolve, was employed to numerically solve the resulting transformed ODE system. The characteristics of gas–liquid two-phase flow were represented by a slip-ratio factor model that was devised and used for similar problems. Good convergence behavior of the proposed eigenfunction expansions is demonstrated for calculating the transverse displacement at various points of pipes conveying air–water two-phase flow. Parametric studies were performed to analyze the effects of the volumetric gas fraction and the volumetric flow rate on the dynamic behavior of pipes conveying air–water two-phase flow. Besides, the normalized volumetric-flow-rate stability envelope for the dynamic system was obtained
DSMC simulation of two-phase plume flow with UV radiation
Energy Technology Data Exchange (ETDEWEB)
Li, Jie; Liu, Ying; Wang, Ning; Jin, Ling [College of Aerospace Science and Engineering, National University of Defense Technology, Changsha, Hunan, 410073 (China)
2014-12-09
Rarefied gas-particle two-phase plume in which the phase of particles is liquid or solid flows from a solid propellant rocket of hypersonic vehicle flying at high altitudes, the aluminum oxide particulates not only impact the rarefied gas flow properties, but also make a great difference to plume radiation signature, so the radiation prediction of the rarefied gas-particle two-phase plume flow is very important for space target detection of hypersonic vehicles. Accordingly, this project aims to study the rarefied gas-particle two-phase flow and ultraviolet radiation (UV) characteristics. Considering a two-way interphase coupling of momentum and energy, the direct simulation Monte Carlo (DSMC) method is developed for particle phase change and the particle flow, including particulate collision, coalescence as well as separation, and a Monte Carlo ray trace model is implemented for the particulate UV radiation. A program for the numerical simulation of the gas-particle two-phase flow and radiation in which the gas flow nonequilibrium is strong is implemented as well. Ultraviolet radiation characteristics of the particle phase is studied based on the calculation of the flow field coupled with the radiation calculation, the radiation model for different size particles is analyzed, focusing on the effects of particle emission, absorption, scattering as well as the searchlight emission of the nozzle. A new approach may be proposed to describe the rarefied gas-particle two-phase plume flow and radiation transfer characteristics in this project.
Dynamic behavior of pipes conveying gas–liquid two-phase flow
Energy Technology Data Exchange (ETDEWEB)
An, Chen, E-mail: anchen@cup.edu.cn [Offshore Oil/Gas Research Center, China University of Petroleum-Beijing, Beijing 102249 (China); Su, Jian, E-mail: sujian@lasme.coppe.ufrj.br [Nuclear Engineering Program, COPPE, Universidade Federal do Rio de Janeiro, CP 68509, Rio de Janeiro 21941-972 (Brazil)
2015-10-15
Highlights: • Dynamic behavior of pipes conveying gas–liquid two-phase flow was analyzed. • The generalized integral transform technique (GITT) was applied. • Excellent convergence behavior and long-time stability were shown. • Effects of volumetric quality and volumetric flow rate on dynamic behavior were studied. • Normalized volumetric-flow-rate stability envelope of dynamic system was determined. - Abstract: In this paper, the dynamic behavior of pipes conveying gas–liquid two-phase flow was analytically and numerically investigated on the basis of the generalized integral transform technique (GITT). The use of the GITT approach in the analysis of the transverse vibration equation lead to a coupled system of second order differential equations in the dimensionless temporal variable. The Mathematica's built-in function, NDSolve, was employed to numerically solve the resulting transformed ODE system. The characteristics of gas–liquid two-phase flow were represented by a slip-ratio factor model that was devised and used for similar problems. Good convergence behavior of the proposed eigenfunction expansions is demonstrated for calculating the transverse displacement at various points of pipes conveying air–water two-phase flow. Parametric studies were performed to analyze the effects of the volumetric gas fraction and the volumetric flow rate on the dynamic behavior of pipes conveying air–water two-phase flow. Besides, the normalized volumetric-flow-rate stability envelope for the dynamic system was obtained.
A criterion for the onset of slugging in horizontal stratified air-water countercurrent flow
Energy Technology Data Exchange (ETDEWEB)
Chun, Moon-Hyun; Lee, Byung-Ryung; Kim, Yang-Seok [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)] [and others
1995-09-01
This paper presents an experimental and theoretical investigation of wave height and transition criterion from wavy to slug flow in horizontal air-water countercurrent stratified flow conditions. A theoretical formula for the wave height in a stratified wavy flow regime has been developed using the concept of total energy balance over a wave crest to consider the shear stress acting on the interface of two fluids. From the limiting condition of the formula for the wave height, a necessary criterion for transition from a stratified wavy flow to a slug flow has been derived. A series of experiments have been conducted changing the non-dimensional water depth and the flow rates of air in a horizontal pipe and a duct. Comparisons between the measured data and the predictions of the present theory show that the agreement is within {plus_minus}8%.
Analytical solution of laminar-laminar stratified two-phase flows with curved interfaces
Energy Technology Data Exchange (ETDEWEB)
Brauner, N.; Rovinsky, J.; Maron, D.M. [Tel-Aviv Univ. (Israel)
1995-09-01
The present study represents a complete analytical solution for laminar two-phase flows with curved interfaces. The solution of the Navier-Stokes equations for the two-phases in bipolar coordinates provides the `flow monograms` describe the relation between the interface curvature and the insitu flow geometry when given the phases flow rates and viscosity ratios. Energy considerations are employed to construct the `interface monograms`, whereby the characteristic interfacial curvature is determined in terms of the phases insitu holdup, pipe diameter, surface tension, fluids/wall adhesion and gravitation. The two monograms are then combined to construct the system `operational monogram`. The `operational monogram` enables the determination of the interface configuration, the local flow characteristics, such as velocity profiles, wall and interfacial shear stresses distribution as well as the integral characteristics of the two-phase flow: phases insitu holdup and pressure drop.
Analytical solution of laminar-laminar stratified two-phase flows with curved interfaces
International Nuclear Information System (INIS)
The present study represents a complete analytical solution for laminar two-phase flows with curved interfaces. The solution of the Navier-Stokes equations for the two-phases in bipolar coordinates provides the 'flow monograms' describe the relation between the interface curvature and the insitu flow geometry when given the phases flow rates and viscosity ratios. Energy considerations are employed to construct the 'interface monograms', whereby the characteristic interfacial curvature is determined in terms of the phases insitu holdup, pipe diameter, surface tension, fluids/wall adhesion and gravitation. The two monograms are then combined to construct the system 'operational monogram'. The 'operational monogram' enables the determination of the interface configuration, the local flow characteristics, such as velocity profiles, wall and interfacial shear stresses distribution as well as the integral characteristics of the two-phase flow: phases insitu holdup and pressure drop
Simulation of two-phase flow for compressible and nearly incompressible regimes
International Nuclear Information System (INIS)
A new finite element formulation for compressible and nearly incompressible problems is applied to the analysis of two-phase flows.The method allows the analysis of nearly incompressible flows without resorting to the incompressible fluid model. Thus, the fluid equation of state is not discarded from the model. This feature is of foremost importance for the approach adopted in this work, where the thermodynamic behaviour of the mixture is constructed from the thermodynamic behaviour of the individual phases. Numerical examples of two-phase steam-water mixtures are presented. The models employed to characterise turbulence and the two-phase mixture are rather simple. Nevertheless, the examples presented show good qualitative behaviour and serve to indicate further developments towards the computational simulation of two-phase flows. (author)
Single and two-phase flow pressure drop for CANFLEX bundle
Energy Technology Data Exchange (ETDEWEB)
Park, Joo Hwan; Jun, Ji Su; Suk, Ho Chun [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of); Dimmick, G. R.; Bullock, D. E. [Atomic Energy of Canada Limited, Ontario (Canada)
1998-12-31
Friction factor and two-phase flow frictional multiplier for a CANFLEX bundle are newly developed and presented in this paper. CANFLEX as a 43-element fuel bundle has been developed jointly by AECL/KAERI to provide greater operational flexibility for CANDU reactor operators and designers. Friction factor and two-phase flow frictional multiplier have been developed by using the experimental data of pressure drops obtained from two series of Freon-134a (R-134a) CHF tests with a string of simulated CANFLEX bundles in a single phase and a two-phase flow conditions. The friction factor for a CANFLEX bundle is found to be about 20% higher than that of Blasius for a smooth circular pipe. The pressure drop predicted by using the new correlations of friction factor and two-phase frictional multiplier are well agreed with the experimental pressure drop data of CANFLEX bundle within {+-} 5% error. 11 refs., 5 figs. (Author)
Institute of Scientific and Technical Information of China (English)
Gao Zhong-Ke; Hu Li-Dan; Jin Ning-De
2013-01-01
We generate a directed weighted complex network by a method based on Markov transition probability to represent an experimental two-phase flow.We first systematically carry out gas-liquid two-phase flow experiments for measuring the time series of flow signals.Then we construct directed weighted complex networks from various time series in terms of a network generation method based on Markov transition probability.We find that the generated network inherits the main features of the time series in the network structure.In particular,the networks from time series with different dynamics exhibit distinct topological properties.Finally,we construct two-phase flow directed weighted networks from experimental signals and associate the dynamic behavior of gas-liquid two-phase flow with the topological statistics of the generated networks.The results suggest that the topological statistics of two-phase flow networks allow quantitative characterization of the dynamic flow behavior in the transitions among different gas-liquid flow patterns.
Gas-liquid two-phase flow across a bank of micropillars
Krishnamurthy, Santosh; Peles, Yoav
2007-04-01
Adiabatic nitrogen-water two-phase flow across a bank of staggered circular micropillars, 100μm long with a diameter of 100μm and a pitch-to-diameter ratio of 1.5, was investigated experimentally for Reynolds number ranging from 5 to 50. Flow patterns, void fraction, and pressure drop were obtained, discussed, and compared to large scale as well as microchannel results. Two-phase flow patterns were determined by flow visualization, and a flow map was constructed as a function of gas and liquid superficial velocities. Significant deviations from conventional scale systems, with respect to flow patterns and trend lines, were observed. A unique flow pattern, driven by surface tension, was observed and termed bridge flow. The applicability of conventional scale models to predict the void fraction and two-phase frictional pressure drop was also assessed. Comparison with a conventional scale void fraction model revealed good agreement, but was found to be in a physically wrong form. Thus, a modified physically based model for void fraction was developed. A two-phase frictional multiplier was found to be a strong function of mass flux, unlike in previous microchannel studies. It was observed that models from conventional scale systems did not adequately predict the two-phase frictional multiplier at the microscale, thus, a modified model accounting for mass flux was developed.
International Nuclear Information System (INIS)
We generate a directed weighted complex network by a method based on Markov transition probability to represent an experimental two-phase flow. We first systematically carry out gas—liquid two-phase flow experiments for measuring the time series of flow signals. Then we construct directed weighted complex networks from various time series in terms of a network generation method based on Markov transition probability. We find that the generated network inherits the main features of the time series in the network structure. In particular, the networks from time series with different dynamics exhibit distinct topological properties. Finally, we construct two-phase flow directed weighted networks from experimental signals and associate the dynamic behavior of gas-liquid two-phase flow with the topological statistics of the generated networks. The results suggest that the topological statistics of two-phase flow networks allow quantitative characterization of the dynamic flow behavior in the transitions among different gas—liquid flow patterns. (general)
Frequency response of forced circulation boiling two-phase flow to inlet flow modulation
International Nuclear Information System (INIS)
This paper presents theoretical analysis and experimental data on the dynamic behavior of two-phase flow in a vertical boiling channel. Continuous, energy and momentum equations are linearized on the basis of small perturbation, and flow to exit void fraction and pressure drop transfer functions are obtained. Experimental frequency response functions are measured with statistical method using Freon-113 as the working fluid over a frequency range of 0.02 to 3 Hz. The data cover mass flux of 450 to 1800 kg/m2s, inlet subcooling of 2 to 300C and various heat flux levels. Influence of flow rate, inlet subcooling and heat flux on frequency response and comparison between experimental and theoretical results are described. (author)
Forced convection flow boiling and two-phase flow phenomena in a microchannel
Na, Yun Whan
2008-07-01
The present study was performed to numerically analyze the evaporation phenomena through the liquid-vapor interface and to investigate bubble dynamics and heat transfer behavior during forced convective flow boiling in a microchannel. Flow instabilities of two-phase flow boiling in a microchannel were studied as well. The main objective of this research is to investigate the fundamental mechanisms of two-phase flow boiling in a microchannel and provide predictive tools to design thermal management systems, for example, microchannel heat sinks. The numerical results obtained from this study were qualitatively and quantitatively compared with experimental results in the open literature. Physical and mathematical models, accounting for evaporating phenomena through the liquid-vapor interface in a microchannel at constant heat flux and constant wall temperature, have been developed, respectively. The heat transfer mechanism is affected by the dominant heat conduction through the thin liquid film and vaporization at the liquid-vapor interface. The thickness of the liquid film and the pressure of the liquid and vapor phases were simultaneously solved by the governing differential equations. The developed semi-analytical evaporation model that takes into account of the interfacial phenomena and surface tension effects was used to obtain solutions numerically using the fourth-order Runge-Kutta method. The effects of heat flux 19 and wall temperature on the liquid film were evaluated. The obtained pressure drops in a microchannel were qualitatively consistent with the experimental results of Qu and Mudawar (2004). Forced convective flow boiling in a single microchannel with different channel heights was studied through a numerical simulation to investigate bubble dynamics, flow patterns, and heat transfer. The momentum and energy equations were solved using the finite volume method while the liquid-vapor interface of a bubble is captured using the VOF (Volume of Fluid
A combined experimental-numerical approach for two-phase flow boiling in a minichannel
Hożejowska Sylwia; Grabowski Mirosław
2016-01-01
The paper addresses experimental and numerical modeling of the two-phase flows in an asymmetrically heated horizontal minichannel. Experimental measurements concerned flows of evaporating ethanol in a minichannel with rectangular cross section 1.8mm × 2 mm. In order to observe the flows, measuring system was designed and built. The system measured and recorded basic heat and flow parameters of flowing fluid, and the temperature of external surface of the heater by using infrared camera and re...
