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• A method for turbulent mass transfer solution using unclosed PDEs and sparse data. • Efficient concentration fields prediction under different boundary condition. • A deep learning method for handling observed data noise with sufficient accuracy. • Inverse computation of turbulent viscosity and mass diffusivity based on PINN. Turbulent mass transfer is widespread in chemical engineering processes including separation, reaction, and others. Traditionally, turbulent mass transfer processes can be simulated by computational fluid dynamics (CFD) methods. However, CFD methods require adequate turbulent models for the fluid flow and mass (and heat) transfer, which are normally difficult to develop for reliable solutions. Moreover, the CFD simulation is computationally intensive and hard to use in the cases like process optimization or analysis where the simulation needs to be called repeatedly. In this paper, physics-informed neural network (PINN) is developed and trained by unclosed mechanism model and sparse observation data of turbulent mass transfer process. The PINN method shows stronger generalization ability in solving the velocity, pressure and concentration fields in a turbulent mass transfer process than traditional deep neural network (DNN) method and turbulent Schmidt model. Under different boundary conditions, the PINN developed in the present paper can instantly predict the concentration distributions with sufficient accuracy and be used for inverse computation for estimating the turbulent viscosity and mass diffusivity as output results. The PINN is also capable of handling data noise by adjusting parameters, suggesting its potential in integrating experimental data. [ABSTRACT FROM AUTHOR]

[Display omitted] • The applicability of CFD-CGDEM in the simulation of packed bed is discussed. • The characteristics show dependence on scaled spring constant for CGDEM. • CGDEM with moderate scaling scheme is less dependent on spring constant. • The scale-up uncertainties for CFD-CGDEM increase with coarsen degree. The numerical modelling with computational fluid dynamics coupled with discrete element method (CFD-DEM) could be of high fidelity but rather time consuming, which leads to the development of coarse grain DEM (CFD-CGDEM). This paper describes the effects of scaling criteria for CFD-CGDEM on the modelling of multi-phase flow in packed bed. Four representative scaling criteria for particles contact interaction are discussed to analyze the packing structure and pressure drop and compare the relative deviation between CFD-CGDEM and CFD-DEM. It is found that when the spring constant in CFD-CGDEM is enlarged by α 3 or α 2 times or remains the same as that in original CFD-DEM, as α is defined as coarsen degree which is referred as the ratio between parcel size and particle size, a relatively large spring constant should be chosen to maintain the similar porosity and pressure drop. However, when the spring constant in CFD-CGDEM was scaled moderately by α times, the modelling results of CFD-CGDEM are comparable to data from CFD-DEM regardless of the value of spring constant. Furthermore, a quantitative analysis shows that the relative deviation in porosity and pressure drop between CFD-DEM and CFD-CGDEM will be enhanced as coarsen degree increases but the variation is insignificant with domain size for periodic boundary. The increase of parcel size could affect the simulation of porosity in packed bed and deviate the predicted hydrodynamics away from the CFD-DEM. In addition, the comparison of computational efficiency illustrates the speed up of CFD-CGDEM increases with the coarsen degree while the relative deviation also increases. This study provides instructive guidance for the application of CFD-CGDEM to model the multiphase flow in packed beds. [ABSTRACT FROM AUTHOR]

The rotating packed bed (RPB) is a promising advanced reactor used in industrial gas-liquid two-phase reaction processes because of its high phase contact efficiency and mixing efficiency. Investigation of RPBs using CFD simulations will improve the understanding of physical behaviours of gas and liquid flows in such reactors. Currently, CFD simulations on the RPBs only focus on the volume of fluid (VOF) method. However, the VOF method is not suitable for simulations of pilot-scale 2D and 3D RPBs due to the limitations in computer resources, while the Eulerian method using a porous media model is a promising alternative method but it is rarely reported. The reason is that there are no suitable porous media models that accurately describe the drag force between the gas and liquid, the gas and solids and the liquid and solids due to the high porosity and the stacked wire screen packing used in RPBs. Therefore, the purpose of this paper is to propose a new model for modelling RPBs. The new proposed model is based on the Kołodziej high porosity wire screen one-phase porous media model. In this work, two experimental counter-current gas–liquid flow cases from the literatures have been used for validating the CFD simulation results. Finally, the new model has been compared with the current porous media models for traditional spherical or structured slit packed beds, which are the Attou, Lappalainen, Iliuta and Zhang models. The simulation results show that the proposed new model is the most appropriate and accurate model for the simulation of RPBs among all the models investigated in this paper. [ABSTRACT FROM AUTHOR]

• GPU-powered CFD-DEM model (GPU- rCFD-DEM) is developed to simulate the large-scale gas–solid reacting flow. • The coupling calculations between CFD and DEM are fully implemented on GPU. • Advanced coupling strategies are employed to enhance numerical stability. • Coke combustion in an industrial-scale blast furnace is simulated. The coupling of CFD (computational fluid dynamics) and DEM (discrete element method) is extensively used for simulating gas–solid reacting flows in various industrial processes, while its high computational cost limits its industry applications, especially large-scale systems with a large number of particles and complex geometries. This paper reports a robust highly efficient GPU (graphics processing unit) − powered CFD-DEM coupling approach that is, for the first time, capable of simulating large-scale gas–solid reacting flow systems with complex geometries (GPU- rCFD-DEM). The fluid flow calculations are performed using CPU parallelization, while the particle flow simulations leverage GPU parallelization, and the coupling calculations between CFD and DEM are fully implemented on GPU. The model includes advanced coupling strategies to enhance numerical stability, especially when handling complex geometries with unstructured CFD meshes. The developed model is validated through experimental measurements and its computational performance is evaluated by comparison with previous GPU-based simulations. It shows good agreement with the experiments and superior performance compared to the traditional coupling method. The model is then applied to simulate raceway dynamics and coke combustion in an industrial-scale blast furnace, showcasing its effectiveness in handling complex geometries and a huge number of particles in gas–solid reacting flows. This work provides an efficient and robust solution for numerically simulating industrial applications of gas–solid reacting flow systems. [ABSTRACT FROM AUTHOR]

• A novel GPU-based DEM-CFD model was developed to simulate the gas–solid flow. • A grid-based approach was proposed to improve efficiency in simulating gas–solid systems with complex geometries. • The effects of tuyere angles on the raceway dynamics were analyzed. • The wear of tuyere for different tuyere angles was analyzed. The coupling of Computational Fluid Dynamics (CFD) and Discrete Element Model (DEM) is a powerful tool for simulating dense particulate systems, yet the conventional CFD-DEM has limits for systems with large particle numbers and complex geometry. This paper reports a novel GPU-based CFD-DEM model to simulate the gas–solid flow with large particle numbers and complex geometry. A novel coupling strategy between the CFD solver and DEM solver is developed, featuring high efficiency and stability. The developed model is validated against the experimental measurements, and its efficiency is compared to the previous CFD-DEM simulations. Then, for demonstration, the model is employed to simulate the dynamic behavior of gas–solid flow in the raceway in ironmaking blast furnaces by considering complex tuyere structure details and the huge particle numbers involved. This model allows to study the effect of the tuyere angle in terms of raceway formulation and tuyere erosion. The results show that the largest and most stable raceway volume can be reached at 5° downward tuyere, although the −5° tuyere nose experiences more wear than 10° downward tuyere. The model provides a cost-effective tool to overcome the longstanding challenge of simulating dense fluid-particle systems with huge particle numbers and complex geometry. [ABSTRACT FROM AUTHOR]

Emulsification carried out in continuous devices offers a series of advantages over batch emulsion, such as better control of the droplet size distribution, reduced volume equipment, and lower operative costs. This paper investigates through Computational Fluid Dynamics simulations the emulsification process inside Sulzer Static Mixers. An analysis aimed to identify the most appropriate turbulence model, from a practical point of view, was performed, finding that the realizable k − ϵ model is more suitable than the well-known k − ω model. Moreover, an operative correlation linking the Sauter diameter to the main operating parameters, in a wide range of fluid properties and operating conditions, was developed. • Emulsification processes were modelled through a CFD approach. • The minimum number of bins to have reliable results was found. • The accuracy of different turbulence models was assessed. • The range of application of the Luo and Lehr breakage kernels was studied. • A correlation valid for a huge range of conditions was found. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simulations of granular collapse scenarios to explore the impact of pile shape on granular material flow. • Innovative CFD integration with experimental results: Achieving accurate 3D modelling of granular flows. • Practical applications: Risk assessment insights for natural disasters using μ(I)-rheology simulations. In recent years, significant progress has been made in modelling granular flows using the μ I -rheology model, which connects the viscosity of a granular medium to the pressure and strain rate via a dimensionless quantity called the inertial number, I. This model allows treating the granular material as a non-Newtonian liquid with a yield stress, making it possible to model the flow using the continuum approach, which is less computationally expensive than discrete element methods. In this paper, we implement the μ I -rheology model in a computational fluid dynamics (CFD) code and couple it with the volume of fluid (VOF) interface tracking approach to model the three-dimensional (3D) flow of monodisperse granular materials. After validating the model using experimental data, we briefly describe a trial-and-error method for evaluating the material properties of powders via a simple collapse experiment. Then, employing the CFD model, we investigate the physics of the unchannelized collapse of granular materials and perform an energy budget analysis to demonstrate the different stages of the granular collapse. To further investigate the effect of the initial shape of the pile on the spreading dynamics, we run a campaign of 3D simulations. Our results show that the μ I -rheology model accurately reproduces the dynamics of the granular material during the collapse and can be used for risk assessment purposes in natural disasters. The findings from our simulations can also aid in developing preventative measures to minimize potential harm. [ABSTRACT FROM AUTHOR]

