NASA Astrophysics Data System (ADS)
Zhou, L.-X.; Liu, Y.; Xu, Y.
2011-08-01
In this paper the present authors measured the gas-particle two-phase velocity correlation in sudden expansion gas-particle flows with a phase Doppler particle anemometer (PDPA) and simulated the system behavior by using both a Reynolds-averaged Navier-Stokes (RANS) model and a large-eddy simulation (LES). The results of the measurements yield the axial and radial time-averaged velocities as well as the fluctuation velocities of gas and three particle-size groups (30 µm, 50 µm, and 95 µm) and the gas-particle velocity correlation for 30 µm and 50 µm particles. From the measurements, theoretical analysis, and simulation, it is found that the two-phase velocity correlation of sudden-expansion flows, like that of jet flows, is less than the gas and particle Reynolds stresses. What distinguishes the two-phase velocity correlations of sudden-expansion flow from those of jet and channel flows is the absence of a clear relationship between the two-phase velocity correlation and particle size in sudden-expansion flows. The measurements, theoretical analysis, and numerical simulation all lead to the above-stated conclusions. Quantitatively, the results of the LES are better than those of the RANS model.
NASA Technical Reports Server (NTRS)
Tacina, Robert R.
1986-01-01
An experimental program to characterize the spray from candidate nozzles for icing-cloud simulation is discussed. One canidate nozzle, which is currently used for icing research, has been characterized for flow and drop size. The median-volume diameter (MVD) from this air-assist nozzle is compared with correlations in the literature. The new experimental spray facility is discussed, and the drop-size instruments are discussed in detail. Since there is no absolute standard for drop-size measurements and there are other limitations, such as drop -size range and velocity range, several instruments are used and results are compared. A two-phase model was developed at Pennsylvania State University. The model uses the k-epsilon model of turbulence in the continous phase. Three methods for treating the discrete phase are used: (1) a locally homogeneous flow (LHF) model, (2) a deterministic separated flow (DSF) model, and (3) a stochastic separated flow (SSF) model. In the LHF model both phases have the same velocity and temperature at each point. The DSF model provides interphase transport but ignores the effects of turbulent fluctuations. In the SSF model the drops interact with turbulent eddies whose properties are determined by the k-epsilon turbulence model. The two-phase flow model has been extended to include the effects of evaporation and combustion.
NASA Astrophysics Data System (ADS)
Zhou, Lixing
2007-06-01
The phase Doppler particle anemometer (PDPA) made by both Aerometrcis Inc. and Dantec Inc. are used to measure the time-averaged gas and particle velocities, RMS values of gas and particle fluctuation velocities, gas-particle velocity correlations, gas turbulence modification and particle concentration for turbulent swirling and non-swirling gas-particle flows and also gas-particle flows with combustion in the Laboratory of Two-phase Flows and Combustion, Department of Engineering Mechanics, Tsinghua University. For strongly swirling gas-particle flows with swirl numbers greater than unity (s=1.5 and s=2.1), it is found that their gas-particle flow behavior is different among each other and is different from that for weakly swirling flows. For example, there are no central reverse flows and there are enlarged solid-body rotation zones for swirling flows with s=1.5. The behavior of swirling gas-particle flows depends on the swirl number and the flow configuration. For sudden-expansion gas-particle flows it is found that the gas-particle velocity correlation has the distribution similar to that of gas and particle RMS fluctuation velocities and its magnitude is smaller than that of both gas and particle RMS fluctuation velocities. For turbulence modification in sudden-expansion flows it is found that the separating flows increase the gas-turbulence enhancement tendency in comparison with the pipe flows. For combusting gas-particle flows it is found that combustion reduces the velocity slip between the gas and particle phases.
NASA Technical Reports Server (NTRS)
Witte, Larry C.
1994-01-01
The development of instrumentation for the support of research in two-phase flow in simulated microgravity conditions was performed. The funds were expended in the development of a technique for characterizing the motion and size distribution of small liquid droplets dispersed in a flowing gas. Phenomena like this occur in both microgravity and normal earth gravity situations inside of conduits that are carrying liquid-vapor mixtures at high flow rates. Some effort to develop a conductance probe for the measurement of liquid film thickness was also expended.
NASA Technical Reports Server (NTRS)
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.
Strongly coupled turbulent gas-particle flows in vertical channels
NASA Astrophysics Data System (ADS)
Fox, Rodney O.; Capecelatro, Jesse; Desjardins, Olivier
2015-11-01
Eulerian-Lagrangian (EL) simulations of strongly coupled (high mass loading) gas-particle flows in vertical channels are performed with the purpose of exploring the fundamental physics of fully developed, wall-bounded multiphase turbulence. An adaptive spatial filter is developed that accurately decomposes the total granular energy of the particles into correlated and uncorrelated components at each location in the wall-normal direction of the flow. In this manner, Reynolds- and phase-averaged (PA) two-phase turbulence statistics up to second order are reported for both phases and for three values of the PA mean fluid velocity. As expected due to the high mass loading, in all cases the turbulence production due to mean drag dominates production due to mean shear. A multiphase LRR-IP Reynolds-stress turbulence model is developed to predict the turbulent flow statistics as a function of the wall-normal distance. Using a correlation for the vertical drift velocity developed from the EL data, the turbulence model predictions agree satisfactorily with all of one-point EL statistics for the vertical channel flows, as well as for the homogeneous cluster-induced turbulence (CIT) statistics reported previously. Funded by U.S. National Science Foundation (CBET-1437865).
DSMC simulation of two-phase plume flow with UV radiation
Li, Jie; Liu, Ying; Wang, Ning; Jin, Ling
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.
Two-phase flows in solid rocket motors
NASA Astrophysics Data System (ADS)
Murakami, Takuji; Shimada, Toru
Axisymmetric gas-particle two-phase flows in solid-rocket-motor combustion chambers and nozzles with small throat radius of curvature and with submerged configuration are investigated numerically by utilizing a second-order finite-volume method with van Leer's flux-vector splitting in conjunction with a technique of body-fitted cell system. Effects of the particle radius and the particle mass fraction on the two-phase flow, especially on the particle density distribution, the particle-free zone, and the rate of deceleration of the gas are studied. The scheme can capture the particle-free zone with a relatively coarse cell system without numerical oscillation, being benefited by internal dissipative effect which this high-resolution upwind method involves. The validity of the present numerical simulation is thus confirmed.
Two-Phase Flow Separator Investigation
The goal of the Two-Phase Flow Separator investigation is to help increase understanding of how to separate gases and liquids in microgravity. Many systems on the space station contain both liquids...
Apparatus for monitoring two-phase flow
Sheppard, John D.; Tong, Long S.
1977-03-01
A method and apparatus for monitoring two-phase flow is provided that is particularly related to the monitoring of transient two-phase (liquid-vapor) flow rates such as may occur during a pressurized water reactor core blow-down. The present invention essentially comprises the use of flanged wire screens or similar devices, such as perforated plates, to produce certain desirable effects in the flow regime for monitoring purposes. One desirable effect is a measurable and reproducible pressure drop across the screen. The pressure drop can be characterized for various known flow rates and then used to monitor nonhomogeneous flow regimes. Another useful effect of the use of screens or plates in nonhomogeneous flow is that such apparatus tends to create a uniformly dispersed flow regime in the immediate downstream vicinity. This is a desirable effect because it usually increases the accuracy of flow rate measurements determined by conventional methods.
Daniels, L.
1995-06-01
Gas- and vapor-liquid flows through pipework or equipment often pose major difficulties in both design and operation. Typically, two-phase fluid systems are susceptible to flow instabilities, blockages, and pressure and temperature fluctuations. As a result, gas-liquid flows are avoided whenever possible by separating the two phases into individual streams of nearly homogeneous gas and liquid. However, certain process conditions require or inevitably produce two phases. Examples include condensate-return lines flashing into steam, vapor-liquid feed lines entering distillation columns, and refrigerant-return lines that must maintain a specific vapor-liquid ratio for efficient operation. The thermohydraulic behavior of two-phase systems includes variations in pressure drop, flow patterns, and liquid holdup or void fraction. Increasing the pipe diameter reduces the pressure drop for a given flowrate, or alternatively produces an increase in the flowrate for a given pressure drop in a piping system. However, increased pipeline diameters lead to higher costs, and may require installation of more expensive equipment to accommodate the resulting larger slug volumes. There have been numerous improvements in correlations and methods for the prediction of pressure drop in gas-liquid flows. A few of them attempt to take into account the highly complex flow structure of a two-phase flow. One must keep in mind that the flow structure varies with time and position in the pipework. The paper discusses empirical correlations, pressure drop due to friction, gravity, and acceleration, transitions in flow patterns, liquid inventories, and erosion. 46 refs.
Two-phase flow in horizontal pipes
Maeder, P.F.; Michaelides, E.E.; DiPippo, R.
1981-09-01
A method is developed in this paper which calculates the two-phase flow friction factor at any state of the fluid in the pipe. The mixing-length theory was employed for the calculation of the Reynolds stresses in turbulent two-phase flow. The friction factors obtained this way are in good agreement with experimental data. It is clear that the choice of the parameter m, or the density distribution, is rather arbitrary. Careful experimentation is required to refine the analysis given in this study, and in particular to provide guidance in the proper selection of the parameter m.
Microgravity Two-Phase Flow Transition
NASA Technical Reports Server (NTRS)
Parang, M.; Chao, D.
1999-01-01
Two-phase flows under microgravity condition find a large number of important applications in fluid handling and storage, and spacecraft thermal management. Specifically, under microgravity condition heat transfer between heat exchanger surfaces and fluids depend critically on the distribution and interaction between different fluid phases which are often qualitatively different from the gravity-based systems. Heat transfer and flow analysis in two-phase flows under these conditions require a clear understanding of the flow pattern transition and development of appropriate dimensionless scales for its modeling and prediction. The physics of this flow is however very complex and remains poorly understood. This has led to various inadequacies in flow and heat transfer modeling and has made prediction of flow transition difficult in engineering design of efficient thermal and flow systems. In the present study the available published data for flow transition under microgravity condition are considered for mapping. The transition from slug to annular flow and from bubbly to slug flow are mapped using dimensionless variable combination developed in a previous study by the authors. The result indicate that the new maps describe the flow transitions reasonably well over the range of the data available. The transition maps are examined and the results are discussed in relation to the presumed balance of forces and flow dynamics. It is suggested that further evaluation of the proposed flow and transition mapping will require a wider range of microgravity data expected to be made available in future studies.
Gas-Particle Interactions in a Microgravity Flow Cell
NASA Technical Reports Server (NTRS)
Louge, Michel; Jenkins, James
1999-01-01
We are developing a microgravity flow cell in which to study the interaction of a flowing gas with relatively massive particles that collide with each other and with the moving boundaries of the cell. The absence of gravity makes possible the independent control of the relative motion of the boundaries and the flow of the gas. The cell will permit gas-particle interactions to be studied over the entire range of flow conditions over which the mixture is not turbulent. Within this range, we shall characterize the viscous dissipation of the energy of the particle fluctuations, measure the influence of particle-phase viscosity on the pressure drop along the cell, and observe the development of localized inhomogeneities that are likely to be associated with the onset of clusters. These measurements and observations should contribute to an understanding of the essential physics of pneumatic transport.
The research of gas-particle flow in a curved channel
Lin, B.; Zhang, X.
1995-12-31
A two-phase kinetic model is established and used in two-dimensional gas-particle flow in a curved channel of an inertial separator which is used in CFB, and the particle density, gas velocity and particle velocity are obtained through numerical simulation. The results show that, the motion of particles is mainly controlled by the rebound of particles on wall, the drag force of gas and collision between particles. Particles rebound on wall can reduce the separation efficiency. As the result of collision between particles, more particles concentrate near the channel wall, and make the separation efficiency increase.
Pressure drop in two-phase flow
NASA Astrophysics Data System (ADS)
Akashah, S. A.
1980-12-01
A computer program was developed containing some of the methods for predicting pressure drop in two-phase flow. The program contains accurate methods for predicting phase behavior and physical properties and can be used to calculate pressure drops for horizontal, inclined and vertical phases. The program was used to solve test cases for many types of flow, varying the diameter, roughness, composition, overall heat transfer coefficient, angle of inclination, and length. The Lockhart-Martinelli correlation predicts the highest pressure drop while the Beggs and Brill method predicts the lowest. The American Gas Association-American Petroleum Institute method is consistent and proved to be reliable in vertical, horizontal and inclined flow. The roughness of the pipe diameter had great effect on pressure drop in two-phase flow, while the overall heat transfer coefficient had little effect.
Stability of oscillatory two phase Couette flow
NASA Technical Reports Server (NTRS)
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.
NASA Technical Reports Server (NTRS)
Moerk, J. Steven (Inventor); Youngquist, Robert C. (Inventor); Werlink, Rudy J. (Inventor)
1999-01-01
A quality and/or flow meter employs a capacitance probe assembly for measuring the dielectric constant of flow stream, particularly a two-phase flow stream including liquid and gas components.ne dielectric constant of the flow stream varies depending upon the volume ratios of its liquid and gas components, and capacitance measurements can therefore be employed to calculate the quality of the flow, which is defined as the volume ratio of liquid in the flow to the total volume ratio of gas and liquid in the flow. By using two spaced capacitance sensors, and cross-correlating the time varying capacitance values of each, the velocity of the flow stream can also be determined. A microcontroller-based processing circuit is employed to measure the capacitance of the probe sensors.The circuit employs high speed timer and counter circuits to provide a high resolution measurement of the time interval required to charge each capacitor in the probe assembly. In this manner, a high resolution, noise resistant, digital representation of each of capacitance value is obtained without the need for a high resolution A/D converter, or a high frequency oscillator circuit. One embodiment of the probe assembly employs a capacitor with two ground plates which provide symmetry to insure that accurate measurements are made thereby.
Continuum modeling of two-phase flows
Bataille, J.; Kestin, J.
1981-12-01
Continuum modeling of two-phase flows can essentially be achieved in two ways. The first approach, the so-called continuum theory of mixtures, ignores the details of the flow occurring on the microscopic level, while the second one is the result of some averaging procedure. Although they both lead, as expected, to the same set of basic equations, they differ strongly in their spirit when closure equations have to be found. In the present report, we have attempted to give a brief critical review of both approaches, to compare them and to discuss some of the major difficulties which arise. It is shown that the application of the continuum theory of mixtures is, in most cases, questionable and that the only appropriate way of finding closure equations, besides correlating experimental results, consists in a useful investigation of the microscopic flow pattern associated with an adequate averaging technique.
Numerical Simulation of Two Phase Flows
NASA Technical Reports Server (NTRS)
Liou, Meng-Sing
2001-01-01
Two phase flows can be found in broad situations in nature, biology, and industry devices and can involve diverse and complex mechanisms. While the physical models may be specific for certain situations, the mathematical formulation and numerical treatment for solving the governing equations can be general. Hence, we will require information concerning each individual phase as needed in a single phase. but also the interactions between them. These interaction terms, however, pose additional numerical challenges because they are beyond the basis that we use to construct modern numerical schemes, namely the hyperbolicity of equations. Moreover, due to disparate differences in time scales, fluid compressibility and nonlinearity become acute, further complicating the numerical procedures. In this paper, we will show the ideas and procedure how the AUSM-family schemes are extended for solving two phase flows problems. Specifically, both phases are assumed in thermodynamic equilibrium, namely, the time scales involved in phase interactions are extremely short in comparison with those in fluid speeds and pressure fluctuations. Details of the numerical formulation and issues involved are discussed and the effectiveness of the method are demonstrated for several industrial examples.
Dynamics of annular two-phase flow
NASA Astrophysics Data System (ADS)
Sawant, Pravin Hanamantrao
A basic understanding of various hydrodynamic phenomena in annular two-phase is essential to develop mechanistic model for the prediction dryout. The major objective of this investigation was to perform experimental and theoretical analysis of the important hydrodynamic phenomena such as droplet entrainment, droplet deposition, and liquid film interfacial waves in vertical annular two-phase flow. Towards this end, adiabatic air-water and organic fluid (Freon-113) annular flow experiments have been conducted in 1 cm diameter test sections at pressures up to 6 and 8.5 bar, respectively. The organic fluid experiments simulated high pressure steam-water conditions representative of dryout in the Advanced Boiling Water Reactor (ABWR). A liquid film extraction method was applied for the measurement of entrainment fraction, droplet entrainment rate, and droplet deposition rate. Instantaneous liquid film thickness was measured in the air-water experiments using ring shaped conductance probes and properties of interfacial waves were estimated from the statistical analysis of the film thickness measurement. Detailed analysis of the experimental data revealed several inadequacies of the existing annular flow correlations available for the predictions of entrainment fraction, droplet entrainment rate, and droplet deposition rate including their inability to predict the limiting conditions observed under high gas phase velocity. Based on the detailed analysis of the air-water data, a new, non-dimensional and explicit correlation was developed for the prediction of entrainment fraction. The new correlation accounted for the existence of an upper limit on entrainment fraction as well as for the existence of critical liquid and gas velocities below which no entrainment is possible. Additionally, an improved correlation was proposed for the estimation of minimum liquid film flow rate at the maximum entrainment fraction. The newly developed entrainment fraction correlation
Flow Pattern Phenomena in Two-Phase Flow in Microchannels
NASA Astrophysics Data System (ADS)
Keska, Jerry K.; Simon, William E.
2004-02-01
Space transportation systems require high-performance thermal protection and fluid management techniques for systems ranging from cryogenic fluid management devices to primary structures and propulsion systems exposed to extremely high temperatures, as well as for other space systems such as cooling or environment control for advanced space suits and integrated circuits. Although considerable developmental effort is being expended to bring potentially applicable technologies to a readiness level for practical use, new and innovative methods are still needed. One such method is the concept of Advanced Micro Cooling Modules (AMCMs), which are essentially compact two-phase heat exchangers constructed of microchannels and designed to remove large amounts of heat rapidly from critical systems by incorporating phase transition. The development of AMCMs requires fundamental technological advancement in many areas, including: (1) development of measurement methods/systems for flow-pattern measurement/identification for two-phase mixtures in microchannels; (2) development of a phenomenological model for two-phase flow which includes the quantitative measure of flow patterns; and (3) database development for multiphase heat transfer/fluid dynamics flows in microchannels. This paper focuses on the results of experimental research in the phenomena of two-phase flow in microchannels. The work encompasses both an experimental and an analytical approach to incorporating flow patterns for air-water mixtures flowing in a microchannel, which are necessary tools for the optimal design of AMCMs. Specifically, the following topics are addressed: (1) design and construction of a sensitive test system for two-phase flow in microchannels, one which measures ac and dc components of in-situ physical mixture parameters including spatial concentration using concomitant methods; (2) data acquisition and analysis in the amplitude, time, and frequency domains; and (3) analysis of results
NASA Technical Reports Server (NTRS)
Penny, M. M.; Smith, S. D.; Anderson, P. G.; Sulyma, P. R.; Pearson, M. L.
1976-01-01
A computer program written in conjunction with the numerical solution of the flow of chemically reacting gas-particle mixtures was documented. The solution to the set of governing equations was obtained by utilizing the method of characteristics. The equations cast in characteristic form were shown to be formally the same for ideal, frozen, chemical equilibrium and chemical non-equilibrium reacting gas mixtures. The characteristic directions for the gas-particle system are found to be the conventional gas Mach lines, the gas streamlines and the particle streamlines. The basic mesh construction for the flow solution is along streamlines and normals to the streamlines for axisymmetric or two-dimensional flow. The analysis gives detailed information of the supersonic flow and provides for a continuous solution of the nozzle and exhaust plume flow fields. Boundary conditions for the flow solution are either the nozzle wall or the exhaust plume boundary.
Observation of two-phase flow in low gravity environment
NASA Astrophysics Data System (ADS)
Yoshimura, Yoshinori; Masuda, Suechika; Morioka, Mikio; Nakao, Keizo; Sugawara, Toshihiro
A drop tower was used to study two-phase flow composed of liquid and gas in a low gravity enviroment. The effect of gravitational acceleration on the flow pattern is discussed. Two nondimensional correlations were derived to estimate the transition of the flow pattern in a horizontal two-phase flow.
Next steps in two-phase flow: executive summary
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)
Two-Phase Flow Pressure Drop of High Quality Steam
Curtis, J. M.; Coffield, R. D.
2001-10-01
Two-phase pressure drop across a straight test pipe was experimentally determined for high Reynolds (Re) number steam flow for a flow quality range of 0.995 to 1.0. The testing described has been performed in order to reduce uncertainties associated with the effects of two-phase flow on pressure drop. Two-phase flow develops in steam piping because a small fraction of the steam flow condenses due to heat loss to the surroundings. There has been very limited two-phase pressure drop data in open literature for the tested flow quality range. The two-phase pressure drop data obtained in this test has enabled development of a correlation between friction factor, Reynolds number, and flow quality.
Two-phase flow measurements with advanced instrumented spool pieces
Turnage, K.C.
1980-09-01
A series of two-phase, air-water and steam-water tests performed with instrumented piping spool pieces is described. The behavior of the three-beam densitometer, turbine meter, and drag flowmeter is discussed in terms of two-phase models. Results from application of some two-phase mass flow models to the recorded spool piece data are shown. Results of the study are used to make recommendations regarding spool piece design, instrument selection, and data reduction methods to obtain more accurate measurements of two-phase flow parameters. 13 refs., 23 figs., 1 tab.
Confined Two-Phase Incompressible Flows,
1996-03-01
computation of incompressible flows Re Reynolds number = UL/v with density variations, free surfaces and bubbles rising t time and interacting with...layers, driven cavities and bubbles . frequency Wo over-relaxation parameter This paper applies the level set approach"" 3 to a interface thickness...the level the mid-point along the interface. As in the many recent set method. The example problems demonstrated the bubble computations, the interface
Two-phase-flow models and their limitations
Ishii, M.; Kocamustafaogullari, G.
1982-01-01
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.
Nonisothermal Two-Phase Porous Flow
1992-02-21
NORIA is a finite element program that simultaneously solves four nonlinear parabolic, partial differential equations that describe the transport of water, water vapor, air, and energy through partially saturated porous media. NORIA is designed for the analysis of two-dimensional, non-isothermal, unsaturated porous flow problems. Nearly all material properties, such as permeability, can either be set to constant values or defined as functions of the dependent and independent variables by user-supplied subroutines. The gas phase is taken to be ideal. NORIA is intended to solve nonisothermal problems in which large gradients are expected in the gas pressure.
Void fraction correlations in two-phase horizontal flow
Papathanassiou, G.; Maeder, P.F.; DiPippo, R.; Dickinson, D.A.
1983-05-01
This study examines some physical mechanisms which impose limits on the possible existence of two-phase flow in a horizontal pipe. With the aid of this analysis and the use of the Martinelli variable, X, a method is developed which determines the range of possible void fractions for a given two-phase flow. This method affords a means of direct comparison among void fraction correlations, as well as between correlation predictions and experimental results. In this respect, four well-known void fraction correlations are compared against each other and with experimental results obtained in the Brown University Two-Phase Flow Research Facility.
Momentum flux in two phase two component low quality flow
NASA Technical Reports Server (NTRS)
Baumeister, K. J.; Graham, R. W.; Henry, R. E.
1972-01-01
In two phase flow systems line losses comprise frictional and momentum pressure drops. For design purposes, it would be desirable to estimate the line losses employing a one-dimensional calculation. Two methods for computing one-dimensional momentum flux at a test section discharge station are compared to the experimental value for a range of two-phase flow conditions. The one-dimensional homogeneous model appears to be more accurate generally in predicting the momentum than the variable slip model.
Studies on Normal and Microgravity Annular Two Phase Flows
NASA Technical Reports Server (NTRS)
Balakotaiah, V.; Jayawardena, S. S.; Nguyen, L. T.
1999-01-01
Two-phase gas-liquid flows occur in a wide variety of situations. In addition to normal gravity applications, such flows may occur in space operations such as active thermal control systems, power cycles, and storage and transfer of cryogenic fluids. Various flow patterns exhibiting characteristic spatial and temporal distribution of the two phases are observed in two-phase flows. The magnitude and orientation of gravity with respect to the flow has a strong impact on the flow patterns observed and on their boundaries. The identification of the flow pattern of a flow is somewhat subjective. The same two-phase flow (especially near a flow pattern transition boundary) may be categorized differently by different researchers. Two-phase flow patterns are somewhat simplified in microgravity, where only three flow patterns (bubble, slug and annular) have been observed. Annular flow is obtained for a wide range of gas and liquid flow rates, and it is expected to occur in many situations under microgravity conditions. Slug flow needs to be avoided, because vibrations caused by slugs result in unwanted accelerations. Therefore, it is important to be able to accurately predict the flow pattern which exists under given operating conditions. It is known that the wavy liquid film in annular flow has a profound influence on the transfer of momentum and heat between the phases. Thus, an understanding of the characteristics of the wavy film is essential for developing accurate correlations. In this work, we review our recent results on flow pattern transitions and wavy films in microgravity.
Nonequilibrium hydrogen combustion in one- and two-phase supersonic flow
Chang, H.T.; Hourng, L.W.; Chien, L.C.
1997-05-01
A time-splitting method for the numerical simulation of stiff nonequilibrium combustion problem was developed. The algorithm has been applied to simulate the shock-induced combustion and to investigate a supersonic one-and two-phase flowfield. The results are physically reasonable and demonstrate that the presence of particles has a dramatic effect on the nozzle flowfield and the thrust. Supersonic combustion usually happens in high speed flying aerodynamic problems, such as supersonic combustion ramjet (scramjet) engine for hypersonic airbreathing vehicles. Particularly for the scramjet engine, due to short residence time in the combustion chamber, it still contains incomplete combustion fuel as it enters the nozzle. For solid propellant rocket motors, the exhaust stream contains particles of aluminum oxide. In these two-phase nozzle flows, transfer of momentum and heat between gas particles often result in a decrease of nozzle efficiency.
Definition of two-phase flow behaviors for spacecraft design
NASA Technical Reports Server (NTRS)
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.
Definition of two-phase flow behaviors for spacecraft design
NASA Technical Reports Server (NTRS)
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.
Two-phase flow modeling with discrete particles
Mortensen, G.A.; Trapp, J.A. |
1992-03-23
The design of efficient heat exchangers in which the working fluid changes phase requires accurate modeling of two-phase fluid flow. The local Navier-Stokes equations form the basic continuum equations for this flow situation. However, the local instantaneous model using these equations is intractable for afl but the simplest problems. AH the practical models for two-phase flow analysis are based on equations that have been averaged over control volumes. These models average out the detailed description within the control volumes and rely on flow regime maps to determine the distribution of the two phases within a control volume. Flow regime maps depend on steady state models and probably are not correct for dynamic models. Numerical simulations of the averaged two-phase flow models are usually performed using a two-fluid Eulerian description for the two phases. Eulerian descriptions have the advantage of having simple boundary conditions, but the disadvantage of introducing numerical diffusion, i.e., sharp interfaces are not maintained as the flow develops, but are diffused. Lagrangian descriptions have the advantage of being able to track sharp interfaces without diffusion, but they have the disadvantage of requiring more complicated boundary conditions. This paper describes a numerical scheme and attendant computer program, DISCON2, for the calculation of two-phase flows that does not require the use of flow regime maps. This model is intermediate between the intractable local instantaneous and the averaged two-fluid model. This new model uses a combination of an Eulerian and a Lagrangian representation of the two phases. The dispersed particles (bubbles or drops) are modeled individually using a large representative number of particles, each with their own Lagrangian description. The continuous phases (liquid or gas) use an Eulerian description.
A turbulent two-phase flow model for nebula flows
NASA Technical Reports Server (NTRS)
Champney, Joelle M.; Cuzzi, Jeffrey N.
1990-01-01
A new and very efficient turbulent two-phase flow numericaly model is described to analyze the environment of a protoplanetary nebula at a stage prior to the formation of planets. Focus is on settling processes of dust particles in flattened gaseous nebulae. The model employs a perturbation technique to improve the accuracy of the numerical simulations of such flows where small variations of physical quantities occur over large distance ranges. The particles are allowed to be diffused by gas turbulence in addition to settling under gravity. Their diffusion coefficients is related to the gas turbulent viscosity by the non-dimensional Schmidt number. The gas turbulent viscosity is determined by the means of the eddy viscosity hypothesis that assumes the Reynolds stress tensor proportional to the mean strain rate tensor. Zero- and two-equation turbulence models are employed. Modeling assumptions are detailed and discussed. The numerical model is shown to reproduce an existing analytical solution for the settling process of particles in an inviscid nebula. Results of nebula flows are presented taking into account turbulence effects of nebula flows. Diffusion processes are found to control the settling of particles.
Study of two-phase flows in reduced gravity
NASA Astrophysics Data System (ADS)
Roy, Tirthankar
Study of gas-liquid two-phase flows under reduced gravity conditions is extremely important. One of the major applications of gas-liquid two-phase flows under reduced gravity conditions is in the design of active thermal control systems for future space applications. Previous space crafts were characterized by low heat generation within the spacecraft which needed to be redistributed within the craft or rejected to space. This task could easily have been accomplished by pumped single-phase loops or passive systems such as heat pipes and so on. However with increase in heat generation within the space craft as predicted for future missions, pumped boiling two-phase flows are being considered. This is because of higher heat transfer co-efficients associated with boiling heat transfer among other advantages. Two-phase flows under reduced gravity conditions also find important applications in space propulsion as in space nuclear power reactors as well as in many other life support systems of space crafts. Two-fluid model along with Interfacial Area Transport Equation (IATE) is a useful tool available to predict the behavior of gas-liquid two-phase flows under reduced gravity conditions. It should be noted that considerable differences exist between two-phase flows under reduced and normal gravity conditions especially for low inertia flows. This is because due to suppression of the gravity field the gas-liquid two-phase flows take a considerable time to develop under reduced gravity conditions as compared to normal gravity conditions. Hence other common methods of analysis applicable for fully developed gas-liquid two-phase flows under normal gravity conditions, like flow regimes and flow regime transition criteria, will not be applicable to gas-liquid two-phase flows under reduced gravity conditions. However the two-fluid model and the IATE need to be evaluated first against detailed experimental data obtained under reduced gravity conditions. Although lot of studies
Closures for Course-Grid Simulation of Fluidized Gas-Particle Flows
Sankaran Sundaresan
2010-02-14
Gas-particle flows in fluidized beds and riser reactors are inherently unstable, and they manifest fluctuations over a wide range of length and time scales. Two-fluid models for such flows reveal unstable modes whose length scale is as small as ten particle diameters. Yet, because of limited computational resources, gas-particle flows in large fluidized beds are invariably simulated by solving discretized versions of the two-fluid model equations over a coarse spatial grid. Such coarse-grid simulations do not resolve the small-scale spatial structures which are known to affect the macroscale flow structures both qualitatively and quantitatively. Thus there is a need to develop filtered two-fluid models which are suitable for coarse-grid simulations and capturing the effect of the small-scale structures through closures in terms of the filtered variables. The overall objective of the project is to develop validated closures for filtered two-fluid models for gas-particle flows, with the transport gasifier as a primary, motivating example. In this project, highly resolved three-dimensional simulations of a kinetic theory based two-fluid model for gas-particle flows have been performed and the statistical information on structures in the 100-1000 particle diameters length scale has been extracted. Based on these results, closures for filtered two-fluid models have been constructed. The filtered model equations and closures have been validated against experimental data and the results obtained in highly resolved simulations of gas-particle flows. The proposed project enables more accurate simulations of not only the transport gasifier, but also many other non-reacting and reacting gas-particle flows in a variety of chemical reactors. The results of this study are in the form of closures which can readily be incorporated into existing multi-phase flow codes such as MFIX (www.mfix.org). Therefore, the benefits of this study can be realized quickly. The training provided
Two-phase flow in helical and spiral coils
NASA Technical Reports Server (NTRS)
Keshock, Edward G.; Bush, Mia L.; Omrani, Adel; Yan, An
1995-01-01
Coiled tube heat exchangers involving two-phase flows are used in a variety of application areas, extending from the aerospace industry to petrochemical, refrigeration land power generation industries. The optimal design in each situation requires a fundamental understanding of the heat, mass and momentum transfer characteristic of the flowing two-phase mixture. However, two-phase flows in lengths of horizontal or vertical straight channels with heat transfer are often quite difficult in themselves to understand sufficiently well to permit accurate system designs. The present study has the following general objectives: (1) Observe two-phase flow patterns of air-water and R-113 working fluids over a range of flow conditions, for helical and spiral coil geometries, of circular and rectangular cross-section; (2) Compare observed flow patterns with predictions of existing flow maps; (3) Study criteria for flow regime transitions for possible modifications of existing flow pattern maps; and (4) Measure associated pressure drops across the coiled test sections over the rage of flow conditions specified.
Two-phase flow in helical and spiral coils
NASA Technical Reports Server (NTRS)
Keshock, Edward G.; Bush, Mia L.; Omrani, Adel; Yan, An
1995-01-01
Coiled tube heat exchangers involving two-phase flows are used in a variety of application areas, extending from the aerospace industry to petrochemical, refrigeration land power generation industries. The optimal design in each situation requires a fundamental understanding of the heat, mass and momentum transfer characteristic of the flowing two-phase mixture. However, two-phase flows in lengths of horizontal or vertical straight channels with heat transfer are often quite difficult in themselves to understand sufficiently well to permit accurate system designs. The present study has the following general objectives: (1) Observe two-phase flow patterns of air-water and R-113 working fluids over a range of flow conditions, for helical and spiral coil geometries, of circular and rectangular cross-section; (2) Compare observed flow patterns with predictions of existing flow maps; (3) Study criteria for flow regime transitions for possible modifications of existing flow pattern maps; and (4) Measure associated pressure drops across the coiled test sections over the rage of flow conditions specified.
NASA Astrophysics Data System (ADS)
Zhou, Lixing
2014-04-01
In earlier studies of gas-particle flows the effect of wall roughness was not taken into account. The present author and his colleagues did detailed PDPA measurements and numerical studies for the effect of wall roughness on the gas-particle flow behavior. This paper gives a review of our studies, showing the following results. The PDPA measurements of backward-facing step gas-particle flows shows that as the wall roughness increases, the longitudinal and transverse particle fluctuation velocities increase. The numerical simulation of swirling gas-particle flows shows that the simulation results accounting for the wall roughness agree well with the measurement results. The numerical simulation of gas-particle channel flows indicates the increase of particle fluctuation velocity with increasing wall roughness.
Method and apparatus for monitoring two-phase flow. [PWR
Sheppard, J.D.; Tong, L.S.
1975-12-19
A method and apparatus for monitoring two-phase flow is provided that is particularly related to the monitoring of transient two-phase (liquid-vapor) flow rates such as may occur during a pressurized water reactor core blow-down. The present invention essentially comprises the use of flanged wire screens or similar devices, such as perforated plates, to produce certain desirable effects in the flow regime for monitoring purposes. One desirable effect is a measurable and reproducible pressure drop across the screen. The pressure drop can be characterized for various known flow rates and then used to monitor nonhomogeneous flow regimes. Another useful effect of the use of screens or plates in nonhomogeneous flow is that such apparatus tends to create a uniformly dispersed flow regime in the immediate downstream vicinity. This is a desirable effect because it usually increases the accuracy of flow rate measurements determined by conventional methods.
Two-phase flow regime map predictions under microgravity
Karri, S.B.R.; Mathur, V.K.
1988-01-01
In this paper, the widely used models of Taitel-Dukler and Weisman et al. are extrapolated to microgravity levels to compare predicted flow pattern boundaries for horizontal and vertical flows. Efforts have been made to analyze how the two-phase flow models available in the literature predict flow regime transitions in microgravity. The models of Taitel-Dukler and Weisman et al. have been found to be more suitable for extrapolation to a wide range of system parameters than the other two-phase flow regime maps available in the literature. The original criteria for all cases are used to predict the transition lines, except for the transition to dispersed flow regime in case of the Weisman model for horizontal flow. The constant 0.97 on the righthand side of this correlation should be two times that value, i.e., 1.94, in order to match this transition line in their original paper.
Two- phase flow patterns and heat transfer in parallel microchannels
NASA Astrophysics Data System (ADS)
Mosyak, A.; Segal, Z.; Pogrebnyak, E.; Hetsroni, G.
2002-11-01
Microchannel heat sinks with two-phase flow can satisfy the increasing heat removal requirements of modern micro electronic devices. One of the important aspects associated with two- phase flows in microchannels is to study the bubble behavior. However, in the literature most of the reports present data of only a single channel. This does not account for flow mixing and hydrodynamic instability that occurs in parallel microchannels, connected by common inlet and outlet collectors. In the present study, experiments were performed for air- water and steam- water flow in parallel triangular microchannels with a base of 200 300 µ m. The experimental study is based on systematic measurements of temperature and flow pattern by infrared radiometry and high-speed digital video imaging. In air-water flow, different flow patterns were observed simultaneously in the various microchannels at a fixed values of water and gas flow rates. In steam-water flow, instability in uniformly heated microchannels was observed. This work develops a practical modeling approach for two-phase microchannel heat sinks and considers discrepancy between flow patterns of air- water and steam- water flow in microchannels.
DNS of two-phase flow in an inclined pipe
NASA Astrophysics Data System (ADS)
Xie, Fangfang; Zheng, Xiaoning; Triantafyllou, Michael; Constantinides, Yiannis; Karniadakis, George
2016-11-01
We study the de-stabilization mechanisms of two-phase flow in an inclined pipe subject to gravity with a phase-field approach. At the inlet, a stratified flow is imposed with a parabolic velocity profile. We found that due to gravity, the stratified flow will become unstable, causing a complex transitional flow inside the pipe. Firstly, a 2D channel geometry is considered. When the heavy fluid is injected in the top layer, inverted vortex shedding emerges, interacting periodically with the bottom wall as it develops further downstream. The accumulation of heavy fluid in the bottom wall causes a backflow, which interacts with the previous jet. On the other hand, when the heavy fluid is placed in the bottom layer, a big slug is formed and subsequently breaks into small pieces, some of which will be shed along the pipe. To describe the generation of vorticity from the two-phase interface and pipe walls, we analyze the circulation dynamics and connect it to the two-phase flow pattern. Moreover, we analyze the two-phase flow induced forces along the pipe, which is capable of producing unwanted and destructive vibrations. Finally, we conduct 3D simulations in the circular pipe and compared the differences of flow dynamics against the 2D simulation results.
Two Phase Flow and Space-Based Applications
NASA Technical Reports Server (NTRS)
McQuillen, John
1999-01-01
A reduced gravity environment offers the ability to remove the effect of buoyancy on two phase flows whereby density differences that normally would promote relative velocities between the phases and also alter the shape of the interface are removed. However, besides being a potent research tool, there are also many space-based technologies that will either utilize or encounter two-phase flow behavior, and as a consequence, several questions must be addressed. This paper presents some of these technologies missions. Finally, this paper gives a description of web-sites for some funding.
Definition of two-phase flow behaviors for spacecraft design
NASA Technical Reports Server (NTRS)
Reinarts, Thomas R.; Best, Frederick R.; Miller, Katherine M.; Hill, Wayne S.
1991-01-01
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. A boiling and condensing experiment was built in which R-12 was used as the working fluid. A two-phase pump was used to circulate a freon mixture and allow separate measurements of the vapor and liquid flow streams. The experimental package was flown five times aboard the NASA KC-135 aircraft which simulates zero-g conditions by its parabolic flight trajectory. Test conditions included stratified and annual flow regimes in 1-g which became bubbly, slug, or annular flow regimes on 0-g. A portion of this work is the analysis of adiabatic flow regimes. The superficial velocities of liquid and vapor have been obtained from the measured flow rates and are presented along with the observed flow regimes.
Low gravity two-phase flow with heat transfer
NASA Technical Reports Server (NTRS)
Antar, Basil N.
1991-01-01
A realistic model for the transfer line chilldown operation under low-gravity conditions is developed to provide a comprehensive predictive capability on the behavior of liquid vapor, two-phase diabatic flows in pipes. The tasks described involve the development of numerical code and the establishment of the necessary experimental data base for low-gravity simulation.
Numerical simulation of compressible, turbulent, two-phase flow
NASA Astrophysics Data System (ADS)
Coakley, T. J.; Champney, J. M.
1985-07-01
A computer program for numerically simulating compressible, turbulent, two-phase flows is described and applied. Special attention is given to flows in which dust is ingested into the turbulent boundary layer behind shock waves moving over the earth's surface. it is assumed that the two phases are interpenetrating continua which are coupled by drag forces and heat transfer. The particle phase is assumed to be dilute, and turbulent effects are modeled by zero- and two-equation eddy viscosity models. An important feature of the turbulence modeling is the treatment of surface boundary conditions which control the ingestion of particles into the boundary layer by turbulent friction and diffusion. The numerical method uses second-order implicit upwind differencing of the inviscid terms of the equations and second-order central differencing of the viscous terms. A diagonal form of the implicit algorithm is used to improve efficiency, and the transformation to a curvilinear coordinate system is accomplished by the finite volume techniques. Applications to a series of representative flows include a two-phase nozzle flow, the steady flow of air over a sand bed, and the air flow behind a normal shock wave in uniform motion over a sand bed. Results of the latter two applications are compared with experimental results.
Two-phase flow instabilities in a vertical annular channel
Babelli, I.; Nair, S.; Ishii, M.
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.
Non-Darcy behavior of two-phase channel flow.
Xu, Xianmin; Wang, Xiaoping
2014-08-01
We study the macroscopic behavior of two-phase flow in porous media from a phase-field model. A dissipation law is first derived from the phase-field model by homogenization. For simple channel geometry in pore scale, the scaling relation of the averaged dissipation rate with the velocity of the two-phase flow can be explicitly obtained from the model which then gives the force-velocity relation. It is shown that, for the homogeneous channel surface, Dacry's law is still valid with a significantly modified permeability including the contribution from the contact line slip. For the chemically patterned surfaces, the dissipation rate has a non-Darcy linear scaling with the velocity, which is related to a depinning force for the patterned surface. Our result offers a theoretical understanding on the prior observation of non-Darcy behavior for the multiphase flow in either simulations or experiments.
Two-Phase Flow Hydrodynamics in Superhydrophobic Channels
NASA Astrophysics Data System (ADS)
Stevens, Kimberly; Crockett, Julie; Maynes, Daniel; Iverson, Brian
2016-11-01
Superhydrophobic surfaces have been shown to reduce drag in single-phase channel flow; however, little work has been done to characterize the drag reduction found in two-phase channel flow. Adiabatic, air-water mixtures were used to gain insight into the effect of hydrophobicity on two-phase flows and the hydrodynamics which might be present in flow condensation. Pressure drop in a parallel plate channel with one superhydrophobic wall (cross-section 0.5 x 10 mm) and a transparent hydrophilic wall were explored. Data for air/water mixtures with superficial Reynolds numbers from 20-215 and 50-210, respectively, were obtained for superhydrophobic surfaces with three different cavity fractions. Agreement between experimentally obtained two-phase pressure drops and correlations in the literature for conventional smooth control surfaces was better than 20 percent. The reduction in pressure drop for channels with a single superhydrophobic wall were found to be more significant than that for single phase flow. The effect of cavity fraction on drag reduction was within experimental error.
Neutron Imaging of a Two-Phase Refrigerant Flow
Geoghegan, Patrick J
2015-01-01
Void fraction remains a crucial parameter in understanding and characterizing two-phase flow. It appears as a key variable in both heat transfer and pressure drop correlations of two-phase flows, from the macro to micro- channel scale. Void fraction estimation dictates the sizing of both evaporating and condensing phase change heat exchangers, for example. In order to measure void fraction some invasive approach is necessary. Typically, visualization is achieved either downstream of the test section or on top by machining to expose the channel. Both approaches can lead to inaccuracies. The former assumes the flow will not be affected moving from the heat exchanger surface to the transparent section. The latter distorts the heat flow path. Neutron Imaging can provide a non-invasive measurement because metals such as Aluminum are essentially transparent to neutrons. Hence, if a refrigerant is selected that provides suitable neutron attenuation; steady-state void fraction measurements in two-phase flow are attainable in-situ without disturbing the fluid flow or heat flow path. Neutron Imaging has been used in the past to qualitatively describe the flow in heat exchangers in terms of maldistributions without providing void fraction data. This work is distinguished from previous efforts because the heat exchanger has been designed and the refrigerant selected to avail of neutron imaging. This work describes the experimental flow loop that enables a boiling two-phase flow; the heat exchanger test section and downstream transparent section are described. The flow loop controls the degree of subcooling and the refrigerant flowrate. Heating cartridges embedded in the test section are employed to control the heat input. Neutron-imaged steady-state void fraction measurements are captured and compared to representative high-speed videography captured at the visualization section. This allows a qualitative comparison between neutron imaged and traditional techniques. The
Sub-grid drag models for horizontal cylinder arrays immersed in gas-particle multiphase flows
Sarkar, Avik; Sun, Xin; Sundaresan, Sankaran
2013-09-08
Immersed cylindrical tube arrays often are used as heat exchangers in gas-particle fluidized beds. In multiphase computational fluid dynamics (CFD) simulations of large fluidized beds, explicit resolution of small cylinders is computationally infeasible. Instead, the cylinder array may be viewed as an effective porous medium in coarse-grid simulations. The cylinders' influence on the suspension as a whole, manifested as an effective drag force, and on the relative motion between gas and particles, manifested as a correction to the gas-particle drag, must be modeled via suitable sub-grid constitutive relationships. In this work, highly resolved unit-cell simulations of flow around an array of horizontal cylinders, arranged in a staggered configuration, are filtered to construct sub-grid, or `filtered', drag models, which can be implemented in coarse-grid simulations. The force on the suspension exerted by the cylinders is comprised of, as expected, a buoyancy contribution, and a kinetic component analogous to fluid drag on a single cylinder. Furthermore, the introduction of tubes also is found to enhance segregation at the scale of the cylinder size, which, in turn, leads to a reduction in the filtered gas-particle drag.
Measurement of Two-Phase Flow Characteristics Under Microgravity Conditions
NASA Technical Reports Server (NTRS)
Keshock, E. G.; Lin, C. S.; Edwards, L. G.; Knapp, J.; Harrison, M. E.; Xhang, X.
1999-01-01
This paper describes the technical approach and initial results of a test program for studying two-phase annular flow under the simulated microgravity conditions of KC-135 aircraft flights. A helical coil flow channel orientation was utilized in order to circumvent the restrictions normally associated with drop tower or aircraft flight tests with respect to two-phase flow, namely spatial restrictions preventing channel lengths of sufficient size to accurately measure pressure drops. Additionally, the helical coil geometry is of interest in itself, considering that operating in a microgravity environment vastly simplifies the two-phase flows occurring in coiled flow channels under 1-g conditions for virtually any orientation. Pressure drop measurements were made across four stainless steel coil test sections, having a range of inside tube diameters (0.95 to 1.9 cm), coil diameters (25 - 50 cm), and length-to-diameter ratios (380 - 720). High-speed video photographic flow observations were made in the transparent straight sections immediately preceding and following the coil test sections. A transparent coil of tygon tubing of 1.9 cm inside diameter was also used to obtain flow visualization information within the coil itself. Initial test data has been obtained from one set of KC-135 flight tests, along with benchmark ground tests. Preliminary results appear to indicate that accurate pressure drop data is obtainable using a helical coil geometry that may be related to straight channel flow behavior. Also, video photographic results appear to indicate that the observed slug-annular flow regime transitions agree quite reasonably with the Dukler microgravity map.
Transient two-phase flow in microfluidics and nanofluidics
NASA Astrophysics Data System (ADS)
Velasco, Angel; Song, Andrew; Friedman, Serah; Pevarnik, Matthew; Siwy, Zuzanna; Taborek, Peter
2012-11-01
We have studied the flow of a high pressure liquid (nitrogen and water) into vacuum through large aspect ratio pipes with diameters ranging from 25 microns to 50 nanometers. The decreasing pressure in the pipe induces boiling when the saturated vapor pressure is reached, creating a two-phase liquid/vapor flow. A novel method of measuring extremely small flow rates based on mass spectrometry will be presented. The validity of the method was verified using measurements of the flow of helium and argon through standard micron scale capillary tubes; subsequent measurements used single ion track pores which were 12 microns long with diameters in the range of 800-50 nm. A systematic study with nitrogen at 77 K was done with inlet pressures above and below the saturated vapor pressure. When the applied pressure is below the saturated vapor pressure the single phase flow was observed to obey the compressible Navier-Stokes equation. At pressures greater than the saturated vapor pressure, a stable flow was observed in pipes with diameters greater than 5 microns. For diameters below 2 microns significant fluctuations in the flow rate are observed at applied pressures up to 35 Atm, suggesting the onset of two-phase flow.
Turbulent two-phase flow in annular seals
NASA Technical Reports Server (NTRS)
Beatty, P. A.; Hughes, W. F.
1986-01-01
Steady, turbulent two-phase fluid flow in a rotating annular seal with no eccentricity is analyzed. The fluid is assumed to be a homogeneous mixture of liquid and vapor in thermodynamic equilibrum. Further, the flow is assumed to be adiabatic, but the effects due to heat generation by viscous dissipation are accounted for fully. Solution of the model governing differential equations is accomplished by use of a fourth-order Runge-Kutta numerical integration scheme. The calculation of mass leakage rates under choked and unchoked conditions are discussed and the phenomenon of all-liquid choked flow is explained. Several numerical examples are presented supposing cyrogenic oxygen as the sealed fluid.
Two-fluid model for two-phase flow
Ishii, M.
1987-01-01
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. 87 refs.
Two-Phase Annular Flow in Helical Coil Flow Channels in a Reduced Gravity Environment
NASA Technical Reports Server (NTRS)
Keshock, Edward G.; Lin, Chin S.
1996-01-01
A brief review of both single- and two-phase flow studies in curved and coiled flow geometries is first presented. Some of the complexities of two-phase liquid-vapor flow in curved and coiled geometries are discussed, and serve as an introduction to the advantages of observing such flows under a low-gravity environment. The studies proposed -- annular two-phase air-water flow in helical coil flow channels are described. Objectives of the studies are summarized.
By-pass pigs for two-phase flow pipelines
Wu, H.L.; Spronsen, G. van; Klaus, E.H.; Stewart, D.M.
1996-12-31
Pigging two-phase pipelines normally leads to the generation of large liquid slug volumes in front of the pig requiring excessively large separators or slug catchers. The concept of using a high by-pass pig to disperse the liquid and reduce the maximum liquid production rate prior to pig arrival is under investigation by Shell Exploration and Production companies. A simulation model of the dynamics of the pig and related two-phase flow behavior in the pipeline was used to predict the performance of by-pass pigs. Field trials in a dry gas pipeline were carried out to provide friction data and to validate the model. It was then used to explore operating possibilities in a two-phase lie which led to the follow-up trial in a 15.6 km, 20 inch OD two-phase offshore interfield pipeline with risers. Whereas the volume of liquid swept in front of the pig would be 179 m{sup 3} if the by-pass fraction were zero, a reduction of 70% to 53m{sup 3} was achieved in the field with a by-pass fraction of 10%. The predicted mobility of the high by-pass pig in the pipeline and risers was verified and the beneficial effects due to the by-pass concept exceeded the prediction of the simplified model. The significant gains of using a by-pass pig in modifying gas and liquid production rates during pigging operation have been demonstrated. The method can widen the possibility of applying two-phase flow pipeline transportation to cases where separator or slug catcher capacity are limited for reasons of practicality or cost.
Recent advances in two-phase flow numerics
Mahaffy, J.H.; Macian, R.
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.
Optical investigations of He II two phase flow
NASA Astrophysics Data System (ADS)
di Muoio, E.; Jager, B.; Puech, L.; Rousset, B.; Thibault, P.; van Weelderen, R.; Wolf, P. E.
2002-05-01
We describe the optical techniques we used to detect droplets in the HeII two phase flow of the Cryoloop experiment. These include quantitative light scattering, imaging, and laser phase sensitive anemometry and granulometry (PDPA). We demonstrate that droplets appear for vapor velocities larger than 5 m/s, and that they progressively invade the entire pipe cross section as the vapor velocity is increased. Estimates are given for the droplet size and density.
Heat transfer analysis of two-phase dispersed swirl flow
Chang Ching.
1991-01-01
A thermodynamic nonequilibrium model was developed for a two-phase, vapor and liquid droplet, dispersed swirl flow in a vertical tube with a twisted-tape insert. It takes account of the heat transfer phenomena between two phases, and each phase with solid boundary where a variable heat flux along axial direction is imposed. A numerical method is developed to solve the system of nonlinear differential equations. The local equilibrium conditions of the fluid at the point of critical heat flux (CHF) are chosen as the initial conditions to start the numerical integration to the downstream. Wall temperature, superheat vapor temperature, heat transfer rate from two phases, and velocity distributions of two phases were predicted and analyzed, which were then verified by comparing them with the low wall-superheat heat exchanger experimental data of water-steam in the range of 900.0 {le} G {le} 1,900.0, 2.51 {le} y {le} 7.53, X{sub CHF} {ge} 0.444. Additional parametric studies of the CHF quality, mass flux, and tape-twist ratio are presented. It is found that higher mass flux, lower tape-twist ratio, and low wall-superheat will give a stronger direct wall-droplet interaction and less superheating of vapor.
Investigation of two phase (oil, tensid) flow in capillaries
NASA Astrophysics Data System (ADS)
Szekely, G.
1980-07-01
Capillary flow phenomena were studied. The feasibility of a crude extraction method which can increase the eventual output of existing oil wells is discussed. A gas/water solution together with other additives is pumped into the well. This solution acts on the crude trapped in permeable stone formations. The state of the trapped oil is similar to oil in a capillary tube. Using laboratory apparatus, the characteristic two phase flow resulting when the tensid solution forces the oil out of the capillary was demonstrated.
Similarity considerations in one-component two-phase flow
Maeder, P.F.; DiPippo, R.; Dickinson, D.A.; Nikitopoulos, D.E.
1984-07-01
The simplified model fluid presented here for two-phase flow can serve as a basis for the similarity analysis of a variety of substance flows. For the special case of water and R114, it is seen that exact similarity does not exist in the range of interest for geothermal applications, but that conditions can be found for reasonable similarity which permit one to replace water with R114 in laboratory-size apparatus. Thus experimental data and results obtained using R114 in a properly scaled laboratory setup can be converted with reasonable accuracy to those for water.
Investigation of single-substance horizontal two-phase flow
Dickinson, D.A.; Maeder, P.F.
1984-03-01
Despite the abundance of work in the field of two-phase flow, it seems as though a consensus has not been reached on some of the fundamental points. Although exceptions exist, adequate physical interpretation of the flow seems to be hindered either by complexity of analysis or, in the opposite extreme, the trend toward limited-range analysis and correlations. The dissertation presents the derivation of basic conservation equations for the phases. The combined equations are used to examine the phenomenon of slip and its practical limitations, the Fanno line for single-substance flow and the effect of slip on choking. Equations for critical mass flux in the presence of slip are derived. The Mach, Reynolds and Froude numbers based on conditions at flashing are introduced as the characteristic parameters, and the importance of compressibility in single-substance two-phase flow is discussed. Experimental measurements of pressure change and void fraction for flow in the highly compressible range (.5 < Ma < 1) are presented. The working fluid is Refrigerant R-114, at room temperature, in a test section of diameter 5 cm and length 8 m. The effect of the Froude and Mach numbers is examined. The experimental facility is operated intermittently with running times of approximately two minutes and is instrumented for rapid measurements using a computer data acquisition and control system. A description of the facility and procedure is provided.
Biofluid dynamics of two phase stratified flow through flexible membranes
NASA Astrophysics Data System (ADS)
Bhagavatula Nvssr, Dinesh; Pushpavanam, S.
2016-11-01
Two phase stratified flows between flexible membranes arise in biological flows like lung airway reopening, blood flow in arteries and movement of spinal cord. It is important to understand the physics behind the interaction of flexible membranes and the fluid flow. In this work, a theoretical model is developed and different types of instabilities that arise due to the fluid flow are understood. The solid membrane is modeled as an incompressible linear viscoelastic solid. To simplify the analysis, inertia in the solid is neglected. Linear stability analysis is carried around the base state velocity of the fluid and displacement field of the solid. The flow is perturbed by a small disturbance and a normal mode analysis is carried out to study the growth rate of the disturbance. An eigenvalue problem in formulated using Chebyshev spectral method and is solved to obtain the growth rate of the disturbance. The effect of different parameters such as thickness of the flexible membrane, Reynolds number, viscosity ratio, density ratio, Capillary number and Weissenberg number on the stability characteristics of the flow is studied in detail. Dispersion curves are obtained which explain the stability of the flow. A detail energy analysis is carried out to determine different ways through which energy transfers from the base flow to the disturbed flow.