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
International Nuclear Information System (INIS)
In the development of advanced light water reactors, thermohydraulic phenomena are versatile in comparison with the present concepts. The new features are the passive safety systems, where energy transport takes place by natural circulation instead of forced flow. For cooling of the molten core, new concepts have been created including external vessel cooling and core catchers. In all new concepts, two-phase flow circulation patterns exist. The calculational tools should be capable of analysing multidimensional circulation created by the gravity field instead of the forced pump circulation. In spite of extensive model development for the one-dimensional Eulerian solutions for two-phase flow, multidimensional calculation is still a great challenge. The momentum transfer terms and turbulence models for the two-phase flow still require large efforts, although the turbulence models for the single phase flow are versatile and rather advanced at present. Two-phase models exist already now in several CFD codes. In VTT, most experience has been achieved with Fluent-4 Fluent-5 and at last Fluent-6 codes. Fluent-4 and Fluent-6 have the Euler-Euler solution for two-phase conservation equations, which is required for the flow conditions, where the volume fraction of both liquid and gas phases is important and the flow circulation is largely created by the gravity field. VTT is participating in several experimental projects on ALWRs, where multidimensional two-phase circulation is essential. This paper presents three examples of the use of CFD codes for analyses of ALWRs. The first example is connected with SWR 1000 reactor form Framatome ANP. Framatome ANP is performing experiments for evaluation of external cooling of the Reactor Pressure Vessel (RPV) of SWR 1000. The experiments are aimed for determining the limits to avoid critical heat fluxes (CHFs). The experimental programme is carried out in three steps. The first part, the air-water experiments, has been analysed at
Experimental study on two-phase flow in horizontal tube bundle using SF6-water
International Nuclear Information System (INIS)
It is important to know the flow structure in industrial products that use gas-liquid two-phase flow. The gas-liquid density ratio is one of the most important parameters in the simulation of flow structure. In this study, a vertical upward two-phase flow in a horizontal tube bundle, which occurs frequently on the shell side of heat exchangers such as PWR steam generators, was measured. This test facility can simulate the behaviors of water-vapor two-phase flow at high pressures (5.6 MPaabs) by using sulfur hexafluoride (SF6) gas for the gas phase and water for liquid phase at ambient temperatures and low pressures. These results were compared with the values generated by previous empirical equations to verify soundness of this facility and measurement method. (author)
Computational Two-phase Flow Analysis for Subcooled Boiling in Annulus Channel
International Nuclear Information System (INIS)
The interfacial area concentration (IAC) is one of the most important parameters with respect to the interfacial transfer terms between two phases. In recent researches, the IAC transport equation has been developed for adiabatic bubbly flow or nucleate boiling flow. That can make it possible to analyze the two phase flow dynamically, instead of the conventional static approach for modeling IAC. This study is a part of the development of computational fluid dynamics (CFD) code for investigating the boiling flow with two-fluid model and IAC transport equation. Multi-dimensional approach was utilized in order to overcome the limitation in one dimensional analysis of two-phase flow. As the step for checking the robustness of the developed code, the problem for subcooled boiling was benchmarked
Analysis of forced convective transient boiling by homogeneous model of two-phase flow
International Nuclear Information System (INIS)
Transient forced convective boiling is of practical importance in relation to the accident analysis of nuclear reactor etc. For large length-to-diameter ratio, the transient boiling characteristics are predicted by transient two-phase flow calculations. Based on homogeneous model of two-phase flow, the transient forced convective boiling for power and flow transients are analysed. Analytical expressions of various parameters of transient two-phase flow have been obtained for several simple cases of power and flow transients. Based on these results, heat flux, velocity and time at transient CHF condition are predicted analytically for step and exponential power increases, and step, exponential and linear velocity decreases. The effects of various parameters on heat flux, velocity and time at transient CHF condition have been clarified. Numerical approach combined with analytical method is proposed for more complicated cases. Solution method for pressure transient are also described. (author)
International Nuclear Information System (INIS)
In this study, fluctuating force acting on pipe turning section due to two-phase flow is considered. A novel tool to predict upward two-phase flow induced force fluctuations is developed. In order to eliminate tool's dependencies on experimental measurement input, creation of artificial void signal (AVS) was considered by carefully analyzing area-averaged void fraction properties, including probability density and frequency spectra from 36 flow conditions. Generated AVS was successfully coupled with the predictive tool, and as a result, it is capable of predicting fluctuating force magnitude and dominant force frequency from the inlet superficial velocities alone. The tool is applicable for small inner diameter pipe (<∼10 cm) consist of 0-90 degree turning element, and covers two-phase flow regime up to churn-turbulent flow. (author)
Flow regime identification and analysis in adiabatic upward two-phase flow in an annulus geometry
International Nuclear Information System (INIS)
The main objective of this work is to identify and analyze two-phase flow regimes in adiabatic upward flow conditions in an concentric annulus geometry with an inner diameter of 19.1 mm and an outer diameter of 38.1 mm, at three axial locations (z/DH: 51.5, 148.8, 229.9). In this regard, both Global Flow Regimes (GFRs) and Local Flow Regimes (LFRs) have been identified. In both cases, neural networks techniques have been used to obtain objective identification results. However, the flow regime indicator will be different depending on the type of flow regime: the cumulative probability distribution function (CPDF) of the area averaged void fraction obtained by impedance meters in the case of GFRs and the CPDF of the bubble chord length measured by a four-sensor conductivity probe in the case of LFRs. The GFRs maps have been compared with those obtained in previous research works and flow regime transitions existing correlations. The LFRs have been identified in five radial locations. The LFRs combinations maps have been compared with the GFRs and those combinations obtained in round pipes. (author)
Flow regime identification using chaotic characteristics of two-phase flow
International Nuclear Information System (INIS)
Chaotic nature of two-phase flow is investigated for its dependency upon the flow regime by constructing the pseudo phase space with the time sequential impedance signals of the void fraction. In order to construct the pseudo phase space, the autocorrelation function (ACF) and the average mutual information (AMI) for the delayed time, and the false nearest neighborhood (FNN) for the dimensions as the embedding parameters were employed here. It was found that the delayed time and embedded dimension are highly dependent upon the flow regime. To visualize the trajectory of signals in the phase space, a density map is produced by the projection of the trajectory into the two-dimensional plane which is correspondent with the two-dimensional probability distribution functions (2D-PDF). Since the density map of 2D-PDF showed clear distinction of flow patterns, we developed a method to identify flow regime by applying simple classification rules to the density map. The proposed method successfully identifies the flow regimes of the experimental data of impedance signals for the void fraction produced flow regime map for the vertical channel with diameter of 25.4 and 50.8 mm
Consistent flow regime map and friction factors for two-phase flow
International Nuclear Information System (INIS)
Many of the existing constitutive models found in large computer codes for two-phase transient flow contain errors and discontinuities. This paper presents a model which can eliminate these difficulties for steam-water flow in vertical pipes. The same model defines the flow regime and the geometry used for the evaluation of both the interphase and wall friction factors. A continuity of models traverses the void fraction domain from small bubbles recombining to larger bubbles, large bubbles elongating into slugs, and long slugs becoming infinite to produce annular flow. The bubble slug transition occurs at a void fraction of Pi/6 and the slug annular transition occurs at Pi/4. Cocurrent and countercurrent flow can be represented with a new flow regime map because the phasic velocity difference and void fraction are used as coordinates. The Moody model is used to obtain all friction factors and substructure sizes determine the roughness. Representative results are obtained from this model to show the reasonableness of the calculated friction forces for a range of flow regimes and phase velocities
Application of non-equilibrium thermodynamics to two-phase flows with a change of phase
International Nuclear Information System (INIS)
In this report we use the methods of non-equilibrium thermodynamics in two-phase flows. This paper follows a prior one in which we have studied the conservation laws and derived the general equations of two-phase flow. In the first part the basic ideas of thermodynamics of irreversible systems are given. We follow the classical point of view. The second part is concerned with the derivation of a closed set of equations for the two phase elementary volume model. In this model we assume that the elementary volume contains two phases and that it is possible to define a volumetric local concentration. To obtain the entropy balance we can choose either the reversibility of the barycentric motion or the reversibility of each phase. We adopt the last assumption and our derivation is the same as this of I.Prigogine and P. Mazur about the hydrodynamics of liquid helium. The scope of this work is not to find a general solution to the problems of two phase flows but to obtain a new set of equations which may be used to explain some characteristic phenomena of two-phase flow such as wave propagation or critical states. (author)
IMPROVED SUBGRID SCALE MODEL FOR DENSE TURBULENT SOLID-LIQUID TWO-PHASE FLOWS
Institute of Scientific and Technical Information of China (English)
TANG Xuelin; QIAN Zhongdong; WU Yulin
2004-01-01
The dense solid-phase governing equations for two-phase flows are obtained by using the kinetic theory of gas molecules. Assuming that the solid-phase velocity distributions obey the Maxwell equations, the collision term for particles under dense two-phase flow conditions is also derived.In comparison with the governing equations of a dilute two-phase flow, the solid-particle's governing equations are developed for a dense turbulent solid-liquid flow by adopting some relevant terms from the dilute two-phase governing equations. Based on Cauchy-Helmholtz theorem and Smagorinsky model,a second-order dynamic sub-grid-scale (SGS) model, in which the sub-grid-scale stress is a function of both the strain-rate tensor and the rotation-rate tensor, is proposed to model the two-phase governing equations by applying dimension analyses. Applying the SIMPLEC algorithm and staggering grid system to the two-phase discretized governing equations and employing the slip boundary conditions on the walls, the velocity and pressure fields, and the volumetric concentration are calculated. The simulation results are in a fairly good agreement with experimental data in two operating cases in a conduit with a rectangular cross-section and these comparisons imply that these models are practical.
Measurement of local two-phase flow parameters of nanofluids using conductivity double-sensor probe
Park, Yu Sun; Chang, Soon Heung
2011-12-01
A two-phase flow experiment using air and water-based γ-Al2O3 nanofluid was conducted to observe the basic hydraulic phenomenon of nanofluids. The local two-phase flow parameters were measured with a conductivity double-sensor two-phase void meter. The void fraction, interfacial velocity, interfacial area concentration, and mean bubble diameter were evaluated, and all of those results using the nanofluid were compared with the corresponding results for pure water. The void fraction distribution was flattened in the nanofluid case more than it was in the pure water case. The higher interfacial area concentration resulted in a smaller mean bubble diameter in the case of the nanofluid. This was the first attempt to measure the local two-phase flow parameters of nanofluids using a conductivity double-sensor two-phase void meter. Throughout this experimental study, the differences in the internal two-phase flow structure of the nanofluid were identified. In addition, the heat transfer enhancement of the nanofluid can be resulted from the increase of the interfacial area concentration which means the available area of the heat and mass transfer.
Measurement of local two-phase flow parameters of nanofluids using conductivity double-sensor probe
Directory of Open Access Journals (Sweden)
Park Yu sun
2011-01-01
Full Text Available Abstract A two-phase flow experiment using air and water-based γ-Al2O3 nanofluid was conducted to observe the basic hydraulic phenomenon of nanofluids. The local two-phase flow parameters were measured with a conductivity double-sensor two-phase void meter. The void fraction, interfacial velocity, interfacial area concentration, and mean bubble diameter were evaluated, and all of those results using the nanofluid were compared with the corresponding results for pure water. The void fraction distribution was flattened in the nanofluid case more than it was in the pure water case. The higher interfacial area concentration resulted in a smaller mean bubble diameter in the case of the nanofluid. This was the first attempt to measure the local two-phase flow parameters of nanofluids using a conductivity double-sensor two-phase void meter. Throughout this experimental study, the differences in the internal two-phase flow structure of the nanofluid were identified. In addition, the heat transfer enhancement of the nanofluid can be resulted from the increase of the interfacial area concentration which means the available area of the heat and mass transfer.
Numerical investigation of the mechanism of two-phase flow instability in parallel narrow channels
Energy Technology Data Exchange (ETDEWEB)
Hu, Lian [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China); Chen, Deqi, E-mail: chendeqi@cqu.edu.cn [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China); CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Huang, Yanping, E-mail: hyanping007@163.com [CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Yuan, Dewen; Wang, Yanling [CNNC Key Laboratory on Nuclear Reactor Thermal Hydraulics Technology, Nuclear Power Institute of China, Chengdu 610041 (China); Pan, Liangming [Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Chongqing University (China)
2015-06-15
Highlights: • A mathematical model is proposed to predict the two-phase flow instability. • The mathematical model predicted result agrees well with the experimental result. • Oscillation characteristics of the two-phase flow instability is discussed in detail. - Abstract: In this paper, the mechanism of two-phase flow instability in parallel narrow channels is studied theoretically, and the characteristic of the flow instability is discussed in detail. Due to the significant confining effect of the narrow channel on the vapor–liquid interface, the two-phase flow resistance in the narrow channel is probably different from that in conventional channel. Therefore, the vapor confined number (N{sub conf}), defined by the size of narrow channel and bubble detachment diameter, is considered in the “Chisholm B model” to investigate the two-phase flow pressure drop. The flow instability boundaries are plotted in parameter plane with phase-change-number (N{sub pch}) and subcooling-number (N{sub sub}) under different working conditions. It is found that the predicted result agrees well with the experimental result. According to the predicted result, the oscillation behaviors near the flow instability boundary indicate that the Supercritical Hopf bifurcation appears in high sub-cooled region and the Subcritical Hopf bifurcation appears in low sub-cooled region. Also, a detailed analysis about the effects of key parameters on the characteristic of two-phase flow instability and the flow instability boundary is proposed, including the effects of inlet subcooling, heating power, void distribution parameter and drift velocity.
Quasi 3-D measurements of turbulence structure in horizontal air-water bubbly flow
International Nuclear Information System (INIS)
Quasi 3-D measurements of the turbulence structure of air-water bubbly flow in a horizontal tube with 35 mm i.d. are undertaken with two TSI 'X''-type hot-film probes. The turbulent fluctuations, uf,vf,wf, in axial, radial and circumferential directions, respectively, and Reynolds tresses -UV-bar and -u w-bar are obtained. It is found that in the lower portion of the tube, the profiles of turbulent fluctuation and Reynolds tress resemble those of single phase flow; whereas in the upper portion of he tube, where the bubble population is high, the turbulence, especially the circumferential fluctuation wf, is substantially enhanced, and the radial turbulence assumes highest value in the radial position -0.7< r/R<0.5. The magnitudes of Reynolds stresses -u w-bar and -UV-bar in our measurements are in the same level except in the lower portion of the tube where -u w-bar assumes a value close to zero as is the case in single phase flow and vertical air-water bubbly flow
Multi-needle capacitance probe for non-conductive two-phase flows
Monrós-Andreu, G.; Martinez-Cuenca, R.; Torró, S.; Escrig, J.; Hewakandamby, B.; Chiva, S.
2016-07-01
Despite its variable degree of application, intrusive instrumentation is the most accurate way to obtain local information in a two-phase flow system, especially local interfacial velocity and local interfacial area parameters. In this way, multi-needle probes, based on conductivity or optical principles, have been extensively used in the past few decades by many researchers in two-phase flow investigations. Moreover, the signal processing methods used to obtain the time-averaged two-phase flow parameters in this type of sensor have been thoroughly discussed and validated by many experiments. The objective of the present study is to develop a miniaturized multi-needle probe, based on capacitance measurements applicable to a wide range of non-conductive two-phase flows and, thus, to extend the applicability of multi-needle sensor whilst also maintaining a signal processing methodology provided in the literature for conductivity probes. Results from the experiments performed assess the applicability of the proposed sensor measurement principle and signal processing method for the bubbly flow regime. These results also provide an insight into the sensor application for more complex two-phase flow regimes.
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
Study of two-phase flow thermal-hydraulics during bottom reflooding of nuclear reactor cores
International Nuclear Information System (INIS)
Based on experimental observation of two-phase flow void fraction behavior during reflooding, and empirical correlation is proposed for fitting reflooding two-phase void fraction distribution. The empirical void fraction distribution is used to correct Hsu's transition boiling correlation for the effect of local void fraction. The UCLA Multi-Channel Reflood Model for analysis of reflooding thermal hydraulics is reviewed. Simple methods proposed for treatment of two-phase phenomena and core multi-dimensional effects are shown to be adequate. The model predictions are shown to be adequate. The model predictions are shown to compare well with experiment
Energy Technology Data Exchange (ETDEWEB)
Shim, Hee-Sang; Kim, Kyung Mo; Hur, Do Haeng [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Kim, Seung Hyun; Kim, Ji Hyun [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)
2015-05-15
Since the occurrence of a Surry-2 pipe rupture accident, a lot of effort has been made to prevent FAC of carbon steel piping. Some of the chemicals were suggested as a corrosion inhibitor. A platinum decoration was applied as another prevention strategy of carbon steel thinning. The severe FAC-damaged carbon steel pipings were replaced by tolerant materials such as SA335 Gr.P22. However, some components such as the piping materials between moisture separator and turbine have still suffered from the FAC degradation. This work provides a coating method to prevent the FAC degradation of the SA106 Gr.B, which is a piping material between moisture separator and high-pressure turbine, under two-phase flow. We suggested the coating materials to prevent FAC of SA106Gr.B under two-phase water-vapor flow. The FAC resistance of SA106Gr.B was improved with 5 times by electroless-deposited Ni-P protective layer. Other coating materials also enhanced the tolerance up to 5 times for the FAC in a condition of 150 .deg. C and 3.8 bar at 9.5 compared to non-coated SA106Gr.B.
Fast X-ray imaging of two-phase flows: Application to cavitating flows
International Nuclear Information System (INIS)
A promising method based on fast X-ray imaging has been developed to investigate the dynamics and the structure of complex two-phase flows. It has been applied in this work on cavitating flows created inside a Venturi-type test section and helped therefore to better understand flows inside cavitation pockets. Seeding particles were injected into the flow to trace the liquid phase. Thanks to the characteristics of the beam provided by the APS synchrotron (Advance Photon Source, USA), high definition X-ray images of the flow containing simultaneously information for both liquid and vapour were obtained. Velocity fields of both phases were thus calculated using image cross-correlation algorithms. Local volume fractions of vapour have also been obtained using local intensities of the images. Beforehand however, image processing is required to separate phases for velocity measurements. Validation methods of all applied treatments were developed, they allowed to characterise the measurement accuracy. This experimental technique helped us to have more insight into the dynamic of cavitating flows and especially demonstrates the presence of significant slip velocities between phases. (author)
Two-phase flow measurements using a photochromic dye activation technique
International Nuclear Information System (INIS)
A novel flow visualization method called photochromic dye activation (PDA) technique has been used to investigate flow structures and mechanisms in various two-phase flow regimes. This non-intrusive flow visualization technique utilizes light activation of a photochromic dye material dissolved in a clear liquid and is a molecular tagging technique, requiring no seed particles. It has been used to yield both quantitative and qualitative flow data in the liquid phase in annular flow, slug flow and stratified-wavy flows. (author)
Features concerning capillary pressure and the effect on two-phase and three-phase flow
2008-01-01
The effect of capillary pressure related to immiscible WAG (Water Alternate Gas) is studied by use of a numerical simulator. The capillary pressure is found to have a significant effect on the pressure gradient and the total oil production both in two-phase and three-phase flow situations. When the capillary pressure is included in the simulation the total oil production is considerably lower than when the capillary pressure is neglected. Experimentally measured two-phase capil...
Hydraulic Behaviour of He II in Stratified Counter-Current Two-Phase Flow
Rousset, B; Jäger, B; Van Weelderen, R; Weisend, J G
1998-01-01
Future large devices using superconducting magnets or RF cavities (e.g. LHC or TESLA) need He II two-phase flow for cooling. The research carried out into counter-current superfluid two-phase flow was the continuation of work on co-current flow and benefited from all the knowledge acquired both experimentally and theoretically. Experiments were conducted on two different pipe diameters (40 and 65 m m I.D. tube) for slopes ranging between 0 and 2%, and for temperatures ranging between 1.8 and 2 K. This paper introduces the theoretical model, describes the tests, and provides a critical review of the results obtained in He II counter current two-phase flow.
A New Appraoch to Modeling Immiscible Two-phase Flow in Porous Media
DEFF Research Database (Denmark)
Yuan, Hao; Shapiro, Alexander; Stenby, Erling Halfdan
based on Rapoport-Leas Equation and Film Model, a systematic literature review of the LBM CFD methods including the particle-based LBM and porous-medium-based LBM for multiphase flow, and the sample calculation of particle-based LBM in a random porous medium. Finally we come to present a new approach to......In this work we present a systematic literature review regarding the macroscopic approaches to modeling immiscible two-phase flow in porous media, the formulation process of the incorporate PDE based on Film Model(viscous coupling), the calculation of saturation profile around the transition zone...... modeling immiscible two-phase flow in porous media. The suggested approach to immiscible two-phase flow in porous media describes the dispersed mesoscopic fluids’ interfaces which are highly influenced by the injected interfacial energy and the local interfacial energy capacity. It reveals a new...
Two-phase flow transients and the stability of once-through steam generators
International Nuclear Information System (INIS)
The study of the behaviour of once-through steam-generators and in particular of their stability (occurence of self-sustained oscillations for example) requires the calculation under transient conditions of once-through two phase flows. Starting from the general conservation principles, and to allow the review of the necessary assumptions and models, the ideal description of the development and use of a practical mathematical model is made. It is thus possible to introduce rationally the constitutive laws which are necessary for the two phase flow description, as also the concepts of superabondant constitutive law and of coherence of the mathematical model (in practice of the computer program). The conservation principles impose compatibility constraints to the various elementary models (i.e. to the constitutive equations) which have to be put in the computer program. With the assumption of one dimensional flow, six partial differential equations appear to be necessary for the transient description of two-phase flows
The questions of liquid metal two-phase flow modelling in the FBR core channels
International Nuclear Information System (INIS)
The two-fluid model representation for calculations of two-phase flow characteristics in the FBR fuel pin bundles with liquid metal cooling is presented and analysed. Two conservation equations systems of the mass, momentum and energy have been written for each phase. Components accounted the mass-, momentum- and heat transfer throughout the interface occur in the macro-field equations after the averaging procedure realisation. The pattern map and correlations for two-fluid model in vertical liquid metal flows are presented. The description of processes interphase mass- and heat exchange and interphase friction is determined by the two-phase flow regime. The opportunity of the liquid metal two-phase flow regime definition is analysed. (author)
Hierarchy of two-phase flow models for autonomous control of cryogenic loading operation
Luchinskiy, Dmitry G.; Ponizovskaya-Devine, Ekaterina; Hafiychuk, Vasyl; Kashani, Ali; Khasin, Michael; Timucin, Dogan; Sass, Jared; Perotti, Jose; Brown, Barbara
2015-12-01
We report on the development of a hierarchy of models of cryogenic two-phase flow motivated by NASA plans to develop and maturate technology of cryogenic propellant loading on the ground and in space. The solution of this problem requires models that are fast and accurate enough to identify flow conditions, detect faults, and to propose optimal recovery strategy. The hierarchy of models described in this presentation is ranging from homogeneous moving- front approximation to separated non-equilibrium two-phase cryogenic flow. We compare model predictions with experimental data and discuss possible application of these models to on-line integrated health management and control of cryogenic loading operation.
