Search

Hypothesis Interactions between droplets are of fundamental importance for understanding phenomena involving droplet collision and coalescence that determine multiphase flow behavior. The quantitative understanding of these interactions is essential for the manipulation and control of emulsions or complex fluids. The existing methods for interaction force determination are typically based on expensive mechanical probes and fine distance control. Therefore, further development of new techniques for interaction force determination is expected to be beneficial for research on surface force. Experiments In this study, droplet deformation during the interaction between two droplets was captured and analyzed to determine the interaction force. The approach speed of the two droplets was controlled by the injection rate of the fluid. The dynamic interaction force between two tetradecane droplets in various aqueous solutions was determined using the newly developed method, and the effects of two-phase physical properties and operating conditions on the measurement errors were investigated. Findings The droplet profile deformation was first applied as a probe to detect the interaction force. The measurement results were in good agreement with those obtained using the precise weighing sensor of a commercial interfacial tensiometer (K100, Kruss, Germany). The newly developed method was reliable, simple, and did not require the use of expensive devices. Furthermore, droplet deformability was found to be the key parameter in determining the total interaction force between the droplets.

The dynamics of a laser-induced bubble on top of a solid cylinder is studied both experimentally and numerically. When the bubble is generated close to the flat top along the axis of the cylinder and its maximum radius exceeds the one of the flat top surface, it collapses in the form of a mushroom with a footing on the cylinder, a long stem and a hat-like cap typical for a mushroom head. The head may collapse forming a thin, fast liquid jet into the stem, depending on bubble size and bubble distance to the top of the cylinder. Several experimental and numerical examples are given. The results represent a contribution to understand the behavior of bubbles collapsing close to structured surfaces and in particular, how thin, fast jets are generated.

Air-core vortex occurred at the hydraulic intakes deteriorates the performance and operation stability of hydraulic machineries. To investigate the evolution process and generation mechanism of the air-core vortex formed at the vertical intake, large-eddy simulation with the coupled level-set and volume-of-fluid method is performed in a pump sump. This paper elucidates the evolution of velocity distribution caused by pump suction, and associations between vortices motions and velocity evolution and the accompanying free-surface deformations are clarified, which reveals the generation mechanism and evolution characteristics of air-core vortex. Vortices are created by the disturbances of small recirculation zone around the intake pipe. The recirculation is caused by the interaction of the wall of vertical pipe and converging flows with opposite directions driven by the pump suction. The enhancement of vortices due to vortex distortion dominates the air-core vortex formation, and the vertical stretching effect accounts for about 70%. The meandering characteristics of air-core vortex are characterized through analyses of meandering scope and velocity distribution, and the convection of mean flow and sump wall take the leading role in causing its meandering.

The side-blown vortex smelting reduction reactor proposed in this paper is a new type of metal extraction equipment. The study of fluid dynamics is significant for improving reactor performance. Physical simulation is used to analyze the effects of the angle and number of blown lances, nozzle diameter, gas flow rate, and measuring depths on the reactor’s transfer and mixing characteristics. Dimensional analysis is used to correlate dimensionless numbers (Reynolds number Re, modified Froude number Fr′, capillary number Ca, number of blown lances n, and horizontal angle of the blown lance α) with mixing time and multiphase flow behavior. The results show that when the nozzle diameter and the number of blown lances are constant, Fr′, Ca and α are negatively correlated with the mixing time, and Re is positively correlated with the mixing time. When the angle of the blown lance is constant, Re and Ca are negatively correlated with mixing time, and Fr′ is positively correlated with mixing time. With the increase of Re, Fr′, Ca, the mixing behavior will gradually change from the bubbling regime to the transition regime and then to the steady jetting regime.

The investigation of flow field can provide strong theoretical support for improving the flotation performance of fine particles in a cyclonic flotation column. In this study, particle image velocimetry (PIV) is combined with endoscopic measurement and phase discrimination technique to measure the cross section and axial section of gas–liquid two-phase flow field in a lab-scale cyclonic flotation column. The axial, radial, and tangential velocity of both gas and liquid phases are obtained. Based on the PIV experimental data, computational fluid dynamics (CFD)-based numerical models are validated. The results show the good prediction ability of Eulerian–Eulerian multiphase model, Reynolds stress model (RSM), and Tomiyama drag model. Then the simulated results with validated models are displayed to indicate the flow characteristics of the flotation column. The gas concentration is observed to be higher in the center and low on the sides. The gas phase always moves upward, while the liquid phase moves upward at the axis, downward between the axis and the wall, and upward again near the wall. Overall, this study provides an innovative approach for PIV measurement of complex multiphase flow field, and a useful reference for appropriate numerical models selection.

The spatial structure of the constrained space determines the polishing efficiency and polishing quality of the soft abrasive flow (SAF) polishing method. A basic SAF polishing mode with universal guiding significance was built in this paper, and the effect of the spatial structure of constrained space on SAF polishing was studied. Based on the coupling of the Euler’s multiphase flow model and the standard turbulence model, a SAF hydrodynamic model was constructed to obtain the dynamic characteristics of the abrasive flow in the constrained flow passage and to reveal how the key parameters determining the spatial structure of constrained space affect the SAF polishing. The results showed that the inlet angle of the constrained space determines the injection posture of the abrasive flow. When the inlet angle reduces, the impact between the abrasive flow and the constrained wall is weakened, and the distributions of fluid turbulent kinetic energy, dynamic pressure, and granular pressure tend to be uniform. The height of the constrained space is a key factor affecting the polishing efficiency of the SAF. As the height of the space decreases, the material removal rate is enhanced significantly, but the turbulent impact ability of the abrasive particles is weakened. The height of the constrained space should be set to near the critical value of turbulent flow variation. Based upon the simulation, an experimental platform for SAF polishing was built, and the accuracy of the simulation results and the effectiveness of the polishing method were verified by the comparative polishing experiments.