Fluid Catalytic Cracking (FCC) is one of the most important conversion processes used in refineries all over the world. It is used for the conversion of heavy oil feed with high boiling temperature to produce gasoline, diesel, propylene and other valuable products. Coke deposits on the catalyst during the catalytic conversion and deactivates it, therefore catalyst is continuously regenerated in the FCC process. The regeneration step is essential as it directly impacts the products yields. The coke combustion also generates NOx and SOx emissions which levels are highly influenced by the bed hydrodynamics, the operation parameters and the reactor configuration, and are important to quantify. For all these reasons, the understanding of the regenerator hydrodynamic and kinetic is essential. This paper presents a study on the coupling of Barracuda™ CFD code with a coke combustion kinetic model developed at IFP Energies nouvelles to simulate an industrial FCC regenerator. Regenerator operating and performance data, including catalyst samples for coke analysis, are acquired on a selected industrial unit to evaluate the model. The results provide useful insight on the regenerator performance characteristics in terms of air distribution, coke burning rate and temperature profile in the regenerator. The steady state flue gas composition and regenerator dense and dilute phase temperatures are well predicted by the CFD simulation. The CFD prediction of the bed density is underestimated compared to the industrial data. The duration required to completely regenerate the catalyst is also estimated from the results. The CFD coupled coke combustion kinetic model presented in this paper enables us to evaluate the influence of the fluidized bed hydrodynamic on the catalyst regeneration in an industrial FCC regenerator. The developed model serves as a useful tool for the evaluation of future technology development in the FCC regenerator. [ABSTRACT FROM AUTHOR]

Precipitation crystallization is one possibility of producing nanoscaled solid particles from the liquid phase. High nucleation and growth rates are generated by mixing two well soluble reactants and by their subsequent reaction to a sparingly soluble product. Primary processes, such as nucleation and growth, can be especially very fast (<1 s). Therefore, experimental access to such internal flow-dependent rates is insufficient due to predominantly very short process times. Computational fluid dynamics (CFD)-based approaches combined with a suitable population balance algorithm are a promising simulative alternative to gain insight into such swift processes. They enable the precipitation process to be resolved, starting from the turbulent mixing of reactants, followed by the supersaturation build-up as the driving force for nucleation and growth and, finally, the solid formation of nanoparticles. The aim of this paper is to predict the influence of mixing on the particle formation process using the valuable synergies of CFD and the population balance solver. In this paper, a confined impinging jet mixer is used as a benchmark apparatus. This type of apparatus enables the adjustment of highly reproducible mixing conditions. Precipitation is carried out using the sparingly soluble model system BaSO 4 –water. Formation of solids at low Reynolds numbers is mixing-controlled, which anticipates that local gradients, inhomogeneous mixing and the characteristic residence time distribution influences the particle formation process significantly. Firstly, this contribution compares the standard scalar transport model for the ion concentration involved to results from a micromixing model (joint probability density function). Secondly, transient coupled CFD-population balance equations (PBE) simulations using the sophisticated detached eddy turbulence model and a direct quadrature method of moments for the solution of the PBE are compared to experimental results. [ABSTRACT FROM AUTHOR]

• A novel valve mechanism with solvent freezing using recirculating jackets was developed. • A wide range of recirculating flow-rates were tested using computational fluid dynamics. • Several prototypes were 3D-printed in a titanium alloy and tested for pressure resistance. • The switching times and dead volumes were measured for a range of heating-jacket temperatures. In this paper, we demonstrate a proof-of-principle of a freeze-thaw valve (FTV) created in a 3D-printed fluidic device. Portions of channels are enveloped by cooling and heating jackets, and a heat transfer liquid is recirculated through the two jackets. A frozen plug is created in selected portions of the target-channel and the heating jacket ensures that a selected temperature is maintained in the rest of the channel. An FTV can be 3D-printed in a wide variety of materials as single piece devices with no moving parts without high resolution requirements of the printing process. Such valves can therefore be incorporated in devices for liquid chromatography or multi-step synthesis process. Computational fluid dynamic simulations of a prototype T-junction piece show the two zones to be well defined at coolant and heating jacket flow-rates greater than 1 mL/min, with power consumptions of 1–3 W. The prototype was printed in Titanium 6Al-4V using selective laser melting and the frozen plug was shown to withstand 20 MPa of pressure. Switching times between states 1 (with a frozen section) and 2 (with both sections thawed) were 0.2–3 min in computational and experimental tests. The scalability of the freeze-thaw system was demonstrated using a multi-gate valve containing 33 junctions without a proportionate increase in operational complexity or switching times. [ABSTRACT FROM AUTHOR]

Abstract: Design and analysis of photoreactors is significantly more challenging than conventional reactors due to participation of radiation in chemical reactions. This problem is further compounded in case of photocatalytic reactors because of presence of photocatalytic particles, which not only produce complex light scattering effects but, in case of slurry systems, also act as an additional phase, the hydrodynamics of which is essential to characterize for evaluating the phase distribution of photocatalyst particles without which it is not possible to calculate the light intensity distribution. This then necessitates the use of a computational fluid dynamics (CFD)-based simulation approach which can simultaneously take into account the hydrodynamics of multiple phases, light intensity distribution and reaction kinetics. This paper presents a sequential review of all steps for CFD simulations of photocatalytic reactors. The hydrodynamic modeling has been considered first with an emphasis on the Eulerian–Eulerian model because of its ability to handle large-scale photocatalytic reactor systems with only relatively moderate computational resources. This has been followed by a review of lamp emission models, which in CFD models are used as boundary conditions for solving the radiation transport equation (RTE). Before discussing the kinetics of photocatalytic reactors, a review of numerical models for solving the RTE has also been presented for both slurry and immobilized reactor systems. Finally, the paper discusses important factors for setting up the boundary conditions for CFD modeling of photocatalytic reactors. [Copyright &y& Elsevier]

Abstract: This study is a sequel to the paper of Savage and Oger ( this issue) that reviewed experimental studies of airslides. These devices make use of fluidization to facilitate the transport of granular materials over long distances. The present paper describes a detailed and comprehensive consideration of the various contributions to the governing multiphase flow equations and proceeds to carry out numerical simulations of airslide flows and compare the results with laboratory experiments. It was carried out in part using the open source multiphase flow CFD program MFIX. Revisions and additions to the governing equations used in the distribution version of MFIX were made. The results of previously published molecular dynamics simulations were used to formulate a revised radial distribution function. The forms of the quasi-static stress contributions were designed to permit the development of higher concentration flows typical of experimentally observed airslide flows. Finally, additional terms were included in the particle fluctuation energy equation to account for (i) the viscous dissipation of the fluctuating particles due to the interstitial air, and (ii) the energy source term arising from the transfer of energy from the fluid to the particles. These expressions have been incorporated in the computational scheme and simulations of fluidized granular flows in a rectangular channel having frictional side walls were carried out. Some initial exploratory calculations were performed to examine the effects of various parameters on the mass flow rates and the velocity profiles. Different wall conditions were studied by varying the particle and wall restitution coefficients. The effects of varying the minimum fluidization velocity and the solid fraction thresholds were also examined. The simulation scheme was then applied to model two of the better documented fluidized chute flow experiments; those of Botterill and Bessant (1976), and the McGill University fluidized solids flow channel experiments of Liot (1979) and Chan (1979). Results of these computations and comparisons with observed experimental airslide behavior are discussed. Good agreement is found between the simulations and the experimental airslide flow characteristics. [Copyright &y& Elsevier]