Water holdup measurement in kerosene water two-phase flows
NASA Astrophysics Data System (ADS)
Huang, S.-F.; Zhang, X.-G.; Wang, D.; Lin, Z.-H.
2007-12-01
This paper proposes an intrusive method for measurement of water holdup based on water layer thickness in horizontal pipes. Water layer thickness is measured by a capacitance probe, which is made of a metal wire with an insulating film. The capacitance is linearly proportional to the water layer thickness and is independent of water salinity and its distribution. Seven thicknesses over the cross section of the pipe are measured simultaneously to compute water holdup. A curve of water layer thickness as a function of time is compared with a flow structure photo and the measured time-averaged water holdup is compared with that of a quick-closing valve (QCV) system. The experiments were carried out in kerosene-oil two-phase flows with high water fraction in horizontal pipes of 29 mm diameter. Four flow patterns with continuous water are reported, namely wavy stratified flow (WS), three-layer flow (3 L), water and dispersed oil in water flow (W&DO/W) and dispersed oil in water flow (DO/W). The results show that the layer thickness curves are in reasonable agreement with the flow structures to different extents under different flow patterns and that the accuracies of the measured water holdup mainly depend on flow patterns. The relative error limits of water holdup are -15.2% for WS, 12.9% and -14.5% (positive and negative) for 3 L, 34.9% for W&DO/W and 15.8% for DO/W.
On drag reduction in a two-phase flow
NASA Astrophysics Data System (ADS)
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.
Two-phase flow key to offshore line design
Corteville, J.; Besse, J.; Grouvel, J.M.; Roux, A.
1981-08-10
The aim of the research project is to supply engineers with a good knowledge of two-phase oil and gas flow and the means to predict flow regimes; average pressure drop; average liquid hold-up; and, for slug flow, the volume, frequency, and velocity of slugs. The research group has developed a theoretical stratified flow model based on the equations published by Y. Taitel and A.E. Dukler, J.M. Fitremann, and others. This model considers the gas and the liquid layers independently and takes into account the interaction at the interface. Standard fluid mechanics is applied to each phase. The geometry and the transfer characteristics of the interface are modeled semiempirically. The coefficients are obtained from regression analysis of the experimental data measured in the 6-in. test loop. This model gives the liquid hold-up as well as the pressure drop. 7 refs.
A real two-phase submarine debris flow and tsunami
Pudasaini, Shiva P.; Miller, Stephen A.
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
NASA Astrophysics Data System (ADS)
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
Interfacial characteristic measurements in horizontal bubbly two-phase flow
NASA Astrophysics Data System (ADS)
Wang, Z.; Huang, W. D.; Srinivasmurthy, S.; Kocamustafaogullari, G.
1990-10-01
Advances in the study of two-phase flow increasingly require detailed internal structure information upon which theoretical models can be formulated. The void fraction and interfacial area are two fundamental parameters characterizing the internal structure of two-phase flow. However, little information is currently available on these parameters, and it is mostly limited to vertical flow configurations. In view of the above, the internal phase distribution of concurrent, air-water bubbly flow in a 50.3 mm diameter transparent pipeline has been experimentally investigated by using a double-sensor resistivity probe. Liquid and gas volumetric superficial velocities ranged from 3.74 to 5.60 m/s and 0.25 to 1.59 m/s, respectively, and average void fractions ranged from 2.12 to 22.5 percent. The local values of void fractions, interfacial area concentration, mean bubble diameter, bubble interface velocity, bubble chord-length and bubble frequency distributions were measured. The experimental results indicate that the void fraction interfacial area concentration and bubble frequency have local maxima near the upper pipe wall, and the profiles tend to flatten with increasing void fraction. The observed peak void fraction can reach 0.65, the peak interfacial area can go up to 900 approximately 1000 sq m/cu m, and the bubble frequency can reach a value of 2200 per s. These ranges of values have never been reported for vertical bubbly flow. It is found that either decreasing the liquid flow rate or increasing the gas flow would increase the local void fraction, the interfacial area concentration and the bubble frequency.
Sound speed criterion for two-phase critical flow
NASA Astrophysics Data System (ADS)
Chung, M.-S.; Park, S.-B.; Lee, H.-K.
2004-09-01
Critical flow simulation for non-homogeneous, non-equilibrium two-phase flows is improved by applying a new sound speed model which is derived from the characteristic analysis of hyperbolic two-fluid model. The hyperbolicity of two-fluid model was based on the concept of surface tension for the interfacial pressure jump terms in the momentum equations. Real eigenvalues obtained as the closed-form solution of characteristic polynomial represent the sound speeds in the bubbly flow regime that agree well with the existing experimental data. The analytic sound speed is consistent with that obtained by the earlier study of Nguyen et al. though there is a difference between them especially in the limiting condition. The present sound speed shows more reasonable result in that condition than Nguyen et al.'s does. The present critical flow criterion derived by the present sound speed is employed in the MARS code and is assessed by treating several nozzle flow tests. The assessment results, without any adjustment made by some discharge coefficients, demonstrate more accurate predictions of critical flow rate than those of the earlier critical flow calculations in the bubbly flow regime.
Particle-fluid two-phase flow modeling
Mortensen, G.A.; Trapp, J.A. |
1992-09-01
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.
Particle-fluid two-phase flow modeling
Mortensen, G.A. ); Trapp, J.A. Idaho National Engineering Lab., Idaho Falls, ID )
1992-01-01
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 Mapping and Transition Under Microgravity Conditions
NASA Technical Reports Server (NTRS)
Parang, Masood; Chao, David F.
1998-01-01
In this paper, recent microgravity two-phase flow data for air-water, air-water-glycerin, and air- water-Zonyl FSP mixtures are analyzed for transition from bubbly to slug and from slug to annular flow. It is found that Weber number-based maps are inadequate to predict flow-pattern transition, especially over a wide range of liquid flow rates. It is further shown that slug to annular flow transition is dependent on liquid phase Reynolds number at high liquid flow rate. This effect may be attributed to growing importance of liquid phase inertia in the dynamics of the phase flow and distribution. As a result a new form of scaling is introduced to present data using liquid Weber number based on vapor and liquid superficial velocities and Reynolds number based on liquid superficial velocity. This new combination of the dimensionless parameters seem to be more appropriate for the presentation of the microgravity data and provides a better flow pattern prediction and should be considered for evaluation with data obtained in the future. Similarly, the analysis of bubble to slug flow transition indicates a strong dependence on both liquid inertia and turbulence fluctuations which seem to play a significant role on this transition at high values of liquid velocity. A revised mapping of data using a new group of dimensionless parameters show a better and more consistent description of flow transition over a wide range of liquid flow rates. Further evaluation of the proposed flow transition mapping will have to be made after a wider range of microgravity data become available.
Statistical descriptions of polydisperse turbulent two-phase flows
NASA Astrophysics Data System (ADS)
Minier, Jean-Pierre
2016-12-01
Disperse two-phase flows are flows containing two non-miscible phases where one phase is present as a set of discrete elements dispersed in the second one. These discrete elements, or 'particles', can be droplets, bubbles or solid particles having different sizes. This situation encompasses a wide range of phenomena, from nano-particles and colloids sensitive to the molecular fluctuations of the carrier fluid to inertia particles transported by the large-scale motions of turbulent flows and, depending on the phenomenon studied, a broad spectrum of approaches have been developed. The aim of the present article is to analyze statistical models of particles in turbulent flows by addressing this issue as the extension of the classical formulations operating at a molecular or meso-molecular level of description. It has a three-fold purpose: (1) to bring out the thread of continuity between models for discrete particles in turbulent flows (above the hydrodynamical level of description) and classical mesoscopic formulations of statistical physics (below the hydrodynamical level); (2) to reveal the specific challenges met by statistical models in turbulence; (3) to establish a methodology for modeling particle dynamics in random media with non-zero space and time correlations. The presentation is therefore centered on organizing the different approaches, establishing links and clarifying physical foundations. The analysis of disperse two-phase flow models is developed by discussing: first, approaches of classical statistical physics; then, by considering models for single-phase turbulent flows; and, finally, by addressing current formulations for discrete particles in turbulent flows. This brings out that particle-based models do not cease to exist above the hydrodynamical level and offer great interest when combined with proper stochastic formulations to account for the lack of equilibrium distributions and scale separation. In the course of this study, general results
Turbulent transition modification in dispersed two-phase pipe flow
NASA Astrophysics Data System (ADS)
Winters, Kyle; Longmire, Ellen
2014-11-01
In a pipe flow, transition to turbulence occurs at some critical Reynolds number, Rec , and transition is associated with intermittent swirling structures extending over the pipe cross section. Depending on the magnitude of Rec , these structures are known either as puffs or slugs. When a dispersed second liquid phase is added to a liquid pipe flow, Rec can be modified. To explore the mechanism for this modification, an experiment was designed to track and measure these transitional structures. The facility is a pump-driven circuit with a 9m development and test section of diameter 44mm. Static mixers are placed upstream to generate an even dispersion of silicone oil in a water-glycerine flow. Pressure signals were used to identify transitional structures and trigger a high repetition rate stereo-PIV system downstream. Stereo-PIV measurements were obtained in planes normal to the flow, and Taylor's Hypothesis was employed to infer details of the volumetric flow structure. The presentation will describe the sensing and imaging methods along with preliminary results for the single and two-phase flows. Supported by Nanodispersions Technology.
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.
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
COARSE-GRID SIMULATION OF REACTING AND NON-REACTING GAS-PARTICLE FLOWS
Sankaran Sundaresan
2004-03-01
The principal goal of this project, funded under the ''DOE Vision 21 Virtual Demonstration Initiative'' is virtual demonstration of circulating fluidized bed performance. We had proposed a ''virtual demonstration tool'', which is based on the open-domain CFD code MFIX. The principal challenge funded through this grant is to devise and implement in this CFD code sound physical models for the rheological characteristics of the gas-particle mixtures. Within the past year, which was the third year of the project, we have made the following specific advances. (a) We have completed a study of the impact of sub-grid models of different levels of detail on the results obtained in coarse-grid simulations of gas-particle flow. (b) We have also completed a study of a model problem to understand the effect of wall friction, which was proved in our earlier work to be very important for stable operation of standpipes in a circulating fluidized bed circuit. These are described in a greater detail in this report.
Two-phase flow cell for chemiluminescence and bioluminescence measurements
Mullin, J.L.; Seitz, W.R.
1984-01-01
A new approach to two-phase CL (chemiluminescence) measurements is reported. A magnetically stirred reagent phase is separated from the analyte phase by a dialysis membrane so that only smaller molecules can go from one phase to the other. The system is designed so that the analyte phase flows through a spiral groove on an aluminum block that is flush against the dialysis membrane. As solution flows through the spiral grove, analyte diffuses into the reagent phase where it reacts to produce light. A simple model is developed to predict how this system will behave. Experimentally, the system is evaluated by using the luminol reaction catalyzed by peroxidase, the firefly reaction, and the bacterial bioluminescence reaction. 10 references, 4 tables, 6 figures.
Interfacial shear modeling in two-phase annular flow
Kumar, R.; Edwards, D.P.
1996-11-01
A new interfacial shear stress model called the law of the interface model, based on the law of the wall approach in turbulent flows, has been developed and locally applied in a fully developed, adiabatic, two-phase annular flow in a duct. Numerical results have been obtained using this model in conjunction with other models available in the literature that are required for the closure of the continuity and momentum equations. These results have been compared with droplet velocity data (using laser Doppler velocimetry and hot film anemometry), void fraction data (using gamma densitometry) and pressure drop data obtained in a R-134A refrigerant test facility. Droplet velocity results match the experimental data well, however, the prediction of the void fraction is less accurate. The poor prediction of void fraction, especially for the low void fraction cases, appears to be due to the lack of a good mechanistic model for entrainment.
Interfacial shear modeling in two-phase annular flow
Kumar, R.; Edwards, D.P.
1996-07-01
A new interfacial shear stress model called the law of the interface model, based on the law of the wall approach in turbulent flows, has been developed and locally applied in a fully developed, adiabatic, two-phase annular flow in a duct. Numerical results have been obtained using this model in conjunction with other models available in the literature that are required for the closure of the continuity and momentum equations. These results have been compared with droplet velocity data (using laser Doppler velocimetry and hot film anemometry), void fraction data (using gamma densitometry) and pressure drop data obtained in a R-134A refrigerant test facility. Droplet velocity results match the experimental data well, however, the prediction of the void fraction is less accurate. The poor prediction of void fraction, especially for the low void fraction cases, appears to be due to the lack of a good mechanistic model for entrainment.
Flooding in counter-current two-phase flow
Ragland, W.A.; Ganic, E.N.
1982-01-01
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.
Conceptual design for spacelab two-phase flow experiments
NASA Technical Reports Server (NTRS)
Bradshaw, R. D.; King, C. D.
1977-01-01
KC-135 aircraft tests confirmed the gravity sensitivity of two phase flow correlations. The prime component of the apparatus is a 1.5 cm dia by 90 cm fused quartz tube test section selected for visual observation. The water-cabin air system with water recycle was a clear choice for a flow regime-pressure drop test since it was used satisfactorily on KC-135 tests. Freon-11 with either overboard dump or with liquid-recycle will be used for the heat transfer test. The two experiments use common hardware. The experimental plan covers 120 data points in six hours with mass velocities from 10 to 640 kg/sec-sq m and qualities 0.01 to 0.64. The apparatus with pump, separator, storage tank and controls is mounted in a double spacelab rack. Supporting hardware, procedures, measured variables and program costs are defined.
Tsunami Generated by a Two-Phase Submarine Debris Flow
NASA Astrophysics Data System (ADS)
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
Calculation of two-phase flow in gas turbine combustors
Tolpadi, A.K.
1995-10-01
A method is presented for computing steady two-phase turbulent combusting flow in a gas turbine combustor. The gas phase equations are solved in an Eulerian frame of reference. The two-phase calculations are performed by using a liquid droplet spray combustion a model and treating the motion of the evaporating fuel droplets in a Lagrangian frame of reference. The numerical algorithm employs nonorthogonal curvilinear coordinates, a multigrid iterative solution procedure, the standard k-{epsilon} turbulence model, and a combustion model comprising an assumed shape probability density function and the conserved scalar formulation. The trajectory computation of the fuel provides the source terms for all the gas phase equations. This two-phase model was applied to a real piece of combustion hardware in the form of a modern GE/SNECMA single annular CFM56 turbofan engine combustor. For the purposes of comparison, calculations were also performed by treating the fuel as a single gaseous phase. The effect on the solution of two extreme situations of the fuel as a gas and initially as a liquid was examined. The distribution of the velocity field and the conserved scalar within the combustor, as well as the distribution of the temperature field in the reaction zone and in the exhaust, were all predicted with the combustor operating both at high-power and low-power (ground idle) conditions. The calculated exit gas temperature was compared with test rig measurements. Under both low and high-power conditions, the temperature appeared to show an improved agreement with the measured data when the calculations were performed with the spray model as compared to a single-phase calculation.
Modelling compressible dense and dilute two-phase flows
NASA Astrophysics Data System (ADS)
Saurel, Richard; Chinnayya, Ashwin; Carmouze, Quentin
2017-06-01
Many two-phase flow situations, from engineering science to astrophysics, deal with transition from dense (high concentration of the condensed phase) to dilute concentration (low concentration of the same phase), covering the entire range of volume fractions. Some models are now well accepted at the two limits, but none are able to cover accurately the entire range, in particular regarding waves propagation. In the present work, an alternative to the Baer and Nunziato (BN) model [Baer, M. R. and Nunziato, J. W., "A two-phase mixture theory for the deflagration-to-detonation transition (DDT) in reactive granular materials," Int. J. Multiphase Flow 12(6), 861 (1986)], initially designed for dense flows, is built. The corresponding model is hyperbolic and thermodynamically consistent. Contrarily to the BN model that involves 6 wave speeds, the new formulation involves 4 waves only, in agreement with the Marble model [Marble, F. E., "Dynamics of a gas containing small solid particles," Combustion and Propulsion (5th AGARD Colloquium) (Pergamon Press, 1963), Vol. 175] based on pressureless Euler equations for the dispersed phase, a well-accepted model for low particle volume concentrations. In the new model, the presence of pressure in the momentum equation of the particles and consideration of volume fractions in the two phases render the model valid for large particle concentrations. A symmetric version of the new model is derived as well for liquids containing gas bubbles. This model version involves 4 characteristic wave speeds as well, but with different velocities. Last, the two sub-models with 4 waves are combined in a unique formulation, valid for the full range of volume fractions. It involves the same 6 wave speeds as the BN model, but at a given point of space, 4 waves only emerge, depending on the local volume fractions. The non-linear pressure waves propagate only in the phase with dominant volume fraction. The new model is tested numerically on various
NASA Astrophysics Data System (ADS)
Zhou, L. X.
2009-02-01
Innovative coal combustors were developed, and measurement and simulation of gas-particle flows and coal combustion in such combustors were done in the Department of Engineering Mechanics, Tsinghua University. LDV/PDPA measurements are made to understand the behavior of turbulent gas-particle flows in coal combustors. Coal combustion test was done for the non-slagging cyclone coal combustor. The full two-fluid model developed by the present author was used to simulate turbulent gas-particle flows, coal combustion and NOx formation. It is found by measurements and simulation that the optimum design can give large-size recirculation zones for improving the combustion performance for all the combustors. The combustion test shows that the nonslagging coal combustor can burn 3-5mm coal particles with good combustion efficiency and low NO emission. Simulation in comparison with experiments indicates that the swirl number can significantly affect the NO formation in the swirl coal combustor.
Measurement of two-phase flow momentum with force transducers
Hardy, J.E.; Smith, J.E.
1990-01-01
Two strain-gage-based drag transducers were 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 accident (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 a PWR. 9 refs., 15 figs.
A Dissipative Particle Dynamics model for two-phase flows
NASA Astrophysics Data System (ADS)
Tiwari, Anupam
2005-11-01
A Dissipative Particle Dynamics (DPD) model for two-phase flows is presented. The new model, unlike existing models [1, 2], uses different cut-off radii for the attractive and repulsive components of the inter-particle interaction potential and allows for larger density ratios between the phases. Surface tension arises due to the attractive component and a forcing term that depends on higher order density gradients. The model is shown to reproduce the Laplace law and analytical results for drop oscillations. A new method that couples a Lennard-Jones type potential with a coarse-grained potential is also presented. References: [1] Pagonabarraga, I. and Frenkel, D. (2001). Journal of Chemical Physics, 115(11): 5015-5026. [2] Warren, P.B. (2003). Physical Review E. 68. 066702: 1-8.
Higher order time integration methods for two-phase flow
NASA Astrophysics Data System (ADS)
Kees, Christopher E.; Miller, Cass T.
Time integration methods that adapt in both the order of approximation and time step have been shown to provide efficient solutions to Richards' equation. In this work, we extend the same method of lines approach to solve a set of two-phase flow formulations and address some mass conservation issues from the previous work. We analyze these formulations and the nonlinear systems that result from applying the integration methods, placing particular emphasis on their index, range of applicability, and mass conservation characteristics. We conduct numerical experiments to study the behavior of the numerical models for three test problems. We demonstrate that higher order integration in time is more efficient than standard low-order methods for a variety of practical grids and integration tolerances, that the adaptive scheme successfully varies the step size in response to changing conditions, and that mass balance can be maintained efficiently using variable-order integration and an appropriately chosen numerical model formulation.
Vapor core turbulence in annular two-phase flow
Trabold, T.A.; Kumar, R.
1998-06-01
This paper reports a new technique to measure vapor turbulence in two-phase flows using hot-film anemometry. Continuous vapor turbulence measurements along with local void fraction, droplet frequency, droplet velocity and droplet diameter were measured in a thin, vertical duct. By first eliminating the portion of the output voltage signal resulting from the interaction of dispersed liquid droplets with the HFA sensor, the discrete voltage samples associated with the vapor phase were separately analyzed. The data revealed that, over the range of liquid droplet sizes and concentrations encountered, the presence of the droplet field acts to enhance vapor turbulence. In addition, there is evidence that vapor turbulence is significantly influenced by the wall-bounded liquid film. The present results are qualitatively consistent with the limited data available in the open literature.
Particle migration in two-phase, viscoelastic flows
NASA Astrophysics Data System (ADS)
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.
Unsteady flow analysis of a two-phase hydraulic coupling
NASA Astrophysics Data System (ADS)
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.
DYNAMIC MODELING STRATEGY FOR FLOW REGIME TRANSITION IN GAS-LIQUID TWO-PHASE FLOWS
X. Wang; X. Sun; H. Zhao
2011-09-01
In modeling gas-liquid two-phase flows, the concept of flow regime has been 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 are developed for steady-state, fully-developed flows and widely applied in nuclear reactor system safety analysis codes, such as RELAP5. As two-phase flows are observed to be 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 for more accurate predictions of two-phase flows. The present work aims to develop a dynamic modeling strategy for determining flow regimes in gas-liquid two-phase flows through the 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 shape (which are correlated), namely small bubbles and large bubbles. A preliminary approach to dynamically identifying the flow regimes is provided, in which discriminators are based on the predicted information, such as the void fraction and interfacial area concentration of small bubble and large bubble groups. This method is expected to be applied to computer codes to improve their predictive capabilities of gas-liquid two-phase flows, in particular for the applications in
Two-phase flow research. Phase I. Two-phase nozzle research. Final report
Toner, S.J.
1981-07-01
An investigation of energy transfer in two-phase nozzles was conducted. Experimental performance of converging-diverging nozzles operating on air-water mixtures is presented for a wide range of parameters. Thrust measurements characterized the performance and photographic documentation was used to visually observe the off-design regimes. Thirty-six nozzle configurations were tested to determine the effects of convergence angle, area ratio, and nozzle length. In addition, the pressure ratio and mass flowrate ratio were varied to experimentally map off-design performance. The test results indicate the effects of wall friction and infer temperature and velocity differences between phases and the effect on nozzle performance. The major conclusions reached were: the slip ratio between the phases, gas velocity to liquid velocity, is shown to be below about 4 or 5, and, in most of the test cases run, was estimated to between about 1-1/2 to 2-1/2; in all cases except the free-jet the mass )
Two-phase choked flow of subcooled nitrogen through a slit. [flow rate and pressure distribution
NASA Technical Reports Server (NTRS)
Simoneau, R. J.
1974-01-01
Two-phase choked flow rate and pressure distribution data are reported for subcooled nitrogen flowing through a slit. The slip was a narrow rectangular passage of equal length and width. The inlet stagnation pressure ranged from slightly above saturation to twice the thermodynamic critical pressure. Four stagnation isotherms were investigated covering a range which spanned the critical temperature. The results suggested a uniform two-phase flow pattern with vaporization occurring at or near the exit in most cases. The results compared favorably with the theory of Henry for nonequilibrium subcooled two-phase choked flow in long tubes.
Tracking Interfaces in Vertical Two-Phase Flows
Aktas, Birol
2002-07-01
The presence of stratified liquid-gas interfaces in vertical flows poses difficulties to most classes of solution methods for two-phase flows of practical interest in the field of reactor safety and thermal-hydraulics. These difficulties can plague the reactor simulations unless handled with proper care. To illustrate these difficulties, the US NRC Consolidated Thermal-hydraulics Code (TRAC-M) was exercised with selected numerical bench-mark problems. These numerical benchmarks demonstrate that the use of an average void fraction for computational volumes simulating vertical flows is inadequate when these volumes consist of stratified liquid-gas interfaces. In these computational volumes, there are really two regions separated by the liquid-gas interface and each region has a distinct flow topology. An accurate description of these divided computational volumes require that separate void fractions be assigned to each region. This strategy requires that the liquid-gas interfaces be tracked in order to determine their location, the volumes of regions separated by the interface, and the void fractions in these regions. The idea of tracking stratified liquid-gas interfaces is not new. There are examples of tracking methods that were developed for reactor safety codes and applied to reactor simulations in the past with some limited success. The users of these safety codes were warned against potential flow oscillations, conflicting water levels, and pressure disturbances which could be caused by the tracking methods themselves. An example of these methods is the level tracking method of TRAC-M. A review of this method is given here to explore the reasons behind its failures. The review shows that modifications to the field equations are mostly responsible for these failures. Following the review, a systematic approach to incorporate interface tracking methods is outlined. This approach is applicable to most classes of solution methods. For demonstration, the approach to
Degassing and two-phase flow pilot hole test report
Geller, J.T.; Jarsjoe, J.
1995-03-01
A pilot hole test was conducted to support the design of the Degassing of Groundwater and Two-Phase Flow experiments planned for the Hard Rock Laboratory, Aespoe, Sweden. The test consisted of a sequence of constant pressure borehole inflow tests (CPTs) and pressure recovery tests (PRTs) in borehole KA2512A. The test sequence was designed to detect degassing effects from the change in transmissivity, or hydraulic conductivity, and storativity when the borehole pressure is lowered below the groundwater bubble pressure. The entire 37.3m of the borehole section was tested without packers. Flow response to pressure changes in CPTs occurred rapidly. Flowrates fluctuated before attaining a steady trend, probably due to effective stress changes when borehole pressure was reduced for the first time. These factors decreased the sensitivity of type-curve fits to values of specific storage. The relationship between borehole pressure and steady-state flowrates was linear over borehole pressures of 1500 kPa (abs) down to 120 kPa (abs) during testing in December 1994, indicating that processes that may change hydraulic conductivity at low borehole pressures, such as degassing, calcite precipitation or turbulence, did not occur to a measurable degree. Test results during January and February of 1995 suggest that degassing may have occurred. The hydraulic conductivity measured at a borehole pressure equal to 120 kPa (abs) was 20% lower than the hydraulic conductivity measured at a borehole pressure of 1500 kPa (abs); the latter value was 10% lower than the hydraulic conductivity measured in December, 1994. The volumetric gas content measured during this time was 1% v/v. Pressures in monitoring well KA2511A responded to the testing in KA2512A. Step-changes in flowrates coincided with blasting at 3300-3400 m tunnel length. The magnitude of these changes was greater at the lower borehole pressures. Step increases in pressures in KA2511A also coincided with the blasts.
NASA Technical Reports Server (NTRS)
Penny, M. M.; Smith, S. D.; Anderson, P. G.; Sulyma, P. R.; Pearson, M. L.
1976-01-01
A numerical solution for chemically reacting supersonic gas-particle flows in rocket nozzles and exhaust plumes was described. The gas-particle flow solution is fully coupled in that the effects of particle drag and heat transfer between the gas and particle phases are treated. Gas and particles exchange momentum via the drag exerted on the gas by the particles. Energy is exchanged between the phases via heat transfer (convection and/or radiation). Thermochemistry calculations (chemical equilibrium, frozen or chemical kinetics) were shown to be uncoupled from the flow solution and, as such, can be solved separately. The solution to the set of governing equations is obtained by utilizing the method of characteristics. The equations cast in characteristic form are shown to be formally the same for ideal, frozen, chemical equilibrium and chemical non-equilibrium reacting gas mixtures. The particle distribution is represented in the numerical solution by a finite distribution of particle sizes.
Two parametric flow measurement in gas-liquid two-phase flow
NASA Astrophysics Data System (ADS)
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.
Fusion Research of Electrical Tomography with Other Sensors for Two-phase Flow Measurement
NASA Astrophysics Data System (ADS)
Deng, Xiang; Yang, W. Q.
2012-01-01
The two-phase flow widely exists in the nature and industrial processes. The measurement of two-phase flows, including gas/solids, gas/liquid and liquid/liquid flows, is still challenging. Fusions of electrical tomography with conventional sensors provide possibilities to improve two-phase flow accurate measurement. In this paper, fusions of (1) electrical resistance tomography (ERT) with electromagnetic (EM) flowmeter, (2) electrical capacitance tomography (ECT) with ERT and (3) ECT with electrostatic sensor are introduced. Some research results of fusion methods are presented and discussed. This paper can provide the theoretical support for the multi-sensor fusion for two-phase flow measurement.
Analysis of two-phase flow included vibrations in piping systems
Hiramatsu, T.; Komura, Y.; Yano, S.
1982-01-01
The purpose of this analysis is to predict the vibration level of a pipe conveying a two-phase flowing fluid. Experiments were carried out with a horizontally supported U-type piping system, conveying an air-water two-phase flow in a steady state condition. A theoretical analysis is achieved using the transfer method for vibration responses of the system excited by the forces of traveling liquid piston and the momentum change of two-phase flow. Comparing experimental and theoretical studies, the author concluded that the vibrational behavior of piping systems conveying two-phase flowing fluid can be predicted quantitatively. 8 refs.
A chaotic system of two-phase flow in a small, horizontal, rectangular channel
Cai, Y.; Wambsganss, M.W.; Jendrzejczyk, J.A.
1995-07-01
Various measurement tools that are used in chaos theory were applied to analyze two-phase pressure signals with the objective of identifying and interpreting flow pattern transitions for two-phase flows in a small, horizontal rectangular channel. These measurement tools included power spectral density function, autocorrelation function, pseudo-phase-plane trajectory, Lyapunov exponents, and fractal dimensions. It was demonstrated that the randomlike pressure fluctuations characteristic of two-phase flow in small rectangular channels are chaotic. As such, they are governed by a high-order deterministic system. The correlation dimension is potentially a new approach for identifying certain two-phase flow patterns and transitions.
Two-phase flows simulation in closed volume
NASA Astrophysics Data System (ADS)
Fedorov, A. V.; Lavruk, S. A.
2016-10-01
In this paper gas flow field was considered in the model volumes that correspond to real experimental ones. During simulation flow fields were defined in volumes, matching of the flow fields in different volumes and comparison of the velocity values along the plate that models fuel tank element was done.
Stability of stratified two-phase flows in inclined channels
NASA Astrophysics Data System (ADS)
Barmak, I.; Gelfgat, A. Yu.; Ullmann, A.; Brauner, N.
2016-08-01
Linear stability of the stratified gas-liquid and liquid-liquid plane-parallel flows in the inclined channels is studied with respect to all wavenumber perturbations. The main objective is to predict the parameter regions in which the stable stratified configuration in inclined channels exists. Up to three distinct base states with different holdups exist in the 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 the non-unique stable stratified configurations in inclined channels. The stability boundaries of each branch of the steady state solutions are presented on the flow pattern map and are accompanied by the critical wavenumbers and the spatial profiles of the most unstable perturbations. Instabilities of different nature are visualized by the streamlines of the neutrally stable perturbed flows, consisting of the critical perturbation superimposed on the base flow. The present analysis confirms the existence of two stable stratified flow configurations in a region of low flow rates in the countercurrent liquid-liquid flows. These configurations become unstable with respect to the shear mode of instability. It was revealed that in slightly upward inclined flows the lower and middle solutions for the holdup are stable in the part of the triple solution region, while the upper solution is always unstable. In the case of downward flows, in the triple solution region, none of the solutions are stable with respect to the short-wave perturbations. These flows are stable only in the single solution region at low flow rates of the heavy phase, and the long-wave perturbations are the most unstable ones.
Capacitive Sensing Of Gaseous Fraction In Two-Phase Flow
NASA Technical Reports Server (NTRS)
Crowley, Christopher J.; Sahm, Michael K.
1995-01-01
Instrument makes nonintrusive, real-time capacitive measurements to determine volume fraction of vapor or other gas in flowing, electrically nonconductive liquid/gas mixture. Works even with liquids having relatively low permittivities. Useful for measuring proportions of vapor in boiling, condensing, and flowing heat-transfer fluids and in cryogenic fluids.
Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume I. Chapters 1-5)
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)
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 IV. Chapters 15-19)
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)
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.
Sarkar, Avik; Milioli, Fernando E.; Ozarkar, Shailesh; Li, Tingwen; Sun, Xin; Sundaresan, Sankaran
2016-10-01
The accuracy of fluidized-bed CFD predictions using the two-fluid model can be improved significantly, even when using coarse grids, by replacing the microscopic kinetic-theory-based closures with coarse-grained constitutive models. These coarse-grained constitutive relationships, called filtered models, account for the unresolved gas-particle structures (clusters and bubbles) via sub-grid corrections. Following the previous 2-D approaches of Igci et al. [AIChE J., 54(6), 1431-1448, 2008] and Milioli et al. [AIChE J., 59(9), 3265-3275, 2013], new filtered models are constructed from highly-resolved 3-D simulations of gas-particle flows. Although qualitatively similar to the older 2-D models, the new 3-D relationships exhibit noticeable quantitative and functional differences. In particular, the filtered stresses are strongly dependent on the gas-particle slip velocity. Closures for the filtered inter-phase drag, gas- and solids-phase pressures and viscosities are reported. A new model for solids stress anisotropy is also presented. These new filtered 3-D constitutive relationships are better suited to practical coarse-grid 3-D simulations of large, commercial-scale devices.
2013-11-01
Figure 1. The apparatus for the current work consists of two separate loops , 1) R-134a test loop and 2) Water Cooling loop . A pumped refrigeration loop ...measurements are taken between an L/D of 280 and 300 to ensure that the two phase flow is fully developed. Testing was performed with refrigerant...analysis demonstrates the liquid vapor distributions for each flow regime as seen in Figure 3. Each test point described in this paper is accompanied
Modeling of a turbine flowmeter in transient two-phase flow. [PWR
Chen, N.C.J.; Felde, D.K.
1981-01-01
A transient turbine meter model by Kamath and Lahey was applied to calculate two-phase mass flux from test data at the Thermal Hydraulic Test Facility (THTF). Comparisons are made with homogeneous models based on measured average density and volumetric flow rate in an effort to determine uncertainites introduced by two-phase flow effects such as slip ratio and void fraction.
Two-phase flow research using the learjet apparatus
NASA Astrophysics Data System (ADS)
McQuillen, John B.; Neumann, Eric S.
1995-05-01
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 flow research using the learjet apparatus
NASA Technical Reports Server (NTRS)
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.
Flow regime classification in air-magnetic fluid two-phase flow.
Kuwahara, T; De Vuyst, F; Yamaguchi, H
2008-05-21
A new experimental/numerical technique of classification of flow regimes (flow patterns) in air-magnetic fluid two-phase flow is proposed in the present paper. The proposed technique utilizes the electromagnetic induction to obtain time-series signals of the electromotive force, allowing us to make a non-contact measurement. Firstly, an experiment is carried out to obtain the time-series signals in a vertical upward air-magnetic fluid two-phase flow. The signals obtained are first treated using two kinds of wavelet transforms. The data sets treated are then used as input vectors for an artificial neural network (ANN) with supervised training. In the present study, flow regimes are classified into bubbly, slug, churn and annular flows, which are generally the main flow regimes. To validate the flow regimes, a visualization experiment is also performed with a glycerin solution that has roughly the same physical properties, i.e., kinetic viscosity and surface tension, as a magnetic fluid used in the present study. The flow regimes from the visualization are used as targets in an ANN and also used in the estimation of the accuracy of the present method. As a result, ANNs using radial basis functions are shown to be the most appropriate for the present classification of flow regimes, leading to small classification errors.
Flow regime classification in air magnetic fluid two-phase flow
NASA Astrophysics Data System (ADS)
Kuwahara, T.; DeVuyst, F.; Yamaguchi, H.
2008-05-01
A new experimental/numerical technique of classification of flow regimes (flow patterns) in air-magnetic fluid two-phase flow is proposed in the present paper. The proposed technique utilizes the electromagnetic induction to obtain time-series signals of the electromotive force, allowing us to make a non-contact measurement. Firstly, an experiment is carried out to obtain the time-series signals in a vertical upward air-magnetic fluid two-phase flow. The signals obtained are first treated using two kinds of wavelet transforms. The data sets treated are then used as input vectors for an artificial neural network (ANN) with supervised training. In the present study, flow regimes are classified into bubbly, slug, churn and annular flows, which are generally the main flow regimes. To validate the flow regimes, a visualization experiment is also performed with a glycerin solution that has roughly the same physical properties, i.e., kinetic viscosity and surface tension, as a magnetic fluid used in the present study. The flow regimes from the visualization are used as targets in an ANN and also used in the estimation of the accuracy of the present method. As a result, ANNs using radial basis functions are shown to be the most appropriate for the present classification of flow regimes, leading to small classification errors.
Irreversible entropy production in two-phase flows with evaporating drops
NASA Technical Reports Server (NTRS)
Bellan, J.; Okong'o, N. A.
2002-01-01
A derivation of the irreversible entropy production, that is the dissipation, in two-phase flows is presented for the purpose of examining the effect of evaporative-drop modulation of flows having turbulent features.
Experimental on two sensors combination used in horizontal pipe gas-water two-phase flow
Wu, Hao; Dong, Feng
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.
Atomization of Wall-Bounded Two-Phase Flows (Preprint)
2006-11-07
stream may be subjected to a coflowing or cross-flowing gas stream or it may be introduced into a quiescent environment. Sheet atomization is...to an imposed gas velocity on either of its sides, both of its sides or neither side. Finally, a film is similar to a sheet, but is bounded on one...side by a wall; the other side may or may not be subjected to an imposed gas flow. Films may have several geometries, but the most common in
A continuum theory for two-phase flows of particulate solids: application to Poiseuille flows
NASA Astrophysics Data System (ADS)
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
An improved stochastic separated flow model for turbulent two-phase flow
NASA Astrophysics Data System (ADS)
Chan, C. K.; Zhang, H. Q.; Lau, K. S.
An improved stochastic separated flow model is proposed to obtain reasonable statistical characteristics of a two-phase flow. Effects of the history of a particle and its current trajectory position on the mean-square fluctuating velocity of the dispersed phase are continuously considered in this model. Comparing with the conventional model, results using the improved model are more reasonable and can also be obtained more easily. Furthermore, the improved model requires less computational particles for simulating dispersed-phase turbulence at the beginning of the stochastic trajectory. In this paper, an application in turbulent two-phase flow of planar mixing layer is carried out. Numerical results including velocity, mean-square fluctuating velocity, particle number density and pdf of fluctuation velocity of dispersed phase are shown to compare well with experimental data.
Deposition in two phase flow in porous media
NASA Astrophysics Data System (ADS)
Adler, P. M.
2007-12-01
The study of dispersion and deposition of an active tracer in multiphase flow through a porous medium is a difficult topic which has not received much attention in the past though it has a lot of practical and fundamental interest. For instance, asphaltene flocculation implies its deposition on the solid walls and this has two effects. The first one is to change the wettability of the walls; if they are initially water wet, they may become oil wet. The second one is to reduce the pore space. In both cases, the flow properties of the porous medium are expected to be influenced. Our purpose was to develop a new tool to analyse these two effects; this new tool had to be constructed by integrating existing codes. First, the basic ingredients which are necessary for the determination of dispersion and deposition at the local scale are presented. The pore space can be generated by means of the method of reconstructed media (1). The instantaneous phase distribution and the velocity fields are computed by an Immiscible Lattice Boltzmann model (2). The solute dispersion is obtained by the Random Walk technique (3); its deposition at the walls is supposed to follow a first order reaction (4). Finally, the rules for the solid and/or wettability changes will be precised. The main results of our calculations can be summarized as follows. The possibilities of the code are demonstrated on a three-dimensional medium; the evolution of the solid space, of the wettability properties and of the phase configurations are illustrated; dramatic results are shown for the evolution of the relative permeabilities and of the capillary pressures. Then, various parameters are studied in a systematic way, such as the porosity, the partition coefficient, the diffusion coefficient, the saturation and the kinetic coefficients. Some concluding remarks end up this study. Ref: (1) Adler P.M., Jacquin C.G., Quibier J.A., 1990, Flow in simulated porous media, Int. J. Multiphase flow, 16, 691- 712. (2
A simple delay model for two-phase flow dynamics
Clausse, A.; Delmastro, D.F.; Juanico`, L.E.
1995-09-01
A model based in delay equations for density-wave oscillations is presented. High Froude numbers and moderate ones were considered. The equations were numerically analyzed and compared with more sophisticated models. The influence of the gravity term was studied. Different kinds of behavior were found, particularly sub-critical and super-critical Hopf bifurcations. Moreover the present approach can be used to better understand the complicated dynamics of boiling flows systems.
Analysis of Developing Gas/liquid Two-Phase Flows
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.
Rarefaction Waves at the Outlet of the Supersonic Two-Phase Flow Nozzle
NASA Astrophysics Data System (ADS)
Nakagawa, Masafumi; Miyazaki, Hiroki; Harada, Atsushi
Two-phase flow nozzles are used in the total flow system for geothermal power plants and in the ejector of the refrigerant cycle, etc. One of the most important functions of a two-phase flow nozzle is to convert the thermal energy to the kinetic energy of the two-phase flow. The kinetic energy of the two-phase flow exhausted from a nozzle is available for all applications of this type. There exist the shock waves or rarefaction waves at the outlet of a supersonic nozzle in the case of non-best fitting expansion conditions when the operation conditions of the nozzle are widely chosen. Those waves affect largely on the energy conversion efficiency of the two-phase flow nozzle. The purpose of the present study is to elucidate the character of the rarefaction waves at the outlet of the supersonic two-phase flow nozzle. The high pressure hot water blow down experiment has been carried out. The decompression curves by the rarefaction waves are measured by changing the flow rate of the nozzle and inlet temperature of the hot water. The back pressures of the nozzle are also changed in those experiments. The divergent angles of the two-phase flow flushed out from the nozzle are measured by means of the photograph. The experimental results show that the recompression curves are different from those predicted by the isentropic homogenous two-phase flow. The regions where the rarefaction waves occur become wide due to the increased outlet speed of two-phase flow. The qualitative dependency of this expansion character is the same as the isotropic homogenous flow, but the values obtained from the experiments are quite different. When the back pressure of the nozzle is higher, these regions do not become small in spite of the super sonic two-phase flow. This means that the disturbance of the down-stream propagate to the up-stream. It is shown by the present experiments that the rarefaction waves in the supersonic two-phase flow of water have a subsonic feature. The measured
Study of hydrodynamic characteristics of two-phase flow in closed thermosiphons
NASA Astrophysics Data System (ADS)
Bezrodnyi, M. K.; Volkov, S. S.
Typical regions of development of the process of heat carrier phases interaction are studied experimentally and their boundaries in the closed two-phase counter-current flow system are determined. The influence of the two-phase medium compressible effects on the stability of the wave flow of the liquid film in the counter-current flow with the vapor flow is established. It is shown that the heat transfer limits in two-phase thermosiphons are determined by the conditions of counteraction of the heat carrier phases along the axis of the apparatus.
Two-phase choked flow of subcooled nitrogen through a slit
NASA Technical Reports Server (NTRS)
Simoneau, R. J.
1974-01-01
Two-phase choked flow rate and pressure distribution data are reported for subcooled nitrogen flowing through a slit. The slit was a narrow rectangular passage of equal length and width. The inlet stagnation pressure ranged from slightly above saturation to twice the thermodynamic critical pressure. Four stagnation isotherms were investigated, covering a range which spanned the critical temperature. The results suggested a uniform two-phase flow pattern with vaporization occurring at or near the exit in most cases. The results compared favorably with the theory of Henry (1970) for nonequilibrium subcooled two-phase choked flow in long tubes.
Experimental study of flow oscillations in parallel evaporators of a carbon dioxide two-phase loop
NASA Astrophysics Data System (ADS)
Sun, Xihui; He, Zhenhui; Huang, Zhencheng
2013-07-01
Stability is a key factor that limits the application of liquid-vapor two-phase loop. in this paper, we investigated the two-phase flow stability boundaries of two evaporators in parallel in a mechanically pumped CO2 two-phase loop(MPTL), which distinguish steady flow, flow oscillations at the inlet, and temperature oscillations at the outlets of the evaporators. We inferred that the instability is the result of density wave oscillation (DWO), and found that the periods of the flow oscillations are comparable with the residence time of CO2 fluid particle in the evaporator.
Enhanced two phase flow in heat transfer systems
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.
Structural rheological model of two-phase interlayer shear flow
NASA Astrophysics Data System (ADS)
Altoiz, B. A.; Aslanov, S. K.; Kiriyan, S. V.
2011-04-01
This paper presents a study of an epitropic liquid crystal layer formation at a metal substrate. Such layer structurization leads to non-Newtonian flow of thin interlayer with wall-adjacent orientation-ordered layers. Rheological characteristics of micron interlayers of n-hexadecane and Vaseline oil with surfactant addition are investigated. The features of structural "variable viscosity" layer are defined within the framework of a proposed rheological model. An increase in the rate of shear deformation leads to a reduction in near-surface layer viscosity due to molecular reorientation. Estimation of model parameters, performed on basis of the experimental rheological data, is carried out.
Experimental investigation of two-phase flow in rock salt
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.
Exact Integral Solutions for Two-Phase Flow
NASA Astrophysics Data System (ADS)
McWhorter, David B.; Sunada, Daniel K.
1990-03-01
Exact integral solutions for the horizontal, unsteady flow of two viscous, incompressible fluids are derived. Both one-dimensional and radial displacements are calculated with full consideration of capillary drive and for arbitrary capillary-hydraulic properties. One-dimensional, unidirectional displacement of a nonwetting phase is shown to occur increasingly like a shock front as the pore-size distribution becomes wider. This is in contrast to the situation when an inviscid nonwetting phase is displaced. The penetration of a nonwetting phase into porous media otherwise saturated by a wetting phase occurs in narrow, elongate distributions. Such distributions result in rapid and extensive penetration by the nonwetting phase. The process is remarkably sensitive to the capillary-hydraulic properties that determine the value of knw/kw at large wetting phase saturations, a region in which laboratory measurements provide the least resolution. The penetration of a nonwetting phase can be expected to be dramatically affected by the presence of fissures, worm holes, or other macropores. Calculations for radial displacement of a nonwetting phase resident at a small initial saturation show the displacement to be inefficient. The fractional flow of the nonwetting phase falls rapidly and, for a specific example, becomes 1% by the time one pore volume of water has been injected.
Two-phase flow in a chemically active porous medium
Darmon, Alexandre Dauchot, Olivier; Benzaquen, Michael; Salez, Thomas
2014-12-28
We study the problem of the transformation of a given reactant species into an immiscible product species, as they flow through a chemically active porous medium. We derive the equation governing the evolution of the volume fraction of the species, in a one-dimensional macroscopic description, identify the relevant dimensionless numbers, and provide simple models for capillary pressure and relative permeabilities, which are quantities of crucial importance when tackling multiphase flows in porous media. We set the domain of validity of our models and discuss the importance of viscous coupling terms in the extended Darcy’s law. We investigate numerically the steady regime and demonstrate that the spatial transformation rate of the species along the reactor is non-monotonous, as testified by the existence of an inflection point in the volume fraction profiles. We obtain the scaling of the location of this inflection point with the dimensionless lengths of the problem. Eventually, we provide key elements for optimization of the reactor.
A Level Set Method for vaporizing two-phase flows
NASA Astrophysics Data System (ADS)
Tanguy, Sébastien; Ménard, Thibaut; Berlemont, Alain
2007-02-01
Development and applications of numerical methods devoted to reactive interface simulations are presented. Emphasis is put on vaporization, where numerical difficulties arise in imposing accurate jump conditions for heat and mass transfers. We use both the Level Set Method and the Ghost Fluid Method to capture the interface motion accurately and to handle suitable jump conditions. A local vaporization mass flow rate per unit of surface area is defined and Stefan flow is involved in the process. Specific care has been devoted to the extension of discontinuous variables across the interface to populate ghost cells, in order to avoid parasitic currents and numerical diffusion across the interface. A projection method is set up to impose both the velocity field continuity and a divergence-free condition for the extended velocity field across the interface. The d2 law is verified in the numerical simulations of the vaporization of an isolated static drop. Results are then presented for a water droplet moving in air. Vapor mass fraction and temperature fields inside and outside the droplet are presented.
Expansion Waves at the Outlet of the Supersonic Two-Phase Flow Nozzle
NASA Astrophysics Data System (ADS)
Nakagawa, Masafumi; Miyazaki, Hiroki; Harada, Atsushi; Ibragimov, Zokirjon
Two-phase flow nozzles are used in the total flow system of geothermal power plants and in the ejector of the refrigeration cycle, etc. One of the most important functions of the two-phase flow nozzle is converting two-phase flow thermal energy into kinetic energy. The kinetic energy of the two-phase flow exhausted from a nozzle is available for all applications of this type. In the case of non-best fitting expansion conditions, when the operation conditions of the supersonic nozzle are widely chosen, there exist shock waves or expansion waves at the outlet of the nozzle. Those waves affect largely the energy conversion efficiency of the two-phase flow nozzle. The purpose of the present study is to elucidate character of the expansion waves at the outlet of the supersonic two-phase flow nozzle. High-pressure hot water blowdown experiments have been carried out. The decompression curves of the expansion waves are measured by changing the flowrate in the nozzle and inlet temperature of the hot water. The back pressures of the nozzle are also changed in those experiments. The expansion angles of the two-phase flow flushed out from the nozzle are measured by means of the photograph. The experimental results show that the decompression curves are different from those predicted by the isentropic homogeneous two-phase flow theory. The regions where the expansion waves occur become wide due to the increased outlet speed of the two-phase flow. The qualitative dependency of this expansion character is the same as the isentropic homogeneous flow, but the values obtained from the experiments are quite different. When the back pressure of the nozzle is higher, these regions do not become small in spite of the supersonic two-phase flow. This means that the disturbance in the downstream propagates to the upstream. It is shown by the present experiments that the expansion waves in the supersonic two-phase flow of water have a subsonic feature. The measured expansion angles become
Analysis of Fractional Flow for Transient Two-Phase Flow in Fractal Porous Medium
NASA Astrophysics Data System (ADS)
Lu, Ting; Duan, Yonggang; Fang, Quantang; Dai, Xiaolu; Wu, Jinsui
2016-03-01
Prediction of fractional flow in fractal porous medium is important for reservoir engineering and chemical engineering as well as hydrology. A physical conceptual fractional flow model of transient two-phase flow is developed in fractal porous medium based on the fractal characteristics of pore-size distribution and on the approximation that porous medium consist of a bundle of tortuous capillaries. The analytical expression for fractional flow for wetting phase is presented, and the proposed expression is the function of structural parameters (such as tortuosity fractal dimension, pore fractal dimension, maximum and minimum diameters of capillaries) and fluid properties (such as contact angle, viscosity and interfacial tension) in fractal porous medium. The sensitive parameters that influence fractional flow and its derivative are formulated, and their impacts on fractional flow are discussed.
Analytical solution for two-phase flow in a wellbore using the drift-flux model
Pan, L.; Webb, S.W.; Oldenburg, C.M.
2011-11-01
This paper presents analytical solutions for steady-state, compressible two-phase flow through a wellbore under isothermal conditions using the drift flux conceptual model. Although only applicable to highly idealized systems, the analytical solutions are useful for verifying numerical simulation capabilities that can handle much more complicated systems, and can be used in their own right for gaining insight about two-phase flow processes in wells. The analytical solutions are obtained by solving the mixture momentum equation of steady-state, two-phase flow with an assumption that the two phases are immiscible. These analytical solutions describe the steady-state behavior of two-phase flow in the wellbore, including profiles of phase saturation, phase velocities, and pressure gradients, as affected by the total mass flow rate, phase mass fraction, and drift velocity (i.e., the slip between two phases). Close matching between the analytical solutions and numerical solutions for a hypothetical CO{sub 2} leakage problem as well as to field data from a CO{sub 2} production well indicates that the analytical solution is capable of capturing the major features of steady-state two-phase flow through an open wellbore, and that the related assumptions and simplifications are justified for many actual systems. In addition, we demonstrate the utility of the analytical solution to evaluate how the bottomhole pressure in a well in which CO{sub 2} is leaking upward responds to the mass flow rate of CO{sub 2}-water mixture.
Two-phase interfacial area and flow regime modeling in FLOWTRAN-TF code
Smith, F.G. III; Lee, S.Y.; Flach, G.P.; Hamm, L.L.
1992-01-01
FLOWTRAN-TF is a new two-component, two-phase thermal-hydraulics code to capture the detailed assembly behavior associated with loss-of-coolant accident analyses in multichannel assemblies of the SRS reactors. The local interfacial area of the two-phase mixture is computed by summing the interfacial areas contributed by each of three flow regimes. For smooth flow regime transitions, the code uses an interpolation technique in terms of component void fraction for each basic flow regime.
Two-phase interfacial area and flow regime modeling in FLOWTRAN-TF code
Smith, F.G. III; Lee, S.Y.; Flach, G.P.; Hamm, L.L.
1992-12-31
FLOWTRAN-TF is a new two-component, two-phase thermal-hydraulics code to capture the detailed assembly behavior associated with loss-of-coolant accident analyses in multichannel assemblies of the SRS reactors. The local interfacial area of the two-phase mixture is computed by summing the interfacial areas contributed by each of three flow regimes. For smooth flow regime transitions, the code uses an interpolation technique in terms of component void fraction for each basic flow regime.
Scaling analysis of gas-liquid two-phase flow pattern in microgravity
NASA Technical Reports Server (NTRS)
Lee, Jinho
1993-01-01
A scaling analysis of gas-liquid two-phase flow pattern in microgravity, based on the dominant physical mechanism, was carried out with the goal of predicting the gas-liquid two-phase flow regime in a pipe under conditions of microgravity. The results demonstrated the effect of inlet geometry on the flow regime transition. A comparison of the predictions with existing experimental data showed good agreement.
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. © 2015 The Author(s).
A two phase Mach number description of the equilibrium flow of nitrogen in ducts
NASA Technical Reports Server (NTRS)
Bursik, J. W.; Hall, R. M.; Adcock, J. B.
1979-01-01
Some additional thermodynamic properties of the usual two-phase form which is linear in the moisture fraction are derived which are useful in the analysis of many kinds of duct flow. The method used is based on knowledge of the vapor pressure and Gibbs function as functions of temperature. With these, additional two-phase functions linear in moisture fraction are generated, which ultimately reveal that the squared ratio of mixture specific volume to mixture sound speed depends on liquid mass fraction and temperature in the same manner as do many weighted mean two-phase properties. This leads to a simple method of calculating two-phase Mach numbers for various duct flows. The matching of one- and two-phase flows at a saturated vapor point with discontinuous Mach number is also discussed.
Single and two-phase flow fluid dynamics in parallel helical coils
NASA Astrophysics Data System (ADS)
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.
Digital image processing based mass flow rate measurement of gas/solid two-phase flow
NASA Astrophysics Data System (ADS)
Song, Ding; Peng, Lihui; Lu, Geng; Yang, Shiyuan; Yan, Yong
2009-02-01
With the rapid growth of the process industry, pneumatic conveying as a tool for the transportation of a wide variety of pulverized and granular materials has become widespread. In order to improve plant control and operational efficiency, it is essential to know the parameters of the particle flow. This paper presents a digital imaging based method which is capable of measuring multiple flow parameters, including volumetric concentration, velocity and mass flow rate of particles in the gas/solid two phase flow. The measurement system consists of a solid state laser for illumination, a low-cost CCD camera for particle image acquisition and a microcomputer with bespoke software for particle image processing. The measurements of particle velocity and volumetric concentration share the same sensing hardware but use different exposure time and different image processing methods. By controlling the exposure time of the camera a clear image and a motion blurred image are obtained respectively. The clear image is thresholded by OTSU method to identify the particles from the dark background so that the volumetric concentration is determined by calculating the ratio between the particle area and the total area. Particle velocity is derived from the motion blur length, which is estimated from the motion blurred images by using the travelling wave equation method. The mass flow rate of particles is calculated by combining the particle velocity and volumetric concentration. Simulation and experiment results indicate that the proposed method is promising for the measurement of multiple parameters of gas/solid two-phase flow.
Numerical simulation of multi-dimensional two-phase flow based on flux vector splitting
Staedtke, H.; Franchello, G.; Worth, B.
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.
Predicting single-phase and two-phase non-Newtonian flow behavior in pipes
Kaminsky, R.D.
1998-12-31
Improved and novel prediction methods are described for single-phase and two-phase flow of non-Newtonian fluids in pipes. Good predictions are achieved for pressure drop, liquid holdup fraction, and two-phase flow regime. The methods are applicable to any visco-inelastic non-Newtonian fluid and include the effect of surface roughness. The methods utilize a reference fluid for which validated models exist. For single-phase flow the use of Newtonian and power-law reference fluids are illustrated. For two-phase flow a Newtonian reference fluid is used. Focus is given to shear-thinning fluids. The approach is theoretically based and is better suited than correlation methods for two-phase flow in high pressure pipelines, for which no experimental data is available in the literature.
