Showing papers in "The Journal of Computational Multiphase Flows in 2010"
TL;DR: This review introduces the important attributes of two phase flow in microchannels and then focuses on the Taylor flow regime, which is the most common flow regime encountered in many modern chemical plants.
Abstract: Over the past few decades an enormous interest in two-phase flow in microchannels has developed because of their application in a wide range of new technologies, ranging from lab-on-a-chip devices used in medical and pharmaceutical applications to micro-structured process equipment used in many modern chemical plants. Taylor flow, in which gas bubbles are surrounded by a liquid film and separated by liquid plugs, is the most common flow regime encountered in such applications. This review introduces the important attributes of two phase flow in microchannels and then focuses on the Taylor flow regime. The existing knowledge from both experimental and computational studies is presented. Finally, perspectives for future work are suggested.
136 citations
TL;DR: In this article, an Algebraic Interfacial Area Density (AIAD) model based on the implemented mixture model was introduced, which allows the detection of the morphological form of the two-phase flow and the corresponding switching via a blending function of each correlation from one object pair to another.
Abstract: Stratified two-phase flow regimes can occur in the main cooling lines of Pressurized Water Reactors, Chemical plants and Oil pipelines. A relevant problem occurring is the development of wavy stratified flows, which can lead to slug generation. In the last decade, stratified flows have increasingly been modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated. Recent improvements of the multiphase flow modelling in the ANSYS CFX code, now make it possible to simulate these mechanisms in detail. In order to validate existing and further developed multiphase flow models, a high spatial and temporal resolution of measurement data are required. For the experimental investigation of co-current air/water flows, the HA WAC (Horizontal Air/Water Channel) was built. The channel allows in particular the study of air/water slug flow under atmospheric pressure. Parallel to the experiments, CFD calculations were carried out. The two-fluid model was applied with a special turbulence damping procedure at the free surface. An Algebraic Interfacial Area Density (AIAD) model based on the implemented mixture model was introduced, which allows the detection of the morphological form of the two-phase flow and the corresponding switching via a blending function of each correlation from one object pair to another . As a result, this model can distinguish between bubbles, droplets and the free surface using the local value of the volume fraction of the liquid phase. The behaviour of slug generation and propagation was qualitatively reproduced by the simulation, while local deviations require a continuation of the work.
59 citations
TL;DR: In this article, a computational fluid dynamics (CFD) model for the study of bubble driven bath flow in aluminium reduction cells is presented, which can capture the key flow patterns determined by Particle Image Velocimetry (PIV).
Abstract: This paper presents the development of a computational fluid dynamics (CFD) model for the study of bubble driven bath flow in aluminium reduction cells. For validation purposes, the model development was conducted using a full scale air-water model of part of an aluminium reduction cell as a test-bed. The bubble induced turbulence has been modelled by either modifying bubble induced turbulence viscosity directly or by modifying bubble induced turbulence kinetic energy in a standard k-ϵ turbulence model. The relative performance of the two modelling approaches has been examined through comparison with experimental data taken under similar conditions using Particle Image Velocimetry (PIV). Detailed comparison has been conducted by point-wise comparison of liquid velocities to quantify the level of agreement between CFD simulation and PIV measurement. Both models can capture the key flow patterns determined by PIV measurement, while the modified turbulence kinetic energy model gives better agreement with flo...
26 citations
TL;DR: In this paper, two different methods for capturing the free interface movement are applied, namely the volume-of-fluid method and the level-set method, and the results obtained are in good agreement with the linear stability theory for small wave amplitudes.
Abstract: The two-dimensional Kelvin-Helmholtz instability which arises in two immiscible co-currently moving horizontal liquid layers is studied numerically. Two different methods for capturing the free interface movement are applied, namely the volume-of-fluid method and the level-set method. Both methods are very popular and available within commercial computational fluid dynamics tools. The wave is initialized using two different perturbations implemented into the model. As a case study, a system comprising a toluene layer and an aqueous layer is chosen. Numerical results obtained by both methods are in a good agreement with the linear stability theory for small wave amplitudes. The application of both methods is compared and their advantages and drawbacks are highlighted.
14 citations
TL;DR: In this paper, a multi-fluid Euler-Euler model was developed to describe electrostatic forces on charged particles in gas-solid fluidized beds, where particles are assumed to carry a prescribed size-dependent charge, and charge generation and dissipation are not modeled.