Abstract: Among many research studies on fluidized bed membrane reactors, only very few focus on the details of the effects of gas permeation through the membranes on the hydrodynamic properties of the membrane-assisted fluidized bed. For this reason, in the first part of this paper, a novel hybrid Immersed Boundary Method (IBM) Discrete Particle Model (DPM) has been developed. In the second part of the paper, this model is employed to investigate fluidized bed membrane reactors in more detail. Simulations without membrane inserts (having vertical membranes at the side walls instead), with membrane tubes in an in-line arrangement and membranes in a staggered arrangement are compared with each other. The time-averaged particle fraction maps display a lower bed height for the simulations with inserts. A very important aspect of the simulation with gas extraction/addition via the side walls is the solids circulation; an inversion of the solids circulation is observed when gas is added via the side walls with altered bubble properties. Because of this phenomenon, the bubble size counter-intuitively decreases when gas is added, and increases slightly when gas is extracted. The latter is a result of the existence of compacted zones near the membranes. For the simulation cases with membrane inserts, the solids circulation and bubble properties are different; in these cases they mainly depend on the local fluidization velocity, and not so much on the extent of permeation itself. Although the arrangement of the membrane tubes plays only a minor role in this matter, their presence has a pronounced influence on the bubble size. The system''s energy and energy dissipation are both smaller for the simulations with inserts compared to those with permeation via the side walls. Also in this respect, the local fluidization velocity is found to be more important than the extent of permeation. [Copyright &y& Elsevier]

Abstract: This paper proposes that a diesel oxidation catalyst (DOC) operating within the fully turbulent flow regime is an efficient means of reducing the contents of particulate matter in the exhaust gases. The suggested mode of operation is in contrast to the fact that the DOCs are typically operated within the laminar flow regime. In the paper, the particle trapping efficiency and pollutant conversion in turbulent ceramic DOCs are calculated using both mass-transfer correlations available in the literature and computational fluid dynamics (CFD). It is shown that a turbulent DOC substantially increases the removal of small particulates from the exhaust gases. This indicates the potential of the aftertreatment system to comply with the forthcoming number-based emission legislations on particulate matter. In addition, the turbulent DOC can be used to optimize the overall performance of a combined system consisting of a DOC and a diesel particulate filter. [Copyright &y& Elsevier]

• Gas bubbles in highly viscous fluids can take a wide variety of bubble shapes. • Initial predictions of bubble shape & velocity differ from experimental measurements. • A new viscosity averaging rule is presented and implemented within OpenFOAM. • Simulation accuracy depends on mesh resolution and viscosity averaging method. • Additional insight into bubble structure can be obtained from validated simulations. This paper reports an experimental and computational study on the shape and motion of an air bubble, contained in a highly viscous Newtonian liquid, as it passes through a rectangular channel having a constriction orifice. The magnitude of the viscosity ratios, λ , and capillary numbers, Ca , explored is high: 5.5 × 10 5 < λ < 3.9 × 10 6 and 2.9 < C a < 35.9 respectively. A multipass rheometer is used for the experimental work: air bubbles are suspended in 10 Pa s and 70 Pa s polybutene viscosity standards and passed through an orifice-plate geometry constructed within an optical flow-cell. High levels of bubble distortion are observed, including bubbles that resemble 'crescent moons'. Simulation work is carried out using an implementation of the volume of fluid method in the freely-available finite-volume computational fluid dynamics code OpenFOAM. Quantitative data pertaining to the motion and shape of the bubble was extracted from both the experimental and simulation work. Initially, a good match between numerical simulation and experimental work could not be obtained: this problem was alleviated by changing the viscosity averaging method from an arithmetic mean to a logarithmically-weighted arithmetic mean. Medium- and high-resolution simulations using this new viscosity averaging method were able to match experimental data with coefficients of determination, R 2 , typically 0.898 < R 2 < 0.985. [ABSTRACT FROM AUTHOR]

Highlights • PEPT tracks of a particle flowing through a hydrocyclone are shown. • The tracks reveal hitherto unseen features. The effect of the fluid viscosity is shown. • The cyclone axis was found by minimizing the sum of squared distances to the positions. • Excursions to the inner vortex and a complex particle flow pattern around the end of the vortex (EOV) is seen. • The residence time in different cyclone sections show where clogging can occur. Abstract Cyclone separators are widely used for separation of solids or droplets from gases or liquid fluids. They represent an elegant and robust separation technology involving low capital and maintenance costs. It is therefore interesting, to extend cyclone technology to new applications, particularly in the oil and gas industry where separation duties are becoming ever more demanding and diverse, and separation processes are moving to more remote installations, such as sub-sea or even down-hole installations. The objective of this paper is to elucidate the working of hydrocyclones including ones acting on liquids of elevated viscosity using state-of-the-art experimental and analysis techniques, namely positron emission particle tracking (PEPT) and computational fluid dynamics (CFD) with large-eddy simulation of turbulence effects. The results show a number of interesting and anomalous features of the liquid and particle flow, such as unexpected excursions of particles to the inner vortex and the effect of the vortex end on the particle flow. It is shown that it is possible to determine the axis of the hydrocyclone very precisely by a minimization technique and thus convert the output from the tracking algorithm in Cartesian coordinates to cylindrical coordinates with the cyclone as axis. This throws additional light on the results. Tracks of different particles, some of which are eventually captured and some which are lost, are shown both in 3-D Cartesian and 2-D cylindrical coordinates and the effects of the fluid and particle properties are discussed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A new mesoscale 3D CFD model is proposed to predict the liquid flow in an RPB. • Detailed liquid flow patterns in the RPB are obtained. • Liquid holdup, percentage of droplets and interfacial area in the RPB are analysed. • New correlations for liquid holdup and effective interfacial area are developed. • Parametric sensitivity analyses of the RPB for influencing CO 2 capture are performed. Abstract Rotating packed beds (RPBs), as a type of process intensification technology, are promising to be employed as high-efficiency CO 2 absorbers. However, the detailed understanding of the liquid flow in the RPB is still very limited. The complex and dense packing of the bed and the multiscale of the RPB make it very difficult to perform numerical simulations in detail, in particular for full 3D simulations. In this paper, a mesoscale 3D CFD modelling approach is proposed which can be used to investigate the liquid flow in both laboratory- and large-scale RPBs in detail and accuracy. A 3D representative elementary unit of the RPB has been built and validated with experimental observations, and then it is employed to investigate the gas–liquid flows at different locations, across a typical RPB, so that the overall characteristics of the liquid flow in the RPB can be assembled. The proposed approach enables the detailed prediction of the liquid holdup, droplets formation, effective interfacial area, wetted packing area and specific surface area of the liquid within real 3D packing structures throughout the bed. New correlations to predict the liquid holdup, effective interfacial area, and specific surface area of the liquid are proposed, and the sensitivities of these quantities to the rotational speed, liquid flow rate, viscosity and contact angle have been investigated. The results have been compared with experimental data, previous correlations and theoretical values and it shows that the new correlations have a good accuracy in predicting these critical quantities. Further, recommendations for scale-up and operation of an RPB for CO 2 capture are provided. This proposed model leads to a much better understanding of the liquid flow behaviours and can assist in the RPB optimisation design and scaling up. [ABSTRACT FROM AUTHOR]

Highlights • First time use of moving overset meshes to simulate agitator motion. • Reynolds and Strouhal number equations account for non-linear impact of amplitude. • DSD comparison reveals a closer approximation using volume of fluid multiphase model. • User-defined functions are applied to model oscillatory translational velocity. Abstract This paper presents a CFD model and hydrodynamic study of a moving-baffle oscillatory baffled column (moving-baffle OBC). This work marks the first instance that moving overset meshing was used to simulate agitator motion in a fluid system. Population balance results are validated with experimental data for the inverse-suspension of non-reactive aqueous acrylamide in Isopar oil. A comparison of the droplet size distributions produced via various multiphase simulation methods was performed, resulting in a better overall agreement with the experimental literature for simulations applying the volume of fluid (VOF) multiphase method. Hydrodynamic studies reveal patterns of local flow circulations and centermost axial currents in relation to agitator position. Examination of the dimensionless groups traditionally used to describe flow conditions for moving-baffle OBCs reveal a considerable discrepancy between the previously-defined oscillatory Reynolds number and oscillatory Strouhal number with numbers derived from fluid flow within the column. A numerical correction has been presented to illustrate the nonlinear effect of oscillation amplitude on fluid flow through the system and to provide a more realistic estimation of the Reynolds number and Strouhal number for the modeled moving-baffle OBC. [ABSTRACT FROM AUTHOR]