Scalewise investigation of two-phase flow turbulence in upward turbulent bubbly pipe flows
NASA Astrophysics Data System (ADS)
Lee, Jun Ho; Kim, Hyunseok; Park, Hyungmin
2015-11-01
In the present study, the two-phase flow turbulence in upward turbulent bubbly pipe flows (at the Reynolds number of 5300) is invesgitated, especially focusing on the changes in flow structures with bubbles depending on the length scales. For the scalewise investigation, we perform the wavelet multi-resolution analysis on the velocity fields at three streamwise locations, measured with high-speed two-phase particle image velocimetry technology. While we intentaionlly introduce asymmetrically distributed bubbles at the pipe inlet, the mean volume void fraction is varied from from 0.3% to 1.86% and the considered mean bubble diameter is roughly maintained at 3.8 mm. With the present condition, turbulence enhancement is achieived for most cases but the turbulent suppression is also captured near the wall for the smallest void fraction case. Comparing the scalewise energy contribution, it is understood that the flow structures with length scales between bubble radius and bubble wake size are enhanced due to bubbles, resulting in the turbulence enhancement. On the other hand, flow structure with smaller length scales (mostly existing near the wall) may decrease depending on the bubble condition, which may be one of the explanations in turbulence suppression with bubbles. Supported by the NRF grant funded by the Korea government (NRF-2012M2A8A4055647) via SNU-IAMD.
NASA Astrophysics Data System (ADS)
Cordoba, G.; Sheridan, M.; Pitman, B.
2009-04-01
Ground-hugging particle-laden flows constitute some of the most dangerous natural phenomena on Earth. Such currents, in the form of snow avalanches, pyroclastic flows, debris flows, lahars, and landslides, are among the most destructive processes in nature. Humans tend to settle in areas near rich soils, volcanoes, or watercourses, all of which could be strongly affected by these dangerous flows. In order to improve risk preparedness and site management in the affected zones, an appropriate knowledge of these natural hazardous phenomena is required. Their evolution in time, flow dynamics and run out distance are key aspects that help in the planning for hazardous events, development of hazardous regions and design of management policy to prepare in advance of potential natural disasters. This paper describes a depth-averaged model for two phase flows that is currently in develop at the University at Buffalo. It will be fully implemented within the TITAN2D framework that presently simulates dry geophysical mass flows over natural-scale terrains. The initial TITAN2D code was developed to simulate granular flow. But because the introduction of an interstitial fluid strongly modifies the dynamics of the flow, a new, more general, two-phase model was developed to account for a broad range in volume fraction of solids. The proposed mathematical model depth-integrates the Navier-Stokes equations for each phase, solid and fluid. The solid phase is modeled assuming a Coulomb constitutive behavior (at the theoretical limit of pure solids), whereas the fluid phase conforms to a typical hydraulic approach (at the limit of pure fluid). The linkage for compositions between the pure end-member phases is accommodated by the inclusion of a phenomenological-based drag coefficient. The model is capable of simulating particle volumetric fractions as dilute as 0.001 and as concentrated as 0.55.
NASA Astrophysics Data System (ADS)
Cordoba, G. A.; Sheridan, M.; Pitman, B.
2009-05-01
Ground-hugging particle-laden flows constitute some of the most dangerous natural phenomena on Earth. Such currents, in the form of snow avalanches, pyroclastic flows, debris flows, lahars, and landslides, are among the most destructive processes in nature. Humans tend to settle in areas near rich soils, volcanoes, or watercourses, all of which could be strongly affected by these dangerous flows. In order to improve risk preparedness and site management in the affected zones, an appropriate knowledge of these natural hazardous phenomena is required. Their evolution in time, flow dynamics and run out distance are key aspects that help in the planning for hazardous events, development of hazardous regions and design of management policy to prepare in advance of potential natural disasters. This paper describes a depth-averaged model for two phase flows that is currently in develop at the University at Buffalo. It is presently implemented within the TITAN2D framework to improve the version that currently simulates dry geophysical mass flows over natural-scale terrains. The initial TITAN2D code was developed to simulate granular flow. But because the introduction of an interstitial fluid strongly modifies the dynamics of the flow, a new, more general, two-phase model was developed to account for a broad range in volume fraction of solids. The proposed mathematical model depth-integrates the Navier-Stokes equations for each phase, solid and fluid. The solid phase is modeled assuming a Coulomb constitutive behavior (at the theoretical limit of pure solids), whereas the fluid phase conforms to a typical hydraulic approach (at the limit of pure fluid). The linkage for compositions between the pure end-member phases is accommodated by the inclusion of a phenomenological-based drag coefficient. The model is capable of simulating particle volumetric fractions as dilute as 0.001 and as concentrated as 0.55.
Importance of Considering Hysteresis in Macroscopic Models of Two-phase Flow in Porous Media
NASA Astrophysics Data System (ADS)
Cihan, A.; Birkholzer, J. T.; Trevisan, L.; Gonzalez-Nicolas Alvarez, A.; Illangasekare, T. H.
2016-12-01
Considering hysteresis in the traditional Darcy equation-based models is necessary to accurately capture the two phase flow behavior when subsurface systems experience successive drainage and imbibition processes such as in the case of geological carbon storage (GCS). Numerical simulators solving two-phase flow equations must make reliable predictions of fluid distributions during injection and post-injection redistribution of CO2, which is essential for developing appropriate monitoring and assessment plans in order to minimize risks of leakage (e.g., through fractures and/or abandoned wells). Generally, existing numerical simulators of the two-phase flow either neglect the hysteresis or include hysteresis based on the empirical constitutive relationships, not suitably incorporating basic physics of capillary flow with entrapment. This study presents testing of new mathematical hysteretic capillary pressure - saturation - relative permeability models with the goal of more accurately predicting the post-injection distribution of the fluids. The developed macroscopic constitutive models are based on basic physics of two-phase capillary displacements at pore-scale and void volume fraction distribution and connectivity properties. To test the new models, a traditional two-phase flow model with the developed hysteretic functions as input is compared against some intermediate-scale flow cell experiments conducted under macroscopically homogeneous and heterogeneous conditions. The model testing results that will be presented demonstrate the importance of taking into account hysteresis in the constitutive models of the traditional two-phase flow models for more accurate prediction of post-injection plume distribution.
A theoretical evaluation of aluminum gel propellant two-phase flow losses on vehicle performance
NASA Technical Reports Server (NTRS)
Mueller, Donn C.; Turns, Stephen R.
1993-01-01
A one-dimensional model of a hydrocarbon/Al/O2(gaseous) fueled rocket combustion chamber was developed to study secondary atomization effects on propellant combustion. This chamber model was coupled with a two dimensional, two-phase flow nozzle code to estimate the two-phase flow losses associated with solid combustion products. Results indicate that moderate secondary atomization significantly reduces propellant burnout distance and Al2O3 particle size; however, secondary atomization provides only moderate decreases in two-phase flow induced I(sub sp) losses. Despite these two-phase flow losses, a simple mission study indicates that aluminum gel propellants may permit a greater maximum payload than the hydrocarbon/O2 bi-propellant combination for a vehicle of fixed propellant volume. Secondary atomization was also found to reduce radiation losses from the solid combustion products to the chamber walls, primarily through reductions in propellant burnout distance.
Future directions in two-phase flow and heat transfer in space
NASA Technical Reports Server (NTRS)
Bankoff, S. George
1994-01-01
Some areas of opportunity for future research in microgravity two-phase flow and heat transfer are pointed out. These satisfy the dual requirements of relevance to current and future needs, and scientific/engineering interest.
Numerical simulation of the two-phase flows in a hydraulic coupling by solving VOF model
NASA Astrophysics Data System (ADS)
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.
Two-phase air-water stratified flow measurement using ultrasonic techniques
Fan, Shiwei; Yan, Tinghu; Yeung, Hoi
2014-04-11
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.
Bubble Generation in a Flowing Liquid Medium and Resulting Two-Phase Flow in Microgravity
NASA Technical Reports Server (NTRS)
Kamotani, Yasuhiro
1996-01-01
An experimental and theoretical research program is described herein to study bubble generation in a liquid flow in a pipe under reduced gravity conditions. The objective of the work is to study the bubble size and frequency of the generation and the resulting two-phase flow but it also concerns the fluid mechanical aspects of boiling in forced flow in microgravity. By injecting a gas into a liquid flow in a pipe through a small hole in the pipe wall we will investigate how the bubble expands and detaches from the wall, without involving the complexities of boiling. The experiments will be conducted both under isothermal conditions and with heat transfer from the wall. In the experiments with heat transfer the effect of thermocapillarity on the bubble formation and detachment will be the main subject.
Ong, C.L.; Thome, J.R.
2011-01-15
The classification of macroscale, mesoscale and microscale channels with respect to two-phase processes is still an open question. The main objective of this study focuses on investigating the macro-to-microscale transition during flow boiling in small scale channels of three different sizes with three different refrigerants over a range of saturation conditions to investigate the effects of channel confinement on two-phase flow patterns and liquid film stratification in a single circular horizontal channel (Part 2 covers the flow boiling heat transfer and critical heat flux). This paper presents the experimental two-phase flow pattern transition data together with a top/bottom liquid film thickness comparison for refrigerants R134a, R236fa and R245fa during flow boiling in small channels of 1.03, 2.20 and 3.04 mm diameter. Based on this work, an improved flow pattern map has been proposed by determining the flow patterns transitions existing under different conditions including the transition to macroscale slug/plug flow at a confinement number of Co {approx} 0.3-0.4. From the top/bottom liquid film thickness comparison results, it was observed that the gravity forces are fully suppressed and overcome by the surface tension and shear forces when the confinement number approaches 1, Co {approx} 1. Thus, as a new approximate rule, the lower threshold of macroscale flow is Co = 0.3-0.4 while the upper threshold of symmetric microscale flow is Co {approx} 1 with a transition (or mesoscale) region in-between. (author)
Simulation of two-phase flow using lattice gas automata methods
Tsumaya, Akira; Ohashi, Hirotada; Akiyama, Mamoru
1996-08-01
Two-phase flow simulation has been primarily based on experimental data in the sense that constitutive relations necessary for solving fundamental equations are experimentally determined. This assures validity of simulation of two-phase flow within the experimental conditions, but it is difficult to predict the behavior of two-phase flow under extreme or complex conditions which occur, for example, in severe accidents of nuclear reactors. Lattice gas automaton (LGA) simulation has recently attracted attention as a method for numerical simulation of multi phase flow. The authors extend phase-separation LGA models and develop methods for two-phase flow simulation. First, they newly added a flow model to the immiscible lattice gas model and applied it to two-dimensional Poiseuille flow. They obtained a result looking like lubricated pipelining of crude oil with water. Also, considering the gravity effect, they introduced a buoyancy force into the liquid-gas model. As a result, they demonstrated that gas bubbles of various diameters rise and gradually coalesce each other turning into larger bubbles. Using these newly developed LGA models, they succeeded in simulating various flow patterns of two-phase flow.
Vibration of a tube bundle in two-phase Freon cross-flow
Pettigrew, M.J.; Taylor, C.E.; Jong, J.H.; Currie, I.G.
1995-11-01
Two-phase cross-flow exists in many shell-and-tube heat exchangers. The U-bend region of nuclear steam generators is a prime example. Testing in two-phase flow simulated by air-water provides useful results inexpensively. However, two-phase flow parameters, in particular surface tension and density ratio, are considerably different in air-water than in steam-water. A reasonable compromise is testing in liquid-vapor Freon, which is much closer to steam-water while much simpler experimentally. This paper presents the first results of a series of tests on the vibration behavior of tube bundles subjected to two-phase Freon cross-flow. A rotated triangular tube bundle of tube-to-diameter ratio of 1.5 was tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, and damping were investigated. Well-defined fluidelastic instabilities were observed in continuous two-phase flow regimes. However, intermittent two-phase flow regimes had a dramatic effect on fluidelastic instability. Generally, random turbulence excitation forces are much lower in Freon than in air-water. Damping is very dependent on void fraction, as expected.
A study of two-phase flow in a reduced gravity environment
NASA Technical Reports Server (NTRS)
Hill, D.; Downing, Robert S.
1987-01-01
A test loop was designed and fabricated for observing and measuring pressure drops of two-phase flow in reduced gravity. The portable flow test loop was then tested aboard the NASA-JSC KC135 reduced gravity aircraft. The test loop employed the Sundstrand Two-Phase Thermal Management System (TPTMS) concept which was specially fitted with a clear two-phase return line and condenser cover for flow observation. A two-phase (liquid/vapor) mixture was produced by pumping nearly saturated liquid through an evaporator and adding heat via electric heaters. The quality of the two-phase flow was varied by changing the evaporator heat load. The test loop was operated on the ground before and after the KC135 flight tests to create a one-gravity data base. The ground testing included all the test points run during the reduced gravity testing. Two days of reduced gravity tests aboard the KC135 were performed. During the flight tests, reduced-gravity, one-gravity, and nearly two-gravity accelerations were experienced. Data was taken during the entire flight which provided flow regime and pressure drop data for the three operating conditions. The test results show that two-phase pressure drops and flow regimes can be accurately predicted in zero-gravity.
The bubbly-slug transition in a boiling two-phase flow under microgravity
NASA Technical Reports Server (NTRS)
Kiper, Ali M.; Swanson, T. D.
1993-01-01
A theory is presented to describe, in reduced gravity flow boiling, the transition from bubbly two-phase flow to slug flow. It is shown that characteristics of the bubbly flow and the transition were controlled by the mechanism of vapor bubble growth dynamics. By considering in nucleate boiling, behavior of vapor bubbles at departure from a heated surface a condition required for transition was determined. Although required, this condition alone could not ensure coalescence of bubbles to cause the transition to slug two-phase flow. The condition leading to coalescence, therefore, was obtained by examining oscillations of vapor bubbles following their departure from the heated surface. The predicted transition conditions were compared with the prediction and test data reported for adiabatic reduced gravity two-phase flow, and good qualitative agreement was found.
The bubbly-slug transition in a boiling two-phase flow under microgravity
NASA Technical Reports Server (NTRS)
Kiper, Ali M.; Swanson, T. D.
1993-01-01
A theory is presented to describe, in reduced gravity flow boiling, the transition from bubbly two-phase flow to slug flow. It is shown that characteristics of the bubbly flow and the transition were controlled by the mechanism of vapor bubble growth dynamics. By considering in nucleate boiling, behavior of vapor bubbles at departure from a heated surface a condition required for transition was determined. Although required, this condition alone could not ensure coalescence of bubbles to cause the transition to slug two-phase flow. The condition leading to coalescence, therefore, was obtained by examining oscillations of vapor bubbles following their departure from the heated surface. The predicted transition conditions were compared with the prediction and test data reported for adiabatic reduced gravity two-phase flow, and good qualitative agreement was found.
Analytical solution of laminar-laminar stratified two-phase flows with curved interfaces
Brauner, N.; Rovinsky, J.; Maron, D.M.
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.
Scaling of Two-Phase Flows to Partial-Earth Gravity
NASA Technical Reports Server (NTRS)
Hurlbert, Kathryn M.; Witte, Larry C.
2003-01-01
A report presents a method of scaling, to partial-Earth gravity, of parameters that describe pressure drops and other characteristics of two-phase (liquid/ vapor) flows. The development of the method was prompted by the need for a means of designing two-phase flow systems to operate on the Moon and on Mars, using fluid-properties and flow data from terrestrial two-phase-flow experiments, thus eliminating the need for partial-gravity testing. The report presents an explicit procedure for designing an Earth-based test bed that can provide hydrodynamic similarity with two-phase fluids flowing in partial-gravity systems. The procedure does not require prior knowledge of the flow regime (i.e., the spatial orientation of the phases). The method also provides for determination of pressure drops in two-phase partial-gravity flows by use of a generalization of the classical Moody chart (previously applicable to single-phase flow only). The report presents experimental data from Mars- and Moon-activity experiments that appear to demonstrate the validity of this method.
Gas-liquid two-phase flow across a bank of micropillars
NASA Astrophysics Data System (ADS)
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.
An experimental study of single-phase and two-phase flow in annular helicoidal pipes
Xin, R.C.; Awwad, A.; Dong, Z.F.; Ebadian, M.A.
1996-12-31
In this study, experimental investigations were conducted for single-phase and two-phase flow in annular helicoidal pipes with vertical and horizontal orientations using air and water as working fluids. Three test sections were tested. The outer diameters of the inner tube were 12.7 mm, 9.525 mm, and 6.35 mm, while the inner diameters of the outer tube were 21.18 mm, 15.748 mm, and 10.21 mm, respectively. The experiments were performed for superficial water Reynolds numbers in the range of 210--23,000 and superficial air Reynolds numbers in the range of 30--30,000. The effects of coil geometry and the flow rates of air and water on single-phase and two-phase flow pressure drop were experimentally investigated for annular helicoidal pipes. The data were correlated as the relationship of the pressure drop multiplier versus the Lockhart-Martinelli parameter for the two-phase flow. The average void fraction was also measured in the experiments by means of the quick acting valve method. Unlike two-phase flow in straight pipe, the pressure drop multiplier of two-phase flow in annular helicoidal pipe has been found to be dependent on the flow rate besides the Lockhart-Martinelli parameter for large pipe diameter in annular helicoidal pipe. The Lockhart-Martinelli correlation is not valid in the prediction. Correlations for two-phase flow in horizontal and vertical annular helicoidal pipe have been established for both single-phase and two-phase flow based on the present experimental data.
NASA Astrophysics Data System (ADS)
Pettigrew, M. J.; Zhang, C.; Mureithi, N. W.; Pamfil, D.
2005-05-01
Two-phase cross-flow exists in many shell-and-tube heat exchangers. A detailed knowledge of the characteristics of two-phase cross-flow in tube bundles is required to understand and formulate flow-induced vibration parameters such as damping, fluidelastic instability, and random excitation due to turbulence. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures. The array is made of relatively large diameter cylinders (38 mm) to allow for detailed two-phase flow measurements between cylinders. Fiber-optic probes were developed to measure local void fraction. Local flow velocities and bubble diameters or characteristic lengths of the two-phase mixture are obtained by using double probes. Both the dynamic lift and drag forces were measured with a strain gauge instrumented cylinder.
Two-phase flow patterns in adiabatic and diabatic corrugated plate gaps
NASA Astrophysics Data System (ADS)
Polzin, A.-E.; Kabelac, S.; de Vries, B.
2016-09-01
Correlations for two-phase heat transfer and pressure drop can be improved considerably, when they are adapted to specific flow patterns. As plate heat exchangers find increasing application as evaporators and condensers, there is a need for flow pattern maps for corrugated plate gaps. This contribution presents experimental results on flow pattern investigations for such a plate heat exchanger background, using an adiabatic visualisation setup as well as a diabatic setup. Three characteristic flow patterns were observed in the considered range of two-phase flow: bubbly flow, film flow and slug flow. The occurrence of these flow patterns is a function of mass flux, void fraction, fluid properties and plate geometry. Two different plate geometries having a corrugation angle of 27° and 63°, respectively and two different fluids (water/air and R365mfc liquid/vapor) have been analysed. A flow pattern map using the momentum flux is presented.
Characterization of annular two-phase gas-liquid flows in microgravity
NASA Technical Reports Server (NTRS)
Bousman, W. Scott; Mcquillen, John B.
1994-01-01
A series of two-phase gas-liquid flow experiments were developed to study annular flows in microgravity using the NASA Lewis Learjet. A test section was built to measure the liquid film thickness around the perimeter of the tube permitting the three dimensional nature of the gas-liquid interface to be observed. A second test section was used to measure the film thickness, pressure drop and wall shear stress in annular microgravity two-phase flows. Three liquids were studied to determine the effects of liquid viscosity and surface tension. The result of this study provide insight into the wave characteristics, pressure drop and droplet entrainment in microgravity annular flows.
Characterization of annular two-phase gas-liquid flows in microgravity
NASA Astrophysics Data System (ADS)
Bousman, W. Scott; McQuillen, John B.
1994-08-01
A series of two-phase gas-liquid flow experiments were developed to study annular flows in microgravity using the NASA Lewis Learjet. A test section was built to measure the liquid film thickness around the perimeter of the tube permitting the three dimensional nature of the gas-liquid interface to be observed. A second test section was used to measure the film thickness, pressure drop and wall shear stress in annular microgravity two-phase flows. Three liquids were studied to determine the effects of liquid viscosity and surface tension. The result of this study provide insight into the wave characteristics, pressure drop and droplet entrainment in microgravity annular flows.
An investigation into the performance of a venturi in two-phase helium flow
Huang, X.; Van Sciver, S.W.
1994-12-31
The present paper discusses the use of venturi flow meters for measurement of vapor quality of helium two-phase flow. Tests were performed by connecting two identical venturis with 2.29 mm throat and 4.57 mm inlet diameters in series with a vertical two-phase helium flow loop. With one venturi operating in liquid and the second one operating in two-phase regime as controlled by an inline heater, the ratio of the pressure drop across the two venturis is found to be well correlated to the vapor quality of the two-phase flow. Data presented are for vertical upflow of two-phase helium at 4.2 K with vapor quality between zero and 100% under both forced flow and natural circulating flow conditions. The forced flow rates, controlled by a flexible bellows acting as a positive displacement pump, range from 1.0 g/s up to 2.5 g/s. Within the parameter range covered in this test, the result can be well described by the homogeneous model.
Air-water two-phase flow in a 3-mm horizontal tube
NASA Astrophysics Data System (ADS)
Chen, Ing Youn; Chang, Yu-Juei; Wang, Chi-Chung
2000-01-01
Two-phase flow pattern and friction characteristics for air-water flow in a 3.17 mm smooth tube are reported in this study. The range of air-water mass flux is between 50 to 700 kg/m2.s and gas quality is between 0.0001 to 0.9. The pressure drop data are analyzed using the concept of the two-phase frictional multipliers and the Martinelli parameter. Experimental data show that the two-phase friction multipliers are strongly related to the flow pattern. Taitel & Dukler flow regime map fails to predict the stratified flow pattern data. Their transition lines between annular-wavy and annular-intermittent give fair agreement with data. A modified correlation from Klimenko and Fyodoros criterion is able to distinguish the annular and stratified data. For two-phase flow in small tubes, the effect of surface tension force should be significantly present as compared to gravitational force. The tested empirical frictional correlations couldn't predict the pressure drop in small tubes for various working fluids. It is suggested to correlate a reliable frictional multiplier for small horizontal tubes from a large database of various working fluids, and to develop the flow pattern dependent models for the prediction of two-phase pressure drop in small tubes. .
Effect of heat transfer augmentation on two-phase flow instabilities in a vertical boiling channel
NASA Astrophysics Data System (ADS)
Mentes, A.; Gurgenci, H.; Yildirim, O. T.; Kakac, S.; Veziroglu, T. N.
1983-05-01
The effect of different heater surface configuration on two-phase flow instabilities has been investigated in a single channel, forced convection, open loop, up-flow system. Freon-11 is used as the test fluid, and six different heater tubes with various inside surface configurations have been tested at five different heat inputs. In addition to temperature and pressure recordings, high speed motion pictures of the two-phase flow were taken for some of the experiments to study the two-phase behavior at different operating points. Experimental results are shown on system pressure drop versus mass flow rate curves, and stability boundaries are also indicated on these curves. Comparisons of different heater tubes is made by the use of the stability boundary maps and the plots of inlet throttling necessary to stabilize the system versus mass flow rate. Tubes with internal springs were found to be more stable than the other tubes.
Experimental study of two-phase water flow in vertical thin rectangular channels
NASA Astrophysics Data System (ADS)
Wright, Christopher T.; O'Brien, James E.; Anderson, Elgin A.
2001-11-01
An experimental heat transfer study of two-phase water flow in vertical thin rectangular channels with side vents is conducted. A multiple, heated channel configuration with up- and down-flow conditions is investigated. Parallel heated and unheated flow channels test the effects of cross flow on the onset of nucleate boiling (ONB) and critical heat flux (CHF). The test apparatus provides pressure and substrate temperature data and visual data of the boiling regimes and side-vent flow patterns. The objectives are to determine the two-phase, heat and mass transfer characteristics between adjacent channels as permitted by side-vent cross flow. These data will help develop ONB and CHF correlations for flow geometries typical of plate-type nuclear reactors and heat exchangers. Fundamentally, the data shows how the geometry, flow conditions, and channel configurations affect the heat transfer characteristics of interior channel flows, essential in understanding the ONB and CHF phenomena.
Gas-Liquid Two-Phase Flow Distribution Using Phase Separation Method
NASA Astrophysics Data System (ADS)
Zhang, B. D.; Liu, D.; Wang, D.
2010-03-01
A method for gas-liquid two-phase flow distribution is proposed in this study, which can be called the phase separation method. The advantage of the new method is that it converts two-phase flow distribution into single-phase distribution, which overcomes the problem of phase splitting in the distribution process of two-phase flow radically, and an equal quality distribution is guaranteed. At first, separate the mixture of gas and liquid into single or near single phase fluids by enhancing phase splitting in distributor, then distribute the single gas and liquid flow respectively as required, finally recombine each couple of gas and liquid stream respectively to form a two phase stream exiting a branch. Experiments were conducted in an air-water multiphase flow test loop. The flow pattern in the experiments included stratified flow, wave flow, slug flow and a part of annular flow. The experimental results show that the phase separation method and apparatus could be feasible to make an equal quality distribution and the deviation of stream quality among the branches is less than 1.6%.
Measurement of local two-phase flow parameters of nanofluids using conductivity double-sensor probe.
Park, Yu Sun; Chang, Soon Heung
2011-04-04
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
2011-01-01
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. PMID:21711823
Bubble Generation in a Flowing Liquid Medium and Resulting Two-Phase Flow in Microgravity
NASA Technical Reports Server (NTRS)
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
Experimental investigation of two-phase flow patterns in minichannels at horizontal orientation
NASA Astrophysics Data System (ADS)
Saljoshi, P. S.; Autee, A. T.
2017-09-01
Two-phase flow is the simplest case of multiphase flow in which two phases are present for a pure component. The mini channel is considered as diameter below 3.0-0.2 mm and conventional channel is considered diameter above 3.0 mm. An experiment was conducted to study the adiabatic two-phase flow patterns in the circular test section with inner diameter of 1.1, 1.63, 2.0, 2.43 and 3.0 mm for horizontal orientation using air and water as a fluid. Different types of flow patterns found in the experiment. The parameters that affect most of these patterns and their transitions are channel size, phase superficial velocities (air and liquid) and surface tension. The superficial velocity of liquid and gas ranges from 0.01 to 66.70 and 0.01 to 3 m/s respectively. Two-phase flow pattern photos were recorded using a high speed CMOS camera. In this experiment different flow patterns were identified for different tube diameters that confirm the diameter effect on flow patterns in two-phase flows. Stratified flow was not observed for tube diameters less than 3.0 mm. Similarly, wavy-annular flow pattern was not observed in 1.6 and 1.0 mm diameter tubes due to the surface-tension effect and decrease in tube diameter. Buoyancy effects were clearly visible in 2.43 and 3.0 mm diameter tubes flow pattern. It has also observed that as the test-section diameter decreases the transition lines shift towards the higher gas and liquid velocity. However, the result of flow pattern lines in the present study has good agreement with the some of the existing flow patterns maps.
A new two-phase erosion-deposition model for mass flows
NASA Astrophysics Data System (ADS)
Pudasaini, Shiva P.; Fischer, Jan-Thomas
2016-04-01
Erosion, entrainment and deposition are complex and dominant, but yet poorly understood, mechanical processes in geophysical mass flows. Here, we propose a novel, two-phase, erosion-deposition model capable of adequately describing these complex phenomena commonly observed in landslides, avalanches, debris flows and bedload transports. The model enhances an existing general two-phase mass flow model (Pudasaini, 2012) by introducing a two-phase variably saturated erodible basal morphology. The adaptive basal morphology allows for the evolution of erosion-deposition-depths, incorporating the inherent physical process and rheological changes of the flowing mixture. With rigorous derivation, we show that appropriate incorporation of the mass and momentum productions and losses in conservative model formulation is essential for the physically correct and mathematically consistent description of erosion-entrainment-deposition processes. Simulation indicates a sharp erosion-front and steady-state-rear erosion depth. The model appropriately captures the emergence and propagation of complex frontal surge dynamics associated with the frontal ambient-drag which is a new hypothesis associated with erosion. The novel enhanced real two-phase model also allows for simulating fluid-run-off during the deposition process. The model resembles laboratory experiments for particle-fluid mixture flows and reveals some major aspects of the mechanics associated with erosion, entrainment and deposition. Reference: Shiva P. Pudasaini (2012): A general two-phase debris flow model. J. Geophys. Res., 117, F03010, doi: 10.1029/2011JF002186.
Determination and characteristics of the transition to two-phase slug flow in small channels
Wambsganss, M.W.; Jendrzejczyk, J.A.; France, D.M.
1992-12-01
Two-phase pressure drop was measured in a small horizontal rectangular channel (hydraulic diameter = 5.44 mm). The two-phase fluid was an air/water mixture at atmospheric pressure tested over a mass flux range of 50 to 2000 kg/m{sup 2}{center_dot}s. Two-phase flow patterns were identified and an objective method was found for determining the flow pattern transition from bubble or plug flow to slug flow. The method is based on an RMS pressure measurement. In particular, it is shown that the transition is accompanied by a clear and abrupt increase in the RMS pressure when plotted as a function of mass quality. Use of the RMS pressure as a two-phase flow pattern transition indicator is shown to have advantages over pressure-versus-time trace evaluations reported in the literature. The transition is substantiated by a clear local change in slope in the curve of two-phase pressure drop plotted as a function of either Martinelli parameter or mass quality. For high mass fluxes, the change in slope is distinguished by a local peak. Some degree of substantiation was found in previous work for both of the results (the RMS pressure change and the local pressure drop change) at the transition to slug flow.
Determination and characteristics of the transition to two-phase slug flow in small channels
Wambsganss, M.W.; Jendrzejczyk, J.A. ); France, D.M. . Dept. of Mechanical Engineering)
1992-01-01
Two-phase pressure drop was measured in a small horizontal rectangular channel (hydraulic diameter = 5.44 mm). The two-phase fluid was an air/water mixture at atmospheric pressure tested over a mass flux range of 50 to 2000 kg/m[sup 2][center dot]s. Two-phase flow patterns were identified and an objective method was found for determining the flow pattern transition from bubble or plug flow to slug flow. The method is based on an RMS pressure measurement. In particular, it is shown that the transition is accompanied by a clear and abrupt increase in the RMS pressure when plotted as a function of mass quality. Use of the RMS pressure as a two-phase flow pattern transition indicator is shown to have advantages over pressure-versus-time trace evaluations reported in the literature. The transition is substantiated by a clear local change in slope in the curve of two-phase pressure drop plotted as a function of either Martinelli parameter or mass quality. For high mass fluxes, the change in slope is distinguished by a local peak. Some degree of substantiation was found in previous work for both of the results (the RMS pressure change and the local pressure drop change) at the transition to slug flow.
Study of two-phase flow and heat transfer in reduced gravities
NASA Technical Reports Server (NTRS)
Abdollahian, Davood; Barez, Fred
1994-01-01
Design of the two-phase systems which are anticipated to be utilized in future spacecraft thermal management systems requires a knowledge of two-phase flow and heat transfer parameters in reduced gravities. A program has been initiated by NASA to design a two-phase test loop and perform a series of experiments to generate the data for the Critical Heat Flux (CHF) and onset of instability under reduced gravities. In addition to low gravity airplane trajectory testing, the experimental program consists of a set of laboratory tests with vertical upflow and downflow configurations. Modularity is considered in the design of this experiment and the test loop in instrumented to provide data for two-phase pressure drop and flow regime behavior. Since the program is in the final stages of the design and construction task, this article is intended to discuss the phenomena, design approach, and the description of the test loop.
Effect of corona discharge on the gas composition of the sample flow in a Gas Particle Partitioner.
Asbach, Christof; Kuhlbusch, Thomas A J; Fissan, Heinz
2005-09-01
A Gas Particle Partitioner (GPP) that allows highly efficient separation of gas and particles with no effect on the thermodynamic conditions and substantially no change of the gas composition has been developed. The GPP is a coaxial arrangement with inner and outer electrodes and utilizes a corona discharge to electrically charge the particles and a strong electric field to remove them from the sample flow. Several measures were taken to avoid an influence of the corona discharge on the gas composition. The GPP can be applied for various applications. This paper focuses on the use of the GPP as a pre-filter for gas analyzers, where zero pressure drop and a minimization of the influence of the corona discharge on the gas composition are the main objective. Due to its design, the GPP introduces no changes to the thermodynamic conditions. However, corona discharge is known to produce significant amounts of ozone and oxides of nitrogen. The effect of the corona on the gas composition of the sample flow was determined under various conditions. The gas concentrations strongly depended on several aspects, such as material and diameter of the corona wire and polarity of the corona voltage. Due to the measures taken to minimize an effect on the gas composition, the concentrations of these gases could effectively be reduced. Along with the maximum gas-particle separation efficiency of near 100%, the additional O3 concentration was 42 ppbV and the additional NO2 concentration 15 ppbV. If an efficiency of 95% is acceptable, the added concentrations can be as low as 2.5 ppbV (O3) and 0.5 ppbV (NO2), respectively.
Two-phase flow characterization for fluid components and variable gravity conditions
NASA Technical Reports Server (NTRS)
Dzenitis, John M.; Miller, Kathryn M.
1992-01-01
This paper describes a program initiated by the NASA Johnson Space Center to investigate vapor-liquid flow regimes and pressure drops in pipe components and variable gravity conditions. This program supports the Space Station Freedom External Active Thermal Control System design and future space missions, including the Space Exploration Initiative activities. The objectives for this program include studying two-phase flow behavior in fluid components (smooth pipes, bellows lines, quick-disconnect fittings), expanding the two-phase database for zero-g conditions, developing a database for low-g conditions (for example, Moon-g, Mars-g), and validating models for two-phase flow analyses. Zero-g and low-g data will be gathered using a Freon-12 flow loop during four test series on the KC-135 aircraft beginning in August 1991.
Air/water two-phase flow test tunnel for airfoil studies
NASA Astrophysics Data System (ADS)
Ohashi, H.; Matsumoto, Y.; Ichikawa, Y.; Tsukiyama, T.
1990-02-01
A test tunnel for the study of airfoil performances under air/water two-phase flow condition has been designed and constructed. This facility will serve for a better understanding of the flow phenomena and characteristics of hydraulic machinery under gas/ liquid two-phase flow operating conditions. At the test section of the tunnel, a two-dimensional isolated airfoil or a cascade of airfoils is installed in a two-phase inlet flow with a uniform velocity (up to 10 m/s) and void fraction (up to 12%) distribution. The details of the tunnel structure and the measuring systems are described and the basic characteristics of the constructed tunnel are also given. As an example of the test results, void fraction distribution around a test airfoil is shown.
Air/water two-phase flow test tunnel for airfoil studies
NASA Astrophysics Data System (ADS)
Ohashi, H.; Matsumoto, Y.; Ichikawa, Y.; Tsukiyama, T.
1994-01-01
A test tunnel for the study of airfoil performances under air/water two-phase flow condition has been designed and constructed. This facility will serve for a better understanding of the flow phenomena and characteristics of hydraulic machinery under gas/ liquid two-phase flow operating conditions. At the test section of the tunnel, a two-dimensional isolated airfoil or a cascade of airfoils is installed in a two-phase inlet flow with a uniform velocity (up to 10 m/s) and void fraction (up to 12%) distribution. The details of the tunnel structure and the measuring systems are described and the basic characteristics of the constructed tunnel are also given. As an example of the test results, void fraction distribution around a test airfoil is shown.
Reduced-gravity two-phase flow experiments in the NASA KC-135
NASA Technical Reports Server (NTRS)
Cuta, Judith M.; Michener, Thomas E.; Best, Frederick R.; Kachnik, Leo J.
1988-01-01
An adequate understanding is sought of flow and heat transfer behavior in reduced and zero gravity conditions. Microgravity thermal-hydraulic analysis capabilities were developed for application to space nuclear power systems. A series of reduced gravity two phase flow experiments using the NASA KC-135 were performed. The objective was to supply basic thermal hydraulic information that could be used in development of analytical tools for design of space power systems. The experiments are described. Two main conclusions were drawn. First, the tests demonstrate that the KC-135 is a suitable test environment for obtaining two phase flow and heat transfer data in reduced gravity conditions. Second, the behavior of two phase flow in low gravity is sufficiently different from that obtained in 1 g to warrant intensive investigation of the phenomenon if adequate analytical tools are to be developed for microgravity conditions.
Two-phase flow characterization for fluid components and variable gravity conditions
NASA Technical Reports Server (NTRS)
Dzenitis, John M.; Miller, Kathryn M.
1992-01-01
This paper describes a program initiated by the NASA Johnson Space Center to investigate vapor-liquid flow regimes and pressure drops in pipe components and variable gravity conditions. This program supports the Space Station Freedom External Active Thermal Control System design and future space missions, including the Space Exploration Initiative activities. The objectives for this program include studying two-phase flow behavior in fluid components (smooth pipes, bellows lines, quick-disconnect fittings), expanding the two-phase database for zero-g conditions, developing a database for low-g conditions (for example, Moon-g, Mars-g), and validating models for two-phase flow analyses. Zero-g and low-g data will be gathered using a Freon-12 flow loop during four test series on the KC-135 aircraft beginning in August 1991.
Numerical simulation of the two-phase flow produced by spraying a liquid by a nozzle
NASA Astrophysics Data System (ADS)
Simakov, N. N.
2017-07-01
A numerical experiment on the simulation of the two-phase flow formed during spraying of a liquid by a nozzle has been described. The radial and axial velocity profiles of the droplets and gas in the free spray and in the two-phase flow through a cylindrical apparatus have been calculated and represented taking into account the early drag crisis of droplets and peculiarities of turbulent friction in the gas, which was detected in previous experiments. The distinguishing feature of the numerical model of the two-phase flow is that it employs the differential equations describing the nonstationary flow of a compressible gas as the initial equations. In transition to their difference analog, the familiar Lax-Wendorff algorithm has been used. A comparison of the results of calculations based on this model with experimental data has demonstrated their concordance.
Magnetic liquid metal two-phase flow research. Phase 1. Final report
Graves, R.D.
1983-04-01
The Phase I research demonstrates the feasibility of the magnetic liquid metal (MLM) two-phase flow concept. A dispersion analysis is presented based on a complete set of two-phase-flow equations augmented to include stresses due to magnetic polarization of the fluid. The analysis shows that the stability of the MLM two-phase flow is determined by the magnetic Mach number, the slip ratio, geometry of the flow relative to the applied magnetic field, and by the voidage dependence of the interfacial forces. Results of a set of experiments concerned with magnetic effects on the dynamics of single bubble motion in an aqueous-based, viscous, conducting magnetic fluid are presented. Predictions in the theoretical literature are qualitatively verified using a bench-top experimental apparatus. In particular, applied magnetic fields are seen to lead to reduced bubble size at fixed generating orifice pressure.
On the peculiarities of LDA method in two-phase flows with high concentrations of particles
NASA Astrophysics Data System (ADS)
Poplavski, S. V.; Boiko, V. M.; Nesterov, A. U.
2016-10-01
Popular applications of laser Doppler anemometry (LDA) in gas dynamics are reviewed. It is shown that the most popular method cannot be used in supersonic flows and two-phase flows with high concentrations of particles. A new approach to implementation of the known LDA method based on direct spectral analysis, which offers better prospects for such problems, is presented. It is demonstrated that the method is suitable for gas-liquid jets. Owing to the progress in laser engineering, digital recording of spectra, and computer processing of data, the method is implemented at a higher technical level and provides new prospects of diagnostics of high-velocity dense two-phase flows.
Phase distribution of nitrogen-water two-phase flow in parallel micro channels
NASA Astrophysics Data System (ADS)
Zhou, Mi; Wang, Shuangfeng; Zhou, You
2017-04-01
The present work experimentally investigated the phase splitting characteristics of gas-liquid two-phase flow passing through a horizontal-oriented micro-channel device with three parallel micro-channels. The hydraulic diameters of the header and the branch channels were 0.6 and 0.4 mm, respectively. Five different liquids, including de-ionized water and sodium dodecyl sulfate (SDS) solution with different concentration were employed. Different from water, the surface tension of SDS solution applied in this work decreased with the increment of mass concentration. Through series of visual experiments, it was found that the added SDS surfactant could obviously facilitate the two-phase flow through the parallel micro channels while SDS solution with low concentration would lead to an inevitable blockage of partial outlet branches. Experimental results revealed that the two phase distribution characteristics depended highly on the inlet flow patterns and the outlet branch numbers. To be specific, at the inlet of slug flow, a large amount of gas preferred flowing into the middle branch channel while the first branch was filled with liquid. However, when the inlet flow pattern was shifted to annular flow, all of the gas passed through the second and the last branches, with a little proportion of liquid flowing into the first channel. By comparison with the experimental results obtained from a microchannel device with five parallel micro-T channels, uneven distribution of the two phase can be markedly noticed in our present work.
Three dimensional numerical prediction of two phase flow in industrial CFB boiler
Balzer, G.; Simonin, O.
1997-12-31
Gas-solid two phase flows are encountered in number of industrial applications such as pneumatic transport, catalytic cracking, coal combustors. The paper aims at presenting the numerical model of gas-solid flows which have been developed for several years at the Laboratoire National d`Hydraulique of Electricite de France and its application to the prediction of an industrial CFB Boiler.
Toward the use of similarity theory in two-phase choked flows
NASA Technical Reports Server (NTRS)
Hendericks, R. C.; Sengers, J. V.; Simoneau, R. J.
1980-01-01
Comparison of two phase choked flows in normalized coordinates were made between pure components and available data using a reference fluid to compute the thermophysical properties. The results are favorable. Solution of the governing equations for two LNG mixtures show some possible similarities between the normalized choked flows of the two mixtures, but the departures from the pure component loci are significant.
Toward the use of similarity theory in two-phase choked flows
NASA Technical Reports Server (NTRS)
Hendricks, R. C.; Simoneau, R. J.; Sengers, J. V.
1980-01-01
Comparison of two-phase choked flows in normalized coordinates were made between pure components and available data using a reference fluid to compute the thermophysical properties. The results are favorable. Solution of the governing equations for two LNG mixtures show some possible similarities between the normalized choked flows of the two mixtures, but the departures from the pure component locii are significant.
Self-sustained hydrodynamic oscillations in a natural-circulation two-phase-flow boiling loop
NASA Technical Reports Server (NTRS)
Jain, K. C.
1969-01-01
Results of an experimental and theoretical study of factors affecting self-sustaining hydrodynamic oscillations in boiling-water loops are reported. Data on flow variables, and the effects of geometry, subcooling and pressure on the development of oscillatory behavior in a natural-circulation two-phase-flow boiling loop are included.
Well logging interpretation of production profile in horizontal oil-water two phase flow pipes
NASA Astrophysics Data System (ADS)
Zhai, Lu-Sheng; Jin, Ning-De; Gao, Zhong-Ke; Zheng, Xi-Ke
2012-03-01
Due to the complicated distribution of local velocity and local phase hold up along the radial direction of pipe in horizontal oil-water two phase flow, it is difficult to measure the total flow rate and phase volume fraction. In this study, we carried out dynamic experiment in horizontal oil-water two phases flow simulation well by using combination measurement system including turbine flowmeter with petal type concentrating diverter, conductance sensor and flowpassing capacitance sensor. According to the response resolution ability of the conductance and capacitance sensor in different range of total flow rate and water-cut, we use drift flux model and statistical model to predict the partial phase flow rate, respectively. The results indicate that the variable coefficient drift flux model can self-adaptively tone the model parameter according to the oil-water two phase flow characteristic, and the prediction result of partial phase flow rate of oil-water two phase flow is of high accuracy.
Phase distribution of nitrogen-water two-phase flow in parallel micro channels
NASA Astrophysics Data System (ADS)
Zhou, Mi; Wang, Shuangfeng; Zhou, You
2016-08-01
The present work experimentally investigated the phase splitting characteristics of gas-liquid two-phase flow passing through a horizontal-oriented micro-channel device with three parallel micro-channels. The hydraulic diameters of the header and the branch channels were 0.6 and 0.4 mm, respectively. Five different liquids, including de-ionized water and sodium dodecyl sulfate (SDS) solution with different concentration were employed. Different from water, the surface tension of SDS solution applied in this work decreased with the increment of mass concentration. Through series of visual experiments, it was found that the added SDS surfactant could obviously facilitate the two-phase flow through the parallel micro channels while SDS solution with low concentration would lead to an inevitable blockage of partial outlet branches. Experimental results revealed that the two phase distribution characteristics depended highly on the inlet flow patterns and the outlet branch numbers. To be specific, at the inlet of slug flow, a large amount of gas preferred flowing into the middle branch channel while the first branch was filled with liquid. However, when the inlet flow pattern was shifted to annular flow, all of the gas passed through the second and the last branches, with a little proportion of liquid flowing into the first channel. By comparison with the experimental results obtained from a microchannel device with five parallel micro-T channels, uneven distribution of the two phase can be markedly noticed in our present work.
Two-phase flow and pressure drop in flow passages of compact heat exchangers
Wambsganss, M.W.; Jendrzejczyk, J.A.; France, D.M.
1992-01-01
Two-phase flow experiments were performed with air/water mixtures in a small rectangular channel measuring 9.52 {times} 1.59 mm (aspects ratio equal to 6), for applications to compact heat exchangers. Pressure drop and flow pattern definition data were obtained over a large range of mass qualities (0.0002 to 1), and in the case of flow pattern data, a large range of mass fluxes (50 to 2,000 kg/m{sup 2}s). A flow pattern map, based on visual observations and photographs of the flow patterns, is presented and compared with a map developed for a rectangular channel of the same aspect ratio but with dimensions twice those of the test channel, and with a map developed for a circular tube with the same hydraulic diameter of 3 mm. Pressure drop data are presented as a function of both mass quality and Martinelli parameter and are compared with state-of-the-art correlations and a modified Chisholm correlation. 13 refs.
Two-phase flow and pressure drop in flow passages of compact heat exchangers
Wambsganss, M.W.; Jendrzejczyk, J.A.; France, D.M.
1992-02-01
Two-phase flow experiments were performed with air/water mixtures in a small rectangular channel measuring 9.52 {times} 1.59 mm (aspects ratio equal to 6), for applications to compact heat exchangers. Pressure drop and flow pattern definition data were obtained over a large range of mass qualities (0.0002 to 1), and in the case of flow pattern data, a large range of mass fluxes (50 to 2,000 kg/m{sup 2}s). A flow pattern map, based on visual observations and photographs of the flow patterns, is presented and compared with a map developed for a rectangular channel of the same aspect ratio but with dimensions twice those of the test channel, and with a map developed for a circular tube with the same hydraulic diameter of 3 mm. Pressure drop data are presented as a function of both mass quality and Martinelli parameter and are compared with state-of-the-art correlations and a modified Chisholm correlation. 13 refs.
Two-phase gas-liquid flow characteristics inside a plate heat exchanger
Nilpueng, Kitti; Wongwises, Somchai
2010-11-15
In the present study, the air-water two-phase flow characteristics including flow pattern and pressure drop inside a plate heat exchanger are experimentally investigated. A plate heat exchanger with single pass under the condition of counter flow is operated for the experiment. Three stainless steel commercial plates with a corrugated sinusoidal shape of unsymmetrical chevron angles of 55 and 10 are utilized for the pressure drop measurement. A transparent plate having the same configuration as the stainless steel plates is cast and used as a cover plate in order to observe the flow pattern inside the plate heat exchanger. The air-water mixture flow which is used as a cold stream is tested in vertical downward and upward flow. The results from the present experiment show that the annular-liquid bridge flow pattern appeared in both upward and downward flows. However, the bubbly flow pattern and the slug flow pattern are only found in upward flow and downward flow, respectively. The variation of the water and air velocity has a significant effect on the two-phase pressure drop. Based on the present data, a two-phase multiplier correlation is proposed for practical application. (author)
Numerical Simulation of Two-Phase Critical Flow with the Phase Change in the Nozzle Tube
NASA Astrophysics Data System (ADS)
Ishigaki, Masahiro; Watanabe, Tadashi; Nakamura, Hideo
Two-phase critical flow in the nozzle tube is analyzed numerically by the best estimate code TRACE and the CFD code FLUENT, and the performance of the mass flow rate estimation by the numerical codes is discussed. For the best estimate analysis by the TRACE code, the critical flow option is turned on. The mixture model is used with the cavitation model and the evaporation-condensation model for the numerical simulation by the FLUENT code. Two test cases of the two-phase critical flow are analyzed. One case is the critical flashing flow in a convergent-divergent nozzle (Super Moby Dick experiment), and the other case is the break nozzle flow for a steam generator tube rupture experiment of pressurized water reactors at Large Scale Test Facility of Japan Atomic Energy Agency. The calculation results of the mass flow rates by the numerical simulations show good agreements with the experimental results.
Two-dimensional Rarefaction Waves in the High-speed Two-phase Flow
NASA Astrophysics Data System (ADS)
Nakagawa, Masafumi; Harada, Atsushi
Two-phase flow nozzles are used in the total flow system for geothermal power plants and in the ejector of the refrigerant cycle, etc. One of the most important functions of a two-phase flow nozzle is to convert the thermal energy to the kinetic energy of the two-phase flow. The kinetic energy of the two-phase flow exhausted from a nozzle is available for all applications of this type. There exist the shock waves or rarefaction waves at the outlet of a supersonic nozzle in the case of non-best fitting expansion conditions when the operation conditions of the nozzle are widely chosen. The purpose of the present study is to elucidate theoretically the character of the rarefaction waves at the outlet of the supersonic two-phase flow nozzle. Two-dimensional basic equations for the compressible two-phase flow are introduced considering the inter-phase momentum transfer. Sound velocities are obtained from these equations by using monochromatic wave approximation. Those depend on the relaxation time that determines the momentum transfer. The two-phase flow with large relaxation times has a frozen sound velocity, and with small one has an equilibrium sound velocity. Rarefaction waves which occurred behind the two-phase flow nozzle are calculated by the CIP method. Although the frozen Mach number, below one, controls these basic equations, the rarefaction waves appeared for small relaxation time. The Mach line behind which the expansion starts depends on the inlet velocity and the relaxation time. Those relationships are shown in this paper. The pressure expansion curves are only a function of the revolution angle around the corner of the nozzle outlet for the relaxation time less than 0.1. For the larger relaxation time, the pressure decays because of internal friction caused by inter phase momentum transfer, and the expansion curves are a function of not only the angle but also the flow direction. The calculated expansion curves are compared with the experimental ones
Numerical simulation and analysis of solid-liquid two-phase flow in centrifugal pump
NASA Astrophysics Data System (ADS)
Zhang, Yuliang; Li, Yi; Cui, Baoling; Zhu, Zuchao; Dou, Huashu
2013-01-01
The flow with solid-liquid two-phase media inside centrifugal pumps is very complicated and the relevant method for the hydraulic design is still immature so far. There exist two main problems in the operation of the two-phase flow pumps, i.e., low overall efficiency and severe abrasion. In this study, the three-dimensional, steady, incompressible, and turbulent solid-liquid two-phase flows in a low-specific-speed centrifugal pump are numerically simulated and analyzed by using a computational fluid dynamics (CFD) code based on the mixture model of the two-phase flow and the RNG k- ɛ two-equation turbulence model, in which the influences of rotation and curvature are fully taken into account. The coupling between impeller and volute is implemented by means of the frozen rotor method. The simulation results predicted indicate that the solid phase properties in two-phase flow, especially the concentration, the particle diameter and the density, have strong effects on the hydraulic performance of the pump. Both the pump head and the efficiency are reduced with increasing particle diameter or concentration. However, the effect of particle density on the performance is relatively minor. An obvious jet-wake flow structure is presented near the volute tongue and becomes more remarkable with increasing solid phase concentration. The suction side of the blade is subject to much more severe abrasion than the pressure side. The obtained results preliminarily reveal the characteristics of solid-liquid two-phase flow in the centrifugal pump, and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.
Two-phase flow and transport in the air cathode of proton exchange membrane fuel cells
NASA Astrophysics Data System (ADS)
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.
Gas Bubbles and Slugs Crossover in Air-Water Two-phase Flow by Multifractals
NASA Astrophysics Data System (ADS)
Gorski, Grzegorz; Litak, Grzegorz; Mosdorf, Romuald; Rysak, Andrzej
2017-05-01
Slugs and bubbles two-phase flow patterns dynamics in a minichannel are analysed. During the experiment, the volume flow rates of air and water were changed. We study transition of bubbles to slugs two-phase flow patterns using Fourier and multifractal approaches to optical transitivity signal. The sequences of light transmission time series are recorded by a laser-phototransistor sensor. Multifractal analysis helps to identify the two-phase structure and estimate the signal complexity. Especially, we discuss occurrence and identification of a self-aggregation phenomenon. These results are compared to corresponding Fourier spectra. The results indicate that the fractality is a an important factor influencing the distribution of the gas phase in water.
Cryogenic two-phase flow and phase-change heat transfer in microgravity
NASA Astrophysics Data System (ADS)
Tai, Cheng-Feng
The applications of cryogenic flow and heat transfer are found in many different types of industries, whether it be the liquid fuel for propulsion or the cryogenic cooling in medical applications. It is very common to find the transportation of cryogenic flow under microgravity in space missions. For example, the liquid oxygen and hydrogen are used to power launch vehicles and helium is used for pressurizing the fuel tank. During the transportation process in pipes, because of high temperature and heat flux from the pipe wall, the cryogenic flow is always in a two-phase condition. As a result, the physics of cryogenic two-phase flow and heat transfer is an important topic for research. In this research, numerical simulation is employed to study fluid flow and heat transfer. The Sharp Interface Method (SIM) with a Cut-cell approach (SIMCC) is adopted to handle the two-phase flow and heat transfer computation. In SIMCC, the background grid is Cartesian and explicit true interfaces are immersed into the computational domain to divide the entire domain into different sub-domains/phases. In SIMCC, each phase comes with its own governing equations and the interfacial conditions act as the bridge to connect the information between the two phases. The Cut-cell approach is applied to handle nonrectangular cells cut by the interfaces and boundaries in SIMCC. With the Cut-cell approach, the conservative properties can be maintained better near the interface. This research will focus on developing the numerical techniques to simulate the two-phase flow and phase change phenomena for one of the major flow patterns in film boiling, the inverted annular flow.
Two-phase flow patterns characteristics analysis based on image and conductance sensors
NASA Astrophysics Data System (ADS)
Wang, Zhenya; Jin, Ningde; Wang, Chun; Wang, Jinxiang
2008-10-01
In order to study the temporal and spatial evolution characteristics of gas-liquid two-phase flow pattern, the two-phase flow monitoring system composed of high-speed dynamic camera and Vertical Multi-Electrode Array conductance sensor (VMEA) was utilized to shoot dynamic images and acquire the conductance fluctuating signals of 5 typical vertical gas-liquid two-phase flow patterns in a 125mm i.d. upward pipe. Gray level co-occurrence matrix (GLCM) was used to extract four time-varying characteristic parameter indices which represented different flow image texture structures and also Lempel-Ziv complexity of them were calculated. Then the transition of flow structure and flow property were comprehensively analyzed, combining the result derived from image information with recurrence plots (RPs) and Lempel-Ziv complexity of conductance fluctuating signals. The study showed that the line texture structure of RPs enabled to indicate flow pattern characteristics; the flow image texture structure characteristic parameters sequence described the variance of flow structure and dynamical complexity of different flow patterns.
Experimental and Analytical Study of Two-Phase Flow in Microgravity
NASA Technical Reports Server (NTRS)
Abdollahian, D.; Howerton, J.; Barez, F.; McQuillen, John
1999-01-01
A two-phase test loop has been designed and constructed to generate the necessary data for two-phase pressure drop and Critical Heat Flux (CHF) under reduced gravity conditions. A series of airplane trajectory tests aboard NASA KC-135 were performed and the data was used to evaluate the applicability of the earth gravity models for prediction of the reduced gravity data. Several commonly used correlations for the two-phase friction multiplier and critical heat flux were used to predict the data. It was generally concluded that the two-phase pressure drop can be predicted by the earth gravity correlations. The critical heat flux under reduced gravity conditions did not show a strong dependence on mass flow rate and the measured CHF were generally lower than the equivalent 1g conditions. The earth gravity models need to be modified for application to reduced gravities.
Multi-scale symbolic time reverse analysis of gas-liquid two-phase flow structures
NASA Astrophysics Data System (ADS)
Wang, Hongmei; Zhai, Lusheng; Jin, Ningde; Wang, Youchen
Gas-liquid two-phase flows are widely encountered in production processes of petroleum and chemical industry. Understanding the dynamic characteristics of multi-scale gas-liquid two-phase flow structures is of great significance for the optimization of production process and the measurement of flow parameters. In this paper, we propose a method of multi-scale symbolic time reverse (MSTR) analysis for gas-liquid two-phase flows. First, through extracting four time reverse asymmetry measures (TRAMs), i.e. Euclidean distance, difference entropy, percentage of constant words and percentage of reversible words, the time reverse asymmetry (TRA) behaviors of typical nonlinear systems are investigated from the perspective of multi-scale analysis, and the results show that the TRAMs are sensitive to the changing of dynamic characteristics underlying the complex nonlinear systems. Then, the MSTR analysis is used to study the conductance signals from gas-liquid two-phase flows. It is found that the multi-scale TRA analysis can effectively reveal the multi-scale structure characteristics and nonlinear evolution properties of the flow structures.
