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• Solidification of a liquid bridge between two curved surfaces is numerically studied. • A ring caused by volume expansion tends to shift above the bridge midplane. • Convex surfaces yields longer solidification and a higher ring shift compared to concave surfaces. • Increasing the bridge volume prolongs solidification and reduces the ring shift. Liquid bridge solidification is a key process in many engineering problems. To advance its applications, we present a numerical investigation of the solidification of a bridge vertically connecting two rods with curved ends. The rod ends are spherical caps to which the bridge interface is pinned. The bridge begins to solidify from its stable vase-like shape. Owing to gravity, when the solid is less dense than the liquid, a ring is formed around the bridge and shifted a certain distance above the bridge midplane. Changing the rod cap from concave to convex enlarges the size of the ring but reduces the ring shift and the solidification time. Increasing the initial liquid volume of the bridge reduces the ring asymmetry but increases the solidification time. The effects of the solid density relative to the liquid, the length of the bridge, and gravity are also revealed in detail. [ABSTRACT FROM AUTHOR]

Bromate formation and insufficient micropollutant degradation are two major problems in wastewater ozonation. The conventional process using bubble columns has the drawback of an inhomogeneous ozone distribution, causing increased bromate formation. Membrane contactors are a promising alternative as they can dissolve ozone bubble-free. This work presents a simulation of a tubular membrane contactor in COMSOL Multiphysics that includes flow, mass transfer, ozone decay, and reactions of organic molecules and bromide with ozone and hydroxyl radicals. Gaseous ozone and water flow on the lumen and shell side of the membrane, respectively. Static mixers are placed in the water channel, coaxial between the membrane and housing. The simulations show a 75% increase in ozone flux through the membrane, a homogenized ozone distribution, and 13 times higher degradation of a medium-oxidizable micropollutant in the presence of additional static mixers. Furthermore, static mixers enable the use of a lower gaseous ozone concentration, resulting in 31% lower bromate formation at the same ozone exposure without affecting micropollutant degradation. Overall, we demonstrate that membrane contactors with static mixers can be used as a strategy to reduce bromate formation. • Membrane contactor model including flow, mass transport, and chemical reactions. • Static mixers prevent hotspots of dissolved ozone in the bulk phase. • 75% increase in membrane ozone flux with static mixers. • Bromate formation is lowered by 31% at same ozone exposure with static mixers. • Micropollutant degradation is not affected by this bromate mitigation strategy. [ABSTRACT FROM AUTHOR]

[Display omitted] • Deterministic modeling of cationic ROP of ε-CL based on the method of moment. • Revealing the effect of transesterification reaction on molar mass averages of PCL. • Applying the developed model to metal free ROP system catalyzed by TrBF 4. • Playing with process conditions to increase the industrial sustainability of PCL synthesis. Ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) is an efficient way to produce a widely used biodegradable polymer, i.e., poly(ε-caprolactone) (PCL). Compared to coordination ROP, ionic ROP receives great attentions in recent years due to mild reaction conditions and well-defined polymer microstructure. To fully exploit the potential of ionic ROP, in this work, a mathematical kinetic model for activated monomer mechanism (AMM) based cationic ROP of ε-CL was developed based on method of moments (MoM). Using the developed model, we estimated the values of the kinetic coefficients of monomer activation and monomeric units' protonation reactions. The simulated results are found to be in good agreement with experimental data, as well as the benchmark by kinetic equation. Moreover, the simulations reveal the crucial role of transesterification reaction in molar mass distribution broadening and how the concentrations of acid and alcohol affect the monomer conversion and average molar masses of the polymer. Finally, the model was successfully extended to a newly reported system using trityl tetrafluoroborate (TrBF 4) as catalyst, proving the universality of our model. This study provides deeper understanding of the cationic ROP and allows to optimize process conditions to increase the industrial sustainability of PCL-based materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ablative resistance CF-ZrO 2 composite with gradient structure was designed. • The key influencing factors of layered filtration efficiency was investigated. • The mechanism through computational simulation and practical experimental results were explained. • Gradient distribution of greatest ablative resistance composite is provided. The ablative resistance composites with gradient structures are potentially applied to the protection on the outer wall of a solid rocket engine nozzle. We successfully prepared the ablative-resistant ZrO 2 -doped carbon fiber (CF-ZrO 2) composite with the gradient structure via pressure-assisted osmosis. We analyzed the interception efficiency of ZrO 2 particles per layer in the gradient structure and the ablative resistance mechanism of the composite using CFD-DEM simulations and experiments. The results indicate that the surface density of carbon cloth and the properties of fluid phase, including ZrO 2 particle size, solid content, kinematic viscosity and flow rate can significantly affect the distribution of ZrO 2 particles and mass interception efficiency per layer in the gradient composite. Importantly, we successfully prepared an optimal CF-ZrO 2 gradient composite that exhibited a decrease in the mass ablation rate by 0.125 mg/s compared to the undoped CF composite. This is primarily due to the presence of dense and molten layers of ZrO 2 particles embedded in the composite, resulting in the excellent ablative resistance performance of the functional gradient composite. [ABSTRACT FROM AUTHOR]

• SuperPro and Design Expert used to optimize industrial-scale biogas production from POME. • Recirculation ratio of 148 % and HRT of 22 days yield highest methane yield. • Results offer potential for sustainable and efficient large-scale biogas production. The palm oil industry generates a considerable amount of waste, known as palm oil mill effluent (POME), which is characterized by high levels of chemical and biological oxygen demand (COD and BOD). The anaerobic digestion of POME is a potential solution for generating biogas, a renewable energy source that can be used for power generation. However, optimizing biogas production from POME is a challenging task, particularly at the industry scale due to the complex nature of the waste stream. This study aimed to improve the performance of an existing POME-based biogas plant through simulation and optimization. The POME treatment process was simulated using SuperPro Designer software. The simulated results were validated against data obtained from the existing plant, including the environmental properties of COD, BOD, total suspended solids (TSS), and total solids (TS), as well as the composition of the biogas produced. The simulation results showed good agreement with the existing plant data, although some parameters had a high relative difference due to assumptions made during the simulation. The process parameters, including the recirculation ratio and hydraulic retention time, were optimized using Design Expert software. The optimized parameters obtained were a recirculation ratio of 148 % and an HRT of 22 days, resulting in a maximum biogas flow of 859 m3/h, corresponding to a methane yield of 0.259 m3 CH 4 /kg COD removed. Confirmatory experiments were conducted over a period of 3 months using the optimized variables in the biogas plant. The results showed a high level of consistency between the predicted and experimental values with a percentage error difference ranging from 0.03 % to 2.3 %. This study's novelty lies in the integration of simulation and optimization tools to improve the performance of POME-based biogas plant. The findings of this study have significant implications for sustainable development in the palm oil industry, providing an efficient and cost-effective approach for treating POME and producing renewable energy. [ABSTRACT FROM AUTHOR]