Highlights • Flux-dependent model developed for effective diffusivity in CFD calculations. • Anisotropic diffusivity tensor needed to allow non-constant flux ratios. • Choice of diffusivity model is more important for longer diffusion paths. • Resolved-particle 3D simulations show differences between models. • Small changes in a single pellet can be significant under extreme conditions. Abstract The implementation of multicomponent diffusion in porous catalyst particles into resolved-particle fixed bed computational fluid dynamics (CFD) presents challenges. Usually an isotropic effective diffusivity is employed for each species, which includes molecular diffusion, Knudsen diffusion and viscous flow. To obtain this quantity, constant and isotropic molar flux ratios are assumed. In fixed bed models, pellets composed of isotropic materials are situated in non-isotropic fluid-phase gradients in the bed, which call the assumptions into question. In this paper we present an extended model using a non-isotropic effective diffusivity tensor, which allows evaluation of the flux assumptions. The method is illustrated for resolved particle steady-state CFD simulations of ethylene oxidation in small test beds of spheres and four-hole cylinders. Comparisons to the original constant molar flux ratio model are made, which show that the flux changes affect reaction, species and temperature profiles in the particles, and are stronger in particles with longer diffusion paths. Larger differences between results from the two diffusion models are also seen when the effective diffusivity is decreased by reducing porosity and increasing tortuosity, typical of a reaction system where deactivation increases by carbon deposition. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • This study was conducted to simulate removal of diesel engine exhaust gas pollutants. • Proposed process consists of plasmacatalytic after treatment. • Nitrogen oxides, propane, and radical produced dependence of the electric field modeled. • Nitrogen oxide, carbon monoxide, methane, and propane reduction in different velocities and temperatures achieved. Abstract In the present paper, computational fluid dynamic (CFD) model was applied to simulate for the first time a synergetic application of a hybrid plasma and catalyst comprising DOC (Diesel Oxidation Catalyst) with Pt/CeO 2 -Al 2 O 3 and SCR (Selective Catalytic Reaction) with V 2 O 5 /TiO 2. Plasma-catalytic can be used in cold start diesel engine exhaust to reduce pollutants when catalyst is not hot enough. Plasma system was a pulsed corona consisting of the coaxial wire-cylinder reactor. NO x and C 3 H 6 reduction, NO 2 , NO, and radical produced concentration dependence of the electric field intensity were achieved. Transient temperature and CO distribution at catalyst channel, catalyst back pressure, and NO distribution all over the CC (catalytic converter) concentration were investigated to determine the steady state reduction efficiency of NO, CO, CH 4 , and C 3 H 6 with respect to inlet velocities and temperatures. In velocity 3 m/s, temperature 600 K, highest electric field before sparkover at 17 kV/cm, and 80 s engine cold start time, the reduction efficiencies of NO and C 3 H 6 got about 9% and 99% respectively. In steady state condition CO, NO, and C 3 H 6 reduction in catalyst are about 98%, 29%, and 95% in order. [ABSTRACT FROM AUTHOR]

Highlights • 2D RANS simulation sufficient to resolve turbulence in a stirred autoclave. • Simulation data can be used with a correlation function to predict the mean droplet size. • Minor modification to the stirred tank Reynolds Number improves correlation to pipes. • Simulation data can be used to improve the correlation between pipes and autoclaves. Abstract The prediction of droplet sizes in emulsions is important for fields ranging from the chemical process industry to emergency planning in the event of an underwater oil release. Typically scale models have needed to be built and the results scaled up, but as computational resources have grown and turbulence models have matured it has become possible to use computational fluid dynamics (CFD) to simulate the behaviour of the fluid/s. While direct simulation of multiphase breakup at high Reynolds number is currently computationally impractical, this paper looks into the use of CFD along with a correlation function based on maximum turbulent kinetic energy dissipation rate to predict the Sauter mean diameter of droplets in a 1 in. baffle-and-vane type autoclave. The results show that using a RNG-k ∊ turbulence model with a simplified 2D geometry gave droplet sizes within 26.2 μm of the Sauter mean diameter observed in experiments with no additional tuning of parameters. Correlating pipe and autoclave flows through the Reynolds number and the turbulent kinetic energy dissipation rate was also investigated. Using the traditional definitions of the Reynolds numbers the correlation is poor, the coefficient of determination of the linear fit to the log-log data is 0.64. The first modification replaced the diameter of the blade as characteristic length with the tip swept circumference which increased the coefficient of determination to 0.960. A further modification using data obtained from the turbulent fields of the simulation showed a significant improvement with the coefficient of determination increasing to 0.988. [ABSTRACT FROM AUTHOR]

Highlights • A two-fluid Eulerian-Eulerian CFD model is used to study bubbly flows. • Multiphase turbulence is modelled using an elliptic blending Reynolds- stress model. • Bubbly flows are studied in pipes, a square channel and a rod bundle. • Impact of the turbulence field and the lift on the lateral void distribution are comparable. • Void distribution is well-predicted without any wall force contribution. Abstract Eulerian-Eulerian two-fluid computational fluid dynamic (CFD) models are increasingly used to predict bubbly flows at an industrial scale. In these approaches, interface transfer is modelled with closure models and correlations. Normally, the lateral void fraction distribution is considered to mainly result from a balance between the lift and wall lubrication forces. However, and despite the numerous models available that achieve, at least in pipe flows, a reasonable predictive accuracy, agreement on a broadly applicable and accurate modelling approach has not yet been reached. Additionally, the impact of turbulence modelling on the lateral void fraction distribution has not, in general, been examined in detail. In this work, an elliptic blending Reynolds stress model (EB-RSM), capable of resolving the turbulence field in the near-wall region and improved to account for the contribution of bubble-induced turbulence, is evaluated against best-practice k - ε and high-Reynolds second-moment turbulence closures. Lift and wall lubrication forces are initially deliberately neglected in the EB-RSM. Comparisons for flows in pipes and a square duct show that the EB-RSM reproduces the lateral void fraction distribution, including the peak in the void fraction in the near-wall region, and reaches an accuracy comparable to the other two models noted above. In rod bundles, even if none of the models considered performs with sufficient accuracy, the EB-RSM detects features of the flow that are not predicted by the other two approaches. Overall, the results demonstrate a much more prominent role of the turbulence structure and the induced cross-sectional pressure field on the lateral void fraction distribution than is normally considered. These effects need to be accounted for if more physically-consistent modelling of bubbly flows is to be achieved. The lift force is added to the EB-RSM in the final part of the paper, to provide a two-fluid formulation that can be used as the basis for additional developments aimed at improving the accuracy and general applicability of two-fluid CFD models. [ABSTRACT FROM AUTHOR]

Highlights • A CFD model for bubble columns equipped with dense vertical internals was developed. • The population balance model was coupled to the CFD model to study the bubble size distributions. • The inclusion of lift and wall lubrication forces was studied by applying different models. • The effect of the internals with different arrangements on the hydrodynamics in bubble columns was investigated. • A modification factor for the breakage and coalescence kernels was proposed. Abstract In this paper, the effects of dense vertical internals (rods) on gas holdup and local gas and liquid velocities were investigated by using the Eulerian-Eulerian model coupled with the population balance model. The inclusion of lift and wall lubrication forces was studied by applying different models. The results indicated that just by choosing the appropriate interfacial forces, the numerical model agrees well with the experimental data. A sharper gas holdup, a stronger gas velocity gradient, and a more intense liquid recirculation were observed as the important impacts of the internals. Moreover, three circular internals' arrangements were considered to study the effect of wall and core clearance distances on the bubble column hydrodynamics. The results revealed that by increasing the wall clearance distance, flatter gas holdup and velocity distributions could be achieved. Also, the turbulence parameters were used to evaluate the capability of the model in the prediction of the bubble size distribution. A modification factor for the breakage and coalescence kernels was proposed; the factor enabled the model to reach equilibrium mean diameters for bubbles. The comparison of the probability distribution function (PDF) of bubble sizes in the bubble column with and without internals showed a narrower bubble size distribution with a smaller mean diameter in the presence of internals. [ABSTRACT FROM AUTHOR]

Abstract: This paper documents experiments and CFD simulations of the hydrodynamics of our two-phase (water, air) laboratory internal loop airlift reactor (40l). The experiments and simulations were aimed at obtaining global flow characteristics (gas holdup and liquid interstitial velocity in the riser and in the downcomer) in our particular airlift configurations. The experiments and simulations were done for three different riser tubes with variable length and diameter. Gas (air) superficial velocities in riser were in range from 1 to 7.5cm/s. Up to three circulation regimes were experimentally observed (no bubbles in downcomer, bubbles in downcomer but not circulating, and finally the circulating regime). The primary goal was to test our CFD simulation setup using only standard closures for interphase forces and turbulence, and assuming constant bubble size is able to capture global characteristics of the flow for our experimental airlift configurations for the three circulation regimes, and if the simulation setup could be later used for obtaining the global characteristic for modified geometries of our original airlift design or for different fluids. The CFD simulations were done in commercial code Fluent 6.3 using algebraic slip mixture multiphase model. The secondary goal was to test the sensitivity of the simulation results to different closures for the drag coefficient and the resulting bubble slip velocity and also for the turbulence. In addition to the simulations done in Fluent, simulation results using different code (CFX 12.1) and different model (full Euler–Euler) are also presented in this paper. The experimental measurements of liquid interstitial velocity in the riser and in the downcomer were done by evaluating the response to the injection of a sulphuric acid solution measured with pH probes. The gas holdup in the riser and downcomer was measured with the U-tube manometer. The results showed that the simulation setup works quite well when there are no bubbles present in the downcomer, and that the sensitivity to the drag closure is rather low in this case. The agreement was getting worse with the increase of gas holdup in the downcomer. The use of different multiphase model in the different code (CFX) gave almost the same results as the Fluent simulations. [Copyright &y& Elsevier]