Two-group interfacial area transport in vertical air-water flow -II. Model evaluation
International Nuclear Information System (INIS)
In a companion paper, mechanistic models of major fluid particle interaction phenomena involving two bubble groups have been proposed. The prediction of interfacial area concentration evolution using the one-dimensional two-group transport equation and evaluation with experimental results are performed in the paper. These evaluations are based on solid databases for a 2-inch air-water loop with sufficient information on the axial development and the radial distribution of the local parameters. Model evaluation strategies are systematically analyzed. The predictions for the interfacial area concentration evolution demonstrate satisfactory accuracy. The proposed model predicts a smooth transition across the bubbly-to-slug flow regime boundary and demonstrates mechanisms for the generation and development of the cap/slug bubble group. The two-group interfacial area transport equation covers a wide range from bubbly, slug, to churn turbulent flow regimes for adiabatic air-water upward flow in moderate diameter pipes. The generality of the interfacial transport model is also discussed
Pressure drop modeling and comparisons with experiments for single- and two-phase sodium flow
International Nuclear Information System (INIS)
Highlights: → We present further validation of the TRACE code to sodium two-phase flow modeling. → We qualify correlations for pressure-loss modeling in tube and bundle geometries. → The validation is done on the basis of experiments from the Ispra Research Center. → We give recommendations for the modeling of pressure drop in sodium two-phase flow. - Abstract: The thermal-hydraulic code TRACE is currently being extended at the Paul Scherrer Institute (PSI) for enabling the study of sodium-cooled fast reactor (SFR) core behavior during transients in which boiling is anticipated. An accurate prediction of pressure losses across fuel bundles - under both single- and two-phase sodium flow conditions - is necessary in this context. The present paper addresses the assessment, and implementation in TRACE, of appropriate friction factor models for round tubes and wire-wrapped fuel bundles, as well as local pressure drop models for grid spacers. Validity of the implemented correlations has been confirmed via the analysis of a range of experiments conducted earlier at the Joint Research Centre, Ispra. The measurements utilized are those of single- and two-phase pressure loss for sodium flow in tubes and 12-pin bundles, as a function of the inlet velocity under quasi steady-state conditions. The reported study thus represents an important further development step for the reliable simulation of two-phase sodium flow in TRACE.
Application of x-ray CT scanner to two-phase flow measurement
International Nuclear Information System (INIS)
The recent advance of the thermo-hydraulic analysis codes for LWRs is conspicuous, and regarding the momentum, heat and mass transfer between steam/water two phases, more detailed information has been obtained. For this purpose, many researches have been carried out for visually grasping the aspect of two-phase flow. Also in the field of two-phase flow study, the X-ray CT scanners which can visualize the state of flow without disturbing it and also can quantify it can be regarded as very attractive measuring instrument. A number of the examples of the application of X-ray CT scanners to two-phase flow measurement have been published. In this report, the principle of the measurement using X-ray CT scanners is briefly explained, and the application of X-ray CT scanners to the two-phase flow measurement in a horizontal pipe and in a fuel assembly of a nuclear reactor is outlined. For the experiment, an industrial X-ray CT scanner TOSCANER 3200 made by Toshiba Corp. was used mainly for the measurement of the distribution of void fraction. It may be considered that this technology of void fraction measurement has been established. In the case of the measurement at higher temperature and pressure, more studies are necessary. (Kako, I.)
A Derivation of the Nonlocal Volume-Averaged Equations for Two-Phase Flow Transport
Directory of Open Access Journals (Sweden)
Gilberto Espinosa-Paredes
2012-01-01
Full Text Available In this paper a detailed derivation of the general transport equations for two-phase systems using a method based on nonlocal volume averaging is presented. The local volume averaging equations are commonly applied in nuclear reactor system for optimal design and safe operation. Unfortunately, these equations are limited to length-scale restriction and according with the theory of the averaging volume method, these fail in transition of the flow patterns and boundaries between two-phase flow and solid, which produce rapid changes in the physical properties and void fraction. The non-local volume averaging equations derived in this work contain new terms related with non-local transport effects due to accumulation, convection diffusion and transport properties for two-phase flow; for instance, they can be applied in the boundary between a two-phase flow and a solid phase, or in the boundary of the transition region of two-phase flows where the local volume averaging equations fail.
Characteristics of horizontal two-phase helium flow at low mass velocities
International Nuclear Information System (INIS)
Two-phase helium flows experimental and theoretical exploration results, including data on flow regimes, pressure drop, and void fraction, are presented. The circular, annular, and slot channels are examined. All the considered data are for low mass velocities and near-adiabatic conditions
Two-phase flow in membrane processes: A technology with a future
Wibisono, Y.; Cornelissen, E.R.; Kemperman, A.J.B.; Meer, van der W.G.J.; Nijmeijer, K.
2014-01-01
Worldwide, the application of a (gas/liquid) two-phase flow in membrane processes has received ample scientific deliberation because of its potential to reduce concentration polarization and membrane fouling, and therefore enhance membrane flux. Gas/liquid flows are now used to promote turbulence an
Experimental study on average frictional pressure drop of gas-liquid two-phase pulsatile flow
International Nuclear Information System (INIS)
The gas-liquid two-phase pulsatile flow was studied in a rectangular channel with 40 mm × 3 mm cross section under different periods, flow rate amplitudes and its mean values (mean Re1<10000, mean Reg<800). There was difference between the single phase pulsatile flow and the gas-liquid two-phase pulsatile flow, and pulsation period and amplitude were not sensitive for the average frictional pressure drop. There was no significant difference on the values and distribution between the calculation deviations in pulsatile flow and the calculation deviations in steady flow by using different empirical formulas. Almost all of the relative deviations were less than 20%, and the relative deviations of Mishima-Hibiki method and Lee-Lee method were less than 10%. The results show that the empirical formulas for the two-phase steady flow frictional pressure drop are also suitable for the calculation of the average value of two-phase pulsatile flow. (authors)
International Nuclear Information System (INIS)
1 - Description of test facility: The test facility consists of a vertical flow channel with different internals. The test section was principally made of transparent acrylic material to allow visual observations. One fuel bundle top area structure of the Soviet-type pressurized water reactors VVER-1000 and VVER-440 in full scale was the principal test section. In order to get experimental data on the effects of different parameters on the CCFL behaviour, various configurations of the principal test sections were studied. Plate 1 corresponds to the perforated upper tie plate in full scale of the reactor VVER-1000 and plate 12 to the upper tie plate in full scale of the reactor VVER-440. 2 - Description of test: The procedure of the model tests consisted of establishing the air inlet flow rate and then increasing the water flow rate so that the given liquid head above the perforated plate, or above the fuel rod bundle when the flow channel provided only with the bundle was reached. After the stationary conditions maintained for a prolonged period, the injected water and air flows, and the average height of the mixture level above the perforated plate were registered. All reported air and water flow rates are average values at each test point. The distance of the water inlet from the perforated plate was 2000 mm, and the water level in the water collection chamber was kept constant. Small-size plates were tested. Also the effect of the unheated fuel rod bundle and the size of the free flow channel on the CCFL behaviour were studied
Impedance void-meter and neural networks for vertical two-phase flows
International Nuclear Information System (INIS)
Most two-phase flow measurements, including void fraction measurements, depend on correct flow regime identification. There are two steps towards successful identification of flow regimes: one is to develop a non-intrusive instrument to demonstrate area-averaged void fluctuations, the other to develop a non-linear mapping approach to perform objective identification of flow regimes. A non-intrusive impedance void-meter provides input signals to a neural mapping approach used to identify flow regimes. After training, both supervised and self-organizing neural network learning paradigms performed flow regime identification successfully. The methodology presented holds considerable promise for multiphase flow diagnostic and measurement applications. (author)
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
In this paper, the air-water vapor-water system is taken as an example, and the formula of constantpressure specific heat during non-equilibrium phase change process in the two-phase flow system is deduced using the theory of two-phase flow and thermophysics. The constant-pressure specific heat of non-equilibrium phase change process is calculated with the corresponding numerical model, and the numerical results are compared to those of the equilibrium phase change process. It is shown that in evaporation process, the variational rate of the non-equilibrium specific heat increases with increasing initial fluid temperature and particle mass fraction. The smaller particle radius is, the faster the variational rate is. Meanwhile, the constant-pressure specific heat of equilibrium process is higher than that of the non-equilibrium process all the time.
International Nuclear Information System (INIS)
Stationary experiments with a convergent nozzle are performed in order to validate advanced two-phase computer codes, which find application in the blowdown-phase of a loss-of-coolant accident (LOCA). The steam/water flow presents a broad variety of initial conditions: The pressure varies between 2 and 13 MPa, the void fraction between 0 (subcooled) and about 80%, a great number of subcritical as well as critical experiments with different flow pattern is investigated. Additional air/water experiments serve for the separation of phase transition effects. The transient acceleration of the fluid in the LOCA-case is simulated by a local acceleration in the experiments. The layout of the nozzle and the applied measurement technique allow for a separate testing of physical models and the determination of empirical model parameters, respectively: In the four codes DUESE, DRIX-20, RELAP4/MOD6 and STRUYA the models - if they exist - for slip between the phases, thermodynamic non-equilibrium, pipe friction and critical mass flow rate are validated and criticised in comparison with the experimental data, and the corresponding model parameters are determined. The parameters essentially are a function of the void fraction. (orig.)
A New Method for Ultrasound Detection of Interfacial Position in Gas-Liquid Two-Phase Flow
Directory of Open Access Journals (Sweden)
Fábio Rizental Coutinho
2014-05-01
Full Text Available Ultrasonic measurement techniques for velocity estimation are currently widely used in fluid flow studies and applications. An accurate determination of interfacial position in gas-liquid two-phase flows is still an open problem. The quality of this information directly reflects on the accuracy of void fraction measurement, and it provides a means of discriminating velocity information of both phases. The algorithm known as Velocity Matched Spectrum (VM Spectrum is a velocity estimator that stands out from other methods by returning a spectrum of velocities for each interrogated volume sample. Interface detection of free-rising bubbles in quiescent liquid presents some difficulties for interface detection due to abrupt changes in interface inclination. In this work a method based on velocity spectrum curve shape is used to generate a spatial-temporal mapping, which, after spatial filtering, yields an accurate contour of the air-water interface. It is shown that the proposed technique yields a RMS error between 1.71 and 3.39 and a probability of detection failure and false detection between 0.89% and 11.9% in determining the spatial-temporal gas-liquid interface position in the flow of free rising bubbles in stagnant liquid. This result is valid for both free path and with transducer emitting through a metallic plate or a Plexiglas pipe.
Two-phase wall function for modeling of turbulent boundary layer in subcooled boiling flow
International Nuclear Information System (INIS)
Full text of publication follows: The heat transfer and phase-change mechanisms in the subcooled flow boiling are governed mainly by local multidimensional mechanisms near the heated wall, where bubbles are generated. The structure of such 'wall boiling flow' is inherently non-homogeneous and is further influenced by the two-phase flow turbulence, phase-change effects in the bulk, interfacial forces and bubble interactions (collisions, coalescence, break-up). In this work the effect of two-phase flow turbulence on the development of subcooled boiling flow is considered. Recently, the modeling of two-phase flow turbulence has been extensively investigated. A notable progress has been made towards deriving reliable models for description of turbulent behaviour of continuous (liquid) and dispersed phase (bubbles) in the bulk flow. However, there is a lack of investigation considering the modeling of two-phase flow boundary layer. In most Eulerian two-fluid models standard single-phase wall functions are used for description of turbulent boundary layer of continuous phase. That might be a good approximation at adiabatic flows, but their use for boundary layers with high concentration of dispersed phase is questionable. In this work, the turbulent boundary layer near the heated wall will be modeled with the so-called 'two-phase' wall function, which is based on the assumption of additional turbulence due to bubble-induced stirring in the boundary layer. In the two-phase turbulent boundary layer the wall function coefficients strongly depend on the void fraction. Moreover, in the turbulent boundary layer with nucleating bubbles, the bubble size variation also has a significant impact on the liquid phase. As a basis, the wall function of Troshko and Hassan (2001), developed for adiabatic bubbly flows will be used. The simulations will be performed by a general-purpose CFD code CFX-4.4 using additional models provided by authors. The results will be compared to the boiling
Two-phase flow and transport in the air cathode of proton exchange membrane fuel cells
Wang, Z. H.; Wang, C. Y.; Chen, K. S.
Two-phase flow and transport of reactants and products in the air cathode of proton exchange membrane (PEM) fuel cells is studied analytically and numerically. Single- and two-phase regimes of water distribution and transport are classified by a threshold current density corresponding to first appearance of liquid water at the membrane/cathode interface. When the cell operates above the threshold current density, liquid water appears and a two-phase zone forms within the porous cathode. A two-phase, multicomponent mixture model in conjunction with a finite-volume-based computational fluid dynamics (CFD) technique is applied to simulate the cathode operation in this regime. The model is able to handle the situation where a single-phase region co-exists with a two-phase zone in the air cathode. For the first time, the polarization curve as well as water and oxygen concentration distributions encompassing both single- and two-phase regimes of the air cathode are presented. Capillary action is found to be the dominant mechanism for water transport inside the two-phase zone of the hydrophilic structure. The liquid water saturation within the cathode is predicted to reach 6.3% at 1.4 A cm -2 for dry inlet air.
Study of interfacial area transport and sensitivity analysis for air-water bubbly flow
International Nuclear Information System (INIS)
The interfacial area transport equation applicable to the bubbly flow is presented. The model is evaluated against the data acquired by the state-of-the-art miniaturized double-sensor conductivity probe in an adiabatic air-water co-current vertical test loop under atmospheric pressure condition. In general, a good agreement, within the measurement error of plus/minus 10%, is observed for a wide range in the bubbly flow regime. The sensitivity analysis on the individual particle interaction mechanisms demonstrates the active interactions between the bubbles and highlights the mechanisms playing the dominant role in interfacial area transport. The analysis employing the drift flux model is also performed for the data acquired. Under the given flow conditions, the distribution parameter of 1.076 yields the best fit to the data
Study of interfacial area transport and sensitivity analysis for air-water bubbly flow
Energy Technology Data Exchange (ETDEWEB)
Kim, S.; Sun, X.; Ishii, M.; Beus, S.G.
2000-09-01
The interfacial area transport equation applicable to the bubbly flow is presented. The model is evaluated against the data acquired by the state-of-the-art miniaturized double-sensor conductivity probe in an adiabatic air-water co-current vertical test loop under atmospheric pressure condition. In general, a good agreement, within the measurement error of plus/minus 10%, is observed for a wide range in the bubbly flow regime. The sensitivity analysis on the individual particle interaction mechanisms demonstrates the active interactions between the bubbles and highlights the mechanisms playing the dominant role in interfacial area transport. The analysis employing the drift flux model is also performed for the data acquired. Under the given flow conditions, the distribution parameter of 1.076 yields the best fit to the data.
Mean interfacial shear stress and liquid film thickness in countercurrent air-water flow
International Nuclear Information System (INIS)
Countercurrent air-water flow experimental results in a tubular vertical test section 2.2 m long and 0.02 m ID are presented; the relations between the mean value of the interfacial shear stress and the mean liquid film thickness and flow rate of gas and liquid phases are derived. The experiments were performed in the laminar regime of the liquid film, for Reynolds number = 250:950, at the flooding conditions, before and after the flooding occurrence. Flooding data are compared with the Wallis correlation and with the Bharathan-Wallis theoretical model. Experimental values of the mean interfacial shear stress and wall shear stress are compared with the prediction of the empirical correlations that are used for the countercurrent flow modelling. An interfacial friction factor correlation is also presented
Analysis of data obtained in two-phase flow tests of primary heat transport pumps
International Nuclear Information System (INIS)
This report analyzes data obtained in two-phase flow tests of primary heat transport pumps performed during the period 1980-1983. Phenomena which have been known to cause pump-induced flow oscillations in pressurized piping systems under two-phase conditions are reviewed and the data analyzed to determine whether any of the identified phenomena could have been responsible for the instabilities observed in those tests. Tentative explanations for the most severe instabilities are given based on those analyses. It is shown that suction pipe geometry probably plays an important role in promoting instabilities, so additional experiments to investigate the effect of suction pipe geometry on the stability of flow in a closed pipe loop under two-phase conditions are recommended
OPTIMIZATION DESIGN OF GAS-PARTICLE TWO-PHASE AXIAL-FLOW FAN
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
Based on the shaping theory of writhed blade in streamline design, the geometric shape of blade is designed and then computational formulas for the dynamic design of fan with writhed the blades in gas-particle two-phase axial-flow are derived with the two-phase continuum coupling model. Concurrently, the correlation between the structure of impeller and flow-field dynamic functional parameters is presented. Further, the software for the optimization design of gas-particle two-phase axial-flow fan with writhed blades is obtained. By means of the available software, a sample fan is formed with its all dynamic characteristic curves and geometric shape. Finally, the conclusion on the effect of particles on fan running is reached, quantitatively and qualitatively, as is expected in the fan industry.
