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Multiphase Flow (multiphase + flow)

Distribution by Scientific Domains

Chemistry	51%
Engineering	38%
3 Other Domains	11%

Terms modified by Multiphase Flow

multiphase flow system

Selected Abstracts

On the Governing Equations and Model Assumptions for Multiphase Flow in Porous Media

GROUND WATER, Issue 4 2000
Amir Gamliel
No abstract is available for this article. [source]

Instabilities during batch sedimentation in geometries containing obstacles: A numerical and experimental study,

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2007
Rekha R. Rao
Abstract Batch sedimentation of non-colloidal particle suspensions is studied with nuclear magnetic resonance flow visualization and continuum-level numerical modelling of particle migration. The experimental method gives particle volume fraction as a function of time and position, which then provides validation data for the numerical model. A finite element method is used to discretize the equations of motion, including an evolution equation for the particle volume fraction and a generalized Newtonian viscosity dependent on local particle concentration. The diffusive-flux equation is based on the Phillips model (Phys. Fluids A 1992; 4:30,40) and includes sedimentation terms described by Zhang and Acrivos (Int. J. Multiphase Flow 1994; 20:579,591). The model and experiments are utilized in three distinct geometries with particles that are heavier and lighter than the suspending fluid, depending on the experiment: (1) sedimentation in a cylinder with a contraction; (2) particle flotation in a horizontal cylinder with a horizontal rod; and (3) flotation around a rectangular inclusion. Secondary flows appear in both the experiments and the simulations when a region of higher density fluid is above a lower density fluid. The secondary flows result in particle inhomogeneities, Rayleigh,Taylor-like instabilities, and remixing, though the effect in the simulations is more pronounced than in the experiments. Published in 2007 by John Wiley & Sons, Ltd. [source]

Adiabatic capillary tube flow of carbon dioxide in a transcritical heat pump cycle

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2007
Neeraj Agrawal
Abstract Flow characteristics of an adiabatic capillary tube in a transcritical CO2 heat pump system have been investigated employing the homogeneous model. The model is based on fundamental equations of mass, energy and momentum which are solved simultaneously. Two friction factor empirical correlations (Churchill, Lin et al., Int. J. Multiphase Flow 1991; 17(1):95,102) and four viscosity models (Mcadams, Cicchitti, Dukler and Lin) are comparatively used to investigate the flow characteristics. Choked condition at the outlet is also investigated for maximum mass flow rate. Subcritical and supercritical thermodynamic and transport properties of CO2 are calculated employing a precision property code. Choice of viscosity model causes minor variation in results unlike in chlorofluorocarbons (CFCs) refrigerants. Relationships between cooling capacity with capillary tube diameter, length and maximum mass flow rate are presented. A lower evaporating temperature yields a larger cooling capacity due to the unique thermodynamic properties of CO2. It is also observed that an optimum cooling capacity exists for a specified capillary tube. Copyright © 2006 John Wiley & Sons, Ltd. [source]

CFD simulation of gas,solid bubbling fluidized bed: A new method for adjusting drag law