Abstract: Foreseen standards regarding microorganism content for drinking water require assessment of the capability of existing plants to reach the upcoming requirements. This paper presents the development of a tool to assess this capability in a commonly encountered key step of water disinfection: ozonation. In this paper, this tool is applied to the test case of an ozonation channel of the Belgian drinking water producer Vivaqua. This tool is based on a mathematical model of the momentum and mass transport phenomena in an ozonation channel. The gas–liquid flow is coupled to ozone mass transfer and kinetics describing the ozone and microorganisms concentrations decay. The degradation of Bacillus subtilis spores, as a representative of resistant microorganisms, is implemented in the model. The model takes explicitly into account the bubble size variation and its impact on mass transfer. Bubbles sizes and kinetics parameters are estimated based on dedicated experiments. The model is partially validated by comparing simulations results, obtained using computational fluid dynamics, to experimental residence time distributions, residual ozone concentration and Bacillus subtilis spores degradation efficiency measurements obtained on the studied ozonation channel. It is shown that, at the industrial scale, bubble diameter variation has a significant impact on ozone concentration in the liquid at the reactor exit. Using the tool, it is also shown that, the ozonation channel of Vivaqua can be used to achieve degradation of resistant microorganisms but only with its maximal flow rate and concentration of ozone injection. Moreover, at low operating temperature, some microorganisms that present latency towards reaction with dissolved ozone might hardly be destroyed. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to investigate the entrainment behavior and performance of gas–liquid ejectors. computational fluid dynamics (CFD) model and the corresponding algorithm are developed and validation experiment has been carried out over a wide range of operation conditions for ejector with different configurations. Good agreement has been achieved between the predicted values from CFD simulation and the actual data by experimental measurement. The flow patterns that occur within the primary nozzle region are analyzed on the basis of one-dimensional isentropic compressible flow theory. The fluid pairs, consisting of the motive and the entrained fluids, are considered during the investigation with N2–H2O and He–LO2 selected as the representative fluids. The investigation results indicate that for fixed primary flow and secondary flow pressures (P P and P S , respectively), the entrained mass flow rate m S decreases linearly with the increasing pressure difference ΔP, while for fixed ΔP and secondary flow pressure P S , the entrainment rate m S monotonically increases with an increase in primary flow pressure P P until a constant value is reached. Moreover, the mixing tube length has proven to be an important design parameter and can exert a remarkable influence on ejector performance. The optimum mixing tube length of gas–liquid ejector is about 1–2 times the mixing tube diameter, and deviation from the optimum value can dramatically degrade its entrainment performance. In other words, an obvious peak value of entrainment ratio appears at the optimum L/D. However, the optimum value of L/D for single-phase ejector happens in the range of 5–7, which differs significantly from that of gas–liquid ejector. Moreover, an inapparent effect has been observed when the mixing tube of single-phase ejector is longer than the optimum value. A detailed description of this phenomenon is presented in this paper. The conclusions of the research can be served as a guideline for ejector design. [Copyright &y& Elsevier]

Graphical abstract Highlights • Lagrangian Mixing Simulation (LMS) method to characterise mixing is developed. • LMS is applied over a 2D CFD simulation in a CIJ reactor. • LMS results were used to characterise mixing: calculation of interfacial area generation and segregation scales. • LMS is able to simulate and compute even the smallest mixing scales. • LMS has short CPU time when compared to CFD mixing simulations. Abstract This paper introduces Lagrangian Mixing Simulation (LMS), which is a new method that uses particles to track the flow front between two fluids in a mixer. The line formed by an ensemble of particles enables the calculation of the instantaneous rate of interfacial area generation between the fluids and the computation of segregation scales. LMS uses the Eulerian velocity field from CFD simulation, which has a spatial resolution determined from the flow dynamics, for the simulation of mixing at scales that are several orders of magnitude below the CFD gridscale. Since only the interface between the two fluids is simulated, the LMS is orders of magnitude faster than the flow field simulation. In this work, LMS is applied to 2D CFD simulations of the flow in Confined Impinging Jets (CIJ) reactors for Re = 100, 300 and 500. LMS shows that the interfacial area generation is exponential for chaotic flow regimes (Re = 300 and 500) and linear for steady flows (Re = 100). Moreover, LMS is able to simulate segregation scales smaller than 10−8 m, i.e., LMS result spans and overcomes the entire range of spatial scales that have physical meaning. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes several improvements to a numerical model introduced by for collisional exchange and damping in dense particle flows. use a Bhatnagar, Gross, and Krook (BGK) approximation to the collision terms in a particle distribution function transport equation to model the effects of particle collisions on damping fluctuating particle velocities and, in gas/liquid/solid beds, fluctuating temperatures and compositions of liquid films on particle surfaces. In this paper we focus on particle flows in which the particles have no liquid films and report on an improved expression we have developed for the collision damping time of particle velocity fluctuations used in the BGK approximation. The improved expression includes the effects on the collision damping time of the particle material coefficient of restitution and of non-equilibrium particle velocity distributions. The collision model improvements are incorporated into the general-purpose computational-particle fluid dynamics (CPFD) numerical methodology for dense particle flows. Three computational examples show the benefits of using the new collision time in calculations of particle separation in polydisperse dense particle flows and calculations of colliding particle jets. [ABSTRACT FROM AUTHOR]

Abstract: In the last years, there has been a rapid growth of research and development activities on high temperature molten salts for nuclear and non-nuclear applications. The study of their heat transfer characteristics is a key issue in the current development of the molten salt reactor (MSR) that is one of the innovative nuclear reactors proposed by the Generation IV International Forum. The MSR is a sort of circulating fuel reactor (CFR), which adopts a molten halide salt mixture containing the fissile material and playing the distinctive role of both fuel and coolant. In a thermal-neutron-spectrum MSR, the reactor core is composed by a graphite matrix (neutron moderator), through which the liquid nuclear fuel flows and leads to a strong and intrinsic coupling between thermo-hydrodynamics and neutronics. This peculiar feature requires a suitable and qualified multi-physics simulation environment for a proper description of the system (fuel/coolant+graphite) behaviour. With reference to such complex and non-linear system, the present work is intended to give two different but linked contributions, in the perspective of a multi-physics modelling able to accurately describe the synergy of the involved different physical phenomena (e.g., by means of software). [(I)] On one hand, this work is aimed at establishing a useful validation framework for the assessment of computational fluid-dynamics (CFD) analyses of liquids with internal heat generation. For this purpose, an analytic approach for both fluid velocity and temperature fields in a circular pipe surrounded by a solid region has been developed. It is an extension of the approach elaborated for pipe flow in (Di Marcello, V., Cammi, A., Luzzi, L., 2010. A generalized approach to heat transfer in pipe flow with internal heat generation. Chemical Engineering Science 65, 1301−1310), in order to take into account the heat conduction in the solid domain (represented by the graphite matrix in the specific case of interest). [(II)] On the other hand, the paper presents a preliminary investigation of the thermal-hydraulic behaviour occurring in a typical graphite-moderated MSR core channel. The developed analytic approach has been conveniently applied to this case study: (i) by testing the capabilities of to evaluate the heat transfer characteristics and the hydrodynamic behaviour of such system; and (ii) by investigating the applicability of correlations for the Nusselt number to fluids with internal heat generation. For a deeper insight into the numerical solutions provided by COMSOL, a code-to-code comparison has been also carried out, adopting a dedicated CFD finite volume software (i.e., FLUENT®). As a result, a satisfactory agreement has been found between the analytic solution and the numerical computations provided by COMSOL and FLUENT for a wide range of Reynolds numbers. As concerns the Nusselt number evaluation, the correlations usually adopted for molten salts have been proved as unsuitable for the analysed system, whereas the correlation advanced in the above mentioned paper (that explicitly takes account of the internal heat source) appears more appropriate. The results of the present work are thought to be useful because they provide: (i) a “generalized” analytic approach to the heat transfer that is applicable in a more general context; (ii) an insight into the heat transfer characteristics of the considered graphite-moderated MSR core channel; and (iii) a preliminary assessment of computations that is essential in view of the adoption of multi-physics tools (like COMSOL) for more complex and representative simulations of the dynamic behaviour of the molten salt reactor, and more in general of other kinds of CFRs. [Copyright &y& Elsevier]