International Nuclear Information System (INIS)
Quasi-diabatic two-flow pattern visualizations and measurements of elongated bubble velocity, frequency and length were performed. The tests were run for R134a evaporating in a stainless steel tube with diameter of 2.32 mm, mass velocities from 50 to 600 kg/m2s and saturation temperatures of 22 deg C, 31 deg C and 41 deg C. The tube was heated by applying a direct DC current to its surface. Images from a high-speed video-camera (8000 frames/s) obtained through a transparent tube just downstream of the heated section were used to identify the following flow patterns: bubbly, elongated bubbles, churn and annular. Dryout conditions were also characterized. Local heat transfer results were considered when investigating the presence of stratified flows. The visualized flow patterns were compared against the predictions provided by Barnea et al., Felcar et al. and Revellin and Thome. For the present database, the method recently proposed by Felcar et al. provides the best predictions. Additionally, elongated bubble velocities, frequencies and lengths were determined based on an analysis of high speed videos. Results suggested that the elongated bubble velocity depends on mass velocity, vapor quality and saturation temperature, and is independent of bubble length. The bubble velocity increases with increasing mass velocity and vapor quality and decreases with increasing saturation temperature. Additionally, bubble velocity was correlated as a linear function of the two-phase superficial velocity. (author)
Mechanistic multidimensional analysis of two-phase flow in horizontal tube with 90 deg elbow
International Nuclear Information System (INIS)
The development of modeling and simulation capabilities of two-phase flow and heat transfer is very important for the design, operation and safety of nuclear reactors. Whereas a significant progress in this field has been made over the recent years, further advancements are clearly needed for new concepts of advanced (Generation-IV in particular) reactors. Difficulties in analyzing gas/liquid flows are due to the fact that such two-phase mixtures can assume several different flow patterns, each characterized by flow-regime specific interfacial phenomena of mass, momentum and energy transfer. The level of difficulty increases even further in the case of a complex tube geometries and spatial orientations. The purpose of this paper is to discuss the results of the analysis of a two-phase flow in a horizontal pipe with a 90-degree elbow. The overall objective of the present work is the development of a 3-dimensional computational model of a two-phase high-Reynolds number turbulent flow. The overall new model has been encoded in the next-generation Computational Multiphase Fluid Dynamics (CMFD) computer code, NPHASE. The model has been tested parametrically and the results of NPHASE calculations have been compared against experimental data. It has been demonstrated that the proposed model is consistent both physically and numerically, the predictions are in a reasonable agreement with the measurements
Analysis of void fraction distributions and prediction of DNB in boiling two-phase flow
International Nuclear Information System (INIS)
Analyses were carried out for the void fraction distributions in boiling two-phase flow in various flow channel such as round tube, rectangular pipe. Based on the simple assumptions of bubble shape, distribution of bubble number density were calculated based on the models of bubble diffusion considering bubbles due to boiling. Some of the models of turbulence structure and turbulent bubble diffusion in non-boiling two-phase flow which are well established are applied to the boiling two-phase flow with appropriate modification considering the effect of bubble growth and detachment from heated wall. From the distributions of bubble number density, void fraction distributions were calculated based on the simple assumption of bubble shape. The calculated void fraction distributions show the wall peak of which magnitude depends upon heat flux, bubble size hydraulic diameter of flow passage, bubble dispersion coefficient etc. Extensive parameter survey of these parameters on the void fraction distributions were carried out and mechanisms of bubble behaviors in boiling two-phase flow were considered in details. The predicted void fraction distributions reasonably agree with experimental data. Based on the calculated void fraction distributions, DNB heat flux were predicted with simple model where DNB occurs the wall peak void fraction exceeds the certain value. Although the model is quite simple, reasonable prediction of DNB was shown to become possible. (author)
Conceptual plan: Two-Phase Flow Laboratory Program for the Waste Isolation Pilot Plant
International Nuclear Information System (INIS)
The Salado Two-Phase Flow Laboratory Program was established to address concerns regarding two-phase flow properties and to provide WIPP-specific, geologically consistent experimental data to develop more appropriate correlations for Salado rock to replace those currently used in Performance Assessment models. Researchers in Sandia's Fluid Flow and Transport Department originally identified and emphasized the need for laboratory measurements of Salado threshold pressure and relative permeability. The program expanded to include the measurement of capillary pressure, rock compressibility, porosity, and intrinsic permeability and the assessment of core damage. Sensitivity analyses identified the anhydrite interbed layers as the most likely path for the dissipation of waste-generated gas from waste-storage rooms because of their relatively high permeability. Due to this the program will initially focus on the anhydrite interbed material. The program may expand to include similar rock and flow measurements on other WIPP materials including impure halite, pure halite, and backfill and seal materials. This conceptual plan presents the scope, objectives, and historical documentation of the development of the Salado Two-Phase Flow Program through January 1993. Potential laboratory techniques for assessing core damage and measuring porosity, rock compressibility, capillary and threshold pressure, permeability as a function of stress, and relative permeability are discussed. Details of actual test designs, test procedures, and data analysis are not included in this report, but will be included in the Salado Two-Phase Flow Laboratory Program Test Plan pending the results of experimental and other scoping activities in FY93
Investigation on two-phase flow instability in steam generator of integrated nuclear reactor
Institute of Scientific and Technical Information of China (English)
无
1996-01-01
In the pressure range of 3-18MPa,high pressure steam-water two-phase flow density wave instability in vertical upward parallel pipes with inner diameter of 12mm is studied experimentally.The oscillation curves of two-phase flow instability and the effects of several parameters on the oscillation threshold of the system are obtained.Based on the small pertubation linearization method and the stability principles of automatic control system,a mathematical model is developed to predict the characteristics of density wave instability threshold.The predictions of the model are in good agreement with the experimental results.
A study on nuclear propulsion using gas-solid two-phase flow
Energy Technology Data Exchange (ETDEWEB)
Miyato, Naoaki; Kataoka, Isao; Serizawa, Akimi [Kyoto Univ. (Japan). Faculty of Engineering
1997-05-01
A solid core nuclear rocket has been considered a candidate for the first manned mission to Mars. The reason is that the solid core nuclear rocket has higher specific impulse than a chemical rocket. But its engine thrust is as much as that of the chemical rocket. We have thought of use of gas-solid two-phase flow for higher engine thrust on nuclear thermal propulsion and examined the effect of gas-solid two-phase flow on the engine thrust and the specific impulse of the solid core nuclear rocket. (author)
Two-phase flow stability structure in a natural circulation system
Energy Technology Data Exchange (ETDEWEB)
Zhou, Zhiwei [Nuclear Engineering Laboratory Zurich (Switzerland)
1995-09-01
The present study reports a numerical analysis of two-phase flow stability structures in a natural circulation system with two parallel, heated channels. The numerical model is derived, based on the Galerkin moving nodal method. This analysis is related to some design options applicable to integral heating reactors with a slightly-boiling operation mode, and is also of general interest to similar facilities. The options include: (1) Symmetric heating and throttling; (2) Asymmetric heating and symmetric throttling; (3) Asymmetric heating and throttling. The oscillation modes for these variants are discussed. Comparisons with the data from the INET two-phase flow stability experiment have qualitatively validated the present analysis.
Two-Phase Flow Measurements with 252Cf: Design Aspects and Considerations
International Nuclear Information System (INIS)
For many years 252Cf has been used for measuring moisture content, particularly in the ground's soil, by detecting the amount of slowing down (thermalization) of the source's fission neutrons by the hydrogen nuclei in water. The same concept has been employed for measuring the phase volume fraction in two-phase flows. Although the principle of using neutron slowing down to measure hydrogen content is basic and straightforward, its application in a confined and evolving medium such as two-phase flow can be challenging. This paper identifies some of these challenges and presents some approaches for dealing with them
Theoretical studies of fluid-structure interactions in two-phase flow through vibration models
International Nuclear Information System (INIS)
On the basis of reduced characteristic equations for calculation of continuity, momentum and energy of a two-phase flow, relations are derived for a substitute of the gas-fluid mixture, covering position and time-dependent density and velocity data, and are verified by a boiling fluid model. The results are applied to a 1D and a 2D vibration model (pendulum in two-phase flow), taking into account the flui-structure interaction and the calculation of eigenfrequencies and damping. (orig.)
International Nuclear Information System (INIS)
The Forschungszentrum Rossendorf (FZR) e. V. is constructing a new large-scale test facility, TOPFLOW, for thermalhydraulic single effect tests. The acronym stands for transient two phase flow test facility. It will mainly be used for the investigation of generic and applied steady state and transient two phase flow phenomena and the development and validation of models of computational fluid dynamic (CFD) codes. The manual of the test facility must always be available for the staff in the control room and is restricted condition during operation of personnel and also reconstruction of the facility. (orig./GL)
Analytical Simulation of Flow and Heat Transfer of Two-Phase Nanofluid (Stratified Flow Regime
Directory of Open Access Journals (Sweden)
Mohammad Abbasi
2014-01-01
Full Text Available Nanofluids have evoked immense interest from researchers all around the globe due to their numerous potential benefits and applications in important fields such as cooling electronic parts, cooling car engines and nuclear reactors. An analytical study of fluid flow of in-tube stratified regime of two-phase nanofluid has been carried out for CuO, Al2O2, TiO3, and Au as applied nanoparticles in water as the base liquid. Liquid film thickness, convective heat transfer coefficient, and dryout length have been calculated. Among the considered nano particles, Al2O3 and TiO2 because of providing more amounts of heat transfer along with longer lengths of dryout found as the most appropriate nanoparticles to achieve cooling objectives.
Technique and apparatus for two-phase systems analysis directly in a flow
International Nuclear Information System (INIS)
Method and apparatus for X-ray spectrum analysis of flowing material, and particularly where the material has two phases such as a suspension. A flow of gas or floats are used to separate the flowing material from an X-ray window in a casing containing an X-ray source and detector, which casing is located directly in the stream of flowing material. The gas flow provides a protective curtain across the window. An electrode structure is moveably mounted adjacent to the window and enables the solid state phase to be deposited for separated analysis of the solid and liquid phases of the flowing material
Two-phase fluid flow measurements in small diameter channels using real-time neutron radiography
International Nuclear Information System (INIS)
A series of real-time, neutron radiography, experiments are ongoing at the Texas A and M Nuclear Science Center Reactor (NSCR). These tests determine the resolving capabilities for radiographic imaging of two phase water and air flow regimes through small diameter flow channels. Though both film and video radiographic imaging is available, the real-time video imaging was selected to capture the dynamic flow patterns with results that continue to improve. (author)
Monitoring Gas Void Fraction In Two-Phase Flow With Acoustic Emission
Addali, Abdulmajid
2010-01-01
The two-phase gas/liquid flow phenomenon can be encountered over a range of gas and liquid flow rates in the chemical engineering industry, particularly in oil and gas production transportation pipelines. Monitoring and measurement of their characteristics, such as the gas void fraction, are necessary to minimise the disruption of downstream process facilities. Thus, over the last decade, the investigation, development and use of multiphase flow metering system have been a major focus for the...
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)
Modelling of interfacial area and turbulence in two-phase flow
International Nuclear Information System (INIS)
Full text of publication follows: Computational Two-Fluid Dynamics (CTFD) modelling is still under development. The single pressure two-fluid model is widely used as a model basis for the multidimensional simulation of typical two-phase flow phenomena, e.g. void and pressure wave propagation, phase transitions, sharp interface movements, thermal and mechanical non-equilibrium /1/. The conservation equations based on an averaging procedure are written for each phase allowing both phases to co-exist at any point in space. The local volumetric fraction alone, one of the solution variables of the two-fluid model, is not sufficient to describe the topology of the two phases and consequently the flow regime can not be determined by the two-fluid model. A determination of the flow situation requires additional knowledge of the interface. The concentration of the interfacial area is one of the key parameters that gives information of the flow pattern. It is also an important parameter for the modelling of interfacial friction forces and interfacial transfer terms. The modelling of a transport equation for the interfacial area concentration covering the whole two-phase flow range is outlined in this paper. In this transport equation the forces acting on the interface and mass transfer are modelled. Observed phenomena, e.g. bubble coalescence or disintegration, are not explicitly modelled, they are the result of the interacting forces on bubble interface. Thus the modelling is mainly based on first principles and is largely free from empiricism /2/. First validation calculations will be presented. For the modelling of turbulence in two-phase flows new transport equations for the turbulent kinetic energy and its dissipation are proposed, where turbulent shear stress for two-phase flows will be modelled. Beyond this the new turbulence model differentiates between turbulent scales and the usual constants of the dissipation rate equation are modelled /2/. A first verification
Nonlinear analysis of gas-water/oil-water two-phase flow in complex networks
Gao, Zhong-Ke; Wang, Wen-Xu
2014-01-01
Understanding the dynamics of multi-phase flows has been a challenge in the fields of nonlinear dynamics and fluid mechanics. This chapter reviews our work on two-phase flow dynamics in combination with complex network theory. We systematically carried out gas-water/oil-water two-phase flow experiments for measuring the time series of flow signals which is studied in terms of the mapping from time series to complex networks. Three network mapping methods were proposed for the analysis and identification of flow patterns, i.e. Flow Pattern Complex Network (FPCN), Fluid Dynamic Complex Network (FDCN) and Fluid Structure Complex Network (FSCN). Through detecting the community structure of FPCN based on K-means clustering, distinct flow patterns can be successfully distinguished and identified. A number of FDCN’s under different flow conditions were constructed in order to reveal the dynamical characteristics of two-phase flows. The FDCNs exhibit universal power-law degree distributions. The power-law exponent ...
Film boiling on spheres in single- and two-phase flows.
Energy Technology Data Exchange (ETDEWEB)
Liu, C.; Theofanous, T. G.
2000-08-29
Film boiling on spheres in single- and two-phase flows was studied experimentally and theoretically with an emphasis on establishing the film boiling heat transfer closure law, which is useful in the analysis of nuclear reactor core melt accidents. Systematic experimentation of film boiling on spheres in single-phase water flows was carried out to investigate the effects of liquid subcooling (from 0 to 40 C), liquid velocity (from 0 to 2 m/s), sphere superheat (from 200 to 900 C), sphere diameter (from 6 to 19 mm), and sphere material (stainless steel and brass) on film boiling heat transfer. Based on the experimental data a general film boiling heat transfer correlation is developed. Utilizing a two-phase laminar boundary-layer model for the unseparated front film region and a turbulent eddy model for the separated rear region, a theoretical model was developed to predict the film boiling heat transfer in all single-phase regimes. The film boiling from a sphere in two-phase flows was investigated both in upward two-phase flows (with void fraction from 0.2 to 0.65, water velocity from 0.6 to 3.2 m/s, and steam velocity from 3.0 to 9.0 m/s) and in downward two-phase flows (with void fraction from 0.7 to 0.95, water velocity from 1.9 to 6.5 m/s, and steam velocity from 1.1 to 9.0 m/s). The saturated single-phase heat transfer correlation was found to be applicable to the two-phase film boiling data by making use of the actual water velocity (water phase velocity), and an adjustment factor of (1 - {alpha}){sup 1/4} (with a being the void fraction) for downward flow case only. Slight adjustments of the Reynolds number exponents in the correlation provided an even better interpretation of the two-phase data. Preliminary experiments were also conducted to address the influences of multi-sphere structure on the film boiling heat transfer in single- and two-phase flows.
Film boiling on spheres in single- and two-phase flows. Final report
Energy Technology Data Exchange (ETDEWEB)
Liu, C.; Theofanous, T.G.
1994-12-01
Film boiling on spheres in single- and two-phase flows was studied experimentally and theoretically with an emphasis on establishing the film boiling heat transfer closure law, which is useful in the analysis of nuclear reactor core melt accidents. Systematic experimentation of film boiling on spheres in single-phase water flows was carried out to investigate the effects of liquid subcooling (from 0 to 40{degrees}C), liquid velocity (from 0 to 2 m/s), sphere superheat (from 200 to 900{degrees}C), sphere diameter (from 6 to 19 mm), and sphere material (stainless steel and brass) on film boiling heat transfer. Based on the experimental data a general film boiling heat transfer correlation is developed. Utilizing a two-phase laminar boundary-layer model for the unseparated front film region and a turbulent eddy model for the separated rear region, a theoretical model was developed to predict the film boiling heat transfer in all single-phase regimes. The film boiling from a sphere in two-phase flows was investigated both in upward two-phase flows (with void fraction from 0.2 to 0.65, water velocity from 0.6 to 3.2 m/s, and steam velocity from 3.0 to 9.0 m/s) and in downward two-phase flows (with void fraction from 0.7 to 0.95, water velocity from 1.9 to 6.5 m/s, and steam velocity from 1.1 to 9.0 m/s). The saturated single-phase heat transfer correlation was found to be applicable to the two-phase film boiling data by making use of the actual water velocity (water phase velocity), and an adjustment factor of (1-{alpha}){sup 1/4} (with {alpha} being the void fraction) for downward flow case only. Slight adjustments of the Reynolds number exponents in the correlation provided an even better interpretation of the two-phase data. Preliminary experiments were also conducted to address the influences of multisphere structure on the film boiling heat transfer in single- and two-phase flows.
New four-sensor probe theory for multi-dimensional two-phase flow measurement
International Nuclear Information System (INIS)
This paper has newly developed a complete four-sensor probe measurement theory of local instantaneous 3D bubble velocity vector, local instantaneous bubble diameter and local instantaneous interfacial normal unit vector and local time-averaged interfacial area concentration (IAC) in a multi-dimensional two-phase flow by assuming the bubbles to be spherical. The newly-developed theory has opened a way for the measurement of bubble diameter with a four-sensor probe. The conventional IAC, 3D bubble velocity vector and interfacial normal unit vector measurement theories of a four-sensor probe have become an example of the newly-developed theory when the bubbles have much larger sizes than a four-sensor probe. Spherical bubbles in a practical two-phase flow are distinguished from non-spherical bubbles by introducing a bubble deviation coefficient from spherical shape. Based on the spherical bubbles, the newly-developed theory was employed to measure local parameters in a two-phase flow. Its measurement results were checked against void fraction measurement using differential pressure (DP) gauges, superficial gas velocity measurement using gas flow meters, bubble diameter measurement using photographic image and IAC measurement using the conventional four-sensor probe theory. The satisfactory comparing results show that the newly-developed theory can perform the accurate and reliable measurements for practical multi-dimensional two-phase flow. (author)
A new correlation of two-phase frictional pressure drop for condensing flow in pipes
International Nuclear Information System (INIS)
Highlights: • Survey of two-phase frictional pressure drop (THFPD) experimental data of condensing flow is conducted. • Applicability of the existing THFPD correlations to condensing flow is assessed. • A new THFPD correlation for condensing flow in pipes is proposed. -- Abstract: The calculation of two-phase frictional pressure drop for condensing flow in pipes is essential in many areas. Although numerous studies concerning this issue have been conducted, an accurate correlation is still required. In this paper, an overall survey of correlations and experimental investigations of two-phase frictional pressure drop is carried out. There 525 experimental data points of 9 refrigerants are gathered from literature, with hydraulic diameter from 0.1 to 10.07 mm, mass flux from 20 to 800 kg/m2 s, and heat flux from 2 to 55.3 kW/m2. The 29 existing correlations are evaluated against the experimental database, among which the best one has a mean absolute relative deviation (MARD) of 25.2%. Based on all the experimental data, a new correlation which has an MARD of 19.4% is proposed, improving significantly the prediction of two-phase frictional pressure drop for pipe condensing flow
A two-phase flow model of the Rayleigh endash Taylor mixing zone
International Nuclear Information System (INIS)
The Rayleigh endash Taylor instability of an interface separating fluids of distinct density is driven by an acceleration across the interface. Low order statistical moments of fluctuating fluid quantities characterize the hydrodynamics of the mixing zone. A new model is proposed for the momentum coupling between the two phases. This model is validated against computational data for compressible flows, including flows near the incompressible limit. Our main result is a zero parameter first order closure for ensemble averaged two phase flow equations. We do not, however, fully solve the closure problem, as the equations we derive are missing an (internal) boundary condition along any surface for which either phase goes to zero volume fraction. In this sense, the closure problem is reduced from a volume to a surface condition, rather than being solved completely. We compare two formulations of the statistical moments, one based on two phase flow and the other on turbulence models. These formulations describe different aspects of the mixing process. For the problem considered, the two phase flow moments appear to be preferable, in that they subsume the turbulence moments but not conversely. copyright 1996 American Institute of Physics
MICROGRAVITY EXPERIMENTS OF TWO-PHASE FLOW PATTERNS ABOARD MIR SPACE STATION
Institute of Scientific and Technical Information of China (English)
赵建福; 解京昌; 林海; 胡文瑞; A.V. Ivanov; A.Yu. Belyaev
2001-01-01
A first experimental study on two-phase flow patterns at a long-term,steady microgravity condition was conducted on board the Russian Space Station "MIR" in August 1999. Carbogal and air are used as the liquid and the gas phase,respectively. Bubble, slug, slug-annular transitional, and annular flows are observed.A new region of annular flow with lower liquid superficial velocity is discovered,and the region of the slug-annular transitionalfiow is wider than that observed by experiments on board the parabolic aircraft. The main patterns are bubble, slug annular transitional and annular flows based on the experiments on board MIR space station. Some influences on the two-phase flow patterns in the present experiments are discussed.
