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This paper proposes the improvement of microfluidic mixture using the unsteady electroosmotic vortices induced by a staggered array of electrodes. The unsteady electroosmotic forces near two walls, having opposite directions near two walls, were shown to drive organized vortices to contribute for the enhanced mixing. Examination was given to the flow field involving unsteady vortices and their role for the particle mixing. Numerical simulation was made to evaluate the particle mixing process and to reveal how the particle mixing occurred under influence of disturbance by unsteady vortices. The Reynolds number was set to 0.005 and 1.0 changing the oscillation frequency and the electric field intensity. Efficiency of particle mixing was evaluated by the variance intensity of particle number fraction. The agreement between the simulation for the steady electroosmotic flow and the existing paper, and the grid convergence vindicated the simulation code presently used. The numerical results for unsteady electroosmotic flow demonstrated that the particle mixing was controlled by the oscillation frequency and the balanced time scales of the flow perturbation and convection was essential to the particle mixing. The particle flow was displayed to discuss the phenomenology related to the particle mixing. This revealed that the intermingling of particles within main and secondary vortices crucial for the mixing process whereas the outside streams exerted by the vortices were not effective on it. [ABSTRACT FROM AUTHOR]

Rotating bioreactor, such as the NASA bioreactor, which was designed by the National Aeronautics and Space Administration (NASA), USA, can be used to mimic micro-gravity conditions and simulate the effects of microgravity on cells growth. The cell growth in the bioreactor depends on the nutrient availability which in turn depends on the cell density and distribution within the bioreactor. In this work, we use a numerical model of suspended particle motion to simulate the cell motion and distribution in a specific variant of the NASA bioreactor, namely, the high aspect ratio vessel (HARV) bioreactor. The nutrient distribution in the bioreactor is simulated based on a convection–diffusion-reaction supplemented by laboratory experiments aimed at obtaining the required data. We present the modelling framework in this paper and discuss the most salient simulated results. For example, the simulation results show that the distributions of the cells in the bioreactor appear as concentric circles and that the cells density is higher in the middle of the HARV bioreactor. These cell distributions imply that they may accumulate in the middle of the bioreactor at sufficiently high cell density. The results also demonstrate that the concentration of nutrient is fairly uniform in the bioreactor but decreases slightly from the outer radius of the HARV bioreactor to the inner radius. This is possibly caused by the higher consumption of glucose due to the higher cell density in the middle of the radius. We expect that the modelling framework in this paper would help optimise the culture conditions for the cells in HARV bioreactors. [ABSTRACT FROM AUTHOR]

For the design of a fixed-bed adsorber, it is essential to know the prediction of the column breakthrough. This paper compares two modeling approaches of the dynamic behavior of a fixed bed that contains treated sewage-sludge for biogas desulfurization. The first approach is based on the simple model by Bohart and Adams, which has been widely used to describe the adsorption dynamics when chemical reaction takes place, and the second one uses the linear driving force model (LDF), solving it analytically by Klinkenberg equation and numerically with the aid of Aspen Adsorption. While the Bohart-Adams model uses rectangular isotherm to describe the equilibrium, the LDF model is solved with a more realistic and suitable isotherm. The Klinkenberg solution implies a linear isotherm, and the prediction is not good enough, although better than that of the approach of Bohart-Adams. The trouble is that the linear isotherm used in the analytical solution is not realistic and a nonlinear isotherm is required. This paper presents a methodology to estimate the overall mass transfer coefficient dynamically as well as the isotherm that best fits. Thus, the LDF model with the Freundlich isotherm provide a breakthrough curve that match the experimental results much better than the Bohart-Adams approach. In order to apply the prediction obtained, a scaling up of the lab scale was performed, discussed and assessed. [ABSTRACT FROM AUTHOR]