Measurement and prediction of two-phase flow patterns for new refrigerants inside horizontal tubes
Kattan, N.; Favrat, D.; Thome, J.R.
1995-12-31
Two-phase flow pattern data were obtained with 12-mm-bore sight glasses for five refrigerants: R-123, R-134a, R-502, R-402A, and R-404A. The existing flow pattern maps of Taitel and Dukler (1976) and Hashizume (1983) poorly represented the data, while, with the exception of mist flows, the VDI map identified the flow patterns successfully. Methods used in horizontal flow boiling correlations to determine the threshold between all wet wall and partially wet wall flows were shown to be unreliable.
Two-Phase Flow in Geothermal Wells: Development and Uses of a Good Computer Code
Ortiz-Ramirez, Jaime
1983-06-01
A computer code is developed for vertical two-phase flow in geothermal wellbores. The two-phase correlations used were developed by Orkiszewski (1967) and others and are widely applicable in the oil and gas industry. The computer code is compared to the flowing survey measurements from wells in the East Mesa, Cerro Prieto, and Roosevelt Hot Springs geothermal fields with success. Well data from the Svartsengi field in Iceland are also used. Several applications of the computer code are considered. They range from reservoir analysis to wellbore deposition studies. It is considered that accurate and workable wellbore simulators have an important role to play in geothermal reservoir engineering.
Two-phase flow stability structure in a natural circulation system
Zhou, Zhiwei
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.
Analysis of the Hydrodynamics and Heat Transfer Aspects of Microgravity Two-Phase Flows
NASA Technical Reports Server (NTRS)
Rezkallah, Kamiel S.
1996-01-01
Experimental results for void fractions, flow regimes, and heat transfer rates in two-phase, liquid-gas flows are summarized in this paper. The data was collected on-board NASA's KC-135 reduced gravity aircraft in a 9.525 mm circular tube (i.d.), uniformly heated at the outer surface. Water and air flows were examined as well as three glycerol/water solutions and air. Results are reported for the water-air data.
Modelling of two-phase flow in a minichannel using level-set method
NASA Astrophysics Data System (ADS)
Grzybowski, H.; Mosdorf, R.
2014-08-01
Today there is a great interest in micro-scale multiphase fluid flow. In the paper, the numerical simulation of two-phase flow inside 3 mm minichannel was carried out. The liquid- gas interface was captured using the level-set method. During the calculation, the stabilization and reinitialization of level set function was performed in order to obtain the proper accuracy of the simulation. Incompressible Navier-Stokes equations were solved using the COMSOL Multiphysics® on a two-dimensional mesh. The process of formation of different two-phase flow patterns in the minichannel has been investigated. During the simulation it has been analysed three flow patterns: the bubbly flow and two kinds of slug flow with short and long slugs. It has been shown that unsteady flow at the inlet of the minichannel is responsible for the chaotic character of changes of the slug and bubble sizes. Such unsteady flow modifies the distance between the bubbles and slugs. It has been shown that for the low water inlet velocity the two-phase flow pattern becomes more stable.
Propagation characteristics of pulverized coal and gas two-phase flow during an outburst.
Zhou, Aitao; Wang, Kai; Fan, Lingpeng; Tao, Bo
2017-01-01
Coal and gas outbursts are dynamic failures that can involve the ejection of thousands tons of pulverized coal, as well as considerable volumes of gas, into a limited working space within a short period. The two-phase flow of gas and pulverized coal that occurs during an outburst can lead to fatalities and destroy underground equipment. This article examines the interaction mechanism between pulverized coal and gas flow. Based on the role of gas expansion energy in the development stage of outbursts, a numerical simulation method is proposed for investigating the propagation characteristics of the two-phase flow. This simulation method was verified by a shock tube experiment involving pulverized coal and gas flow. The experimental and simulated results both demonstrate that the instantaneous ejection of pulverized coal and gas flow can form outburst shock waves. These are attenuated along the propagation direction, and the volume fraction of pulverized coal in the two-phase flow has significant influence on attenuation of the outburst shock wave. As a whole, pulverized coal flow has a negative impact on gas flow, which makes a great loss of large amounts of initial energy, blocking the propagation of gas flow. According to comparison of numerical results for different roadway types, the attenuation effect of T-type roadways is best. In the propagation of shock wave, reflection and diffraction of shock wave interact through the complex roadway types.
Implementation of the interfacial area transport equation in trace for boiling two-phase flows
NASA Astrophysics Data System (ADS)
Bernard, Matthew S.
Correctly predicting the interfacial area concentration (a i) is vital to the overall accuracy of the two-fluid model because ai describes the amount of surface area that exists between the two-phases, and is therefore directly related to interfacial mass, momentum and energy transfer. The conventional method for specifying ai in the two-fluid model is through flow regime-based empirical correlations coupled with regime transition criteria. However, a more physically consistent approach to predicting ai is through the interfacial area transport equation (IATE), which can address the deficiencies of the flow regime-based approach. Some previous studies have been performed to demonstrate the feasibility of IATE in developmental versions of the nuclear reactor systems analysis code, TRACE. However, a full TRACE version capable of predicting boiling two-phase flows with the IATE has not been established. Therefore, the current work develops a version of TRACE that is capable of predicting boiling two-phase flows using the IATE. The development is carried out in stages. First, a version of TRACE which employs the two-group IATE for adiabatic, vertical upward, air-water conditions is developed. An in-depth assessment on the existing experimental database is performed to select reliable experimental data for code assessment. Then, the implementation is assessed against the qualified air-water two-phase flow experimental data. Good agreement is observed between the experimental data for ai and the TRACE code with an average error of +/-9% for all conditions. Following the initial development, one-group IATE models for vertical downward and horizontal two-phase flows are implemented and assessed against qualified data. Finally, IATE models capable of predicting subcooled boiling two-phase flows are implemented. An assessment of the models shows that TRACE is capable of generating ai in subcooled boiling two-phase flows with the IATE and that heat transfer effects dominate
Studies of Gas-Particle Interactions in a Microgravity Flow Cell
NASA Technical Reports Server (NTRS)
Louge, Michel Y.; Jenkins, James T.
2002-01-01
The ability to transport particulate materials predictably and efficiently using a flowing gas is likely to play an important role in the development of lunar and Martian environments that are hospitable to humans. Lunar soil contains significant amounts of oxygen, hydrogen and other critical materials that are chemically bound in various minerals. Through appropriate processing, these resources may be recovered for use in propulsion, life support systems and mining operations. Similarly, it is believed that Martian soil contains significant amounts of water which can be electrolyzed into oxygen and hydrogen, again for propellants and life support. The transport of such granular soils from where they are mined and between stages of their processing is likely to involve pneumatic transport carried out in systems of pipes using flows of the liberated gases. On earth, the transport and processing of solid materials are also crucial in a number of applications from the chemical, mining, power and oil industries. For these flows, an appreciation has recently developed for the influence of collisional interactions among particles, both in suspensions where the flow is laminar and turbulent. Collisions between such particles can transfer a significant amount of momentum within the flow and at the boundaries. This provides an additional resistance to the passage of the gas, but it also introduces a mechanism that promotes more homogeneous flows and, at least in small-diameter pipes, may forestall the development of clusters.
Studies of Gas-Particle Interactions in a Microgravity Flow Cell
NASA Technical Reports Server (NTRS)
Louge, Michel Y.; Jenkins, James T.
2002-01-01
The ability to transport particulate materials predictably and efficiently using a flowing gas is likely to play an important role in the development of lunar and Martian environments that are hospitable to humans. Lunar soil contains significant amounts of oxygen, hydrogen and other critical materials that are chemically bound in various minerals. Through appropriate processing, these resources may be recovered for use in propulsion, life support systems and mining operations. Similarly, it is believed that Martian soil contains significant amounts of water which can be electrolyzed into oxygen and hydrogen, again for propellants and life support. The transport of such granular soils from where they are mined and between stages of their processing is likely to involve pneumatic transport carried out in systems of pipes using flows of the liberated gases. On earth, the transport and processing of solid materials are also crucial in a number of applications from the chemical, mining, power and oil industries. For these flows, an appreciation has recently developed for the influence of collisional interactions among particles, both in suspensions where the flow is laminar and turbulent. Collisions between such particles can transfer a significant amount of momentum within the flow and at the boundaries. This provides an additional resistance to the passage of the gas, but it also introduces a mechanism that promotes more homogeneous flows and, at least in small-diameter pipes, may forestall the development of clusters.
Film boiling on spheres in single- and two-phase flows. Final report
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.
Film boiling on spheres in single- and two-phase flows.
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.
Direct imaging of two-phase flows by electrical impedance measurements
NASA Astrophysics Data System (ADS)
Seleghim, Paulo, Jr.; Hervieu, Eric
1998-09-01
This paper presents a two-phase flow direct imaging sensor, based on multiple electrical impedance measurements. The electrode configuration is optimized to provide imaged information on the phase distribution within the probe's sensing volume. As a consequence, the time evolution of the flow topology can be represented by simply plotting the signals corresponding to the peripheral impedance measurements, and therefore needs no numerical reconstruction from the experimental data. Several transient tests are performed in a two-phase air-water loop. They demonstrate that the sensor exhibits not only large structures such as slugs and plugs, but also some finer details such as the wavy or rugged interface in stratified flow, or liquid film drainage during the transition between intermittent and annular flows. The methodology proposed in this work constitutes a simple and inexpensive alternative to tomographic imaging techniques, and is thus fully adapted to online process monitoring of multiphase flow systems.
Thermal and dynamical regimes of single- and two-phase magmatic flow in dikes
NASA Technical Reports Server (NTRS)
Carrigan, Charles R.; Schubert, Gerald; Eichelberger, John C.
1992-01-01
The coupling between thermal and dynamical regimes of single- and two-phase magmatic flow in dikes, due to temperature-dependent viscosity and dissipation, was investigated using finite element calculations of magma flow in dikelike channels with length-to-width ratios of 1000:1 or more. Solutions of the steady state equations governing magma flow are obtained for a variety of conditions ranging from idealized plane-parallel models to cases involving nonparallel geometry and two-phase flows. The implications of the numerical simulations for the dynamics of flow in a dike-reservoir system and the consequences of dike entrance conditions on magmatic storage are discussed. Consideration is also given to an unmixing/self-lubrication mechanism which may be important for the lubrication of silicic magmas rising to the earth's surface in mixed magma ascent scenarios, which naturally segregates magma mixtures of two components with differing viscosities to minimize the driving pressure gradient.
Numerical Study of Two-Phase Flow in Micro-/Nanobubble Generating Pump
NASA Astrophysics Data System (ADS)
Syaeful Alam, Hilman; Bahrudin; Sugiarto, Anto Tri
2017-05-01
Gas-liquid mixing pump is one of the multiphase flow problem in industrial applications as a micro-/nanobubble generator. However, very few report that studied the two-phase flow for application of microbubble generation because of the analysis complexity. In this paper, a steady state numerical simulation of gas-liquid two-phase flow in the gas-liquid mixing pump was employed to predict a performance and characteristic of fluid flow. Based on simulation results, it is demonstrated that the pump can work in self suction, and generates a vortex flow pattern at every stage of the impeller as regenerative. Performance pump of the numerical simulation is slightly higher than the design specifications Because of mechanical and volume losses was neglected. However, the evaluation method and simulation results from this work can be used as a reference for the design and improvement of the gas-liquid mixing pump.
Time integration for diffuse interface models for two-phase flow
Aland, Sebastian
2014-04-01
We propose a variant of the θ-scheme for diffuse interface models for two-phase flow, together with three new linearization techniques for the surface tension. These involve either additional stabilizing force terms, or a fully implicit coupling of the Navier–Stokes and Cahn–Hilliard equation. In the common case that the equations for interface and flow are coupled explicitly, we find a time step restriction which is very different to other two-phase flow models and in particular is independent of the grid size. We also show that the proposed stabilization techniques can lift this time step restriction. Even more pronounced is the performance of the proposed fully implicit scheme which is stable for arbitrarily large time steps. We demonstrate in a Taylor-flow application that this superior coupling between flow and interface equation can decrease the computation time by several orders of magnitude.
Evaluation of the Sensitivity of Two-Phase Flow Model for the Steam Separator Analysis
Michio Murase; Masao Chaki
2006-07-01
Reducing of the pressure losses of steam separator systems of boiling water reactor (BWR) plants is useful to reduce the required pump head and enhance core stability design margin. The need to reduce the pressure losses of steam separator systems is especially important in BWR plants that have high power density cores and natural circulation systems. The core flow rate of a BWR plant with a natural circulation system is affected by the pressure losses of steam separator systems. In BWR plants with high power density cores, the core stability design margin is affected by these pressure losses. Generally, reducing the pressure losses of the steam separator systems leads to increased carry-under and carryover. Reducing the pressure losses while keeping the characteristics of both carry-under and carryover is desired, so many studies have been done. The steam separator of a BWR plant consists of a standpipe section, a swirl vane section and three-barrel sections. Two-phase flow of steam and water enters the steam separator through the standpipe section and reaches the swirl vane section. In the swirl vane section, the two-phase flow is given centrifugal force and is basically separated into steam and water. Therefore investigating the two-phase flow characteristics of the swirl vane section is very important. After the swirl vane section, the two-phase flow enters the barrel sections. Each barrel has a pick-off ring. The water in the barrel section is mainly removed by these pick-off rings because the water mainly flows upward as a liquid film in the barrel section due to the centrifugal force given in the swirl vane section. We researched the effect of using the drag force model of the swirling two-phase flow in analyzing a steam separator and we found that the drag force model greatly affects the results of the analysis. (authors)
Dynamics of face and annular seals with two-phase flow
NASA Technical Reports Server (NTRS)
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.
Entropy analysis on non-equilibrium two-phase flow models
Karwat, H.; Ruan, Y.Q.
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.
NASA Astrophysics Data System (ADS)
Dong, S.
2014-06-01
We present an effective outflow boundary condition, and an associated numerical algorithm, within the phase-field framework for dealing with two-phase outflows or open boundaries. The set of two-phase outflow boundary conditions for the phase-field and flow variables are designed to prevent the un-controlled growth in the total energy of the two-phase system, even in situations where strong backflows or vortices may be present at the outflow boundaries. We also present an additional boundary condition for the phase field function, which together with the usual Dirichlet condition can work effectively as the phase-field inflow conditions. The numerical algorithm for dealing with these boundary conditions is developed on top of a strategy for de-coupling the computations of all flow variables and for overcoming the performance bottleneck caused by variable coefficient matrices associated with variable density/viscosity. The algorithm contains special constructions, for treating the variable dynamic viscosity in the outflow boundary condition, and for preventing a numerical locking at the outflow boundaries for time-dependent problems. Extensive numerical tests with incompressible two-phase flows involving inflow and outflow boundaries demonstrate that, the two-phase outflow boundary conditions and the numerical algorithm developed herein allow for the fluid interface and the two-phase flow to pass through the outflow or open boundaries in a smooth and seamless fashion, and that our method produces stable simulations when large density ratios and large viscosity ratios are involved and when strong backflows are present at the outflow boundaries.
Multiphase turbulence in vertical wall-bounded collisional gas-particle flows
NASA Astrophysics Data System (ADS)
Fox, Rodney O.; Capecelatro, Jesse; Desjardins, Olivier
2014-11-01
Wall-bounded particle-laden flows are common in many environmental and industrial applications, and are often turbulent. In vertical flows, strong coupling between the phases leads to the spontaneous generation of dense clusters that fall due to gravity at the walls, while dilute suspensions of particles rise in the central region. Sustained volume fraction and velocity fluctuations caused by the clusters result in the production of fluid-phase turbulent kinetic energy, referred to as cluster-induced turbulence (CIT). To better understand the nature of CIT in wall-bounded flows, Eulerian-Lagrangian simulations of statistically stationary three-dimensional gas-solid flows in vertical pipes are performed. To extract useful information consistent with Eulerian turbulence models, a separation of length scales is introduced to decompose correlated and uncorrelated granular motion. To accomplish this, an adaptive spatial filter is employed on the particle data with an averaging volume that varies with the local particle-phase volume fraction. Radial profiles of turbulence statistics are generated from the Eulerian-Lagrangian results. Details on the nature of the turbulence are described, as well as the challenges they present to turbulence modeling. Marie-Curie Senior Fellow, Ecole Centrale Paris.
Ojovan, M. I.; Klimov, V. L.; Karlina, O. K.
2002-02-26
A ''quasi-equilibrium'' approach for thermodynamic calculation of chemical composition and properties of metal-containing fuel combustion products has been developed and used as a part of the mathematical model of heterogeneous reacting flow which carry burning and/or evaporating particles. By using of this approach, the applicable mathematical model has been devised, which allows defining the change in chemical composition and thermal characteristics of combustion products along the incineration chamber. As an example, the simulation results of the reacting flow of magnesium-sodium nitrate-organic mixture are presented. The simulation results on the gas phase temperature in the flow of combustion products are in good agreement with those obtained experimentally. The proposed method of ''quasi-equilibrium'' thermodynamic calculation and mathematical model provide a real possibility for performing of numerical experiments on the basis of mathematical simulation of nonequilibrium flows of combustion products. Numerical experiments help correctly to estimate the work characteristics in the process of treatment devices design saving time and costs.
Large eddy simulation of the gas-particle turbulent wake flow.
Luo, Kun; Jin, Han-hui; Fan, Jian-ren; Cen, Ke-fa
2004-01-01
To find out the detailed characteristics of the coherent structures and associated particle dispersion in free shear flow, large eddy simulation method was adopted to investigate a two-dimensional particle-laden wake flow. The well-known Sub-grid Scale mode introduced by Smagorinsky was employed to simulate the gas flow field and Lagrangian approach was used to trace the particles. The results showed that the typical large-scale vortex structures exhibit a stable counter rotating arrangement of opposite sign, and alternately form from the near wall region, shed and move towards the downstream positions of the wake with the development of the flow. For particle dispersion, the Stokes number of particles is a key parameter. At the Stokes numbers of 1.4 and 3.8 the particles concentrate highly in the outer boundary regions. While the particles congregate densely in the vortex core regions at the Stokes number of 0.15, and the particles at Stokes number of 15 assemble in the vortex braid regions and the rib regions between the adjoining vortex structures.
NASA Astrophysics Data System (ADS)
Carcano, Susanna; Bonaventura, Luca
2014-05-01
During explosive volcanic eruptions a mixture of gases, magma fragments, crystals and eroded rocks is injected in the atmosphere at high velocity, pressure and temperature. In the proximity of the volcanic vent, the erupted underexpanded multiphase mixture can manifest the features of supersonic flows, while the subsequent column behaviour is controlled by the (subsonic) turbulent mixing and mass and thermal exchange between the gas-particle mixture and the atmosphere. One of the main difficulties of the numerical simulation of explosive volcanic eruptions is therefore the need of modeling a multiphase process where different fluid dynamic regimes coexist and develop on on a wide range of temporal and spatial scales. From a computational point of view, this requires robust numerical techniques able to resolve supersonic regimes and to capture flow discontinuities (shock waves), as well as to reduce, where needed, the so-called numerical diffusion (while increasing the numerical accuracy) in order to simulate gas-particle non-equilibrium phenomena. Several examples of numerical approximation of multiphase gas-particle equations based on finite volume approach have been proposed in the literature, able to simulate the multiphase mixture up to second-order accuracy in space and time. However, achieving higher order of accuracy in the finite volume framework implies an increasing computational cost related to the extension of the computational stencil, in particular when a parallel implementation has to be employed. In this work, a mixture of gas and solid particles is described with a set of coupled partial differential equations for the mass, momentum and energy of each phase. Solid particles and the gas phase are considered as non-equilibrium interpenetrating continua, following an Eulerian-Eulerian approach. Each phase is compressible and inviscid. The gas and particles dynamics are coupled through the drag term in the momentum equations and the heat exchange term
NASA Astrophysics Data System (ADS)
Deubelbeiss, Y.; Kaus, B. J. P.; Connolly, J. A. D.
2010-02-01
We analyze the mechanical behavior of a two-phase system consisting of rigid grains and an interconnected pore fluid. For this purpose we use 2D direct numerical simulations on the spatial scale of individual grains for Newtonian and non-Newtonian fluid rheology. By using the stress-strain rate relation we derive scaling laws for effective viscosity of two-phase particle suspensions. We demonstrate that the effective rheology of the assemblage is non-Newtonian only if the fluid has a non-Newtonian rheology. At small fluid fraction, inter-granular strain rates are up to 3 orders of magnitude higher than the applied background strain rate. We suggest that this effect explains the experimentally observed change at higher strain rates in rheology, from Newtonian to non-Newtonian aggregate rheology. To establish the conditions at which the fluid-solid aggregate deforms coherently as a consequence of Rayleigh-Taylor instabilities we studied flow patterns of particle suspensions and characterized them as a function of fluid fraction, viscosity, density, shape and size of the grains. From initial conditions with homogeneously distributed grains and interstitial fluid above a layer of pure fluid, our results show that the Rayleigh-Taylor instability dominates for moderate to large fluid fractions. At large fluid fractions, we observed a transition to a Stokes suspension mode, in which grains do not interact but sink independently. An analytical expression is derived that predicts the transition from Rayleigh-Taylor instability to Stokes suspension mode. The transition is a function of fluid fraction, radius of the grains, height of the interface and initial amplitude. Systematic numerical simulations are in good agreement with the analytical predictions.
Using a Fast X-Ray Microtomography Study to Better Inform Two-Phase Flow Theories
NASA Astrophysics Data System (ADS)
Meisenheimer, D.; Wildenschild, D.
2016-12-01
Understanding multiphase flow in porous media is important to many fields including groundwater management and remediation, soil and agricultural practices, petroleum engineering, and geologic sequestration of CO2. Scientists and engineers in these fields require experimental data acquired under field conditions to accurately create models of the dynamic multiphase flow processes being studied. The recent introduction of fast x-ray microtomography (fast-µCT) allows multiphase flow experiments to be performed in 3-dimensions under field-consistent pressure conditions removing the decision to either sacrifice the 3rd dimension with 2D micromodels or impose a pseudo-equilibrium pressure condition using standard-µCT methods. This new experimental method allows for the acquisition of data under more relevant conditions to validate multiphase theories with greater confidence and inform more accurate models. One such multiphase flow theory introduces interfacial area as a state variable that can be used to better describe the characteristics of two-phase flow by reducing or eliminating the hysteric effect that is prevalent in many two-phase models. Using fast-µCT, interfacial area production and evolution can unprecedentedly be tracked in 3D under valid flow conditions. Previously, we presented a preliminary analysis that suggested that the capillary pressure-saturation-interfacial area (Pc-Sw-Awn) surface established under flow conditions does not coincide with the surface obtained under pseudo-equilibrium conditions, which is complementary to work done in 2D micromodel studies. Here we present a more in-depth analysis on the relationship between Pc-Sw-Anw surfaces obtained under flow or pseudo-equilibrium conditions. In addition, we present an analysis of the measured interfacial area production rate term (Ewn) in relation to the rate of change of saturation (dS/dt) during the two-phase flow experiments which is an important relationship in two-phase theories.
Experimental and Analytical Study of Two-Phase Flow in Microgravity
NASA Technical Reports Server (NTRS)
McQuillen, John B.; Abdollahian, Davood; Quintal, J.; Zahm, J.
1996-01-01
Design of the two-phase flow systems which are anticipated to be utilized in future spacecraft thermal management systems requires a knowledge of two-phase flow and heat transfer parameters in reduced gravities. A program has been initiated by NASA to design a two-phase test loop and to perform a series of experiments to study the effect of gravity on the Critical Heat Flux (CHF) and onset of instability. The test loop is also instrumented to generate data for two-phase pressure drop. In addition to low gravity airplane trajectory testing, the experimental program consisted of a set of laboratory tests which were intended to generate data under the bounding conditions (+1 g and -1 g) in order to plan the test matrix. One set of airplane trajectory tests has been performed and several modifications to the test set-up have been identified. Preliminary test results have been used to demonstrate the applicability of the earth gravity models for prediction of the two-phase friction pressure drop.
Mechanisms of self-excitation of thermoacoustic vibrations in two-phase bubble flows
Skalozubov, V.I. )
1991-01-01
In this paper, the mechanisms of self-excitation of thermoacoustic vibrations in two-phase bubble flows are described. It is shown that a theory of this process must take into consideration the work performed by bubbles traveling in the acoustic wave. The results of the theory herein developed agree with previous experimental data of the author.
COMPARING SIMULATED AND EXPERIMENTAL HYSTERETIC TWO- PHASE TRANSIENT FLUID FLOW PHENOMENA
A hysteretic model for two-phase permeability (k)-saturation (S)-pressure (P) relations is outlined that accounts for effects of nonwetting fluid entrapment. The model can be employed in unsaturated fluid flow computer codes to predict temporal and spatial fluid distributions. Co...
Comparison of Two-Phase Pipe Flow in OpenFOAM with a Mechanistic Model
NASA Astrophysics Data System (ADS)
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.
A boundary element approach to estimate the free surface in stratified two-phase flow
NASA Astrophysics Data System (ADS)
Ren, Shangjie; Dong, Feng; Tan, Chao; Xu, Yaoyuan
2012-10-01
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.
Numerically induced pressure excursions in two-phase-flow calculations. Final report
Mahaffy, J.H.; Liles, D.R.
1983-01-01
Pressure spikes that cannot be traced to any physical origin sometimes are observed when standard Eulerian finite-difference methods are used to calculate two-phase-flow transients. This problem occurs with varying frequency in nuclear reactor safety codes such as RELAP, RETRAN, COBRA, and TRAC. These spikes usually result from numerical water packing or from interactions between spatial discretization and heat transfer.
COMPARING SIMULATED AND EXPERIMENTAL HYSTERETIC TWO- PHASE TRANSIENT FLUID FLOW PHENOMENA
A hysteretic model for two-phase permeability (k)-saturation (S)-pressure (P) relations is outlined that accounts for effects of nonwetting fluid entrapment. The model can be employed in unsaturated fluid flow computer codes to predict temporal and spatial fluid distributions. Co...
Two-Phase Flows in the Wake of In-Cylinder Projectiles.
1987-12-01
shown by computational communities (references 3and 4) which, it is hoped, will provide means of interpolation and extrapolation of the experimental...ballistic reeearch: state of the art of ci;utational and experiental efforts". zDC report Ezpl-Nr 029. 2. Gough P S. "Modelling of two phase flows in
Simulation experiments on two-phase natural circulation in a freon-113 flow visualization loop
Lee, Sang Yong; Ishii, Mamoru
1988-01-01
In order to study the two-phase natural circulaton and flow termination during a small break loss of coolant accident in LWR, simulation experiments have been performed using a Freon-113 flow visualization loop. The main focus of the present experiment was placed on the two-phase flow behavior in the hot-leg U-bend typical of B and W LWR systems. The loop was built based on the two-phase flow scaling criteria developed under this program to find out the effect of fluid properties, phase changes and coupling between hydrodynamic and heat transfer phenomena. Significantly different flow behaviors have been observed due to the non-equilibrium phase change phenomena such as the flashing and condensation on the Freon loop in comparison with the previous adiabatic experiment. The phenomena created much more unstable hydrodynamic conditions which lead to cyclic or oscillatory flow behaviors. Also, the void distribution and primary loop flow rate were measured in detail in addition to the important key paramaters, such as the power input, loop friction and the liquid level inside the simulated steam generator.
Waves, Instabilities, and Rivulets in High Quality Microgap Two-Phase Flow
NASA Astrophysics Data System (ADS)
Bar-Cohen, A.; Holloway, C.
2016-09-01
Two-phase flow in sub-millimeter microgap channels offers highly potent thermal management capability and is the foundation for the emerging "embedded cooling" paradigm of electronic cooling. While the thermofluid characteristics and operational limits of such microcoolers are intimately tied to distinct forms of vapor-liquid aggregation in the microgap channel, insufficient attention has been paid to the formation of distinct wave patterns and instabilities on the thin liquid films associated with high-quality microgap channel flow. This paper focuses on the results of visualization and heat transfer studies of such two-phase flows, under both adiabatic and diabatic conditions, for FC-72 flowing in a 184 micron microgap channel at a mass flux of 230 kg/(m2.s). The study has revealed the existence of a post-annular, high-quality Rivulet flow regime, in which the liquid film breakdown and local wall dryout drives large surface anisothermalities and limits the heat transfer rate from the wall. As predicted by the prevailing flow regime models, annular flow is found to be the dominant flow regime for this microgap configuration.. For the adiabatic conditions, flow qualities ranged between 27% and 81%, and widely spaced, 3D waves, with a wavelength that decreases with increasing flow quality, were observed on the liquid-vapor interface. For the diabatic condition, the inlet flow quality was maintained at 36% and the exit flow quality varied between 47% and 97%. For exit qualities greater than 61%, the liquid film would periodically rupture into rivulet of varying width and length. The spacing, length, and width of the rivulets varied considerably, and can easily stretch well into dryout region. The axial variation of the wall heat transfer coefficient was found to reflect and confirm the expected axial propagation of the two- phase flow regimes and the onset of local dryout associated with the newly-defined Rivulet regime.
Synchrotron 4-dimensional imaging of two-phase flow through porous media
Kim, F.H.; Penumadu, D.; Patel, P.; Xiao, X.; Garboczi, E.J.; Moylan, S.P.; Donmez, M.A.
2016-01-01
Near real-time visualization of complex two-phase flow in a porous medium was demonstrated with dynamic 4-dimensional (4D) (3D + time) imaging at the 2-BM beam line of the Advanced Photon Source (APS) at Argonne National Laboratory. Advancing fluid fronts through tortuous flow paths and their interactions with sand grains were clearly captured, and formations of air bubbles and capillary bridges were visualized. The intense X-ray photon flux of the synchrotron facility made 4D imaging possible, capturing the dynamic evolution of both solid and fluid phases. Computed Tomography (CT) scans were collected every 12 s with a pixel size of 3.25 µm. The experiment was carried out to improve understanding of the physics associated with two-phase flow. The results provide a source of validation data for numerical simulation codes such as Lattice-Boltzmann, which are used to model multi-phase flow through porous media. PMID:27891248
Localized heat transfer to verticle forced flow two-phase helium
Panek, J.; Huang, X.; Van Sciver, S.W.
1996-12-31
Localized heat transfer measurements in vertical two-phase helium are reported. The test loop contains two short heat transfer sections made of 5 mm thick oxygen-free high conductivity (OFHC) copper discs. These test sections were installed in a U-shaped vertical flow loop driven by a single-stroke bellows pump. The surface temperature of each test section is measured with two germanium thermometers placed on different radial positions in each test section. With one test section placed on the downflow side and one on the upflow side of the loop, the effect of flow orientation on heat transfer characteristics in vertical two-phase helium flow is investigated. The study includes the effects of system pressure, mass flow rate, and geometry on the heat transfer coefficient, critical heat flux, and recovery heat flux.
Two phase choke flow in tubes with very large L/D
NASA Technical Reports Server (NTRS)
Hendricks, R. C.; Simoneau, R. J.
1977-01-01
Data were obtained for two phase and gaseous choked flow nitrogen in a long constant area duct of 16200 L/D with a diverging diffuser attached to the exit. Flow rate data were taken along five isotherms (reduced temperature of 0.81, 0.96, 1.06, 1.12, and 2.34) for reduced pressures to 3. The flow rate data were mapped in the usual manner using stagnation conditions at the inlet mixing chamber upstream of the entrance length. The results are predictable by a two phase homogeneous equilibrium choking flow model which includes wall friction. A simplified theory which in essence decouples the long tube region from the high acceleration choking region also appears to predict the data resonably well, but about 15 percent low.
Damping and fluidelastic instability in two-phase cross-flow heat exchanger tube arrays
NASA Astrophysics Data System (ADS)
Moran, Joaquin E.
An experimental study was conducted to investigate damping and fluidelastic instability in tube arrays subjected to two-phase cross-flow. The purpose of this research was to improve our understanding of these phenomena and how they are affected by void fraction and flow regime. The model tube bundle had 10 cantilevered tubes in a parallel-triangular configuration, with a pitch ratio of 1.49. The two-phase flow loop used in this research utilized Refrigerant 11 as the working fluid, which better models steam-water than air-water mixtures in terms of vapour-liquid mass ratio as well as permitting phase changes due to pressure fluctuations. The void fraction was measured using a gamma densitometer, introducing an improvement over the Homogeneous Equilibrium Model (HEM) in terms of void fraction, density and velocity predictions. Three different damping measurement methodologies were implemented and compared in order to obtain a more reliable damping estimate. The methods were the traditionally used half-power bandwidth, the logarithmic decrement and an exponential fitting to the tube decay response. The decay trace was obtained by "plucking" the monitored tube from outside the test section using a novel technique, in which a pair of electromagnets changed their polarity at the natural frequency of the tube to produce resonance. The experiments showed that the half-power bandwidth produces higher damping values than the other two methods. The primary difference between the methods is caused by tube frequency shifting, triggered by fluctuations in the added mass and coupling between the tubes, which depend on void fraction and flow regime. The exponential fitting proved to be the more consistent and reliable approach to estimating damping. In order to examine the relationship between the damping ratio and mass flux, the former was plotted as a function of void fraction and pitch mass flux in an iso-contour plot. The results showed that damping is not independent of mass
Coupling of two-phase flow in fractured-vuggy reservoir with filling medium
NASA Astrophysics Data System (ADS)
Xie, Haojun; Li, Aifen; Huang, Zhaoqin; Gao, Bo; Peng, Ruigang
2017-01-01
Caves in fractured-vuggy reservoir usually contain lots of filling medium, so the two-phase flow in formations is the coupling of free flow and porous flow, and that usually leads to low oil recovery. Considering geological interpretation results, the physical filled cave models with different filling mediums are designed. Through physical experiment, the displacement mechanism between un-filled areas and the filling medium was studied. Based on the experiment model, we built a mathematical model of laminar two-phase coupling flow considering wettability of the porous media. The free fluid region was modeled using the Navier-Stokes and Cahn-Hilliard equations, and the two-phase flow in porous media used Darcy's theory. Extended BJS conditions were also applied at the coupling interface. The numerical simulation matched the experiment very well, so this numerical model can be used for two-phase flow in fracture-vuggy reservoir. In the simulations, fluid flow between inlet and outlet is free flow, so the pressure difference was relatively low compared with capillary pressure. In the process of water injection, the capillary resistance on the surface of oil-wet filling medium may hinder the oil-water gravity differentiation, leading to no fluid exchange on coupling interface and remaining oil in the filling medium. But for the water-wet filling medium, capillary force on the surface will coordinate with gravity. So it will lead to water imbibition and fluid exchange on the interface, high oil recovery will finally be reached at last.
Interfacial area transport for reduced-gravity two-phase flows
NASA Astrophysics Data System (ADS)
Vasavada, Shilp
An extensive experimental and theoretical study of two-phase flow behavior in reduced-gravity conditions has been performed as part of the current research and the results of the same are presented in this thesis. The research was undertaken to understand the behavior of two-phase flows in an environment where the gravity field is reduced as compared to that on earth. The goal of the study was to develop a model capable of predicting the flow behavior. An experimental program was developed and accomplished which simulated reduced-gravity conditions on earth by using two liquids of similar density, thereby decreasing the body force effect akin to actual reduced-gravity conditions. The justification and validation of this approach has been provided based on physical arguments as well as comparison of acquired data with that obtained aboard parabolic flights by previous researchers. The experimental program produced an extensive dataset of local and averaged two-phase flow parameters using state-of-the-art instrumentation. Such data were acquired for a wide range of flow conditions at different radial and axial locations in a 25 mm inner diameter test facility. The current dataset is, in the author's opinion, the most extensive and detailed dataset available for such conditions at present. Analysis of the data revealed important differences between two-phase flows in normal and reduced-gravity conditions. The data analysis also highlighted key interaction mechanisms between the fluid particles and physical phenomena occurring in two-phase flows under reduced-gravity conditions. The interfacial area transport equation (IATE) for reduced-gravity conditions has been developed by considering two groups of bubbles/drops and mechanistically modeling the interaction mechanisms. The developed model has been benchmarked against the acquired data and the predictions of the model compared favorably against the experimental data. This signifies the success achieved in modeling
Analysis of flow, gas-particle radiation, and particulate deposition in radiant boilers
Im, Kwan H.; Ahluwalia, R. K.; Berry, G. F.
1981-04-01
Flow, heat and mass transfer processes in the radiant boilers of magnetohydynamic power plants are analyzed. Flow field in the radiant boiler is simulated by assuming a uniformly mixed zone to exist in the entrance region, followed by a developing boundary layer region. Heat transfer is presumed to occur by both turbulent convection and radiation. The radiation model includes the simultaneous contribution to heat transfer of carbon dioxide, water vapor, potassium atoms, and slag particles which are allowed to absorb as well as scatter thermal radiation. The absorption coefficients of gaseous species are determined from band correlations and experimental data. The extinction and scattering coefficients of slag particles are computed directly from Mie theory. For computing heat transfer, radiation transport equation is solved on a spectral basis. The complete flow, heat and mass transfer model is used to study the thermal characteristics of the radiant boilers. Impacts of slag-refractory interface temperature on corrosion and erosion of refractory, and of slag layer thickness on plant start-up time are discussed. By presenting the scale-up of heat transfer with refractory thickness and boiler diameter, the factors involved in designing an experimental facility for simulating base load boilers are highlighted. The temperature history computed from the heat transfer model is used in an extant chemical kinetics code to determine the practical levels to which NO/sub x/ can be decomposed in MHD radiant boilers. Calculations indicate that the EPA specified limit on NO/sub x/ levels can be met in properly designed radiant boilers operating with sub-stoichiometric products of combustion. The potential of the complete model to serve as a strong analytical tool in selecting an optimum geometry for radiant boilers is stressed by proposing an optimization procedure. (WHK)
Stochastic Discrete Equation Method (sDEM) for two-phase flows
Abgrall, R.; Congedo, P.M.; Geraci, G.; Rodio, M.G.
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.
Approaches to myosin modelling in a two-phase flow model for cell motility
NASA Astrophysics Data System (ADS)
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.
An ALE Finite Element Approach for Two-Phase Flow with Phase Change
NASA Astrophysics Data System (ADS)
Gros, Erik; Anjos, Gustavo; Thome, John; Ltcm Team; Gesar Team
2016-11-01
In this work, two-phase flow with phase change is investigated through the Finite Element Method (FEM) in the Arbitrary Lagrangian-Eulerian (ALE) framework. The equations are discretized on an unstructured mesh where the interface between the phases is explicitly defined as a sub-set of the mesh. The two-phase interface position is described by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The methodology proposed for computing the curvature leads to very accurate results with moderate programming effort and computational costs. Such a methodology can be employed to study accurately many two-phase flow and heat transfer problems in industry such as oil extraction and refinement, design of refrigeration systems, modelling of microfluidic and biological systems and efficient cooling of electronics for computational purposes. The latter is the principal aim of the present research. The numerical results are discussed and compared to analytical solutions and reference results, thereby revealing the capability of the proposed methodology as a platform for the study of two-phase flow with phase change.
Single- and Two-Phase Flow Characterization Using Optical Fiber Bragg Gratings
Baroncini, Virgínia H.V.; Martelli, Cicero; da Silva, Marco José; Morales, Rigoberto E.M.
2015-01-01
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. PMID:25789494
Single- and two-phase flow characterization using optical fiber bragg gratings.
Baroncini, Virgínia H V; Martelli, Cicero; da Silva, Marco José; Morales, Rigoberto E M
2015-03-17
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.
The Two-Phase Hell-Shaw Flow: Construction of an Exact Solution
NASA Astrophysics Data System (ADS)
Malaikah, K. R.
2013-03-01
We consider a two-phase Hele-Shaw cell whether or not the gap thickness is time-dependent. We construct an exact solution in terms of the Schwarz function of the interface for the two-phase Hele-Shaw flow. The derivation is based upon the single-valued complex velocity potential instead of the multiple-valued complex potential. As a result, the construction is applicable to the case of the time-dependent gap. In addition, there is no need to introduce branch cuts in the computational domain. Furthermore, the interface evolution in a two-phase problem is closely linked to its counterpart in a one-phase problem
Interfacial structures of confined air-water two-phase bubbly flow
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.
A modified homogeneous relaxation model for CO2 two-phase flow in vapour ejector
NASA Astrophysics Data System (ADS)
Haida, M.; Palacz, M.; Smolka, J.; Nowak, A. J.; Hafner, A.; Banasiak, K.
2016-09-01
In this study, the homogenous relaxation model (HRM) for CO2 flow in a two-phase ejector was modified in order to increase the accuracy of the numerical simulations The two- phase flow model was implemented on the effective computational tool called ejectorPL for fully automated and systematic computations of various ejector shapes and operating conditions. The modification of the HRM was performed by a change of the relaxation time and the constants included in the relaxation time equation based on the experimental result under the operating conditions typical for the supermarket refrigeration system. The modified HRM was compared to the HEM results, which were performed based on the comparison of motive nozzle and suction nozzle mass flow rates.
Use of two-phase flow heat transfer method in spacecraft thermal system
NASA Technical Reports Server (NTRS)
Hye, A.
1985-01-01
In space applications, weight, volume and power are critical parameters. Presently liquid freon is used in the radiator planels of the Space Shuttle to dissipate heat. This requires a large amount of freon, large power for pumps, large volume and weight. Use of two-phase flow method to transfer heat can reduce them significantly. A modified commercial vapor compression refrigerator/freezer was sucessfully flown in STS-4 to study the effect of zero-gravity on the system. The duty cycle was about 5 percent higher in flight as compared to that on earth due to low flow velocity in condenser. The vapor Reynolds number at exit was about 4000 as compared to about 12,000. Efforts are underway to design a refrigerator/freezer using an oil-free compressor for Spacelab Mission 4 scheduled to fly in January 1986. A thermal system can be designed for spacecraft using the two-phase flow to transfer heat economically.
Time-resolved Fast Neutron Radiography of Air-water Two-phase Flows
NASA Astrophysics Data System (ADS)
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.
Analysis of nanoscale two-phase flow of argon using molecular dynamics
NASA Astrophysics Data System (ADS)
Verma, Abhishek Kumar; Kumar, Rakesh
2014-12-01
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.
Investigation of Two-Phase Flows in Piping Bends and Elbows
NASA Technical Reports Server (NTRS)
Duncan, Allen B.; Sciascia, Vincent M.
1996-01-01
An experimental investigation of the hydrodynamic characteristics of two-phase R-113 flow has been carried out. Straight tube pressure drop data, as a function of mass flow rate (mass flux) and flow quality has been obtained using the Two-Phase Flow Test Facility located in the Advanced Thermal Laboratories of the Crew and Thermal Systems Division at the Lyndon B. Johnson Space Center. Additionally, after successfully obtaining the straight tube pressure drop data, the test facility was modified in order to obtain pressure drop data for the flow of two-phase R-113 through 180 deg piping bends. Inherent instabilities of the test facility prevented the successful acquisition of pressure drop data through the piping bends. The experimental straight tube data will be presented and compared with existing predictive correlations in an attempt to gain insight into the utility of such correlations as the basis for developing design criteria. A discussion of the instabilities which rendered successful acquisition of the piping bend data will be presented and suggestions will be made for eliminating these system tendencies. Finally, recommendations for future investigations, based on successful reconfiguration of the test facility, will be made.
Analysis of nanoscale two-phase flow of argon using molecular dynamics
Verma, Abhishek Kumar; Kumar, Rakesh
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 Flow Simulations In a Natural Rock Fracture using the VOF Method
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
Design and construction of an experiment for two-phase flow in fractured porous media
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.
A two-phase solid/fluid model for dense granular flows including dilatancy effects
NASA Astrophysics Data System (ADS)
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
Oil-water two-phase flow measurement with combined ultrasonic transducer and electrical sensors
NASA Astrophysics Data System (ADS)
Tan, Chao; Yuan, Ye; Dong, Xiaoxiao; Dong, Feng
2016-12-01
A combination of ultrasonic transducers operated in continuous mode and a conductance/capacitance sensor (UTCC) is proposed to estimate the individual flow velocities in oil-water two-phase flows. Based on the Doppler effect, the transducers measure the flow velocity and the conductance/capacitance sensor estimates the phase fraction. A set of theoretical correlations based on the boundary layer models of the oil-water two-phase flow was proposed to describe the velocity profile. The models were separately established for the dispersion flow and the separate flow. The superficial flow velocity of each phase is calculated with the velocity measured in the sampling volume of the ultrasonic transducer with the phase fraction through the velocity profile models. The measuring system of the UTCC was designed and experimentally verified on a multiphase flow loop. The results indicate that the proposed system and correlations estimate the overall flow velocity at an uncertainty of U J = 0.038 m s-1, and the water superficial velocity at U Jw = 0.026 m s-1, and oil superficial velocity at U Jo = 0.034 m s-1. The influencing factors of uncertainty were analyzed.
Neutron imaging of diabatic two-phase flows relevant to air conditioning
Geoghegan, Patrick J; Sharma, Vishaldeep
2017-01-01
The design of the evaporator of an air conditioning system relies heavily on heat transfer coefficients and pressure drop correlations that predominantly involve an estimate of the changing void fraction and the underlying two-phase flow regime. These correlations dictate whether the resulting heat exchanger is oversized or not and the amount of refrigerant charge necessary to operate. The latter is particularly important when dealing with flammable or high GWP refrigerants. Traditional techniques to measure the void fraction and visualize the flow are either invasive to the flow or occur downstream of the evaporator, where some of the flow distribution will have changed. Neutron imaging has the potential to visualize two-phase flow in-situ where an aluminium heat exchanger structure becomes essentially transparent to the penetrating neutrons. The subatomic particles are attenuated by the passing refrigerant flow. The resulting image may be directly related to the void fraction and the overall picture provides a clear insight into the flow regime present. This work presents neutron images of the refrigerant Isopentane as it passes through the flow channels of an aluminium evaporator at flowrates relevant to air conditioning. The flow in a 4mm square macro channel is compared to that in a 250 m by 750 m rectangular microchannel in terms of void fraction and regime. All neutron imaging experiments were conducted at the High Flux Isotope Reactor, an Oak Ridge National Laboratory facility
Conceptual plan: Two-Phase Flow Laboratory Program for the Waste Isolation Pilot Plant
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.
NASA Technical Reports Server (NTRS)
Smith, S. D.
1984-01-01
The overall contractual effort and the theory and numerical solution for the Reacting and Multi-Phase (RAMP2) computer code are described. The code can be used to model the dominant phenomena which affect the prediction of liquid and solid rocket nozzle and orbital plume flow fields. Fundamental equations for steady flow of reacting gas-particle mixtures, method of characteristics, mesh point construction, and numerical integration of the conservation equations are considered herein.
Analysis of Two-Phase Flow in Damper Seals for Cryogenic Turbopumps
NASA Technical Reports Server (NTRS)
Arauz, Grigory L.; SanAndres, Luis
1996-01-01
Cryogenic damper seals operating close to the liquid-vapor region (near the critical point or slightly su-cooled) are likely to present two-phase flow conditions. Under single phase flow conditions the mechanical energy conveyed to the fluid increases its temperature and causes a phase change when the fluid temperature reaches the saturation value. A bulk-flow analysis for the prediction of the dynamic force response of damper seals operating under two-phase conditions is presented as: all-liquid, liquid-vapor, and all-vapor, i.e. a 'continuous vaporization' model. The two phase region is considered as a homogeneous saturated mixture in thermodynamic equilibrium. Th flow in each region is described by continuity, momentum and energy transport equations. The interdependency of fluid temperatures and pressure in the two-phase region (saturated mixture) does not allow the use of an energy equation in terms of fluid temperature. Instead, the energy transport is expressed in terms of fluid enthalpy. Temperature in the single phase regions, or mixture composition in the two phase region are determined based on the fluid enthalpy. The flow is also regarded as adiabatic since the large axial velocities typical of the seal application determine small levels of heat conduction to the walls as compared to the heat carried by fluid advection. Static and dynamic force characteristics for the seal are obtained from a perturbation analysis of the governing equations. The solution expressed in terms of zeroth and first order fields provide the static (leakage, torque, velocity, pressure, temperature, and mixture composition fields) and dynamic (rotordynamic force coefficients) seal parameters. Theoretical predictions show good agreement with experimental leakage pressure profiles, available from a Nitrogen at cryogenic temperatures. Force coefficient predictions for two phase flow conditions show significant fluid compressibility effects, particularly for mixtures with low mass
Computation of Space Shuttle high-pressure cryogenic turbopump ball bearing two-phase coolant flow
NASA Technical Reports Server (NTRS)
Chen, Yen-Sen
1990-01-01
A homogeneous two-phase fluid flow model, implemented in a three-dimensional Navier-Stokes solver using computational fluid dynamics methodology is described. The application of the model to the analysis of the pump-end bearing coolant flow of the high-pressure oxygen turbopump of the Space Shuttle main engine is studied. Results indicate large boiling zones and hot spots near the ball/race contact points. The extent of the phase change of the liquid oxygen coolant flow due to the frictional and viscous heat fluxes near the contact areas has been investigated for the given inlet conditions of the coolant.
Computation of Space Shuttle high-pressure cryogenic turbopump ball bearing two-phase coolant flow
NASA Technical Reports Server (NTRS)
Chen, Yen-Sen
1990-01-01
A homogeneous two-phase fluid flow model, implemented in a three-dimensional Navier-Stokes solver using computational fluid dynamics methodology is described. The application of the model to the analysis of the pump-end bearing coolant flow of the high-pressure oxygen turbopump of the Space Shuttle main engine is studied. Results indicate large boiling zones and hot spots near the ball/race contact points. The extent of the phase change of the liquid oxygen coolant flow due to the frictional and viscous heat fluxes near the contact areas has been investigated for the given inlet conditions of the coolant.
Identification of microfluidic two-phase flow patterns in lab-on-chip devices.
Yang, Zhaochu; Dong, Tao; Halvorsen, Einar
2014-01-01
This work describes a capacitive sensor for identification of microfluidic two-phase flow in lab-on-chip devices. With interdigital electrodes and thin insulation layer utilized, this sensor is capable of being integrated with the microsystems easily. Transducing principle and design considerations are presented with respect to the microfluidic gas/liquid flow patterns. Numerical simulation results verify the operational principle. And the factors affecting the performance of the sensor are discussed. Besides, a feasible process flow for the fabrication is also proposed.
Ensemble distribution for immiscible two-phase flow in porous media
NASA Astrophysics Data System (ADS)
Savani, Isha; Bedeaux, Dick; Kjelstrup, Signe; Vassvik, Morten; Sinha, Santanu; Hansen, Alex
2017-02-01
We construct an ensemble distribution to describe steady immiscible two-phase flow of two incompressible fluids in a porous medium. The system is found to be ergodic. The distribution is used to compute macroscopic flow parameters. In particular, we find an expression for the overall mobility of the system from the ensemble distribution. The entropy production at the scale of the porous medium is shown to give the expected product of the average flow and its driving force, obtained from a black-box description. We test numerically some of the central theoretical results.
Study of dynamics of two-phase flow through a minichannel by means of recurrences
NASA Astrophysics Data System (ADS)
Litak, Grzegorz; Górski, Grzegorz; Mosdorf, Romuald; Rysak, Andrzej
2017-05-01
By changing air and water flow rates in the two-phase (air-water) flow through a minichannel, we observed the evolution of air bubbles and slugs patterns. This spatiotemporal behaviour was identified qualitatively by using a digital camera. Simultaneously, we provided a detailed analysis of these phenomena by using the corresponding sequences of light transmission time series recorded with a laser-phototransistor sensor. To distinguish particular patterns, we used recurrence plots and recurrence quantification analysis. Finally, we showed that the maxima of various recurrence quantificators obtained from the laser time series could follow the bubble and slugs patterns in studied ranges of air and water flows.
A Novel Hyperbolization Procedure for The Two-Phase Six-Equation Flow Model
Samet Y. Kadioglu; Robert Nourgaliev; Nam Dinh
2011-10-01
We introduce a novel approach for the hyperbolization of the well-known two-phase six equation flow model. The six-equation model has been frequently used in many two-phase flow applications such as bubbly fluid flows in nuclear reactors. One major drawback of this model is that it can be arbitrarily non-hyperbolic resulting in difficulties such as numerical instability issues. Non-hyperbolic behavior can be associated with complex eigenvalues that correspond to characteristic matrix of the system. Complex eigenvalues are often due to certain flow parameter choices such as the definition of inter-facial pressure terms. In our method, we prevent the characteristic matrix receiving complex eigenvalues by fine tuning the inter-facial pressure terms with an iterative procedure. In this way, the characteristic matrix possesses all real eigenvalues meaning that the characteristic wave speeds are all real therefore the overall two-phase flowmodel becomes hyperbolic. The main advantage of this is that one can apply less diffusive highly accurate high resolution numerical schemes that often rely on explicit calculations of real eigenvalues. We note that existing non-hyperbolic models are discretized mainly based on low order highly dissipative numerical techniques in order to avoid stability issues.
Simulation experiments for hot-leg U-bend two-phase flow phenomena
Ishii, M.; Hsu, J.T.; Tucholke, D.; Lambert, G.; Kataoka, I.
1986-01-01
In order to study the two-phase natural circulation and flow termination during a small break loss of coolant accident in LWR, simulation experiments have been performed. Based on the two-phase flow scaling criteria developed under this program, an adiabatic hot leg U-bend simulation loop using nitrogen gas and water and a Freon 113 boiling and condensation loop were built. The nitrogen-water system has been used to isolate key hydrodynamic phenomena from heat transfer problems, whereas the Freon loop has been used to study the effect of phase changes and fluid properties. Various tests were carried out to establish the basic mechanism of the flow termination and reestablishment as well as to obtain essential information on scale effects of parameters such as the loop frictional resistance, thermal center, U-bend curvature and inlet geometry. In addition to the above experimental study, a preliminary modeling study has been carried out for two-phase flow in a large vertical pipe at relatively low gas fluxes typical of natural circulation conditions.
Internal structure and interfacial area in two-phase flow systems
Kojasoy, G.
1991-01-01
The interfacial transfer terms and the importance of the interfacial area concentration are reviewed first with respect to the two-fluid model formulation of two-phase flow systems. Then the available measurement techniques for interfacial area are reviewed. At present, it appears that various methods such as the chemical, light attenuation, photographic, ultrasound attenuation and probe techniques have a number of limitations. Among these measurement techniques, however, the local probe method using one or more double sensors seems to have the greatest potential in terns of accuracy and wider applicability in various two-phase flow patterns. From the brief review of existing interfacial area modeling methods, it is concluded that the conventional approaches might not be sufficient, and new directions are indicated. Recent experimental results on local interfacial structural characteristics of horizontal bubbly two-phase flow and internal flow structure development are presented. More specifically, experimental results on local void fraction, interfacial area concentration, bubble size, bubble interface velocity and bubble frequency are documented in detail. Finally, a theoretical model predicting the mean bubble size and interfacial area concentration is proposed. The theoretically predicted bubble size and interfacial area concentration are found to agree reasonably well with those measured by using a double-sensor resistivity technique.
Internal structure and interfacial area in two-phase flow systems
Kojasoy, G.
1991-12-31
The interfacial transfer terms and the importance of the interfacial area concentration are reviewed first with respect to the two-fluid model formulation of two-phase flow systems. Then the available measurement techniques for interfacial area are reviewed. At present, it appears that various methods such as the chemical, light attenuation, photographic, ultrasound attenuation and probe techniques have a number of limitations. Among these measurement techniques, however, the local probe method using one or more double sensors seems to have the greatest potential in terns of accuracy and wider applicability in various two-phase flow patterns. From the brief review of existing interfacial area modeling methods, it is concluded that the conventional approaches might not be sufficient, and new directions are indicated. Recent experimental results on local interfacial structural characteristics of horizontal bubbly two-phase flow and internal flow structure development are presented. More specifically, experimental results on local void fraction, interfacial area concentration, bubble size, bubble interface velocity and bubble frequency are documented in detail. Finally, a theoretical model predicting the mean bubble size and interfacial area concentration is proposed. The theoretically predicted bubble size and interfacial area concentration are found to agree reasonably well with those measured by using a double-sensor resistivity technique.