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009
Farshid Vejahati
Abstract In computational fluid dynamics modelling of gas,solid two phase flow, drag force is one of the dominant mechanisms for interphase momentum transfer. Despite the profusion of drag models, none of the available drag functions gives accurate results in their own original form. In this work the drag correlations of Syamlal and O'Brien (Syamlal and O'Brien, Int. J. Multiphase Flow. 1988; 14(4):473,481), Gidaspow (Gidaspow, Appl. Mech. Rev. 1986; 39:1,23), Wen and Yu (Wen and Yu, Chem. Eng. Prog. Symp. Ser. 1966; 62(2):100,111), Arastoopour et al. (Arastoopour et al., Powder Technol. 1990; 62(2): 163,170), Gibilaro et al. (Gibilaro et al., Chem. Eng. Sci. 1985; 40:1817,1823), Di Felice (Di Felice, Int. J. Multiphase Flow. 1994; 20(1):153,159), Zhang-Reese (Zhang and Reese, Chem. Eng. Sci. 2003; 58(8):1641,1644) and Hill et al. (Hill et al., J. Fluid Mech. 2001; 448:243,278) are reviewed using a multi-fluid model of FLUENT V6.3.26 (FLUENT, 2007. Fluent 6.3 User's Guide, 23.5 Eulerian Model, Fluent, Inc.) software with the resulting hydrodynamics parameters being compared with experimental data. The main contribution of this work is to propose an easy to implement and efficient method for adjustment of Di Felice drag law which is more efficient compared to the one proposed by Syamlal-O'Brien. The new method adopted in this work showed a quantitative improvement compared to the adjusted drag model of Syamlal-O'Brien. Prediction of bed expansion and pressure drop showed excellent agreement with results of experiments conducted in a Plexiglas fluidized bed. A mesh size sensitivity analysis with varied interval spacing showed that mesh interval spacing with 18 times the particle diameter and using higher order discretization methods produces acceptable results. Dans la modélisation par la dynamique des fluides par ordinateur de l'écoulement diphasique gaz-solide, la force de traînée est l'un des mécanismes dominants dans le transfert de quantité de mouvement interphase. Malgré la profusion des modèles de traînée, aucune des fonctions de traînée disponibles ne donnent de résultats précis dans leur forme originale. Dans cet article, les corrélations de traînée de Syamlal and O'Brien (Syamlal and O'Brien, Int. J. Multiphase Flow. 1988; 14(4):473,481), Gidaspow (Gidaspow, Appl. Mech. Rev. 1986; 39:1,23), Wen and Yu (Wen and Yu, Chem. Eng. Prog. Symp. Ser. 1966; 62(2):100,111), Arastoopour et al. (Arastoopour et al., Powder Technol. 1990; 62(2):163,170), Gibilaro et al. (Gibilaro et al., Chem. Eng. Sci. 1985; 40:1817,1823), Di Felice (Di Felice, Int. J. Multiphase Flow. 1994; 20(1):153,159), Zhang-Reese (Zhang and Reese, Chem. Eng. Sci. 2003; 58(8):1641,1644) et Hill et al. (Hill et al., J. Fluid Mech. 2001; 448:243,278) sont examinées à l'aide du modèle multi-fluides du logiciel FLUENT V6.3.26 (FLUENT, 2007. Fluent 6.3 User's Guide, 23.5 Eulerian Model, Fluent, Inc.), les paramètres hydrodynamiques résultants étant comparés aux données expérimentales. La principale contribution de ce travail est de proposer une méthode efficace et facile à mettre en ,uvre pour l'ajustement de la loi de traînée de Di Felice qui est plus efficace comparativement à celle proposée par Syamlal-O'Brien. La nouvelle méthode adoptée dans ce travail montre une amélioration quantitative par rapport au modèle de traînée ajusté de Syamlal-O'Brien. La prédiction de l'expansion de lit et de la perte de charge montre un excellent accord avec les résultats des expériences menées dans un lit fluidisé en plexiglass. Une analyse de sensibilité de la taille des mailles avec des mailles de taille variable variés montre qu'une taille de maille égale à 18 fois le diamètre des particules et l'utilisation de méthodes de discrétisation d'ordre supérieur donnent des résultats acceptables. [source]

Simulating the Dynamics of Spouted-Bed Nuclear Fuel Coaters,

CHEMICAL VAPOR DEPOSITION, Issue 9 2007
S. Pannala
Abstract We describe simulation studies of the dynamics of spouted beds used for CVD coating of nuclear fuel particles. Our principal modeling tool is the Multiphase Flow with Interphase eXchanges (MFIX) code that was originally developed by the National Energy Technology Laboratory (NETL) for fossil energy process applications. In addition to standard MFIX features that allow coupling of transient hydrodynamics, heat and mass transfer, and chemical kinetics, we employ special post-processing tools to track particle mixing and circulation as functions of operating conditions and bed design. We describe in detail one major feature of the dynamics, which is the occurrence of very regular spontaneous pulsations of gas and particle flow in the spout. These pulsations appear to be critically linked to the entrainment and circulation of solids, and they produce readily accessible dynamic pressure variations that can be used for direct comparisons of model predictions with experiments. Spouted-bed dynamics are important from a CVD perspective because they directly determine the magnitude and variability of the concentration and species gradients in the zone where reactant gases first come into contact with hot particles. As this unsteady spouted-bed environment differs from other types of CVD reactors, the design and scale-up of such reactors is likely to involve unique modeling issues. Our primary goal here is to lay the groundwork for how computational simulation can be used to address these modeling issues in the specific context of nuclear fuel particle coating. [source]