• The influence mechanism of E and D is revealed by experiments and simulations. • Increasing E strengthens the electric field distortion and charge polarization. • The high-pressure gradient region is easier to form in large D. • The vertical collapse evolution is suppressed with the increase of E and D. Under high-strength electric fields, partial coalescence may occur, thus producing fine secondary droplets, which are undesirable for separating water from oil. In this study, experimental and numerical methods are employed to investigate the coalescence behavior under a DC electric field to comprehensively understand the effect of electric field strength (E) and droplet diameter (D) on coalescence. The Level-set method is employed to capture the moving interface, and the numerical data are validated through experimental tests. The results reveal the easy formation of secondary droplets with increasing E and D values. In particular, the electric field strength suppresses the expansion of the liquid bridge and hinders the vertical collapse of the droplets. The distortion of the electric field at the liquid bridge and the polarized charge both increase with E , thus resulting in stronger electric field repulsion. Moreover, the enhancement in D significantly affects the shrinkage of the liquid bridge and prevents the vertical collapse of the droplet. The pressure gradient at the liquid bridge from the outside to inside decreases as a function of D , thereby inhibiting the contraction speed. Furthermore, the number of polarized charges concentrated on the top of the droplet increases, thus resulting in an enhanced electric field tension. The results obtained herein can potentially act as guide for the design and optimization of electric dehydrators. [ABSTRACT FROM AUTHOR]

• An aminophosphine-based automated synthesis of InP QDs with high reproducibility was demonstrated. • PSDs derived from the UV–vis spectra can be interpreted as volume equivalent diameters in case of InP QDs with tetrahedral shape. • A predictive model based on population balance equation was proposed. • With the identified parameter set, a very good agreement between experimental results and simulations was obtained, including activation energies. Despite great progress in the synthetic chemistry of InP QDs, a predictive model to describe their temporal formation is still missing. In this work, we introduce a population balance model incorporating liquid phase reactions, homogeneous nucleation and reaction-limited growth of InP supported with the highly reproducible and reliable experimental data acquired from an automated robotic synthesis platform. A comparison between experimental kinetic data (different initial concentrations and temperatures) and simulations was made. The proposed model describes the temporal evolution of solid concentration, particle diameter and particle size distribution very well. The quantitative agreement between experiments and simulations was only achieved by global optimization to identify unknown and hardly measurable material parameters and kinetic constants such as surface energy, growth rate constants or activation energies. We see this model rendering the first step towards the development of more refined models that enable rigorous optimization and control of the production process for III-V semiconductors. [ABSTRACT FROM AUTHOR]

• A model that merges the coalescence with the hindered sedimentation is presented. • Two terms are incorporated into the model in order to conserve the mass of the dispersed phase. • The model was calibrated and validated through an experiment with an oil-water system. • Effects of standard deviation of the initial droplet volumes and coalescence frequency are investigated. Population balance equations (PBE) provide a suitable a framework for dealing with drop breakage and coalescence. In addition, modeling of the solid particle sedimentation process based on Kynch's theory has been successfully used and validated in mineral processing and wastewater treatment. In this work, we present a model that merges the coalescence process with hindered polydisperse sedimentation. The PBE model is projected onto a partial differential equation (PDE) system by discretizing the droplet volume. Because there is loss of mass in the system when the daughter droplets are greater than the larger species considered for the numerical solution, two terms that produce the conservation of the mass or total volume of the dispersed phase are incorporated into the PDE system. The resulting PDE system is split into two systems: homogeneous PDEs and ordinary differential equations (ODEs). The homogeneous PDEs and the ODEs are discretized using a first-order central differencing scheme and the second-order, two-stage Runge-Kutta method, respectively. The model predicts the vertical variation of the composition of the dispersed phase layer that forms at the top or bottom of the gravity settler. The proposed model was calibrated and validated through an experiment with an oil and water system. In particular, simulations illustrate the effects of: the continuity of the dispersion (oil-in-water and water-in-oil) and the standard deviation of the initial droplet volumes on phase separation quality, as well as the influence of the coalescence frequency on the average droplet volume. [ABSTRACT FROM AUTHOR]

• The empirical cluster correlation can be replaced by a cluster evolution equation. • A general EMMS drag model is suggested for the overall fluidization regime. • The EMMS drag is used to simulate gas-solid turbulent beds and cocurrent downers. • The EMMS-based simulation shows better prediction than traditional CFD simulation. Eulerian-Eulerian models incorporated with the kinetic theory of granular flow were widely used in the simulation of gas-solid two-phase flow, while the effects of mesoscale structures such as particle clusters and gas bubbles could not be considered adequately if traditional homogeneous drag models were adopted in the coarse grid simulations. The energy minimization multiscale (EMMS) model has been proved to facilitate calculating a structure-dependent drag coefficient by considering particle clustering phenomena, which can be coupled with the two-fluid model (TFM) to improve the accuracy of coarse-grid simulation of gas-solid circulating fluidized beds. However, the original EMMS drag model cannot be further applied to the simulation of gas-solid fluidized beds with solids flow rate smaller than zero, e.g., turbulent fluidized beds and cocurrent downward flow, because the original cluster diameter correlation gives rise to a value smaller than single particle diameter or even negative value at extremely low solids fluxes or downward gas-solid flow. In this study, a new proposed cluster evolution equation is proposed by quantifying local clustering dynamics to replace the original cluster diameter correlation. The newly formulated EMMS drag model can be used to avoid a negative cluster diameter to be involved in calculating interphase drag force in the overall fluidization regime. The improved EMMS drag law is incorporated into the Eulerian-Eulerian model to simulate gas-solid turbulent fluidized beds and cocurrent downer reactors, since they both were widely used in many industrial processes. By analyzing local hydrodynamics as well as the axial and radial heterogeneous distributions in the two kinds of fluidized beds, it is clarified that the simulation using the improved EMMS drag model shows a better agreement with the experimental data than the computation using the homogeneous drag law. [ABSTRACT FROM AUTHOR]