• A mathematical model of oxygen transport in the HF membrane has been developed. • The model is based on balance conditions for oxygen flows in feed and sweep gases. • The geometric shape of the HF membrane was taken into account. • The model adequately describes the oxygen flows for HF membranes. The paper presents a model of oxygen transport in oxygen-permeable hollow fiber membranes taking into account the gradual changes of oxygen partial pressure in flows of feed and sweep gases along the HF membrane. The model is based on fulfilling local mass balance conditions linking oxygen flows in feed and sweep gases with the oxygen flux through the membrane. Computer simulation of oxygen permeation data for hollow fiber membranes made from mixed ionic electronic conducting oxides (Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3- δ , Ba 0.5 Sr 0.5 Co 0.78 W 0.02 Fe 0.2 O 3- δ and Ba 0.5 Sr 0.5 Co 0.75 Mo 0.05 Fe 0.2 O 3- δ) was carried out using different models. The oxygen permeability model based on the semi-empirical dependence of the oxygen flux on oxygen partial pressure J O 2 = γ (T) (p O 2 , 1 n - p O 2 , 2 n) gives the most accurate description of the experimental data. An analysis of the activation energy of the effective oxygen flux coefficient γ(T) indicates that the rate determining step is a surface reaction. [ABSTRACT FROM AUTHOR]

Highlights • Experimentally investigated impact of laterally sprayed water on methane jet flame. • Studied impact on flame shape, temperature, radiation intensity, and extinguishment. • Developed relationship between the mean flame tilt angle and Froude number. • 3D numerical simulation showed sound agreement with experimental data. Abstract This paper investigates the impact of a laterally sprayed water mist on a methane-air jet flame. An experimental apparatus for suppressing a flame using laterally sprayed water mist was developed and used to investigate the effect of the mist on the flame shape, temperature field, velocity field, radiation intensity, and extinguishment. A 3D numerical simulation was then performed to reveal the underlying mechanisms observed in the experiments, with the simulations showing reasonable agreement with the experimental data. Increasing the pressure of the water mist decreased the flame height and increased its tilt angle. For a given water mist pressure, lower–velocity flames exhibited larger tilt angles, because they were more strongly affected by the transverse shear forces exerted by the water mist; additionally, they were more likely to be extinguished by the mist. A relationship between the mean flame tilt angle, and the Froude number was deduced. Water mist was also discovered to substantially decrease the radiation intensity of the flame. Moreover, the influence of gas velocity and water mist pressure on the turbulence intensity, radiation temperature, and velocity field were discussed numerically. This can theoretically help interpret the suppressing effect of water mist on a methane-air jet flame. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the application of the ADM1 model to simulate the dynamic behaviour of an anaerobic reactor treating the condensate effluent (EC) generated in a sulphite pulp mill. The model was implemented in the simulation software AQUASIM® 2.1d and its predictions were compared to experimental data obtained in lab-scale semi-continuous assays treating the industrial effluent. Sensitivity analysis revealed high influence of kinetic parameters on the process behaviour, which were further estimated: maximum specific uptake rate (k m =13.2d−1) and half-saturation constant (K s =0.06kgCODm−3). The accuracy of the optimised parameters was assessed against experimental data from a second lab-scale reactor treating EC effluent with an additional carbon source (molasses). It was concluded that the model predicted reasonably the dynamic behaviour of the anaerobic reactor under different loading rates. In addition, simulations successfully predicted a better stability and performance of the process (lower VFA accumulation and higher COD removal and methane production) for the EC treatment when an external carbon source is added to the reactor, specifically at high organic loads (2kgCODm−3 d−1 or higher). The model was not able to describe adequately the reactor behaviour at high organic loads when molasses was not added, thus application of the model for the anaerobic treatment of EC effluent needs to be further evaluated. [Copyright &y& Elsevier]

Abstract: Agricultural crop residues (palm oil empty fruit bunches—EFB) were used as raw material for cellulose, lignin and hemicelluloses obtaining following sustainable criteria. An organosolv pulping process based on ethylene glycol–water mixtures, which allowed an easy recycling of solvents as well as the recovery of generated by-products, was used to induce delignification. Computer simulations using commercial software (Aspen Plus) were made on the whole process in order to design the solvents recovery stages and optimise the operation conditions. Laboratory experiments were carried out with the aim of characterizing raw material, black liquors and released by-products. Considerable high proportion of recycled solvents (91wt% ethylene glycol and 88wt% water) was reached with the proposed scheme. This resulted in 70 and 80wt% reduction of fresh solvent input for ethylene glycol and water respectively, thus reducing the environmental impact of the process. EFB organosolv pulp could be considered an acceptable alternative for producing certain paper qualities with moderate strength requirements while allowing an agricultural residue from a major economic activity (viz. oil palm production) to be exploited. [Copyright &y& Elsevier]