The computational study of transient immiscible and incompressible two-phase flows is one of the most common and desirable way for investigation of engineering phenomena and physics science. In the previous studies, generally bubbles current have been used as an active method for increasing heat transfer, however, due to existence of hydraulic boundary layers, the bubbles were not able to cross over this layer to thinning the thermal boundary layer and consequently the efficiency of this method was not very considerable. In this study, by considering potential of magnetic field, the effect of co-applying of external non uniform magnetic field and magnetic bubbles in enhancing the heat transfer efficiency in a 3-D tube has been investigated. The computational model consisted of the Navier–Stokes equation for liquid phase and VOF model for interface tracking are carried out by OpenFOAM. The external magnetic field has been considered non-uniform and time dependent. The results predicted that magnetic bubbles and external magnetic field due to their effect on thermal boundary layer increased significantly heat transfer and Nusselt number. Furthermore, results indicated magnetic bubbles can act as an active torbulators in the flow field and can be applied for increasing recirculation and secondary flow in the flow field. The average temperature and magnetic field over times for different cases have been discussed in the results.

The internal flow of the mini pumps for washing machines is complex due to its compact structure and it normally adopts the upper drainage method. Due to decline in liquid level at the end of drainage (empty discharge period), the pump experiences water–air multiphase flow condition and produces unsteady flow. This unstable flow not only results in the deterioration of pump energy performance, but also induces larger vibration and noise, which in turn, reduce the working capability of pumps and disturb the people living environment. Therefore, with the aim of exploring the internal flow features and noise characteristics of drainage pumps during empty discharge period, the energy performance test was processed under pure water condition as well as under different air void fraction and part load conditions. Moreover, the internal flow field is calculated based on (both k − e and k − ω) turbulence model and Euler non-uniform stream model under pure water, and different inlet air content for part load conditions, respectively. All the experimental conditions for test and boundary conditions for simulation are provided. The overall and local results of internal flow field and gas phase distribution are obtained and analyzed. In addition, the research results can provide a theoretical recommendation for designing the lower noise mini pumps.

The current review research's main objective is to develop dispersion models in the multilayer curtain coating with the production of metallized paper. To achieve this, the curtain coating on the paper substrate is employed with respect to multilayer coating of polymers. The first layer of polymer is applied to the paper and then it is subjected to vacuum metallization with aluminum deposition. After it, another second layer of polymer is subjected on it to prevent it from oxidation. These coated polymers are different in nature. The metallized paper will be produced which has high strength will be formulated in this application of curtain coating. The instability of curtain and air entrainment will be minimized from high Weber number, low Reynolds number, Optimum web speed and Coat weights. The above demonstrated process simulation will be modelled in Ansys-CFD. The dispersion of solids in the curtain flow through substrate moving on the web will be evaluated from different numerical methods. Each method has its own characteristics to study the nature of solids dispersion. The high loaded solids dispersion will be investigated from numerical methods including Langrangian Point Particle, Coarse grained molecular dynamics, Stokesian Dynamics, Brownian Dynamics, Point Particle Method Reynolds Averaged Navier Stokes equation, Eulerian Method, Langrangian-Eulerian Point Particle, Large Eddy Simulation point particle, Combined discrete element and Large Eddy Simulation and Discrete Element Methods.

A particle-free surface coupled model has been developed using the Eulerian–Eulerian approach for revealing the gas–steel–slag multiphase flow in the vacuum chamber of a 210-ton RH degasser. The particle submodel preferred to predict the gas–steel and gas–slag interpenetrating phenomena, while the free surface submodel focused on tracking the steel–slag interface flow. The mesh sensitivity analysis has been investigated, and the coupled model was validated by the measured values. Using this coupled model, some previously unknown problems about multiphase flow in the vacuum chamber were revealed, such as the effect of the free surface fluctuation, variation of the liquid level, and slag flow behavior.

The paper proposes a combined approach between numerical modeling and experimental measurements for the analysis of a cogeneration system based on the reaction of liquid aluminum and water steam. Scrap aluminum is used for hydrogen production and the primary one is employed as an energy carrier to transport the energy from the alumina reduction system to the site of the suggested plant. The analysis focuses on the liquid aluminum injection phase immediately downstream the nozzle. High frequency thermo-cameras are employed to qualitatively assess the thermal behaviour the liquid aluminum jet. Fast imaging techniques are used to capture the multiphase flow pattern of the liquid metal jet during the injection phase. The experimental results are used to validate a 2D multi-phase CFD approach. The computational fluid dynamics model of the injection phase is created and used to extend the measurements and deepen the understanding of the thermo-fluid dynamics behaviour of the system. In particular, the influence of different nozzles diameters and different injection pressures on the liquid aluminum jet is investigated. A modular approach is adopted for the domain subdivision in order to represent accurately all the geometrical features, while the volume of fluid approach is used to model the multi-phase flow distribution in the real geometry under actual operating conditions. Finally, a good agreement between the measurements and the calculations is found.

“Generalized mobility” is used to realize the unification of tube flow and seepage in form and the unification of commonly used linear and nonlinear flow laws in form, which makes it possible to use the same form of motion equations to construct unified governing equations for reservoirs of different scales in different regions. Firstly, by defining the generalized mobility under different flow conditions, the basic equation governing fluid flow in reservoir coupling generalized tube flow and seepage is established. Secondly, two typical well test analysis models for coupling tube flow and seepage flow are given, namely, pipe-shaped composite reservoir model and partially open cylindrical reservoir model. The log-log pressure draw-down type-curve of composite pipe-shaped reservoir model can show characteristics of two sets of linear flow. The log-log pressure drawdown plot of partially opened cylindrical reservoir model can show the characteristics of spherical flow and linear flow, as well as spherical flow and radial flow. The pressure build-up derivative curves of the two models basically coincide with their respective pressure drawdown derivative curves in the early stage, pulling down features in the late stage, and the shorter the production time is, the earlier the pulling down feature appears. Finally, the practicability and reliability of the models presented in this paper are verified by three application examples.