Projection and partitioned solution for two-phase flow problems

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2005
Andrea Comerlati
Abstract Multiphase flow through porous media is a highly nonlinear process that can be solved numerically with the aid of finite elements (FE) in space and finite differences (FD) in time. For an accurate solution much refined FE grids are generally required with the major computational effort consisting of the resolution to the nonlinearity frequently obtained with the classical Picard linearization approach. The efficiency of the repeated solution to the linear systems within each individual time step represents the key to improve the performance of a multiphase flow simulator. The present paper discusses the performance of the projection solvers (GMRES with restart, TFQMR, and BiCGSTAB) for two global schemes based on a different nodal ordering of the unknowns (ORD1 and ORD2) and a scheme (SPLIT) based on the straightforward inversion of the lumped mass matrix which allows for the preliminary elimination and substitution of the unknown saturations. It is shown that SPLIT is between two and three time faster than ORD1 and ORD2, irrespective of the solver used. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Multiphase flow and mixing in dilute bubble swarms

AICHE JOURNAL, Issue 9 2010
Stefan Radl
Abstract High-fidelity three-dimensional (3-D) simulations of multiphase flow and mixing in dilute bubble swarms were performed using the Euler-Lagrange simulation approach. Included was species transport, as well as complex chemical reactions in the simulations. It was found that the algebraic SGS model satisfactory predicts experimental data for the mean flow field. A detailed description of multiphase flow was used and developed to simulate the time evolution of scalar and reactive mixing in a bubble column. An analysis involving the scale of segregation ,, a metric that characterizes the mean driving force for mixing, is applied for the first time to multiphase flow. The study shows that , is inversely proportional to the bubble diameter at constant gas-feed rate, but only a weak function of the gas-feed rate. Also, we observed significant differences of mixing metrics in reactive and nonreactive systems. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source]

Multiphase flow at the edge of a steam chamber

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2010
Jyotsna Sharma
Abstract The use of steam-assisted gravity drainage (SAGD) to recover bitumen from Athabasca deposits in Alberta has been growing. Butler [Butler, J. Can. Pet. Tech. 1985;24:42,51] derived a simple theory to calculate the production rate of oil during SAGD in an ideal reservoir. This simple and useful theory made several assumptions about the properties of the reservoir and operating conditions of the process. The theory also assumed that the highest mobility oil is at the edge of the steam chamber and that the oil phase velocity is highest at the chamber edge and reduces with distance into the oil sand. This research examines flow conditions at the edge of the steam chamber. Specifically, a new theory is derived that takes into account the impact of oil saturation and relative permeability on the oil mobility profile at the edge of a steam chamber. It is shown that the flow behaviour at the edge of a steam chamber is more complex and is not fully represented by Butler's theory. Contrary to Butler's theory, the oil mobility has its maximum some distance away from the edge of the steam chamber. The results reveal that the higher the thermal diffusivity of the oil sand, the deeper the location where the oil phase velocity is maximum. The developed model has been validated against published experimental and field data. On a enregistré une forte augmentation de l'utilisation du procédé de drainage gravitaire en présence de vapeur (technique SAGD) pour récupérer le bitume naturel des gisements de l'Athabasca, Alberta. Butler (1985) a mis en place une théorie simple pour calculer le taux de production de pétrole durant l'utilisation de la technique SAGD dans un réservoir idéal. Cette théorie simple et utile fait plusieurs hypothèses sur les propriétés du réservoir et les conditions opératoires du processus. La théorie suppose également que le pétrole ayant la mobilité la plus élevée se trouve au bord de la chambre de vapeur et que la vélocité de la phase huileuse est à son niveau le plus élevé au niveau du bord de la chambre et qu'elle diminue ensuite avec la distance à l'intérieur des sables bitumineux. Ce travail de recherche examine les conditions d'écoulement au niveau des bords de la chambre de vapeur. De façon plus spécifique, une nouvelle théorie est mise en place en tenant compte de l'impact de la saturation en pétrole et de la perméabilité relative sur le profil de mobilité du pétrole au niveau des bords de la chambre de vapeur. On montre que le comportement de l'écoulement au niveau des bords d'une chambre de vapeur est plus complexe que prévu et qu'il n'est totalement représenté par la théorie de Butler. Contrairement à la théorie de Butler, la mobilité du pétrole présente son maximum à une certaine distance à l'écart des bords de la chambre de vapeur. Les résultats révèlent que plus la diffusivité thermique des sables bitumeux est élevée, plus le lieu de vélocité maximale de la phase huileuse est profond. Le modèle développé a été validé contre des données expérimentales publiées et des données obtenues sur le terrain. [source]