Abstract: Electrostatic charges in gas-solid fluidized beds are known to influence the bed dynamics, bubble shape and size, particle agglomeration, segregation and entrainment. In practice, accumulation of electrostatic charges in fluidized beds can lead to operational issues. The present work focuses on the modeling of electrostatics in gas-solid fluidized beds. The particles are assumed to carry a prescribed size-dependent charge, and charge generation and dissipation are not modeled. To consider the effects of bi-polar charging the polarity of the charge carried by fine particles is taken opposite to that of coarse particles. The magnitude of particle charges is approximated to realistic charges reported in the literature. The principal objective is to develop a multi-fluid Euler-Euler model that can describe electrostatic forces on charged particles in gas-solid fluidized beds. The multi-fluid model is solved in a commercial CFD code (ANSYS Fluent 6.3) and uses the kinetic theory of granular flow for calculatin...
14 citations
TL;DR: In this article, the deposition efficiency during the unsteady inhalation cycle by using Computational Fluid Dynamics (CFD) was investigated, and it was found that the first 0.2 second of the inhaling cycle was significant to particle transport, since the majority of particles were deposited during this period.
Abstract: The present study investigates the deposition efficiency during the unsteady inhalation cycle by using Computational Fluid Dynamics (CFD). The unsteady inhalation profile was applied at the outlet of nasopharynx, which had a maximum flow rate of 40.3L/min which corresponds to an equivalent steady inhalation tidal volume flow rate of 24.6L/min. Aerodynamic particle sizes of 5μm and 20μm were studied in order to reflect contrasting Stokes numbered particle behaviour. Two particle deposition efficiencies in the nasal cavity versus time are presented. In general, the deposition of 5μm particles was much less than 20μm particles. The first 0.2 second of the inhalation cycle was found to be significant to the particle transport, since the majority of particles were deposited during this period (i.e. its residence time). Comparisons were also made with its equivalent steady inhalation flow rate which found that the unsteady inhalation produced lower deposition efficiency for both particle sizes.
12 citations
TL;DR: In this article, the authors used the Two Fluid Model (TFM) to simulate the multiphase fluid dynamics in the fluidized bed spray granulation process and measured the particle velocity using Laser Doppler Velocimetry (LDV).
Abstract: Fluidized bed spray granulation is used to produce spherical granules from suspensions, solutions and melts Experimental investigations revealed that fluid dynamics in the granulator plays a crucial role, in particular in the jet The jet causes the particle movement as well as drop propagation and deposition on the particles In this work the “Two Fluid Model” (TFM) is used to simulate the multiphase fluid dynamics in the fluidized bed The results of simulations were validated by measuring the particle velocity using Laser Doppler Velocimetry (LDV) From the TFM-simulations with implemented growth mechanisms the growth kinetics is obtained and is used to describe the transient states of various granulation processes by solving the appropriate population balances
12 citations
TL;DR: In this article, the authors investigated the behavior of large gas bubbles in a liquid bath and the mechanisms of splash generation due to gas bubble rupture in high-intensity bath smelting furnaces by means of physical and mathematical (CFD) modelling techniques.
Abstract: The behaviour of large gas bubbles in a liquid bath and the mechanisms of splash generation due to gas bubble rupture in high-intensity bath smelting furnaces were investigated by means of physical and mathematical (CFD) modelling techniques. In the physical modelling work, a two-dimensional Perspex model of the pilot plant furnace at CSIRO Process Science and Engineering was established in the laboratory. An aqueous glycerol solution was used to simulate liquid slag. Air was injected via a submerged lance into the liquid bath and the bubble behaviour and the resultant splashing phenomena were observed and recorded with a high-speed video camera. In the mathematical modelling work, a two-dimensional CFD model was developed to simulate the free surface flows due to motion and deformation of large gas bubbles in the liquid bath and rupture of the bubbles at the bath free surface. It was concluded from these modelling investigations that the splashes generated in high-intensity bath smelting furnaces are mai...
10 citations
TL;DR: In this article, a combined computational fluid dynamics (CFD) and discrete element method (DEM) was extended from two-phase flow to model the flow in DMCs at the University of New South Wales (UNSW).
Abstract: Dense medium cyclone (DMC) is widely used in mineral industry to separate solids by density. It is simple in design but the flow pattern within it is complex due to the size and density distributions of the feed and process medium solids, and the turbulent vortex formed. Recently, the so-called combined computational fluid dynamics (CFD) and discrete element method (DEM) (CFD-DEM) was extended from two-phase flow to model the flow in DMCs at the University of New South Wales (UNSW). In the CFD-DEM model, the flow of coal particles is modelled by DEM and that of medium flow by CFD, allowing consideration of medium-coal mutual interaction and particleparticle collisions. In the DEM model, Newton's laws of motion are applied to individual particles, and in the CFD model the local-averaged Navier-Stokes equations combined with the volume of fluid (VOF) and mixture multiphase flow models are solved. The application to the DMC studies requires intensive computational effort. Therefore, various simplified versio...