The FDF or LES/PDF method for turbulent two-phase flows
Energy Technology Data Exchange (ETDEWEB)
Chibbaro, S [Institut Jean Le Rond D' Alembert University Pierre et Marie Curie et CNRS UMR7190, 4, place Jussieu 75252 Paris Cedex 05 (France); Minier, Jean-Pierre, E-mail: sergio.chibbaro@upmc.fr [EDF R and D Division Quai Wattiou 78100 Chatou France (France)
2011-12-22
In this paper, a new formalism for the filtered density function (FDF) approach is developed for the treatment of turbulent polydispersed two-phase flows in LES simulations. Contrary to the FDF used for turbulent reactive single-phase flows, the present formalislm is based on Lagrangian quantities and, in particular, on the Lagrangian filtered mass density function (LFMDF) as the central concept. This framework allows modeling and simulation of particle flows for LES to be set in a rigorous context and various links with other approaches to be made. In particular, the relation between LES for particle simulations of single-phase flows and Smoothed Particle Hydrodynamics (SPH) is put forward. Then, the discussion and derivation of possible subgrid stochastic models used for Lagrangian models in two-phase flows can set in a clear probabilistic equivalence with the corresponding LFMDF.
The FDF or LES/PDF method for turbulent two-phase flows
Chibbaro, Sergio
2011-01-01
In this paper, a new formalism for the filtered density function (FDF) approach is developed for the treatment of turbulent polydispersed two-phase flows in LES simulations. Contrary to the FDF used for turbulent reactive single-phase flows, the present formalislm is based on Lagrangian quantities and, in particular, on the Lagrangian filtered mass density function (LFMDF) as the central concept. This framework allows modeling and simulation of particle flows for LES to be set in a rigorous context and various links with other approaches to be made. In particular, the relation between LES for particle simulations of single-phase flows and Smoothed Particle Hydrodynamics (SPH) is put forward. Then, the discussion and derivation of possible subgrid stochastic models used for Lagrangian models in two-phase flows can set in a clear probabilistic equivalence with the corresponding LFMDF.
Two-phase flow in the cooling circuit of a cryogenic rocket engine
Preclik, D.
1992-07-01
Transient two-phase flow was investigated for the hydrogen cooling circuit of the HM7 rocket engine. The nuclear reactor code ATHLET/THESEUS was adapted to cryogenics and applied to both principal and prototype experiments for validation and simulation purposes. The cooling circuit two-phase flow simulation focused on the hydrogen prechilling and pump transient phase prior to ignition. Both a single- and a multichannel model were designed and employed for a valve leakage flow, a nominal prechilling flow, and a prechilling with a subsequent pump-transient flow. The latter case was performed in order to evaluate the difference between a nominal and a delayed turbo-pump start-up. It was found that an extension of the nominal prechilling sequence in the order of 1 second is sufficient to finally provide for liquid injection conditions of hydrogen which, as commonly known, is undesirable for smooth ignition and engine starting transients.
Critical equilibrium two-phase flow with quasi-constant slip
International Nuclear Information System (INIS)
On the basis of the mass-, momentum- and energy-conservation equations, assuming a quasi-constant slip, a mathematical model of the critical non-homogeneous equilibrium two-phase flow is developed. The slip is varied to find the maximum of the critical mass flow rate for low qualities. For qualities greater than 0.1 it is found that the critical mass flow rate has no extreme values and approaches a constant value when the slip increases. Following the concept of Henry and Fauske the model is extended to describe non-homogeneous non-equilibrium two-phase flows, too. The comparison with published experimental data demonstrates that the theory can approximate well different experimental results on determination of the local critical mass flow rate. (orig.)
Analysis of turbulent structure of boiling two-phase flow and prediction of CHF
International Nuclear Information System (INIS)
Analyses were carried out based on the basic equation of bubble number density based on appropriate turbulence model and bubble dispersion coefficient. The calculated distribution of bubble number density was converted to the void fraction distribution with the assumption of spherical bubble. The value of peak void fraction depended upon heat flux, liquid inlet flux, bubble diameter, bubble dispersion coefficient and flow passage diameter. Using void fraction distribution and basic equations and constitutive equations of turbulence, turbulence structure in boiling two-phase flow was analyzed. The result indicated that turbulent velocity distribution showed complicated behaviors compared with single-phase flow and averaged velocity showed flattened distribution compared with single-phase flow. In boiling two-phase flow, it is shown the turbulence generation term due to boiling bubble plays important contribution to the turbulence structure. Based on the results of prediction of void fraction distributions, an attempt will be carried out to predict DNB heat flux. (author)
A state-of-the-art report on two-phase critical flow modelling
International Nuclear Information System (INIS)
This report reviews and analyses two-phase, critical flow models. The purposes of the report are (1) to make a knowledge base for the full understanding and best-estimate of two-phase, critical flow, (2) to analyse the model development trend and to derive the direction of further studies. A wide range of critical flow models are reviewed. Each model, in general, predicts critical flow well only within specified conditions. The critical flow models of best-estimate codes are special process model included in the hydrodynamic model. The results of calculations depend on the nodalization, discharge coefficient, and other user's options. The following topics are recommended for continuing studies: improvement of two-fluid model, development of multidimensional model, data base setup and model error evaluation, and generalization of discharge coefficients. 24 figs., 5 tabs., 80 refs. (Author)
A state-of-the-art report on two-phase critical flow modelling
Energy Technology Data Exchange (ETDEWEB)
Jung, Jae Joon; Jang, Won Pyo; Kim, Dong Soo [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)
1993-09-01
This report reviews and analyses two-phase, critical flow models. The purposes of the report are (1) to make a knowledge base for the full understanding and best-estimate of two-phase, critical flow, (2) to analyse the model development trend and to derive the direction of further studies. A wide range of critical flow models are reviewed. Each model, in general, predicts critical flow well only within specified conditions. The critical flow models of best-estimate codes are special process model included in the hydrodynamic model. The results of calculations depend on the nodalization, discharge coefficient, and other user`s options. The following topics are recommended for continuing studies: improvement of two-fluid model, development of multidimensional model, data base setup and model error evaluation, and generalization of discharge coefficients. 24 figs., 5 tabs., 80 refs. (Author).
Directory of Open Access Journals (Sweden)
Lam Ghai Lim
2016-07-01
Full Text Available A 360° twisted helical capacitance sensor was developed for holdup measurement in horizontal two-phase stratified flow. Instead of suppressing nonlinear response, the sensor was optimized in such a way that a ‘sine-like’ function was displayed on top of the linear function. This concept of design had been implemented and verified in both software and hardware. A good agreement was achieved between the finite element model of proposed design and the approximation model (pure sinusoidal function, with a maximum difference of ±1.2%. In addition, the design parameters of the sensor were analysed and investigated. It was found that the error in symmetry of the sinusoidal function could be minimized by adjusting the pitch of helix. The experiments of air-water and oil-water stratified flows were carried out and validated the sinusoidal relationship with a maximum difference of ±1.2% and ±1.3% for the range of water holdup from 0.15 to 0.85. The proposed design concept therefore may pose a promising alternative for the optimization of capacitance sensor design.
Lim, Lam Ghai; Pao, William K. S.; Hamid, Nor Hisham; Tang, Tong Boon
2016-01-01
A 360° twisted helical capacitance sensor was developed for holdup measurement in horizontal two-phase stratified flow. Instead of suppressing nonlinear response, the sensor was optimized in such a way that a ‘sine-like’ function was displayed on top of the linear function. This concept of design had been implemented and verified in both software and hardware. A good agreement was achieved between the finite element model of proposed design and the approximation model (pure sinusoidal function), with a maximum difference of ±1.2%. In addition, the design parameters of the sensor were analysed and investigated. It was found that the error in symmetry of the sinusoidal function could be minimized by adjusting the pitch of helix. The experiments of air-water and oil-water stratified flows were carried out and validated the sinusoidal relationship with a maximum difference of ±1.2% and ±1.3% for the range of water holdup from 0.15 to 0.85. The proposed design concept therefore may pose a promising alternative for the optimization of capacitance sensor design. PMID:27384567
Entropy analysis on non-equilibrium two-phase flow models
Energy Technology Data Exchange (ETDEWEB)
Karwat, H.; Ruan, Y.Q. [Technische Universitaet Muenchen, Garching (Germany)
1995-09-01
A method of entropy analysis according to the second law of thermodynamics is proposed for the assessment of a class of practical non-equilibrium two-phase flow models. Entropy conditions are derived directly from a local instantaneous formulation for an arbitrary control volume of a structural two-phase fluid, which are finally expressed in terms of the averaged thermodynamic independent variables and their time derivatives as well as the boundary conditions for the volume. On the basis of a widely used thermal-hydraulic system code it is demonstrated with practical examples that entropy production rates in control volumes can be numerically quantified by using the data from the output data files. Entropy analysis using the proposed method is useful in identifying some potential problems in two-phase flow models and predictions as well as in studying the effects of some free parameters in closure relationships.
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.
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)
Two-phase flow can trigger vibration phenomena that are not well predicted by models like the homogeneous model. Concerning the steam generator of a Candu type reactor, these vibrations may lead to the failure of tubes. The coupling between thermo-hydraulic and vibration phenomena requires models that treat sliding between liquid and vapor phases. The purpose of this work is to study a series of experiments performed in a freon loop. These experiments simulate a two-phase flow through a bundle of tubes. Most estimations of vibratory parameters are based on the assumption of a uniform distribution of the void fraction. An optic probe has been used to measure the void fraction. The first part of this study is devoted to the processing of the response spectra given by the probe. The second part presents an estimation of the void fraction given by different models, a comparison between experimental and theoretical results allows to discuss their validity range. (A.C.)
Energy Technology Data Exchange (ETDEWEB)
Seidel, Tobias; Vallee, Christophe; Lucas, Dirk; Beyer, Matthias; Deendarlianto
2011-09-15
In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at FZD. The hot leg model is operated in the pressure chamber of the TOPFLOW test facility, which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. This technique makes it possible to visualise the two-phase flow through large windows, also at reactor-typical pressure levels. In order to optimise the optical observation possibilities, the test section was designed with a rectangular cross-section. Experiments were performed with air and water at 1.5 and 3.0 bar at room temperature as well as with steam and water at 15, 30 and 50 bar and the corresponding saturation temperature (i.e. up to 264 C). The total of 194 runs are divided into 4 types of experiments covering stationary co-current flow, counter-current flow, flow without water circulation and transient counter-current flow limitation (CCFL) experiments. This report provides a detailed documentation of the experiments including information on the experimental setup, experimental procedure, test matrix and on the calibration of the measuring devices. The available data is described and data sheets were arranged for each experiment in order to give an overview of the most important parameters. For the cocurrent flow experiments, water level histograms were arranged and used to characterise the flow in the hot leg. In fact, the form of the probability distribution was found to be sensitive to the boundary conditions and, therefore, is useful for the CFD comparison. Furthermore, the flooding characteristics of the hot leg model plotted in terms of the classical Wallis parameter or Kutateladze number were found to fail to properly correlate the data of the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which
International Nuclear Information System (INIS)
In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at FZD. The hot leg model is operated in the pressure chamber of the TOPFLOW test facility, which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. This technique makes it possible to visualise the two-phase flow through large windows, also at reactor-typical pressure levels. In order to optimise the optical observation possibilities, the test section was designed with a rectangular cross-section. Experiments were performed with air and water at 1.5 and 3.0 bar at room temperature as well as with steam and water at 15, 30 and 50 bar and the corresponding saturation temperature (i.e. up to 264 C). The total of 194 runs are divided into 4 types of experiments covering stationary co-current flow, counter-current flow, flow without water circulation and transient counter-current flow limitation (CCFL) experiments. This report provides a detailed documentation of the experiments including information on the experimental setup, experimental procedure, test matrix and on the calibration of the measuring devices. The available data is described and data sheets were arranged for each experiment in order to give an overview of the most important parameters. For the cocurrent flow experiments, water level histograms were arranged and used to characterise the flow in the hot leg. In fact, the form of the probability distribution was found to be sensitive to the boundary conditions and, therefore, is useful for the CFD comparison. Furthermore, the flooding characteristics of the hot leg model plotted in terms of the classical Wallis parameter or Kutateladze number were found to fail to properly correlate the data of the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which
EFFECT OF SURFACTANT ON TWO-PHASE FLOW PATTERNS OF WATER-GAS IN CAPILLARY TUBES
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Flow patterns of liquid-gas two-phase flow were experimentally investigated. The experiments were carried out in both vertical and horizontal capillary tubes having inner diameters of 1.60 mm. The working liquid was the mixture of water and Sodium Dodecyl Benzoyl Sulfate (SDBS). The working gas was Nitrogen. For the water/SDBS mixture-gas flow in the vertical capillary tube, flow-pattern transitions occurred at lower flow velocities than those for the water-gas flow in the same tube. For the water/SDBS mixture-gas flow in the horizontal capillary tube, surface tension had little effect on the bubbly-intermittent transition and had only slight effect on the plug-slug and slug-annular transitions. However, surface tension had significant effect on the wavy stratified flow regime. The wavy stratified flow regime of water/SDBS mixture-gas flow expanded compared with that of water-gas.
A boundary element approach to estimate the free surface in stratified two-phase flow
International Nuclear Information System (INIS)
Two-phase flows widely exist in many industries. Measuring the phase distribution in two-phase flow is important for the optimization and control of some industrial processes. Electrical resistance tomography (ERT) is a promising non-intrusive visualization technique for monitoring the two-phase flow. However, due to its nonlinear and ill-posed character, high-quality image reconstruction is difficult and some iterative approach is time consuming. In this paper, a boundary element approach is presented for directly estimating the free-surface in two-phase flow using ERT. The unknown free surface is parameterized by a Bézier curve. Coefficients of its control points are estimated by minimizing a residual function using the iterative Levenberg–Marquardt method. To speed up the estimation process, the physical model of ERT is formulated using a boundary element method. Based on this formulation, the forward problem is fast solved through a small size system matrix and the Jacobian matrix is efficiently calculated using an analytic method. After several numerical experiments, this approach is proved fast and precise and several factors influencing the estimation quality are analyzed based on these simulations. (paper)
Using the conductometric technique for two-phase flow parameter definition in heat power engineering
International Nuclear Information System (INIS)
Data are given on using conductometric transducers of steam and gas content for control and measuring of thermal power coolant parameters. Basic relations for the calculation of two-phase flow-conductivity are given as well. The potentialities of lead-in wires, measuring circuits, transducer structures used are briefly analyzed
Comparison of Two-Phase Pipe Flow in OpenFOAM with a Mechanistic Model
Shuard, Adrian M.; Mahmud, Hisham B.; King, Andrew J.
2016-03-01
Two-phase pipe flow is a common occurrence in many industrial applications such as power generation and oil and gas transportation. Accurate prediction of liquid holdup and pressure drop is of vast importance to ensure effective design and operation of fluid transport systems. In this paper, a Computational Fluid Dynamics (CFD) study of a two-phase flow of air and water is performed using OpenFOAM. The two-phase solver, interFoam is used to identify flow patterns and generate values of liquid holdup and pressure drop, which are compared to results obtained from a two-phase mechanistic model developed by Petalas and Aziz (2002). A total of 60 simulations have been performed at three separate pipe inclinations of 0°, +10° and -10° respectively. A three dimensional, 0.052m diameter pipe of 4m length is used with the Shear Stress Transport (SST) k - ɷ turbulence model to solve the turbulent mixtures of air and water. Results show that the flow pattern behaviour and numerical values of liquid holdup and pressure drop compare reasonably well to the mechanistic model.
International Nuclear Information System (INIS)
The undertaken study is an examination of a two phase dispersed air bubble mixing flow within a rectangular vessel. The technique of Particle Image Velocimetry (PIV) is utilized in order to obtain non-invasive velocity measurements of the resulting bubbly flow field and its induced effects upon a surrounding liquid medium. The method provides not only a visualization of the various patterns and structures of a given flow field, but also yields quantitative full-field instantaneous velocity data from both phases of a two phase system in a concurrent manner. PIV is a rapidly advancing flow visualization technique in which the instantaneous velocity profile of a given flow field is determined by photographically recording tracer particle and/or bubble images within the flow at discrete instances in time, and then conducting computational analysis of the digitized data. The use of developed analysis algorithms which perform a point-by-point matching of particle and bubble images from one digital image frame to the next subsequently allows reconstruction of the respective instantaneous velocity profiles. The ability to simultaneously measure the velocity fields of both components of a two phase flow is an important contribution toward the goal of developing improved correlations for flow regime determination as well as improved models for key two phase flow parameters such as the interfacial drag. In this work, results were obtained which indicate that the described PIV method is an effective tool in the study of the specific interactions which occur between components in a wide variety of multiphase systems. (author)
A simple model for two-phase slug flow induced damping
International Nuclear Information System (INIS)
The two-phase flows are prevalent in various industrial fields such as nuclear engineering, chemical engineering and the petroleum industry. At high speeds, flows through piping may generate significant excitation forces, particularly at joints and bends in piping systems. Interestingly, the flows may also generate significant damping forces which can be desirable from a vibration damping point of view. The question of exactly how internal two-phase flows generate damping remains largely unanswered. Indeed so is the question for external two-phase flows, which are even more complex. The problem addressed in this study is related to the behavior of tubular structures subjected to internal two-phase slug flow or nearly slug flow. The observation of slug flow subjected to transverse vibration led to consideration of the effects of sloshing liquid slugs due to the external vibration. Indeed, in flow visualization tests, the upper free surface of the slugs in vertical flow was found to deform significantly as the tube vibrated. This suggested a possible mechanism for energy transfer from the structure to the fluid which could be (at least partially) responsible for the observed two-phase flow-induced damping. An analytical model is developed aimed at incorporating the most basic sloshing effects of liquid slugs travelling through a tube at low speed. The first part of the work demonstrates that considering slugs as as simple points masses travelling through the tube leads only to low energy transfer from the tube to the flow and thus cannot explain the level of energy transfer observed in experimental damping tests. In the second part of the work, the flow dynamics within the slug are modeled to account for linear order free surface oscillations related to first mode sloshing. Numerical solution of the resulting equations shows that the energy transfer is much higher and results in damping levels of the same order as found in experimental measurements. The results
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The perforated plate weeping phenomena have been studied in both air/water and steam/cold water systems. The air/water experiment is designed to investigate the effect of geometric factors of the perforated plate on the rate of weeping. A new dimensionless flow rate in the form of H star is suggested. The data obtained are successfully correlated by this H star scaling in the conventional flooding equation. The steam/cold water experiment is concentrated on locating the boundary between weeping and no weeping. The effects of water subcooling, water inlet flow rate, and position of water spray are investigated. Depending on the combination of these factors, several types of weeping were observed. The data obtained at high water spray position can be related to the air/water flooding correlation by replacing the stream flow rate to an effective stream flow rate, which is determined by the mixing efficiency above the plate
Blob population dynamics during immiscible two-phase flows in reconstructed porous media
Yiotis, A. G.; Talon, L.; Salin, D.