Numerical simulation of flow and heat transfer in connection of gasifier to the radiant syngas cooler

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009
Jianjun Ni
Abstract The connection of gasifier to the radiant syngas cooler has been regarded as a key technology for heat recovery system. Multiphase flow and heat transfer processes presented in this work considers particle deposition and radiation model to mixture of non-gray gas with particles. An axisymmetric simulation of the multiphase flow in an industrial scale connection is performed. The standard k -, model, Renormalization group (RNG) k -, model and Realizable k -, model turbulence model are proposed. The particle motion is modeled by discrete random walk model. The discrete ordinates model (DOM), P-1 and discrete transfer model (DTRM) are used to model the radiative heat transfer. The effect of particles on the radiative heat transfer was taken into account when the DOM and P-1 model were used. The absorption coefficient of the gas mixture is calculated by means of a weighted-sum-of-gray-gas (WSGG) model. The results with the DOM and P-1 model are very similar and close to practical condition. A large number of particles are deposited on the cone of gasifier which is the top of connection. Maximum temperature difference is approximate 7 K when the cooling tube heights change from 0.5 m to 1.5 m. The temperature inside has a linear relationship with operating temperature. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]

Grain transport mechanics in shallow overland flow

ECOHYDROLOGY, Issue 3 2009
S.N. Prasad
Abstract A physical model based on continuum multiphase flow is described to represent saltating transport of grains in shallow overland flows. The two-phase continuum flow of water and sediment considers coupled StVenant-type equations. The interactive cumulative effect of grains is incorporated by a dispersive stress term. The mean fluid thrust on the particle in the saltation layer of grains is expressed in terms of a slip velocity. The continuum model leads to the unexpected, but an interesting result is that particle velocity increases with the solid concentration. This increase predicts monotonic behaviour leading to overestimates of particle velocity at higher sediment concentration. To improve the predictions, grain dynamic equations, which incorporate bed collision, are analysed. The analysis leads to an improved model for predicting saltation height. Incorporation of the results in the continuum model yields a velocity-concentration relationship that is consistent with experimental observations for increasing concentration. Laboratory flume experiments explore the evaluation of various parameters from the measured particle velocities by photonic probes. Copyright © 2009 John Wiley & Sons, Ltd. [source]

An upscaling method and a numerical analysis of swelling/shrinking processes in a compacted bentonite/sand mixture

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2004
M. Xie
Abstract This paper presents an upscaling concept of swelling/shrinking processes of a compacted bentonite/sand mixture, which also applies to swelling of porous media in general. A constitutive approach for highly compacted bentonite/sand mixture is developed accordingly. The concept is based on the diffuse double layer theory and connects microstructural properties of the bentonite as well as chemical properties of the pore fluid with swelling potential. Main factors influencing the swelling potential of bentonite, i.e. variation of water content, dry density, chemical composition of pore fluid, as well as the microstructures and the amount of swelling minerals are taken into account. According to the proposed model, porosity is divided into interparticle and interlayer porosity. Swelling is the potential of interlayer porosity increase, which reveals itself as volume change in the case of free expansion, or turns to be swelling pressure in the case of constrained swelling. The constitutive equations for swelling/shrinking are implemented in the software GeoSys/RockFlow as a new chemo-hydro-mechanical model, which is able to simulate isothermal multiphase flow in bentonite. Details of the mathematical and numerical multiphase flow formulations, as well as the code implementation are described. The proposed model is verified using experimental data of tests on a highly compacted bentonite/sand mixture. Comparison of the 1D modelling results with the experimental data evidences the capability of the proposed model to satisfactorily predict free swelling of the material under investigation. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Comparison of GMRES and ORTHOMIN for the black oil model on unstructured grids