An innovative separation system based on dielectric electrophoresis (DEP-on-a-chip system) is proposed to separate different particulate matters. A discrete phase model (DPM) and coupling model was utilized to simulate the movement characteristics in liquid-solid two phase flows and gas-liquid-solid three phase flows, respectively. In liquid-solid fluid systems, the effect of the liquid viscosity and density on the movement displacement of particles was studied. In gas-liquid-solid fluid systems, the effect of physical parameters, such as inlet velocity, liquid viscosity, liquid density and surface tension force, on the trajectory of PM2.5 (particulate matter 2.5) and PM10 was discussed. Conclusively, the theoretical separation time of the DEP-on-a-chip system is successfully achieved at the second level. The optimized physical parameters with the inlet velocity around 1.0 m/s, the liquid viscosity of 1×10−5 Pas, the liquid density of 1500 kg/m3 and the surface tension of 0.065 N/m for the separation system are established.

A newly developed frosting simulation method, pseudo-VOF (p-VOF) method, has applied to simulate the dynamic frost formation on the NACA0012 airfoil under strong convection. The p-VOF method is a pseudo volume of fraction simulation method of the multiphase flow with phase change. By solving a simplified mass conservation equation explicitly instead of the original volume fraction equations in CFD software, the efficiency and robustness of calculation are greatly improved. This progress makes it possible to predict a long-time frost formation. The p-VOF method was successfully applied to the simulation of dynamic frosting on the two-dimensional NACA0012 airfoil under strong convection conditions with constant frost physical properties. The simulation result shows that the average thickness of the frost layer increases, and the frost bulges and flow separation appear earlier, when the airfoil surface temperature decreases or the air humidity increases. The frost bulges and flow separation appear earlier, when the air velocity is faster, the growth rate of the frost layer at the early stage is greater, but the final frost layer is thinner.

Flow field characteristics of Falcon separator are studied by CFD simulation based on Euler-Euler model as multiphase flow model and Reynolds stress model as turbulence model, including particle mo...

Based on multiphase flow theory and capillary mechanics, the dimensionless bond number expression of the influence of string grille wire spacing on droplet spreading is derived. Taking a liquid film formed by spreading droplets based on Kelvin correlation, the Young–Laplace equation, and the Hagen–Poiseuille law, an equation for calculating the thickness and height of the liquid film is established with temperature, relative humidity and molar volume of liquid phase as independent variables. According to the theory of string grille filtration and dust removal, a dust removal efficiency calculation model covering the wet string grille wire group is constructed based on the liquid film thickness, height, wire diameter, water film area, and vortex shedding frequency. Finally, a theoretical analysis of the influence of water film area on the efficiency of wet string grille dust removal is carried out based on the spray pressure and the ratio of string grille wire distance to wire diameter. It is found that the effect of spray pressure on water film area and dust removal efficiency is more significant than the string grille wire distance diameter ratio. Moreover, the optimized combination of wet string grille wire distance diameter ratio 0.84, wind speed 3 m/s and spray pressure 0.8 MPa is found, which could provide an important reference for engineering applications.

In this paper, a large-eddy simulation study of turbulent free surface flow over a natural rough bed is presented. A three-dimensional multiphase flow model is employed to study the roughness effects on the turbulence properties and free surface dynamics. The governing equations have been discretized using the finite volume method, with the Cartesian cut-cell method being implemented to deal with the precise scanned gravel bed topography and the deformable free surface being captured by a volume of fluid method. The predicted mean flow velocities and turbulence statistics have been compared with experimental data. A close agreement has been obtained between the two sets of results, providing confirmation that this complementary approach to experimental investigations gives further insight into the turbulent free surface flow dynamics over rough beds. It is found that small waves are generated on the free surface due to the roughness effect for the relative low submergence case.

The performances of the Color-Gradient (CG) and of the Shan-Chen (SC) multicomponent Lattice Boltzmann models are quantitatively compared side-by-side on multiple physical flow problems where breakup, coalescence and contraction of fluid ligaments are important. The flow problems are relevant to microfluidic applications, jetting of microdroplets as seen in inkjet printing, as well as emulsion dynamics. A significantly wider range of parameters is shown to be accessible for CG in terms of density-ratio, viscosity-ratio and surface tension values. Numerical stability for a high density ratio $\mathcal{O}(1000)$ is required for simulating the drop formation process during inkjet printing which we show here to be achievable using the CG model but not using the SC model. In terms of physical accuracy, the CG model shows good agreement with analytical solutions for droplet oscillation and ligament contraction test-cases. The SC model is effective in accurately simulating ligament contraction, but less accurate in handling droplet oscillations. Rayleigh-Plateau instability simulations show that both the CG and SC models give physically realistic results when breakup occurs, although smaller satellite droplets quickly vanish in the SC model due to droplet mass evaporating into the ambient phase. Our results show that the CG model is a suitable choice for challenging simulations of droplet formation, due to a combination of both numerical stability and physical accuracy. We also present a novel approach to incorporate repulsion forces between interfaces for CG, with possible applications to the study of stabilized emulsions. Specifically, we show that the CG model can produce similar results to a known multirange potentials extension of the SC model for modelling a disjoining pressure, opening up its use for the study of dense stabilized emulsions.

The multiphase flow in the mold has a significant impact on the surface quality of the slab. In this paper, the multiphase flow in the mold is studied by establishing a one-quarter scale water mold, with the aid of a high-speed camera and particle image velocimetry (PIV). The oil phase will make the liquid surface velocity around the nozzle smaller. The greater the viscosity of the oil, the greater the critical water model casting speed and the shallower the critical immersion depth of submerged entry nozzle (SEN). Blowing will enhance the turbulence of the flow field in the mold and have a suppressing effect on the surface velocity. However, the vertical velocity of the narrow surface does not change significantly. The randomness of the bubble entering the mold from the nozzle can easily cause asymmetry of the instantaneous flow. The number of bubbles with a diameter less than 1 mm increase with the increase in gas flow rate. The larger the bubble size, the more buoyant around the nozzle when it escapes. The larger the diameter of bubble, the closer the vortex center of the upper circulation is to the nozzle and the closer the center of the lower circulation is to the narrow surface.