Particle resolved direct numerical simulation (PR-DNS) has emerged as a promising method to improve gas-particle heat transfer closure models. To date, this method has been applied in random and regular particle assemblies at comparably high void fractions. This paper presents a new methodology for deriving heat transfer correlations from PR-DNS of very dense particle packings relevant for packed bed applications. First particle packings were generated using the discrete element method (DEM). After geometric modifications in regions of close particle-particle proximity, a fine mesh with low cell skewness was created for PR-DNS. Grid independence and the effect of the geometry modification were thoroughly investigated. It was also established that steady state simulations are accurate for PR-DNS in this case. Simulations carried out in different assemblies of ∼100 particles showed significant variation of local transfer rates, implying that it is important to specify a confidence interval when reporting correlations derived from PR-DNS. A newly developed Nusselt number correlation predicts values in the lower range of predictions from literature correlations. This implies that the use of the currently available correlations may over-predict heat transfer in densely packed beds. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multi-modal framework combining experiments, simulations and AI techniques. • Two-way coupled CFD-DEM simulation of stirred media mill. • Comparison with magnetic tomography measurements. • Relative velocity and energy investigation with parameter and geometry comparisons. • Proposal of an extended mechanistic model of wet stirred media mills. Stirred media mills are used in many industries from mechanochemistry, to ore crushing, battery production and pharmaceutics. Investigation and modelling can be a costly, difficult and time consuming endeavour, limiting the investigable parameter space with some aspects only being accessible via numerical methods such as simulations or artificial intelligence (AI). Simulations allow investigations of inner mechanisms and generate large quantities of data while being computationally demanding. AI requires large data quantities yet is applicable with limited computing power for large parameter spaces. For this reason, the intelligent integration of different methods holds great promise to achieve maximum benefits at minimum cost by synergistically combining respective advantages. Here, a multi-modal framework is demonstrated, combining experiments, simulations and AI. In this first paper direct magnetic measurements via a tracer particle are compared with simulations of wet mills. With two way coupled CFD-DEM simulations inner mechanisms like the impact of disc geometry, tip speed and grinding bead size are investigated. Differences in translational and relative velocity distributions are investigated, showing a consistent displacement of a factor three toward higher energies throughout the complete distribution for the hole disc in comparison to the full disc, and less consistent deviations for translational velocity, specifically for the higher energy collisions, being larger by a factor of 8. Also comparisons with the existing mechanistic model of Kwade are performed. An additional indirect influence of diameter on tip speed could be detected. In a second publication AI modelling will be performed on the basis of the simulations. [ABSTRACT FROM AUTHOR]

Mathematical models of automotive exhaust aftertreatment catalysts are often based on reaction kinetics developed using laboratory reactor light-off data. This paper investigates an effect observed while developing CO oxidation kinetics for a Diesel Oxidation Catalyst: it was found that while several different sets of kinetic parameters would give an equivalent prediction of the reactor data, they gave different predictions over a vehicle drive cycle. This represents a major problem when developing an aftertreatment catalyst model. This effect may be observed with any reaction which is strongly inhibited by one of the reactants and which can become external transport limited. The main cause of this effect is that the reaction exhibits hysteresis; kinetic parameters which predict the same behaviour when the temperature is increasing, give different predictions when the temperature is decreasing. The size of the hysteresis increases with the magnitude of the self-inhibition constant in the rate equation and with reactant concentration. A second cause for this effect is that if lower concentrations are encountered in the drive cycle than were used for kinetic development; kinetic parameters which give equivalent predictions at higher concentration may give different predictions at lower concentration. To avoid this problem, reactor data during both temperature ramp up and ramp down should be used for developing kinetics. However, it should be noted that it has been found that (i) not all experiments exhibit hysteresis and (ii) that discretisation of the catalyst into an exceptionally large number of elements is required for accurate prediction during ramp down. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the gasification of sawdust in an air cyclone gasifier was investigated to produce a high quality fuel gas with less tar. The effect of air to fuel ratio on the gasification characteristics was studied. The results indicate that as the air to fuel ratio varying from 0.23 to 0.35, the lower heating value of the produced gas is 4.5–5.7MJ/Nm3, the carbon conversion is 77.0–94.2%, the cold gas efficiency of the gasification system is 53.6–63.0%, while the tar content is 4.4–8.4g/Nm3. A detailed CFD model of a cyclone gasifier has been developed, based on the Fluent package. Models of sawdust pyrolysis and combustion of volatiles and char have been added to the standard model. The model provides information on the gas temperature in the gasifier and the composition of the outlet gas. [Copyright &y& Elsevier]