NASA Technical Reports Server (NTRS)
Karimi, Amir
1991-01-01
NASA's effort for the thermal environmental control of the Space Station Freedom is directed towards the design, analysis, and development of an Active Thermal Control System (ATCS). A two phase, flow through condenser/radiator concept was baselined, as a part of the ATCS, for the radiation of space station thermal load into space. The proposed condenser rejects heat through direct condensation of ATCS working fluid (ammonia) in the small diameter radiator tubes. Analysis of the condensation process and design of condenser tubes are based on the available two phase flow models for the prediction of flow regimes, heat transfer, and pressure drops. The prediction formulas use the existing empirical relationships of friction factor at gas-liquid interface. An attempt is made to study the stability of interfacial waves in two phase annular flow. The formulation is presented of a stability problem in cylindrical coordinates. The contribution of fluid viscosity, surface tension, and transverse radius of curvature to the interfacial surface is included. A solution is obtained for Kelvin-Helmholtz instability problem which can be used to determine the critical and most dangerous wavelengths for interfacial waves.
A Simple and Efficient Diffuse Interface Method for Compressible Two-Phase Flows
Ray A. Berry; Richard Saurel; Fabien Petitpas
2009-05-01
In nuclear reactor safety and optimization there are key issues that rely on in-depth understanding of basic two-phase flow phenomena with heat and mass transfer. For many reasons, to be discussed, there is growing interest in the application of two-phase flow models to provide diffuse, but nevertheless resolved, simulation of interfaces between two immiscible compressible fluids – diffuse interface method (DIM). Because of its ability to dynamically create interfaces and to solve interfaces separating pure media and mixtures for DNS-like (Direct Numerical Simulation) simulations of interfacial flows, we examine the construction of a simple, robust, fast, and accurate numerical formulation for the 5-equation Kapila et al. [1] reduced two-phase model. Though apparently simple, the Kapila et al. model contains a volume fraction differential transport equation containing a nonlinear, non-conservative term which poses serious computational challenges. To circumvent the difficulties encountered with the single velocity and single pressure Kapila et al. [1] multiphase flow model, a 6-equation relaxation hyperbolic model is built to solve interface problems with compressible fluids. In this approach, pressure non-equilibrium is first restored, followed by a relaxation to an asymptotic solution which is convergent to the solutions of the Kapila et al. reduced model. The apparent complexity introduced with this extended hyperbolic model actually leads to considerable simplifications regarding numerical resolution, and the various ingredients used by this method are general enough to consider future extensions to problems involving complex physics.
NASA Astrophysics Data System (ADS)
Burkholder, Michael B.; Litster, Shawn
2016-05-01
In this study, we analyze the stability of two-phase flow regimes and their transitions using chaotic and fractal statistics, and we report new measurements of dynamic two-phase pressure drop hysteresis that is related to flow regime stability and channel water content. Two-phase flow dynamics are relevant to a variety of real-world systems, and quantifying transient two-phase flow phenomena is important for efficient design. We recorded two-phase (air and water) pressure drops and flow images in a microchannel under both steady and transient conditions. Using Lyapunov exponents and Hurst exponents to characterize the steady-state pressure fluctuations, we develop a new, measurable regime identification criteria based on the dynamic stability of the two-phase pressure signal. We also applied a new experimental technique by continuously cycling the air flow rate to study dynamic hysteresis in two-phase pressure drops, which is separate from steady-state hysteresis and can be used to understand two-phase flow development time scales. Using recorded images of the two-phase flow, we show that the capacitive dynamic hysteresis is related to channel water content and flow regime stability. The mixed-wettability microchannel and in-channel water introduction used in this study simulate a polymer electrolyte fuel cell cathode air flow channel.
Burkholder, Michael B.; Litster, Shawn
2016-05-15
In this study, we analyze the stability of two-phase flow regimes and their transitions using chaotic and fractal statistics, and we report new measurements of dynamic two-phase pressure drop hysteresis that is related to flow regime stability and channel water content. Two-phase flow dynamics are relevant to a variety of real-world systems, and quantifying transient two-phase flow phenomena is important for efficient design. We recorded two-phase (air and water) pressure drops and flow images in a microchannel under both steady and transient conditions. Using Lyapunov exponents and Hurst exponents to characterize the steady-state pressure fluctuations, we develop a new, measurable regime identification criteria based on the dynamic stability of the two-phase pressure signal. We also applied a new experimental technique by continuously cycling the air flow rate to study dynamic hysteresis in two-phase pressure drops, which is separate from steady-state hysteresis and can be used to understand two-phase flow development time scales. Using recorded images of the two-phase flow, we show that the capacitive dynamic hysteresis is related to channel water content and flow regime stability. The mixed-wettability microchannel and in-channel water introduction used in this study simulate a polymer electrolyte fuel cell cathode air flow channel.
Modelling Air and Water Two-Phase Annular Flow in a Small Horizontal Pipe
NASA Astrophysics Data System (ADS)
Yao, Jun; Yao, Yufeng; Arini, Antonino; McIiwain, Stuart; Gordon, Timothy
2016-06-01
Numerical simulation using computational fluid dynamics (CFD) has been carried out to study air and water two-phase flow in a small horizontal pipe of an inner diameter of 8.8mm, in order to investigate unsteady flow pattern transition behaviours and underlying physical mechanisms. The surface liquid film thickness distributions, determined by either wavy or full annular flow regime, are shown in reasonable good agreement with available experimental data. It was demonstrated that CFD simulation was able to predict wavy flow structures accurately using two-phase flow sub-models embedded in ANSYS-Fluent solver of Eulerian-Eulerian framework, together with a user defined function subroutine ANWAVER-UDF. The flow transient behaviours from bubbly to annular flow patterns and the liquid film distributions revealed the presence of gas/liquid interferences between air and water film interface. An increase of upper wall liquid film thickness along the pipe was observed for both wavy annular and full annular scenarios. It was found that the liquid wavy front can be further broken down to form the water moisture with liquid droplets penetrating upwards. There are discrepancies between CFD predictions and experimental data on the liquid film thickness determined at the bottom and the upper wall surfaces, and the obtained modelling information can be used to assist further 3D user defined function subroutine development, especially when CFD simulation becomes much more expense to model full 3D two-phase flow transient performance from a wavy annular to a fully developed annular type.
A numerical method for a model of two-phase flow in a coupled free flow and porous media system
NASA Astrophysics Data System (ADS)
Chen, Jie; Sun, Shuyu; Wang, Xiao-Ping
2014-07-01
In this article, we study two-phase fluid flow in coupled free flow and porous media regions. The model consists of coupled Cahn-Hilliard and Navier-Stokes equations in the free fluid region and the two-phase Darcy law in the porous medium region. We propose a Robin-Robin domain decomposition method 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. Numerical examples are presented to illustrate the effectiveness of this method.
The role of heater thermal response in reactor thermal limits during oscillartory two-phase flows
Ruggles, A.E.; Brown, N.W.; Vasil`ev, A.D.; Wendel, M.W.
1995-09-01
Analytical and numerical investigations of critical heat flux (CHF) and reactor thermal limits are conducted for oscillatory two-phase flows often associated with natural circulation conditions. It is shown that the CHF and associated thermal limits depend on the amplitude of the flow oscillations, the period of the flow oscillations, and the thermal properties and dimensions of the heater. The value of the thermal limit can be much lower in unsteady flow situations than would be expected using time average flow conditions. It is also shown that the properties of the heater strongly influence the thermal limit value in unsteady flow situations, which is very important to the design of experiments to evaluate thermal limits for reactor fuel systems.
Vertical two-phase flow regimes and pressure gradients under the influence of SDS surfactant
Duangprasert, Tanabordee; Sirivat, Anuvat; Siemanond, Kitipat; Wilkes, James O.
2008-01-15
Two-phase gas/liquid flows in vertical pipes have been systematically investigated. Water and SDS surfactant solutions at various concentrations were used as the working fluids. In particular, we focus our work on the influence of surfactant addition on the flow regimes, the corresponding pressure gradients, and the bubble sizes and velocity. Adding the surfactant lowers the air critical Reynolds numbers for the bubble-slug flow and the slug flow transitions. The pressure gradients of SDS solutions are lower than those of pure water especially in the slug flow and the slug-churn flow regimes, implying turbulent drag reduction. At low Re{sub air}, the bubble sizes of the surfactant solution are lower than those of pure water due to the increase in viscosity. With increasing and at high Re{sub air}, the bubble sizes of the SDS solution become greater than those of pure water which is attributed to the effect of surface tension. (author)
Vertical two-phase flow regimes and pressure gradients: Effect of viscosity
Da Hlaing, Nan; Sirivat, Anuvat; Siemanond, Kitipat; Wilkes, James O.
2007-05-15
The effect of liquid viscosity on the flow regimes and the corresponding pressure gradients along the vertical two-phase flow was investigated. Experiment was carried out in a vertical transparent tube of 0.019 m in diameter and 3 m in length and the pressure gradients were measured by a U-tube manometer. Water and a 50 vol.% glycerol solution were used as the working fluids whose kinematic viscosities were 0.85 x 10{sup -6} and 4.0 x 10{sup -6} m{sup 2}/s, respectively. In our air-liquid annular two-phase flow, the liquid film of various thicknesses flowed adjacent to the wall and the gas phase flowed at the center of the tube. The superficial air velocity, j{sub air}, was varied between 0.0021 and 58.7 m/s and the superficial liquid velocity, j{sub liquid}, was varied between 0 and 0.1053 m/s. In the bubble, the slug and the slug-churn flow regimes, the pressure gradients decreased with increasing Reynolds number. But in the annular and the mist flow regimes, pressure gradients increased with increasing Reynolds number. Finally, the experimentally measured pressure gradient values were compared and are in good agreement with the theoretical values. (author)
Targeted delivery by smart capsules for controlling two-phase flow in porous media
NASA Astrophysics Data System (ADS)
Fan, Jing; Abbaspourrad, Alireza; Weitz, David; Harvard Weitzgroup Team
2015-11-01
Two-phase flow in porous media is significantly influenced by the physical properties of the fluids and the geometry of the medium. We develop a variety of smart microcapsules that can deliver and release specific substances to the target location in the porous medium, and therefore change the fluid property or medium geometry at certain locations. In this talk, I will present two types of smart capsules for targeted surfactant delivery to the vicinity of oil-water interface and targeted microgel delivery for improving the homogeneity of the porous medium, respectively. We further prove the concept by monitoring the capsule location and the fluid structure in the porous media by micro-CT and confocal microscopy. This technique not only is of particular importance to the relevant industry applications especially in the oil industry but also opens a new window to study the mechanism of two-phase flow in porous media. Advanced Energy Consortium BEG08-027.
Membrane-less micro fuel cell based on two-phase flow
NASA Astrophysics Data System (ADS)
Hashemi, S. M. H.; Neuenschwander, M.; Hadikhani, P.; Modestino, M. A.; Psaltis, D.
2017-04-01
Most microfluidic fuel cells use highly soluble fuels and oxidants in streams of liquid electrolytes to overcome the mass transport limitations that result from the low solubility of gaseous reactants such as hydrogen and oxygen. In this work, we address these limitations by implementing controlled two-phase flows of these gases in a set of microchannels electrolytically connected through a narrow gap. Annular flows of the gases reshape the concentration boundary layer over the surface of electrodes and increase the mass-transport limited current density in the system. Our results show that the power density of a two-phase system with hydrogen and oxygen streams is an order of magnitude higher than that of single phase system consisting of liquid electrolytes saturated with the same reactants. The reactor design described here can be employed to boost the performance of MFFCs and put them in a more competitive position compared to membrane based fuel cells.
Two-phase dusty fluid flow along a cone with variable properties
NASA Astrophysics Data System (ADS)
Siddiqa, Sadia; Begum, Naheed; Hossain, Md. Anwar; Mustafa, Naeem; Gorla, Rama Subba Reddy
2017-05-01
In this paper numerical solutions of a two-phase natural convection dusty fluid flow are presented. The two-phase particulate suspension is investigated along a vertical cone by keeping variable viscosity and thermal conductivity of the carrier phase. Comprehensive flow formations of the gas and particle phases are given with the aim to predict the behavior of heat transport across the heated cone. The influence of (1) air with particles, (2) water with particles and (3) oil with particles are shown on shear stress coefficient and heat transfer coefficient. It is recorded that sufficient increment in heat transport rate can be achieved by loading the dust particles in the air. Further, distribution of velocity and temperature of both the carrier phase and the particle phase are shown graphically for the pure fluid (air, water) as well as for the fluid with particles (air-metal and water-metal particle mixture).
Performance of WPA Conductivity Sensor during Two-Phase Fluid Flow in Microgravity
NASA Technical Reports Server (NTRS)
Carter, Layne; O'Connor, Edward W.; Snowdon, Doug
2003-01-01
The Conductivity Sensor designed for use in the Node 3 Water Processor Assembly (WPA) was based on the existing Space Shuttle application for the fuel cell water system. However, engineering analysis has determined that this sensor design is potentially sensitive to two-phase fluid flow (gadliquid) in microgravity. The source for this sensitivity is the fact that gas bubbles will become lodged between the sensor probe and the wall of the housing without the aid of buoyancy in l-g. Once gas becomes lodged in the housing, the measured conductivity will be offset based on the volume of occluded gas. A development conductivity sensor was flown on the NASA Microgravity Plan to measure the offset, which was determined to range between 0 and 50%. Based on these findings, a development program was initiated at the sensor s manufacturer to develop a sensor design fully compatible with two-phase fluid flow in microgravity.
Not Available
1991-07-01
The possible head degradation of the SRPR pumps may be attributable to two independent phenomena, one due to the inception of cavitation and the other due to the two-phase flow phenomena. The head degradation due to the appearance of cavitation on the pump blade is hardly likely in the conventional pressurized water reactor (PWR) since the coolant circulating line is highly pressurized so that the cavitation is difficult to occur even at LOCA (loss of coolant accident) conditions. On the other hand, the suction pressure of SRPR pump is order-of-magnitude smaller than that of PWR so that the cavitation phenomena, may prevail, should LOCA occur, depending on the extent of LOCA condition. In this study, therefore, both cavitation phenomena and two-phase flow phenomena were investigated for the SRPR pump by using various analytical tools and the numerical results are presented herein.
Some issues in the simulation of two-phase flows: The relative velocity
Gräbel, J.; Hensel, S.; Ueberholz, P.; Farber, P.; Zeidan, D.
2016-06-08
In this paper we compare numerical approximations for solving the Riemann problem for a hyperbolic two-phase flow model in two-dimensional space. The model is based on mixture parameters of state where the relative velocity between the two-phase systems is taken into account. This relative velocity appears as a main discontinuous flow variable through the complete wave structure and cannot be recovered correctly by some numerical techniques when simulating the associated Riemann problem. Simulations are validated by comparing the results of the numerical calculation qualitatively with OpenFOAM software. Simulations also indicate that OpenFOAM is unable to resolve the relative velocity associated with the Riemann problem.
Targeted Delivery by Smart Capsules for Controlling Two-phase Flow in Porous Media
NASA Astrophysics Data System (ADS)
Fan, J.; Weitz, D.
2015-12-01
Understanding and controlling two-phase flow in porous media are of particular importance to the relevant industry applications, such as enhanced oil recovery, CO2 sequestration, and groundwater remediation. We develop a variety of smart microcapsules that can deliver and release specific substances to the target location in the porous medium, and therefore change the fluid property or medium geometry at certain locations. In this talk, I will present two types of smart capsules for (a) delivering surfactant to the vicinity of oil-water interface and (b) delivering microgels to the high permeability region and therefore blocking the pore space there, respectively. We also show that flooding these two capsules into porous media effectively reduces the trapped oil and improves the homogeneity of the medium, respectively. Besides of its industrial applications, this technique also opens a new window to study the mechanism of two-phase flow in porous media.
Two-phase flow interfacial structures in a rod bundle geometry
NASA Astrophysics Data System (ADS)
Paranjape, Sidharth S.
Interfacial structure of air-water two-phase flow in a scaled nuclear reactor rod bundle geometry was studied in this research. Global and local flow regimes were obtained for the rod bundle geometry. Local two-phase flow parameters were measured at various axial locations in order to understand the transport of interfacial structures. A one-dimensional two-group interfacial area transport model was evaluated using the local parameter database. Air-water two-phase flow experiments were performed in an 8 X 8 rod bundle test section to obtain flow regime maps at various axial locations. Area averaged void fraction was measured using parallel plate type impedance void meters. The cumulative probability distribution functions of the signals from the impedance void meters were used along with a self organizing neural network to identify flow regimes. Local flow regime maps revealed the cross-sectional distribution of flow regimes in the bundle. Local parameters that characterize interfacial structure, that is, void fraction alpha, interfacial area concentration, ai, bubble Sauter mean diameter, DSm and bubble velocity, vg were measured using four sensor conductivity probe technique. The local data revealed the distribution of the interfacial structure in the radial direction, as well as its development in the axial direction. In addition to this, the effect of spacer grid on the flow structure at different gas and liquid velocities was revealed by local parameter measurements across the spacer grids. A two-group interfacial area transport equation (IATE) specific to rod bundle geometry was derived. The derivation of two-group IATE required certain assumption on the bubble shapes in the subchannels and the bubbles spanning more than a subchannel. It was found that the geometrical relationship between the volume and the area of a cap bubble distorted by rods was similar to the one derived for a confined channel under a specific geometrical transformation. The one
Cai, Y.; Wambsganss, M.W.; Jendrzejczyk, J.A.
1996-02-01
Various measurement tools of chaos theory were applied to analyze two-phase pressure signals with the objective to identify and interpret flow pattern transitions for two-phase flows in a small, horizontal rectangular channel. These measurement tools included power spectral density function, autocorrelation function, pseudo-phase-plane trajectory, Lyapunov exponents, and fractal dimensions. It was demonstrated that the randomlike pressure fluctuations characteristic of two-phase flow in small rectangular channels are chaotic in nature. As such, they are governed by a high-order deterministic system. The correlation dimension is potentially a new approach for identification of certain two-phase flow patterns and transitions.
Numerical Study of Two-Phase Flow Field in a Simplified Swirl Cup Combustor (Preprint)
2007-09-24
Article 3 . DATES COVERED (From - To) 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Numerical Study of Two-Phase Flow Field in a Simplified Swirl Cup...swirl provides a recirculation zone which enhances mixing and flame stability. Some high-performance aircraft engines such as in GE/SNECMA CFM56 ...downstream of a GE/SNECMA CFM56 engine combustor swirl cup in which the primary and secondary swirlers provide co-axial, counter-swirling airstreams
Analytical study on two-phase MHD flow of electrically conducting magnetic fluid
Okubo, Masaaki; Ishimoto, Jun; Nishiyama, Hideya; Kamiyama, Shinichi
1994-01-01
An energy conversion system using magnetic fluids proposed by Resler and Rosensweig was based on the principle that the magnetization of magnetic fluids changes with temperature. However, significant results have not been obtained up to the present. To overcome this limit and to increase the acceleration of fluid flow the authors have contributed a new energy conversion system using two-phase flow produced by heat addition. This idea came from the two-phase liquid-metal MHD power generation system proposed by Petrick and Branover. If temperature sensitive magnetic fluids are used, such a system can produce a larger force than conventional systems because the properties of apparent magnetization change not only by temperature rise but also by gas inclusion. In the present paper, an analytical study is extended to the case of electrically conducting magnetic fluid as a basic study for demonstrating the possibility of application of electrically conducting magnetic fluid to working fluid in a liquid-metal MHD power generation system. Electrically conducting magnetic fluid is usually prepared by dispersing fine iron particles into a liquid metal such as mercury. To prevent a solidification of particles and keep a homogeneous dispersion, a thin film of tin is attached to the particle`s surface. Thus the electrically conducting liquid behaves as fluid itself having magnetization. The equations governing a one-dimensional boiling two-phase duct flow of such an electrically conducting magnetic fluid in a traverse magnetic field are numerically solved. The analytical results of the two-phase flow characteristics of the magnetic fluid are compared with ones of an electrically conducting nonmagnetic fluid.
Two-phase flow and heat transfer in porous beds under variable body forces, part 7
NASA Technical Reports Server (NTRS)
Henry, H. R.
1970-01-01
The design of an experiment to determine the behavior of two-phase vapor-liquid and gas-liquid flow through porous beds in low gravity environments is discussed. The selection of porous materials, liquids, and gases is described. The parameters necessary for the design and development of a flight experimental system are examined. The general specifications for system elements requiring additional development are identified.
Disturbed zone effects: Two phase flow in regionally water-saturated fractured rock
Geller, J.T.; Doughty, C.; Long, J.C.S.
1995-01-01
Field evidence suggests that two-phase flow may develop near underground excavations in regionally-saturated fractured crystalline rock, resulting in lower inflow rates compared to undisturbed rock. Mechanisms for the development of two-phase flow conditions include depressurization of formation water that is supersaturated with dissolved gas and buoyancy-driven air invasion into fractures from the drift. Models that assume gas-liquid phase equilibrium indicate that for constant head boundary conditions, the build-up of pressure behind the gas phase evolving from depressurization should redissolve the gas and maintain higher flowrates, requiring unreasonably high dissolved gas concentrations to produce observed flow reductions at the Stripa Mine in Sweden. This discrepancy initiated a laboratory-scale investigation. Gas evolution following depressurization is simulated in two different 8 cm x 8 cm transparent fracture replicas for linear flow with constant head boundary conditions. Gas forms and accumulates in the large apertures and the extent of flow reduction is greater when the flow through the fracture is controlled by a large aperture channel, compared to a fracture where large aperture regions are relatively isolated. An effective continuum numerical model (TOUGH2) is used to describe the development of two-phase flow under degassing conditions. Numerical simulations were made for a homogeneous porous medium and for a heterogeneous medium using the aperture distribution of one of the fractures used in the laboratory experiments, which allows a direct comparison between laboratory and numerical results. The incorporation of kinetic expressions into the numerical model will allow the prediction of resaturation rates of a repository following closure.
Shadow imaging in bubbly gas-liquid two-phase flow in porous structures
NASA Astrophysics Data System (ADS)
Altheimer, Marco; Häfeli, Richard; Wälchli, Carmen; Rudolf von Rohr, Philipp
2015-09-01
Shadow imaging is used for the investigation of bubbly gas-liquid two-phase flow in a porous structure. The porous structure is made of Somos WaterShed XC 11122, a clear epoxy resin used in rapid prototyping. Optical access is provided by using an aqueous solution of sodium iodide and zinc iodide having the same refractive index as the structure material (). Nitrogen is injected into the continuous phase at volumetric transport fractions in the range of resulting in a hold-up of . The obtained images of overlapping bubble shadows are processed to measure the bubble dimensions. Therefore, a new processing sequence is developed to determine bubble dimensions from overlapping bubble shadows by ellipse fitting. The accuracy of the bubble detection and sizing routine is assessed processing synthetic images. It is shown that the developed technique is suitable for volumetric two-phase flow measurements. Important global quantities such as gas hold-up and total interfacial area can be measured with only one camera. Operation parameters for gas-liquid two-phase flows are determined to improve mass and heat transfer between the phases.
Two-phase flow in geothermal energy sources. Final technical report
Not Available
1981-07-01
A geothermal well consisting of single and two-phase flow sections was modeled in order to explore the variables important to the process. For this purpose a computer program was developed in a versatile form in order to be able to incorporate a variety of two phase flow void fraction and friction correlations. A parametric study indicated that the most significant variables controlling the production rate are: hydrostatic pressure drop or void fraction in the two-phase mixture; and, heat transfer from the wellbore to the surrounding earth. Downhole instrumentation was developed and applied in two flowing wells to provide experimental data for the computer program. The wells (East Mesa 8-1, and a private well) behaved differently. Well 8-1 did not flash and numerous shakedown problems in the probe were encountered. The private well did flash and the instrumentation detected the onset of flashing. A Users Manual was developed and presented in a workshop held in conjunction with the Geothermal Resources Council.
Two-phase Flow Ejector as Water Refrigerant by Using Waste Heat
NASA Astrophysics Data System (ADS)
Yamanaka, H.; Nakagawa, M.
2013-04-01
Energy saving and the use of clean energy sources have recently become significant issues. It is expected that clean energy sources such as solar panels and fuel cells will be installed in many private dwellings. However, when electrical power is generated, exhaust heat is simultaneously produced. Especially for the summer season, the development of refrigeration systems that can use this waste heat is highly desirable. One approach is an ejector that can reduce the mechanical compression work required in a normal refrigeration cycle. We focus on the use of water as a refrigerant, since this can be safely implemented in private dwellings. Although the energy conversion efficiency is low, it is promising because it can use heat that would otherwise be discarded. However, a steam ejector refrigeration cycle requires a large amount of energy to change saturated water into vapour. Thus, we propose a more efficient two-phase flow ejector cycle. Experiments were carried out in which the quality of the two-phase flow from a tank was varied, and the efficiency of the ejector and nozzle was determined. The results show that a vacuum state can be achieved and suction exerted with a two-phase flow state at the ejector nozzle inlet.
Thermally induced flow oscillation in vertical two-phase natural circulation loop
Lee, Sang Yong; Ishii, Mamoru
1988-01-01
In order to study the two-phase natural circulation during a small break loss of coolant accident in LWR, simulation experiments have been performed using Freon-113 boiling and condensation loop. In quasi-steady state, the flow became relatively stabilized and certain regular patterns of flow oscillations were detected with ranges of periods in 8-/approximately/35 seconds and 2.5-/approximately/4 minutes. In order to find out the nature of these oscillations, one-dimensional field equations for the single-phase (liquid) and two-phase region were set up, and these field equations were integrated along the loop. The homogeneous flow model was used for the two-phase region. Then the characteristic equation was derived using perturbation method. Thermal non-equilibrium and compressibility of each phase were not considered in the present analysis. The characteristic equation derived can be used to obtain the stability criteria. A simplified approach showed that the short-period oscillation were the manometer oscillation. The longer period oscillations were the density wave oscillation which had the period of oscillations close to the residence time of a fluid around the loop.
Dynamics of face and annular seals with two-phase flow
NASA Technical Reports Server (NTRS)
Hughes, William F.; Basu, Prithwish; Beatty, Paul A.; Beeler, Richard M.; Lau, Stephen
1989-01-01
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. High pressure, water pumps, industrial chemical pumps, and cryogenic pumps are mentioned as a few of many applications. The initial motivation was the LOX-GOX seals for the space shuttle main engine, but the study was expanded to include any face or annular seal where boiling occurs. Some of the distinctive behavior characteristics of two-phase seals were discussed, particularly their axial stability. While two-phase seals probably exhibit instability to disturbances of other degrees of freedom such as wobble, etc., under certain conditions, such analyses are too complex to be treated at present. Since an all liquid seal (with parallel faces) has a neutral axial stiffness curve, and is stabilized axially by convergent coning, other degrees of freedom stability analyses are necessary. However, the axial stability behavior of the two-phase seal is always a consideration no matter how well the seal is aligned and regardless of the speed. Hence, axial stability is thought of as the primary design consideration for two-phase seals and indeed the stability behavior under sub-cooling variations probably overshadows other concerns. The main thrust was the dynamic analysis of axial motion of two-phase face seals, principally the determination of axial stiffness, and the steady behavior of two-phase annular seals. 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. A simplified combined computer code for the performance prediction over the
Two-Phase Solid/Fluid Simulation of Dense Granular Flows With Dilatancy Effects
NASA Astrophysics Data System (ADS)
Mangeney, Anne; Bouchut, Francois; Fernandez-Nieto, Enrique; Narbona-Reina, Gladys; Kone, El Hadj
2017-04-01
Describing grain/fluid interaction in debris flows models is still an open and challenging issue with key impact on hazard assessment [1]. 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 [2]. The model is derived from a 3D two-phase model proposed by Jackson [3] and the mixture equations are closed by a weak compressibility relation. 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 account for this transfer of fluid into and out of the mixture, a two-layer model is proposed with a fluid or a solid layer on top of the two-phase mixture layer. Mass and momentum conservation are satisfied for the two phases, and mass and momentum are transferred between the two layers. A thin-layer approximation is used to derive average equations. Special attention is paid to the drag friction terms that are responsible for the transfer of momentum between the two phases and for the appearance of an excess pore pressure with respect to the hydrostatic pressure. Interestingly, when removing the role of water, our model reduces to a dry granular flow model including dilatancy. We first compare experimental and numerical results of dilatant dry granular flows. Then, by quantitatively comparing the results of simulation and laboratory experiments on submerged granular flows, we show that our model
Experimental study on interfacial area transport in downward two-phase flow
NASA Astrophysics Data System (ADS)
Wang, Guanyi
In view of the importance of two group interfacial area transport equations and lack of corresponding accurate downward flow database that can reveal two group interfacial area transport, a systematic database for adiabatic, air-water, vertically downward two-phase flow in a round pipe with inner diameter of 25.4 mm was collected to gain an insight of interfacial structure and provide benchmarking data for two-group interfacial area transport models. A four-sensor conductivity probe was used to measure the local two phase flow parameters and data was collected with data sampling frequency much higher than conventional data sampling frequency to ensure the accuracy. Axial development of local flow parameter profiles including void fraction, interfacial area concentration, and Sauter mean diameter were presented. Drastic inter-group transfer of void fraction and interfacial area was observed at bubbly to slug transition flow. And the wall peaked interfacial area concentration profiles were observed in churn-turbulent flow. The importance of local data about these phenomenon on flow structure prediction and interfacial area transport equation benchmark was analyzed. Bedsides, in order to investigate the effect of inlet conditions, all experiments were repeated after installing the flow straightening facility, and the results were briefly analyzed. In order to check the accuracy of current data, the experiment results were cross-checked with rotameter measurement as well as drift-flux model prediction, the averaged error is less than 15%. Current models for two-group interfacial area transport equation were evaluated using these data. The results show that two-group interfacial area transport equations with current models can predict most flow conditions with error less than 20%, except some bubbly to slug transition flow conditions and some churn-turbulent flow conditions. The disagreement between models and experiments could result from underestimate of inter
A multi-scale network method for two-phase flow in porous media
NASA Astrophysics Data System (ADS)
Khayrat, Karim; Jenny, Patrick
2017-08-01
Pore-network models of porous media are useful in the study of pore-scale flow in porous media. In order to extract macroscopic properties from flow simulations in pore-networks, it is crucial the networks are large enough to be considered representative elementary volumes. However, existing two-phase network flow solvers are limited to relatively small domains. For this purpose, a multi-scale pore-network (MSPN) method, which takes into account flow-rate effects and can simulate larger domains compared to existing methods, was developed. In our solution algorithm, a large pore network is partitioned into several smaller sub-networks. The algorithm to advance the fluid interfaces within each subnetwork consists of three steps. First, a global pressure problem on the network is solved approximately using the multiscale finite volume (MSFV) method. Next, the fluxes across the subnetworks are computed. Lastly, using fluxes as boundary conditions, a dynamic two-phase flow solver is used to advance the solution in time. Simulation results of drainage scenarios at different capillary numbers and unfavourable viscosity ratios are presented and used to validate the MSPN method against solutions obtained by an existing dynamic network flow solver.
Stability analysis of two phase stratified flow in a rectangular channel
NASA Astrophysics Data System (ADS)
Bhagavatula, Dinesh; S, Pushpavanam
2015-11-01
Two phase stratified flows arise in extraction operations in microfluidic systems. It is well established that stratified flows in between two infinite plates is always unstable. However such flows are experimentally observed in micro channels. To understand this paradox we perform a linear stability analysis of stratified two phase Poiseuille flow in a rectangular duct. A two-dimensional fully developed flow through the rectangular channel is considered. The linearized equations along with the boundary conditions in primitive variable formulation are numerically solved using Chebyshev collocation method. All the primitive variables, which are the velocity and pressure fields, are retained in the linearised governing equations. Since boundary conditions for disturbance pressure do not exist, the corresponding compatibility conditions derived from the Navier-Stokes equations are collocated both at the walls and the interface. The resulting eigen-value problem is solved using a shift and invert Arnoldi algorithm. The role of different parameters such as Aspect ratio, density ratio, viscosity ratio on the stability characteristics is analyzed. The stability results are validated in the limit of large Aspect Ratios. The flow fields are sought as a combination of Chebyshev polynomials in both y and z directions. Ministry of Human Resource and Development (MHDR).
Velocity Profile measurements in two-phase flow using multi-wave sensors
NASA Astrophysics Data System (ADS)
Biddinika, M. K.; Ito, D.; Takahashi, H.; Kikura, H.; Aritomi, M.
2009-02-01
Two-phase flow has been recognized as one of the most important phenomena in fluid dynamics. In addition, gas-liquid two-phase flow appears in various industrial fields such as chemical industries and power generations. In order to clarify the flow structure, some flow parameters have been measured by using many effective measurement techniques. The velocity profile as one of the important flow parameter, has been measured by using ultrasonic velocity profile (UVP) technique. This technique can measure velocity distributions along a measuring line, which is a beam formed by pulse ultrasounds. Furthermore, a multi-wave sensor can measure the velocity profiles of both gas and liquid phase using UVP method. In this study, two types of multi-wave sensors are used. A sensor has cylindrical shape, and another one has square shape. The piezoelectric elements of each sensor have basic frequencies of 8 MHz for liquid phase and 2 MHz for gas phase, separately. The velocity profiles of air-water bubbly flow in a vertical rectangular channel were measured by using these multi-wave sensors, and the validation of the measuring accuracy was performed by the comparison between the velocity profiles measured by two multi-wave sensors.
Chemical reaction by plasma in gas-liquid two-phase flow system
NASA Astrophysics Data System (ADS)
Goto, Motonobu; Mano, Kakeru; Hayashi, Yui; Takada, Noriharu; Kanda, Hideaki
2016-09-01
Two plasma processes using gasliquid two-phase flow were developed. One is gas/liquid slug flow in capillary glass tube where gas bubbles moved stably in liquid flow. Plasma was generated in bubbles by pulsed bipolar voltage and the liquid phase was mixed by circulated convection due to shearing force. As a gas, air, argon, helium, oxygen, or nitrogen was used. The pulsed bipolar voltage of 10 kV was applied at 10 kHz. The generated plasma was evaluated by ICCD image and high speed camera. The optical emission spectra was analyzed to identify the active species. By using this process, organic compound dissolved in liquid aqueous phase was reacted with oxidation. Another process was creeping plasma on flowing liquid film along glass tube outer surface. Owing to the thin film thickness, organic compound dissolved in liquid phase was reacted effectively. Therefore, effective reaction process could be established in gas/liquid two-phase flow by controlling the gas/liquid flow.
Network simulation of steady-state two-phase flow in consolidated porous media
Constantinides, G.N.; Payatakes, A.C.
1996-02-01
Multiphase flow in porous media is a complex process encountered in many fields of practical engineering interest, such as oil recovery from reservoir rocks, aquifer pollution by liquid wastes and soil reconstitution, and agricultural irrigation. A computer-aided simulator of steady-state two-phase flow in consolidated porous media is developed. The porous medium is modeled as a 3-D pore network of suitably shaped and randomly sized unit cells of the constricted-tube type. The problem of two-phase flow is solved using the network approach. The wetting phase saturation, the viscosity ratio, the capillary number, and the probability of coalescence between two colliding ganglia are changed systematically, where as the geometrical and topological characteristics of the porous medium and wettability (dynamic contact angles) are kept constant. In the range of the parameter values investigated, the flow behavior observed is ganglion population dynamics (intrinsically unsteady, but giving a time-averaged steady state). The mean ganglion size and fraction of the nonwetting phase in the form of stranded ganglia are studied as functions of the main dimensionless parameters. Fractional flows and relative permeabilities are determined and correlated with flow phenomena at pore level. Effects of the wetting phase saturation, the viscosity ratio, the capillary number, and the coalescence factor on relative permeabilities are examined.
Effects of Gravity on Cocurrent Two-Phase Gas-Liquid Flows Through Packed Columns
NASA Technical Reports Server (NTRS)
Motil, Brian J.; Balakotaiah, Vemuri; Kamotani, Yasuhiro
2001-01-01
This work presents the experimental results of research on the influence of gravity on flow pattern transitions, pressure drop and flow characteristics for cocurrent gas-liquid two-phase flow through packed columns. The flow pattern transition data indicates that the pulse flow regime exists over a wider range of gas and liquid flow rates under reduced gravity conditions compared to normal gravity cocurrent down-flow. This is illustrated by comparing the flow regime transitions found in reduced gravity with the transitions predicted by Talmor. Next, the effect of gravity on the total pressure drop in a packed column is shown to depend on the flow regime. The difference is roughly equivalent to the liquid static head for bubbly flow but begins to decrease at the onset of pulse flow. As the spray flow regime is approached by increasing the gas to liquid ratio, the effect of gravity on pressure drop becomes negligible. Finally, gravity tends to suppress the amplitude of each pressure pulse. An example of this phenomenon is presented.
Characterization of flooding and two-phase flow in polymer electrolyte membrane fuel cell stacks
NASA Astrophysics Data System (ADS)
Karimi, G.; Jafarpour, F.; Li, X.
A partially flooded gas diffusion layer (GDL) model is proposed and solved simultaneously with a stack flow network model to estimate the operating conditions under which water flooding could be initiated in a polymer electrolyte membrane (PEM) fuel cell stack. The models were applied to the cathode side of a stack, which is more sensitive to the inception of GDL flooding and/or flow channel two-phase flow. The model can predict the stack performance in terms of pressure, species concentrations, GDL flooding and quality distributions in the flow fields as well as the geometrical specifications of the PEM fuel cell stack. The simulation results have revealed that under certain operating conditions, the GDL is fully flooded and the quality is lower than one for parts of the stack flow fields. Effects of current density, operating pressure, and level of inlet humidity on flooding are investigated.
Determination of void fraction in two phase liquid-gas flow using gamma absorption
NASA Astrophysics Data System (ADS)
Zych, M.; Hanus, R.; Jaszczur, M.; Strzępowicz, A.; Petryka, L.; Mastej, W.
2016-09-01
Full description of a two-phase liquid-gas flow requires the designation of lot parameters. First one, which describes which part of the pipeline is fulfilled by the gas, is the void fraction. Moreover the share of gas in a flowing mixture determines the structure of the flow and also affects the velocity of the individual phases. In that case void fraction can be determined by use the gamma absorption method, as well as other flow parameters may be evaluated by the same equipment. In addition the article presents the calibration of radiometric set, which consists of gamma radiation source Am-241 and scintillation probe NaI(Tl), for determination of the void fraction, illustrated by exemplary results of the described method application to various structures of air-water flow in the horizontal pipeline.
Prediction of gas-liquid two-phase flow regime in microgravity
NASA Technical Reports Server (NTRS)
Lee, Jinho; Platt, Jonathan A.
1993-01-01
An attempt is made to predict gas-liquid two-phase flow regime in a pipe in a microgravity environment through scaling analysis based on dominant physical mechanisms. Simple inlet geometry is adopted in the analysis to see the effect of inlet configuration on flow regime transitions. Comparison of the prediction with the existing experimental data shows good agreement, though more work is required to better define some physical parameters. The analysis clarifies much of the physics involved in this problem and can be applied to other configurations.
Two phase flow and heat transfer in porous beds under variable body forces, part 2
NASA Technical Reports Server (NTRS)
Evers, J. L.; Henry, H. R.
1969-01-01
Analytical and experimental investigations of a pilot model of a channel for the study of two-phase flow under low or zero gravity are presented. The formulation of dimensionless parameters to indicate the relative magnitude of the effects of capillarity, gravity, pressure gradient, viscosity, and inertia is described. The investigation is based on the principal equations of fluid mechanics and thermodynamics. Techniques were investigated by using a laser velocimeter for measuring point velocities of the fluid within the porous material without disturbing the flow.
Electrical impedance imaging in two-phase, gas-liquid flows: 1. Initial investigation
NASA Technical Reports Server (NTRS)
Lin, J. T.; Ovacik, L.; Jones, O. C.
1991-01-01
The determination of interfacial area density in two-phase, gas-liquid flows is one of the major elements impeding significant development of predictive tools based on the two-fluid model. Currently, these models require coupling of liquid and vapor at interfaces using constitutive equations which do not exist in any but the most rudimentary form. Work described herein represents the first step towards the development of Electrical Impedance Computed Tomography (EICT) for nonintrusive determination of interfacial structure and evolution in such flows.
Separated Vs. homogeneous two-phase flow in violent strombolian activity
NASA Astrophysics Data System (ADS)
Pioli, L.; Cashman, K.; Wallace, P.
2007-12-01
The term "violent Strombolian" was first used to describe mafic eruptions that formed ash-charged columns up to 6 km high, and dispersed material up to a few hundred km from the source (Walker, 1971). These eruptions are often discontinuous and strongly pulsatory and are typically associated with simultaneous effusive activity: they form composite deposits constituted by a cinder cone, tephra blanket, and lava flows spreading from lateral vents. This eruptive regime is typical of water-rich mafic magmas and is characterized by average mass flows (103-105 kg/s) intermediate between Hawaiian and subplinian regimes. Within this interval, there is a direct correlation between explosivity, as defined by tephra production, and magma flux. When magma flow exceeds 105 kg/s, gas segregation is no longer possible and eruptive activity takes the form of sustained columns (subplinian to plinian activity). At eruption rates below 103 kg/s passive degassing processes dominate, causing lava effusion and/or mild explosive activity (Strombolian to Hawaiian). We suggest that very shallow gas segregation processes play a fundamental role in violent strombolian dynamics, affecting both explosive and effusive activity. Simultaneous eruption of tephra from the cone and lava flows from lateral vents requires both a gas-rich mixture ascending the central conduit and gas-poor lava flowing in the lateral system. Uneven distribution of liquid and gas phases is possible only when gas and magma are characterized by different momentum, i.e. the flow is separated. At a first approximation, the phase distribution is controlled by the two-phase flow regime (bubbly, slug, churn or annular), both gas and liquid fluxes, and the ratio between conduit and dike diameters. To quantify this process, we analyze in detail the dynamics of a particularly long-lived and well-known eruption of the last century- the Paricutin eruption (1943-1952) of central Mexico. Specific two-phase flow models are then used to
NASA Astrophysics Data System (ADS)
Ramon, Jorge; Schreiber, Willard
2009-11-01
A novel atomization mechanism known as Flow Blurring (FB) mixes air with liquid to produce a fine spray. While the geometry of Flow Blurring is simple, the fluid mechanics of the two-phase mixing is complicated. CFD modeling of the Flow Blurring injector has been attempted previously assuming laminar one phase mixing between two different density gases. The objective of the present work was to study the effect of adding turbulence and two-phase flow to the previous CFD model. The k-ɛ, k-φ, and Reynolds stress models were investigated for representing turbulence. The k-ɛ realizable model produces the best results both from the standpoint of physical realism and numerical convergence and allows the Reynolds number based on flow characteristics of the FB injector to be increased by a factor of six. Three models of two-phase flow were examined: Volume of Fluid, Mixture, and Eulerian, none of which satisfactorily simulated two-phase mixing in the FB atomizer.
Device for measuring the liquid portion of a two-phase flow of gas and liquid
Schleimann-Jensen, A.H.
1986-09-02
A device is described for measuring the liquid portion of a two-phase flow of gas and liquid, particularly in conveying a liquid by means of a gas, in which two-phase flow the ratio of mixture between gas and liquid is widely varying. The device consists of a tubular housing and a turbine wheel with axial throw-flow rotatably mounted therein, the turbine wheel being provided with at least one magnetic element at a radially outward portion thereof, the element having limited extent axially and peripherally of the turbine wheel. The device furthermore consists of magnetic pick-up means adapted to emit output signals responsive to the rotary speed of the turbine wheel, the wheel being mounted for axial movement in the direction of flow from an initial position against a biassing force, characterized in that pick-up means are arranged axially spaced along the housing for allowing a measuring of rotary speed of the turbine wheel at various positions of movement within the housing responsive to density as well as speed changes of the flow and hence a determination of the liquid portion thereof by means of a converting device connected to all of the pick-up means. The tubular housing preferably is mounted vertically with the turbine wheel in its initial position being located lowermost.
Central Upwind Scheme for a Compressible Two-Phase Flow Model
Ahmed, Munshoor; Saleem, M. Rehan; Zia, Saqib; Qamar, Shamsul
2015-01-01
In this article, a compressible two-phase reduced five-equation flow model is numerically investigated. The model is non-conservative and the governing equations consist of two equations describing the conservation of mass, one for overall momentum and one for total energy. The fifth equation is the energy equation for one of the two phases and it includes source term on the right-hand side which represents the energy exchange between two fluids in the form of mechanical and thermodynamical work. For the numerical approximation of the model a high resolution central upwind scheme is implemented. This is a non-oscillatory upwind biased finite volume scheme which does not require a Riemann solver at each time step. Few numerical case studies of two-phase flows are presented. For validation and comparison, the same model is also solved by using kinetic flux-vector splitting (KFVS) and staggered central schemes. It was found that central upwind scheme produces comparable results to the KFVS scheme. PMID:26039242
NASA Astrophysics Data System (ADS)
Wiederhold, A.; Boeck, T.; Resagk, C.
2017-08-01
We report a method to detect and to measure the size and velocity of elongated bubbles or drops in a dispersed two-phase flow. The difference of the magnetic susceptibilities between two phases causes a force on the interface between both phases when it is exposed to an external magnetic field. The force is measured with a state-of-the-art electromagnetic compensation balance. While the front and the back of the bubble pass the magnetic field, two peaks in the force signal appear, which can be used to calculate the velocity and geometry parameters of the bubble. We achieve a substantial advantage over other bubble detection techniques because this technique is contactless, non-invasive, independent of the electrical conductivity and can be applied to opaque or aggressive fluids. The measurements are performed in an inclined channel with air bubbles and paraffin oil drops in water. The bubble length is in the range of 0.1-0.25 m and the bubble velocity lies between 0.02-0.22 m s-1. Furthermore we show that it is possible to apply this measurement principle for nondestructive testing (NDT) of diamagnetic and paramagnetic materials like metal, plastics or glass, provided that defects are in the range of 10‒2 m. This technique opens up new possibilities in industrial applications to measure two-phase flow parameters and in material testing.
A 3D moving mesh Finite Element Method for two-phase flows
NASA Astrophysics Data System (ADS)
Anjos, G. R.; Borhani, N.; Mangiavacchi, N.; Thome, J. R.
2014-08-01
A 3D ALE Finite Element Method is developed to study two-phase flow phenomena using a new discretization method to compute the surface tension forces. The computational method is based on the Arbitrary Lagrangian-Eulerian formulation (ALE) and the Finite Element Method (FEM), creating a two-phase method with an improved model for the liquid-gas interface. An adaptive mesh update procedure is also proposed for effective management of the mesh to remove, add and repair elements, since the computational mesh nodes move according to the flow. The ALE description explicitly defines the two-phase interface position by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The proposed methodology for computing the curvature leads to accurate results with moderate programming effort and computational cost. Static and dynamic tests have been carried out to validate the method and the results have compared well to analytical solutions and experimental results found in the literature, demonstrating that the new proposed methodology provides good accuracy to describe the interfacial forces and bubble dynamics. This paper focuses on the description of the proposed methodology, with particular emphasis on the discretization of the surface tension force, the new remeshing technique, and the validation results. Additionally, a microchannel simulation in complex geometry is presented for two elongated bubbles.
Two-Phase Solid/Fluid Simulation of Dense Granular Flows With Dilatancy Effects
NASA Astrophysics Data System (ADS)
Mangeney, A.; Bouchut, F.; Fernández-Nieto, E. D.; Kone, E. H.; Narbona-Reina, G.
2016-12-01
Describing grain/fluid interaction in debris flows models is still an open and challenging issue with key impact on hazard assessment [1]. 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 [2]. The model is derived from a 3D two-phase model proposed by Jackson [3] and the mixture equations are closed by a weak compressibility relation. 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 account for this transfer of fluid into and out of the mixture, a two-layer model is proposed with a fluid or a solid layer on top of the two-phase mixture layer. Mass and momentum conservation are satisfied for the two phases, and mass and momentum are transferred between the two layers. A thin-layer approximation is used to derive average equations. Special attention is paid to the drag friction terms that are responsible for the transfer of momentum between the two phases and for the appearance of an excess pore pressure with respect to the hydrostatic pressure. By comparing quantitatively the results of simulation and laboratory experiments on submerged granular flows, we show that our model contains the basic ingredients making it possible to reproduce the interaction between the granular and fluid phases through the change in pore fluid pressure. In particular, we analyse the different time
NASA Astrophysics Data System (ADS)
Seyed Ahmadi, Mehran; Argyropoulos, Stavros A.; Bussmann, Markus; Doutre, Don
2015-03-01
Following on a study of Si dissolution in molten Al, the effect of gas agitation is examined. The effects of gas flow rate, liquid bulk velocity, the position of a top injection lance, and bath temperature on the dissolution rate are quantified. A higher gas flow rate produced larger bubbles while bubble frequency remained relatively unchanged. This resulted in larger bubble-induced fluctuating velocities which in turn increased the dissolution rate. At lower bulk velocities, the effect of gas agitation is localized around the lance. By increasing the velocity, the effect of gas agitation is transported further into the bath. The dissolution rate enhancement varies with increasing bulk velocity, and explanations are provided. When combined with a bulk flow, gas agitation increases the dissolution rate regardless of lance position. Also, the enhancement of dissolution rate due to gas injection decreases at higher superheats, as the higher bath temperature increases the mass boundary thickness. In addition, the dissolution rate without gas agitation (single-phase flow) and with gas agitation (two-phase flow) is compared in terms of mean mass transfer coefficients. It was found that for the same liquid bulk velocities, the mean mass transfer coefficients are higher in two-phase flow than in single-phase flow. Finally, an increment to the single-phase flow bulk velocity that would be required to gain parity with the two-phase flow dissolution rate rise is demonstrated.
Flow regimes of adiabatic gas-liquid two-phase under rolling conditions
NASA Astrophysics Data System (ADS)
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.
Separation of endosomes by aqueous two-phase partition and free-flow electrophoresis.
Morré, D J; Morré, D M; Van Alstine, J M
1998-06-26
We have developed two endosome models to evaluate the separation of endosome populations by aqueous two-phase partition. In the first model, bovine kidney endosomes were used. In the second model. HeLa endosomes were identified in homogenates by means of a latent drug-(capsaicin-)inhibited NADH oxidase (NOX). Endosomes were first isolated by aqueous two-phase partition. To separate early and late endosomes, the endosomes were incubated with ATP to acidify the endosome interiors by activating a proton-translocating ATPase. Thus far, we have been able to resolve the early and late endosomes from any source only by preparative free-flow electrophoresis and not by phase-partition. Previous studies have shown that gravitational forces may be important for separation of endosomes by phase partition. Low-speed centrifugation (< or =12.5 g) during phase resolution altered the activity of the latent NADH oxidase used as a marker for HeLa cell endosomes.
An acoustic-convective splitting-based approach for the Kapila two-phase flow model
NASA Astrophysics Data System (ADS)
ten Eikelder, M. F. P.; Daude, F.; Koren, B.; Tijsseling, A. S.
2017-02-01
In this paper we propose a new acoustic-convective splitting-based numerical scheme for the Kapila five-equation two-phase flow model. The splitting operator decouples the acoustic waves and convective waves. The resulting two submodels are alternately numerically solved to approximate the solution of the entire model. The Lagrangian form of the acoustic submodel is numerically solved using an HLLC-type Riemann solver whereas the convective part is approximated with an upwind scheme. The result is a simple method which allows for a general equation of state. Numerical computations are performed for standard two-phase shock tube problems. A comparison is made with a non-splitting approach. The results are in good agreement with reference results and exact solutions.
Well-posed Euler model of shock-induced two-phase flow in bubbly liquid
NASA Astrophysics Data System (ADS)
Tukhvatullina, R. R.; Frolov, S. M.
2017-07-01
A well-posed mathematical model of non-isothermal two-phase two-velocity flow of bubbly liquid is proposed. The model is based on the two-phase Euler equations with the introduction of an additional pressure at the gas bubble surface, which ensures the well-posedness of the Cauchy problem for a system of governing equations with homogeneous initial conditions, and the Rayleigh-Plesset equation for radial pulsations of gas bubbles. The applicability conditions of the model are formulated. The model is validated by comparing one-dimensional calculations of shock wave propagation in liquids with gas bubbles with a gas volume fraction of 0.005-0.3 with experimental data. The model is shown to provide satisfactory results for the shock propagation velocity, pressure profiles, and the shock-induced motion of the bubbly liquid column.
Measurement of Two-Phase Flow Fields by Application of Dynamic Electrical Impedance Imaging
Kim, KyungYoun; Kang, Sook In; Kim, Ho Chan; Kim, Sin; Lee, Yoon Joon; Kim, Min Chan; Anghaie, Samim
2002-07-01
This study presents a visualization technique for the phase distribution in a two-phase flow field with an electrical impedance imaging technique, which reconstructs the resistivity distribution with electrical responses that are determined by corresponding excitations. Special emphasis is placed on the development of dynamic imaging technique for two-phase system undergoing a rapid transient, which could not be visualized with conventional static imaging techniques. The proposed algorithm treats the image reconstruction problem as a nonlinear state estimation problem and the unknown state (resistivity distribution, i.e. phase distribution) is estimated with the aid of a Kalman filter in a minimum mean square error sense. Several illustrative examples with computer simulations are successfully provided to verify the reconstruction performance of the proposed algorithm. (authors)
Development of electro-optical instrumentation for annular two-phase flow studies
NASA Astrophysics Data System (ADS)
Leskovar, B.
1981-05-01
Th development of new electro-optical instrumentation for studying the annular dispersed two phase flow regime is described. The system measures the thickness of the water film and droplet size and velocity distributions which would be encountered in such a flow regime. The water film thickness is measured by an improved capacitance method with a short time constant using newly developed sensor electrodes. The electrodes are made flush with the inner wall of a cylindrical tube and do not disturb the flow. In the test equipment, steady, laminar flow of water along the inner wall of the tube is controlled by appropriate valves and a porous jacket while droplets are introduced by means of a special spray nozzle.
Two-phase Flow Patterns in High Temperature Generator of Absorption Chiller / Heater
NASA Astrophysics Data System (ADS)
Furukawa, Masahiro; Kanuma, Hitoshi; Sekoguchi, Kotohiko; Takeishi, Masayuki
There is a lack of information about vapor-liquid two-phase flow patterns determined using void signals in high temperature generator of absorption chiller/heater. Sensing void fraction has been hampered because lithium bromide aqueous solution of strong alkalinity is employed as working fluid at high temperature and high level of vacuum. New void sensor applicable to such difficult conditions was developed. The void Fractions at 48 locations in a high temperature generator were measured simultaneously in both cooling and heating operations. Analysis of void signals detected reveals that the most violent boiling occurs at the upper part of rear plate of combustion chamber and the first line of vertical tubes located in the flue. The flow patterns are strongly affected by the system pressure difference between the cooling and heating operations: there appear bubbly, slug and froth flows in the cooling operation, but only bubbly flow in the heating operation.
Ceccio, S.L.; George, D.L.; O'Hern, T.J.; Shollenberger, K.A.; Torczynski, J.R.
1998-10-16
A series of studies is presented in which an electrical-impedance tomography (EXT) system is validated for two-phase flow measurements. The EIT system, developed at Sandia National Laboratories, is described along with the computer algorithm used for reconstructing phase volume fraction profiles. The algorithm is first tested using numerical data and experimental phantom measurements, with good results. The EIT system is then applied to solid-liquid and gas-liquid flows, and results are compared to an established gamma-densitometry tomography (GDT) system. In the solid-liquid flows, the average solid volume fractions measured by EIT are in good agreement with nominal values; in the gas-liquid flows, average gas volume fractions and radial gas volume fraction profiles from GDT and EIT are also in good agreement.
Non-equilibrium one-dimensional two-phase flow in variable area channels
NASA Technical Reports Server (NTRS)
Rohatgi, U. S.; Reshotko, E.
1975-01-01
A one-dimensional nonequilibrium flow analysis has been formulated for a one component two phase flow. The flow is considered homogeneous and essentially isothermal. Phase change is assumed to occur at heterogeneous nucleation sites and the growth of the vapor bubbles is governed by heat conduction from the liquid to the bubble. The analysis adjusted for friction is applied to liquid nitrogen flow in a venturi and comparison is made with the NASA experimental results of Simoneau. Good agreement with the experiments is obtained when one assumes the effective activation energy for nucleus formation to be small but nonzero. The computed pressure distributions deviate from the experimental results in the throat region of the venturi in a manner consistent with centrifugal effects not accounted for in the one-dimensional theory. The results are shown to depend not only on cavitation number but on additional dimensionless parameters governing the nonequilibrium production and subsequent growth of nuclei.
Ishii, M.; Denten, J.P.