This study investigates the effects of elbow on the transition and development of multiphase flow using computational fluid dynamics modelling techniques. The Eulerian - Multifluid VOF model coupled with an Interfacial Area Transport Equation has been employed to simulate air-water two-phase flow in a pipe with two standard 90 degree elbows mounted in series. Turbulence effects were accounted for by the RNG k-ε model. The effects of separation distance on two-phase flow development have been studied for initial slug and churn flow regimes. Computational fluid dynamics simulation results of phase distribution and time series of void fraction fluctuations were obtained and they showed good agreement with available experimental data. The results show that for initial slug flow regime, there is no flow regime transformation upstream and downstream of the two elbows. While at initial churn flow regime, flow regime transformation occurs at different sections of the flow domain before and after the two elbows. It was noticed that irrespective of the flow regime, the amplitudes and frequencies of void fraction fluctuation become smaller as the fluid flows along the pipe. Changes in the separation distance between the two elbows have larger effects on the flow at churn flow regime.

Digital rock analysis provides us a powerful tool for predicting geophysical properties and studying fluid and interfacial transport mechanisms in rocks. However, people have to struggle and find a balance between scanning resolution and sample size due to current limitations of imaging technologies. With satisfaction of resolution requirement, the sample size has to be larger than the critical size of representative element volume (REV), so that the consequent pore-scale models are able to provide meaningful geophysical predictions for upscaling to Darcy-scale analysis. Following our previous work [Energies, 11: 1798, 2018] on REV size for single-phase flow, this work considers the critical size of REV for multiphase flow in porous media. A multiphase lattice Boltzmann model has been developed for simulation of two-phase immiscible flow. The relative permeability, which can be influenced by the capillary number and wettability, and the saturation of phases are calculated for upscaling. The critical size of REV for multiphase flow in porous media is therefore found and compared with that for single-phase flow. It is found that the REV size for the relative permeability–saturation curve of multiphase flow, which is influenced by the phase interaction and wettability, is beyond twice of that for the absolute permeability of single-phase flow in the present study.

Substantial challenges must be addressed to simulate food processing operations including realistic prediction of liquid and solid mixing, fragmentation of solids and liquids, multiphase behaviour, and interactions with complex machinery geometries. A particle-based modelling approach is presented which comprises Smoothed Particle Hydrodynamics (SPH) representations of continua (liquids and solids), coupled with Discrete Element Model (DEM) representations of discrete components such as solid particulates and bubbles. The simulation framework is demonstrated for six example applications that are common in food manufacturing and that are difficult to model with other numerical approaches. Simulations are presented for liquid mixing in a planetary mixer of fluids of varied viscosity, solid particulate blending in a ribbon blender, particle size reduction of almonds fragmented in a food processor, sieving of fine cohesive flour, multiphase flow of ice and liquid in a Slushie machine, and delivery of post-mix soft drink including bubble and foam generation. Each of these example applications are discussed in context of the needs of the simulation for improving process and the benefits of the particle-based modelling approach.

In this study, a computational fluid dynamics (CFD) simulation based on an Eulerian-Eulerian approach was used to evaluate the mixing performance of a mud agitator through the distribution of bulk particles. Firstly, the commercial CFD software Star-CCM+ was verified by performing numerical simulations of single-phase water mixing problems in an agitator with various turbulence models, and the simulation results were compared with an experiment. The standard model was selected as an appropriate turbulence model, and a grid convergence test was performed. Then, a simulation of the liquid-solid multi-phase mixing in an agitator was simulated with different multi-phase interaction models, and lift and drag models were selected. In the case of the lift model, the results were not significantly affected, but Syamlal and O’Brien’s drag model showed more reasonable results with respect to the experiment. Finally, with the properly determined simulation conditions, a multi-phase flow simulation of a mud agitator was performed to predict the mixing time and spatial distribution of solid particles. The applicability of the CFD multi-phase simulation for the practical design of a mud agitator was confirmed.

This work presents the numerical modeling of a sliding droplet on a vertical smooth wall under hydrophobic and hydrophilic conditions using the multiphase Shan–Chen Lattice Boltzmann Model (SC-LBM). The gravitational action above the interfacial force was introduced through the variation of the Bond number and contact angle between droplet, solid surface and surrounding fluid. A critical Bond number, above which the droplet would keep indefinitely deforming, was found for different wettability conditions as well as density and viscosity ratios. The critical Bond number proved to be insensitive to the viscosity ratio (Fluid 1/ Fluid 2, Fluid 1: liquid; Fluid 2: gas), but largely dependent on the density ratio (Fluid 1/ Fluid 2, Fluid 1: liquid; Fluid 2: gas). The present SC-LBM results demonstrate the excellent suitability of the multiphase SC-LBM for the prediction of the dynamic contact angle and reproduction of the continuous droplet deformation and eventual breakup of a sliding droplet subject to gravity force.

The main objective of the current work is to enhance consistency and capabilities of Moving Particle Semi-implicit (MPS) method for simulating a wide range of free-surface flows and convection heat transfer. For this purpose, two novel high-order gradient and Laplacian operators are derived from the Taylor series expansion and are applied for the discretization of governing equations. Furthermore, the combination of the explicit Third-order TVD Runge-Kutta scheme and two-step projection algorithm is employed to approximate transient terms in the Navier-stokes and energy equations. To further improve the accuracy and performance of the method, a new kernel function is constructed by a combination of the Gaussian and cosine functions and then implemented for modeling the 1D Sod shock tube problem. Validation and verification of the proposed model are conducted through the simulations of several canonical test cases such as: dam break, rotation of a square patch of fluid, two-phase Rayleigh-Taylor instability, oscillating concentric circular drop and good agreement are achieved. The proposed model is then employed to simulate three-phase Rayleigh-Taylor instability and entropy generation due to natural convection heat transfer (Differentially Heated Cavity and Rayleigh-Benard convection). The obtained results reveal that, the newly constructed kernel function provides more reliable results in comparison with two frequently used kernel functions namely; quartic spline and Wendland. Furthermore, it is found that, the enhanced MPS model is capable of handling multiphase flow problems with low and high density contrast.