• Novel multiregional DOM with anisotropic scattering developed for OpenFOAM. • Successful validation vs analytical solution and verification vs standard DOM. • Quadrature rotation reduces significantly the directional error in parallel beams. • Power cosine or cone shaped adjusted quadrature for improved simulation of LED. This work describes adaptive quadrature, a new feature designed to improve the Discrete Ordinate Method (DOM) in parallel and cone-shaped radiation sources. OpenFOAM was chosen as the simulation framework to implement the new feature. It already included a Discrete Ordinate Method (fvDOM), but it focuses on thermal radiation and is limited to isotropic emission, diffuse phenomena, and non-scattering media. The model was completed to cover volumetric and superficial absorption, isotropic and anisotropic scattering (with user-defined phase functions), diffuse and specular reflection, diffuse and parallel transmission, and three types of superficial emission sources, i.e., isotropic, cone-shaped, and parallel. Additionally, the model is prepared to work in grey mode or with wavelength bands. Multiple regions with different optical properties are also allowed. Most of the model has been validated by individual simulations of every feature in simple geometries that permit an analytical solution, with errors between 0% and 6.08%. These simulations were also verified in a comparison with an established version of the standard DOM, with differences between model implementations below 2.5%. Some advantages of the developed adaptive quadrature are also analysed using simulation results for different radiative sources and angular discretization. The main conclusion is that adaptive quadrature better defines view angle and light direction of emission sources compared to the established DOM, improving significantly the accuracy of the simulation of non-isotropic sources. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Simulated spinodal decomposition under thermal gradient with diffuse interface model. • Assumed very viscous binary regular mixture as a polymer melt. • Dendrites formed from phase separation do not change orientation for low Lewis number. • On the contrary, dendrites change orientation when heat propagates faster than mass. • The same patterns hold for non-equimolar mixtures and different conductivity ratios. Abstract While the spinodal decomposition of mixtures in unbounded systems has been largely investigated, little is known about phase separation constrained within a slab. In this study, spinodal decomposition of a very viscous regular binary mixture bounded within two walls cooled at different temperatures is simulated by using the diffuse interface model in 2D. Under a temperature gradient, phase separation starts from the cooler wall forming dendritic structures growing anisotropically with time. Two remarkably different dynamics are identified depending on whether heat propagates slower or faster than mass. For small thermal conductivity (i.e., small Lewis number), dendrites grow parallelly to the temperature gradient, keeping such an alignment until the steady-state. On the other hand, for large Lewis number, during the early stages phase separation proceeds within stripes oriented along iso-temperature lines, i.e., with dendrites aligned perpendicularly to the temperature gradient, which, however, gradually shift their orientation parallel to the temperature gradient as the steady-state is approached. Such a dynamic transition of dendrite orientation upon a temperature gradient when heat propagates faster than mass is found to hold also for non-equimolar mixtures and for different species thermal conductivities. These results shed light on the dynamics of phase separation in constrained systems and anisotropic conditions. [ABSTRACT FROM AUTHOR]

• Novel algorithm presented for contact detection in DEM between bi-convex tablets. • Especially suited for parallel GPU implementations due to higher execution convergence. • Comparison made with experimental data and glued-sphere approach, favoring the dedicated shape. • Performance numbers showed huge benefit over glued-sphere approach. The coating of tablets to prevent product degradation or control dissolution is a typical process in its production. Coating uniformity is critical for the quality of final product and batch acceptance. Therefore, the coating process needs to be optimized in order to achieve the desired uniformity and reduce manufacturing costs. Thus, understanding how process parameters such as spray properties, equipment geometry and tablet shape influence the coating process is critical for process optimization and approval by regulatory bodies. However this is a non-trivial task as obtaining information about the detailed processes in a tablet coater via experimental means is limited. Thus, computational modeling is the most feasible option to obtain information about the physical processes affecting the performance of tablet coaters. The most widely used computational method for such numerical modelling is the Discrete Element Method (DEM) where individual particles (tablets) are simulated. However, the computational cost of representing the typical shape of tablets is high for industrially relevant simulations. Thus tablet shape is typically approximated by simpler shapes such as spheres or multi spheres. Even with such simplifications, typical simulations take months to complete making it unfeasible for process optimization and design. In the last decade, the Graphical Processor Unit (GPU) has enabled large-scale simulations of tens of millions of spheres and millions of shaped particles using the XPS code. In this paper, we present an algorithm for modeling accurate bi-convex tablets that is tailored to the GPU. We firstly validate the algorithm and implementation against a number of experiments. Finally we perform a simulation of 20 million tablets in a drum coater to illustrate the usefulness of GPU computing for industrial coating applications. We found that the proposed method yields a good match against the lab scale experiments. For the industrial simulation the proposed method gave a more accurate result compared to the multi sphere approach while being significantly faster. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlight • The effect of the pressure on the hydrodynamics in a bubble column was studied. • Radial gas holdup was determined using electrical resistance tomography techniques. • Numerical simulations were presented with three drag model of bubble swarm. • Three drag models of bubble swarms successfully evaluated the characteristics of hydordynamics in a high-pressure bubble column. Abstract The gas–liquid flow characteristics in an air–water system were studied using electrical resistance tomography (ERT) in a pressurized gas–liquid bubble column with an inner diameter of 0.30 m and a height of 6.60 m. The effects of the superficial gas velocity and system pressure on the radial gas holdup were investigated under superficial gas velocities (0.120–0.312 m/s) and system pressures (0.5–2.0 MPa). Two-fluid computational fluid dynamics (CFD) was used to simulate the hydrodynamics of the bubble column in two- and three-dimensions, and the drag force, transverse lift force, turbulent dispersion force, and wall lubrication force were introduced for model correction. Based on the determination of the transverse lift force, turbulent diffusion force, and wall lubrication force in previous works of our group, three different of drag model schemes were proposed in this study. In the Model A, based on Roghair's drag model, a density correction and the gas holdup of large and small bubbles were introduced to correct the model; in the Model B, while the gas holdup of large bubbles was greater than 0.08, the influence of small bubbles was ignored. The small bubbles and liquid were integrated into a single phase (the dense phase), while the large bubbles were the dilute phase; in the Model C, an energy minimization multi-scale (EMMS) concept based on the double bubble size model was used, and relationship between the drag coefficient and the bubble diameter were introduced to modify the models. Moreover, through optimizing adjustment of the model parameter, the simulation results with the three models were found to be consistent with the experimental results obtained from ERT technique. These results may facilitate improvements in the design and scale-up of bubble columns with high-pressure and high superficial gas velocities, as well as the significance of further research. [ABSTRACT FROM AUTHOR]