Abstract: Randomly packed bed reactors are widely used in chemical process industries, because of their low cost and ease of use compared to other packing methods. However, the pressure drops in such packed beds are usually much higher than those in other packed beds, and the overall heat transfer performances may be greatly lowered. In order to reduce the pressure drops and improve the overall heat transfer performances of packed beds, structured packed beds are considered to be promising choices. In this paper, the flow and heat transfer inside small pores of some novel structured packed beds are numerically studied, where the packed beds with ellipsoidal or non-uniform spherical particles are investigated for the first time and some new transport phenomena are obtained. Three-dimensional Navier–Stokes equations and RNG k–ε turbulence model with scalable wall function are adopted for present computations. The effects of packing form and particle shape are studied in detail and the flow and heat transfer performances in uniform and non-uniform packed beds are also compared with each other. Firstly, it is found that, with proper selection of packing form and particle shape, the pressure drops in structured packed beds can be greatly reduced and the overall heat transfer performances will be improved. The traditional correlations of flow and heat transfer extracted from randomly packings are found to overpredict the pressure drops and Nusselt number for all these structured packings, and new correlations of flow and heat transfer are obtained. Secondly, it is also revealed that, both the effects of packing form and particle shape are significant on the flow and heat transfer in structured packed beds. With the same particle shape (sphere), the overall heat transfer efficiency of simple cubic (SC) packing is the highest. With the same packing form, such as face center cubic (FCC) packing, the overall heat transfer performance of long ellipsoidal particle model is the best. Furthermore, with the same particle shape and packing form, such as body center cubic (BCC) packing with spheres, the overall heat transfer performance of uniform packing model is higher than that of non-uniform packing model. The models and results presented in this paper would be useful for the optimum design of packed bed reactors. [Copyright &y& Elsevier]

This paper presents a series of numerical simulation on solid-liquid two-phase flow in cross fractures based on the Two-Fluid Model and the kinetic theory of granular flow (KTGF). First, the model is validated by previous experimental data. Second, the dimensionless controlling parameters are derived to describe the particle-laden flow in cross fractures, including the angle between the main and branch slots (bypass angle) θ , inlet particle volume fraction α s0 , the ratio of particle size to branch slot width d s / w b , the Archimedes number Ar and the Reynolds number Re . Third, the effects of the dimensionless parameters are investigated. The results show that particles tend to accumulate at the intersection between the main slot and the branch slot. Larger bypass angle between the main slot and branch slot leads to less particle’s flow into the branch slot. The distance of the branch fracture from the inlet of the main fracture induces different particle-flow characteristics into the branch slot. Particle volume fraction at the stable stage increases with the decrease of d s / w b . The deposition thickness of particles increases with the increase of the inlet volume fraction and Ar number, while decreases with the increase of Re number. [ABSTRACT FROM AUTHOR]

This paper presents a coupled volume-of-fluid and level set (VOSET) method for unstructured triangular meshes to simulate incompressible two phase flows. In the method, a multi-dimensional advection algorithm, which includes 11 different cases for computing volume fluxes across cell faces, is proposed for the evolution of the volume fraction. An iterative geometric operation is presented to calculate the level set function. Thus, both advantages of volume-of-fluid (VOF) and level set (LS) methods are preserved in this unstructured VOSET method. Finally, the feasibility and accuracy of the current method are validated by three classical test cases – static drop, dam break, Rayleigh-Taylor instability problems. The current simulation results show good agreement with the experimental and numerical results in the literature. [ABSTRACT FROM AUTHOR]

The best-known paper on non-Newtonian fluids in mixing systems is the Metzner and Otto’s work. A central idea of their contribution is based on the assumption that in laminar flow there exists an average shear rate ( γ ̇ av ) around the impeller (whose exact location and geometric shape is not clearly specified), and that it is proportional to the impeller speed ( N ), i.e., γ ̇ av = K s N , where K s is the Metzner-Otto constant. In this work, an in-depth investigation of this assumption is carried out by using computational fluid dynamics (CFD) to calculate the three-dimensional flow induced by a Rushton turbine (RT). It was found that the volume swept by the blades is the region where K s may be computed explicitly as K s = γ ̇ av / N directly from non-Newtonian flow simulations. The obtained K s values in this region were found in good agreement with reported data. Furthermore, power number measurements and data from literature were used to validate the simulations. The CFD method developed in this study can be used to readily and reliably evaluate K s of industrial mixing impellers without resorting to power data of Newtonian fluids. [ABSTRACT FROM AUTHOR]

Rotating packed beds (RPBs) have been proposed as an emerging technology to be used for post-combustion CO 2 capture (PCC) from the flue gas. However, due to the complex structure of the packing in RPBs, characteristics of the liquid flow within RPBs are very difficult to be fully investigated by experimental methods. Therefore, in this paper, a two-dimensional (2D) CFD model has been built for analysing the characteristics of liquid flow within an RPB. The volume of fluid (VOF) multiphase flow model is implemented to calculate the flow field and capture the interface between the gas and liquid phases in the RPB. The simulation results show good agreement with the experimental data. The distinct liquid flow patterns in different regions of an RPB are clearly observed. The simulation results indicate that increasing the rotational speed dramatically decreases the liquid holdup and increases the degree of the liquid dispersion. The increasing liquid jet velocity decreases the liquid residence time but slightly increases the liquid holdup. In addition, the liquid holdup increases and the degree of the liquid dispersion decreases with increasing MEA concentration, but the effects are weaker at a higher rotational speed. With the increasing of the contact angle, both the liquid holdup and the degree of the liquid dispersion are reduced. This proposed model leads to a much better understanding of the liquid flow characteristics within RPBs. [ABSTRACT FROM AUTHOR]

The paper presents investigations of flow hydrodynamics and power consumption in a vibromixer (mixer with a reciprocating agitator). Solid or perforated discs different in diameter were used as agitators. Basing on CFD simulations and measurements flow parameters and power requirement for vibro-mixing were found. Power input was estimated using original measuring procedure with modified dimensionless numbers. Results were processed in quantitative correlations, describing an influence of process and operating conditions on vibromixer performance. Utilitarian effects of this study can be used for description and clarification of processes occurring in mixing vessels with reciprocating agitators as well as during design optimization of apparatuses of this kind. [ABSTRACT FROM AUTHOR]

Wave-plate mist eliminator with porous foam layers as enhanced structures on vanes to improve separation efficiency for tiny droplets was proposed in this paper. Overall separation efficiency, grade separation efficiency and pressure drop of the mist eliminators were systematically studied by using Computational Fluid Dynamics (CFD) method. The Shear Stress Transport (SST) k-ω turbulence model and Discrete Phase Model (DPM) were adopted to describe the motion of gas phase and liquid phase, respectively. The computational field was simplified by introducing an assumption that the real 3D structure of porous foam can be equivalent to 2D layout with randomly arranged circles. The CFD results showed that the separation efficiency was enhanced by increasing the foam layer thickness. Moreover, a gradual increase in the foam porosity at fixed PPI (pores per inch) value made the separation efficiency increased to a maximum value, then fall to a lower level, while by decreasing the PPI value of the foam at fixed porosity, the separation efficiency increased. Pressure drop was increased both with the increase in the foam layer thickness and PPI value as well as the decrease of the porosity. Furthermore, the flow field and the droplet trajectories were also analyzed. [ABSTRACT FROM AUTHOR]

• A CFD-DEM model in a rotating frame of reference is developed. • It is adapted to the modeling of solid-fluid operation such as solid-liquid mixing. • It is suitable to all symmetrical impeller geometries. • The model is validated by comparison with experimental measurements. Mixing applications operating in the laminar regime are used in numerous industrial processes in the pharmaceutical, chemical, and food industries. The aim of this paper is to introduce a numerical model adapted to solid-liquid mixing situations in stirred tanks. The method presented herein is based on a Euler-Lagrange approach using the CFD-DEM method. This method couples computational fluid dynamics (CFD) for the fluid with the discrete element method (DEM) for the solid particles. We introduce a rotating frame of reference approach, which is the first of its kind for CFD-DEM. In this paper we discuss the main issues related to the modeling of complex rotating impeller geometries, we explain the various issues involved in conducting a CFD-DEM simulation in a non-inertial frame, we compare our model with experimental results obtained with a pitched blade turbine and, lastly, we use our model to study solid-liquid mixing with a double helical ribbon. [ABSTRACT FROM AUTHOR]