Slug flow is the most common multi-phase flow encountered in oil and gas industry. In this study, the hydrodynamic features of flow in pipes investigated numerically using computational fluid dynamic (CFD) simulations for the effect of slug flow on the vertical and bent pipeline. The compressible Reynold averaged Navier-Stokes (RANS) equation was used as the governing equation, with the volume of fluid (VOF) method to capture the outline of the bubble in a pipeline. The simulations were tested for the grid and time step convergence, and validated with the experimental and theoretical results for the main hydrodynamic characteristics of the Taylor bubble, i.e., bubble shape, terminal velocity of bubble, and the liquid film velocity. The slug flow was simulated with various air and water injection velocities in the pipeline. The simulations revealed the effect of slug flow as the pressure occurring in the wall of the pipeline. The peak pressure and pressure oscillations were observed, and those magnitudes and trends were compared with the change in air and water injection velocities. The mechanism of the peak pressures was studied in relation with the change in bubble length, and the maximum peak pressures were investigated for the different positions and velocities of the air and water in the pipeline. The pressure oscillations were investigated in comparison with the bubble length in the pipe and the oscillation was provided with the application of damping. The pressures were compared with the case of a bent pipe, and a 1.5 times higher pressures was observed due to the compression of the bubbles at the corner of the bent. These findings can be used as a basic data for further studies and designs on pipeline systems with multi-phase flow.

The interaction of two impinging liquid jets in a confined impinging jet reactor (CIJR) is explored. Multiphase flow simulations were performed using the volume of fluids (VOF) approach to investig...

A three-dimensional computational model, combining the large eddy simulation (LES) turbulent model, VOF multiphase model for air phase, and discrete phase model (DPM) for injected bubbles, was established to evaluate the effects of drag force, lift force, pressure gradient force, virtual mass force, and wall lubrication force on the fluid flow and spatial distribution of bubbles in a continuous casting (CC) strand. The effect of lift force and wall lubrication force on the fluid flow was achieved via a user defined subroutine (UDF). The contribution of interphase forces was quantitatively evaluated using UDF. The appropriate interphase force model was determined by comparing the predicted fluid flow and bubble distribution in the CC strand with the measured results one using particle image velocimetry (PIV). The interphase force had a significant effect on the spatial distribution of bubbles and the flow field near the meniscus. The drag force and buoyancy force were the dominant ones at low turbulent kinetic locations. Moreover, the magnitude of the lift force, pressure gradient force, and virtual mass force was increased sharply at high turbulent kinetic locations, approximately one to two orders greater than that of the buoyancy force.

Non-uniform grids inevitably arise in multiphase flow simulation scenarios due to the need to resolve near-wall phenomena and/or large L/D ratios associated with the reactor configuration. This in conjunction with large density ratios of the constituent phases can retard the convergence of the pressure-correction equation that results from applying operator-splitting methods to the incompressible Navier-Stokes equations. Various pre-conditioning strategies to this ill-conditioned pressure-correction matrix are explored in this study for a class of bubbling bed simulations encompassing: different particle densities, bed-heights and dimensions (2D/3D). The right-side Block Jacobi preconditioning option resulted in a 20 - 35% decrease in CPU time that correlated well with a decrease in the number of iterations to reach a specified tolerance.

Computational fluid dynamics (CFD) is a powerful tool for prediction and analysis of complex multiphase flow hydrodynamics and residence time distribution (RTD) in chemical reactors. This study presented the validation and application of a filtered drag model for solid RTD prediction in a pilot-scale fluid catalytic cracking (FCC) circulating fluidized bed (CFB) riser with Geldart A particles. First, the filtered drag model implemented in the open-source MFiX-TFM solver was validated for flow hydrodynamics simulation in a FCC CFB riser. After that, the model was further employed to validate its ability for solid RTD prediction in the same riser by comparing the simulation results with the experimental data. The simulation with the filtered drag model well reproduced the tracer response experiment which is more accurate than that with the Gidaspow drag model. Simulations with both pulse and step tracer injection methods were compared, which reveals the limitation of solid RTD measurement using a pulse tracer injection method in the experiment.

A combined experimental and numerical simulation study of gas–liquid two-phase flow inside straight and spiral microchannels is presented. Dynamics of Taylor bubble formation was investigated in both types of channels and it was canvassed that presence of centrifugal force in spiral channel has consequential influence on the Taylor bubble dynamics. Effect of gas–liquid flow ratio and hydrophobicity of channel wall on the Taylor bubble formation was also investigated through numerical simulations. Formation of Dean's vortices inside spiral microchannel was shown via 3D CFD based simulations. Quantification of the strength of such vortices was done by calculating vorticity (ω) which is the curl of the velocity vector field. The effect of curvature on the formation of Dean's vortices was shown using Dean Number (De) and Dean velocity (VDe). The effect of two phase flow on the vorticity was also emphasized by presenting a comparative study with single phase flow. Presence of Dean's vortices inside such spiral micro-channel can be utilized in many futuristic micro-contrivances.