1988-01-01
Inverted annular flow can be visualized as a liquid jet-like core surrounded by a vapor annulus. While many analytical and experimental studies of heat transfer in this regime have been performed, there is very little understanding of the basic hydrodynamics of the post-CHF flow field. However, a recent experimental study was done that was able to successfully investigate the effects of various steady-state inlet flow parameters on the post-CHF hydrodynamics of the film boiling of a single phase liquid jet. This study was carried out by means of a visual photographic analysis of an idealized single phase core inverted annular flow initial geometry (single phase liquid jet core surrounded by a coaxial annulus of gas). In order to extend this study, a subsequent flow visualization of an idealized two-phase core inverted annular flow geometry (two-phase central jet core, surrounded by a coaxial annulus of gas) was carried out. The objective of this second experimental study was to investigate the effect of steady-state inlet, pre-CHF two-phase jet core parameters on the hydrodynamics of the post-CHF flow field. In actual film boiling situations, two-phase flows with net positive qualities at the CHF point are encountered. Thus, the focus of the present experimental study was on the inverted bubbly, slug, and annular flow fields in the post dryout film boiling region. Observed post dryout hydrodynamic behavior is reported. A correlation for the axial extent of the transition flow pattern between inverted annular and dispersed droplet flow (the agitated regime) is developed. It is shown to depend strongly on inlet jet core parameters and jet void fraction at the dryout point. 45 refs., 9 figs., 4 tabs.
Two-phase Flow Characteristics in a Gas-Flow Channel of Polymer Electrolyte Membrane Fuel Cells
NASA Astrophysics Data System (ADS)
Cho, Sung Chan
Fuel cells, converting chemical energy of fuels directly into electricity, have become an integral part of alternative energy and energy efficiency. They provide a power source of high energy-conversion efficiency and zero emission, meeting the critical demands of a rapidly growing society. The proton exchange membrane (PEM) fuel cells, also called polymer electrolyte fuel cells (PEFCs), are the major type of fuel cells for transportation, portable and small-scale stationary applications. They provide high-power capability, work quietly at low temperatures, produce only water byproduct and no emission, and can be compactly assembled, making them one of the leading candidates for the next generation of power sources. Water management is one of the key issues in PEM fuel cells: appropriate humidification is critical for the ionic conductivity of membrane while excessive water causes flooding and consequently reduces cell performance. For efficient liquid water removal from gas flow channels of PEM fuel cells, in-depth understanding on droplet dynamics and two-phase flow characteristics is required. In this dissertation, theoretical analysis, numerical simulation, and experimental testing with visualization are carried out to understand the two-phase flow characteristics in PEM fuel cell channels. Two aspects of two-phase phenomena will be targeted: one is the droplet dynamics at the GDL surface; the other is the two-phase flow phenomena in gas flow channels. In the former, forces over a droplet, droplet deformation, and detachment are studied. Analytical solutions of droplet deformation and droplet detachment velocity are obtained. Both experiments and numerical simulation are conducted to validate analytical results. The effects of contact angle, channel geometry, superficial air velocity, properties of gas phase fluids are examined and criteria for the detachment velocity are derived to relate the Reynolds number to the Weber number. In the latter, two-phase flow
Advanced numerical methods for three dimensional two-phase flow calculations
Toumi, I.; Caruge, D.
1997-07-01
This paper is devoted to new numerical methods developed for both one and three dimensional two-phase flow calculations. These methods are finite volume numerical methods and are based on the use of Approximate Riemann Solvers concepts to define convective fluxes versus mean cell quantities. The first part of the paper presents the numerical method for a one dimensional hyperbolic two-fluid model including differential terms as added mass and interface pressure. This numerical solution scheme makes use of the Riemann problem solution to define backward and forward differencing to approximate spatial derivatives. The construction of this approximate Riemann solver uses an extension of Roe`s method that has been successfully used to solve gas dynamic equations. As far as the two-fluid model is hyperbolic, this numerical method seems very efficient for the numerical solution of two-phase flow problems. The scheme was applied both to shock tube problems and to standard tests for two-fluid computer codes. The second part describes the numerical method in the three dimensional case. The authors discuss also some improvements performed to obtain a fully implicit solution method that provides fast running steady state calculations. Such a scheme is not implemented in a thermal-hydraulic computer code devoted to 3-D steady-state and transient computations. Some results obtained for Pressurised Water Reactors concerning upper plenum calculations and a steady state flow in the core with rod bow effect evaluation are presented. In practice these new numerical methods have proved to be stable on non staggered grids and capable of generating accurate non oscillating solutions for two-phase flow calculations.
1983-01-01
Covolume 1.08 xO 10 m/kg Ratio of Specific Heats 1.271 Initial Gas Pressure 300 MPa nIitial Gas Temperature 3000 K The axial iomain is uniformly divided...Cycle. (Adaptation from Ref. 1) ................................. 7 2 Pressure Histories at the Breech (-)-) and at Projectile Base (---) and Their...gas-particle flow from the igniter. As the flame spreads throughout the propellant bed, gases are generated, pressure waves evolve, fluidization of
Two-equation turbulence model for free and bounded two-phase flows
Rizk, M.A.H.T.A.
1985-01-01
A theoretical investigation of turbulent, free and bounded, two-phase flows was conducted. The objective was to develop a two-equation turbulence model which accounts for the interaction between the two phases for two-dimensional, isothermal, free and confined turbulent flows. The two equations describe the conservation turbulence kinetic energy and dissipation rate of that energy for the carrier fluid. The suspension is assumed to be dilute. The dispersed phase is assumed to consist of particles spherical in shape and uniform in size. The physical properties of each phase are assumed to be constant. The two conservation equations are rigorously derived from the momentum equations of the carrier fluid. Closure for high-Reynolds number turbulence is obtained by modeling the turbulent correlations up to third order. Predictions obtained with the high-Reynolds number closure of the model are in very good agreement with available experimental data for the flow of a turbulent round jet laden with spherical, uniform-size solid particles. The high-Reynolds number closure of the model is then extended to enable its use right up to a solid wall by developing a second order closure for low-Reynolds number turbulence which provides a reliable basis for calculating wall-bounded flows.
Capture of circulating tumor cells using photoacoustic flowmetry and two phase flow
NASA Astrophysics Data System (ADS)
O'Brien, Christine M.; Rood, Kyle D.; Bhattacharyya, Kiran; DeSouza, Thiago; Sengupta, Shramik; Gupta, Sagar K.; Mosley, Jeffrey D.; Goldschmidt, Benjamin S.; Sharma, Nikhilesh; Viator, John A.
2012-06-01
Melanoma is the deadliest form of skin cancer, yet current diagnostic methods are unable to detect early onset of metastatic disease. Patients must wait until macroscopic secondary tumors form before malignancy can be diagnosed and treatment prescribed. Detection of cells that have broken off the original tumor and travel through the blood or lymph system can provide data for diagnosing and monitoring metastatic disease. By irradiating enriched blood samples spiked with cultured melanoma cells with nanosecond duration laser light, we induced photoacoustic responses in the pigmented cells. Thus, we can detect and enumerate melanoma cells in blood samples to demonstrate a paradigm for a photoacoustic flow cytometer. Furthermore, we capture the melanoma cells using microfluidic two phase flow, a technique that separates a continuous flow into alternating microslugs of air and blood cell suspension. Each slug of blood cells is tested for the presence of melanoma. Slugs that are positive for melanoma, indicated by photoacoustic waves, are separated from the cytometer for further purification and isolation of the melanoma cell. In this paper, we evaluate the two phase photoacoustic flow cytometer for its ability to detect and capture metastastic melanoma cells in blood.
Isolation of circulating tumor cells using photoacoustic flowmetry and two phase flow
NASA Astrophysics Data System (ADS)
O'Brien, Christine M.; Rood, Kyle D.; Gupta, Sagar K.; Mosley, Jeffrey D.; Goldschmidt, Benjamin S.; Sharma, Nikhilesh; Sengupta, Shramik; Viator, John A.
2011-03-01
Melanoma is the deadliest form of skin cancer, yet current diagnostic methods are inadequately sensitive. Patients must wait until secondary tumors form before malignancy can be diagnosed and treatment prescribed. Detection of cells that have broken off the original tumor and flow through the blood or lymph system can provide data for diagnosing and monitoring cancer. Our group utilizes the photoacoustic effect to detect metastatic melanoma cells, which contain the pigmented granule melanin. As a rapid laser pulse irradiates melanoma, the melanin undergoes thermo-elastic expansion and ultimately creates a photoacoustic wave. Thus, melanoma patient's blood samples can be enriched, leaving the melanoma in a white blood cell (WBC) suspension. Irradiated melanoma cells produce photoacoustic waves, which are detected with a piezoelectric transducer, while the optically transparent WBCs create no signals. Here we report an isolation scheme utilizing two-phase flow to separate detected melanoma from the suspension. By introducing two immiscible fluids through a t-junction into one flow path, the analytes are compartmentalized. Therefore, the slug in which the melanoma cell is located can be identified and extracted from the system. Two-phase immiscible flow is a label free technique, and could be used for other types of pathological analytes.
Capture of circulating tumor cells using photoacoustic flowmetry and two phase flow
O’Brien, Christine M.; Rood, Kyle D.; Bhattacharyya, Kiran; DeSouza, Thiago; Sengupta, Shramik; Gupta, Sagar K.; Mosley, Jeffrey D.; Goldschmidt, Benjamin S.; Sharma, Nikhilesh
2012-01-01
Abstract. Melanoma is the deadliest form of skin cancer, yet current diagnostic methods are unable to detect early onset of metastatic disease. Patients must wait until macroscopic secondary tumors form before malignancy can be diagnosed and treatment prescribed. Detection of cells that have broken off the original tumor and travel through the blood or lymph system can provide data for diagnosing and monitoring metastatic disease. By irradiating enriched blood samples spiked with cultured melanoma cells with nanosecond duration laser light, we induced photoacoustic responses in the pigmented cells. Thus, we can detect and enumerate melanoma cells in blood samples to demonstrate a paradigm for a photoacoustic flow cytometer. Furthermore, we capture the melanoma cells using microfluidic two phase flow, a technique that separates a continuous flow into alternating microslugs of air and blood cell suspension. Each slug of blood cells is tested for the presence of melanoma. Slugs that are positive for melanoma, indicated by photoacoustic waves, are separated from the cytometer for further purification and isolation of the melanoma cell. In this paper, we evaluate the two phase photoacoustic flow cytometer for its ability to detect and capture metastastic melanoma cells in blood. PMID:22734751
Capture of circulating tumor cells using photoacoustic flowmetry and two phase flow.
O'Brien, Christine M; Rood, Kyle D; Bhattacharyya, Kiran; DeSouza, Thiago; Sengupta, Shramik; Gupta, Sagar K; Mosley, Jeffrey D; Goldschmidt, Benjamin S; Sharma, Nikhilesh; Viator, John A
2012-06-01
Melanoma is the deadliest form of skin cancer, yet current diagnostic methods are unable to detect early onset of metastatic disease. Patients must wait until macroscopic secondary tumors form before malignancy can be diagnosed and treatment prescribed. Detection of cells that have broken off the original tumor and travel through the blood or lymph system can provide data for diagnosing and monitoring metastatic disease. By irradiating enriched blood samples spiked with cultured melanoma cells with nanosecond duration laser light, we induced photoacoustic responses in the pigmented cells. Thus, we can detect and enumerate melanoma cells in blood samples to demonstrate a paradigm for a photoacoustic flow cytometer. Furthermore, we capture the melanoma cells using microfluidic two phase flow, a technique that separates a continuous flow into alternating microslugs of air and blood cell suspension. Each slug of blood cells is tested for the presence of melanoma. Slugs that are positive for melanoma, indicated by photoacoustic waves, are separated from the cytometer for further purification and isolation of the melanoma cell. In this paper, we evaluate the two phase photoacoustic flow cytometer for its ability to detect and capture metastatic melanoma cells in blood.
Numerical simulation of two-phase flow in horizontal interconnected subchannels
Shourki, M.; Carver, M.B.; Tahir, A.
1985-11-01
Different subchannel computer codes have been successfully used for the thermal-hydraulic analysis of coolant flow in vertical fuel channels. None of these methods, however, is suitable for two-phase flow in horizontal fuel channels, such as those of the CANDU nuclear reactors, due to the lack of appropriate constitutive relationships that can correctly account for the gravity separation effects. A transverse vapor drift model that accounts for the combined effect of gravity separation and turbulent diffusion has been incorporated into the existing subchannel computer code SAGA. Although the basic structure of the code remains similar to SAGA III, some modifications in both the mathematical formulation and numerical solution have been incorporated. These modifications resulted in significant improvements in the code's ability to model horizontal two-phase subchannel flow. The new version of the code was tested and found to be capable of simulating the complex exchange phenomenon between adjacent horizontal subchannels caused by the interaction of turbulent diffusion, pressure gradient, and gravity-induced cross flows. The code predictions were compared with experimental data obtained from two different sources and showed good agreement.
Formation of parallel two-phase flow in nanochannel and application to solvent extraction
NASA Astrophysics Data System (ADS)
Kazoe, Yutaka; Ugajin, Takuya; Ohta, Ryoichi; Mawatari, Kazuma; Kitamori, Takehiko; The University of Tokyo Team
2015-11-01
Micro chemical systems have realized high-throughput analysis in ultra small volumes. Our group has established unit operations such as extraction, separation and reaction, and a concept of integration of chemical processes using parallel multi-phase flows in microchannels. Recently, the research field has been extended to 10-1000 nm space (extended-nanospace). Exploiting extended-nanospace, we developed ultra high performance chemical operations such as aL-chromatography and single molecule immunoassay. However, formation of parallel multi-phase flow in nanochannels has been difficult. The challenge is to control liquid-liquid/gas-liquid interfaces in 100 nm-scale. For this purpose, this study developed a partial surface modification method of nanochannel and verified formation of parallel two-phase flow. We achieved partial hydrophobic modification using focused ion beam (FIB). Using this method, formation of parallel water/dodecane two-phase flow in a nanochannel of 1500 nm width and 890 nm depth was succeeded. Solvent extraction of lipid, which is a basic separation in bioanalysis, was achieved in 25 fL volume much smaller than single cell. This study will greatly contribute to develop novel nanofluidic devices for chemical analysis and chemical synthesis. This work was supported by Japan Science and Technology Agency, Core Research for Evolutional Science and Technology.
Prediction of annular two-phase flow in microgravity and earth-normal gravity
Reinarts, T.R.; Ungar, E.K.
1996-12-31
Annular flow occurs in zero-g over a much broader range of conditions than in Earth-normal gravity (one-g). In horizontal tubing at one-g, annular flow is typically limited to the case of small tubing (where surface tension overwhelms the gravity effects) and the case of high speed vapor flow (where inertial effects overwhelm the gravity effects). Data obtained from one-g experiments in these conditions can be applied to the case of zero-g two-phase flow, but care must be taken that they are applied correctly. The analysis here utilizes the available, validated data-base of annular zero-g data and accompanying (where available) pure annular one-g flow. This data base includes ammonia, dichlordifluoromethane (R12), air/water, air/water-glycerin, and air/water Zonyl FSP in a variety of tube inside diameters. The first step is an analysis of the flow regime data and the flow regime prediction models for annular flow. The applicability and validity of each model is analyzed. The pressure drop data are then presented, analyzed, and compared with the available predictive models. A comparison of one-g and microgravity pressure drop is made, and the limits of using small ID tubing and high speed vapor flows to simulate micro gravity conditions are given.
Bilicki, Z.; Kestin, J.
1980-12-01
A derivation of the field equations for two-phase flow is presented, based on the classical methods of thermodynamics of irreversible processes and resulting in a homogeneous diffusion model. The equations are local and instantaneous and ignore turbulent fluctuations as well as the observable fluctuations of the phase boundaries. (MHR)
Sharma, Abhinav; Tiwari, Vijeet; Kumar, Vineet; Mandal, Tapas Kumar; Bandyopadhyay, Dipankar
2014-10-01
Strategic application of external electrostatic field on a pressure-driven two-phase flow inside a microchannel can transform the stratified or slug flow patterns into droplets. The localized electrohydrodynamic stress at the interface of the immiscible liquids can engender a liquid-dielectrophoretic deformation, which disrupts the balance of the viscous, capillary, and inertial forces of a pressure-driven flow to engender such flow morphologies. Interestingly, the size, shape, and frequency of the droplets can be tuned by varying the field intensity, location of the electric field, surface properties of the channel or fluids, viscosity ratio of the fluids, and the flow ratio of the phases. Higher field intensity with lower interfacial tension is found to facilitate the oil droplet formation with a higher throughput inside the hydrophilic microchannels. The method is successful in breaking down the regular pressure-driven flow patterns even when the fluid inlets are exchanged in the microchannel. The simulations identify the conditions to develop interesting flow morphologies, such as (i) an array of miniaturized spherical or hemispherical or elongated oil drops in continuous water phase, (ii) "oil-in-water" microemulsion with varying size and shape of oil droplets. The results reported can be of significance in improving the efficiency of multiphase microreactors where the flow patterns composed of droplets are preferred because of the availability of higher interfacial area for reactions or heat and mass exchange. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Garg, P.; Picardo, J. R.; Pushpavanam, S.
2014-07-15
In this work, we investigate the fully developed flow field of two vertically stratified fluids (one phase flowing above the other) in a curved channel of rectangular cross section. The domain perturbation technique is applied to obtain an analytical solution in the asymptotic limit of low Reynolds numbers and small curvature ratios (the ratio of the width of the channel to its radius of curvature). The accuracy of this solution is verified by comparison with numerical simulations of the nonlinear equations. The flow is characterized by helical vortices within each fluid, which are driven by centrifugal forces. The number of vortices and their direction of circulation varies with the parameters of the system (the volume fraction, viscosity ratio, and Reynolds numbers). We identify nine distinct flow patterns and organize the parameter space into corresponding flow regimes. We show that the fully developed interface between the fluids is not horizontal, in general, but is deformed by normal stresses associated with the circulatory flow. The results are especially significant for flows in microchannels, where the Reynolds numbers are small. The mathematical results in this paper include an analytical solution to two coupled biharmonic partial differential equations; these equations arise in two-phase, two-dimensional Stokes flows.
Flow in geothermal wells. Part IV. Transition criteria for two-phase flow patterns
Bilicki, Z.; Kestin, J.
1980-12-01
Detailed considerations justifying the criteria for transitions between flow patterns are presented. The following are covered: transition from bubble to plug (or slug) flow, transition from plug flow to froth flow, transition from froth to annular mist flow, and model comparisons. (MHR)
NASA Astrophysics Data System (ADS)
Goto, H.; Aichi, M.; Tokunaga, T.; Yamamoto, H.; Ogawa, T.; Aoki, T.
2013-12-01
Coupled two-phase fluid flow and deformation of Berea sandstone was discussed through laboratory experiments and numerical simulation. In the experiment, a triaxial compression apparatus with flow pipes to pass fluids through a rock sample was used. The experimental procedures were as follows. Firstly, external stresses close to hydrostatic condition were applied to a water saturated cylindrical Berea sandstone sample. Then, compressed air was infiltrated from the bottom of the sample. During the experiment, both axial and circumferential strains at half the height of the sample and volumetric discharge of water at the outlet were measured. Both strains showed sudden extensions after a few seconds, and monotonically extended thereafter. The volumetric discharge of water showed that air breakthrough occurred in around 100 seconds after the commencement of the air injection. Numerical simulations based on thermodynamically consistent constitutive equations were conducted in order to quantitatively analyze the experimental results. In a simulation in which the material was assumed to be homogeneous isotropic, the axial strain at half the height of the sample and the volumetric discharge of water at the outlet were reproduced well by using reasonable parameters, while that was not the case with the circumferential strain at half the height of the sample. On the other hand, in a simulation in which anisotropy of the material was introduced, all experimental data were reproduced well by using reasonable parameters. This result is reasonable because Berea sandstone is well known to be anisotropic under such Terzaghi effective stress condition as used in our experiment, i.e., 3.0 MPa (Hart and Wang, 1999; Hart, 2000). Our results indicate that the theory of poroelasticity for two-phase fluid system can explain the strain behavior of porous media for two-phase fluid flow observed in laboratory experiments.
Zero-G experiments in two-phase fluids flow regimes
NASA Technical Reports Server (NTRS)
Heppner, D. B.; King, C. D.; Littles, J. W.
1975-01-01
The two-phase flows studied were liquid and gas mixtures in a straight flow channel of circular cross-section. Boundaries between flow regimes have been defined for normogravity on coordinates of gas quality and total mass velocity; and, when combined with boundary expressions having a Froude number term, an analytical model was derived predicting boundary shifts with changes in gravity level. Experiments with air and water were performed, first in the normogravity environment of a ground laboratory and then in 'zero gravity' aboard a KC-135 aircraft flying parabolic trajectories. Data reduction confirmed regime boundary shifts in the direction predicted, although the magnitude was a little less than predicted. Pressure drop measurements showed significant increases for the low gravity condition.
Bubble dynamics, two-phase flow, and boiling heat transfer in a microgravity environment
NASA Technical Reports Server (NTRS)
Chung, Jacob N.
1994-01-01
The two-phase bubbly flow and boiling heat transfer in microgravity represents a substantial challenge to scientists and engineers and yet there is an urgent need to seek fundamental understanding in this area for future spacecraft design and space missions. At Washington State University, we have successfully designed, built and tested a 2.1 second drop tower with an innovation airbag deceleration system. Microgravity boiling experiments performed in our 0.6 second Drop Tower produced data flow visualizations that agree with published results and also provide some new understanding concerning flow boiling and microgravity bubble behavior. On the analytical and numerical work, the edge effects of finite divergent electrode plates on the forces experienced by bubbles were investigated. Boiling in a concentric cylinder microgravity and an electric field was numerically predicted. We also completed a feasibility study for microgravity boiling in an acoustic field.
Zero-G experiments in two-phase fluids flow regimes
NASA Technical Reports Server (NTRS)
Heppner, D. B.; King, C. D.; Littles, J. W.
1975-01-01
The two-phase flows studied were liquid and gas mixtures in a straight flow channel of circular cross-section. Boundaries between flow regimes have been defined for normogravity on coordinates of gas quality and total mass velocity; and, when combined with boundary expressions having a Froude number term, an analytical model was derived predicting boundary shifts with changes in gravity level. Experiments with air and water were performed, first in the normogravity environment of a ground laboratory and then in 'zero gravity' aboard a KC-135 aircraft flying parabolic trajectories. Data reduction confirmed regime boundary shifts in the direction predicted, although the magnitude was a little less than predicted. Pressure drop measurements showed significant increases for the low gravity condition.
Dynamic model for horizontal two-phase flow predicting low head flooding
Saarinen, M. . Nuclear Engineering Lab.)
1994-10-01
The countercurrent flow of gas and water in a short horizontal pipe is studied numerically with a two-phase flow model. It is observed that the onset of flooding cannot be predicted at low liquid flow rates using conventional one-dimensional equations. The conventional equations yield the same underestimated results as the Taitel-Dukler criterion. Utilizing physical reasoning, improved equations have been derived. The basic idea is that the distribution of the phase velocities should not be treated as uniform in the cross-sectional area occupied by phases but transverse dependencies for the velocities should be allowed. By comparing measurement data and calculated results, it is shown that flooding transition can be predicted accurately with these equations.
Thermal Lattice Boltzmann Simulations for Vapor-Liquid Two-Phase Flows in Two Dimensions
NASA Astrophysics Data System (ADS)
Wei, Yikun; Qian, Yuehong
2011-11-01
A lattice Boltzmann model with double distribution functions is developed to simulate thermal vapor-liquid two-phase flows. In this model, the so-called mesoscopic inter-particle pseudo-potential for the single component multi-phase lattice Boltzmann model is used to simulate the fluid dynamics and the internal energy field is simulated by using a energy distribution function. Theoretical results for large-scale dynamics including the internal energy equation can be derived and numerical results for the coexistence curve of vapor-liquid systems are in good agreement with the theoretical predictions. It is shown from numerical simulations that the model has the ability to mimic phase transitions, bubbly flows and slugging flows. This research is support in part by the grant of Education Ministry of China IRT0844 and the grant of Shanghai CST 11XD1402300.
Behavior of embedded phase in shock-driven two-phase flow
NASA Astrophysics Data System (ADS)
Kuehner, Garrett; Wayne, Patrick; Olmstead, Dell; Corbin, Clint; Bernard, Tennille; Vorobieff, Peter; Truman, C. Randall
2013-11-01
We present an experimental study of droplet acceleration in a shock-driven two-phase flow (air with embedded liquid droplets). The droplets (propylene glycol, diameter 0.5-3 μm) were pre-mixed with the air in the test section of a shock tube, then impulsively accelerated with planar shock wave with a Mach number of 1.7. A cross-section of the flow is illuminated with multiple pulses from Nd:YAG lasers, producing time-resolved visualizations of the seeded volume. The images are then analyzed to quantify droplet velocity and acceleration from the shock passage to about 1.5 ms after the shock. Based on the velocity measurements, we can resolve the droplet lag after the shock, when the massive droplets ``catch up'' with the flow of the surrounding air, as well as validate our earlier estimates of boundary layer growth. This research is supported by NNSA (US National Nuclear Security Agency).
Parasitic Currents in Diffuse-Interface Two-Phase Flow Simulations
NASA Astrophysics Data System (ADS)
Milani, Pedro; Mirjalili, Seyedshahabaddin; Mani, Ali
2016-11-01
Two phase flow phenomena are important in a wide range of applications, such as bubble generation in ocean waves and droplet dynamics in fuel injectors. Several methods can be used to simulate such phenomena. The focus of this study is the diffuse-interface method, in which the interface is described via a mixing energy and spans a few computational cells, while surface tension is modeled as a force density term on the right-hand side of the momentum equation. The advantages of this method include the ability to easily simulate complex geometries since it does not require special treatment around the interface, and to conserve mass exactly. However, this method suffers from parasitic currents, an unphysical velocity field generated close to the interface due to numerical imprecisions in the surface tension term. This can be a serious problem in low speed flows, where the parasitic currents are significant compared to the velocity scale of the problem. In this study, we consider a wide range of diffuse-interface schemes for two-phase flows, including different options for discrete representation of the surface tension force. By presenting an assessment of each method's performance in scenarios involving parasitic currents, we develop accuracy estimates and guidelines for selection among these models. Supported by the ONR.
Two Phase Compressible Flow Fields in One Dimensional and Eulerian Grid Framework
NASA Astrophysics Data System (ADS)
Lee, Sungsu; Park, Chan Wook
2008-11-01
Numerical investigation for two phase compressible flow fields of air-water in one dimensional tube are performed in the fixed Eulerian grid framework. Using an equation of states of Tait's type for a multiphase cell, the two phase compressible flow is modeled as equivalent single phase which is discretized using the Roe`s approximate Riemann solver, while the phase interface is captured via volume fractions of each phase. The most common problem found in the computational approaches in compressible multiphase flow is occurrence of the pressure oscillation at the phase interface. In order to suppress that phenomenon, tried are two approaches; a passive advection of volume fraction and a direct pressure relaxation with the compressible form of volume fraction equation. The results show that the direct pressure equalizing method suppresses pressure oscillation successfully and generates sharp discontinuities, transmitting and reflecting acoustic waves naturally at the phase interface. This work was supported by a research fund granted from Agency for Defense Development, South Korea
Two-phase flow modeling for the cathode side of a polymer electrolyte fuel cell
NASA Astrophysics Data System (ADS)
Qin, Chaozhong; Rensink, Dirk; Fell, Stephan; Majid Hassanizadeh, S.
2012-01-01
Liquid water flooding in micro gas channels is an important issue in the water management of polymer electrolyte fuel cells (PEFCs). However, in most previous numerical studies liquid water transport in the gas channels (GC) has been simplified by the mist flow assumption. In this work, we present a two-phase flow model for the cathode side of a PEFC. The GC is assumed to be a structured porous medium with the porosity of 1.0. The two-phase Darcy's law is applied to both diffusion layers and GC. Based on the developed model, the liquid water flooding in the GC and its impact on the liquid water distribution in the diffusion layers are explored in detail. Furthermore, we study the effect of the immobile saturation on the predicted liquid water distribution in the diffusion layers. The results show that neglecting the GC flooding leads to an incorrect prediction of liquid water distribution in the diffusion layers and an overestimation of the cell performance. The gas flow rate in the GC can be optimized to achieve the best cell performance. Finally, when considering the immobile saturation in the model, more liquid water is predicted in the diffusion layers.
Riemann-problem-based techniques for computing reactive two-phased flows
NASA Astrophysics Data System (ADS)
Toro, E. F.
We consider Riemann-problem based (RPB) numerical techniques for two-phase reactive flows with moving boundaries. Given the still unresolved problem of hyperbolicity we adopt a mixed hyperbolic-elliptic mathematical model. A successful strategy consists of identifying two hyperbolic homogeneous systems, one for each phase. The remaining terms are regarded as (stiff) source terms. The associated Riemann problems are solved exactly and approximately. Two RPB methods are then used, namely Roe's method and a Weighted Average Flux Method (WAF) due to the author. Application of the technioues to a shock tube problem and a ballistics problem are carried out.
Two-Phase Flow Research on the ISS for Thermal Control Applications
NASA Technical Reports Server (NTRS)
Motil, Brian J.
2013-01-01
With the era of full utilization of the ISS now upon us, this presentation will discuss some of the highest-priority areas for two-phase flow systems with thermal control applications. These priorities are guided by recommendations of a 2011 NRC Decadal Survey report, Recapturing a Future for Space Exploration, Life and Physical Sciences for a New Era as well as an internal NASA exercise in response to the NRC report conducted in early 2012. Many of these proposals are already in various stages of development, while others are still conceptual.
Decay of the 3D viscous liquid-gas two-phase flow model with damping
Zhang, Yinghui
2016-08-15
We establish the optimal L{sup p} − L{sup 2}(1 ≤ p < 6/5) time decay rates of the solution to the Cauchy problem for the 3D viscous liquid-gas two-phase flow model with damping and analyse the influences of the damping on the qualitative behaviors of solution. It is observed that the fraction effect of the damping affects the dispersion of fluids and enhances the time decay rate of solution. Our method of proof consists of Hodge decomposition technique, L{sup p} − L{sup 2} estimates for the linearized equations, and delicate energy estimates.
Impact of the initialisation on population balance CFD models coupled with two-phase flow
NASA Astrophysics Data System (ADS)
Hliwa, Ghizlane Zineb; Bannari, Rachid; Belghiti, Mly Taib
2017-07-01
Several studies have been made about Computational Fluid Dynamics simulations of bubble columns and compared to experimental data. In the present work, a rectangular bubble column is simulated using a model of two-phase flows. The inter-phase forces are used. A population balance equation is introduced by comparing two different models to account the effects of bubble size distribution. The turbulence model k-ɛ is used with mixture transport properties. In this work, the impact of boundary conditions at the inlet is studied. The numerical predictions are validated with experimental data available in the literature.
Progress on the simulation of a mixture two-phase flow model
NASA Astrophysics Data System (ADS)
Gräbel, J.; Zeidan, D.; Bähr, P.; Ueberholz, P.; Farber, P.
2017-07-01
This paper reports a recent progress in the simulation results for a compressible two-phase mixture model. A two-dimensional explosion problem is numerically investigated by implementing the Lax-Friedrich scheme on the basis of gas and liquid flows with velocity non-equilibrium. It is implemented with the help of finite volume splitting approach on a Cartesian grid. The relative motion containing both smooth and discontinuous solutions are included to verify the model equations behaviour, in addition to the accuracy of the numerical treatment.
Two-phase flow modelling of sediment suspension in the Ems/Dollard estuary
NASA Astrophysics Data System (ADS)
Xu, Chunyang; Dong, Ping
2017-05-01
Understanding and quantifying mud suspension and sediment transport processes are of great importance for effective exploitation and sustainable management of estuarine environments. Event-based predictive models are widely used to identify the key interactions and mechanisms that govern the dynamics involved and to provide the essential parameterisation for assessing the long-term morphodynamic evolution of the estuaries. This study develops a one-dimensional-vertical (1DV) Reynolds averaged two-phase model for cohesive sediments resuspension driven by tidal flows. To capture the time-dependent flocculation process more accurately, a new drag force closure which relates empirically to settling velocity of mud flocs with suspended sediment concentration (SSC) is incorporated into the two-phase model. The model is then applied to simulate mud suspension in the Ems/Dollard estuary during two periods (June and August 1996) of tidal forcing. Numerical predictions of bed shear stresses and sediment concentrations at different elevations above the bed are compared with measured variations. The results confirm the importance of including flocculation effects in calculating the settling velocity of mud flocs and demonstrates the sensitivity of prediction with the settling velocity in terms of flocs concentration. Although the two-phase modelling approach can in principle better capture the essential interactions between fluid and sediment phases, its practical advantages over the simpler single phase approach cannot be confirmed for the data periods simulated, partly because the overall suspended sediment concentration measured is rather low and the interaction between the two phases is weak and also because the uncertainties in the relationship between the settling velocity and flocs concentration.
Experimental study of liquid-solid two phase flow over a step using PIV
NASA Astrophysics Data System (ADS)
Cando, E. H.; Luo, X. W.; Hidalgo, V. H.; Zhu, L.; Aguinaga, A. G.
2016-05-01
The present investigation focuses on the water-sand flow through a rectangular tunnel with a step using the Particle Image Velocimetry (PIV). Two cameras with appropriate optical filters have been used to capture each phase image separately. The optical filters were selected according to the optical properties of the sand and fluorescent tracers. Through data processing the experimental flow field such as the velocity profiles of sand and water had been obtained. In order to compare with the experiment, the steady state two phase flow fields were simulated using RANS method with k-ω SST turbulence model. It is noted that the numerical results matches the experimental results fairly good. Furthermore, the flow rates obtained from experimental and numerical velocity profiles also have a good match with the measurement by flow meter. The flow analysis shows that the water velocity variation induced by the presence of the step in the water-sand flow is equivalent to those cases with low sand concentration. However, the sand velocity in downstream region is 5% greater than the water velocity when the cross section is reduced in 25%.
A combined experimental-numerical approach for two-phase flow boiling in a minichannel
NASA Astrophysics Data System (ADS)
Hożejowska, Sylwia; Grabowski, Mirosław
2016-03-01
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 recorded images of flow with high-speed camera. The second aim of the paper was to formulate appropriate flow boiling heat transfer model, which would minimises the use of experimentally determined constants. The procedure of calculating the temperature of the ethanol is coupled with concurrent process of determining the temperature distributions in the isolating foil and the heating surface. The two-dimensional temperature distributions in three subsequent domains were calculated with Trefftz method. Due to the Robin condition, heat transfer coefficient at the heating surface-ethanol interface was calculated based on the known temperature distributions of the foil and liquid. Additionally, the paper describes the relation between two sets of functions used in the calculation. Numerical calculations made by Trefftz method were performed with using experimental data.
Experimental and modeling studies of two-phase flow in pipelines
Manabe, Ryo; Tochikawa, Tetsuro; Tsukuda, M.; Arihara, Norio
1997-11-01
The objectives of this study are to develop and evaluate a mechanistic model for gas/liquid two-phase flow in pipelines. A mechanistic model has been developed by combining currently available models and correlations. The approach of the modeling study was based on the work by Xiao et al. Modifications have been made on the annular flow model by implementing the currently developed film-thickness-distribution model. An experimental database has been developed for model evaluation. Seventy-five runs of steady-state air/water flow tests in horizontal and slightly inclined pipes were conducted using a large-scale experimental facility. The experimental program was set up in a wide range of experimental conditions to cover the intermittent, dispersed bubble, and annular flow patterns. An evaluation of the model was carried out for each flow pattern, namely, intermittent, dispersed bubble, and annular flow. The comparisons between the measured and calculated pressure drops show good agreement for each flow pattern. Also, overall evaluation revealed that the proposed model provided the best performance among the commonly used empirical correlations, such as Beggs and Brill, Mukherjee and Brill, and Dukler et al.
Bottoni, M.; Ajuha, S.; Sengpiel, W.
1994-12-31
Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy derived for a two-phase flow by volume-averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration; bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities makes the rigorously formulated terms useless for computational purposes, modeling of these terms is discussed.
Bottoni, M.; Sengpiel, W.
1992-12-01
Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy, derived for a two-phase flow by volume averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration, bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities make the rigorously formulated terms useless for computational purposes, modelling of these terms is discussed. 3 figs., 15 refs.
Bottoni, M. . Materials and Components Technology Div.); Sengpiel, W. . Inst. fuer Reaktorsicherheit)
1992-01-01
Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy, derived for a two-phase flow by volume averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration, bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities make the rigorously formulated terms useless for computational purposes, modelling of these terms is discussed. 3 figs., 15 refs.
NASA Astrophysics Data System (ADS)
Hernández, Leonor; Juliá, José Enrique; Chiva, Sergio; Paranjape, Sidharth; Ishii, Mamoru
2007-06-01
Important aspects of the hydrodynamics and thus, the correct identification of the flow regime could enhance safety and overall performance in multiphase flow systems. Several works on flow regime identification have been carried out in the past. Most of them consist, in a first stage, on measuring certain flow parameters that can be used as good flow regime indicators and, then, developing a flow regime map using these indicators. In this work, a vertical two-phase flow loop facility was used, whereby local conductivity signals were recorded and utilized for the development of an Artificial Neural Network (ANN) based method for the flow regime classification. The experimental database consists of a total number of 125 test cases covering a wide range of situations in the loop working area. Each experiment flow regime was identified by visual inspection, and classified into bubbly (B), cap-bubbly (CB), slug (S), churn turbulent (CT) or annular (A). The bubble chord length cumulative probability function (CPDF), calculated from the measured conductivity signals was selected as flow regime indicator. Different ANN configurations were designed, trained and optimized. The ANN types and the statistical parameters of the CPFD used as inputs were two of the four parameters varied in the ANN optimization process. The temporal length in the conductivity signal used to calculate the CPDF, was also modified during this study. The range of variation of the temporal signal was from 1 to 60 seconds. Together with this temporal variation, the number of training patterns (increasing with decreasing CPDF processing times or not) was also modified. The modification of all these variables allowed the identification of the ANN configuration that better fit the requirements of the specific study of flow regime classification.
Probe measures gas and liquid mass flux in high mass flow ratio two-phase flows
NASA Technical Reports Server (NTRS)
Burick, R. J.
1972-01-01
Deceleration probe constructed of two concentric tubes with separator inlet operates successfully in flow fields where ratio of droplet flow rate to gas flow rate ranges from 1.0 to 20, and eliminates problems of local flow field disturbances and flooding. Probe is effective tool for characterization of liquid droplet/gas spray fields.
Photochromic flow visualization in single-phase and two-phase flows
NASA Astrophysics Data System (ADS)
Davis, J.; Bottcher, J.; Johnson, G.; Marschall, E.
A photochromic flow visualization technique that was originally introduced by Popovich and Hummel permits qualitative and quantitative velocity information to be obtained in a variety of complex flow situations. Examples of flow visualization studies include drop and bubble formation, distortion of flow fields caused by velocity probes, and others. While qualitative information on flow velocities can be obtained with relative ease, quantitative information cannot be extracted as readily and requires a modification of the visualization technique or use of an iterative evaluation method.
NASA Astrophysics Data System (ADS)
Seymour, Joseph Daniel
Nuclear magnetic resonance (NMR) imaging, a non -invasive spectroscopic technique, is used to measure velocity in the fluid phase of suspensions in tube flow by a position encode pulsed gradient spin echo (PGSE) technique. The mean velocity of an ensemble of nuclei within a discrete volume element (voxel) of the sample, localized by the NMR experiment, causes a residual phase shift in nuclei precession and random displacements due to Brownian motion of the nuclei and fluctuations about the mean velocity cause attenuation of signal. The average macroscopic and fluctuating velocity distributions in suspensions of spheres and fibers at concentrations from the dilute to concentrated regimes are measured. The fluctuational motion in low Reynolds number flow is due to the many body hydrodynamic interactions of the non-colloidal particles. The fluctuational motion measured depends on the length and time scales of the NMR experiment and it is the stationary Gaussian Markov statistics of the fluctuation in motion that is measured. Interpretation of the signal in NMR PGSE experiments depends on a model of the motion and the fluctuations are modelled as a colored noise stochastic process. The stochastic model is connected to the averaged theory of two-phase flow through formulation of the averaged theory as an equivalent stochastic differential equation. Tube flow is studied to increase understanding of NMR measurements in two-phase solid-liquid systems and provide data on systems inaccessible to standard velocity measurement techniques. Macroscopic rheological characterization of materials by NMR imaging is possible using 1-D and 2 -D NMR velocity phase encoded data. 1-D velocity probability distribution data is used to characterize the macroscopic material flow behavior of a Newtonian standard, a 3% polyacrylamide solution, tomato juice and paper pulp. The measurement of yield stress rheological behavior using 2-D position dependent velocity data is presented and used to
Sub-grid combustion modeling for compressible two-phase reacting flows
NASA Astrophysics Data System (ADS)
Sankaran, Vaidyanathan
2003-06-01
A generic formulation for modeling the turbulent combustion in compressible, high Reynolds number, two-phase; reacting flows has been developed and validated. A sub-grid mixing/combustion model called Linear Eddy Mixing (LEM) model has been extended to compressible flows and used inside the framework of Large Eddy Simulation (LES) in this LES-LEM approach. The LES-LEM approach is based on the proposition that the basic mechanistic distinction between the convective and the molecular effects should be preserved for accurate prediction of complex flow-fields such as those encountered in many combustion systems. Liquid droplets (represented by computational parcels) are tracked using the Lagrangian approach wherein the Newton's equation of motion for the discrete particles are integrated explicitly in the Eulerian gas field. The gas phase LES velocity fields are used to estimate the instantaneous gas velocity at the droplet location. Drag effects due to the droplets on the gas phase and the heat transfer between the gas and the liquid phase are explicitly included. Thus, full coupling is achieved between the two phases in the simulation. Validation of the compressible LES-LEM approach is conducted by simulating the flow-field in an operational General Electric Aircraft Engines combustor (LM6000). The results predicted using the proposed approach compares well with the experiments and a conventional (G-equation) thin-flame model. Particle tracking algorithms used in the present study are validated by simulating droplet laden temporal mixing layers. Quantitative and qualitative comparison with the results of spectral DNS exhibits good agreement. Simulations using the current LES-LEM for freely propagating partially premixed flame in a droplet-laden isotropic turbulent field correctly captures the flame structure in the partially premixed flames. Due to the strong spatial variation of equivalence ratio a broad flame similar to a premixed flame is realized. The current
NMR studies of granular media and two-phase flow in porous media
NASA Astrophysics Data System (ADS)
Yang, Xiaoyu
This dissertation describes two experimental studies of a vibrofluidized granular medium and a preliminary study of two-phase fluid flow in a porous medium using Nuclear Magnetic Resonance (NMR). The first study of granular medium is to test a scaling law of the rise in center of mass in a three-dimensional vibrofluidized granular system. Our granular system consisted of mustard seeds vibrated vertically at 40 Hz from 0g to 14g. We used Magnetic Resonance Imaging (MRI) to measure density profile in vibrated direction. We observed that the rise in center of mass scaled as nu 0alpha/Nlbeta with alpha = 1.0 +/- 0.2 and beta = 0.5 +/- 0.1, where nu 0 is the vibration velocity and Nl is the number of layers of grains in the container. A simple theory was proposed to explain the scaling exponents. In the second study we measured both density and velocity information in the same setup of the first study. Pulsed Field Gradient (PFG)-NMR combined with MRI was used to do this measurement. The granular system was fully fluidized at 14.85g 50 Hz with Nl ≤ 4. The velocity distributions at horizontal and vertical direction at different height were measured. The distributions were nearly-Gaussian far from sample bottom and non-Gaussian near sample bottom. Granular temperature profiles were calculated from the velocity distributions. The density and temperature profile were fit to a hydrodynamic theory. The theory agreed with experiments very well. A temperature inversion near top was also observed and explained by additional transport coefficient from granular hydrodynamics. The third study was the preliminary density measurement of invading phase profile in a two-phase flow in porous media. The purpose of this study was to test an invasion percolation with gradient (IPG) theory in two-phase flow of porous media. Two phases are dodecane and water doped with CuSO4. The porous medium was packed glass beads. The front tail width sigma and front width of invading phase were
Studies of Two-Phase Flow Dynamics and Heat Transfer at Reduced Gravity Conditions
NASA Technical Reports Server (NTRS)
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
One-Dimensional, Two-Phase Flow Modeling Toward Interpreting Motor Slag Expulsion Phenomena
NASA Technical Reports Server (NTRS)
Kibbey, Timothy P.
2012-01-01
Aluminum oxide slag accumulation and expulsion was previously shown to be a player in various solid rocket motor phenomena, including the Space Shuttle's Reusable Solid Rocket Motor (RSRM) pressure perturbation, or "blip," and phantom moment. In the latter case, such un ]commanded side accelerations near the end of burn have also been identified in several other motor systems. However, efforts to estimate the mass expelled during a given event have come up short. Either bulk calculations are performed without enough physics present, or multiphase, multidimensional Computational Fluid Dynamic analyses are performed that give a snapshot in time and space but do not always aid in grasping the general principle. One ]dimensional, two ]phase compressible flow calculations yield an analytical result for nozzle flow under certain assumptions. This can be carried further to relate the bulk motor parameters of pressure, thrust, and mass flow rate under the different exhaust conditions driven by the addition of condensed phase mass flow. An unknown parameter is correlated to airflow testing with water injection where mass flow rates and pressure are known. Comparison is also made to full ]scale static test motor data where thrust and pressure changes are known and similar behavior is shown. The end goal is to be able to include the accumulation and flow of slag in internal ballistics predictions. This will allow better prediction of the tailoff when much slag is ejected and of mass retained versus time, believed to be a contributor to the widely-observed "flight knockdown" parameter.
Basic study on an energy conversion system using gas-liquid two-phase flows of magnetic fluid
Okubo, Masaaki; Ishimoto, Jun; Kamiyama, Schinichi.
1994-12-31
The mechanism of the pressure rise in a gas-liquid two-phase pipe flow of magnetic fluid under a nonuniform magnetic field is investigated in detail both theoretically and experimentally. First, governing equations of one-dimensional gas-liquid two-phase magnetic fluid flow are presented and numerically solved. Next, the pressure distribution in a nonuniform magnetic wild region is measured in the cases of two-phase flow, single-phase flow and the stationary state using a new experimental apparatus for the flow system. From the numerical measurement results, the magnitude of the pressure components which contribute to the total driving force is accurately estimated. These results on the pressure distribution will contribute to the development of the new energy conversion system using a gas-liquid two-phase magnetic fluid flow.
Numerical Investigation of Two-Phase Flows With Charged Droplets in Electrostatic Field
NASA Technical Reports Server (NTRS)
Kim, Sang-Wook
1996-01-01
A numerical method to solve two-phase turbulent flows with charged droplets in an electrostatic field is presented. The ensemble-averaged Navier-Stokes equations and the electrostatic potential equation are solved using a finite volume method. The transitional turbulence field is described using multiple-time-scale turbulence equations. The equations of motion of droplets are solved using a Lagrangian particle tracking scheme, and the inter-phase momentum exchange is described by the Particle-In-Cell scheme. The electrostatic force caused by an applied electrical potential is calculated using the electrostatic field obtained by solving a Laplacian equation and the force exerted by charged droplets is calculated using the Coulombic force equation. The method is applied to solve electro-hydrodynamic sprays. The calculated droplet velocity distributions for droplet dispersions occurring in a stagnant surrounding are in good agreement with the measured data. For droplet dispersions occurring in a two-phase flow, the droplet trajectories are influenced by aerodynamic forces, the Coulombic force, and the applied electrostatic potential field.
A consistent projection-based SUPG/PSPG XFEM for incompressible two-phase flows
NASA Astrophysics Data System (ADS)
Liao, Jian-Hui; Zhuang, Zhuo
2012-10-01
In this paper, a consistent projection-based streamline upwind/pressure stabilizing Petrov-Galerkin (SUPG/PSPG) extended finite element method (XFEM) is presented to model incompressible immiscible two-phase flows. As the application of linear elements in SUPG/PSPG schemes gives rise to inconsistency in stabilization terms due to the inability to regenerate the diffusive term from viscous stresses, the numerical accuracy would deteriorate dramatically. To address this issue, projections of convection and pressure gradient terms are constructed and incorporated into the stabilization formulation in our method. This would substantially recover the consistency and free the practitioner from burdensome computations of most items in the residual. Moreover, the XFEM is employed to consider in a convenient way the fluid properties that have interfacial jumps leading to discontinuities in the velocity and pressure fields as well as the projections. A number of numerical examples are analyzed to demonstrate the complete recovery of consistency, the reproduction of interfacial discontinuities and the ability of the proposed projection-based SUPG/PSPG XFEM to model two-phase flows with open and closed interfaces.
Development and validation of an X-ray tomograph for two-phase flow.
Hervieu, Eric; Jouet, Emmanuel; Desbat, Laurent
2002-10-01
This paper describes the development and validation of a high spatial resolution X-ray tomograph designed for the investigation of air-water two-phase flow. The device hardware mainly comprises a 60 keV X-ray source, a detector, and an accurate mechanical bench. Our study concentrated on accurate quantification with emphasis on the reconstruction procedure. As is well known, absorption gradients induce reconstruction artifacts when using standard algorithms based on uniform regularization. In the particular case of two-phase flow in a pipe, this leads to poor measurement accuracy in the vicinity of the walls. To overcome such effects, improved algorithms were developed during this study that involve spatially adaptive regularization methods. Preliminary calibration performed on static phantoms clearly exhibited the benefits of the advanced reconstruction algorithms. A validation procedure was carried out on an air-water bubble column, equipped with an optical probe, which could be translated in order to explore the 80 mm x 80 mm square cross section. Comparisons of local void fraction measurements were performed pixel by pixel. They demonstrate the accuracy improvement induced by the advanced reconstruction algorithms.
Final Report - Advanced Conceptual Models for Unsaturated and Two-Phase Flow in Fractured Rock
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.
Multi-camera PIV of two-phase oscillating sheet flow
NASA Astrophysics Data System (ADS)
Liu, Chang; Kiger, Ken
2016-11-01
We present a multi-camera thin light sheet imaging method to accurately measure dispersed phase concentration and velocity up to optical densities of close to O [1]. The work is an extension of prior single camera methods that utilize particle image characteristics to identify the dispersed phase and infer the effective measurement volume thickness. By introducing multiple camera perspectives, stereo photogrammetry can be combined with the redundancy of information available in the images to provide 1) increased accuracy in determining individual particle locations, and 2) increased reliability in identifying all of the dispersed phase objects. As a byproduct, the velocity of all three components is also available. As an example, this new method is directly applied to oscillating sheet flow conditions. From a single image pair, individual particles are identified and tracked, giving the instantaneous volume concentration and dispersed phase velocity. A median filter method is used to isolate an image composed only of the much smaller tracer particles, and processed to generate a 3-component continuous phase velocity field. Given the concentration and velocities of the two phases, two-phase flow properties such as the sedimentation rate and momentum coupling will be reported.
A Hele-Shaw-Cahn-Hilliard Model for Incompressible Two-Phase Flows with Different Densities
NASA Astrophysics Data System (ADS)
Dedè, Luca; Garcke, Harald; Lam, Kei Fong
2017-07-01
Topology changes in multi-phase fluid flows are difficult to model within a traditional sharp interface theory. Diffuse interface models turn out to be an attractive alternative to model two-phase flows. Based on a Cahn-Hilliard-Navier-Stokes model introduced by Abels et al. (Math Models Methods Appl Sci 22(3):1150013, 2012), which uses a volume-averaged velocity, we derive a diffuse interface model in a Hele-Shaw geometry, which in the case of non-matched densities, simplifies an earlier model of Lee et al. (Phys Fluids 14(2):514-545, 2002). We recover the classical Hele-Shaw model as a sharp interface limit of the diffuse interface model. Furthermore, we show the existence of weak solutions and present several numerical computations including situations with rising bubbles and fingering instabilities.
An Interactive Tool for Discrete Phase Analysis in Two-Phase Flows
NASA Technical Reports Server (NTRS)
Dejong, Frederik J.; Thoren, Stephen J.
1993-01-01
Under a NASA MSFC SBIR Phase 1 effort an interactive software package has been developed for the analysis of discrete (particulate) phase dynamics in two-phase flows in which the discrete phase does not significantly affect the continuous phase. This package contains a Graphical User Interface (based on the X Window system and the Motif tool kit) coupled to a particle tracing program, which allows the user to interactively set up and run a case for which a continuous phase grid and flow field are available. The software has been applied to a solid rocket motor problem, to demonstrate its ease of use and its suitability for problems of engineering interest, and has been delivered to NASA Marshall Space Flight Center.
Switching moving boundary models for two-phase flow evaporators and condensers
NASA Astrophysics Data System (ADS)
Bonilla, Javier; Dormido, Sebastián; Cellier, François E.
2015-03-01
The moving boundary method is an appealing approach for the design, testing and validation of advanced control schemes for evaporators and condensers. When it comes to advanced control strategies, not only accurate but fast dynamic models are required. Moving boundary models are fast low-order dynamic models, and they can describe the dynamic behavior with high accuracy. This paper presents a mathematical formulation based on physical principles for two-phase flow moving boundary evaporator and condenser models which support dynamic switching between all possible flow configurations. The models were implemented in a library using the equation-based object-oriented Modelica language. Several integrity tests in steady-state and transient predictions together with stability tests verified the models. Experimental data from a direct steam generation parabolic-trough solar thermal power plant is used to validate and compare the developed moving boundary models against finite volume models.
Visualization and quantification of two-phase flow in transparent miniature packed beds.
Zhu, Peixi; Papadopoulos, Kyriakos D
2012-10-01
Optical microscopy was used to visualize the flow of two phases [British Petroleum (BP) oil and an aqueous surfactant phase] in confined space, three-dimensional, transparent, natural porous media. The porous media consisted of water-wet cryolite grains packed inside cylindrical, glass microchannels, thus producing microscopic packed beds. Primary drainage of BP oil displacing an aqueous surfactant phase was studied at capillary numbers that varied between 10(-6) and 10(-2). The confinement space had a significant effect on the flow behavior. Phenomena of burst motion and capillary fingering were observed for low capillary numbers due to the domination of capillary forces. It was discovered that breakthrough time and capillary number bear a log-log scale linear relationship, based on which a generalized correlation between oil travel distance x and time t was found empirically.
Two-phase flow of solid hydrogen particles and liquid helium
NASA Astrophysics Data System (ADS)
Xu, J.; Rouelle, A.; Smith, K. M.; Celik, D.; Hussaini, M. Y.; Van Sciver, S. W.
2004-06-01
Atomic hydrogen propellant feed systems may require transporting solid hydrogen particles containing atomic species from storage tanks to the engines using liquid helium as the carrier fluid. In this paper, a three-dimensional two-phase mixture model, along with the standard k- ɛ mixture turbulence model is employed to study the turbulent mixing of the fluid-particle slurry system. Numerical results show that turbulent flow is required to keep the hydrogen particles in suspension, which otherwise form a sliding layer of particles on top of the helium layer. Hydrogen particle concentration profiles in the slurry system are functions of particle size, flow velocity, and influx volume fraction of hydrogen particles. Particle dispersion at different Stokes numbers, different Kolmogorov length scales, and different time scales are discussed.
Two-phase flow in regionally saturated fractured rock near excavations
Geller, J.T.; Doughty, C.; Long, J.C.S.
1994-11-01
Hydrologic characterization for potential nuclear waste repositories relies upon data obtained from testing in excavations. The Simulated Drift Experiment in the Stripa Mine in Sweden, a fractured granitic formation below the water table, investigated excavation effects on hydrologic response. Measured water inflow to the drift at atmospheric pressure was nine times less than the value predicted from the inflow to boreholes with pressure held at 2.7 bars. This flow reduction may be due to dissolved gas that comes out of solution at pressures below 2.7 bars, creating a two-phase regime. To investigate this possibility, theoretical studies of flow through fractures when the water is super-saturated with respect to dissolved gas are carried out, using a simple analytical solution followed by a numerical model which relaxes some of the simplifying assumptions. Laboratory experiments that simulate degassing in transparent fracture replicas are conducted to test the assumptions used in the theoretical studies.
Development of the Two Phase Flow Separator Experiment for a Reduced Gravity Aircraft Flight
NASA Technical Reports Server (NTRS)
Golliher, Eric; Gotti, Daniel; Owens, Jay; Gilkey, Kelly; Pham, Nang; Stehno, Philip
2016-01-01
The recent hardware development and testing of a reduced gravity aircraft flight experiment has provided valuable insights for the future design of the Two Phase Flow Separator Experiment (TPFSE). The TPFSE is scheduled to fly within the Fluids Integration Rack (FIR) aboard the International Space Station (ISS) in 2020. The TPFSE studies the operational limits of gas and liquid separation of passive cyclonic separators. A passive cyclonic separator utilizes only the inertia of the incoming flow to accomplish the liquid-gas separation. Efficient phase separation is critical for environmental control and life support systems, such as recovery of clean water from bioreactors, for long duration human spaceflight missions. The final low gravity aircraft flight took place in December 2015 aboard NASA's C9 airplane.