Abstract: Though discrete particle simulation (DPS) has been widely used for investigating gas–solid flows from a more detailed level as compared to traditional two-fluid models (TFMs), it is still seriously limited by the computational cost when large scale systems are simulated. GPUs (graphic processing units), with their massive parallel architecture and high floating point performance, provide new possibilities for large-scale DPS. In this paper, a multi-scale CPU (central processing unit)–GPU hybrid computation mode is developed, in which the fluid flow is computed by CPU(s) while the particle motion is computed by GPU(s). To explore its feasibility, this mode is adopted to simulate the flow structures in the fluidization of Geldart D and A particles, respectively. Further coupled with an EMMS (energy minimization multi-scale) based meso-scale model, the flow behavior in an industrial fluidized bed is finally simulated, shedding light on the engineering applications of DPS, as an alternative to TFM. [Copyright &y& Elsevier]

Abstract: A multi-component two-phase lattice Boltzmann method of the Shan–Chen type has been developed for simulating the complex interplay of diffusion and surface reaction in a multi-component gas–liquid catalytic chemical reactor. This method development comprised of various steps, viz. the formulation, implementation, and validation of lattice Boltzmann techniques capable of reproducing, among other things, species transport across a phase interface, a chemical reaction at a catalytic surface, and a phase change due to the surface reaction, which all are relevant to the Fischer–Tropsch Synthesis (FTS). The most important steps taken in developing method and implementation, along with some validations are discussed. This paper presents the results of the simulations for a simplified isothermal 1-D FTS case with a liquid film covering a catalytic surface and gradually growing due to the surface reaction. [Copyright &y& Elsevier]

Abstract: This paper reports a study of steady-state heat transfer of gas and liquid flowing through a packed bed with spherical particles of 2.06mm and constant wall temperature with Computational Fluid Dynamics (CFDs). The effect of gas and liquid flow rates on heat transfer in packed beds are discussed. The effective radial bed conductivity (λ er ) is calculated based on the steady-state two dimensional model. The results of the CFD simulations have been validated with experiments and they are in a good agreement. For most of the cases the results of the CFD simulations deviate from the experimental results not more than 10%. The results show that the effective radial bed conductivity increases with increase of the velocity of gas and liquid. In trickle flow regime the effective radial bed conductivity is much bigger than in a dry gas flow regime. [Copyright &y& Elsevier]

Abstract: This paper proposes a model-based control strategy that can predict the influent and effluent as well as control the effluent water quality in the A2/O (Anaerobic/Anoxic/Oxic) process for 1day in advance. In the model-based control strategy, ANN (Artificial neural network) and modified ASM3+Bio-P model were used to predict the influent and effluent for 1day in advance, respectively. When the predicted effluent NH4–N concentration was higher than the target value, the optimal setpoint schedules of the DO (Dissolved oxygen) could be deduced using a scenario simulation. The scenario simulation was carried out to obtain DO setpoint schedules to reach the effluent NH4–N concentration under the target value. The deduced optimal setpoint schedules were used to control the operation of the process for the next day. The results of model prediction showed that the behavior of the influent and effluent could be predicted successfully. The proposed model-based control strategy was tested in a pilot-scale A2/O process for 2weeks, which confirmed that the effluent NH4–N concentration could be maintained steadily lower than the target value of 5mg/L. The air flow rate during control period was increased by 9% of that during without control period. On the other hand, their corresponding average effluent NH4–N concentrations were 4.42 and 13.89mg/L, respectively, which highlight the significant effect of this control strategy with only a slight increase in air flow rate. These results show that the developed model-based control strategy can be used successfully in the A2/O process and possibly other processes. [Copyright &y& Elsevier]