To investigate the fluid-rigid body interaction issues with free surfaces, a numerical approach has been developed. This algorithm is in an arbitrary Lagrangian–Eulerian description and Volume of Fluid (VOF) framework, using dynamic unstructured mesh to solve the coupled system. The fluid–solid interface uses partitioned Dirichlet–Neumann iterations with Aitken’s relaxation. For the two-phase fluids part, an interface geometric reconstruction approach has been applied to accurately capture the free surfaces. This piecewise linear interface calculation (PLIC) based method uses Newton’s iteration to efficiently reconstruct interfaces on an unstructured mesh, and applies an un-split scheme to transport variables. The algorithm has been successfully implemented in open source code OpenFOAM®, and was compared with the latter’s built-in solver using interface compression method to deal with free surfaces. Numerical results suggest that our solver has better accuracy on multiphase flow problems, while the previous solver fails to obtain correct interfaces. Moreover, the capacity of accurately solving fluid-rigid body interaction problems with free surfaces has been achieved. Validation cases are provided for fluid–structure interaction problems with and without free surfaces, and results are in accordance with analytical and experimental data from the literature. The algorithm and solver in this paper, can be applied on fluid–structure interaction cases with free surfaces in the future, such as sloshing and water entry problems.

Precise predictions of particle motion behavior after injection into a fluid flow are essential for process design and optimization in industrial applications. The goal of this work is to present a numerically inexpensive CFD model to predict lateral particle distribution after injection into a vertical cross flow. To this end, a specially designed and application-oriented flow channel, a so-called particle cross sifter, was built, which was experimentally and numerically analyzed. In the experiments a type of boiler slag powder, consisting of particles with various sizes and shapes, was injected into the cross sifter. For the numerical simulations different turbulence modeling approaches, such as RANS and LES, in combination with the DPM were applied. The results were compared to experimental data. It is highlighted, that only the LES approach in combination with the DPM is able to predict the lateral particle distribution with sufficient accuracy.

This paper is concerned with the simulation of multiphase flow hydrodynamics in an experimental oxyfuel fluidized bed combustor designed for biomass fuels. The aim is to perform cross-validation between several models and solvers that differ in the description of some phenomena in question. We focus on the influence of turbulence modeling, inter-phase drag force models, the presence of biomass in the mixture. Also the possibility to simplify the full 3D description to a quasi-1D model is tested. However, the results indicate that such simplification is not suitable for chaotic phenomena in considered scenarios. The models were developed using ANSYS Fluent and OpenFOAM CFD software packages as well as our in-house CFD code CFBSim. The quantities relevant for comparison (the densities of the dispersed solid phases and the phase velocities) are presented in the form of cross-section averaged vertical profiles.

Particle‐resolved direct numerical simulations are performed to simulate the flow through particle assemblies that are either static or freely moving to demonstrate the influence of particle mobility. To obtain a comprehensive understanding for this influence essential parameters such as the Reynolds number, solids volume fraction, particle‐fluid density ratio, collision parameters and particle shape are varied. The influence of particle mobility is assessed by evaluating the particle‐fluid forces, the particle ensemble structure and particle velocities. It is found that the ability of existing correlations for static particle systems to predict drag and lift forces correctly in dynamic particle‐gas flows is limited and that drift forces perpendicular to the drag force play an important role.

This work presents the implementation, verification and the validation of an incompressible Eulerian multi-fluid model for polydisperse flows. The proposed model uses a novel monolithic, i.e. implicitly coupled phase continuity equation for an arbitrary number of fluids, where the breakup source and sink terms are handled implicitly in the block-system. The implemented model is tested for an upward bubbly flow inside a large vertical pipe. The selected flow conditions exhibit both breakup and coalescence. The grid refinement study is conducted on four structured grids with varying levels of refinement. In the validation section, the numerical results are compared to the TOPFLOW experimental measurements. The last presented test examines the performance of the novel implicitly coupled phase continuity equation to the corresponding segregated formulation and the standard segregated formulation. The performance is evaluated by comparing the conservation error over the non- linear iterations. The presented model exhibits good agreement with the experimental measurements and gives stable results on various grids with different levels of refinement. Moreover, the implicit coupling reduces the conservation error during the calculation.

National audience; This study addresses the resuspension of microscopic glass particles from a monolayer bed into a turbulent gas flow.With an intermediate surface coverage, here set to about 10 % of the field of view, we report two distinct detachmentmechanisms. At relatively low flow velocities, few loosely adhering particles move on the wall to eventually collide withneighboring particles resulting in a clustered resuspension. At higher fluid velocities, mostly individual particlesresuspend due to their interaction with the turbulent flow. The resuspension curve, showing the remaining particlefraction as a function of the flow velocity, exhibits a strong bimodal character, that has not been reported so far.; Nos travaux portent sur la remise en suspension de billes de verre microscopiques formant initialement un dépôt monocouche sous l'action d'un écoulement turbulent. Avec une couverture de surface intermédiaire, ici fixée à environ 10 %, nous avons expérimentalement identifié deux mécanismes de détachement distincts. Pour des vitesses d'écoulement relativement faibles, quelques particules faiblement adhérentes se mettent en mouvement sur la paroi puis entrent en collision avec les particules voisines, ce qui entraîne une remise en suspension en cascade. À des vitesses d'écoulement plus élevées, la plupart des particules individuelles sont mises en suspension via leur interaction avec l'écoulement turbulent. L'évolution de la fraction de particules restant sur la surface en fonction de la vitesse d'écoulement présente un fort caractère bimodal, qui n'a pas été rapporté jusqu'à présent.

Polydispersity is a challenging feature of many industrial and environmental multiphase flows, influencing all related transfer and transport processes. Besides their size, the fluid or solid particles may be distributed with respect to other properties such as their velocity or shape. Here, a population balance model based on the method of classes is combined with a multifluid solver within the open source computational fluid dynamics library OpenFOAM. The model allows for tracking the evolution of one or more size-conditioned secondary properties. It is applied to two different problems, the first being bubbly flow of air and water in a vertical pipe, where considering the velocity as a secondary property allows to resolve the size-dependent radial segregation. The second application is the gas phase synthesis of titania powder, where non-spherical particle aggregates appear whose shape is modeled through a collision diameter, leading to an improved prediction of the size distribution.