Highlights • Effects of fluid viscosity and surface tension were considered in cavitation model. • Cavitation generation in submerged conditions was simulated. • Bubble collapse process was compared in drag-reducer solution and pure water. • Shock effects including cavitation effects were comprehensively analyzed in submerged water jet. Abstract In this paper the cavitation phenomenon and bubble collapse in submerged water jet added with CTAC were studied. The cavitation simulation was based on an improved cavitation model established by introducing coefficients into traditional cavitation model. The coefficients were obtained by fitting the numerical solutions of Rayleigh-Plesset equation in which the viscosity term and surface tension term were not neglected. Cross model was also employed to express the shear-thinning character of the surfactant solution. Simulation results show that the whole cavitation intensity decreased but the scale of cavitation region increased in drag-reducer solution. The submerged water jet added with drag-reducer was less dispersed and the stagnation pressure near the wall was significantly improved. Simulation results of the bubble collapse process show that the bubble collapsed more slowly in drag-reducer solution in comparison with that in pure water. The two pressure peaks near the wall during the collapse process appeared later in drag-reducer solution and the maximum value of the pressure generated in drag-reducer solution was less than that in pure water. [ABSTRACT FROM AUTHOR]

Highlights • We model the coalescence of small bubbles with surfactants. • Surfactant accumulates on the meniscus bridge between the bubbles at the early time. • The surfactant is transported to the back of the bubbles by Marangoni stresses. • These coupled mechanisms retards the bubble coalescence rate. Abstract Bubble coalescence is central to many important technological processes, such as separations, cleaning of oil spills, microfluidics, emulsification and foaming. It is well known that surfactants, which are frequently present as additives or contaminants, delay coalescence by slowing the drainage of the liquid film separating the approaching bubbles before they make contact. However, the coalescence and surfactant transport mechanisms developed after surfactant-laden bubbles make initial contact remain poorly understood. Here, we characterize these mechanisms using high-fidelity numerical simulations to predict the evolution of bubble interfaces, surfactant spreading, and induced Marangoni flows. Our results show that the surfactant initially accumulates on the tiny meniscus bridge formed between the coalescing bubbles due to the rapid and highly localized contraction of meniscus area. At the same time, a Marangoni-driven convective flow is generated at the interface, which drags the accumulated surfactant away from the joining meniscus and toward the back of the bubbles. Together, these transport mechanisms affect the rate bubble coalescence by dynamically modifying the local pull of surface tension on the bubble interfaces. [ABSTRACT FROM AUTHOR]

Highlights • Droplet size distribution development predicted for absorption columns. • Outlet size distribution becomes narrower than the inlet distribution. • Outlet size distribution width increases with droplet number concentration. • Higher CO 2 content leads to larger droplets and narrower distributions. Abstract There are two main mechanisms for amine emissions from absorption columns. The first is connected to the volatility of amine, determining the gaseous concentration. The second mechanism is via aerosol droplets containing amine. Recently, aerosol based emissions in g/Nm3 were identified from typical PCCC plants (Khakharia et al., 2013). Mechanisms for aerosol formation, aerosol growth, emissions related to aerosol formation and in particular the development and testing of aerosol emission reducing systems for amine based post-combustion, are presently under study. However, there is still limited information available in the open literature. In some recent studies, the effect of water wash and demisting equipment was studied and results indicate that aerosol droplets still pass through these equipment sections. On the other hand, water wash systems help in increasing the droplet size as well as reducing both gas phase and aerosol based emission. However, this does not completely solve the problem (da Silva et al., 2013). Recently, modeling studies for mono-disperse droplet swarms are published (Majeed et al., 2017a, 2017b; Majeed and Svendsen, 2018a, 2018b). However, results for multi-sized droplet swarms and for droplet size distributions are missing. Droplets can be described by their size, temperature and composition. All droplet populations will have a size distribution, being just as important as any other parameter. Performing a distribution analysis is the best way to determine the sizes of droplets in a particular stream at any point in an absorber. In this work, both a multi-droplet size model and a size distribution model are implemented. The multi-droplet size model is used for validation and results are in line with findings from the mono-disperse model by (Majeed et al., 2017b; Majeed and Svendsen, 2018a). Droplet distribution model results are compared with experimental data from Toshiba (Fujita, 2017) and reasonable agreement is found. The development of inlet droplet distributions through an absorber and water-wash system is modelled for several flue gas sources. It is found that the outlet distribution mean size increases with inlet gas CO 2 concentration. Similarly, the outlet mean droplet size decreases and the size distribution width increases with incoming droplet number concentration. [ABSTRACT FROM AUTHOR]

In the methanol-to-olefins (MTO) process, coke deposition is closely related to the selectivity of light olefins. Previous simulations of different-sized MTO reactors using two-fluid model (TFM) combined with the EMMS (energy minimization multi-scale)-based drag well predict the hydrodynamic behaviors but poorly predict the product distribution of large reactors due to the unreasonable prediction in coke distribution. In this study, the TFM integrated with the EMMS-based drag is still employed, but the solid phase is treated as a mixture of a series of species with different coke contents. Because the coke content depends on the age of catalyst particles inside the reactor, a continuous stirred tank reactor (CSTR) model mimicking turbulent fluidization while considering the age distribution of catalysts is established to predict the initial coke distribution for speeding up simulation. Compared with the previous simulation without consideration of coke distribution, this approach increases the computational time by a factor of 36% and shows no influence on hydrodynamic predictions, but the reaction quantities such as methanol conversion, mass fractions of gaseous products and selectivity of light olefins, are better predicted. [ABSTRACT FROM AUTHOR]

Solvent exchange or solvent swap is commonly used in production of complex organic molecules when the next processing step requires that the solute be dissolved in a different solvent. The current methods for solvent exchange, batch distillation and diafiltration, also produce a waste stream containing a mixture of the feed and chasing solvents that must be separated, usually by distillation. The results obtained from an Aspen Plus model of the new exchange column are compared with constant volume batch distillation simulations for both still pot and still pot plus column systems. The new solvent exchange column reduces the amount of the waste stream, and when the feed solvent is the more volatile solvent the exchange column can often be designed to produce feed solvent at the desired purity; thus, eliminating the need for an additional distillation column to separate the two solvents. When the initial solvent is the less volatile component, the new exchange column will often be competitive with constant volume diafiltration which is currently used. [ABSTRACT FROM AUTHOR]