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2006
Wenjun Li
Abstract This paper addresses an application of ORTHOMIN and GMRES to petroleum reservoir simulation using the black oil model on unstructured grids. Comparisons between these two algorithms are presented in terms of storage and total flops per restart step. Numerical results indicate that GMRES is faster than ORTHOMIN for all tested petroleum reservoir problems, particularly for large scale problems. The control volume function approximation method is utilized in the discretization of the governing equations of the black oil model. This method can accurately approximate both the pressure and velocity in the simulation of multiphase flow in porous media, effectively reduce grid orientation effects, and be easily applied to arbitrarily shaped control volumes. It is particularly suitable for hybrid grid reservoir simulation. Copyright © 2006 John Wiley & Sons, Ltd. [source]

A projection scheme for incompressible multiphase flow using adaptive Eulerian grid

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2004
T. Chen
Abstract This paper presents a finite element method for incompressible multiphase flows with capillary interfaces based on a (formally) second-order projection scheme. The discretization is on a fixed Eulerian grid. The fluid phases are identified and advected using a level set function. The grid is temporarily adapted around the interfaces in order to maintain optimal interpolations accounting for the pressure jump and the discontinuity of the normal velocity derivatives. The least-squares method for computing the curvature is used, combined with piecewise linear approximation to the interface. The time integration is based on a formally second order splitting scheme. The convection substep is integrated over an Eulerian grid using an explicit scheme. The remaining generalized Stokes problem is solved by means of a formally second order pressure-stabilized projection scheme. The pressure boundary condition on the free interface is imposed in a strong form (pointwise) at the pressure-computation substep. This allows capturing significant pressure jumps across the interface without creating spurious instabilities. This method is simple and efficient, as demonstrated by the numerical experiments on a wide range of free-surface problems. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Hydrodynamic considerations on optimal design of a three-phase airlift bioreactor with high solids loading

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2003
Jaroslav Klein
Abstract The hydrodynamic study of a three-phase airlift (TPAL) bioreactor with an enlarged gas,liquid dual separator was carried out. Different lengths and diameters of the draft tube were tested to show how the design of the separator zone affects the hydrodynamic performance of the TPAL reactor. Ca-alginate beads with entrapped yeast biomass at different loadings (0, 7, 14 and 21% v/v) were used in order to mimic the solid phase of conventional high cell density systems, such as those with cells immobilized on carriers or flocculating cells. Important information on multiphase flow and distribution of gas and solid phases in the internal-loop airlift reactor (ALR) with high solids loading was obtained, which can be used for suggesting optimal hydrodynamic conditions in a TPAL bioreactor with high solids loading. It is finally suggested that the ALR with a dual separator and a downcomer to riser cross-sectional area ratio (AD/AR) ranging from 1.2 to 2.0 can be successfully applied to batch/continuous high cell density systems, where the uniform distribution of solid phase, its efficient separation of particles from the liquid phase, and an improved residence time of air bubbles inside the reactor are desirable. Copyright © 2003 Society of Chemical Industry [source]

Multiphase flow and mixing in dilute bubble swarms

Investigation of nonuniformity in a liquid,solid fluidized bed with identical parallel channels