Abstract: Three flow patterns of flooding, loading and complete recirculation in a gas–liquid stirred Rushton tank were identified based on experimental observation. The gas–liquid system was composed of air and water. Under different operating conditions of gas flow rate and impeller rotating speed, the distribution of gas holdup near the region of impeller was measured using a γ-CT scan method. Both quantitative digital distribution curves of gas holdup and their qualitative color CT images were obtained. At the region of impeller, there was a convex characteristic peak of gas holdup distribution both in radial and in axial directions, and with the region being gradually away from the impeller, the distribution of gas holdup became flatter. The values of gas holdup in S33 regime were a little higher than those in L33 regime. Higher impeller rotating speed had some effect on the increasing of gas holdup at the region of higher axial height. The experimental measurement results were basically consistent with those previously published by Bombač. The hole number and diameter of sparger had little influence on the distribution of gas holdup, while the sparger''s installed height had significant influence on them. When the sparger was installed close to the bottom of Rushton tank, a comparatively smoother distribution of gas holdup above the space of impeller could be obtained. The research results in this paper were useful for better understanding of gas holdup distribution near the region of impeller of Rushton tank, and could also provide experimental data for CFD simulation. [Copyright &y& Elsevier]

Abstract: Mixing is crucial yet challenging work in the laminar, low Reynolds number microfluidic devices. In this paper, a microchannel comprising a mixing unit embedded with geometric features is designed to enhance the mixing. Instead of complex spatial geometries and sample strategies, simple periodic geometric features are applied to decrease the required mixing distances. In computer simulations and experiments, geometric features in the mixing unit increase periodically and good mixing occurs after a 28-period mixing unit. [Copyright &y& Elsevier]

In this paper, we report the effect of the number and position of the adenosine triphosphate (ATP) and luciferase streams on the diffusion-based continuous bioluminescent reaction in a microchannel. The detectable bioluminescent reaction between substrate (ATP) and enzyme (luciferase) was maximized when the total flow rate of the substrate and the enzyme solution was around 3 and 8μl/min for the 2- and 3-stream configurations, respectively. Most of the light was generated inside the luciferase phase, because the diffusion of over 100 times smaller ATP than luciferase into luciferase phase is a limiting factor of continuous flow bioluminescence reaction in microchannel. The diffusion-based reaction of luciferase was enhanced by increasing the number of streams from 2 to 3. The bioluminescence was higher up to 41% when ATP solution was infused as a middle of three streams (L_A_L configuration) comparing with the A_L_A configuration. The optimized flow rates of ATP and luciferase solutions on a thick poly(dimethylsiloxane) layer were obtained as 0.15μl/min:0.7μl/min:0.15μl/min for luciferase:ATP:luciferase solutions, respectively. In addition, a diffusion-based simulation model was developed for the characterization of the bioluminescent reaction in a microchannel. The numerical simulation using the model was closely matched with the experimental results with 0.01 level significant correlations in bivariate correlation coefficient analysis. The reaction between ATP and the luciferase solution in a microfluidic device can be used for a flow-type bioluminescence sensor for rapid detection of cells. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a technique for enhancing the mixing of electroosmotic flows in a microchannel by means of aperiodic spatio-temporal variations in the zeta potential. The effects of the magnitude of the time-varying zeta potential, the length of the heterogeneous surface zeta potential patterns, and the aperiodic switching frequency of the zeta potential on the fluid flow characteristics and mixing performance are analyzed by performing a series of numerical simulations in which the aperiodic oscillating source used to modulate the switching frequency of the zeta potential over time is derived using the Sprott system. The results show that the aperiodic spatio-temporal variations in the zeta potential generate irregularly alternating flow recirculations over time, which in turn produce a stirring of the species. In addition, it is shown that an effective enhancement in the mixing performance can be obtained through the application of a suitable switching frequency. Moreover, the mixing performance can be further improved by increasing the strength of the heterogeneous surface zeta potential or the length of the heterogeneous surface zeta potential patterns, respectively. Overall, it is shown that an average mixing efficiency of over 90% can be obtained when the length of the heterogeneous surface zeta potential patterns is equal to twice the channel width, the magnitude of the heterogeneous surface zeta potential is twice that of the homogeneous surface zeta potential, and the value of the oscillating frequency used to modulate the variation of the zeta potential is assigned within an appropriate range. [Copyright &y& Elsevier]