9 citations
TL;DR: In this paper, a large scale flotation cell designed by BGRIMM has been modelled by using the Eulerian two-fluid method and the surface velocity of gas, the power required at varying impeller speeds and gas flow rates have been compared against measured values obtained from industrial tests.
Abstract: The actual performance of a new flotation cell is commonly examined through industrial tests. Since the controlled environment of industrial tests differ from laboratory tests, we cannot know the hydrodynamic features in flotation cells and these features are difficult to examine in the industrial test situations. CFD simulation of flotation cells provides a tool that can predict the hydrodynamic features and analyse the influence of variations in design features and operating conditions on the performance of flotation cells. A large scale flotation cell designed by BGRIMM has been modelled by using the Eulerian two-fluid method. Complex gas-liquid flow fields within the cells and the gas volume fraction are predicted. The surface velocity of gas, the power required at varying impeller speeds and gas flow rates have been found and compared against measured values obtained from industrial tests. The effects of some boundary conditions, such as the outlet setting and the timescale, which are important to th...
9 citations
TL;DR: In this paper, the internal phase distributions of gas-liquid bubbly flow in a horizontal pipe have been predicted using the population balance model based on Average Bubble Number Density approach.
Abstract: In this study, the internal phase distributions of gas-liquid bubbly flow in a horizontal pipe have been predicted using the population balance model based on Average Bubble Number Density approach. Four flow conditions with average gas volume fraction ranging from 4.4% to 20% have been investigated. Predicted local radial distributions of void fraction, interfacial area concentration and gas velocity have been validated against the experimental data. In general, satisfactory agreements between predicted results and measured values have been achieved. For high superficial gas velocity, it has been ascertained that peak local void fraction of 0.7 with interfacial area concentration of 800 m-1 can be encountered near the top wall of the pipe. Some discrepancies have nonetheless been found between the numerical and experimental results at certain locations of the pipe. The insufficient resolution of the turbulent model in fully accommodating the strong turbulence in the current pipe orientation and the inclu...
TL;DR: In this article, a computational fluid dynamics (CFD) model of a 375 MW utility furnace is used to predict wall incident radiation flux based on two radiation models, namely, discrete transfer (DT) model and P-1 model, compared with power plant measurements.
Abstract: This paper describes the mathematical formulation and modelling issues of a computational fluid dynamics (CFD) model of a 375 MW utility furnace. This tangentially-fired furnace is fuelled by high moisture content brown coal from coal mines at Latrobe Valley in Victoria, Australia. The influences of different turbulence models, particle dispersion, and radiation models on the CFD prediction are investigated. Two turbulence models, standard k-ϵ model and Shear-Stress Transport (SST) model, provide similar predictions that are in good agreement with the plant data. The effect of particle dispersion on the prediction is found to be insignificant for this high-volatile brown coal. The predicted wall incident radiation flux based on two radiation models, namely, discrete transfer (DT) model and P-1 model are compared against power plant measurements. The comparison reveals that the DT model provides good prediction of the radiation profiles, while the P-1 model considerably underpredicts the wall incident radi...
TL;DR: This work investigates the predictive performance of the Large Eddy Simulation (LES) model vis-a-vis the PIV experimental results and RANS based model and compares the flow patterns predicted by the LES model to RANS model prediction and PIV data.
Abstract: Mixer-settler equipment is widely used for solvent extraction (SX) operations. The pump mixer is the heart of an SX process. Any improvement in understanding of hydrodynamics and flow instabilities within a SX pump mixer unit would enable effective design of the mixer-settler equipment. In this direction, the present work investigates the predictive performance of the Large Eddy Simulation (LES) model vis-a-vis the PIV experimental results and RANS based model. Comparisons have been made initially for single phase operation of a Mixer unit, and then for the multiphase operation. The ANSYS/CFX modelling package has been used to set-up a transient three-dimensional CFD model using the sliding mesh approach for impeller motion and Eulerian-Eulerian approach for multi-phase flows. The present paper compares the flow patterns predicted by the LES model and compares them to RANS model prediction and PIV data. The prediction of flow structures and turbulence intensities will eventually pave the way for determina...
TL;DR: In this paper, a steam-bitumen jet injected into the steam-coke fluidized bed is simulated by using the Eulerian-Lagrangian splitting method.
Abstract: Simulation of the steam-bitumen jet injected into the steam-coke fluidized bed is presented. The computational method is based on the Eulerian-Lagrangian splitting. The Eulerian two-fluid model is used for the steam and the coke phases; the latter is composed of dry and wet coke particles. The Lagrangian model is applied to the bitumen droplets and the primary bitumen-coke agglomerates, generated by the random collisions of the droplets with the coke particles. A simple primary agglomeration-breakup model based on the experimental evidence is used. The gravity and the fluidizing cross-flow are neglected. Consequently, the computational problem is led to the axisymmetric form. Realistic results were obtained for the steam parameters at the end of the nozzle, the jet half-angle, and the location of the areas with the predominant agglomerations and breakups. The composition and stability of the agglomerates, and the mass transfer between the agglomerates and the coke phase are investigated.