In this work, we investigate the oxygen reduction reaction (ORR) on Pt(1 1 1), Pt(2 2 1), and Ni/Au 1 Pt 3 (2 2 1) surfaces using periodic density functional theory (DFT) calculations augmented with kinetic Monte Carlo (KMC) simulations. In the DFT calculations, both a uniform electric field and an implicit solvent were employed to quantify the changes in the ORR energetics. Based on the DFT values and the reaction mechanism of ORR, KMC simulations were performed to predict the current densities and the surface populations as a function of the electrode potential on the different catalyst surfaces. These results were compared to an ORR model with energetics approximated using scaling relationships. The two approaches for obtaining energetic parameters yield different KMC-predicted polarization curves. An analysis of the surface species concentrations on Pt(1 1 1), Pt(2 2 1), and Ni/Au 1 Pt 3 (2 2 1) indicates dramatic concentration variations at different potentials. Direct neighbor-neighbor interactions on the surface were also tested, but they were found to only moderately influence the surface species concentrations, and they led to imperceptible changes in the predicted current densities. Overall, we predict that an alloy surface of Ni/Au 1 Pt 3 (2 2 1) can significantly shift the onset potential of the polarization curve to higher potentials, providing guidance for future electrocatalyst design. [ABSTRACT FROM AUTHOR]

This paper aims at proposing a graphical representation composed of several performance maps to help to answer to some current questions that can puzzle membrane end-users facing the arrangement of membranes in cascade in order to better master separation of complex media. Indeed, different compromises can be highlighted according to realistic goals for the separation such as quality and recovery yield of each fraction/component, energy consumption and required membrane area. This representation needed first the systematic simulations of cascades of pre-selected configurations. These last ones were chosen thanks to the target application field, namely the organic solvent nanofiltration of a final synthesis media of hydroformylation that is a homogeneous catalysed reaction. We voluntary assumed the a priori limitation of the number of stages to 5, anticipating that more complex cascades will probably be too expensive (both operating and capital costs). The graphical representation by itself is based on sets of six 2D-maps. Each map highlights relationships selected in an appropriate way between two of the six selected criteria: extraction/recovery, retentate/permeate quality/purity, membrane filtering area and overall energy consumption. For sake of illustration, the separation of 2 components C and A was considered. C / A has been chosen in a 1/1000 molar ratio, where C corresponds to the less retained component of the catalytic system that must be recovered in the retentate and A corresponds to the less transmitted product to extract in the permeate. In realistic nanofiltration conditions achieved in toluene, the rejections were experimentally determined on the initial media to filter. C has a high rejection (88%) whereas A has a low one (30%). The simulations of cascades were established using these constant values for rejection and the experimental permeate flux. For sake of an illustration of the use of the graphical representation, a case study was finally discussed regarding a given target of recovery for the two desired components, namely at least 99% of C recovery and better than 70% of A extraction. A complementary multi-criteria analysis was added aiming at facilitating the decision-making. [ABSTRACT FROM AUTHOR]

This work describes a CFD modeling study of the Water Gas Shift single stage process in adiabatic conditions, operated by COMSOL Multiphysics 5.0, by means of two different catalytic configurations; the real novelty was to show that the use of structured catalysts with high thermal conductivity could greatly improve the performances of the whole process. The simulations are then validated with kinetic data reported in a previous work, and provides a useful springboard for the design of a single stage process. It was demonstrated that the use of highly conductive carriers reduces the difference of temperature throughout the catalytic bed, under adiabatic conditions, by means of a backdiffusion of the heat of reaction from the output to the input of the bed. The redistribution allows to increase the inlet temperature, with a benefit for the kinetics, at the expence of the outlet temperature that, decreasing, promotes the thermodynamics. The use of a highly active catalytic formulation, at low temperatures, coupled with a conductive carrier, provides, in principle, the possibility to realize a strong intensification of the process. [ABSTRACT FROM AUTHOR]

Enantioselective extraction of metoprolol (MT) enantiomers with di-cyclohexyl (D)-tartrate (DT) and boric acid (BA) as chiral extractant was performed. The process involving multiple chemical equilibrium is very complicated and the process optimization is difficult. On the basis of an interfacial reaction mechanism, a single-stage extraction model was established. The operation conditions of pH and DT to BA ratio were obtained through simulation and optimization of the equilibrium of the two phase extraction system. Based on the single-stage extraction model and the law of mass conservation, a fractional extraction model was established to simulate and optimize the fractional extraction process. To pursue a high productivity and reduce the required stages, a high feed to aqueous phase ratio (F/W = 1) and an asymmetric separation mode were applied. By asymmetric separation where the optical purity of the product in extract phase and raffiniate phase is not equal, enantiomeric excess ( ee ) value for the eutomer of MT can reach up to 98.64% and yield can reach up to 64.68% with 20 extraction stages. [ABSTRACT FROM AUTHOR]

Recently an efficient method for the simulation of packed bed adsorbers with implicit adsorption isotherms was presented. It uses a method of lines approach and exploits standard software for the simultaneous solution of the resulting differential algebraic equations (DAEs). Application was demonstrated for stoichiometric ion exchange. In the present paper, the approach is extended to systems described by the adsorbed solution theory. For that purpose, the relation between the differential index of the DAE system and the spectral properties of the underlying adsorption equilibrium is established. In particular, it is shown that real and positive eigenvalues of the Jacobian of the underlying conservation equations will lead to a differential index of one. It is further shown that real and positive eigenvalues of the Jacobian related to the IAST can be guaranteed for binary mixtures with any type of pure component adsorption isotherm or for multicomponent mixtures with certain restricted types of pure component isotherms. The new method is illustrated for different explicit and implicit pure component adsorption isotherms belonging to this class. It is compared with alternative solution approaches using the modified FastIAS method by Do and Myers and semi-analytical solutions from equilibrium theory. [ABSTRACT FROM AUTHOR]

The direct propylene epoxidation reaction has been investigated experimentally in the past by several different groups, and gold-based catalysts tend to provide high selectivity for propylene oxide, but the conversion is relatively low. Models that can connect the atomistic catalytic details to the observed experimental data are desired, in order to identify new catalyst structures and formulations. While electronic structure calculations have been used to quantify some of the key reaction steps in the direct propylene epoxidation reaction, atomistic models for translating this information into more experimentally-relevant data are needed. Here, kinetic Monte Carlo (KMC) simulations are used to bridge this gap in the modeling hierarchy. Relevant data from previous experiments and electronic structure calculations are used to parameterize a KMC model for predicting propylene oxide production from an Au/TiO 2 /SiO 2 catalyst. The model connects the H 2 /O 2 -related reactions occurring on the Au sites with the epoxidation step on the isolated Ti surface sites. In addition, the composition in the bulk gas phase is synchronized with the dynamic reaction events occurring on the surface. The KMC model is able to adequately reproduce the experimental trends with respect to temperature and different reactant partial pressures. However, this is only achieved by considering the re-adsorption of trace amounts of the oxidant (H 2 O 2 ) from the gas phase, versus merely assuming that desorbed species are immediately swept away in the gas stream. [ABSTRACT FROM AUTHOR]