AICHE JOURNAL, Issue 1 2010
Long Fan
Abstract Previous work has demonstrated that multiphase flow through identical parallel channels and multiple cyclones can give rise to significant nonuniformity among the flow paths. This article presents results from a study where the distribution of voidage and flux through parallel channels in liquid,solid fluidized beds is investigated. Experiments and computational fluid dynamics simulations were performed with 1.2 mm glass beads fluidized by water where a cross baffle divided a 191 mm diameter column into four identical parallel channels. Voidages were measured by optical fiber probes. Simulations from a three-dimensional unsteady-state Eulerian,Eulerian model based on FLUENT software showed good agreement with the experimental results. Despite the symmetrical geometry of the system, the average voidage and particle velocities in one channel differed somewhat from those in the others. Increasing the superficial liquid velocity could increase voidage greatly and affect the degree of nonuniformity in the four channels. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Volume-of-fluid-based model for multiphase flow in high-pressure trickle-bed reactor: Optimization of numerical parameters

AICHE JOURNAL, Issue 11 2009
Rodrigo J. G. Lopes
Abstract Aiming to understand the effect of various parameters such as liquid velocity, surface tension, and wetting phenomena, a Volume-of-Fluid (VOF) model was developed to simulate the multiphase flow in high-pressure trickle-bed reactor (TBR). As the accuracy of the simulation is largely dependent on mesh density, different mesh sizes were compared for the hydrodynamic validation of the multiphase flow model. Several model solution parameters comprising different time steps, convergence criteria and discretization schemes were examined to establish model parametric independency results. High-order differencing schemes were found to agree better with the experimental data from the literature given that its formulation includes inherently the minimization of artificial numerical dissipation. The optimum values for the numerical solution parameters were then used to evaluate the hydrodynamic predictions at high-pressure demonstrating the significant influence of the gas flow rate mainly on liquid holdup rather than on two-phase pressure drop and exhibiting hysteresis in both hydrodynamic parameters. Afterwards, the VOF model was applied to evaluate successive radial planes of liquid volume fraction at different packed bed cross-sections. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Stretching operational life of trickle-bed filters by liquid-induced pulse flow

AICHE JOURNAL, Issue 7 2005
Ion Iliuta
Abstract When dilute liquid suspensions contaminated with fine solids are treated in catalytic trickle-bed reactors, bed plugging develops and increases the resistance to two-phase flow until ultimate unit shutdown for bed substitution with pristine catalyst. The release of deposited fines, or the inhibition of fines deposition over some regions of the collector, is expected to alleviate the plugging if liquid flow shock or periodic operation policies are implemented. Current physical models linking gas,liquid phase flow to space,time evolution of fines deposition and release are unable to depict this new type of filtration in trickle beds. This work attempts to fill in this gap by developing a dynamic multiphase flow deep-bed filtration model. The model incorporates the physical effects of porosity and effective specific surface area changes as a result of fines deposition/release, gas and suspension inertial effects, and coupling effects between the filtration parameters and the interfacial momentum exchange force terms. The release of the fine particles from the collector surface was assumed to be induced by the colloidal forces in the case of Brownian particles or by the hydrodynamic forces in the case of non-Brownian particles. An important finding of the work was that for noncolloidal fines both induced pulsing and liquid flow shock operations conferred substantial improvements (measured in terms of reduction in specific deposit and pressure drop) in the mitigation of plugging in trickle-bed reactors. However, because of the highest critical shear stress for fines in the colloidal range, induced pulsing did not substantiate any practically useful effect. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source]

Simulation of Thrombus Formation in Shear Flows Using Lattice Boltzmann Method

ARTIFICIAL ORGANS, Issue 8 2009
Masaaki Tamagawa
Abstract This article describes the prediction of index of thrombus formation in shear blood flow by computational fluid dynamics with the Lattice Boltzmann Method (LBM), applying to backward-facing step flow, which is a simple model of shear flow in the rotary blood pumps and complicated geometry of medical fluid devices. Assuming that the blood flow is a multiphase flow composed of blood plasma and activated fibrinogen, the effects of surface tension and adhesion force to the wall were added to the LBM computational model. It was found that the thrombus formation in the backward-facing step flow occurred just after the reattachment point and behind the step. These results corresponded to our observation results of thrombus formation. For the thrombus formation in every case of blood flow to be predicted, effects of threshold level of physical parameters such as shear rate and adhesion force (effective distance from the wall) were estimated. Moreover, it was also found that the predicted adhesion point on the wall agrees with the visualization of thrombus formation by predicting proper thresholds. [source]