Abstract: This paper proposes a novel design concept for the enhancement of methane combustion in a microchannel that uses the combined effects of catalyst segmentation and cavities. The effects and combustion characteristics are evaluated using numerical simulation with detailed heterogeneous and homogeneous chemistries. The effects of a multi-segment catalyst and cavities on channel walls are examined and discussed in terms of various catalyst layouts, cavity dimensions, flow conditions, and reactor properties. In general, the chemical process of conventional catalytic combustion is a competition between hetero- and homogeneous reactions for fuel, oxygen, and radicals. The objective of using catalyst segmentation and cavities in a micro-reactor is to integrate the advantages of the hetero- and homogeneous reactions to enhance fuel conversion and to promote complete combustion in a confined distance. In this catalyst configuration, the pre-reaction of the heterogeneous reaction in an upstream catalyst segment can produce intermediate chemical radicals and catalytically induced exothermicity; the homogeneous reaction is subsequently induced and anchored in the cavity. Carbon monoxide is massively discharged after the homogeneous reaction due to incomplete combustion. The downstream catalyst segments strongly deplete carbon monoxide due to its high sticking coefficient on the platinum surface. Full methane conversion and complete combustion can thus be achieved in a short distance. Cavities can appreciably extend the stable operational range of the micro-reactor for a wide variety of inlet flows. Moreover, etching localized cavities in a small-scale system can further stabilize the flame, and cavities can serve as the heat source for reactions. These benefits of the proposed catalyst configuration can be applied in the design of a small-scale power/heating generator. [Copyright &y& Elsevier]

Abstract: Rotating packed bed (RPB) has been widely used in absorption, desorption, distillation, oxidation, crystallization, precipitation, polymerization, and production of nanoparticles. RPB utilizes centrifugal acceleration to intensify the mixing and mass-transfer processes. Under high-gravity, molecule diffusions are much faster than under normal gravity. With the centrifugal force generated by rotation, RPBs have considerable high mass-transfer and micromixing performance. However, because of the complexity of fluid flow inside the RPB, the flow experiments do not easily lead to the deeper understanding on the fluid dynamics in an RPB. In this paper, computational fluid dynamics model and two-, three-dimensional physical models have been developed to describe the RPB. Numerical simulation of the fluid flow and pressure drop in dry bed in an RPB using commercial software, Fluent, as a computational platform has been carried out. Different fluid flow rates, rotator speeds and gas flow rates have been systematically investigated. The preliminary simulation results show that the models used to describe the RPB can give rise to better understanding of the flow in an RPB. [Copyright &y& Elsevier]

Abstract: Falling liquid film is commonly employed in variety of industrial systems, such as LiBr/H2O absorption heat pump or chiller. In this paper, the falling film absorption in aqueous lithium bromide solution was investigated numerically using CFD software package-Fluent. The practical convective boundary condition at the cooling water side was considered. The heat transfer coefficient is assumed constant, and the coolant temperature changes linearly along its flow path. The numerical results indicate that the profile of temperature is exponential and their gradients are high due to the distinct heat effect associated with the absorption at the interface and the cooling effect of coolant at the wall at small downstream distance. As the downstream distance increases, the profile of temperature is nearly linear. The absorption heat and mass fluxes reach a maximum at the inlet region and decrease at the outside of the inlet region. Specially, the effect of variable physical properties on the absorption process was considered and discussed. The prediction of the total absorption mass transfer rate is about 6.5% higher when assuming constant properties. [Copyright &y& Elsevier]