Gas-solid fluidized beds, by their nature, are associated with intense and frequent collisions of solid particles with each other and with the vessel wall, causing tribo-electrification. Accumulation of electrostatic charges in fluidized bed reactors can result in severe problems such as agglomeration, wall fouling, nuisance and hazardous discharge, all reducing the process performance and raising significant safety concerns. Tribo-charging of particles in fluidized beds has also been exploited in a number of useful applications. In this review, the characterization methods of electrostatics and the mechanisms of charge generation and distribution in fluidized beds are presented, followed by an account of the interplay between the hydrodynamics and electrostatic phenomena. Furthermore, techniques of electrostatic charge control in fluidized beds are reviewed, and applications of tribo-electrostatic fluidization systems are summarized. Finally, computational fluid dynamics simulations of the electrostatic effects on the hydrodynamic characteristics of fluidized beds are outlined. [ABSTRACT FROM AUTHOR]

Scale-up of fluidized bed reactors has long been regarded as a big challenge in chemical reaction engineering. While traditional scaling theories are mostly based on hydrodynamics similarity, computational fluid dynamics (CFD) aided approach allows direct coupling between hydrodynamics and reaction factors and is expected to speed up the experiment-based scale-up process with lower cost. In this study, we aim to investigate the scale-up effects through simulations of a series of methanol-to-olefins (MTO) reactors of different sizes. The two-fluid model and energy-minimization multi-scale (EMMS)-based drag models are combined in simulations. The fluidization characteristics in terms of flow structures, velocity distribution, mass fractions of gaseous product and coke distribution are presented against available experimental data for different-sized reactors. It is found that typical hydrodynamic features can be reasonably predicted, while the prediction of reaction behavior shows growing discrepancy with increasing reactor size. Possible reasons are discussed in the last section along with future work presented for scale-up studies. [ABSTRACT FROM AUTHOR]

An efficient method for the simulation of packed bed adsorbers is presented. It is based on equilibrium models and can be applied to any implicit adsorption isotherm. It uses a method of lines approach, avoids explicit differentiation of the adsorption isotherm, and exploits standard numerics for the simultaneous solution of the resulting ordinary differential and implicit algebraic equations. Application is illustrated for stoichiometric ion exchange, which also admits an analytical approach using equilibrium theory. Classical theoretical results from equilibrium theory are summarized, further extended and compared to the numerical calculations for different scenarios. Focus is on selectivity reversals and their influence on process operation. It is shown that the selectivity reversal may introduce multiple solutions. [ABSTRACT FROM AUTHOR]

The catalytic exchange column of countercurrent trickle bed for deuterium removal from hydrogen is simulated based on experimental results along with established reaction and mass transfer models, accounting for the humidification of hydrogen in a catalyst bed filled with platinum/styrene-divinylbenzene copolymer pellets and Dixon rings. Relative deviations of less than 30% are achieved between the experimental and the simulated HD molar fractions at the column outlet. Simulation results indicate that hydrogen humidification exerts a noticeable influence on gas and liquid phase flow rates, leading to an overestimated removal percentage of deuterium when such flow rate variances are neglected. Rate limiting step for the overall gas-liquid isotopic exchange is discussed. Finally, the operation conditions are optimized using the developed model. [ABSTRACT FROM AUTHOR]

A stochastic model based on the axial dispersion model was proposed for the mathematical representation of the fluid dynamics of tubular equipment with irregular behavior. The differential equation was built by inserting randomness in the dispersion coefficient, which added a stochastic term to the model. This term was capable of simulating fluctuations that may arise in the characterization of tubular equipment using the stimulus-response technique. The model was validated by comparing sample paths and computational confidence intervals with three experimental data sets of a tubular milli-reactor for polystyrene production with different configurations. A convergence analysis was carried out in order to determine the number of elements needed for time discretization. An estimator function was developed to calculate the parameter of the stochastic term, while the parameter of the deterministic term was estimated by the least squares method. The stochastic differential equation was discretized and solved by the Euler-Maruyama method. The computational confidence intervals were calculated using the Monte Carlo method. The results were considered satisfactory, once the model was capable of representing the irregular fluid dynamics of a tubular reactor. [ABSTRACT FROM AUTHOR]

Porous media are a vital component in almost every electrochemical device in the form of electrode, support or gas diffusion layers. Microstructural parameters of porous layers such as tortuosity, porosity and pore size diameter are of high importance and crucial for diffusive mass transport calculations. Among these parameters, the tortuosity remains ill-defined in the field of electrochemistry, resulting in a wide range of different calculation approaches. Here, we present a systematic approach of calculating the tortuosity of different porous samples using image and diffusion cell experimental-based methods. Image-based analyses include a selection of geometric and flux-based tortuosity calculation algorithms. Differences between the image and diffusion cell-based results are encountered and attributed to the small pore diameters and thereby induced Knudsen effects within the samples which govern the diffusion flux. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adding PET to the input feed does not increase the syngas yield in the products. • Syngas LHV of 9.45 MJ/Nm3 is achievable at operating conditions of 800 °C, 1 atm. • Steam to feed ratio of 0.57 produces the optimum amounts of syngas. • For such a process, the initial investment can be returned within 2 years. This paper is the first to study the effect of adding PET, separator, and financials on a PE steam gasification plant based in Lebanon. The main aim is to shed light on the possibility of valorizing plastic wastes while reducing the environmental impact of landfilling and creating benefits. Using Aspen Plus, a plant that can turn plastic waste into syngas is designed and modeled. PE and PET model inputs of 797 and 500 kg/hr, respectively, were chosen based on Lebanese data. The addition of PET did not significantly improve the mole fractions of the end product when compared with PE only as an input feed. The final optimum conditions of this model were chosen based on sensitivity analyses of different parameters. There were concluded to be a temperature of 800 °C, pressure of 1 atm, Steam/Feed mass ratio of 0.57, water flowrate of 745 kg/hr, and syngas LHV of 9.45 MJ/Nm3. Calculations showed a total Net Present Value 6 times larger than the initial investment and a Payback Period of 2 years by implementing the model. Although based on a Lebanese case study, this research will urge the establishment of sustainable waste and financial policies in countries facing the same issues. [ABSTRACT FROM AUTHOR]