Physical and numerical models are developed for the analysis of the processes occurring in the multiphase flow in a well during hydrocarbon production. A detailed description of the system of equations, its numerical approximation, methods for calculating the fluid properties and phase transitions in it, and the closing relations for calculating friction and heat transfer in a two-phase flow are presented. The implemented models make it possible to simulate both the stationary distribution of parameters over the wellbore and nonstationary processes, for example, when the speed of the pump shaft changes during oil production. The developed approaches are introduced in the new version of the DataFlow software for analyzing the hydrodynamics of multiphase hydrocarbon flows taking into account the heat exchange with the rocks surrounding the well and phase transitions in the fluid. The results of the test calculations showing the performance of the proposed and implemented models are given.

The study is concerned with the development of a model for predicting the particle size distribution resulting from the impact of nearly spherical cohesive agglomerates at a wall under a variety of impact conditions. For the derivation of the model an extensive number of discrete element simulations is carried out. The matrix of impact conditions consists of eight agglomerate size classes between 10 and 104 primary particles and seven impact angles between a flat (7°) and a normal impact (90°). To include the effect of the van-der-Waals bond strength, three primary particle diameters in the micrometer range are considered. Furthermore, the range of velocities allows to reproduce the full breakage spectrum from a rebound of an intact agglomerate to a full disintegration. The model is intended for the application in Euler-Lagrange simulations based on the hard-sphere approach ignoring the time-consuming resolution and tracking of the detailed agglomerate structure. This allows the prediction of turbulent flows with high mass loadings. For the model derivation the impact outcome is quantified by measures enabling the determination of the particle size distribution, i.e., the overall number of resulting fragments (fragmentation ratio) and the number of primary particles incorporated in the three largest fragments. The results concerning the effect of different agglomerate and impact parameters are consistent with the reported literature. Relying on this broad data base a new physically meaningful dimensionless number πimp is derived based on an empirical approach to characterize the breakage phenomenon. The advantage of the proposed dimensionless number reasonably unifying the results obtained under widely varying impact conditions is demonstrated. In addition, the disagreement detected for some of the cases can be attributed to the re-agglomeration of detached fragments due to the van-der-Waals force. Since agglomeration is separately accounted for in the multiphase simulation approach targeted by the breakage model, the data influenced by high re-agglomeration rates are not considered in the derivation of the data-driven model.

The effects of the surface waves generated by the wind have a significant effect on the currents. A wave current coupled model plays an important role in the design offshore structures. The interaction between fluids such as incompressible ocean waves and current and offshore structures is significant with many real-time applications in offshore engineering. These coupled models can be applied to Offshore Floating Production Operating and offloading (FPSO), Wind or current turbines and offshore pipelines. The complex issues related to the design are analyzed by using Computational Fluid Dynamics, which requires an investigation of the multiphase flow between wave and current and the structure which is considered restrictive due to the computational cost. If viscous effects are neglected then the single-phase flow models have been recommended, where wave-current interaction have been modelled successfully. Models have been developed where velocities and pressure are computed and the results can be verified with the experimental results available in the literature. In this study the existing numerical methods, mesh types are discussed along with their coupling methods. Here single-phase and multiphase models with small and medium movement are reviewed and their applications are highlighted. Commercial CFD code ANSYS Fluent has been found most reliable and easy to use tool for the analysis of fluid flow interacting with offshore structures near the free surface. It can successfully be used for determination of fluid dynamics of offshore environments installed complex multi-component structures. Dynamic mesh facility is more useful for multiphase modelling of floating structures.

International audience; This paper is devoted to an unresolved model for the simulation of air invasion in immersed granular flows without interface reconstruction between the liquid and the gas. Experiments of air invading a granular bed immersed in ethanol were achieved in a Hele-Shaw cell to observe the gas invasion paths and to calibrate the numerical multiscale model. The grains movements are computed at a fine scale using the non-smooth contact dynamics method, a time-stepping method considering impenetrable grains. The fluid flow is modelled by equations averaged using the volume fraction of fluid and computed at a coarse scale with the finite element method. A phase indicator function is used to dissociate the gas and the liquid constituting the fluid and to compute the density and viscosity of the fluid at each position. It is moved using a convection equation at each time step. The fluid, solid and phase indicator function computations are validated on simple cases before being used to reproduce experiments of air invasion in immersed granular flows. The experiments are supported by simulations in two dimensions to refine the study and the understanding of the invasion dynamics at short times.

Hypothesis Based on energy balance during two-phase displacement in porous media, it has recently been shown that a thermodynamically consistent contact angle can be determined from micro-tomography images. However, the impact of viscous dissipation on the energy balance has not been fully understood. Furthermore, it is of great importance to determine the spatial distribution of wettability. We use direct numerical simulation to validate the determination of the thermodynamic contact angle both in an entire domain and on a pore-by-pore basis. Simulations Two-phase direct numerical simulations are performed on complex 3D porous media with three wettability states: uniformly water-wet, uniformly oil-wet, and non-uniform mixed-wet. Using the simulated fluid configurations, the thermodynamic contact angle is computed, then compared with the input contact angles. Findings The impact of viscous dissipation on the energy balance is quantified; it is insignificant for water flooding in water-wet and mixed-wet media, resulting in an accurate estimation of a representative contact angle for the entire domain even if viscous effects are ignored. An increasing trend in the computed thermodynamic contact angle during water injection is shown to be a manifestation of the displacement sequence. Furthermore, the spatial distribution of wettability can be represented by the thermodynamic contact angle computed on a pore-by-pore basis.