Effects of two-phase flow on the deflagration of porous energetic materials
Margolis, S.B.; Williams, F.A.
1994-07-01
Theoretical analyses are developed for the multi-phase deflagration of porous energetic solids, such as degraded nitramine propellants, that experience significant gas flow in the solid preheat region and are characterized by the presence of exothermic reactions in a bubbling melt layer at their surfaces. Relative motion between the gas and condensed phases is taken into account in both regions, and expressions for the mass burning rate and other quantities of interest, such as temperature and volume-fraction profiles, are derived by activation-energy asymptotics. The model extends recent work by allowing for gas flow in the unburned solid, and by incorporating pressure effects through the gas-phase equation of state. As a consequence, it is demonstrated how most aspects of the deflagration wave, including its structure, propagation speed and final temperature, depend on the local pressure in the two-phase regions.
Interfacial area and two-phase flow structure development measured by a double-sensor probe
Leung, Waihung; Revankar, S.T.; Ishii, Yoshihiko; Ishii, Mamoru.
1992-06-01
In this report, we studied the local phasic characters of dispersed flow regime both at the entrance and at the fully developed regions. Since the dispersed phase is distributed randomly in the medium and enclosed in relatively small interfaces, the phasic measurement becomes difficult to obtain. Local probe must be made with a miniaturized sensor in order to reduce the interface distortion. The double-sensor resistivity probe has been widely used in local void fraction and interface velocity measurements because the are small in comparison with the interfaces. It has been tested and proved to be an accurate local phasic measurement tool. In these experiments, a double-sensor probe was employed to measure the local void fraction and interface velocity in an air-water system. The test section was flow regime can be determined by visualization. Furthermore, local phasic measurements can be verified by photographic studies. We concentrated our study on the bubbly flow regime only. The local measurements were conducted at two axial locations, L/D = 8 and 60, in which the first measurement represents the entrance region where the flow develops, and the second measurement represents the fully developed flow region where the radial profile does not change as the flow moves along the axial direction. Four liquid flow rates were chosen in combination with four different gas injection rates. The superficial liquid velocities were j{sub t} = 1.0, 0.6,0.4, and 0.1 m/s and superficial gas velocities were j{sub g} = 0.0965, 0.0696, 0.0384, and 0.0192 m/s. These combinations put the two-phase flow well in the bubbly flow regime. In this sequence of phenomenological studies, the local void fraction, interface area concentration, sauter mean diameter, bubble velocity and bubble frequency were measured.
A Two-Phase Solid/Fluid Model for Dense Granular Flows Including Dilatancy Effects
NASA Astrophysics Data System (ADS)
Mangeney, A.; Bouchut, F.; Fernández-Nieto, E. D.; Narbona-Reina, G.; Kone, E. H.
2014-12-01
We propose a thin layer depth-averaged two-phase model to describe solid-fluid mixtures such as debris flows. It describes the velocity of the two phases, the compression/dilatation of the granular media and its interaction with the pore fluid pressure, that itself modifies the friction within the granular phase (Iverson et al., 2010). 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., 2014). In particular, Pitman and Le 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 equations. We close the mixture equations by a weak compressibility relation involving a critical density, or equivalently a critical pressure. Moreover, we relax one boundary condition, making it possible for the fluid to escape the granular media when compression of the granular mass occurs. Furthermore, we introduce second order terms in the equations making it possible to describe the evolution of the pore fluid pressure in response to the compression/dilatation of the granular mass without prescribing an extra ad-hoc equation for the pore pressure. We prove that the energy balance associated with this Jackson closure is dissipative, as well as its thin layer associated model. We present several numerical tests for the 1D case that are compared to the
A Two-Phase Solid/Fluid Model for Dense Granular Flows Including Dilatancy Effects
NASA Astrophysics Data System (ADS)
Mangeney, Anne; Bouchut, Francois; Fernandez-Nieto, Enrique; Narbona-Reina, Gladys
2015-04-01
We propose a thin layer depth-averaged two-phase model to describe solid-fluid mixtures such as debris flows. It describes the velocity of the two phases, the compression/dilatation of the granular media and its interaction with the pore fluid pressure, that itself modifies the friction within the granular phase (Iverson et al., 2010). 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., 2014). In particular, Pitman and Le 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 equations. We close the mixture equations by a weak compressibility relation involving a critical density, or equivalently a critical pressure. Moreover, we relax one boundary condition, making it possible for the fluid to escape the granular media when compression of the granular mass occurs. Furthermore, we introduce second order terms in the equations making it possible to describe the evolution of the pore fluid pressure in response to the compression/dilatation of the granular mass without prescribing an extra ad-hoc equation for the pore pressure. We prove that the energy balance associated with this Jackson closure is dissipative, as well as its thin layer associated model. We present several numerical tests for the 1D case that are compared to the
NASA Technical Reports Server (NTRS)
Balasubramaniam, R.; Rame, E.; Kizito, J.; Kassemi, M.
2006-01-01
The purpose of this report is to provide a summary of state-of-the-art predictions for two-phase flows relevant to Advanced Life Support. We strive to pick out the most used and accepted models for pressure drop and flow regime predictions. The main focus is to identify gaps in predictive capabilities in partial gravity for Lunar and Martian applications. Following a summary of flow regimes and pressure drop correlations for terrestrial and zero gravity, we analyze the fully developed annular gas-liquid flow in a straight cylindrical tube. This flow is amenable to analytical closed form solutions for the flow field and heat transfer. These solutions, valid for partial gravity as well, may be used as baselines and guides to compare experimental measurements. The flow regimes likely to be encountered in the water recovery equipment currently under consideration for space applications are provided in an appendix.
Steam-water two-phase flow in large diameter vertical piping at high pressures and temperatures
Hasanein, H.A.; Kawaji, Masahiro; Chan, A.M.C.; Yoshioka, Yuzuru
1996-08-01
No information on steam/water two-phase flow behavior in large diameter pipes (10 inch or larger) at elevated pressures is available in the open literature. However, there are many applications, in the nuclear, chemical and petroleum industries among others where two-phase flows in large diameter pipes at elevated pressures and temperatures are encountered routinely or under accident scenarios. Experimental data on steam-water two-phase flow in a large diameter (20 inch, 50.08 cm I.D.) vertical pipe at elevated pressures and temperatures (2.8 MPa/230 C--6.4 MPa/280 C) have been obtained. Void fraction, two-phase mass flux, phase and velocity distributions as well as pressure drop along the test pipe have been measured using the Ontario Hydro Technologies (OHT) Pump Test Loop. The void fraction distributions were found to be axially symmetric and nearly flat over a wide range of two-phase flow conditions. The two-phase flow regime could be inferred from the dynamic void fluctuations data. For the 280 C tests, the flow was found to be relatively stable with bubbly flow at low average void fractions and churn turbulent or wispy-annular flow at higher void fractions. At 230 C, the flow became rather oscillatory and slugging was suspected at relatively low voids. It has also been found that the average void fractions in the test section can be determined reasonably accurately using the axial pressure drop data.
Cihan, Abdullah; Birkholzer, Jens; Trevisan, Luca; Bianchi, Marco; Zhou, Quanlin; Illangasekare, Tissa
2014-12-31
During CO_{2} injection and storage in deep reservoirs, the injected CO_{2} enters into an initially brine saturated porous medium, and after the injection stops, natural groundwater flow eventually displaces the injected mobile-phase CO_{2}, leaving behind residual non-wetting fluid. Accurate modeling of two-phase flow processes are needed for predicting fate and transport of injected CO_{2}, evaluating environmental risks and designing more effective storage schemes. The entrapped non-wetting fluid saturation is typically a function of the spatially varying maximum saturation at the end of injection. At the pore-scale, distribution of void sizes and connectivity of void space play a major role for the macroscopic hysteresis behavior and capillary entrapment of wetting and non-wetting fluids. This paper presents development of an approach based on the connectivity of void space for modeling hysteretic capillary pressure-saturation-relative permeability relationships. The new approach uses void-size distribution and a measure of void space connectivity to compute the hysteretic constitutive functions and to predict entrapped fluid phase saturations. Two functions, the drainage connectivity function and the wetting connectivity function, are introduced to characterize connectivity of fluids in void space during drainage and wetting processes. These functions can be estimated through pore-scale simulations in computer-generated porous media or from traditional experimental measurements of primary drainage and main wetting curves. The hysteresis model for saturation-capillary pressure is tested successfully by comparing the model-predicted residual saturation and scanning curves with actual data sets obtained from column experiments found in the literature. A numerical two-phase model simulator with the new hysteresis functions is tested against laboratory experiments conducted in a quasi-two-dimensional flow cell (91.4cm×5.6cm×61cm
Cihan, Abdullah; Birkholzer, Jens; Trevisan, Luca; ...
2014-12-31
During CO2 injection and storage in deep reservoirs, the injected CO2 enters into an initially brine saturated porous medium, and after the injection stops, natural groundwater flow eventually displaces the injected mobile-phase CO2, leaving behind residual non-wetting fluid. Accurate modeling of two-phase flow processes are needed for predicting fate and transport of injected CO2, evaluating environmental risks and designing more effective storage schemes. The entrapped non-wetting fluid saturation is typically a function of the spatially varying maximum saturation at the end of injection. At the pore-scale, distribution of void sizes and connectivity of void space play a major role formore » the macroscopic hysteresis behavior and capillary entrapment of wetting and non-wetting fluids. This paper presents development of an approach based on the connectivity of void space for modeling hysteretic capillary pressure-saturation-relative permeability relationships. The new approach uses void-size distribution and a measure of void space connectivity to compute the hysteretic constitutive functions and to predict entrapped fluid phase saturations. Two functions, the drainage connectivity function and the wetting connectivity function, are introduced to characterize connectivity of fluids in void space during drainage and wetting processes. These functions can be estimated through pore-scale simulations in computer-generated porous media or from traditional experimental measurements of primary drainage and main wetting curves. The hysteresis model for saturation-capillary pressure is tested successfully by comparing the model-predicted residual saturation and scanning curves with actual data sets obtained from column experiments found in the literature. A numerical two-phase model simulator with the new hysteresis functions is tested against laboratory experiments conducted in a quasi-two-dimensional flow cell (91.4cm×5.6cm×61cm), packed with homogeneous and
Adaptive Multi-Scale Pore Network Method for Two-Phase Flow in Porous Media
NASA Astrophysics Data System (ADS)
Meyer, D. W.; Khayrat, K.; Jenny, P.
2015-12-01
Dynamic pore network simulators are important tools in studying macroscopic quantities in two-phase flow through porous media. However, these simulators have a time complexity of order N2 for N pore bodies, which limits their usage to small domains. Quasi-static pore network simulators, which assume capillary dominated flow, are more efficient with a time complexity of order N log(N), but are unable to capture phenomena caused by viscous effects such as viscous fingering and stable displacement. It has been experimentally observed that, in several flow scenarios, capillary forces are dominant at the pore scale and viscous forces at larger scales. In order to take advantage of this behaviour and to reduce the time complexity of existing dynamic pore network simulators, we propose a multi-scale pore-network method for two phase flow. In our solution algorithm, the pore network is first divided into smaller subnetworks. The algorithm to advance the fluid interfaces within each subnetwork consists of three steps: 1) The saturation rate of each subnetwork is obtained by solving a two-phase meso-scale mass balance equation over the domain of subnetworks. Here, a multi-point flux scheme is used. 2) Depending on the local capillary number computed in the subnetwork, either an invasion percolation algorithm or a dynamic network algorithm is used to locally advance the fluid-fluid interfaces within each subnetwork until a new saturation value is matched. 3) The transmissibilities for the meso-scale equation are updated based on the updated fluid configurations in each subnetwork. For this purpose the methodoloy of the existing multi-scale finite volume (MSFV) method is employed. An important feature of the multi-scale pore-network method is that it maintains consistency of both fluid occupancy and fluxes at subnetwork interfaces. Viscous effects such as viscous fingering (see figure) can be captured at a decreased computational cost compared to dynamic pore network
Gas-liquid two phase flow through a vertical 90 elbow bend
Spedding, P.L.; Benard, E.
2007-07-15
Pressure drop data are reported for two phase air-water flow through a vertical to horizontal 90 elbow bend set in 0.026 m i.d. pipe. The pressure drop in the vertical inlet tangent showed some significant differences to that found for straight vertical pipe. This was caused by the elbow bend partially choking the inflow resulting in a build-up of pressure and liquid in the vertical inlet riser and differences in the structure of the flow regimes when compared to the straight vertical pipe. The horizontal outlet tangent by contrast gave data in general agreement with literature even to exhibiting a drag reduction region at low liquid rates and gas velocities between 1 and 2 m s{sup -1}. The elbow bend pressure drop was best correlated in terms of l{sub e}/d determined using the actual pressure loss in the inlet vertical riser. The data showed a general increase with fluid rates that tapered off at high fluid rates and exhibited a negative pressure region at low rates. The latter was attributed to the flow being smoothly accommodated by the bend when it passed from slug flow in the riser to smooth stratified flow in the outlet tangent. A general correlation was presented for the elbow bend pressure drop in terms of total Reynolds numbers. A modified Lockhart-Martinelli model gave prediction of the data. (author)
A novel gravity-induced flow transition in two-phase fluids
NASA Astrophysics Data System (ADS)
d'Avila, M. A.; Shapley, N. C.; Walton, J. H.; Phillips, R. J.; Powell, R. L.; Dungan, S. R.
2006-10-01
Experimental results are reported that show a gravity-induced flow transition in well-mixed suspensions and emulsions, even when the buoyancy-driven velocity of isolated drops or particles is several orders of magnitude smaller than the imposed velocity. The experiments were conducted with emulsions of isooctane in water and suspensions of polymethyl-methacrylate particles in water. Both the drop and particle diameters were approximately 3-5μm, and concentrations of the dispersed phases ranged from dilute (2%) to concentrated (40%). The two-phase fluids were confined to a horizontal, concentric-cylinder apparatus in which the outer cylinder was rotated, and the velocity profiles were measured by nuclear magnetic resonance imaging. The results show that the flow transition is relatively insensitive to the volume fraction of the dispersed phase. The flow transition occurs because, although the buoyancy-driven velocity is relatively small on the length scale of the particle or drop dimension, the flow itself induces a slight variation in the suspension concentration and, hence, density. Although only on the order of 10-4g/cm3, this density difference spans a macroscopic length scale, making the buoyancy effect competitive with the imposed flow. These arguments yield a dimensionless parameter that predicts very closely the nonequilibrium phase diagram generated by the experiments.
Two-phase flow in complex geometries: A diffuse domain approach
Aland, S.; Voigt, A.
2011-01-01
We present a new method for simulating two-phase flows in complex geometries, taking into account contact lines separating immiscible incompressible components. We combine the diffuse domain method for solving PDEs in complex geometries with the diffuse-interface (phase-field) method for simulating multiphase flows. In this approach, the complex geometry is described implicitly by introducing a new phase-field variable, which is a smooth approximation of the characteristic function of the complex domain. The fluid and component concentration equations are reformulated and solved in larger regular domain with the boundary conditions being implicitly modeled using source terms. The method is straightforward to implement using standard software packages; we use adaptive finite elements here. We present numerical examples demonstrating the effectiveness of the algorithm. We simulate multiphase flow in a driven cavity on an extended domain and find very good agreement with results obtained by solving the equations and boundary conditions in the original domain. We then consider successively more complex geometries and simulate a droplet sliding down a rippled ramp in 2D and 3D, a droplet flowing through a Y-junction in a microfluidic network and finally chaotic mixing in a droplet flowing through a winding, serpentine channel. The latter example actually incorporates two different diffuse domains: one describes the evolving droplet where mixing occurs while the other describes the channel. PMID:21918638
Two-phase electro-hydrodynamic flow modeling by a conservative level set model.
Lin, Yuan
2013-03-01
The principles of electro-hydrodynamic (EHD) flow have been known for more than a century and have been adopted for various industrial applications, for example, fluid mixing and demixing. Analytical solutions of such EHD flow only exist in a limited number of scenarios, for example, predicting a small deformation of a single droplet in a uniform electric field. Numerical modeling of such phenomena can provide significant insights about EHDs multiphase flows. During the last decade, many numerical results have been reported to provide novel and useful tools of studying the multiphase EHD flow. Based on a conservative level set method, the proposed model is able to simulate large deformations of a droplet by a steady electric field, which is beyond the region of theoretic prediction. The model is validated for both leaky dielectrics and perfect dielectrics, and is found to be in excellent agreement with existing analytical solutions and numerical studies in the literature. Furthermore, simulations of the deformation of a water droplet in decyl alcohol in a steady electric field match better with published experimental data than the theoretical prediction for large deformations. Therefore the proposed model can serve as a practical and accurate tool for simulating two-phase EHD flow.
Behavior of Drag Disc Turbine Transducers in Steady-State Two-Phase Flow
NASA Astrophysics Data System (ADS)
Solbrig, C. W.; Reimann, J.
1980-08-01
Many experiments being conducted to investigate the hypothesized loss-of-coolant accident (LOCA) in nuclear power plants involve the measurement of two-phase flow. This paper describes an experiment conducted to determine the behavior of a drag-disc turbine transducer (DTT) in a high pressure, high temperature, steam-water steady state environment. DTTs have been used extensively to measure mass flow rates in the Loss-of-Fluid-Test (LOFT) experiments. Drag discs and turbines have been used in many other safety related facilities. However, the performance of these instruments is highly dependent on flow regime and void fraction and this dependence makes data analysis difficult. Experiments conducted in separated flow are described in this paper. The results show the measured mass flow rates can be corrected if a three-beam gamma densitometer is available, if the calculated density ratio correction is less than three, and if the velocity measured by the turbine is greater than 2 m/ s. The results also suggest that the turbine and drag disc measure local mass average quantities averaged over the area of the DTT.
Flow and Heat Transfer Characteristics in a Two-Phase Loop Thermosyphon
NASA Astrophysics Data System (ADS)
Imura, Hideaki; Saito, Yuji; Katsumata, Yoshikazu
A two-phase loop thermosyphon transports thermal energy by natural convective circulation without any external power supply. Therefore, it has been paid attention as a heat transfer equipment for saving energy. A basic investigation of flow and heat transfer characteristics in the thermosyphon was performed both experimentally and theoretically. The circulation flow rate, pressure and temperature distributions along the loop, and heat transfer coefficients in the heated section were measured using water, ethanol and Freon 113 as the working liquids. And, the effects of the heat input and liquid physical properties on the flow and heat transfer characteristics were examined. In the theoretical study, the circulation flow rate was calculated from the force balance between the driving force arising from density differences and the pressure drop in the loop. The comparison of the calculated with experimental results was made concerning the circulation flow rate and pressure and temperature distributions. For water and ethanol, the comparison presented the considerably close agreement. But, for Freon 113, the agreement was insufficient and further detailed investigation is needed.
NASA Astrophysics Data System (ADS)
Li, R. N.; Y Wang, H.; Han, W.; Ma, W.; Shen, Z. J.
2013-12-01
The screw centrifugal pump is used as an object, and the unsteady numerical simulation of solid-liquid two-phase flow is carried out under different flow rate conditions in one circle by choosing the two-phase flow of sand and water as medium, using the software FLUENT based on the URANS equations, combining with sliding mesh method, and choosing the Mixture multiphase flow model and the SIMPLE algorithm. The results show that, with the flow rate increasing, the change trends for the pressure on volute outlet are almost constant, the fluctuation trends of the impeller axial force have a little change, the pressure and the axial force turn to decrease on the whole, the radial force gradually increases when the impeller maximum radius passes by half a cycle near the volute outlet, and the radial force gradually decreases when the maximum radius passes by the other half a cycle in a rotation cycle. The distributions of the solid particles are very uneven under a small flow rate condition on the face. The solid particles under a big flow rate condition are distributed more evenly than the ones under a small flow rate condition on the back. The theoretical basis and reference are provided for improving its working performance.
NASA Astrophysics Data System (ADS)
Xing, Dianchuan; Yan, Changqi; Sun, Licheng; Wang, Yang
2013-07-01
Effects of rolling motion on single-phase and two-phase flow resistance were compared experimentally under ambient temperature and pressure. In the single-phase flow experiments, the different pump head was obtained by a variable speed electromotor, and the flow rate was adjusted combining with a regulating valve. However, for the two-phase pressure drop measurements, the pump delivering water operated with an invariable pressure head of 48m, in order to neglect the effect of pump head on flow fluctuation. The results indicated that effects of rolling motion on single-phase flow resistance depend on the pump head. The fluctuation amplitude of flow rate and frictional pressure drop decreases rapidly as the pump head increases, finally, the flow will tend to be steady if the pump head dramatically exceeds the additional pressure drop. Different from the case of single-phase flow, transient frictional pressure drop of two-phase flow fluctuates synchronously with the rolling motion when liquid Reynolds number is less than 1400, whereas keeps a stable steady state without obvious oscillation for other cases. The fluctuation amplitude is independent of rolling period and amplitude and decreases with the increase of flow rate. The inclination angle and phase interface distribution is taken into account in analyzing the influence of rolling motion on two-phase flow resistance. Comparing with the vertical condition, rolling motion nearly has no effects on time-averaged frictional resistance for both the single-phase and two-phase flow.
Two-phase flow instability and dryout in parallel channels in natural circulation
Duffey, R.B.; Rohatgi, U.S.; Hughes, E.D.
1993-06-01
The unique feature of parallel channel flows is that the pressure drop or driving head for the flow is maintained constant across any given channel by the flow in all the others, or by having a large downcomer or bypass in a natural circulation loop. This boundary condition is common in all heat exchangers, reactor cores and boilers, it is well known that the two-phase flow in parallel channels can exhibit both so-called static and dynamic instability. This leads to the question of the separability of the flow and pressure drop boundary conditions in the study of stability and dryout. For the areas of practical interest, the flow can be considered as incompressible. The dynamic instability is characterized by density (kinematic) or continuity waves, and the static instability by inertial (pressure drop) or manometric escalations. The static has been considered to be the zero-frequency or lowest mode of the dynamic case. We briefly review the status of the existing literature on both parallel channel static and dynamic instability, and the latest developments in theory and experiment. The difference between the two derivations lies in the retention of the time-dependent terms in the conservation equations. The effects and impact of design options are also discussed. Since dryout in parallel systems follows instability, it has been traditional to determine the dryout power for a parallel channel by testing a single channel with a given (inlet) flow boundary condition without particular regard for the pressure drop. Thus all modern dryout correlations are based on constant or fixed flow tests, a so-called hard inlet, and subchannel and multiple bundle effects are corrected for separately. We review the thinking that lead to this approach, and suggest that for all multiple channel and natural circulation systems close attention should be paid to the actual (untested) pressure drop conditions. A conceptual formulation is suggested as a basis for discussion.
Le Chenadec, Vincent; Pitsch, Heinz
2013-09-15
This paper presents a novel approach for solving the conservative form of the incompressible two-phase Navier–Stokes equations. In order to overcome the numerical instability induced by the potentially large density ratio encountered across the interface, the proposed method includes a Volume-of-Fluid type integration of the convective momentum transport, a monotonicity preserving momentum rescaling, and a consistent and conservative Ghost Fluid projection that includes surface tension effects. The numerical dissipation inherent in the Volume-of-Fluid treatment of the convective transport is localized in the interface vicinity, enabling the use of a kinetic energy conserving discretization away from the singularity. Two- and three-dimensional tests are presented, and the solutions shown to remain accurate at arbitrary density ratios. The proposed method is then successfully used to perform the detailed simulation of a round water jet emerging in quiescent air, therefore suggesting the applicability of the proposed algorithm to the computation of realistic turbulent atomization.
Study of colloids transport during two-phase flow using a novel polydimethylsiloxane micro-model.
Zhang, Qiulan; Karadimitriou, N K; Hassanizadeh, S M; Kleingeld, P J; Imhof, A
2013-07-01
As a representation of a porous medium, a closed micro-fluidic device made of polydimethylsiloxane (PDMS), with uniform wettability and stable hydrophobic properties, was designed and fabricated. A flow network, with a mean pore size of 30 μm, was formed in a PDMS slab, covering an area of 1 mm × 10 mm. The PDMS slab was covered and bonded with a 120-μm-thick glass plate to seal the model. The glass plate was first spin-coated with a thin layer, roughly 10 μm, of PDMS. The micro-model was treated with silane in order to make it uniformly and stably hydrophobic. Fluorescent particles of 300 μm in diameter were used as colloids. It is known that more removal of colloids occurs under unsaturated conditions, compared to saturated flow in soil. At the same time, the change of saturation has been observed to cause remobilization of attached colloids. The mechanisms for these phenomena are not well understood. This is the first time that a closed micro-model, made of PDMS with uniform and stable wettability, has been used in combination with confocal microscopy to study colloid transport under transient two-phase flow conditions. With confocal microscopy, the movement of fluorescent particles and flow of two liquids within the pores can be studied. One can focus at different depths within the pores and thus determine where the particles exactly are. Thus, remobilization of attached colloids by moving fluid-fluid interfaces was visualized. In order to allow for the deposition and subsequent remobilization of colloids during two-phase flow, three micro-channels for the injection of liquids with and without colloids were constructed. An outlet channel was designed where effluent concentration breakthrough curves can be quantified by measuring the fluorescence intensity. A peak concentration also indicated in the breakthrough curve with the drainage event. The acquired images and breakthrough curve successfully confirmed the utility of the combination of such a PDMS
Gamma-ray CT from incomplete projections for two-phase pipe flow
NASA Astrophysics Data System (ADS)
Xin, S.; Wang, H. X.
2017-02-01
A low-energy low-dose γ-ray computed tomography (CT) system used in the gas-liquid two-phase pipe flow measurement has been studied at Tianjin University in recent years. The γ-ray CT system, having a third-generation X-ray CT scanning configuration, is comprised of one 300mCi 241Am source and 17 CdZnTe detector units and achieves a spatial image resolution of about 7 mm. It is primarily intended to measure the two-phase pipe flow and provide improvement suggestions for industrial CT system. Recently we improve the design for image reconstruction from incomplete projection to optimize the scanning parameters and reduce the radiation dose. First, tomographic problem from incomplete projections is briefly described. Next, a system structure and a hardware circuit design are listed and explained, especially on time parameter setting of the pulse shaper. And then a detailed system analysis is provided in Section II, mainly focusing on spatial resolution, temporal resolution, system noise, and imaging algorithm. Finally, we carry on necessary static and dynamic experiments in a full scan (360°) and two sets of partial scan reconstruction tests to determine the feasibility of this γ-ray CT system for reconstructing the images from insufficient projections. And based on an A-variable algebraic reconstruction technique method, a specially designed algorithm, we evaluate the system performance and noise level of this CT system working quantitatively and qualitatively. Results of dynamic test indicate that the acceptable results can be acquired using a multi-source γ-ray CT system with the same parameters when the flow rate is less than 0.04 m/s and the imaging speed is slower than 33 frames/s.
Optical Measurement of Mass Flow of a Two-Phase Fluid
NASA Technical Reports Server (NTRS)
Wiley, John; Pedersen, Kevin; Koman, Valentin; Gregory, Don
2008-01-01
An optoelectronic system utilizes wavelength-dependent scattering of light for measuring the density and mass flow of a two-phase fluid in a pipe. The apparatus was invented for original use in measuring the mass flow of a two-phase cryogenic fluid (e.g., liquid hydrogen containing bubbles of hydrogen gas), but underlying principles of operation can readily be adapted to non-cryogenic two-phase fluids. The system (see figure) includes a laser module, which contains two or more laser diodes, each operating at a different wavelength. The laser module also contains beam splitters that combine the beams at the various wavelengths so as to produce two output beams, each containing all of the wavelengths. One of the multiwavelength output beams is sent, via a multimode fiberoptic cable, to a transmitting optical coupler. The other multiwavelength output beam is sent, via another multimode fiber-optic cable, to a reference detector module, wherein fiber-optic splitters split the light into several multiwavelength beams, each going to a photodiode having a spectral response that is known and that differs from the spectral responses of the other photodiodes. The outputs of these photodiodes are digitized and fed to a processor, which executes an algorithm that utilizes the known spectral responses to convert the photodiode outputs to obtain reference laser-power levels for the various wavelengths. The transmitting optical coupler is mounted in (and sealed to) a hole in the pipe and is oriented at a slant with respect to the axis of the pipe. The transmitting optical coupler contains a collimating lens and a cylindrical lens that form the light emerging from the end of the fiber-optic cable into a fan-shaped beam in a meridional plane of the pipe. Receiving optical couplers similar to the transmitting optical couplers are mounted in the same meridional plane at various longitudinal positions on the opposite side of the pipe, approximately facing the transmitting optical
Thermal effects in two-phase flow through face seals. Ph.D. Thesis
NASA Technical Reports Server (NTRS)
Basu, Prithwish
1988-01-01
When liquid is sealed at high temperature, it flashes inside the seal due to pressure drop and/or viscous heat dissipation. Two-phase seals generally exhibit more erratic behavior than their single phase counterparts. Thermal effects, which are often neglected in single phase seal analyses, play an important role in determining seal behavior under two-phase operation. It is necessary to consider the heat generation due to viscous shear, conduction into the seal rings and convection with the leakage flow. Analytical models developed work reasonably well at the two extremes - for low leakage rates when convection is neglected and for higher leakage rates when conduction is neglected. A preliminary model, known as the Film Coefficient Model, is presented which considers conduction and convection both, and allows continuous boiling over an extended region unlike the previous low-leakage rate model which neglects convection and always forces a discrete boiling interface. Another simplified, semi-analytical model, based on the assumption of isothermal conditions along the seal interafce, has been developed for low leakage rates. The Film Coefficient Model may be used for more accurate and realistic description.
Interface-capturing lattice Boltzmann equation model for two-phase flows
NASA Astrophysics Data System (ADS)
Lou, Qin; Guo, Zhaoli
2015-01-01
In this work, an interface-capturing lattice Boltzmann equation (LBE) model is proposed for two-phase flows. In the model, a Lax-Wendroff propagation scheme and a properly chosen equilibrium distribution function are employed. The Lax-Wendroff scheme is used to provide an adjustable Courant-Friedrichs-Lewy (CFL) number, and the equilibrium distribution is presented to remove the dependence of the relaxation time on the CFL number. As a result, the interface can be captured accurately by decreasing the CFL number. A theoretical expression is derived for the chemical potential gradient by solving the LBE directly for a two-phase system with a flat interface. The result shows that the gradient of the chemical potential is proportional to the square of the CFL number, which explains why the proposed model is able to capture the interface naturally with a small CFL number, and why large interface error exists in the standard LBE model. Numerical tests, including a one-dimensional flat interface problem, a two-dimensional circular droplet problem, and a three-dimensional spherical droplet problem, demonstrate that the proposed LBE model performs well and can capture a sharp interface with a suitable CFL number.
Interface-capturing lattice Boltzmann equation model for two-phase flows.
Lou, Qin; Guo, Zhaoli
2015-01-01
In this work, an interface-capturing lattice Boltzmann equation (LBE) model is proposed for two-phase flows. In the model, a Lax-Wendroff propagation scheme and a properly chosen equilibrium distribution function are employed. The Lax-Wendroff scheme is used to provide an adjustable Courant-Friedrichs-Lewy (CFL) number, and the equilibrium distribution is presented to remove the dependence of the relaxation time on the CFL number. As a result, the interface can be captured accurately by decreasing the CFL number. A theoretical expression is derived for the chemical potential gradient by solving the LBE directly for a two-phase system with a flat interface. The result shows that the gradient of the chemical potential is proportional to the square of the CFL number, which explains why the proposed model is able to capture the interface naturally with a small CFL number, and why large interface error exists in the standard LBE model. Numerical tests, including a one-dimensional flat interface problem, a two-dimensional circular droplet problem, and a three-dimensional spherical droplet problem, demonstrate that the proposed LBE model performs well and can capture a sharp interface with a suitable CFL number.
Gradient Augmented Level Set Method for Two Phase Flow Simulations with Phase Change
NASA Astrophysics Data System (ADS)
Anumolu, C. R. Lakshman; Trujillo, Mario F.
2016-11-01
A sharp interface capturing approach is presented for two-phase flow simulations with phase change. The Gradient Augmented Levelset method is coupled with the two-phase momentum and energy equations to advect the liquid-gas interface and predict heat transfer with phase change. The Ghost Fluid Method (GFM) is adopted for velocity to discretize the advection and diffusion terms in the interfacial region. Furthermore, the GFM is employed to treat the discontinuity in the stress tensor, velocity, and temperature gradient yielding an accurate treatment in handling jump conditions. Thermal convection and diffusion terms are approximated by explicitly identifying the interface location, resulting in a sharp treatment for the energy solution. This sharp treatment is extended to estimate the interfacial mass transfer rate. At the computational cell, a d-cubic Hermite interpolating polynomial is employed to describe the interface location, which is locally fourth-order accurate. This extent of subgrid level description provides an accurate methodology for treating various interfacial processes with a high degree of sharpness. The ability to predict the interface and temperature evolutions accurately is illustrated by comparing numerical results with existing 1D to 3D analytical solutions.
Metal cooldown, flow instability, and heat transfer in two-phase hydrogen flow
NASA Technical Reports Server (NTRS)
Manson, L.; Miller, W. S.
1970-01-01
Studies of the properties of five metals with varying tube-wall thickness, with or without and internal coating of trifluorochloroethylene polymer, show that wall characteristics influence flow stability, affect heat transfer coefficients, and influence the transition point from dry- to wet-wall flow.
A simplified approach for the computation of steady two-phase flow in inverted siphons.
Diogo, A Freire; Oliveira, Maria C
2016-01-15
Hydraulic, sanitary, and sulfide control conditions of inverted siphons, particularly in large wastewater systems, can be substantially improved by continuous air injection in the base of the inclined rising branch. This paper presents a simplified approach that was developed for the two-phase flow of the rising branch using the energy equation for a steady pipe flow, based on the average fluid fraction, observed slippage between phases, and isothermal assumption. As in a conventional siphon design, open channel steady uniform flow is assumed in inlet and outlet chambers, corresponding to the wastewater hydraulic characteristics in the upstream and downstream sewers, and the descending branch operates in steady uniform single-phase pipe flow. The proposed approach is tested and compared with data obtained in an experimental siphon setup with two plastic barrels of different diameters operating separately as in a single-barrel siphon. Although the formulations developed are very simple, the results show a good adjustment for the set of the parameters used and conditions tested and are promising mainly for sanitary siphons with relatively moderate heights of the ascending branch.
Simulation of incompressible two-phase flow in porous media with large timesteps
NASA Astrophysics Data System (ADS)
Cogswell, Daniel A.; Szulczewski, Michael L.
2017-09-01
Multiphase flow in porous media occurs in several disciplines including petroleum reservoir engineering, petroleum systems' analysis, and CO2 sequestration. While simulations often use a fully implicit discretization to increase the time step size, restrictions on the time step often exist due to non-convergence of the nonlinear solver (e.g. Newton's method). Here this problem is addressed for the Buckley-Leverett equations, which model incompressible, immiscible, two-phase flow with no capillary potential. The equations are recast as a gradient flow using the phase-field method, and a convex energy splitting scheme is applied to enable large timesteps, even for high degrees of heterogeneity in permeability and viscosity. By using the phase-field formulation as a homotopy map, the underlying hyperbolic flow equations can be solved with large timesteps. For a heterogeneous test problem, the new homotopy method allows the timestep to be increased by more than six orders of magnitude relative to the unmodified equations while maintaining convergence.
A combined experimental and theoretical study of supercooling by two-phase mist flows
Yang Zhihua.
1991-01-01
A combined experimental and theoretical study of cooling enhancement by mist flow was performed for a square channel with a smooth wall. A new method is proposed for the turbulent deposition of droplets from two-phase mist flow into the wall of the channel. The proposed analytical model shows satisfactory agreement with observations from an experimental measurement using a particle-sizing two-dimensional reference-model laser-Doppler anemometry technique. Supercooling is defined as the simultaneous attainment of high heat flux and a low temperature of a surface to be cooled. Surface cooling is by evaporation from the exposed side of the film. The film is maintained by the continuous deposition of a stream of turbulent mist. An analytical model is provided for the heat-transfer enhancement coefficient due to mist supercooling. Also, experiments were carried out to investigate cooling enhancement. A substantial supercooling by mist flow is reported. The effects on supercooling of flow rate, droplet concentration and size, and wall heat flux are also reported.
Migration of rigid particles in two-phase shear flow of viscoelastic fluids
NASA Astrophysics Data System (ADS)
Anderson, Patrick; Jaensson, Nick; Hulsen, Martien
2015-11-01
In the Stokes regime, non-Brownian, rigid particles in a shear flow will not migrate across streamlines if the fluid is Newtonian. In viscoelastic fluids, however, particles will migrate across streamlines away from areas of higher elastic stresses, e.g. towards the outer cylinder in a wide-gap Couette flow. This migration is believed to be due to a difference in normal stresses. We simulate the two-phase case where this difference in normal stresses is not due to the flow field, but rather due to the properties of the fluids. We apply the diffuse-interface model for the interface between the two fluids, which can naturally handle a changing topology of the interface, e.g. during particle adsorption. Furthermore, the diffuse-interface model includes an accurate description of surface tension and can be used for a moving contact line. A sharp interface is assumed between the particles and the fluids. Initially, a particle is placed close to an interface of two fluids with different viscoelastic properties in a shear flow. We show that based on the properties of the fluids and the interfacial tension, four regimes can be defined: 1) migration away from the interface, 2) halted migration towards the interface, 3) adsorption of the particle at the interface and 4) penetration of the particle into the other fluid. This research forms part of the research programme of the Dutch Polymer Institute (DPI), Project #746.
Two-phase flow research using the DC-9/KC-135 apparatus
NASA Technical Reports Server (NTRS)
McQuillen, John B.; Neumann, Eric S.; Shoemaker, J. Michael
1996-01-01
Low-gravity gas-liquid flow research can be conducted aboard the NASA Lewis Research Center DC-9 or the Johnson Space Center KC-135. Air and water solutions serve as the test liquids in cylindrical test sections with constant or variable inner diameters of approximately 2.54 cm and lengths of up to 3.0 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 at data rates of up to 1000 Hz throughout the 20-sec duration of the experiment. Flow is visualized with a high-speed video system. In addition, the apparatus has a heat-transfer capability whereby sensible heat is transferred between the test-section wall and a subcooled liquid phase so that the heat-transfer characteristics of gas-liquid two-phase flows can be determined.
Numerical Simulation of Two-phase flow with Phase Change Using the Level-set Method
NASA Astrophysics Data System (ADS)
Li, Hongying; Lou, Jing; Pan, Lunsheng; Yap, Yitfatt
2016-11-01
Multiphase flow with phase change is widely encountered in many engineering applications. A distinct feature involves in these applications is the phase transition from one phase to another due to the non-uniform temperature distribution. Such kind of process generally releases or absorbs large amount of energy with mass transfer happened simultaneously. It demands great cautions occasionally such as the high pressure due to evaporation. This article presents a numerical model for simulation of two-fluid flow with phase change problem. In these two fluids, one of them changes its state due to phase change. Such a problem then involves two substances with three phases as well as two different interfaces, i.e. the interface between two substances and the interface of one substance between its two phases. Two level-set functions are used to capture the two interfaces in the current problem. The current model is validated against one-dimensional and two-dimensional liquid evaporation. With the code validated, it is applied to different phase change problems including (1) a falling evaporating droplet and the rising of one bubble and (2) two-fluid stratified flow with solidification of one fluid. Comparisons on the bubble and droplet topologies, flow and temperature fields are made for the first case between the falling evaporating droplet and the falling droplet without evaporation. For the second demonstration case, the effect of the superheated temperature on the solidification process is investigated.
The stability of two-phase flow over a swept-wing
NASA Technical Reports Server (NTRS)
Coward, Adrian; Hall, Philip
1994-01-01
We use numerical and asymptotic techniques to study the stability of a two-phase air/water flow above a flat porous plate. This flow is a model of the boundary layer which forms on a yawed cylinder and can be used as a useful approximation to the air flow over swept wings during heavy rainfall. We show that the interface between the water and air layers can significantly destabilize the flow, leading to traveling wave disturbances which move along the attachment line. This instability occurs for lower Reynolds numbers than in the case of the absence of a water layer. We also investigate the instability of inviscid stationary modes. We calculate the effective wavenumber and orientation of the stationary disturbance when the fluids have identical physical properties. Using perturbation methods we obtain corrections due to a small stratification in viscosity, thus quantifying the interfacial effects. Our analytical results are in agreement with the numerical solution which we obtain for arbitrary fluid properties.
Lateral Mixing Mechanisms in Vertical and Horizontal Interconnected Subchannel Two-Phase Flows
Gencay, Sarman; Teyssedou, Alberto; Tye, Peter
2002-05-15
A lateral mixing model based on equal volume exchange between two laterally interconnected subchannels is presented. The following mixing mechanisms are taken into account in this model: (a) diversion cross flow, caused by the lateral pressure difference between adjacent subchannels; (b) turbulent void diffusion, which is governed by the lateral void fraction difference between the subchannels; (c) void drift, responsible for the tendency of the vapor phase to drift toward unobstructed regions; and (d) buoyancy drift, which takes into account the effect of gravity in horizontal flows. Experimental two-phase air-water data obtained using two test sections having different geometries and orientations are used to determine the diffusion coefficients required by the mixing model. Under the absence of diversion crossflow, i.e., negligible lateral pressure difference between the subchannels, it is observed that the diffusion coefficient increases with increasing average void fraction in the subchannels. Moreover, for vertical flows turbulent void diffusion seems to be considerably affected by the geometry of the subchannels. For horizontal flows under nonsymmetric inlet void fraction conditions, even though the interconnected subchannels have the same geometry, different turbulent void diffusion and void drift coefficients are required to satisfy the conditions of hydrodynamic equilibrium. In the present study this condition is achieved by introducing a new void drift coefficient expressed as a correction term applied to the turbulent void drift term.
PTV implementation on two-phase flow in a forced impinging jet
NASA Astrophysics Data System (ADS)
Mulinti, Rahul; Kiger, Kenneth
2011-11-01
Two-phase flow experiments have been conducted to predict particle suspension and sedimentation within coupled particle-laden flows relevant to rotorcraft brownout conditions. A hybrid PIV/PTV technique has been implemented to improve the performance in high concentration regions, while still retaining the flexibility inherent to PTV to resolve multi-valued velocity displacements within a given interrogation region. These processing tools have been optimized and their reliability has been validated using synthetic particle images in a prescribed Taylor-Green vortex flow model. The parametric space of investigation included particle image density, Stokes number and image delay times. Experiments have been conducted to study the interaction of a mobile sediment bed with characteristic flow structures similar to those within a rotor wake. The mobilization conditions and wall-normal flux of particulates by the vortex-wall interaction will be reported for different particle size classes, and are correlated to the local vortex conditions such as vortex decay and its subsequent three dimensionalization. The effect of turbulent coupling between the particle and fluid momentum, as based on a point-particle drag law valid for dilute concentrations of particles has been examined. Work supported by AFOSR under grant FA9550-08-1-0406.
Condensation of Forced Convection Two-Phase Flow in a Miniature Tube
NASA Technical Reports Server (NTRS)
Begg, E.; Faghri, A.; Krustalev, D.
1999-01-01
A physical/mathematical model of annular film condensation at the inlet of a miniature tube has been developed. In the model, the liquid flow is coupled with the vapor flow along the liquid-vapor interface through the interfacial temperature, heat flux, shear stress, and pressure jump conditions due to surface tension effects. The model predicts the shape of the liquid-vapor interface along the condenser and leads to the conclusion that there is complete condensation at a certain distance from the condenser inlet. The numerical results show that complete condensation of the incoming vapor is possible at comparatively low heat loads and that this is a special case of a more general condensation regime with two-phase bubbly flow downstream of the initial annular film condensation region. Observations from the flow visualization experiment confirm the existence and qualitative features of annular film condensation leading to the complete condensation phenomenon in a small diameter (3.25 mm) circular tube condenser.
Experimental Study of Two Phase Flow Behavior Past BWR Spacer Grids
Ratnayake, Ruwan K.; Hochreiter, L.E.; Ivanov, K.N.; Cimbala, J.M.
2002-07-01
Performance of best estimate codes used in the nuclear industry can be significantly improved by reducing the empiricism embedded in their constitutive models. Spacer grids have been found to have an important impact on the maximum allowable Critical Heat Flux within the fuel assembly of a nuclear reactor core. Therefore, incorporation of suitable spacer grids models can improve the critical heat flux prediction capability of best estimate codes. Realistic modeling of entrainment behavior of spacer grids requires understanding the different mechanisms that are involved. Since visual information pertaining to the entrainment behavior of spacer grids cannot possibly be obtained from operating nuclear reactors, experiments have to be designed and conducted for this specific purpose. Most of the spacer grid experiments available in literature have been designed in view of obtaining quantitative data for the purpose of developing or modifying empirical formulations for heat transfer, critical heat flux or pressure drop. Very few experiments have been designed to provide fundamental information which can be used to understand spacer grid effects and phenomena involved in two phase flow. Air-water experiments were conducted to obtain visual information on the two-phase flow behavior both upstream and downstream of Boiling Water Reactor (BWR) spacer grids. The test section was designed and constructed using prototypic dimensions such as the channel cross-section, rod diameter and other spacer grid configurations of a typical BWR fuel assembly. The test section models the flow behavior in two adjacent sub channels in the BWR core. A portion of a prototypic BWR spacer grid accounting for two adjacent channels was used with industrial mild steel rods for the purpose of representing the channel internals. Symmetry was preserved in this practice, so that the channel walls could effectively be considered as the channel boundaries. Thin films were established on the rod surfaces
Modeling two-phase flow with stochastic coalescence/breakage model
NASA Astrophysics Data System (ADS)
Park, Ki Sun
Gas-particle flows were modeled to account for coalescence and breakup of liquid metal oxide droplets dispersed within the gas phase. The one-way coupled population balance equation (PBE) describing the evolution of number concentration due to particle-particle interactions and aerodynamic forces was solved using the direct quadrature method of moments (DQMOM) along with Reynolds averaged Navier-Stokes equation (RANS). The turbulent feature was assessed by Wilcox's k-ω equations. The fast Eulerian method was used to assess the slip velocity of the dispersed phase which holds a significant inertia. Orthokinetic collision was considered under laminar and turbulent flow where the radial component of relative velocity between two colliding particles is a source of collision. Hydrodynamic and aerodynamic collision frequency functions for turbulent flow were obtained from prior studies and modified to take into account inertia of particles. For a general laminar movement of flow, hydrodynamic and aerodynamic collision frequency functions were derived for spherical particles. The laminar hydrodynamic collision frequency kernel was derived for application to high speed (high Reynolds number) flows. The inclusion of influence of multidimensional and mean flow behavior permits application to flows in which shear layers are present and high Reynolds number flow which necessitates inclusion of compressibility effects. The new model agrees well with prior incompressible formulations. Results indicate that the compressible part of new shearing collision frequency has a significant effect on the collision kernel due to the contraction and dilatation effects of a fluid element. The model was validated using historical data from particle collection experiments (and a correlation based on these data) in solid rocket motors. Considering the error bounds of correlation, the predicted mass mean diameter was in agreement with the measurements/correlation. Further validations performed
Jones, O.C.
1993-05-01
This progress report details the theoretical development, numerical results, experimental design (mechanical), experimental design (electronic), and experimental results for the research program for the development of an electrical impedance computed tomographic two-phase flow analyzer.
Modeling of Two-Phase Immiscible Flow with Moving Contact Lines
NASA Astrophysics Data System (ADS)
Abu Alsaud, Moataz; Soulaine, Cyprien; Riaz, Amir; Tchelepi, Hamdi; Stanford University Collaboration; University of Maryland, College Park Collaboration
2015-11-01
A new numerical method based on the implicit interface approach on Cartesian grids is proposed for modeling two-phase immiscible flow with moving contact lines. The reinitialization of level-set function by computing the minimum distance to linearly reconstructed interface to obtain signed distance function is extended to include the contact angle boundary condition. The physics of contact line dynamics is implemented using the Cox-Voinov hydrodynamic theory that efficiently captures the effect of the microscopic contact line region. The numerical method is validated through various examples. Parasitic currents are studied in the case of static and constantly advected parabolic interface intersecting the domain boundary with an imposed contact angle. Moving contact line in the viscous dominated regime is studied and verified through comparison with experiments.
Study of momentum transfer in two-fluid formulation of two-phase flow
NASA Astrophysics Data System (ADS)
Egely, G.; Saha, P.
Advanced nuclear safety codes such as TRAC and BFIAP5 use two-fluid hydraulic models. However, there are uncertainties for the application of different correlations. The effects and importance of a number of correlations for wall friction, interphase drag, and virtual mass are shown. The homogeneous wall shear model yields good results up to the annular flow regime, the single bubble drag correlation is acceptable, and the inclusion of virtual mass coefficient is helpful. The critical Weber number is not appropriate for bubble radius calculation; it predicts an opposing tendency when compared with the test data. Also, a two phase diffuser efficiency is required for diverging ducts and a correlation for the same was proposed.
A flux splitting method for the Baer-Nunziato equations of compressible two-phase flow
NASA Astrophysics Data System (ADS)
Tokareva, S. A.; Toro, E. F.
2016-10-01
Here we extend the Toro-Vázquez flux vector splitting approach (TV), originally proposed for the ideal 1D Euler equations in [1], to the Baer-Nunziato equations of compressible two-phase flow. Following the TV approach we identify corresponding advection and pressure operators. We perform a rigorous analysis of the associated non-conservative pressure system and derive its complete characteristic structure. The choice of the advection numerical flux is obvious. For the pressure system, several schemes are presented. The complete schemes are then implemented in the setting of finite volume and path-conservative methods and are systematically assessed in terms of accuracy and efficiency, through a carefully selected suite of test problems. The presented schemes constitute a building block for the construction of high-order numerical methods for solving the Baer-Nunziato equations. Here, as an illustrative example of such possibility, we present the construction of a second-order scheme.
Prediction of Parameters Distribution of Upward Boiling Two-Phase Flow With Two-Fluid Models
Yao, Wei; Morel, Christophe
2002-07-01
In this paper, a multidimensional two-fluid model with additional turbulence k - {epsilon} equations is used to predict the two-phase parameters distribution in freon R12 boiling flow. The 3D module of the CATHARE code is used for numerical calculation. The DEBORA experiment has been chosen to evaluate our models. The radial profiles of the outlet parameters were measured by means of an optical probe. The comparison of the radial profiles of void fraction, liquid temperature, gas velocity and volumetric interfacial area at the end of the heated section shows that the multidimensional two-fluid model with proper constitutive relations can yield reasonably predicted results in boiling conditions. Sensitivity tests show that the turbulent dispersion force, which involves the void fraction gradient, plays an important role in determining the void fraction distribution; and the turbulence eddy viscosity is a significant factor to influence the liquid temperature distribution. (authors)
Effects of Porosity and Mixed Convection on MHD Two Phase Fluid Flow in an Inclined Channel
Hasnain, Jafar; Abbas, Zaheer; Sajid, Muhammad
2015-01-01
The present study deals with the flow and heat transfer analysis of two immiscible fluids in an inclined channel embedded in a porous medium. The channel is divided in two phases such that a third grade fluid occupies the phase I and a viscous fluid occupies the phase II. Both viscous and third grade fluids are electrically conducting. A constant magnetic field is imposed perpendicular to the channel walls. The mathematical model is developed by using Darcy's and modified Darcy's laws for viscous and third grade fluids respectively. The transformed ordinary differential equations are solved numerically using a shooting method. The obtained results are presented graphically and influence of emerging parameters is discussed in detail. PMID:25803360
A model for sound velocity in a two-phase air-water bubbly flow
Chung, N.M.; Lin, W.K.; Pei, B.S.; Hsu, Y.Y. )
1992-07-01
In this paper, wave propagation in a homogeneous, low void fraction, two-phase air-water bubbly flow is analyzed through the compressibility of a single bubble to derive a P({rho}) relation; the dispersion relation is then derived by a homogeneous model. The phase velocity and attenuation calculated from the model are compared with existing data and are in good agreement. The momentum transfer effect is considered through the virtual mass term and is significant at a higher void fraction. The interfacial heat transfer between phases is significant at low frequency, while bubble scattering effects are important at high frequency (near resonance). Bubble behavior at both low and high frequency is derived based on the isothermal and the adiabatic cases, respectively. The phase velocity occurs at the limiting condition in both cases. Furthermore, resonance is present in the model, and the resonant frequency is determined.
GPU-centric resolved-particle disperse two-phase flow simulation using the Physalis method
NASA Astrophysics Data System (ADS)
Sierakowski, Adam J.
2016-10-01
We present work on a new implementation of the Physalis method for resolved-particle disperse two-phase flow simulations. We discuss specifically our GPU-centric programming model that avoids all device-host data communication during the simulation. Summarizing the details underlying the implementation of the Physalis method, we illustrate the application of two GPU-centric parallelization paradigms and record insights on how to best leverage the GPU's prioritization of bandwidth over latency. We perform a comparison of the computational efficiency between the current GPU-centric implementation and a legacy serial-CPU-optimized code and conclude that the GPU hardware accounts for run time improvements up to a factor of 60 by carefully normalizing the run times of both codes.
A diffuse-interface method for two-phase flows with soluble surfactants
Teigen, Knut Erik; Song, Peng; Lowengrub, John; Voigt, Axel
2010-01-01
A method is presented to solve two-phase problems involving soluble surfactants. The incompressible Navier–Stokes equations are solved along with equations for the bulk and interfacial surfactant concentrations. A non-linear equation of state is used to relate the surface tension to the interfacial surfactant concentration. The method is based on the use of a diffuse interface, which allows a simple implementation using standard finite difference or finite element techniques. Here, finite difference methods on a block-structured adaptive grid are used, and the resulting equations are solved using a non-linear multigrid method. Results are presented for a drop in shear flow in both 2D and 3D, and the effect of solubility is discussed. PMID:21218125
Dynamic and spectroscopic characteristics of atmospheric gliding arc in gas-liquid two-phase flow
NASA Astrophysics Data System (ADS)
Tu, X.; Yu, L.; Yan, J. H.; Cen, K. F.; Chéron, B. G.
2009-11-01
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.
Effects of porosity and mixed convection on MHD two phase fluid flow in an inclined channel.
Hasnain, Jafar; Abbas, Zaheer; Sajid, Muhammad
2015-01-01
The present study deals with the flow and heat transfer analysis of two immiscible fluids in an inclined channel embedded in a porous medium. The channel is divided in two phases such that a third grade fluid occupies the phase I and a viscous fluid occupies the phase II. Both viscous and third grade fluids are electrically conducting. A constant magnetic field is imposed perpendicular to the channel walls. The mathematical model is developed by using Darcy's and modified Darcy's laws for viscous and third grade fluids respectively. The transformed ordinary differential equations are solved numerically using a shooting method. The obtained results are presented graphically and influence of emerging parameters is discussed in detail.
Two-phase liquid-liquid flows generated by impinging liquid jets
NASA Astrophysics Data System (ADS)
Tsaoulidis, Dimitrios; Li, Qi; Angeli, Panagiota
2015-11-01
Two-phase flows in intensified small-scale systems find increasing applications in (bio)chemical analysis and synthesis, fuel cells, polymerisation, and separation processes (solvent extraction). Current nuclear spent fuel reprocessing separation technologies have been developed many decades ago and have not taken account recent advances on process intensification which can drive down plant size and economics. In this work, intensified impinging jets will be developed to create dispersions by bringing the two liquid phases into contact through opposing small channels. A systematic set of experiments has been undertaken, to investigate the hydrodynamic characteristics, to develop predictive models, and enable comparisons with other contactors. Drop size distribution and mixing intensity will be investigated for liquid-liquid mixtures as a function of various parameters using high speed imaging and conductivity probes.
A new algorithm for impedance imaging of two-phase flows
Lemonnier, H.; Peytraud, J.F.
1995-12-31
This paper describes an original reconstruction procedure for impedance imaging of two-phase flows. It is a two-dimensional algorithm based on the calculation of the electrical potential distribution by the Boundary Element Method (BEM). The use of the BEM to solve the direct problem yields an integral equation to be solved on the domain boundary only. Compared to the Finite Element approach (FEM), it corresponds to the explicit elimination of internal domains (inclusions) and internal elements of the domain. It is therefore much faster for a given spatial resolution. Moreover, the overall reconstruction consists in solving an inverse problem iteratively which requires the knowledge of the sensitivity of the electrical response of the domain to its variations. It is shown that the BEM provides these sensitivities with very little extra effort when the direct problem is already solved. The very good capabilities of the algorithm are shown by various examples.