A new analytical method to calculate crossflow in an interacting capillary bundle has been proposed to analyze immiscible displacement processes in porous media. Capillary force, pressure equilibrium and mass balance were incorporated to develop algebraic equations for crossflow within the interacting bundle respectively before and after water breakthrough. By solving the equations analytically, flow rate in each capillary tube and crossflows among different tubes in the bundle were obtained as a function of water/oil interface positions at different times. The model was then applied to analyze the fluid dynamics of immiscible displacements. The whole process was modelled, from water first entering into the bundle to the moment that no more oil could be further produced. Eight water-displacing-oil cases, including specifically designed scenarios representing a tight reservoir, were modelled in an imbibition process to investigate the effects of pore size distribution, injection rate, and interfacial tension (IFT). The model successfully predicted fingering effect for a tight oil reservoir and even displacement front that could only be achieved by ultra-low IFT. The modelling results are highly consistent with previous experimental and simulation results in the literature. The theoretical model can be used to investigate the effects of different reservoir parameters in immiscible displacement process, such as permeability, wettability, and interfacial tension. The proposed interacting capillary bundle model leads to the pore network simulation in its simplicity as pore connection and topology information is not required. [ABSTRACT FROM AUTHOR]

Data reduction processes based on laboratory-scale experiments related to hydrate formation and dissociation kinetics usually employ isothermal models where the hydrate particles and continuous phase are at the same constant temperature despite the large latent heat in this phase change phenomenon. In this study, we tested this hypothesis by developing a non-isothermal model of methane hydrate formation and dissociation in a three-phase agitated vessel with a cooling jacket. The hydrate particle mass and energy comprised the distribution variables in a bivariate population balance model, which included particle nucleation, growth, breakage, and aggregation. The mass and energy balances in the gas and liquid phases completed the model. The heat transfer between the liquid phase and the coolant in the jacket was also modeled. Under the conditions analyzed, the results showed that the particle temperatures were quite close to that of the liquid phase but large changes occurred during hydrate formation or dissociation due to the slow heat transfer to the cooling fluid. Therefore, hydrate formation or dissociation occur in a environment with a changing temperature, which must be considered to obtain meaningful kinetic data. [ABSTRACT FROM AUTHOR]

Various methodologies have been proposed in literature on modeling microwave drying process. However, in these methodologies moisture diffusion is normally considered in the presence of intensive microwave energy. In the present study, a new theoretical model was developed to simulate microwave drying of thin layer particulate solids, based on the consideration that moisture diffusion along material layer could be ignored due to rapid evaporation under intensive microwave energy. The model was solved numerically by using finite difference method and validated against experimental data. Results indicated good agreement between the model and experimental data, thus providing confidence in the modeling approach. For the system investigated in this study, it was demonstrated that an 80% reduction in drying time was achieved with approximately fivefold increase in microwave power (109–543 W). Furthermore, it was also demonstrated that the drying rate was the maximum corresponding to the optimal layer thickness in microwave thin layer drying process. Qualitative analysis explained the optimal thickness phenomenon using principles of heat and mass transfer. Finally, the validated model was used to predict moisture and temperature distributions along the entire material layer. [ABSTRACT FROM AUTHOR]

Continuous selective crystallization using mixed suspension mixed product removal (MSMPR) crystallizers is an attractive method for separating enantiomers. Recent experimental results confirm the feasibility of the approach, but also indicate that the operation conditions for nominal operation lie in a rather small window. A systematic analysis and an optimal design are needed to exploit the full potential of the method. In this contribution, a mathematical process model based on population balance equations is presented. In contrast to other studies in literature, the considered crystallizer is not a stirred tank, but has a conical shape that requires a spatially distributed model formulation. Parameter studies identify the key operation and design parameters for maximizing the mass of the product crystals and for shaping their size distribution. The proposed model focuses on geometrical and fluid-dynamic aspects, but at the current stage does not include purity aspects. [ABSTRACT FROM AUTHOR]

In this paper we perform direct numerical simulation (DNS) on the problem of fluid flow through a filter plate backed by a packed bed of spheres, resembling a cake layer on top of a membrane. For both the complete problem, and its single components (the filter plate and a bed of spheres of finite height) we have observed three flow regimes, depending on the Reynolds number. In each regime the flow resistance is showing a different scaling with the Reynolds number. In the Stokes flow regime the total flow resistance can be decomposed in linear independent components. The interior flows inside the filter holes and inside the packed bed follow the same correlations as hold for the single component. However, at the transition zone between filter plate and packed bed, there is a diverging flow in the first row of the packed bed, whose contribution in the flow resistance scales with the fractional hole to the power −1.5. Similar scaling exponent has been found earlier for the viscous-inertial regime with Reynolds numbers larger than 10, which has been modelled using the porous medium approach. Our findings suggest that also in the Stokes flow and the weakly flow regime the problem can also be solved with the same porous medium approach using the Navier-Stokes equation having Darcy–Brinkman terms incorporated. This investigation provides a good basis for developing more accurate analytical models for the flow resistance of membrane filters with a cake layer on top. [ABSTRACT FROM AUTHOR]

A simple simulation for chemical-looping combustion (CLC) is discussed: two, coupled fluidised reactors with steady circulation of particles of oxygen carrier between them. In particular, the sensitivity of CLC to different particle kinetics is investigated. The results show that the system is relatively insensitive to different kinetics when the mean residence time of particles in each reactor is greater than the time taken for them to react completely. [ABSTRACT FROM AUTHOR]

• Bubble slurry photoreactor is modeled and simulated. • Hydrodynamic, kinetic and radiation models have been used. • A new design for bubble slurry photoreactor including spargers is proposed. • Parametric study and detailed evaluation of model results and system behavior was performed. • A reliable model validated with minimal error was proposed. One of the attractive but still challenging ways of CO 2 utilization is photocatalytic conversion of CO 2 into fuels. Since reactor design plays an important role in both the efficiency and quality of the product, moving towards modeling and simulation of the photoreactor is vital. Thus, in this work modeling and simulation of photoreactor has been conducted using appropriate hydrodynamic and kinetic modules. The obtained model has been thoroughly validated by the experimental data which can further be utilized to scale-up the photoreduction process. The important parameters in the reactor design including the number of spargers, inlet gas flux, average bubble diameter, and light intensity have been studied. The methanol concentration after 150 s of the reaction under irradiation with light intensity of 120 W/m2 where 12 spargers delivered carbon dioxide gas into the reactor has been reported and the results have been validated accordingly. [ABSTRACT FROM AUTHOR]