This work focuses on a comparison between the Euler-Euler Two Fluid Model (TFM) approach and the coupled coarse grain discrete element CFD-DEM numerical model for the simulation of a 1 MW th CFB carbonator reactor located at TU Darmstadt (TUD). The effect of the drag force formulation and its associated application in the numerical model for both approaches in terms of their numerical accuracy, compared to experimental data is investigated, by implementing either the conventional Gidaspow model or the advanced EMMS one. Moreover, for the coarse grain CFD – DEM model, the range of values for important numerical parameters as the particle per parcel and cell to parcel size ratios are investigated to shed light on the necessary resolution such a model should have in order to reproduce valid and not parameter dependent numerical results. An adequate cell length to parcel diameter ratio is found to be around 2.6 while as concerns the parcel to particle diameter ratio a value around 58.5 proved to be sufficient, at least for the range of parameters investigated in this paper (size of riser, flow rates and particles average diameter). The EMMS model improved the accuracy of results derived by the coarse grain CFD – DEM model, while further research on the appropriate drag models for the coarse grain CFD – DEM is a sine qua non for its successful implementation in similar studies. For instance it is of interest to answer whether the individual particles slip velocity instead of the particles cell averaged slip, should be used for the calculation of the momentum interexchange coefficient (β) as well as the treatment of different particle diameters in the EMMS equation scheme. [ABSTRACT FROM AUTHOR]

In this paper, semi-analytical and numerical models developed in our previous works to study the dynamic behaviour of natural convection are assessed against the experimental data obtained by means of the L2 Natural Circulation Loop (NCL) of DIME-Tec Labs (University of Genoa). As for the experimental campaign, reference is made to a set of nine experiments performed using water as working fluid and providing a thermal power of 2 kW. This set of data is firstly adopted for the validation of a semi-analytical linear analysis tool aimed at studying the asymptotic behaviour of NCLs through the definition of dimensionless stability maps. Then, two different numerical models (adopted in our previous work to confirm the linear analysis) are assessed, namely an Object-Oriented (O-O) one-dimensional model and a three-dimensional Computational Fluid Dynamics (CFD) model. In this regard, the O-O model represents a fast tool for the evaluation of the most important quantities, such as the velocity and the temperature fields in the loop along the axial coordinate. On the other hand, the CFD tool, which is intended as a support to the 1D analysis, is characterised by a high computational burden, but allows highlighting interesting 3D spatial effects. The validation of these tools is not secondary with respect to that of the stability maps. Actually, the numerical approach is fundamental to study the time-dependent behaviour of both stable and unstable natural circulation regimes, for which the stability maps do not provide information. As for the achieved results, the developed models are able to catch the behaviour of the experimental data. In particular, this outcome is possible if an accurate modelling of both the heat-exchanger section and the piping thermal inertia is considered. [ABSTRACT FROM AUTHOR]

An understanding of the fluid dynamics and the transport phenomena in bubble columns (in the homogeneous and heterogeneous flow regimes) is of fundamental importance to support the design and scale-up methods. In this respect, multiphase Computational Fluid-Dynamics (CFD) simulations in the Eulerian multi-fluid framework are particularly useful to study the fluid dynamics in large-scale reactors; in particular, this study concerns the modeling of the fluid dynamics in bubble columns within the boundaries of the homogeneous flow regime. Reliable predictions of the homogeneous flow regime with this approach are, however, limited up to now. One important drawback is that usually the needed closure models for the interphase forces, turbulence and coalescence and break-up are selected case-by-case, which hinder improvement of the predictive value. A set of closure relations has been collected at the Helmholtz-Zentrum Dresden-Rossendorf that represents the best available knowledge and may serve as a baseline model for further investigations. In this paper, the validation of this set of closure relations has been extended to the pseudo-homogeneous flow regime—characterized by a wide spectrum of bubble sizes and typically associated with the large sparger openings used in industrial applications—in large-scale bubble columns, thus establishing a first step towards the simulation of industrial-scale reactors. To this end, the benchmark considered is a comprehensive dataset obtained for a large-scale bubble column, which has been built accordingly with the well-known scale up criteria (large-diameter, high aspect ratio and large sparger openings). The numerical approach has been tested in its fixed-poly-dispersed formulation (considering the two- and four-classes approaches to represent the dispersed phase) and considering the coalescence and break-up closures. The results suggest that the correct simulation of the fluid dynamics in the bubble column requires the definition of coalescence and break-up closures. The results have been critically analyzed and the reasons for the discrepancies between the numerical results and the experimental data have been identified and may serve as basis for future studies. [ABSTRACT FROM AUTHOR]

The following paper presents a combined experimental and numerical approach to analyze single-phase hydrodynamics inside porous SiO 2 glass sponges (=open-cell foams). For this purpose, a µPIV method has been applied to visualize instantaneous velocity fields of refractive index-matched aqueous Dimethyl sulfoxide (=DMSO) solution flow through the voids of the complex, irregular structure. Results have been recorded for a superficial flow velocity range from 0.02 to 0.38 m/s (corresponding to Reynolds number values between 30 and 650), covering – according to available classifications in literature – all distinguished flow regimes inside such porous systems. µPIV data is used to substantiate the existence of different flow regimes in irregular porous media, to detect their particular flow characteristics and to track the transition points between the prevailing flow regimes. Furthermore, µPIV data has been time-averaged and compared to corresponding numerical results of a laminar, steady-state CFD modelling approach, which is based on reconstructions of the real sponge geometry gained from X-ray tomographic scans of the structure. Experimental and numerical results of pore-scale velocity fields have been compared at three different measurement positions and show good agreement in terms of observed flow structure and direction as well as magnitude of the respective mean velocity fields. [ABSTRACT FROM AUTHOR]

For the simulation of industrial-scale bubble column reactors, while modelling the gas distributor as uniform inlets oversimplifies the inhomogeneity introduced by inlets, the direct simulation of the full geometry of gas distributor or sparger brings about enormous pre-processing work and huge computational cost. A new inlet model is therefore proposed in this paper to simplify the modelling of gas distributor and meanwhile maintain the simulation accuracy. The new inlet model is validated by the comparison of the model prediction with experiments and the CFD simulation incorporating the full geometry of gas distributor for bubble columns of small or large diameters. Comparisons of three different inlet boundary conditions, i.e., the direct simulation of gas distributor, the uniform inlet, and the new inlet model, are made in the simulation of the total gas holdup, the radial profiles of gas holdup at different cross-sections along the column height, and the axial velocity of liquid at various superficial gas velocities. The results indicate that the new inlet model is capable of achieving a good balance between simulation accuracy and computational cost for the CFD simulation of large-scale bubble column reactors. [ABSTRACT FROM AUTHOR]

Gas–liquid two phase flows are widely encountered in industry. The design parameters include two phase pressure drop, mixing and axial mixing in both the phases, effective interfacial area, heat and mass transfer coefficients. Currently, there is a high degree of empiricism in the design process of such reactors owing to the complexity of coupled flow and reaction mechanism. Hence, we focus on synthesizing recent advances in computational and experimental techniques that will enable future designs of such reactors in a more rational manner by exploring a large design space with high-fidelity models (computational fluid dynamics) that are validated with high-fidelity measurements (hot film anemometry (HFA), Laser Doppler anemometry (LDA), particle image velocimetry (PIV), etc.) to provide a high degree of rigor. Understanding the spatial distributions of dispersed phases and their interaction during scale up are key challenges that were traditionally addressed through pilot scale experiments, but now can be addressed through advanced modelling. For practically complete knowledge of the fluid mechanical parameters, it is desirable to implement direct numerical simulations (DNS). However, the current computational power does not permit full DNS for real bubble columns. Therefore, we have been using simplified turbulence models (such as large eddy simulation, Reynolds stress, k – ε , etc.) which need the knowledge of turbulence parameters. For the estimation of these parameters, currently semi-empirical procedures are being used pending the knowledge of turbulence. Further, the formulation of governing equations in all the CFD models (except DNS), the knowledge of interface forces (drag, lift, virtual mass, Basset, etc.) is needed and for their estimations empirical correlations are being employed, again pending the knowledge of fluid mechanics under turbulent conditions in bubble columns. In gas–liquid dispersions, the gas is sparged in the form of bubbles. During the bubble rise, the mechanism of wake detachment creates turbulence which can be called as wake generated turbulence. In addition, energy gets transferred from the gas phase to liquid phase. The quantitative amounts are negligible when bubble motion is not hindered and the gas–liquid dispersion is homogenous. The amounts increase with an increase in the extent of hindrance. However, in the homogenous regime, even under extreme conditions, the extent of energy transfer in the bulk gas–liquid dispersions (volume other than wake volume) is fairly limited. On contrast, in the heterogeneous regime, the rates of energy transfer become sizeable. The energy received by the liquid (in both the regimes) also creates turbulent motion and termed as bulk generated turbulence. In turbulent flows a compendium of eddies (flow structures) of different length and time scales contribute towards improved/enhanced mixing, momentum transfer, heat transfer, and mass transfer (transport phenomena). Hence, a proper understanding of the dynamics of these turbulent flow structures, and their role in the transport phenomena, can bring substantial improvement in the scale-up and design procedures. The present paper brings out the current status of knowledge on bubble generated turbulence. All the published literature in experimental measurements and DNS simulations has been critically analysed and coherently presented. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel down-flow jet loop reactor with helical sieve tapes was proposed. • Hydrodynamic behaviors of this novel reactor were studied with detailed CFD simulations. • Effect of geometry of the helical sieve tape on overall gas holdup was evaluated. • Gas holdup, turbulent kinetic energy and radial mixing were significantly increased. • Optimal design parameters of a helical sieve tape were presented based on CFD simulation. Hydrodynamics and mixing in a novel down-flow jet loop reactor (DFJLR) with an internal helical sieve tape (HST) were studied by computational fluid dynamics (CFD) simulations. A helical sieve tape inside the draft tube caused a significant portion of the gas bubbles to flow helically, which increased radial mixing, overall gas holdup, axial liquid velocity, and turbulent kinetic energy. Compared with a similar reactor without a helical sieve tape, the gas holdup in reactors with a helical tape or a helical sieve tape inside the draft tube was increased, respectively, by 50 % and 75 %. A helical sieve tape with an area ratio of 27 % and helical pitch length of 492 mm was efficient in increasing gas holdup while keeping a lower pressure drop. Data and designs presented in this work will give insight and further understanding for reactor scale-up as a function of geometry and flow patterns for industrial applications. [ABSTRACT FROM AUTHOR]