2013-03-01
We study the dynamics of nonwetting liquid blobs during immiscible two-phase flows in stochastically reconstructed porous domains predominantly saturated by a wetting fluid. The flow problem is solved explicitly using a Lattice-Boltzmann model that captures both the bulk phase and interfacial dynamics of the process. We show that the nonwetting blobs undergo a continuous life cycle of dynamic breaking up and coalescence producing two populations of blobs, a mobile and a stranded one, that exchange continuously mass between them. The process reaches a “steady state” when the rates of coalescence and breaking up become equal, and the macroscopic flow variables remain practically constant with time. At steady state, mass partitioning between mobile and immobile populations depends strongly on the applied Bond number Bo and the initial nonwetting phase distributions. Three flow regimes are identified: a single-phase flow Darcy-type regime at low Bo numbers, a non-Darcy two-phase flow regime at intermediate values of Bo, where the capillary number scales as Ca∝Bo2, and a Darcy-type two-phase flow regime at higher values of Bo. Our numerical results are found to be in good agreement with recent experimental and theoretical works.
International Nuclear Information System (INIS)
An accurate subchannel database is crucial for modeling the multidimensional two-phase flow in a rod bundle and for validating subchannel analysis codes. Based on available reference, it can be said that a point-measurement sensor for acquiring void fractions and bubble velocity distributions do not infer interactions of the subchannel flow dynamics, such as a cross flow and flow distribution, etc. In order to acquire multidimensional two-phase flow in a 10×10 rod bundle with an o.d. of 10 mm and 3110 mm length, a new sensor consisting of 11-wire by 11-wire and 10-rod by 10-rod electrodes was developed. Electric potential in the proximity region between two wires creates a void fraction in the center subchannel region, like a so-called wire mesh sensor. A unique aspect of the devised sensor is that the void fraction near the rod surface can be estimated from the electric potential in the proximity region between one wire and one rod. The additional 400 points of void fraction and phasic velocity in 10×10 bundle can therefore be acquired. The devised sensor exhibits the quasi three-dimensional flow structures, i.e. void fraction, phasic velocity and bubble chord length distributions. These quasi three-dimensional structures exhibit the complexity of two-phase flow dynamics, such as coalescence and the breakup of bubbles in transient phasic velocity distributions. (author)
STABILITY OF VORTEX STREET IN GAS-LIQUID TWO-PHASE FLOW
Institute of Scientific and Technical Information of China (English)
Li Yong-guang; Lin Zong-hu
2003-01-01
The stability of the Karmen vortex street in gas-liquid two-phase flow was studied experimentally and theoretically. The values of the parameter h/l characterizing the vortex street structure (I.e., the ratio of the vortex street width to the distance between two vortexes) for a stable vortex street in gas-liquid two-phase flow were obtained for the first time. The parameter h/l was proved to be a variable, not a constant as in single-phase flow. H/l is related to the upstream fluid void fraction. In gas-liquid two-phase fluid flow to form a steady vortex street is more difficult than in a single-phase fluid flow. Because in the unsteady vortex shedding the vortex shedding band frequency is broader than the one in the single phase fluid flow, so it is easier to induce the cross-cylinder resonance than in the single phase fluid flow, and this case should give rise to the attention of engineers.
Bifurcations of a creeping air-water flow in a conical container
Balci, Adnan; Brøns, Morten; Herrada, Miguel A.; Shtern, Vladimir N.
2016-04-01
This numerical study describes the eddy emergence and transformations in a slow steady axisymmetric air-water flow, driven by a rotating top disk in a vertical conical container. As water height Hw and cone half-angle β vary, numerous flow metamorphoses occur. They are investigated for β =30°, 45°, and 60°. For small Hw , the air flow is multi-cellular with clockwise meridional circulation near the disk. The air flow becomes one cellular as Hw exceeds a threshold depending on β . For all β the water flow has an unbounded number of eddies whose size and strength diminish as the cone apex is approached. As the water level becomes close to the disk, the outmost water eddy with clockwise meridional circulation expands, reaches the interface, and induces a thin layer with anticlockwise circulation in the air. Then this layer expands and occupies the entire air domain. The physical reasons for the flow transformations are provided. The results are of fundamental interest and can be relevant for aerial bioreactors.
Numerical approach of multi-field two-phase flow models in the OVAP code
International Nuclear Information System (INIS)
Full text of publication follows: A significant progress has been made in modeling the complexity of vapor-liquid two-phase flow. Different three-dimensional models exist in order to simulate the evolution of parameters which characterize a two-phase model. These models can be classified into various groups depending on the inter-field coupling. A hierarchy of increasing physical complexity can be defined. The simplest group corresponds to the homogeneous mixture models where no interactions are taken into account. Another group is constituted by the two-fluid models employing physically important interfacial forces between two-phases, liquid, and water. The last group is multi-field modeling where inter-field couplings can be taken into account at different degrees, such as the MUltiple Size Group modeling [2], the consideration of separate equations for the transport and generation of mass and momentum for each field under the assumption of the same energy for all the fields of the same phase, and a full multi-field two-phase model [1]. The numerical approach of the general three-dimensional two-phase flow is by complexity of the phenomena a very challenging task; the ideal numerical method should be at the same time simple in order to apply to any model, from equilibrium to multi-field model and conservative in order to respect the fundamental conservation physical laws. The approximate Riemann solvers have the good properties of conservation of mass, momentum and energy balance and have been extended successfully to two-fluid models [3]- [5]. But, the up-winding of the flux is based on the Eigen-decomposition of the two-phase flow model and the computation of the Eigen-structure of a multi-field model can be a high cost procedure. Our contribution will present a short review of the above two-phase models, and show numerical results obtained for some of them with an approximate Riemann solver and with lower-complexity alternative numerical methods that do not
An experimental study on the local two phase distributions in the ERVC flow channel
International Nuclear Information System (INIS)
During ex-vessel cooling two-phase flow around the outside of the inverted hemisphere geometry of the lower reactor head results in a variety void fraction distributions. To study the local features of the void fraction distribution we performed an experimental study with a quarter-circle geometry test section to simulate the RPV lower head. Air is injected in the test section to simulate the two phase flow phenomena and a conductivity probe is used to measure the local void fraction distribution. The test results show that the local void fraction near the bottom of the lower head is a wall peak distribution which then transitions to a near-wall peak distribution near the top of the lower head, and eventually develops into a center-peak distribution outside of the cylindrical shell. A sensitivity study has shown that the air flow rate has a significant effect on the local void fraction distribution in the flow channel. (author)
Velocity measurements in the liquid metal flow driven by a two-phase inductor
Pedcenko, A; Priede, J; Gerbeth, G; Hermann, R
2013-01-01
We present the results of velocity measurements obtained by ultrasonic Doppler velocimetry and local potential probes in the flow of GaInSn eutectic melt driven by a two-phase inductor in a cylindrical container. This type of flow is expected in a recent modification to the floating zone technique for the growth of small-diameter single intermetallic compound crystals. We show that the flow structure can be changed from the typical two toroidal vortices to a single vortex by increasing the phase shift between the currents in the two coils from 0 to 90 degrees. The latter configuration is thought to be favourable for the growth of single crystals. The flow is also computed numerically and a reasonable agreement with the experimental results is found. The obtained results may be useful for the design of combined two-phase electromagnetic stirrers and induction heaters for metal or semiconductor melts.
Some applications of mixed finite elements to an ultra compressible or a two phase flow computations
International Nuclear Information System (INIS)
An homogeneous model solving two phase flow equations leads to study Euler equations as for compressible flow. An application of mixed element method built for Navier-Stokes equations is presented with a semi-implicit scheme (2D and 3D case). Some theoretical results about stability and approximation have been obtained and numerical tests have been performed and have given satisfactory results: the first one is a computation in a steam generator and the second one about a nozzle study
Two-phase flow in steam turbines: EDF R and D division investigations
International Nuclear Information System (INIS)
This report outlines the investigations on wet steam flows in steam turbines. All the softwares developed in the framework of these studies enables analysis of different aspects of these types of flows. The use of two phase codes based on 2 fluid models, which has achieved a sufficient progress, and the integration of the condensation programme in a transonic non stationary code will constitute a second step for these studies, enhancing what has already been achieved in this field
Models and numerical methods for two-phase flow of CO2 in pipes
Reinertsen, Aleksander
2015-01-01
Key to the transport phase of carbon capture and storage (CCS) is understanding the behavior of liquid or supercritical CO2 in pipelines, and the consequences of cracks and pipe depressurization. It is therefore useful to develop mathematical models and numerical methods for two-phase flow of CO2 in pipes in order to better predict such behavior. Such developed tools can also be useful in fluid structure- interaction models. Key to simulating single or multiphase flows is the formulation ...
Use of the electromagnetic flowmeter in a two-phase flow
Bernier, R. N.; Brennen, C. E.
1983-01-01
The use of the transverse field electromagnetic meter for two-phase flows is investigated. It is shown both experimentally and theoretically that this device measures the average velocity of the continuous liquid phase provided this has some minimum electrical conductivity. The calibration is quite independent of void fraction, flow regime, axisymmetric velocity profile, or the electrical conductivity of the continuous liquid phase. The dynamic capability of the meter for use in measuring uns...
Startup Characteristics of a Centrifugal Pump Delivering Gas-Liquid Two-Phase Flow
Yu-Liang Zhang; Jun-Jian Xiao; Jian-Ping Yu; Ying-Yu Ji
2014-01-01
The transient performance of centrifugal pumps during the startup period has drawn more and more attention in recent years due to urgent engineering needs. In order to make certain the transient startup characteristics of a high specific-speed prototype centrifugal pump delivering the gas-liquid two-phase flow, the transient flows inside the pump are numerically simulated during the startup period using the dynamic slip region method in this paper. The results show that the difference in head...
A new set of equations describing immiscible two-phase flow in homogeneous porous media
Hansen, Alex; Bedeaux, Dick; Kjelstrup, Signe; Savani, Isha; Vassvik, Morten
2016-01-01
Based on a simple scaling assumption concerning the total flow rate of immiscible two-phase flow in a homogeneous porous medium under steady-state conditions and a constant pressure drop, we derive two new equations that relate the total flow rate to the flow rates of each immiscible fluid. By integrating these equations, we present two integrals giving the flow rate of each fluid in terms of the the total flow rate. If we in addition assume that the flow obeys the relative permeability (generalized Darcy) equations, we find direct expressions for the two relative permeabilities and the capillary pressure in terms of the total flow rate. Hence, only the total flow rate as a function of saturation at constant pressure drop across the porous medium needs to be measured in order to obtain all three quantities. We test the equations on numerical and experimental systems.
Stochastic Discrete Equation Method (sDEM) for two-phase flows
International Nuclear Information System (INIS)
A new scheme for the numerical approximation of a five-equation model taking into account Uncertainty Quantification (UQ) is presented. In particular, the Discrete Equation Method (DEM) for the discretization of the five-equation model is modified for including a formulation based on the adaptive Semi-Intrusive (aSI) scheme, thus yielding a new intrusive scheme (sDEM) for simulating stochastic two-phase flows. Some reference test-cases are performed in order to demonstrate the convergence properties and the efficiency of the overall scheme. The propagation of initial conditions uncertainties is evaluated in terms of mean and variance of several thermodynamic properties of the two phases
An algebraic stress/flux model for two-phase turbulent flow
International Nuclear Information System (INIS)
An algebraic stress model (ASM) for turbulent Reynolds stress and a flux model for turbulent heat flux are proposed for two-phase bubbly and slug flows. These mathematical models are derived from the two-phase transport equations for Reynolds stress and turbulent heat flux, and provide Cμ, a turbulent constant which defines the level of eddy viscosity, as a function of the interfacial terms. These models also include the effect of heat transfer. When the interfacial drag terms and the interfacial momentum transfer terms are absent, the model reduces to a single-phase model used in the literature
Simulation of two-phase flows and numerical evaluation of interfacial area
International Nuclear Information System (INIS)
Rising bubbles are simulated numerically as one of the fundamental two-phase flow phenomena using the two-component two-phase lattice Boltzmann method, since sharp interfaces are obtained and the coalescence and breakup of bubbles are simulated easily. The variation of interfacial area is measured for one or two rising bubbles. It is found that the interfacial area decreases during the coalescence of two bubbles while it increases during the breakup of a bubble. The change in the interfacial area is shown to correspond to the change in the shape of the bubbles. (authors)
Simulation of two-phase flows and numerical evaluation of interfacial area
International Nuclear Information System (INIS)
Rising bubbles are simulated numerically as one of the fundamental two-phase flow phenomena using the two-component two-phase lattice Boltzmann method, since sharp interfaces are obtained and the coalescence and breakup of bubbles are simulated easily. The variation of interfacial area is measured for one or two rising bubbles. It is found that the interfacial area decreases during the coalescence of two bubbles while it increases during the breakup of a bubble. The change in the interfacial area is shown to correspond to the change in the shape of the bubbles. (author)
Stochastic Discrete Equation Method (sDEM) for two-phase flows
Energy Technology Data Exchange (ETDEWEB)
Abgrall, R., E-mail: remi.abgrall@inria.fr [Institut für Mathematik, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich (Switzerland); Congedo, P.M., E-mail: pietro.congedo@inria.fr [INRIA Bordeaux-Sud-Ouest, Equipe Cardamom, 200 Avenue de la Vieille Tour, 33405 Talence (France); Geraci, G., E-mail: ggeraci@stanford.edu [Flow Physics and Computational Engineering, Stanford University, 488 Escondido Mall, Building 500, Stanford, CA 94305-3035 (United States); Rodio, M.G., E-mail: maria-giovanna.rodio@inria.fr [INRIA Bordeaux-Sud-Ouest, Equipe Cardamom, 200 Avenue de la Vieille Tour, 33405 Talence (France)
2015-10-15
A new scheme for the numerical approximation of a five-equation model taking into account Uncertainty Quantification (UQ) is presented. In particular, the Discrete Equation Method (DEM) for the discretization of the five-equation model is modified for including a formulation based on the adaptive Semi-Intrusive (aSI) scheme, thus yielding a new intrusive scheme (sDEM) for simulating stochastic two-phase flows. Some reference test-cases are performed in order to demonstrate the convergence properties and the efficiency of the overall scheme. The propagation of initial conditions uncertainties is evaluated in terms of mean and variance of several thermodynamic properties of the two phases.
Validation of NEPTUNE-CFD two-phase flow models using experimental data
Jorge Pérez Mañes; Victor Hugo Sánchez Espinoza; Sergio Chiva Vicent; Michael Böttcher; Robert Stieglitz
2014-01-01
This paper deals with the validation of the two-phase flow models of the CFD code NEPTUNEC-CFD using experimental data provided by the OECD BWR BFBT and PSBT Benchmark. Since the two-phase models of CFD codes are extensively being improved, the validation is a key step for the acceptability of such codes. The validation work is performed in the frame of the European NURISP Project and it was focused on the steady state and transient void fraction tests. The influence of different NEPTUNE-CFD ...
Stratified two-phase flow pattern modulation in a horizontal tube by the mesh pore cylinder surface
International Nuclear Information System (INIS)
Highlights: ► A phase separation concept was proposed to modulate flow pattern in a tube. ► The cross section of the tube is divided into an annular region and an inner region. ► Stratified flow pattern was successfully modulated. ► Liquid can be within the mesh pore cylinder with gas contacting with the tube wall surface. ► The idea was expected to enhance the condensation heat transfer. - Abstract: Condensation heat transfer has been studied in the past century due to its wide applications in energy and power systems. The key scientific issue is the thick liquid thickness near the tube wall along the condenser tube length. The fabricated microstructures on the inner wall are the conventional technique to improve the performance. Here a passive phase separation concept was proposed to create distinct phase distribution. An empty cylinder made of a single layer of mesh pore surface was suspended in a tube, dividing the tube into an annular region and an inner region. The mesh pore surface prevents gas phase entering the inner region but sucks liquid towards the inner region. Thus largest possibility for gas directly contacted with the inner wall surface is ensured. An air/water two-phase flow experiment was performed and the stratified flow pattern modulation was investigated. When the liquid level in the horizontal tube is relatively higher, the liquid can be thoroughly within the mesh cylinder to form the “gas-floating-liquid” mode. The whole inner tube wall surface is covered by the gas phase. If the liquid content is relatively smaller, partial liquid can be sucked into the mesh cylinder. The contact area between the inner tube wall and gas is increased. The stratified flow pattern modulation is expected to significantly enhance the condensation heat transfer under low mass fluxes which is being verified by our continuous experiment
Two phase flow in a PWR vessel downcomer during a refill phase of LOCA
International Nuclear Information System (INIS)
The refill stage of the Hypothetical Loss of Coolant Accident (LOCA), of a Pressurized Water Reactor (PWR), has been the subject of considerable analysis and experimental study even through it is a very unlikely event. The Large Break Loss of Coolant Accident has been studied extensively in PWR systems to assess the effectiveness of the emergency core cooling system to maintain the fuel rods within safe temperature level. A particular phase of the transient, known as the Refill phase may be reached when the emergency core coolant, inject via the cold legs could be prevented from completely entering the core due to opposing flow of steam in the annular downcomer of the PWR vessel. Under certain conditions the upward flowing steam can hold-up the liquid and by-pass it around the downcomer annulus to the break. Experiments were performed at close to atmospheric pressure in a polycarbonate 1/10th - scale model of a typical four loop Westinghouse pressurized Water Reactor. The objective of the study was to identify hydraulic conditions and flow regimes that exist during the refill stage of a LOCA in the PWR downcomer, and to study the effects of various liquid inlet conditions (non-uniform liquid injection) into the downcomer on the flooding characteristics. The tests were performed using air and water at the working fluids to simulate the refill process under thermal equilibrium conditions. The effect of hot leg penetrations (blockages) on the flooding characteristics was also investigated and studied. The results were plotted using the Wallis J* parameter, and the mean annular circumference w (was used as the characteristic dimension). The flow regimes types and their spatial distribution in the PWR vessel downcomer for air-water counter-current flow were mapped, presented and discussed. The controlling mechanisms for the flooding were postulated and discussed. The flow pattern maps associated with various liquid modes were constructed. In addition the corresponding
Influence of the initial conditions for the numerical simulation of two-phase slug flow
Energy Technology Data Exchange (ETDEWEB)
Pachas Napa, Alex A.; Morales, Rigoberto E.M.; Medina, Cesar D. Perea
2010-07-01
Multiphase flows in pipelines commonly show several patterns depending on the flow rate, geometry and physical properties of the phases. In oil production, the slug flow pattern is the most common among the others. This flow pattern is characterized by an intermittent succession in space and time of an aerated liquid slug and an elongated gas bubble with a liquid film. Slug flow is studied through the slug tracking model described as one-dimensional and Lagrangian frame referenced. In the model, the mass and the momentum balance equations are applied in control volumes constituted by the gas bubble and the liquid slug. Initial conditions must be determined, which need to reproduce the intermittence of the flow pattern. These initial conditions are given by a sequence of flow properties for each unit cell. Properties of the unit cell in initial conditions should reflect the intermittence, for which they can be analyzed in statistical terms. Therefore, statistical distributions should be obtained for the slug flow variables. Distributions are complemented with the mass balance and the bubble design model. The objective of the present work is to obtain initial conditions for the slug tracking model that reproduce a better adjustment of the fluctuating properties for different pipe inclinations (horizontal, vertical or inclined). The numerical results are compared with experimental data obtained by PFG/FEM/UNICAMP for air-water flow at 0 deg, 45 deg and 90 deg and good agreement is observed. (author)
Two-phase flow measurements with 252Cf: Design aspects and considerations
International Nuclear Information System (INIS)
For many years 252Cf has been used for measuring moisture content, particularly in the ground's soil, by detecting the amount of slowing down (thermalization) of the source's fission neutrons by the hydrogen nuclei in water. The same concept has been employed for measuring the phase volume fraction in two-phase flows. Although two-phase boiling water measurements are in principle similar to those relating to moisture content, they present different challenges. Unlike the extended, stable, and reasonably uniform medium of the ground, two-phase flow measurements are conducted for a limited amount of fluid enclosed within a duct with metallic or polymer walls, and the phenomenon evolves with time, often rapidly, as phase transformation occurs in a heterogeneous fashion. These aspects demand special attention to design details. Although the principle of using neutron slowing down to measure hydrogen content is basic and straightforward, its application in a confined and evolving medium such as two-phase flow can be challenging. This paper identifies some of these challenges and presents some approaches for dealing with them
Approaches to myosin modelling in a two-phase flow model for cell motility
Kimpton, L. S.; Whiteley, J. P.; Waters, S. L.; Oliver, J. M.