Capillarity in two-phase liquid flow of organic contaminants in ground water
Demond, A.H.
1988-01-01
The objective of this research was to examine the influence of capillary forces on two-phase liquid flow in groundwater. This objective was accomplished by investigating interfacial tension, contact angle, capillary pressure, and relative permeability for systems representative of contaminated aquifers. The interfacial tensions of six compounds, benzaldehyde, bromobenzene, n-dodecane, tetrachloroethylene, 1,1,2-trichloroethane, and o-xylene, were measured using the pendant drop method. The contact angles for these six compounds were measured on five solid surfaces: Teflon, glass, steel, calcite, and albite. Drainage and imbibition capillary pressure relationships were measured for four organic compound-water systems in an unconsolidated sand. Drainage and imbibition relative permeabilities were measured at groundwater velocities for three organic compound-water systems in the same sand.
A TEMPERATURE DROP MODEL FOR TWO-PHASE FLOW IN GEOTHERMAL WELLBORES
Michels, D.E.
1985-01-22
This temperature-drop model is formulated as an answer to the question, ''How much further up the wellbore will a unit mass of fluid be when its temperature is exactly one-degree cooler than at its current position''. The repeated calculation yields a temperature profile extending upwardly from the bubble point. This approach is based on a paradigm that emphasizes temperature and volume for a system that is dominated by one component. It has only a small overlap with the more popular paradigm for this topic which involves mechanical pressures and energy balances. A set of plots is given which shows the effects on temperature and pressure profiles due to changes of single factors when all other factors are held constant. The factors include common wellbore and reservoir parameters. These latter plots give considerable insight into wellbore processes and the nature of constraints on two-phase flow for an essentially one-component substance.
A Darcy law for the drift velocity in a two-phase flow model
Guillard, H. . E-mail: Herve.Guillard@sophia.inria.fr; Duval, F.
2007-05-20
This work deals with the design and numerical approximation of an Eulerian mixture model for the simulation of two-phase dispersed flows. In contrast to the more classical two-fluid or Drift-flux models, the influence of the velocity disequilibrium is taken into account through dissipative second-order terms characterized by a Darcy law for the relative velocity. As a result, the convective part of the model is always unconditionally hyperbolic. We show that this model corresponds to the first-order equilibrium approximation of classical two-fluid models. A finite volume approximation of this system taking advantage of the hyperbolic nature of the convective part of the model and of the particular structural form of the dissipative part is proposed. Numerical applications are presented to assess the capabilities of the model.
On the turbulence-particles interaction in turbulent two-phase flows
NASA Astrophysics Data System (ADS)
Mostafa, A. A.; Mongia, H. C.
1986-01-01
A mathematically simple two-equation turbulence model for two-phase flows has been developed to take into account the extra energy dissipation due to the presence of the particles with the carrier phase. The transport equations of mass, momentum, and kinetic energy and its dissipation rate of the carrier phase using an Eulerian formulation are presented. The Lagrangian approach is used to solve for the particles using the Monte Carlo technique. These equations are solved numerically using a finite difference technique to predict a turbulent round gaseous jet laden with solid particles. The predicted mean and turbulence quantities of the carrier and dispersed phases are in good agreement with the recent experimental data.
Two-phase flow of HFC-134a and CFC-12 through short-tube orifices
Kim, Y.; O`Neal, D.L.; Yuan, X.
1994-12-31
Short-tube orifices have been widely used as an expansion device on automotive and residential-sized air conditioners in the United States. The design for optimum performance of these systems requires predicting correct flow characteristics through short tubes for a given set of operating conditions. Insufficient data are available on how any of the new replacement refrigerants will perform in short-tube orifices relative to conventional refrigerants. This paper compares experimental mass flow results with HFC-134a and CFC-12 for a variety of inlet conditions and short-tube geometries. Five sharp-edged short-tube orifices with 7 < LID < 20 and 1.10 mm (0.0435 in.) < D < 1.72 mm (0.0676 in.) were tested with HFC-134a and CFC-12. Both two-phase and subcooled liquid flow conditions entering the short tube were examined for condensing temperatures ranging from 35.4 C (96 F) to 53.8 C (129 F), for subcooling as high as 13.9 C (25 F), and for qualities as high as 10% at the inlet of the short tube. The effects of downstream pressure were also investigated by lowering the downstream pressure from the upstream saturation pressure down to 310 kPa (45 psia). For HFC-134a, two types of measurements were made during this study-mass flow tests and pressure distribution inside the orifice. For CFC-12, only mass flow tests were performed The results with CFC-12 were compared with those of HFC-134a with the same upstream temperature conditions. A comparison of these two refrigerants was made as a function of the main operating variables (upstream pressure, subcooling, and downstream pressure) and short-tube geometry. Semi-empirical models for both HFC-134a and CFC-12 were developed for the prediction of mass flow rate through short tubes.
Investigation of two-phase flow processes in coal slurry/hydrogen heaters. Final report
Sam, R.G.; Crowley, C.J.
1986-08-01
Experimental and analytical results are presented for two-phase slug flow in a horizontal, transparent pipe at large diameter (6.75 in.) at high gas density (20 times the density of air at atmospheric pressure) and at liquid viscosities ranging from 1 to 1000 centipoise. The test section replicates 1 1/2 rectangular coils (40 ft by 10 ft) of a fired heater in a coal liquefaction plant. Regime transtion, pressure drop, void fraction, and slug characteristic data have been obtained for liquid superficial velocities ranging from 0.2 to 6 ft/s and gas superficial velocities ranging from 0.2 to 12 ft/s. Regime transition results have been compared with the Taitel-Dukler analytical flow regime map. The transition from stratified to slug flow, which is underpredicted by the original analysis, has been studied in particular. Comparison with the dimensionless transition criterion (gas Froude number) shows that increased liquid viscosity increases the liquid level at which the transition occurs. Pressure drop data at the transition have been used to evaluate the interfacial shear and to show that it is greater than is assumed in the Taitel-Dukler analysis. Sensitivity studies for the transition criterion and interfacial shear illustrate exactly why the transition is underpredicted on the flow regime map and how the predictions can be improved. Photos of the flow patterns illustrate the mechanism of slug formation at high viscosity compared with low viscosity. Pressure drop, void fraction, and slug characteristic results are compared with an analysis for pressure drop in slug flow, demonstrating better predictive capability of this model at large pipe size, high gas density, and high viscosity, compared with correlations from the literature. The pressure drop model is also shown to be in excellent agreement with coal liquefaction pilot plant data. 34 refs.
Two-Phase Euler-Lagrange Simulations for Sheet Flow Transport of Mixed Size Sediments
NASA Astrophysics Data System (ADS)
Bateman, S. P.; Calantoni, J.; Hsu, T.
2012-12-01
Intense, collision-dominated bedload transport under sheet flow conditions is a primary agent of nearshore bathymetric evolution. We model the process with a series of two-phase flow simulations, using an Eulerian Reynolds-Averaged Navier-Stokes (RANS) fluid solver for turbulent flow, coupled to a Lagrangian Discrete Element Method (DEM) for modeling the motions of individual sediment grains, in a physically small but statistically relevant domain. For the fluid phase, the one-dimensional in the vertical (1DV) ensemble-averaged continuity and momentum equations are solved using a k-ɛ turbulence closure. For the particle phase, the DEM is fully three-dimensional, where particles have spherical shape and the material properties of quartz. Particle- particle interactions use a modified Walton model to compute the normal and tangential forces at the contact point, with viscous damping achieved through an effective coefficient of restitution calculated from the collisional Stokes number. Fluid-particle interactions include buoyancy, drag, and turbulent suspension, which are implemented through an eddy-particle interaction model based on a random walk. The simulations were performed under oscillatory forcing conditions, where the flow is driven by a second order Stokes wave with a period ranging from T = 5 - 7.5 seconds. The simulations included measured grain size distributions from the laboratory, with mixtures of coarse and fine grains (0.1 mm < D < 0.9 mm). Model results are generally in good agreement with laboratory measurements for net transport rates and time-dependent concentration and velocity profiles within the sheet flow layer. Modeling individual particle motion with the DEM allows the direct incorporation of important grain-scale physical processes, including collisional energy dissipation and vertical sorting of grains by size in the active layer. We compare the results of simulations with uniform sized particles versus simulations with the measured
Macroscopic laws for immiscible two-phase flow in porous media: Results From numerical experiments
NASA Astrophysics Data System (ADS)
Rothman, Daniel H.
1990-06-01
Flow through porous media may be described at either of two length scales. At the scale of a single pore, fluids flow according to the Navier-Stokes equations and the appropriate boundary conditions. At a larger, volume-averaged scale, the flow is usually thought to obey a linear Darcy law relating flow rates to pressure gradients and body forces via phenomenological permeability coefficients. Aside from the value of the permeability coefficient, the slow flow of a single fluid in a porous medium is well-understood within this framework. The situation is considerably different, however, for the simultaneous flow of two or more fluids: not only are the phenomenological coefficients poorly understood, but the form of the macroscopic laws themselves is subject to question. I describe a numerical study of immiscible two-phase flow in an idealized two-dimensional porous medium constructed at the pore scale. Results show that the macroscopic flow is a nonlinear function of the applied forces for sufficiently low levels of forcing, but linear thereafter. The crossover, which is not predicted by conventional models, occurs when viscous forces begin to dominate capillary forces; i.e., at a sufficiently high capillary number. In the linear regime, the flow may be described by the linear phenomenological law ui = ΣjLijfj, where the flow rate ui of the ith fluid is related to the force fj applied to the jth fluid by the matrix of phenomenological coefficients Lij which depends on the relative concentrations of the two fluids. The diagonal terms are proportional to quantities commonly referred to as "relative permeabilities." The cross terms represent viscous coupling between the two fluids; they are conventionally assumed to be negligible and require special experimental procedures to observe in a laboratory. In contrast, in this numerical study the cross terms are straightforward to measure and are found to be of significant size. The cross terms are additionally observed to
Field testing the role of heterogeneity at the inter-well scale during two phase flow
NASA Astrophysics Data System (ADS)
Hovorka, S. D.; Gulf Coast Carbon Center; Geoseq
2011-12-01
relative permeability evolution guide flow. Plume evolution was highly non-linear, demonstration dominance of preferential flow though fast paths. CO2 continued to access new flow paths as rate increased and through time; pressure was not linear with injection rate. Over a one year test period at the inter-well test scale, reservoir properties seem more important than either pressure or buoyancy in controlling plume evolution. Three intensively monitored two-phase injection experiments across ranges of inter-well reservoir heterogeneity and flow rate provide data to explore methods for bounding uncertainty. More than 20 fluid flow models from these tests have been or are being built to test approaches to history matching.
Correlation for liquid entrainment in annular two-phase flow of viscous fluid
Ishii, Mamoru; Mishima, Kaichiro
1981-03-01
The droplet entrainment from a liquid film by gas flow is important to mass, momentum, and energy transfer in annular two-phase flow. The amount of entrainment can significantly affect occurrences of the dryout and post-dryout heat flux as well as the rewetting phenomena of a hot dry surface. In view of these, a correlation for the amount of entrained liquid in annular flow has been developed from a simple model and experimental data. There are basically two different regions of entrainment, namely, the entrance and quasiequilibrium regions. The correlation for the equilibrium region is expressed in terms of the dimensionless gas flux, diameter, and total liquid Reynolds number. The entrance effect is taken into account by an exponential relaxation function. It has been shown that this new model can satisfactorily correlate wide ranges of experimental data for water. Furthermore, the necessary distance for the development of entrainment is identified. These correlations, therefore, can supply accurate information on entrainment which have not been available previously. (author)
Comparison of simplified models in the prediction of two phase flow in pipelines
NASA Astrophysics Data System (ADS)
Jerez-Carrizales, M.; Jaramillo, J. E.; Fuentes, D.
2014-06-01
Prediction of two phase flow in pipelines is a common task in engineering. It is a complex phenomenon and many models have been developed to find an approximate solution to the problem. Some old models, such as the Hagedorn & Brown (HB) model, have been highlighted by many authors to give very good performance. Furthermore, many modifications have been applied to this method to improve its predictions. In this work two simplified models which are based on empiricism (HB and Mukherjee and Brill, MB) are considered. One mechanistic model which is based on the physics of the phenomenon (AN) and it still needs some correlations called closure relations is also used. Moreover, a drift flux model defined in steady state that is flow pattern dependent (HK model) is implemented. The implementation of these methods was tested using published data in the scientific literature for vertical upward flows. Furthermore, a comparison of the predictive performance of the four models is done against a well from Campo Escuela Colorado. Difference among four models is smaller than difference with experimental data from the well in Campo Escuela Colorado.
CFD simulation of gas and non-Newtonian fluid two-phase flow in anaerobic digesters.
Wu, Binxin
2010-07-01
This paper presents an Eulerian multiphase flow model that characterizes gas mixing in anaerobic digesters. In the model development, liquid manure is assumed to be water or a non-Newtonian fluid that is dependent on total solids (TS) concentration. To establish the appropriate models for different TS levels, twelve turbulence models are evaluated by comparing the frictional pressure drops of gas and non-Newtonian fluid two-phase flow in a horizontal pipe obtained from computational fluid dynamics (CFD) with those from a correlation analysis. The commercial CFD software, Fluent12.0, is employed to simulate the multiphase flow in the digesters. The simulation results in a small-sized digester are validated against the experimental data from literature. Comparison of two gas mixing designs in a medium-sized digester demonstrates that mixing intensity is insensitive to the TS in confined gas mixing, whereas there are significant decreases with increases of TS in unconfined gas mixing. Moreover, comparison of three mixing methods indicates that gas mixing is more efficient than mixing by pumped circulation while it is less efficient than mechanical mixing.
Hot-film anemometer measurements in adiabatic two-phase flow through a vertical duct
Trabold, T.A.; Moore, W.E.; Morris, W.O.
1997-06-01
A hot-film anemometer (HFA) probe was used to obtain local measurements of void fraction and bubble frequency in a vertically oriented, high aspect ratio duct containing R-134a under selected adiabatic two-phase flow conditions. Data were obtained along a narrow dimension scan over the range 0.03 {le} {bar Z} {le} 0.80, where {bar Z} is the distance from the wall normalized with the duct spacing dimension. The void fraction profiles displayed large gradients in the near-wall regions and broad maxima near the duct centerline. The trends in the bubble frequency data generally follow those for the local void fraction data. However, the relatively large number of bubbles at higher pressure implies a larger magnitude of the interfacial area concentration, for the same cross-sectional average void fraction. For the two annular flow conditions tested, analysis of the HFA output voltage signal enabled identification of three distinct regions of the flow field; liquid film with dispersed bubbles, interfacial waves, and continuous vapor with dispersed droplets.
Non-equilibrium model of two-phase porous media flow with phase change
NASA Astrophysics Data System (ADS)
Cueto-Felgueroso, L.; Fu, X.; Juanes, R.
2014-12-01
The efficient simulation of multi-phase multi-component flow through geologic porous media is challenging and computationally intensive, yet quantitative modeling of these processes is essential in engineering and the geosciences. Multiphase flow with phase change and complex phase behavior arises in numerous applications, including enhanced oil recovery, steam injection in groundwater remediation, geologic CO2 storage and enhanced geothermal energy systems. A challenge of multiphase compositional simulation is that the number of existing phases varies with position and time, and thus the number of state variables in the saturation-based conservation laws is a function of space and time. The tasks of phase-state identification and determination of the composition of the different phases are performed assuming local thermodynamic equilibrium. Here we investigate a thermodynamically consistent formulation for non-isothermal two-phase flow, in systems where the hypothesis of instantaneous local equilibrium does not hold. Non-equilibrium effects are important in coarse-scale simulations where the assumption of complete mixing in each gridblock is not realistic. We apply our model to steam injection in water-saturated porous media.
Hydrodynamic Dryout in Two-Phase Flows: Observations of Low Bond Number Systems
NASA Technical Reports Server (NTRS)
Weislogel, Mark M.; McQuillen, John B.
1998-01-01
Dryout occurs readily in certain slug and annular two-phase flows for systems that exhibit partial wetting. The mechanism for the ultimate rupture of the film is attributed to van der Waals forces, but the pace towards rupture is quickened by the surface tension instability (Rayleigh-type) of the annular film left by the advancing slug and by the many perturbations of the free surface present in the Re(sub g) approximately 0(10(exp 3)), Re(sub l) approximately 0(10(exp 4)), and Ca approximately 0(10(exp -1) flows. Results from low-gravity experiments using three different test fluids are presented and discussed. For the range of tests conducted, the effect of increasing viscosity is shown to eliminate the film rupture while the decrease of surface tension via a surfactant additive is shown to dramatically enhance it. Laboratory measurements using capillary tubes are presented which reveal the sensitivity of the dryout phenomena to particulate and surfactant contamination. Rom such observations, dryout due to the hydrodynamic-van der Waals instability can be expected in a certain range of flow parameters in the absence of heat transfer. The addition of heat transfer may only exacerbate the problem by producing thermal transport lines replete with "hot spots." A caution to this effect is issued to future space systems designers concerning the use of partially wetting working fluids.
"Hypothetical" Heavy Particles Dynamics in LES of Turbulent Dispersed Two-Phase Channel Flow
NASA Technical Reports Server (NTRS)
Gorokhovski, M.; Chtab, A.
2003-01-01
The extensive experimental study of dispersed two-phase turbulent flow in a vertical channel has been performed in Eaton's research group in the Mechanical Engineering Department at Stanford University. In Wang & Squires (1996), this study motivated the validation of LES approach with Lagrangian tracking of round particles governed by drag forces. While the computed velocity of the flow have been predicted relatively well, the computed particle velocity differed strongly from the measured one. Using Monte Carlo simulation of inter-particle collisions, the computation of Yamamoto et al. (2001) was specifically performed to model Eaton's experiment. The results of Yamamoto et al. (2001) improved the particle velocity distribution. At the same time, Vance & Squires (2002) mentioned that the stochastic simualtion of inter-particle collisions is too expensive, requiring significantly more CPU resources than one needs for the gas flow computation. Therefore, the need comes to account for the inter-particle collisions in a simpler and still effective way. To present such a model in the framework of LES/Lagrangian particle approach, and to compare the calculated results with Eaton's measurement and modeling of Yamamoto is the main objective of the present paper.
Measurement of Two-Phase Flow and Heat Transfer Parameters using Infrared Thermometry
NASA Technical Reports Server (NTRS)
Kim, Tae-Hoon; Kommer, Eric; Dessiatoun, Serguei; Kim, Jungho
2012-01-01
A novel technique to measure heat transfer and liquid film thickness distributions over relatively large areas for two-phase flow and heat transfer phenomena using infrared (IR)thermometry is described. IR thermometry is an established technology that can be used to measure temperatures when optical access to the surface is available in the wavelengths of interest. In this work, a midwave IR camera (3.6-5.1 microns) is used to determine the temperature distribution within a multilayer consisting of a silicon substrate coated with a thin insulator. Since silicon is largely transparent to IR radiation, the temperature of the inner and outer walls of the multilayer can be measured by coating selected areas with a thin, IR opaque film. If the fluid used is also partially transparent to IR, the flow can be visualized and the liquid film thickness can be measured. The theoretical basis for the technique is given along with a description of the test apparatus and data reduction procedure. The technique is demonstrated by determining the heat transfer coefficient distributions produced by droplet evaporation and flow boiling heat transfer.
The Annular Two-phase Flow on Rod Bundle: The Effects of Spacers
NASA Astrophysics Data System (ADS)
Kunugi, Tomoaki; Pham, Son; Kawara, Zensaku; Yokomine, Takehiko
2013-11-01
The annular two-phase flow on rod bundle keeps an important role in many heat exchange systems but our knowledge about it, especially the interaction between the liquid film flowing on the rods' surfaces and the spacers is very limited. This study is aimed to the investigation of how the spacer affects the disturbance waves of the flow in a 3 × 3 simulating BWR fuel rod bundle test section. Firstly, the characteristics of the disturbance waves at both upstream and downstream locations of the spacer were obtained by using reflected light arrangement with a high speed camera Phantom V7.1 (Vision Research Inc.) and a Nikon macro lens 105mm f/2.8. The data showed that the parameters such as frequency and circumferential coherence of the disturbance waves are strongly modified when they go through the spacer. Then, the observations at the locations right before and after the spacer were performed by using the back light arrangement with the same high speed camera and a Cassegrain optical system (Seika Cooperation). The obtained images at micro-scale of time and space provided the descriptions of the wavy interface behaviors right before and after the spacer as well as different droplets creation processes caused by the presence of this spacer.
Hydrodynamic dryout in two-phase flows: Observations of low bond number systems
NASA Astrophysics Data System (ADS)
Weislogel, Mark M.; McQuillen, John B.
1998-01-01
Dryout occurs readily in certain slug and annular two-phase flows for systems that exhibit partial wetting. The mechanism for the ultimate rupture of the film is attributed to van der Waals forces, but the pace towards rupture is quickened by the surface tension instability (Rayleigh-type) of the annular film left by the advancing slug and by the many perturbations of the free surface present in the Reg~O(103), Rel~O(104), and Ca~O(10-1) flows. Results from low-gravity experiments using three different test fluids are presented and discussed. For the range of tests conducted, the effect of increasing viscosity is shown to eliminate the film rupture while the decrease of surface tension via a surfactant additive is shown to dramatically enhance it. Laboratory measurements using capillary tubes are presented which reveal the sensitivity of the dryout phenomena to particulate and surfactant contamination. From such observations, dryout due to the hydrodynamic-van der Waals instability can be expected in a certain range of flow parameters in the absence of heat transfer. The addition of heat transfer may only exacerbate the problem by producing thermal transport lines replete with ``hot spots.'' A caution to this effect is issued to future space systems designers concerning the use of partially wetting working fluids.
Acquisition of void fraction of pulsatile gas-liquid two-phase flow in rectangular channel
NASA Astrophysics Data System (ADS)
Zhou, Bao; Liu, Jingxing; Tian, Jingda
2013-07-01
Experiment on two-phase pulsatile flow in a narrow rectangular visualization channel was carried out and photographed. Every frame was treated and restored as a black-white binary picture with the threshold of both gray-scale and gray-scale gradient. The gas-liquid interface in the binary pictures can be recognized well, including some very obvious interface, which either cannot be distinguished, or introduce big wrong-recognized area with the gray-scale threshold only. Then after such as `dilate', `erode', `fill', `filter' and so on operating, the binary pictures can reflect the twophase distinction situation in the experimental channel well; The instantaneous average void frictions at the length that the camera covered were calculated by counting the black and white pixels from the pictures. The average void fractions in the whole length of the test section were calculated with an iteration method. The average void fractions in the special length covered by camera and the ones in the whole length of the test section are different. The former shows that the void frictions dramatically frequently change, while the later at steady flow almost stay peace, at pulsatile flow change smoothly.
Cryogenic two-phase flow during chilldown: Flow transition and nucleate boiling heat transfer
NASA Astrophysics Data System (ADS)
Jackson, Jelliffe Kevin
The recent interest in space exploration has placed a renewed focus on rocket propulsion technology. Cryogenic propellants are the preferred fuel for rocket propulsion since they are more energetic and environmentally friendly compared with other storable fuels. Voracious evaporation occurs while transferring these fluids through a pipeline that is initially in thermal equilibrium with the environment. This phenomenon is referred to as line chilldown. Large temperature differences, rapid transients, pressure fluctuations and the transition from the film boiling to the nucleate boiling regime characterize the chilldown process. Although the existence of the chilldown phenomenon has been known for decades, the process is not well understood. Attempts have been made to model the chilldown process; however the results have been fair at best. A major shortcoming of these models is the use of correlations that were developed for steady, non-cryogenic flows. The development of reliable correlations for cryogenic chilldown has been hindered by the lack of experimental data. An experimental facility was constructed that allows the flow structure, the temperature history and the pressure history to be recorded during the line chilldown process. The temperature history is then utilized in conjunction with an inverse heat conduction procedure that was developed, which allows the unsteady heat transfer coefficient on the interior of the pipe wall to be extracted. This database is used to evaluate present predictive models and correlations for flow regime transition and nucleate boiling heat transfer. It is found that by calibrating the transition between the stratified-wavy and the intermittent/annular regimes of the Taitel and Dukler flow regime map, satisfactory predictions are obtained. It is also found that by utilizing a simple model that includes the effect of flow structure and incorporating the enhancement provided by the local heat flux, significant improvement in the
Numerical experiments on breaking waves on contrasting beaches using a two-phase flow approach
NASA Astrophysics Data System (ADS)
Bakhtyar, R.; Barry, D. A.; Kees, C. E.
2012-11-01
A mechanistic understanding of beach environments needs to account for interactions of oceanic forcing and beach materials, in particular the role of waves on the evolution of the beach profile. A fully coupled two-phase flow model was used to simulate nearshore fluid-sediment turbulent flow in the cross-shore direction. It includes the Reynolds-Averaged Navier-Stokes equations and turbulent stress closures for each phase, and accounts for inter-granular stresses. The model has previously been validated using laboratory-scale data, so the results are likely more reliable for that scale. It was used to simulate wave breaking and the ensuing hydrodynamics and sediment transport processes in the surf/swash zones. Numerical experiments were conducted to investigate the effects of varying beach and wave characteristics (e.g., beach slope, sediment grain size, wave periods and heights) on the foreshore profile changes. Spilling and plunging breakers occur on dissipative and intermediate beaches, respectively. The impact of these wave/beach types on nearshore zone hydrodynamics and beach morphology was determined. The numerical results showed that turbulent kinetic energy, sediment concentrations and transport rate are greater on intermediate than on dissipative beaches. The results confirmed that wave energy, beach grain size and bed slope are main factors for sediment transport and beach morphodynamics. The location of the maximum sediment transport is near the breaking point for both beach types. Coarse- and fine-sand beaches differ significantly in their erosive characteristics (e.g., foreshore profile evolutions are erosive and accretionary on the fine and coarse sand beaches, respectively). In addition, a new parameter (based on main driving factors) is proposed that can characterize the sediment transport in the surf and swash zones. The results are consistent with existing physical observations, suggesting that the two-phase flow model is suitable for the
Multiparticle imaging technique for two-phase fluid flows using pulsed laser speckle velocimetry
Hassan, T.A.
1992-12-01
The practical use of Pulsed Laser Velocimetry (PLV) requires the use of fast, reliable computer-based methods for tracking numerous particles suspended in a fluid flow. Two methods for performing tracking are presented. One method tracks a particle through multiple sequential images (minimum of four required) by prediction and verification of particle displacement and direction. The other method, requiring only two sequential images uses a dynamic, binary, spatial, cross-correlation technique. The algorithms are tested on computer-generated synthetic data and experimental data which was obtained with traditional PLV methods. This allowed error analysis and testing of the algorithms on real engineering flows. A novel method is proposed which eliminates tedious, undersirable, manual, operator assistance in removing erroneous vectors. This method uses an iterative process involving an interpolated field produced from the most reliable vectors. Methods are developed to allow fast analysis and presentation of sets of PLV image data. Experimental investigation of a two-phase, horizontal, stratified, flow regime was performed to determine the interface drag force, and correspondingly, the drag coefficient. A horizontal, stratified flow test facility using water and air was constructed to allow interface shear measurements with PLV techniques. The experimentally obtained local drag measurements were compared with theoretical results given by conventional interfacial drag theory. Close agreement was shown when local conditions near the interface were similar to space-averaged conditions. However, theory based on macroscopic, space-averaged flow behavior was shown to give incorrect results if the local gas velocity near the interface as unstable, transient, and dissimilar from the average gas velocity through the test facility.
Unfitted Two-Phase Flow Simulations in Pore-Geometries with Accurate
NASA Astrophysics Data System (ADS)
Heimann, Felix; Engwer, Christian; Ippisch, Olaf; Bastian, Peter
2013-04-01
The development of better macro scale models for multi-phase flow in porous media is still impeded by the lack of suitable methods for the simulation of such flow regimes on the pore scale. The highly complicated geometry of natural porous media imposes requirements with regard to stability and computational efficiency which current numerical methods fail to meet. Therefore, current simulation environments are still unable to provide a thorough understanding of porous media in multi-phase regimes and still fail to reproduce well known effects like hysteresis or the more peculiar dynamics of the capillary fringe with satisfying accuracy. Although flow simulations in pore geometries were initially the domain of Lattice-Boltzmann and other particle methods, the development of Galerkin methods for such applications is important as they complement the range of feasible flow and parameter regimes. In the recent past, it has been shown that unfitted Galerkin methods can be applied efficiently to topologically demanding geometries. However, in the context of two-phase flows, the interface of the two immiscible fluids effectively separates the domain in two sub-domains. The exact representation of such setups with multiple independent and time depending geometries exceeds the functionality of common unfitted methods. We present a new approach to pore scale simulations with an unfitted discontinuous Galerkin (UDG) method. Utilizing a recursive sub-triangulation algorithm, we extent the UDG method to setups with multiple independent geometries. This approach allows an accurate representation of the moving contact line and the interface conditions, i.e. the pressure jump across the interface. Example simulations in two and three dimensions illustrate and verify the stability and accuracy of this approach.
The Effect of Numerical Diffusion on Oscillatory Flow in Two-Phase Boiling Channel
Chaiwat Muncharoen; Tatchai Sumitra; Takatoshi Takemoto; Masanori Aritomi
2002-07-01
The purpose of this paper is to study the effect of numerical diffusion on the ill-posedness and the accuracy of the model simulated the thermal-hydraulic instabilities in boiling water reactor channels. The model of the upward flow system in two-phase boiling channel simulating BWR core was developed to investigate the oscillatory flow, which was caused by flow instabilities, by using the drift-flux model. The time step was fixed at 1 millisecond at all time and the mesh size was varied as follows: 400, 200, 100, 50 and 20 mm. Then the numerical diffusion in the conservation equations was analyzed in reference to spatial mesh size. The maximums of the absolute ratios of the first order and the second order approximations of the time derivative terms (A/B) and the convective terms (C/D), including the summations of the second power of the ratios of the second order and the first order approximations of the time derivative terms ({sigma}(B/A){sup 2}) and the convective terms ({sigma}(D/C){sup 2}) were calculated to investigate the ill-posedness and the accuracy of numerical calculation of this model. The results from the model showed that the numerical diffusion in the time derivative term and the convective term play the important role in the drift-flux model for the small mesh size and may cause the ill-posedness and degrade the accuracy of the model. It was found that the A/B, the C/D, the {sigma}(B/A){sup 2} and the {sigma}(D/C){sup 2} in the drift-flux model highly fluctuated at the small mesh size of 50 and 20 mm. More importantly, the numerical diffusion due to the oscillation flow and the mesh size variation may have an effect on the amplitude of the pressure drop of the oscillatory flow at the small mesh size. (authors)
Linear stability of layered two-phase flows through parallel soft-gel-coated walls
NASA Astrophysics Data System (ADS)
Dinesh, B.; Pushpavanam, S.
2017-07-01
The linear stability of layered two-phase Poiseuille flows through soft-gel-coated parallel walls is studied in this work. The focus is on determining the effect of the elastohydrodynamic coupling between the fluids and the soft-gel layers on the different instabilities observed in flows between parallel plates. The fluids are assumed Newtonian and incompressible, while the soft gels are modeled as linear viscoelastic solids. A long-wave asymptotic analysis is used to obtain an analytical expression for the growth rate of the disturbances. A Chebyshev collocation method is used to numerically solve the general linearized equations. Three distinct instability modes are identified in the flow: (a) a liquid-liquid long-wave mode; (b) a liquid-liquid short-wave mode; (c) a gel-liquid short-wave mode. The effect of deformability of the soft gels on these three modes is analyzed. From the long-wave analysis of the liquid-liquid mode a stability map is obtained, in which four different regions are clearly demarcated. It is shown that introducing a gel layer near the more viscous fluid has a predominantly stabilizing effect on this mode seen in flows between rigid plates. For parameters where this mode is stable for flow between rigid plates, introducing a gel layer near the less viscous and thinner fluid has a predominantly destabilizing effect. The liquid-liquid short-wave mode is destabilized by the introduction of soft-gel layers. Additional instability modes at the gel-liquid interfaces induced by the deformability of the soft-gel layers are identified. We show that these can be controlled by varying the thickness of the gel layers. Insights into the physical mechanism driving different instabilities are obtained using an energy budget analysis.
Supersonic flow past axisymmetric body with strong local two-phase surface injection
NASA Astrophysics Data System (ADS)
Antonov, V. A.; Gol'Din, V. D.; Grishin, A. M.
1984-01-01
It is known [1 3] that in order to provide heat shield or to improve the aerodynamics of the body strong injection of cooling gas into the supersonic stream is utilized. Analysis of flow characteristics in the neighborhood of the solid body in the presence of strong single-phase injection and the effect of injection on the aerodynamic characteristics of some axisymmetric bodies are given, e.g., in [2 4]. Supersonic flow past a blunt-nosed axisymmetric body with blowing of a mixture of gas and solid particles through a porous segment in the leading edge region is considered in the present paper. Such a situation could occur in modeling the breakdown of the heat shield of a flight vehicle during its reentry into the thick layers of atmosphere and also in the case of forced introduction of particles in the flow of the injected gas in order to break up the leading edge shock and accordingly the variation in the drag of the body [5]. A description of the trajectory of the particles has been obtained as a result of numerical and analytical solution of the problem and their analysis is used to arrive at conclusions on their intersection and, consequently, also on the multiple-valued nature of the flow parameters in the neighborhood of the line dividing the external flow and the injected two-phase mixture. Sufficient conditions for multiple-valuedness have been analytically found which agree with numerical results. It has been established that with a change in composition of sufficiently small particles within the limits 0.1 to 0.6 by weight of the injected mixture the drag coefficient of the body does not change by more than 10%.
Scaling of two-phase flow regimes in a rod bundle with freon
Symolon, P.D.
1990-07-01
Fluid to fluid modeling of the thermal-hydraulics of steam/water systems using Freon has been the subject of research for the past 25 years. However, there is as yet no universally accepted set of scaling laws to define the geometry and velocity scaling requirements of an equivalent Freon test of the full scale steam/water system being simulated. This paper describes a scaling concept where the Weber and Froud numbers of the Freon model are matched to that of the prototype being simulated, thus creating a comparable balance among inertia, surface tension and buoyancy forces. In this test it was demonstrated that similar flow regime transitions are observed in a half scale Freon simulation of a full scale steam/water test run at Dynatech. It is also shown using a two fluid analytical model and existing correlations for friction and interfacial momentum exchange from the open literature, that a half scale simulation leads to nearly the same slip ratio as for full scale steam/water, while the slip ratio for a full scale Freon simulation is too high. A comparison of the predicted flow distribution in the 4-rod bundle is made using the COBRA-IV code for a full scale simulation using Freon, a half scale simulation using Freon and full scale test with water. The COBRA results demonstrated that a half scale test section model using Freon yields a subchannel flow distribution similar to the steam/water case, while a full scale Freon simulation results in a distorted subchannel flow distribution. It is concluded that the appropriate geometric scale factor for Freon simulation of two-phase steam/water flow in tube bundles is one-half for a broad range of thermal-hydraulic conditions. 24 refs., 12 figs., 4 tabs.
Streaming potential generated by two-phase flow in a capillary
NASA Astrophysics Data System (ADS)
Sherwood, J. D.
2007-05-01
The streaming potential generated by pressure-driven two-phase flow in a circular capillary differs from that generated by single-phase flow. Three model problems are considered, in which the dispersed phase consists of either (i) a rigid spherical particle (possibly charged), (ii) an uncharged spherical bubble, and (iii) a long, uncharged Bretherton bubble. In all three cases, the particle or bubble is assumed to lie on the center line of the capillary tube, so that the problem is axisymmetric, and is assumed to be of almost the same diameter as the internal diameter of the capillary, so that lubrication theory can be used. The electrical potentials on the surface of the particle and on the walls of the capillary are ζp and ζc, respectively, and the Debye length is assumed much smaller than the gap between the particle and the walls of the capillary. If the flow rate is held constant, the presence of the rigid particle increases the pressure drop between the ends of the capillary, and also changes the streaming potential by an amount proportional to ζc-ζp. This change in potential will in general be small compared to the total streaming potential developed between the two ends of a long capillary. However, if the capillary is filled with a large number of rigid particles, not only will the changes in pressure drop and streaming potential between the two ends of the capillary be large, but there will be a significant change in the coefficient of proportionality between pressure drop and streaming potential. The presence of an uncharged spherical bubble or Bretherton bubble changes the pressure drop between the ends of the capillary (for a given flow rate) but does not change the linear relation between pressure drop and streaming potential. However, the linear relation between flow rate and streaming potential is modified for the spherical bubble, and becomes nonlinear when a Bretherton bubble is present.
Wang, W.; Rutqvist, J.; Gorke, U.-J.; Birkholzer, J.T.; Kolditz, O.
2010-03-15
The present work compares the performance of two alternative flow models for the simulation of thermal-hydraulic coupled processes in low permeable porous media: non-isothermal Richards and two-phase flow concepts. Both models take vaporization processes into account: however, the Richards model neglects dynamic pressure variations and bulk flow of the gaseous phase. For the comparison of the two approaches first published data from a laboratory experiment is studied involving thermally driven moisture flow in a partially saturated bentonite sample. Then a benchmark test of longer-term thermal-hydraulic behavior in the engineered barrier system of a geological nuclear waste repository is analyzed (DECOVALEX project). It was found that both models can be used to reproduce the vaporization process if the intrinsic permeability is relative high. However, when a thermal-hydraulic coupled problem has the same low intrinsic permeability for both the liquid and the gas phase, only the two-phase flow approach provides reasonable results.
A New Void Fraction Measurement Method for Gas-Liquid Two-Phase Flow in Small Channels.
Li, Huajun; Ji, Haifeng; Huang, Zhiyao; Wang, Baoliang; Li, Haiqing; Wu, Guohua
2016-01-27
Based on a laser diode, a 12 × 6 photodiode array sensor, and machine learning techniques, a new void fraction measurement method for gas-liquid two-phase flow in small channels is proposed. To overcome the influence of flow pattern on the void fraction measurement, the flow pattern of the two-phase flow is firstly identified by Fisher Discriminant Analysis (FDA). Then, according to the identification result, a relevant void fraction measurement model which is developed by Support Vector Machine (SVM) is selected to implement the void fraction measurement. A void fraction measurement system for the two-phase flow is developed and experiments are carried out in four different small channels. Four typical flow patterns (including bubble flow, slug flow, stratified flow and annular flow) are investigated. The experimental results show that the development of the measurement system is successful. The proposed void fraction measurement method is effective and the void fraction measurement accuracy is satisfactory. Compared with the conventional laser measurement systems using standard laser sources, the developed measurement system has the advantages of low cost and simple structure. Compared with the conventional void fraction measurement methods, the proposed method overcomes the influence of flow pattern on the void fraction measurement. This work also provides a good example of using low-cost laser diode as a competent replacement of the expensive standard laser source and hence implementing the parameter measurement of gas-liquid two-phase flow. The research results can be a useful reference for other researchers' works.
Abdollahian, D.; Grief, R.; Carey, V.P.; Li-Ping, W.
1988-03-01
More-effective and -efficient thermal-transport techniques will be needed for heat rejection from equipment on satellites. Circulating two-phase fluid loops were suggested and laboratory tested for possible application in the above areas. In comparison to a single-phase loop, the two-phase system operates at considerably smaller flow rates and maintains a tighter temperature control with higher heat-transfer coefficients. However, the two-phase fluid-flow regimes, pressure gradients, and heat-transfer coefficients must be evaluated for application in the weightless environment of an orbiting satellite. This projecting studies two-phase flow behavior under zero-gravity conditions. The overall objectives of this study were to generate a data base for two-phase pressure drop and the void-quality relationship under simulated zero gravity conditions and to develop analytical models to predict these parameters for bubbly and annular flow. The simulation of zero-gravity two-phase flow was achieved by using two immiscible liquids with equal densities to eliminate the buoyancy component. Although this approach does not eliminate the gravity effects, it provides a representation for void distribution in the absence of gravity. The modeling effort is limited to developing relations for the two-phase friction multiplier and void-quality relation under bubbly and annular-flow conditions. The bubbly flow model is based on the assumption of local homogeneous conditions between the phases but allows for void distribution in the radial direction. Separated-flow conservation equations are used, and single-phase turbulent flow eddy diffusivity relations are employed.
NASA Astrophysics Data System (ADS)
Kim, Jinyong; Luo, Gang; Wang, Chao-Yang
2017-10-01
3D fine-mesh flow-fields recently developed by Toyota Mirai improved water management and mass transport in proton exchange membrane (PEM) fuel cell stacks, suggesting their potential value for robust and high-power PEM fuel cell stack performance. In such complex flow-fields, Forchheimer's inertial effect is dominant at high current density. In this work, a two-phase flow model of 3D complex flow-fields of PEMFCs is developed by accounting for Forchheimer's inertial effect, for the first time, to elucidate the underlying mechanism of liquid water behavior and mass transport inside 3D complex flow-fields and their adjacent gas diffusion layers (GDL). It is found that Forchheimer's inertial effect enhances liquid water removal from flow-fields and adds additional flow resistance around baffles, which improves interfacial liquid water and mass transport. As a result, substantial improvements in high current density cell performance and operational stability are expected in PEMFCs with 3D complex flow-fields, compared to PEMFCs with conventional flow-fields. Higher current density operation required to further reduce PEMFC stack cost per kW in the future will necessitate optimizing complex flow-field designs using the present model, in order to efficiently remove a large amount of product water and hence minimize the mass transport voltage loss.
Reinemann, D J
1996-12-01
Most pipeline systems in dairy and food processing plants are cleaned by circulating cleaning solutions under pressure with a liquid pump. The flow of the circulated solutions is single-phase or flooded flow. Milking system pipelines are subject to special requirements which distinguish them from those in dairy and other food processing plants. Milking system pipelines are considerably larger in diameter than product lines in dairy plants because they must carry both milk and air in a stratified flow condition during the milking process. Milking machine Clean-In-Place (CIP) systems have historically used flooded flow to circulate cleaning solutions. The force to move liquid, however, is typically the vacuum provided by the same vacuum pump used during milking, rather than a positive pressure liquid pump. As the size and complexity of milking machines has increased in recent years, flooded flow CIP systems have become inadequate. The amount of water required to fully flood a milking system becomes impractical with very long and/or large diameter pipelines. The power available to achieve adequate flow velocity is also limited. Air admission has been used to produce two-phase (air/water) slug flow and overcome some of the limitations of fully flooded CIP. Cycled air admission can reduce the amount of water required for circulation and increase flow velocities and thus enhance mechanical cleaning action. Cycled air admission has been implemented in the field largely through trial and error methods. There has been a lack of fundamental design information and testing protocols for air-injected milking machine CIP systems. This has resulted in mixed success in the application of air injected systems. This paper summarizes both laboratory and field research conducted at the University of Wisconsin Milking Research and Instruction lab to provide basic information for the design of air injected CIP systems and methods for field assessment of these systems. Just as properly
Ice melting and downward transport of meltwater by two-phase flow in Europa's ice shell
NASA Astrophysics Data System (ADS)
Kalousová, Klára; Souček, Ondřej; Tobie, Gabriel; Choblet, Gaël.; Čadek, Ondřej
2014-03-01
With its young surface, very few impact craters, and the abundance of tectonic and cryovolcanic features, Europa has likely been subjected to relatively recent endogenic activity. Morphological analyses of chaos terrains and double ridges suggest the presence of liquid water within the ice shell a few kilometers below the surface, which may result from enhanced tidal heating. A major issue concerns the thermal/gravitational stability of these water reservoirs. Here we investigate the conditions under which water can be generated and transported through Europa's ice shell. We address particularly the downward two-phase flow by solving the equations for a two-phase mixture of water ice and liquid water in one-dimensional geometry. In the case of purely temperate ice, we show that water is transported downward very efficiently in the form of successive porosity waves. The time needed to transport the water from the subsurface region to the underlying ocean varies between ˜1 and 100 kyr, depending mostly on the ice permeability. We further show that water produced in the head of tidally heated hot plumes never accumulates at shallow depths and is rapidly extracted from the ice shell (within less than a few hundred kiloyears). Our calculations indicate that liquid water will be largely absent in the near subsurface, with the possible exception of cold conductive regions subjected to strong tidal friction. Recently active double ridges subjected to large tidally driven strike-slip motions are perhaps the most likely candidates for the detection of transient water lenses at shallow depths on Europa.
Study on Two-Phase Flow in Heterogeneous Porous Media by Light Transmission Method
NASA Astrophysics Data System (ADS)
Qiao, W.
2015-12-01
The non-aqueous phase liquid (NAPL) released to the subsurface can form residual ganglia and globules occupying pores and also accumulate and form pools, in which multiphase system forms. Determining transient fluid saturations in a multiphase system is essential to understand the flow characteristics of systems and to perform effective remediation strategies. As a non-destructive and non-invasive laboratory technique utilized for the measurement of liquid saturation in porous media, light transmission is of the lowest cost and safe. Utilization of Coupled Charge Device camera in light transmission systems provides a nearly instantaneous high-density array of spatial measurements over a very large dynamic range. The migration of NAPL and air spariging technique applied to remove NAPL in aquifer systems are typically two-phase flow problem. Because of the natural aquifer normally being heterogeneous, two 2-D sandboxes (Length55cm×width1.3cm×hight45cm) are set up to study the migration of gas and DNAPL in heterogeneous porous media based on light transmission method and its application in two-phase flow. Model D for water/gas system developed by Niemet and Selker (2001) and Model NW-A for water/NAPL system developed by Zhang et al. (2014) are applied for the calculation of fluid saturation in the two experiments, respectively. The gas injection experiments show that the gas moves upward in the irregular channels, piling up beneath the low permeability lenses and starting lateral movement. Bypassing the lenses, the gas moves upward and forms continuous distribution in the top of the sandbox. The faster of gas injects, the wider of gas migration will be. The DNAPL infiltration experiment shows that TCE mainly moves downward as the influence of gravity, stopping vertical infiltration when reaching the low permeability lenses because of its failure to overcome the capillary pressure. Then, TCE accumulates on the surface and starts transverse movement. Bypassing the
Rheology of two-phase composites: implications for flow properties of the lower mantle
NASA Astrophysics Data System (ADS)
Wang, Y.; Nishiyama, N.; Hilairet, N.; Fiquet, G.; Tsuchiya, T.
2011-12-01
We examine flow properties and deformation-induced fabric evolution in two-phase composites using the deformation DIA (D-DIA) and the high-pressure x-ray tomography microscope (HPXTM) with monochromatic synchrotron radiation. Stress-strain curves were determined on an analog lower mantle material CaGeO3 perovskite (GePv) plus MgO. The sintered polycrystalline rock was synthesized from the disproportionation reaction of CaMgGeO4 (olivine) - GePv+MgO at 12 GPa and 1573 K for 4 h. The sample contains 28 vol% MgO, and is an excellent analog material for the lower mantle. Scanning electron microscopy showed that the average grain size was about 1 micron. The sample was deformed in the D-DIA at pressures from 4 to 12 GPa, temperatures 600 to 1200 K, and strain rates from 1x to 3x10-5 s-1. The maximum axial strain was 16 %. Elastic constants for GePv were calculated using first-principles with the generalized gradient corrections (GGC) technique. In order to examine effects of the second phase on flow properties, a pure GePv sample was deformed under identical conditions. Flow properties of MgO are available from our previous studies [1]. The relative stress levels in GePv and MgO in the composite sample are in general agreement with numerical simulations [2]. Another analog, a mixture of San Carlos olivine and Fe-S, was examined in the HPXTM. The strength contrast of two phases is similar to that of perovskite and ferropericlase. The initial texture was of the load-bearing framework (LBF) type, with isolated "weak" Fe-S grains sounded by "strong" silicate framework. During shear deformation, a strong shape preferred orientation began to develop in the sample at shear strains above 300%, forming an interconnected weak layer (IWL) texture. The development of deformation fabric was continuously monitored by tomographic imaging under high pressure to a maximum shear strain of 1300%. Applications of these results to dynamics of the lower mantle are discussed. [1] Uchida, T
Effect of hydrophobicity on colloid transport during two-phase flow in a micromodel
NASA Astrophysics Data System (ADS)
Zhang, Qiulan; Hassanizadeh, S. M.; Liu, B.; Schijven, J. F.; Karadimitriou, N. K.
2014-10-01
The goal of this research was to investigate the difference in behavior of hydrophilic and hydrophobic colloids during transport in two-phase flow, in general, and their attachment and remobilization characters, in particular. Experiments were performed in a hydrophobic polydimethylsiloxane (PDMS) micromodel. Water and fluorinert-FC43 were used as the two immiscible liquids. Given the fact that PDMS is a hydrophobic material, fluorinert was the wetting phase and water was the nonwetting phase in this micromodel. As model colloids, we used hydrophilic polystyrene carboxylate-modified microspheres (dispersible in water) and hydrophobic fluorous-modified silica microspheres (dispersible in fluorinert) in separate experiments. Using a confocal laser scanning microscope, we directly observed fluid distribution and colloid movement within pores of the micromodel. We also obtained concentration breakthrough curves by measuring the fluorescent intensities in the outlet of the micromodel. The breakthrough curves during steady-state flow showed that the colloid attachment rate is inversely related to the background saturation of the fluid in which the colloids were dispersed. Our visualization results showed that the enhanced attachment of hydrophilic colloids at lower water saturations was due to the retention at the fluorinert-water interface and fluorinert-water-solid contact lines. This effect was observed to be much less in the case of hydrophobic colloids (dispersed in fluorinert). In order to explain the colloids behavior, we calculated interaction potential energies of colloids with PDMS surfaces, fluid-fluid interfaces, and fluid-fluid-solid contact lines. Also, balance of forces that control colloid, including DLVO, hydrodynamic, and surface tension forces, were determined. Our calculations showed that there is a stronger repulsive energy barrier between hydrophobic colloids and fluorinert-water interface and solid-fluid interface, compared with the hydrophilic
Huh, D; Kuo, C-H; Grotberg, J B
2010-01-01
Here we map gas–liquid two-phase flow regimes observed in polymeric microchannels with different wetting properties. We utilized video and confocal microscopy to examine two-phase flow patterns produced by parallel injection of air and water through a Y-shaped junction into a rectangular microchannel made of poly(dimethylsiloxane) (PDMS). We observed seven flow regimes in microchannels with hydrophobic walls, whereas only two flow patterns were identified in hydrophilic microchannels. Our study demonstrates that surface wettability has a profound influence on the spatial distribution of air and water moving in microchannels. PMID:20126421
Hybrid Upwinding for Two-Phase Flow in Heterogeneous Porous Media with Buoyancy and Capillarity
NASA Astrophysics Data System (ADS)
Hamon, F. P.; Mallison, B.; Tchelepi, H.
2016-12-01
In subsurface flow simulation, efficient discretization schemes for the partial differential equations governing multiphase flow and transport are critical. For highly heterogeneous porous media, the temporal discretization of choice is often the unconditionally stable fully implicit (backward-Euler) method. In this scheme, the simultaneous update of all the degrees of freedom requires solving large algebraic nonlinear systems at each time step using Newton's method. This is computationally expensive, especially in the presence of strong capillary effects driven by abrupt changes in porosity and permeability between different rock types. Therefore, discretization schemes that reduce the simulation cost by improving the nonlinear convergence rate are highly desirable. To speed up nonlinear convergence, we present an efficient fully implicit finite-volume scheme for immiscible two-phase flow in the presence of strong capillary forces. In this scheme, the discrete viscous, buoyancy, and capillary spatial terms are evaluated separately based on physical considerations. We build on previous work on Implicit Hybrid Upwinding (IHU) by using the upstream saturations with respect to the total velocity to compute the relative permeabilities in the viscous term, and by determining the directionality of the buoyancy term based on the phase density differences. The capillary numerical flux is decomposed into a rock- and geometry-dependent transmissibility factor, a nonlinear capillary diffusion coefficient, and an approximation of the saturation gradient. Combining the viscous, buoyancy, and capillary terms, we obtain a numerical flux that is consistent, bounded, differentiable, and monotone for homogeneous one-dimensional flow. The proposed scheme also accounts for spatially discontinuous capillary pressure functions. Specifically, at the interface between two rock types, the numerical scheme accurately honors the entry pressure condition by solving a local nonlinear problem
Single- and two-phase flow in microfluidic porous media analogs based on Voronoi tessellation.
Wu, Mengjie; Xiao, Feng; Johnson-Paben, Rebecca M; Retterer, Scott T; Yin, Xiaolong; Neeves, Keith B
2012-01-21
The objective of this study was to create a microfluidic model of complex porous media for studying single and multiphase flows. Most experimental porous media models consist of periodic geometries that lend themselves to comparison with well-developed theoretical predictions. However, many real porous media such as geological formations and biological tissues contain a degree of randomness and complexity at certain length scales that is not adequately represented in periodic geometries. To design an experimental tool to study these complex geometries, we created microfluidic models of random homogeneous and heterogeneous networks based on Voronoi tessellations. These networks consisted of approximately 600 grains separated by a highly connected network of channels with an overall porosity of 0.11-0.20. We found that introducing heterogeneities in the form of large cavities within the network changed the permeability in a way that cannot be predicted by the classical porosity-permeability relationship known as the Kozeny equation. The values of permeability found in experiments were in excellent agreement with those calculated from three-dimensional lattice Boltzmann simulations. In two-phase flow experiments of oil displacement with water we found that the wettability of channel walls determined the pattern of water invasion, while the network topology determined the residual oil saturation. The presence of cavities increased the microscopic sweeping efficiency in water-oil displacement. These results suggest that complex network topologies lead to fluid flow behavior that is difficult to predict based solely on porosity. The novelty of this approach is a unique geometry generation algorithm coupled with microfabrication techniques to produce pore scale models of stochastic homogeneous and heterogeneous porous media. The ability to perform and visualize multiphase flow experiments within these geometries will be useful in measuring the mechanism(s) of displacement
NASA Astrophysics Data System (ADS)
Müller, Florian; Jenny, Patrick; Daniel, Meyer
2014-05-01
To a large extent, the flow and transport behaviour within a subsurface reservoir is governed by its permeability. Typically, permeability measurements of a subsurface reservoir are affordable at few spatial locations only. Due to this lack of information, permeability fields are preferably described by stochastic models rather than deterministically. A stochastic method is needed to asses the transition of the input uncertainty in permeability through the system of partial differential equations describing flow and transport to the output quantity of interest. Monte Carlo (MC) is an established method for quantifying uncertainty arising in subsurface flow and transport problems. Although robust and easy to implement, MC suffers from slow statistical convergence. To reduce the computational cost of MC, the multilevel Monte Carlo (MLMC) method was introduced. Instead of sampling a random output quantity of interest on the finest affordable grid as in case of MC, MLMC operates on a hierarchy of grids. If parts of the sampling process are successfully delegated to coarser grids where sampling is inexpensive, MLMC can dramatically outperform MC. MLMC has proven to accelerate MC for several applications including integration problems, stochastic ordinary differential equations in finance as well as stochastic elliptic and hyperbolic partial differential equations. In this study, MLMC is combined with a reservoir simulator to assess uncertain two phase (water/oil) flow and transport within a random permeability field. The performance of MLMC is compared to MC for a two-dimensional reservoir with a multi-point Gaussian logarithmic permeability field. It is found that MLMC yields significant speed-ups with respect to MC while providing results of essentially equal accuracy. This finding holds true not only for one specific Gaussian logarithmic permeability model but for a range of correlation lengths and variances.
Two-Phase Flow Technology Developed and Demonstrated for the Vision for Exploration
NASA Technical Reports Server (NTRS)
Sankovic, John M.; McQuillen, John B.; Lekan, Jack F.
2005-01-01
NASA s vision for exploration will once again expand the bounds of human presence in the universe with planned missions to the Moon and Mars. To attain the numerous goals of this vision, NASA will need to develop technologies in several areas, including advanced power-generation and thermal-control systems for spacecraft and life support. The development of these systems will have to be demonstrated prior to implementation to ensure safe and reliable operation in reduced-gravity environments. The Two-Phase Flow Facility (T(PHI) FFy) Project will provide the path to these enabling technologies for critical multiphase fluid products. The safety and reliability of future systems will be enhanced by addressing focused microgravity fluid physics issues associated with flow boiling, condensation, phase separation, and system stability, all of which are essential to exploration technology. The project--a multiyear effort initiated in 2004--will include concept development, normal-gravity testing (laboratories), reduced gravity aircraft flight campaigns (NASA s KC-135 and C-9 aircraft), space-flight experimentation (International Space Station), and model development. This project will be implemented by a team from the NASA Glenn Research Center, QSS Group, Inc., ZIN Technologies, Inc., and the Extramural Strategic Research Team composed of experts from academia.