• O 2 interfacial transport in production scale mammalian STBR is evaluated numerically. • Film theory in tandem with temperature-dependent Henry's constant is applied. • Predicted k L a values validated experimentally against production scale STBR data. • Optimal operational matrix to cultivate mammalian cells in STBR is presented. Computational fluid dynamics (CFD) is widely used for the prediction of hydrodynamics and mass transfer in a bioreactor. In this paper, a four-way coupled 3-D CFD, population balance model, and species transport model along with temperature-dependent Henry's law has been developed and applied to evaluate hydrodynamics, discrete phase distribution, and interphase O 2 transport in a 300 L STR equipped with discrete sparger for production of monoclonal antibody therapeutics. Momentum, mass, and energy equations have been solved. The temperature dependency of Henry's constant has been studied via coupling the van't Hoff's equation. The proposed coupled CFD model has been successfully validated against experimental k L a data. The optimal conditions for the bioreactor operation were identified as 200 RPM and 4 LPM. For k L a, the film theory (Ranz-Marshall) yielded the best prediction for k L a in the range of aeration and agitation rates examined. [ABSTRACT FROM AUTHOR]

[Display omitted] • Propane dehydrogenation reaction was analyzed with porous media CFD model. • Propane conversion was affected by non-uniform distributions. • Space velocity could influence the temperature uniformity. • The mixed packing can effectively suppress non-uniform distributions. Kinetic experiments can be significantly influenced by fluidic effects and transport limitations within reactors, particularly for strongly exo- and endo-thermic reactions. This paper describes the influence non-uniform physical fields, e.g. temperature, velcocity and species concentration, on the determination of kinetic parameters for endothermic systems with propane dehydrogenation (PDH) as a model process, which was analyzed using computational fluid dynamics (CFD) method based on the porous media model. Propane conversions calculated from 3-D porous media model at various conditions have discrepancies from the reported experimental data and 1-D numerical regression. This is due to the application of kinetic parameters obtained from 1-D plug flow assumption to the 3-D model with inhomogeneous temperature distributions. In the kinetic analysis, it is found that the low space velocity may lead to backward diffusion but can be a preference to minimize the temperature gradients within the catalyst bed. On the other hand, the commonly used higher space velocity may enlarge the temperature inhomogeneity. The sensitivity of temperature distribution with various reaction conditions is further analyzed. In addition, with respect to the packed bed properties, a high thermal conductivity and low loading of catalysts can reduce the non-uniformity of temperature distribution. Therefore, it is proposed that a mixed packing scheme with lower catalyst concentration and higher thermal conductivity could effectively suppress temperature gradients in kinetic analysis. This study exemplifies the necessity to consider the non-ideal distribution of physical fields for the kinetic study of reactions with strong thermal effects. [ABSTRACT FROM AUTHOR]

• A CFD model for designing falling film bioreactors with immobilized cells is shown. • Model matches experimental results without any tuning parameter. • Shear stresses in low Re films are calculated as much less than suspension culture. • Mass transfer calculated and demonstrated as ∼1000 h−1 at ∼10 W/m3 power input. We investigated the hydrodynamics and mass transfer performance of falling liquid films over a rough, hydrophilic paper surface with experiments and finite element modeling. These results are critical for designing a novel gas-to-liquid continuous bioreactor with cells immobilized on the vertical surface of a paper biocomposite. The paper substrate allows investigations at very low Reynolds numbers while maintaining an unbroken liquid film. A finite element model was developed to give 10 fold faster simulation result for designing a prototype laboratory scale bioreactor. Excellent agreement was found in both the film properties and mass transfer performance between experiments and simulations. At Re < 100, mass transfer coefficients k L and k L a were ∼1E-4 m/s and ∼1000 h−1, respectively, at ∼10 W/m3. That power input is 10–1000 fold less than most gas stripping bioreactors. This work highlights the potential of this finite element method for falling film, gas absorbing, bioreactor design and analysis. [ABSTRACT FROM AUTHOR]

• Numerical evaluation of three channel configurations of a plate and shell heat exchangers. • Validated results for internal flow for various Reynolds number. • Analysis of pressure drop, friction factor and Nusselt number for three configurations. • Analysis of the correlations present in the literature for plate heat exchangers. The Plate and Shell Heat Exchanger (PSHE) is a variation of the Plate Heat Exchanger (PHE) with a more compact and robust geometry. This paper presents the analysis of the flow in the inner channel formed by a pair of plates of a PSHE employing computational fluid dynamics to determine the hydrodynamic and thermal characteristics for three Chevron angle configurations, 15° × 15° (High/High-HH), 45° × 45° (Low/Low-LL) and 15° × 45° (High/Low-HL). The ANSYS CFX software was employed with the application of the Standard k-ε and the SST (Shear-Stress-Transport) turbulence models for comparison. Experimental pressure drop data and flow streamlines were used to validate the numerical model and to analyze simplifications in the geometric model. Pressure drop, friction factor, and Nusselt number were evaluated for the three geometries studied. A local analysis of the parameters that describe the channels was also performed in this study. [ABSTRACT FROM AUTHOR]

• Discretisation method for the population balance is developed. • Method is mass conservative, applicable to arbitrary grid, efficient and accurate. • Applicable to any combination of aggregation, fragmentation, nucleation and growth. • Method is tested with reference solutions. • Very accurate results are obtained for both distribution and moments. In the present paper, we present a method for solving the population balance equation (PBE) with the complete range of kinetic processes included: namely aggregation, fragmentation, nucleation and growth. The method is based on the finite volume scheme and features guaranteed conservation of the first moment by construction, accurate prediction of the size distribution, applicability to an arbitrary non-uniform grid, robustness and computational efficiency which is instrumental for coupling with computational fluid dynamics (CFD). The treatment of aggregation is based on the previous work by Liu and Rigopoulos (2019). An analysis of the aggregation terms in the PBE is made, and the source of conservation error in finite element/volume methods is elucidated. It is subsequently shown how this error is overcome in the present method via a coordinate transformation applied to the aggregation birth double integral resulting from the application of the finite volume method. The contributions to the birth term are delineated and their corresponding death fluxes identified. An aggregation map is then constructed for mapping birth and death fluxes, thus allowing the finite volume method to operate in terms of fluxes and achieve conservation of mass. The method is then extended to fragmentation, for which a map is also constructed to represent the birth and death fluxes. In the implementation, the aggregation and fragmentation maps are pre-tabulated to allow fast computation. It is also shown how the method can be coupled with a total variation diminishing (TVD) scheme for the treatment of growth with minimal numerical diffusion. The method is validated with a number of test cases including analytical solutions and numerical solutions of the discrete PBE for aggregation (theoretical and free molecule/Brownian kernels), fragmentation, aggregation-fragmentation and aggregation-growth. In all cases, the method produces very accurate results, while also being computationally efficient due to the pre-tabulation of the maps and the simplicity of the algorithm carried out per time step. [ABSTRACT FROM AUTHOR]