2016-04-01
A wide range of biological processes rely on the ability of cells to move through their environment. Mathematical models have been developed to improve our understanding of how cells achieve motion. Here we develop models that explicitly track the cell's distribution of myosin within a two-phase flow framework. Myosin is a small motor protein which is important for contracting the cell's actin cytoskeleton and enabling cell motion. The two phases represent the actin network and the cytosol in the cell. We start from a fairly general description of myosin kinetics, advection and diffusion in the two-phase flow framework, then identify a number of sub-limits of the model that may be relevant in practice, two of which we investigate further via linear stability analyses and numerical simulations. We demonstrate that myosin-driven contraction of the actin network destabilizes a stationary steady state leading to cell motion, but that rapid diffusion of myosin and rapid unbinding of myosin from the actin network are stabilizing. We use numerical simulation to investigate travelling-wave solutions relevant to a steadily gliding cell and we consider a reduction of the model in which the cell adheres strongly to the substrate on which it is crawling. This work demonstrates that a number of existing models for the effect of myosin on cell motility can be understood as different sub-limits of our two-phase flow model.
Liquid fraction measurement by wire-mesh sensor in air-water stratified flows
International Nuclear Information System (INIS)
In this study, we carried out experiments for measuring the liquid fraction by using the commercial wire-mesh sensor which consists of 16x16 wires and high-speed camera in air-water stratified flows. For evaluating the accuracy of the wire-mesh sensor, static experiment was performed. Also the liquid fractions measured by the wire-mesh sensor in horizontal loop that pipe has inner diameter 40 mm and length is 5 m was compared with that by the high-speed camera. Deviation for the liquid fraction between the wire-mesh sensor and the high-speed camera is 0.02, small. Also it seems to have good agreements since it is showing similar trend. (author)
Modeling and numerical analysis of non-equilibrium two-phase flows
International Nuclear Information System (INIS)
We are interested in the numerical approximation of two-fluid models of nonequilibrium two-phase flows described by six balance equations. We introduce an original splitting technique of the system of equations. This technique is derived in a way such that single phase Riemann solvers may be used: moreover, it allows a straightforward extension to various and detailed exchange source terms. The properties of the fluids are first approached by state equations of ideal gas type and then extended to real fluids. For the construction of numerical schemes , the hyperbolicity of the full system is not necessary. When based on suitable kinetic unwind schemes, the algorithm can compute flow regimes evolving from mixture to single phase flows and vice versa. The whole scheme preserves the physical features of all the variables which remain in the set of physical states. Several stiff numerical tests, such as phase separation and phase transition are displayed in order to highlight the efficiency of the proposed method. The document is a PhD thesis divided in 6 chapters and two annexes. They are entitled: 1. - Introduction (in French), 2. - Two-phase flow, modelling and hyperbolicity (in French), 3. - A numerical method using upwind schemes for the resolution of two-phase flows without exchange terms (in English), 4. - A numerical scheme for one-phase flow of real fluids (in English), 5. - An upwind numerical for non-equilibrium two-phase flows (in English), 6. - The treatment of boundary conditions (in English), A.1. The Perthame scheme (in English) and A.2. The Roe scheme (in English)
Single- and Two-Phase Flow Characterization Using Optical Fiber Bragg Gratings
Directory of Open Access Journals (Sweden)
Virgínia H.V. Baroncini
2015-03-01
Full Text Available Single- and two-phase flow characterization using optical fiber Bragg gratings (FBGs is presented. The sensor unit consists of the optical fiber Bragg grating positioned transversely to the flow and fixed in the pipe walls. The hydrodynamic pressure applied by the liquid or air/liquid flow to the optical fiber induces deformation that can be detected by the FBG. Given that the applied pressure is directly related to the mass flow, it is possible to establish a relationship using the grating resonance wavelength shift to determine the mass flow when the flow velocity is well known. For two phase flows of air and liquid, there is a significant change in the force applied to the fiber that accounts for the very distinct densities of these substances. As a consequence, the optical fiber deformation and the correspondent grating wavelength shift as a function of the flow will be very different for an air bubble or a liquid slug, allowing their detection as they flow through the pipe. A quasi-distributed sensing tool with 18 sensors evenly spread along the pipe is developed and characterized, making possible the characterization of the flow, as well as the tracking of the bubbles over a large section of the test bed. Results show good agreement with standard measurement methods and open up plenty of opportunities to both laboratory measurement tools and field applications.
Flow pattern based correlations of two-phase pressure drop in rectangular microchannels
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Choi, Chiwoong, E-mail: chiwoongchoi@gmail.com [Department of Mechanical Engineering, Pohang University of Science and Technology, Pohang, San 31, Hyoja Dong 790-784 (Korea, Republic of); Kim, Moohwan [Department of Mechanical Engineering, Pohang University of Science and Technology, Pohang, San 31, Hyoja Dong 790-784 (Korea, Republic of)
2011-12-15
Highlights: Black-Right-Pointing-Pointer Glass microchannels with embedded pressure ports were fabricated to obtain accurate measurements. Black-Right-Pointing-Pointer The assessments of seven HFM (Homogeneous Flow Model) and ten SFM (Separated Flow Model) were conducted. Black-Right-Pointing-Pointer The results indicate models shows best estimations. Black-Right-Pointing-Pointer In addition, the pressure drop is well agreed with flow pattern tendency. Black-Right-Pointing-Pointer Based on two-phase flow patterns, new correlations were proposed for both homogeneous and separated flow types. - Abstract: Numerous pressure drop correlations for microchannels have been proposed; most of them can be classified as either a homogeneous flow model (HFM) or a separated flow model (SFM). However, the predictions of these correlations have not been compared directly because they were developed in experiments conducted under a range of conditions, including channel shape, the number of channels, channel material and the working fluid. In this study, single rectangular microchannels with different aspect ratios and hydraulic diameters were fabricated in a photosensitive glass. Adiabatic water-liquid and Nitrogen-gas two-phase flow experiments were conducted using liquid superficial velocities of 0.06-1.0 m/s, gas superficial velocities of 0.06-72 m/s and hydraulic diameters of 141, 143, 304, 322 and 490 {mu}m. A pressure drop in microchannels was directly measured through embedded ports. The flow pattern was visualized using a high-speed camera and a long-distance microscope. A two-phase pressure drop in the microchannel was highly related to the flow pattern. Data were used to assess seven different HFM viscosity models and ten SFM correlations, and new correlations based on flow patterns were proposed for both HFMs and SFMs.
Flow pattern based correlations of two-phase pressure drop in rectangular microchannels
International Nuclear Information System (INIS)
Highlights: ► Glass microchannels with embedded pressure ports were fabricated to obtain accurate measurements. ► The assessments of seven HFM (Homogeneous Flow Model) and ten SFM (Separated Flow Model) were conducted. ► The results indicate models shows best estimations. ► In addition, the pressure drop is well agreed with flow pattern tendency. ► Based on two-phase flow patterns, new correlations were proposed for both homogeneous and separated flow types. - Abstract: Numerous pressure drop correlations for microchannels have been proposed; most of them can be classified as either a homogeneous flow model (HFM) or a separated flow model (SFM). However, the predictions of these correlations have not been compared directly because they were developed in experiments conducted under a range of conditions, including channel shape, the number of channels, channel material and the working fluid. In this study, single rectangular microchannels with different aspect ratios and hydraulic diameters were fabricated in a photosensitive glass. Adiabatic water-liquid and Nitrogen-gas two-phase flow experiments were conducted using liquid superficial velocities of 0.06–1.0 m/s, gas superficial velocities of 0.06–72 m/s and hydraulic diameters of 141, 143, 304, 322 and 490 μm. A pressure drop in microchannels was directly measured through embedded ports. The flow pattern was visualized using a high-speed camera and a long-distance microscope. A two-phase pressure drop in the microchannel was highly related to the flow pattern. Data were used to assess seven different HFM viscosity models and ten SFM correlations, and new correlations based on flow patterns were proposed for both HFMs and SFMs.
1-D Two-phase Flow Investigation for External Reactor Vessel Cooling
International Nuclear Information System (INIS)
During a severe accident, when a molten corium is relocated in a reactor vessel lower head, the RCF(Reactor Cavity Flooding) system for ERVC (External Reactor Vessel Cooling) is actuated and coolants are supplied into a reactor cavity to remove a decay heat from the molten corium. This severe accident mitigation strategy for maintaining a integrity of reactor vessel was adopted in the nuclear power plants of APR1400, AP600, and AP1000. Under the ERVC condition, the upward two-phase flow is driven by the amount of the decay heat from the molten corium. To achieve the ERVC strategy, the two-phase natural circulation in the annular gap between the external reactor vessel and the insulation should be formed sufficiently by designing the coolant inlet/outlet area and gap size adequately on the insulation device. Also the natural circulation flow restriction has to be minimized. In this reason, it is needed to review the fundamental structure of insulation. In the existing power plants, the insulation design is aimed at minimizing heat losses under a normal operation. Under the ERVC condition, however, the ability to form the two-phase natural circulation is uncertain. Namely, some important factors, such as the coolant inlet/outlet areas, flow restriction, and steam vent etc. in the flow channel, should be considered for ERVC design. T-HEMES 1D study is launched to estimate the natural circulation flow under the ERVC condition of APR1400. The experimental facility is one-dimensional and scaled down as the half height and 1/238 channel area of the APR1400 reactor vessel. The air injection method was used to simulate the boiling at the external reactor vessel and generate the natural circulation two-phase flow. From the experimental results, the natural circulation flow rate highly depended on inlet/outlet areas and the circulation flow rate increased as the outlet height as well as the supplied water head increased. On the other hand, the simple analysis using the drift
Simulation of horizontal pipe two-phase slug flows using the two-fluid model
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Ortega Malca, Arturo J. [Pontificia Univ. Catolica do Rio de Janeiro, RJ (Brazil). Dept. de Engenharia Mecanica. Nucleo de Simulacao Termohidraulica de Dutos (SIMDUT); Nieckele, Angela O. [Pontificia Univ. Catolica do Rio de Janeiro, RJ (Brazil). Dept. de Engenharia Mecanica
2005-07-01
Slug flow occurs in many engineering applications, mainly in the transport of hydrocarbon fluids in pipelines. The intermittency of slug flow causes severe unsteady loading on the pipelines carrying the fluids, which gives rise to design problems. Therefore, it is important to be able to predict the onset and development of slug flow as well as slug characteristics. The present work consists in the simulation of two-phase flow in slug pattern through horizontal pipes using the two-fluid model in its transient and one-dimensional form. The advantage of this model is that the flow field is allowed to develop naturally from a given initial conditions as part of the transient calculation; the slug evolves automatically as a product of the computed flow development. Simulations are then carried out for a large number of flow conditions that lead a slug flow. (author)
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)
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Vallee, Christophe
2012-08-22
Stratified two-phase flows were investigated at different test facilities with horizontal test sections in order to provide an experimental database for the development and validation of computational fluid dynamics (CFD) codes. These channels were designed with rectangular cross-sections to enable optimal observation conditions for the application of optical measurement techniques. Consequently, the local flow structure was visualised with a high-speed video camera, delivering data with highresolution in space and time as needed for CFD code validation. Generic investigations were performed at atmospheric pressure and room temperature in two air/water channels made of acrylic glass. Divers preliminary experiments were conducted with various measuring systems in a test section mounted between two separators. The second test facility, the Horizontal Air/Water Channel (HAWAC), is dedicated to co-current flow investigations. The hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was studied in this closed channel. Moreover, the instable wave growth leading to slug flow was investigated from the test section inlet. For quantitative analysis of the optical measurements, an algorithm was developed to recognise the stratified interface in the camera frames, allowing statistical treatments for comparison with CFD calculation results. The third test apparatus was installed in the pressure chamber of the TOPFLOW test facility in order to be operated at reactor typical conditions under pressure equilibrium with the vessel atmosphere. The test section representing a flat model of the hot leg of the German Konvoi pressurised water reactor (PWR) scaled at 1:3 is equipped with large glass side walls in the region of the elbow and of the steam generator inlet chamber to allow visual observations. The experiments were conducted with air and water at room temperature and maximum pressures of 3 bar as well as with steam and water at
International Nuclear Information System (INIS)
Stratified two-phase flows were investigated at different test facilities with horizontal test sections in order to provide an experimental database for the development and validation of computational fluid dynamics (CFD) codes. These channels were designed with rectangular cross-sections to enable optimal observation conditions for the application of optical measurement techniques. Consequently, the local flow structure was visualised with a high-speed video camera, delivering data with highresolution in space and time as needed for CFD code validation. Generic investigations were performed at atmospheric pressure and room temperature in two air/water channels made of acrylic glass. Divers preliminary experiments were conducted with various measuring systems in a test section mounted between two separators. The second test facility, the Horizontal Air/Water Channel (HAWAC), is dedicated to co-current flow investigations. The hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was studied in this closed channel. Moreover, the instable wave growth leading to slug flow was investigated from the test section inlet. For quantitative analysis of the optical measurements, an algorithm was developed to recognise the stratified interface in the camera frames, allowing statistical treatments for comparison with CFD calculation results. The third test apparatus was installed in the pressure chamber of the TOPFLOW test facility in order to be operated at reactor typical conditions under pressure equilibrium with the vessel atmosphere. The test section representing a flat model of the hot leg of the German Konvoi pressurised water reactor (PWR) scaled at 1:3 is equipped with large glass side walls in the region of the elbow and of the steam generator inlet chamber to allow visual observations. The experiments were conducted with air and water at room temperature and maximum pressures of 3 bar as well as with steam and water at
International Nuclear Information System (INIS)
The upper limit to countercurrent flow, namely, flooding, is important to analyze the reactor coolability during an emergency cooling system (ECS) phase as a result of a large-break loss-of-coolant accident (LOCA) such as a double-ended guillotine break in the Savannah River Site (SRS) reactor system. During normal operation, the reactor coolant system utilizes downward flow through concentric heated tubes with ribs, which subdivided each annular channel into four subchannels. In this paper, a new flooding correlation has been developed based on the analytical models and literature data for adiabatic, steady-state, one-dimensional, air-water flow to predict flooding phenomenon in the SRS reactor assembly channel, which may have a counter-current air-water flow pattern during the ECS phase. In addition, the correlation was benchmarked against the experimental data conducted under the Oak Ridge National Laboratory multislit channel, which is close to the SRS assembly geometry. Furthermore, the correlation has also been used as a constitutive relationship in a new two-component two-phase thermal-hydraulics code FLOWTRAN-TF, which has been developed for a detailed analysis of SRS reactor assembly behavior during LOCA scenarios. Finally, the flooding correlation was applied to the predictions of critical heat flux, and the results were compared with the data taken by the SRS heat transfer laboratory under a single annular channel with ribs and a multiannular prototypic test rig
Modelling of the steam generator secondary side two-phase flow with the fluent-4.5.2 code
International Nuclear Information System (INIS)
The CFD analysis methods have been extensively used for the single-phase flow calculations. In the paper the possibilities to expand the calculation capability is discussed. The needs for the more detailed void fraction and temperature distribution data from the secondary side is apparent. Diverse methods in the past have been used in the system codes or in the separate codes to take into account the effect of the multidimensional void fraction and temperature field to the steady state and transient performances of the horizontal steam generators. But the most detailed models are only multidimensional lumped parameter models, however. At first the Eulerian multiphase model in Fluent-4.5.2 is described through the basic equations. After that the adjustment of the two-phase model with the air-water experimental data is described. The studies for the numerical behaviour of Fluent-4.5.2 with sample test cases are further illustrated. After that modelling of the secondary tube sheet area and water level in Fluent-4.5.2 is closer considered. The calculation results for the two-dimensional case over the steam generator cross section is considered at first. After the calculation results for the three-dimensional case are considered closer. The future plans for the modelling are discussed at the end. (orig.)