Numerical simulation of flow and heat transfer in connection of gasifier to the radiant syngas cooler

Multiphase CFD Simulation of a Solid Bowl Centrifuge

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 5 2009
X. Romaní Fernández
Abstract This study presents some results from the numerical simulation of the flow in an industrial solid bowl centrifuge used for particle separation in industrial fluid processing. The computational fluid dynamics (CFD) software Fluent was used to simulate this multiphase flow. Simplified two-dimensional and three-dimensional geometries were built and meshed from the real centrifuge geometry. The CFD results show a boundary layer of axially fast moving fluid at the gas-liquid interface. Below this layer there is a thin recirculation. The obtained tangential velocity values are lower than the ones for the rigid-body motion. Also, the trajectories of the solid particles are evaluated. [source]

Overview of Multiphase Flow Phenomena in Moving Time-Averaged Space

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2006
K. Ueyama
Abstract An overview of multiphase flow phenomena is described on the basis of three relations; a relation between an interaction force and time-averaged physical quantities, a relation between an interaction force and the surrounding flow field, and a relation between time-averaged physical quantities and multiphase flow. The three relations used to theoretically derive the parabolic radial distribution of gas holdup for recirculating turbulent flow in a bubble column are in good agreement with experimental data. General applicability of the three relations for a variety of multiphase flows is also discussed. [source]

Momentum/continuity coupling with large non-isotropic momentum source terms

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2009
J. D. Franklin
Abstract Pressure-based methods such as the SIMPLE algorithm are frequently used to determine a coupled solution between the component momentum equations and the continuity equation. This paper presents a colocated variable pressure correction algorithm for control volumes of polyhedral/polygonal cell topologies. The correction method is presented independent of spatial approximation. The presence of non-isotropic momentum source terms is included in the proposed algorithm to ensure its applicability to multi-physics applications such as gas and particulate flows. Two classic validation test cases are included along with a newly proposed test case specific to multiphase flows. The classic validation test cases demonstrate the application of the proposed algorithm on truly arbitrary polygonal/polyhedral cell meshes. A comparison between the current algorithm and commercially available software is made to demonstrate that the proposed algorithm is competitively efficient. The newly proposed test case demonstrates the benefits of the current algorithm when applied to a multiphase flow situation. The numerical results from this case show that the proposed algorithm is more robust than other methods previously proposed. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Pressure relaxation procedures for multiphase compressible flows

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2005
M.-H. Lallemand
Abstract This paper deals with pressure relaxation procedures for multiphase compressible flow models. Such models have nice mathematical properties (hyperbolicity) and are able to solve a wide range of applications: interface problems, detonation physics, shock waves in mixtures, cavitating flows, etc. The numerical solution of such models involves several ingredients. One of those ingredients is the instantaneous pressure relaxation process and is of particular importance. In this article, we present and compare existing and new pressure relaxation procedures in terms of both accuracy and computational efficiency. Among these procedures we enhance an exact one in the particular case of fluids governed by the stiffened gas equation of state, and approximate procedures for general equations of state, which are particularly well suited for problems with large pressure variations. We also present some generalizations of these procedures in the context of multiphase flows with an arbitrary number of fluids. Some tests are provided to illustrate these comparisons. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A projection scheme for incompressible multiphase flow using adaptive Eulerian grid