Abstract: The paper presents the results of a study carried out using the computer program ZB1 simulating the flocculation of suspended solids. A description of the program is followed by an analysis of the effect of colloidal particle size and settling rate on sol destabilization. It was demonstrated that the tested program is consistent with the classical theories of particle motion and destabilization of colloidal systems. It was also found that the value of the diffusion coefficient increased along with an increase in the particle diameter S, regardless of the settling rate Q. An increase in the particle diameter caused an increase in the diffusion coefficient and allowed to shorten the duration of the destabilization process. [Copyright &y& Elsevier]

Abstract: In the field of gas–solid fluidization, bubbles, and all features regarding them, have a very great importance, as they significantly affect the process performance. Numerous experimental studies on bubbles, and their formation, evolution, and properties, have been performed in the past. These investigations appear particularly difficult, due to the nature of these systems, since the gas phase is distributed in both the bubble and the emulsion phase. Several experimental approaches have been developed to tackle this study. Among these, the Digital Image Analysis Technique purposely developed in Part I of the present work, based on the use of a video camera for monitoring the phenomenon coupled with image analysis has been found viable and effective. Moreover, the bubbles behaviour and characteristics have been described by means of a variety of mathematical models. In recent years, in particular, computational fluid dynamics (CFD) tools have been found to be very effective in providing a powerful framework through which these models can be implemented and numerically solved. This paper combines both experimental and computational studies, presenting the comparison, performed by DIAT, between experimental data and relevant CFD simulations. In particular, simulations have been performed by means of the ANSYS-CFX code. The comparison comprises the following quantities: bed expansion, bubble hold-up, size evolution, distribution, density, aspect ratio, and bubble velocimetry data. [Copyright &y& Elsevier]

• A single DNS simulation of deformable bubbly flow in a vertical channel is conducted. • Turbulence equations for different turbulent models are evaluated by the DNS data. • The bubble-induced turbulence model is re-evaluated based on DNS simulation. Direct numerical simulations (DNS) provide a description of turbulent flow fields at every point in space and time. Since every statistical quantity can be computed, this data should be useful for the development of closure models. In this paper, models for bubbly turbulent flows, in a two-fluid framework, are investigated using DNS data. A front tracking method is employed to simulate turbulent flow with deformable bubbles in a vertical channel. Quantities such as void fraction, average velocities, velocity fluctuations, and turbulence statistics are computed and presented. After processing the DNS data, the turbulence kinetic energy and dissipation equations, based on the k-ε model and explicit algebraic stress model (EASM), are analyzed. The model for bubble-induced turbulence, represented by source terms in the k and ε equations, is re-evaluated using coefficients derived from the DNS results. This work is a first step to show what can be done by using the DNS data to evaluate turbulence closure models. More simulations should be conducted in future works to further improve such models. [ABSTRACT FROM AUTHOR]

Abstract: The present work deals with evaluation of different configurations of sonochemical reactors using a model reaction with justification on the basis of cavitational activity predictions of theoretical simulations. In addition, intensification of the cavitational effects using additives has been investigated and its dependency on the inherent cavitational activity in the reactor has been established. The model reaction used for experimental investigations is the potassium iodide oxidation, also known as the Weissler reaction whereas the theoretical prediction of cavitational activity has been achieved using the numerical simulations of the sound wave equation using Comsol Multi physics software. The effects of various additives for enhancing the cavitational activity such as solid particles like cupric oxide, salts like sodium nitrite and radical promoters such as ferrous sulphate have also been investigated. It has been observed that the configuration with higher transducer areas gives better distribution of the cavitational activity and also gives enhanced effects as quantified using the cavitational yield measurements. Also it has been conclusively established that depending on the mechanism of intensification, the beneficial effects obtained using different additives are strongly dependent on the inherent cavitational activity which in turn depends on the type of reactor and the operating conditions. [Copyright &y& Elsevier]