Experimental study of micron size droplets in a two phase flow in a converging - diverging nozzle
International Nuclear Information System (INIS)
The fluid present in a pressurized vessel in normal operation is generally a mono-phase one. In accidental regime (a breach for example), a two-phase (ring and/or dispersed) flow appears and the flow is submitted to large accelerations when passing through the breach, and is then dispersed in the atmosphere. This research thesis reports an experimental simulation of an accident by generating, through a discharge of an upstream vessel into a downstream vessel, a strongly accelerated gaseous-liquid two-phase flow, with an essentially dispersed configuration in a convergent-divergent nozzle. In order to characterize the speed and diameter evolution of the dispersed liquid phase, the author reports a comparative study of two different liquid aerosols: micron-size droplets of di-octyl phthalate (DOP) of known concentration and diameter, and water droplets obtained by heterogeneous spontaneous condensation
Energy Technology Data Exchange (ETDEWEB)
Laribi, S. (SONATRACH Centre de Recherche et Developpement, Boumerdes (Algeria)); Bertin, H.; Quintard, M. (Laboratoire ' Energetique et Phenomenes de Transfert' -ENSAM, URA CNRS 873, Talence (France))
1995-01-01
Experimental and theoretical results for two-phase flow in vertically stratified systems, the flow being normal to the strata, are presented. The experimental study is focused on the following points: (a) the initial oil-drainage process and the evolution of the water distribution during the capillary equilibrium process, and (b) the time evolution of the saturation fields during water-flooding experiments. Saturation fields were measured using a [gamma]-rays attenuation system. The physics of two-phase flow through vertically stratified porous media can be analysed by a large-scale averaging method. This methodology is described briefly; reference is made to previous publications for detailed presentation. The water-flooding experiments were interpreted using the large-scale averaging method, first in the quasi-static case, second using a simplified closure problem taking into account dynamic effects. The results show a better agreement between experimental and theoretical results when dynamic effects are taken into account
A two-phase solid/fluid model for dense granular flows including dilatancy effects
Mangeney, Anne; Bouchut, Francois; Fernandez-Nieto, Enrique; Koné, El-Hadj; Narbona-Reina, Gladys
2016-04-01
Describing grain/fluid interaction in debris flows models is still an open and challenging issue with key impact on hazard assessment [{Iverson et al.}, 2010]. We present here a two-phase two-thin-layer model for fluidized debris flows that takes into account dilatancy effects. It describes the velocity of both the solid and the fluid phases, the compression/dilatation of the granular media and its interaction with the pore fluid pressure [{Bouchut et al.}, 2016]. The model is derived from a 3D two-phase model proposed by {Jackson} [2000] based on the 4 equations of mass and momentum conservation within the two phases. This system has 5 unknowns: the solid and fluid velocities, the solid and fluid pressures and the solid volume fraction. As a result, an additional equation inside the mixture is necessary to close the system. Surprisingly, this issue is inadequately accounted for in the models that have been developed on the basis of Jackson's work [{Bouchut et al.}, 2015]. In particular, {Pitman and Le} [2005] replaced this closure simply by imposing an extra boundary condition at the surface of the flow. When making a shallow expansion, this condition can be considered as a closure condition. However, the corresponding model cannot account for a dissipative energy balance. We propose here an approach to correctly deal with the thermodynamics of Jackson's model by closing the mixture equations by a weak compressibility relation following {Roux and Radjai} [1998]. This relation implies that the occurrence of dilation or contraction of the granular material in the model depends on whether the solid volume fraction is respectively higher or lower than a critical value. When dilation occurs, the fluid is sucked into the granular material, the pore pressure decreases and the friction force on the granular phase increases. On the contrary, in the case of contraction, the fluid is expelled from the mixture, the pore pressure increases and the friction force diminishes. To
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
Analysis of nanoscale two-phase flow of argon using molecular dynamics
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Verma, Abhishek Kumar; Kumar, Rakesh [Department of Aerospace Engineering, Indian Institute of Technology Kanpur, Kanpur - 208016 (India)
2014-12-09
Two phase flows through micro and nanochannels have attracted a lot of attention because of their immense applicability to many advanced fields such as MEMS/NEMS, electronic cooling, bioengineering etc. In this work, a molecular dynamics simulation method is employed to study the condensation process of superheated argon vapor force driven flow through a nanochannel combining fluid flow and heat transfer. A simple and effective particle insertion method is proposed to model phase change of argon based on non-periodic boundary conditions in the simulation domain. Starting from a crystalline solid wall of channel, the condensation process evolves from a transient unsteady state where we study the influence of different wall temperatures and fluid wall interactions on interfacial and heat transport properties of two phase flows. Subsequently, we analyzed transient temperature, density and velocity fields across the channel and their dependency on varying wall temperature and fluid wall interaction, after a dynamic equilibrium is achieved in phase transition. Quasi-steady nonequilibrium temperature profile, heat flux and interfacial thermal resistance were analyzed. The results demonstrate that the molecular dynamics method, with the proposed particle insertion method, effectively solves unsteady nonequilibrium two phase flows at nanoscale resolutions whose interphase between liquid and vapor phase is typically of the order of a few molecular diameters.
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.
Analysis of nanoscale two-phase flow of argon using molecular dynamics
International Nuclear Information System (INIS)
Two phase flows through micro and nanochannels have attracted a lot of attention because of their immense applicability to many advanced fields such as MEMS/NEMS, electronic cooling, bioengineering etc. In this work, a molecular dynamics simulation method is employed to study the condensation process of superheated argon vapor force driven flow through a nanochannel combining fluid flow and heat transfer. A simple and effective particle insertion method is proposed to model phase change of argon based on non-periodic boundary conditions in the simulation domain. Starting from a crystalline solid wall of channel, the condensation process evolves from a transient unsteady state where we study the influence of different wall temperatures and fluid wall interactions on interfacial and heat transport properties of two phase flows. Subsequently, we analyzed transient temperature, density and velocity fields across the channel and their dependency on varying wall temperature and fluid wall interaction, after a dynamic equilibrium is achieved in phase transition. Quasi-steady nonequilibrium temperature profile, heat flux and interfacial thermal resistance were analyzed. The results demonstrate that the molecular dynamics method, with the proposed particle insertion method, effectively solves unsteady nonequilibrium two phase flows at nanoscale resolutions whose interphase between liquid and vapor phase is typically of the order of a few molecular diameters
Computational Analysis of a Two-phase Flow with an Interfacial Area Transport Equation
International Nuclear Information System (INIS)
For the analysis of a two-phase flow with boiling or condensation, the interaction between two phases such as the interfacial momentum or heat transfer is proportional to the interfacial area. So the interfacial area concentration (IAC), which is defined as the area of interface per unit volume, is one of the most important parameters governing the behavior of each phase. IAC transport equation has been developed for the adiabatic bubbly flow or nucleate boiling flow. It describes the transport phenomena of the IAC with the source term for adiabatic interaction and phase change. In order to implement the IAC transport equation and analyze the characteristics of a two-phase flow, this study focuses on the development of a computational fluid dynamics (CFD) code for investigating a boiling flow with a two-fluid model. As the step for checking the robustness of the developed code, the experiment of a subcooled boiling in a vertical annulus channel was analyzed to validate the capability of the IAC transport equation
Two-Phase Flow Simulations In a Natural Rock Fracture using the VOF Method
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Crandall, Dustin; Ahmadi, Goodarz; Smith, Duane H., Bromhal, Grant
2010-01-01
Standard models of two-phase flow in porous media have been shown to exhibit several shortcomings that might be partially overcome with a recently developed model based on thermodynamic principles (Hassanizadeh and Gray, 1990). This alternative two-phase flow model contains a set of new and non-standard parameters, including specific interfacial area. By incorporating interfacial area production, destruction, and propagation into functional relationships that describe the capillary pressure and saturation, a more physical model has been developed. Niessner and Hassanizadeh (2008) have examined this model numerically and have shown that the model captures saturation hysteresis with drainage/imbibition cycles. Several static experimental studies have been performed to examine the validity of this new thermodynamically based approach; these allow the determination of static parameters of the model. To date, no experimental studies have obtained information about the dynamic parameters required for the model. A new experimental porous flow cell has been constructed using stereolithography to study two-phase flow phenomena (Crandall et al. 2008). A novel image analysis tool was developed for an examination of the evolution of flow patterns during displacement experiments (Crandall et al. 2009). This analysis tool enables the direct quantification of interfacial area between fluids by matching known geometrical properties of the constructed flow cell with locations identified as interfaces from images of flowing fluids. Numerous images were obtained from two-phase experiments within the flow cell. The dynamic evolution of the fluid distribution and the fluid-fluid interface locations were determined by analyzing these images. In this paper, we give a brief introduction to the thermodynamically based two-phase flow model, review the properties of the stereolithography flow cell, and show how the image analysis procedure has been used to obtain dynamic parameters for the
Two-Phase Flow Simulations In a Natural Rock Fracture using the VOF Method
International Nuclear Information System (INIS)
Standard models of two-phase flow in porous media have been shown to exhibit several shortcomings that might be partially overcome with a recently developed model based on thermodynamic principles (Hassanizadeh and Gray, 1990). This alternative two-phase flow model contains a set of new and non-standard parameters, including specific interfacial area. By incorporating interfacial area production, destruction, and propagation into functional relationships that describe the capillary pressure and saturation, a more physical model has been developed. Niessner and Hassanizadeh (2008) have examined this model numerically and have shown that the model captures saturation hysteresis with drainage/imbibition cycles. Several static experimental studies have been performed to examine the validity of this new thermodynamically based approach; these allow the determination of static parameters of the model. To date, no experimental studies have obtained information about the dynamic parameters required for the model. A new experimental porous flow cell has been constructed using stereolithography to study two-phase flow phenomena (Crandall et al. 2008). A novel image analysis tool was developed for an examination of the evolution of flow patterns during displacement experiments (Crandall et al. 2009). This analysis tool enables the direct quantification of interfacial area between fluids by matching known geometrical properties of the constructed flow cell with locations identified as interfaces from images of flowing fluids. Numerous images were obtained from two-phase experiments within the flow cell. The dynamic evolution of the fluid distribution and the fluid-fluid interface locations were determined by analyzing these images. In this paper, we give a brief introduction to the thermodynamically based two-phase flow model, review the properties of the stereolithography flow cell, and show how the image analysis procedure has been used to obtain dynamic parameters for the
Design and construction of an experiment for two-phase flow in fractured porous media
Energy Technology Data Exchange (ETDEWEB)
Ayala, R.E.G.; Aziz, K.
1993-08-01
In numerical reservoir simulation naturally fractured reservoirs are commonly divided into matrix and fracture systems. The high permeability fractures are usually entirely responsible for flow between blocks and flow to the wells. The flow in these fractures is modeled using Darcy`s law and its extension to multiphase flow by means of relative permeabilities. The influence and measurement of fracture relative permeability for two-phase flow in fractured porous media have not been studied extensively, and the few works presented in the literature are contradictory. Experimental and numerical work on two-phase flow in fractured porous media has been initiated. An apparatus for monitoring this type of flow was designed and constructed. It consists of an artificially fractured core inside an epoxy core holder, detailed pressure and effluent monitoring, saturation measurements by means of a CT-scanner and a computerized data acquisition system. The complete apparatus was assembled and tested at conditions similar to the conditions expected for the two-phase flow experiments. Fine grid simulations of the experimental setup-were performed in order to establish experimental conditions and to study the effects of several key variables. These variables include fracture relative permeability and fracture capillary pressure. The numerical computations show that the flow is dominated by capillary imbibition, and that fracture relative permeabilities have only a minor influence. High oil recoveries without water production are achieved due to effective water imbibition from the fracture to the matrix. When imbibition is absent, fracture relative permeabilities affect the flow behavior at early production times.
Conceptual plan: Two-Phase Flow Laboratory Program for the Waste Isolation Pilot Plant
Energy Technology Data Exchange (ETDEWEB)
Howarth, S.M.
1993-07-01
The Salado Two-Phase Flow Laboratory Program was established to address concerns regarding two-phase flow properties and to provide WIPP-specific, geologically consistent experimental data to develop more appropriate correlations for Salado rock to replace those currently used in Performance Assessment models. Researchers in Sandia`s Fluid Flow and Transport Department originally identified and emphasized the need for laboratory measurements of Salado threshold pressure and relative permeability. The program expanded to include the measurement of capillary pressure, rock compressibility, porosity, and intrinsic permeability and the assessment of core damage. Sensitivity analyses identified the anhydrite interbed layers as the most likely path for the dissipation of waste-generated gas from waste-storage rooms because of their relatively high permeability. Due to this the program will initially focus on the anhydrite interbed material. The program may expand to include similar rock and flow measurements on other WIPP materials including impure halite, pure halite, and backfill and seal materials. This conceptual plan presents the scope, objectives, and historical documentation of the development of the Salado Two-Phase Flow Program through January 1993. Potential laboratory techniques for assessing core damage and measuring porosity, rock compressibility, capillary and threshold pressure, permeability as a function of stress, and relative permeability are discussed. Details of actual test designs, test procedures, and data analysis are not included in this report, but will be included in the Salado Two-Phase Flow Laboratory Program Test Plan pending the results of experimental and other scoping activities in FY93.
Modeling of Two-Phase Flow through a Rotating Tube with Twin Exit Branches
Directory of Open Access Journals (Sweden)
Sun-Wen Cheng
2000-01-01
Full Text Available A numerical model is proposed to determine the dynamic behavior of single-phase and twophase, two-component flows through a horizontal rotating tube with identical twin exit branches. The working fluid, oil, enters the tube through a radial duct attached at one end and exits into open air through the twin radial branches, one located at midway and the other at the end of the tube. The branch-to-tube diameter ratio, rotational speed, and total oil flow rate are varied. It is experimentally revealed in previous study that the air cavitation occurs at lower speeds, leading to a two-phase flow with the air-oil ratio (void fraction varying with the rotating speed. A unique characteristic in two-phase flow, i.e., hysteresis, is found to exist in both oil flow rates and inlet pressure. In theoretical modeling, the governing flow equations are incorporated by empirical equations for hydraulic head losses. The predicted and measured exit oil flow rates are compared with good agreement in both the single-phase and annular flow regimes. Only qualitative agreement is achieved in the bubbly and bubbly-slug flow regimes. The model can be applied to improve the design and thus enhance the performance of automatic transmission lines, and the cooling efficiency of rotating machines and petroleum drilling process.
Numerical study of bubble generation in a turbulent two-phase Couette flow
Ovsyannikov, Andrey; Mani, Ali; Moin, Parviz; Kim, Dokyun
2014-11-01
The objective of this work is to develop an understanding bubble generation mechanism due to interactions between free surfaces and turbulent boundary layers as commonly seen near ship walls. To this end, we have focused on a canonical problem that involves Couette flow between two vertical parallel walls with an air-water interface in between. We have considered flow at Reynolds number of 8000 and Froude number of 3.6, both based on half domain dimension and water properties. Our calculations resolve both Kolmogorov lengths and the Hinze scale. Additionally, a conservative VOF method coupled to a subgrid Lagrangian breakup model is used to represent the ligament breakup phenomena and their resulting bubbles and drops. We will present results from these calculations revealing bubble formation rates, bubble size distribution, and effects of bubbles on modulation of turbulence Supported by ONR.
Distribution characteristics of pollutant transport in a turbulent two-phase flow.
Khaldi, Nawel; Marzouk, Salwa; Mhiri, Hatem; Bournot, Philippe
2015-04-01
The distribution characteristics of pollutants released at varied rates and different vertical inlet positions of an open channel are investigated via a three-dimensional numerical model. Pollutants are injected from time-dependent sources in a turbulent free-surface flow. Numerical computations were carried out using Fluent 6.3, which is based on the finite volume approach. The air/water interface was modeled with the volume of fluid method (VOF). By focusing on investigating the influences of the flow on pollutants, it is found that with an increase of the injection rate, the pollutant concentration increases along the channel and the longitudinal dispersion is higher. On the other hand, it is noted that the point of injection modifies significantly the dispersion pattern of pollutant. These findings may be of great help in cost-effective scientific countermeasures to be taken into account for accident or planned pollutants discharged into a river. PMID:25567054
Measurements of local interfacial area concentration in two-phase bubbly flow
International Nuclear Information System (INIS)
The local interfacial characteristics of an air-water, bubbly upflow in a circular pipe has been investigated experimentally cased on the measurements of a miniature two-sensor resistivity probe. Radial profiles of interfacial area concentration (IAC), together with other structural parameters (void fraction, bubble frequency, bubble velocity and Sauter mean bubble diameter) were simultaneously measured at four axial positions with entrance length (L)-to-internal diameter (D) ratios of 30, 60, 90 and 120. The experiments were carried out under various fixed gas and liquid fluxes, with only the bubble size being changed at the flow entrance. It is found that the phase distribution ana IAC are very sensitive to the variation oi the bubble size and the bubble coalescence effects during the development of bubbly flow. This paper summarizes the experimental results on the associated local interfacial parameters and compares the present data with the existing models used in predicting the IAC. (author)
Effects of Particles Collision on Separating Gas–Particle Two-Phase Turbulent Flows
Sihao, L. V.
2013-10-10
A second-order moment two-phase turbulence model incorporating a particle temperature model based on the kinetic theory of granular flow is applied to investigate the effects of particles collision on separating gas–particle two-phase turbulent flows. In this model, the anisotropy of gas and solid phase two-phase Reynolds stresses and their correlation of velocity fluctuation are fully considered using a presented Reynolds stress model and the transport equation of two-phase stress correlation. Experimental measurements (Xu and Zhou in ASME-FED Summer Meeting, San Francisco, Paper FEDSM99-7909, 1999) are used to validate this model, source codes and prediction results. It showed that the particles collision leads to decrease in the intensity of gas and particle vortices and takes a larger effect on particle turbulent fluctuations. The time-averaged velocity, the fluctuation velocity of gas and particle phase considering particles colli-sion are in good agreement with experimental measurements. Particle kinetic energy is always smaller than gas phase due to energy dissipation from particle collision. Moreover, axial– axial and radial–radial fluctuation velocity correlations have stronger anisotropic behaviors. © King Fahd University of Petroleum and Minerals 2013
Hydrodynamics of two phase flow through homogeneous and stratified porous layers
International Nuclear Information System (INIS)
An experimental investigation of two-phase flow through porous layers formed of nonheated glass particles has been made. The effect of particle size, particle size distribution, bed porosity and bed stratification on void fraction and pressure drop through particulate beds formed in a cylindrical and rectangular test section has been investigated. A model based on drift flux approach has been developed for the void fraction in homogeneous beds. Using the two phase friction pressure drop data, the relative permeabilities of the two phases have been concluded with void fraction. The void fraction and two-phase friction pressure gradient in beds composed of mixtures of spherical particles as well as sharps of different nominal sizes have also been examined. It is found that the models for single size particles are also applicable to mixtures of particles if a mean particle diameter for the mixture is defined. The observations in stratified beds indicate depletion or build up of voids at the interface between high and low permeability regions. Blocking of the flow into one of the layers of laterally stratified beds caused the pressures at different horizontal locations at the same bed height to be different from each other