PRICE: primitive centred schemes for hyperbolic systems

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2003
E. F. Toro
Abstract We present first- and higher-order non-oscillatory primitive (PRI) centred (CE) numerical schemes for solving systems of hyperbolic partial differential equations written in primitive (or non-conservative) form. Non-conservative systems arise in a variety of fields of application and they are adopted in that form for numerical convenience, or more importantly, because they do not posses a known conservative form; in the latter case there is no option but to apply non-conservative methods. In addition we have chosen a centred, as distinct from upwind, philosophy. This is because the systems we are ultimately interested in (e.g. mud flows, multiphase flows) are exceedingly complicated and the eigenstructure is difficult, or very costly or simply impossible to obtain. We derive six new basic schemes and then we study two ways of extending the most successful of these to produce second-order non-oscillatory methods. We have used the MUSCL-Hancock and the ADER approaches. In the ADER approach we have used two ways of dealing with linear reconstructions so as to avoid spurious oscillations: the ADER TVD scheme and ADER with ENO reconstruction. Extensive numerical experiments suggest that all the schemes are very satisfactory, with the ADER/ENO scheme being perhaps the most promising, first for dealing with source terms and secondly, because higher-order extensions (greater than two) are possible. Work currently in progress includes the application of some of these ideas to solve the mud flow equations. The schemes presented are generic and can be applied to any hyperbolic system in non-conservative form and for which solutions include smooth parts, contact discontinuities and weak shocks. The advantage of the schemes presented over upwind-based methods is simplicity and efficiency, and will be fully realized for hyperbolic systems in which the provision of upwind information is very costly or is not available. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Numerical simulation of disperse multiphase flows with an application in power engineering

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2003
K. Bernert
Abstract This paper deals with the numerical simulation of two-phase flows based on the solution of the Navier,Stokes equations with a k,,turbulence model for the gas phase and a particle tracking model of the disperse phase fulfilling the framework of the Eulerian,Lagrangian (PSI-Cell) approach. The numerical procedures for the two phases are based on the domain decomposition method applied to a block-structured grid. The complete code is parallelized for computers of MIMD architecture. The paper gives a description of the numerical methods with special attention to the parallelization. Some test calculations demonstrate the performance of the code. The numerical simulation of a flow splitter from the field of power engineering is presented as an example for a real world application of the method. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Magnetic emulation of microgravity for earth-bound multiphase catalytic reactor studies,Potentialities and limitations

AICHE JOURNAL, Issue 5 2009
Faïçal Larachi
Abstract A method is proposed to generate Earth-bound artificial microgravity in a controlled facility capable of emulating lunar/Martian gravity or microgravity for experiments on passive/reactive catalytic multiphase flows. Its applicability was illustrated for trickle beds where flowing gas and liquid experience artificial microgravity inside the bore of a superconducting magnet generating large gradient magnetic fields to compensate for gravity. Artificial gravity is realized by commuting into apparent gravity acceleration the magnetization force at work on common "chemical engineering" non-magnetic fluids. The scaling property to be matched and maintained invariant in multiphase systems to achieve magnetic mimicry is phasic mass magnetic susceptibility. Hydrodynamic (liquid holdup, wetting efficiency, pressure drop) as well as catalytic reaction (conversion and selectivity) measurements were obtained. The main finding is a proof that magnetic fields affect reactor outcomes exclusively via hydrodynamic phenomena making them appealing proxies for emulating non-terrene reactor applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

On the drift-flux analysis of flotation and foam fractionation processes

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2008
Paul Stevenson
Abstract Drift-flux analyses are a common way of estimating the phase fractions and fluxes in vertical multiphase flows. However their use has had scant impact on the flotation and foam fractionation communities despite the publication of a number of such analyses over the past two decades. By recognizing that the physics that underpin the hydrodynamics of the froth are dissimilar to those that pertain to the bubbly liquid beneath, we present a drift-flux analysis with two characteristic curves. A method for obtaining the characteristic curve for the froth from experimental data for the drainage of stationary foams is presented. Les analyses de flux de dérive sont une façon commune d'estimer les fractions et flux de phase dans les écoulements polyphasiques verticaux. Toutefois, leur utilisation a eu un impact négligeable pour les problèmes de flottation et de fractionnement de mousse malgré la publication de plusieurs analyses semblables au cours des deux dernières décennies. Tout en reconnaissant que la physique sur laquelle est fondée l'hydrodynamique de l'écume diffère de celles du liquide bullant situé en dessous, nous présentons une analyse de flux de dérive avec deux courbes caractéristiques. Une méthode pour obtenir la courbe caractéristique de l'écume à partir des données expérimentales de drainage des mousses en régime stationnaire est présentée. [source]