A 3D numerical study of water spray flash evaporation occurring in a positive-pressure saturated vapor environment is conducted. The spray is non-uniform with a Rosin-Rammler droplet size distribution. The characteristics of the flashing spray and vapor flow field are obtained by calculating within the Eulerian-Lagrangian framework. The spray undergoes violent evaporation and significant temperature reduction in the beginning within the vicinity of the nozzle exit. As the spray develops downstream, evaporation becomes moderate. Smaller droplets are found to distribute in the spray central region with a comparatively higher evaporation rate and larger velocity variation. Meanwhile, larger droplets evaporate at a lower speed but cover a wider range. The vapor flow field near the nozzle exit is featured by high velocity and high turbulence intensity. Two sets of vortices with different scales and directions are observed in the upper and lower parts of the chamber.

Numerical simulation of the underwater motion of flight vehicles launched from underwater is performed. The updated method of plane sections is used to determine the hydrodynamic parameters of flight vehicles under multiphase flow. Hydrodynamic loading can be evaluated through the determination of nonstationary boundaries of a gas cavity and the linear load on the water-flown aft. By the method of plane sections, the 3D boundary value problem of the cavitational flow of a flight vehicle at an attack angle resolves itself into a plane hydrodynamic problem, separate for each section of the cavity. The predicted results are compared with the experimental data. Validation and verification were performed by comparing the analysis results with the experimental data. The applicability of the method of plane sections to the determination of the hydrodynamic parameters of flight vehicles under multiphase flow is demonstrated.

This paper aims to present a review of numerical models for the gas-steel-slag three-phase flow in gas-stirred ladles. The modeling frameworks is classified as: mixture model, interfacial model, multi-fluid model and Eulerian-Lagrangian (EL) model. The interfacial model is good at simulating the interfacial structure among phases, while the multi-fluid model is suited for systems consist of different kinds of phases as it separately solves the constitutive equations of each phase with modeling their interactions. Recently, the Eulerian-Lagrangian model is frequently adopted to make the discrete phase more comprehensively resolved. With coupling the interfacial model, the interfacial-Eulerian-Lagrangian (IEL) model shows a good suitability to simulate the gas-steel-slag three-phase flow, and the discrete-continuum transition, regarded as a multiscale approach, is very helpful for revealing the bubble behavior. Moreover, other phenomena including the heat and mass transfer, the erosion at the liquid-solid interface, etc. are still lack of investigation by comprehensive models.

A simulation method for slug flow based on the VOF multiphase flow model was implemented in ANSYS® Fluent via a user-defined function (UDF) and applied to the dissipation of liquid slugs in the inlet pipe of a gas–liquid cylindrical cyclone (GLCC) separator while varying the expanding diameter ratio and angle of inclination. The dissipation of liquid slug in inlet pipe is analyzed under different expanding diameter ratios and inclination angles. In the inlet pipe, it is found that increasing expanding diameter ratio and inclination angle can reduce the liquid slug stability and enhancing the effect of gravity, which is beneficial to slug flow dissipation. In the cylinder, increasing the expanding diameter ratio can significantly reduce the liquid carrying depth of the gas phase but result in a slightly increase of the gas content in the liquid phase space. Moreover, increasing the inclination angle results in a decrease in the carrying depth of liquid in the vapor phase, but enhances gas–liquid mixing and increases the gas-carrying depth in the liquid phase. Taking into consideration the dual effects of slug dissipation in the inlet pipe and carrying capacity of gas/liquid spaces in the cylinder, the optimal expanding diameter ratio and inclination angle values can be determined.

The knowledge of particles that remain in the furnace is important for the efficiency of a thermal particle treatment process. These particles mainly stick to the combustion chamber wall and represent a material loss. To predict the amount of particle-wall contacts in such furnaces, a numerical model based on transient multiphase flow calculations is presented in this work. The proposed model differs from the current state-of-the-art CFD models as follows: Instead of using the commonly used RANS turbulence models (realizable-k-e model, Reynolds stress model) and steady state calculations, large eddy simulations (LES) of the multiphase flow in the furnace in combination with a type of RANS mesh were performed. Furthermore, the applicability of the LES technique was evaluated by comparing the numerical results to measurements. It was found that the proposed numerical model provides more accurate prediction performance than applying common RANS turbulence models.

With the simplicity and robustness of the lattice Boltzmann method (LBM), it is getting more attention nowadays in the multiphase flow applications. Different models of multiphase flow studies are available in LBM. Theory and applications of lattice Boltzmann multiphase models R–K color gradient, Shan–Chen (SC), Free energy (FE) and He–Chen–Zhang (HCZ) approaches have been discussed in this review. The methodologies of these methods have been explained in details. Besides, the advantages and limitations of these models have been explained by considering the application field. Based on the applications in the multiphase flows, recent developments in these models have been explained. The major applications of LBM in multiphase flows are flow through porous media, cavitation phenomenon, bubble rise or droplet fall, Rayleigh–Taylor instabilities, coalescence of bubbles or droplets, wettability and contact angles. An effort has been made to explain the methodologies for the multiphase LBM. Modified R–K color gradient model is more accurate and less efficient. SC model is more efficient and less accurate. FE model is numerically more accurate and less efficient. HCZ model more efficient and more accurate. The efficiency of modified R–K color gradient and free energy models almost similar.

In this paper, a novel computational framework is introduced for simulation of multiphase flow, geomechanics, and fracture propagation in porous media based on Biot’s model for poroelasticity by focusing on interactions between hydraulic and natural fractures. Since realistic porous media contain many natural fractures, it is important not only to stimulate hydraulic fractures but also to study the interaction between natural and hydraulic fractures. Here, state-of-the-art numerical modeling of natural and hydraulic fractures using a diffusive adaptive finite element phase field approach is employed. The locally mass conservative enriched Galerkin finite element methods (EG) are utilized to model two-phase flow in propagating fractures with relative permeability and capillary pressure. Geomechanics approximated by a continuous Galerkin finite element method is coupled to multiphase flow by applying an iteratively coupled scheme. Numerical examples are presented that demonstrate the effectiveness of this framework for different propagation scenarios by varying the degrees of physics. In addition, the capabilities to perform high-fidelity simulations on complex fracture networks, with randomly joined diffusive natural fractures, are illustrated.