TL;DR: In this paper, the effects of coordinate system and spatial resolution on drop shape are investigated for a single drop rising through a vertical pipe, i.e. cylindrical, general curvilinear and Cartesian coordinates.
Abstract: Interface tracking simulations of single drops rising through a vertical pipe are carried out using three coordinate systems, i.e. cylindrical, general curvilinear and Cartesian coordinates, to investigate the effects of coordinate system and spatial resolution on the accuracy of predictions. Experiments of single drops in a vertical pipe are also conducted to obtain experimental data for comparisons with simulations. The drop shape observed are spheroidal and deformed spheroidal at low values of the diameter ratio, λ, of the sphere-volume equivalent diameter of a drop to the pipe diameter, whereas they take bullet-shapes at large λ. The conclusions obtained are as follows: (1) the effects of coordinate system on drop shape are small at low λ. At large λ, the effects are also small for drops in a low viscosity system, whereas non-physical shape distortion takes place when the Cartesian coordinates are used with low spatial resolution for drops in a high viscosity system, and (2) the drop terminal velocity...
TL;DR: In this article, the ANSYS CFX 11.0 code is used to simulate the three-dimensional, turbulent, two-phase, multi-component and reacting flow-field, developed in a stabilised cool flame (SCF) evaporation device.
Abstract: Diesel fuel is used in a variety of technological applications due to its high energy density and ease of distribution and storage. Motivated by the need to use novel fuel utilization techniques, such as porous burners and fuel cells, which have to be fed with a gaseous fuel, a Diesel fuel evaporation device, operating in the “Stabilized Cool Flame” (SCF) regime, is numerically investigated. In this device, a thermo-chemically stable lowtemperature oxidative environment is developed, which produces a well-mixed, heated air-fuel vapour gaseous mixture that can be subsequently fed either to premixed combustion systems or fuel reformer devices for fuel cell applications. In this work, the ANSYS CFX 11.0 CFD code is used to simulate the three-dimensional, turbulent, twophase, multi-component and reacting flow-field, developed in a SCF evaporation device. An innovative modelling approach, based on the fitting parameter concept, has been developed in order to simulate cool flame reactions. The model, based on p...
TL;DR: In this paper, an Eulerian-Eulerian two-fluid model integrated with the population balance approach based on multiple-size-group (MUSIG) model was proposed to simulate on the gas leakage bubbly wake of a ventilated cavitation problem.
Abstract: In this study, an Eulerian-Eulerian two-fluid model integrated with the population balance approach based on Multiple-Size-Group (MUSIG) model was proposed to simulate on the gas leakage bubbly wake of a ventilated cavitation problem. Three selected flow conditions with Froude number ranging from 20 to 29 have been selected for investigation. Predicted void fraction and bubble velocity profiles were validated against the experimental measurements in the high-speed water tunnel of Schauer (2003) and Wosnik (2005). Sensitivity studies on the mesh resolution and three different turbulence closures were first carried out. In comparison with experimental data, the shear stress transport (SST) turbulence model was found to be the best candidate in modelling the re-circulation motions within the cavity wake region. To consider the neighbouring effect of closely packed bubbles, an empirical equation was proposed to correlate the turbulent dispersion coefficient to the local gas void fraction. Based on the propose...
TL;DR: In this article, the authors demonstrate multiphase flows in porous media are driven by gravitational, capillary and viscous forces, and make use of multiscale modeling approaches to transmit information over various lengths scales, ranging from microscale, meso-scale, macroscale and finally to the field scale.
Abstract: Problems involving multiphase flow, heat transfer and multi-component mass transport in porous media arise in a number of scientific engineering disciplines. Important technological applications include thermally enhanced oil recovery, subsurface contamination and remediation, capillary assisted thermal technologies, drying process, thermal insulation materials, multiphase trickle bed reactors, nuclear reactor safety analysis, high level radioactive waste repositories and geothermal energy exploitation. In this paper we demonstrate multiphase flows in porous media are driven by gravitational, capillary and viscous forces. But gravity causes phase migration in the direction of the gravitational field. Microscopic modelling efforts were made to accurately incorporate microscopic interfacial phenomena. Multi-scale modelling approaches were attempted in order to transmit information over various lengths scales, ranging from micro-scale, meso-scale, macro-scale and finally to the field scale.