Microwave hot spots at strongly polarized solid/liquid interface drive energy-efficient dehydration reactions. [Display omitted] • TiO 2 structure control maximizes the density of active center and degrees of interfacial polarization. • Strongly polarized solid/liquid interface promotes reaction energy efficiency under microwave. • 10 times higher energy efficiency was achieved than commercial TiO 2 in fructose dehydration reaction. • Surface sulfonic group polarizes surface water molecules and acts as "hot-spots" to accelerate reaction. A strongly polarized solid/liquid interface is constructed to create a "micro-hydrothermal" environment under microwave and promote reaction energy efficiency. Specifically, TiO 2 with open crystal structure was synthesized to maximize the density of surface-active centers and the degrees of interfacial polarization. Acidic groups were grafted on the catalyst surface, which served as catalytically active sites as well as heat-generation spots under microwave irradiation. Benefited by enhanced interfacial polarization, 10 times higher energy efficiency (6.8 mmol (kJ L)−1) than commercial TiO 2 can be achieved in fructose dehydration reaction. MD simulation revealed that sulfonic group polarized surface water molecules and acted as "hot-spots" to accelerate fructose dehydration to HMF. Such alignment of site-specific heating and reaction by material design has great potential to shift the energy efficiency for a wide range of chemical reactions. [ABSTRACT FROM AUTHOR]

• Time-varying filter aid dosage is superior to optimal but constant filter aid supply. • The cost function of energy minimization also reduces overall filter aid usage. • Constant filter aid supply is approximatively optimal for pure surface filtration. • Filter aid usage can be reduced by up to ≈ 30 % if mainly depth filtration takes place. • Benefit of employing optimal control rises the more compressible the process is. We establish optimal time-dependent dosage strategies for compressible filter aid materials, focusing on dead-end filter aid filtration processes operated in constant flow mode. To this end, we apply a direct optimal control approach by repeatedly evaluating a mathematical filtration model with filter aid concentration as the unknown time-dependent control function. Our algorithm iteratively constructs the sought-for trajectory to minimize a cost functional representing previously defined performance goals. We evaluate our optimal control approach for two different model formulations. In the first one, all impurity particles are separated by pure surface filtration on top of the existing filter cake, whereas in the second one, the model is extended toward depth filtration in the filter cake. Particularly for the latter, optimally controlled dosage strategies yield a significant performance improvement of up to 30% reduced filter aid consumption compared with the already optimized but constant filter aid dosage. [ABSTRACT FROM AUTHOR]

[Display omitted] • The modified fluidized bed improves pyrite roasting. • Eulerian model and conservation of chemical species is used to simulate roasting. • The mechanism of the roasting process was determined via isoconversional method. • The conversion rate of pyrite to hematite is high at 950 °C. • Pyrite depletion is determined using kinetics, modeling, and experimentation. In this study, a modified fluidized bed reactor was used to roast pyrite concentrate (PC). To analyze the pyrite conversion and fluid flow in the bed, a 2D model incorporating the Euler–Euler method and the conservation equation of chemical species was employed. In addition, the reactant and product samples were characterized through X-ray diffraction (XRD), X-ray fluorescence (XRF), particle size distribution, and thermogravimetric analyses (TGA). The kinetic parameters of the pyrite decomposition were also determined. The isoconversional method was used to determine the activation energy, pre-exponential factor of the specific reaction-rate equation, and reaction mechanism from thermogravimetry results. This rate law was then applied in the model to account for the depletion of pyrite in the modified fluidized bed. The main crystallographic phase in the formed product was hematite. XRF and TGA result indicate that the PC had high purity and roasting occurred at a conversion of 80 %. The pyrite decomposition kinetics showed activation energy varies from 33.2 to 281.4 kJ∙mol−1 depending on the stage. The kinetic analysis of roasting and its implementation in the model demonstrated that the simulation achieved 72 % PC conversion into the products. These results validate the experimental conversion, illustrating the compatibility of the model with the experimental data. Specifically, the coupling of the rate law from TGA with the dispersed-phase velocity vector encourages to new research possibilities in this field of chemical engineering. [ABSTRACT FROM AUTHOR]

• The relationship between interfacial area and interfacial velocity in structured packing follow gamma distribution. • Contact angle shows the most important influence on interfacial area, and viscosity shows dominant influence on static area. • Differentiation of static and dynamic interfacial areas can provide accurate prediction of effective mass-transfer area. Effective mass-transfer area plays a key role for post-combustion carbon capture. The static area, an inactive part relative to mass transfer, needs to be differentiated in the interfacial area. In the present study, CFD method is employed to investigate static and dynamic interfacial areas in Mellapak 500.Y structured packing. A wide range of physical properties and loading conditions are included to understand their effects on both areas. The result shows that the relationship between interfacial area and interfacial velocity at the local scale can be described by gamma distribution with good accuracy. The influences of various physical properties derived from simulation are compared with existing experiment-based correlations for both static and interfacial areas. The result shows the dominant influence of viscosity on the static area, and the most importance of the influence of contact angle on the interfacial area. This study also highlights the importance of viscosity, which is usually ignored. [ABSTRACT FROM AUTHOR]

[Display omitted] • Interfacial energy between ellipsoidal particles with rough surfaces was simulated. • Impacts of surface morphology and geometrical shape were considered in the model. • Surface morphology significantly affected the interaction energy between particles. • Prolate particles provided greater interfacial energy than spherical particles did. • Amplifying the aspect ratio diminished interaction energy between oblate particles. Currently, information on the interaction of ellipsoidal particles with rough topography is limited. In this work, a mathematical model was developed based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and surface element integral (SEI) to simulate the total interaction energy created between ellipsoidal particles with rough surfaces, which were constructed by the modified two-variable Weierstrass-Mandelbrot (WM) function. The simulated results revealed that an increase in the fractal roughness and relative fractal roughness of particle surface would increase the surface roughness of particles and weaken the total interaction energy between ellipsoidal particles. Compared with spherical shape particles, the ellipsoidal particles provided greater interaction energy because an ellipsoidal shape would generate a greater interaction area than a spherical shape between particles. Amplifying the aspect ratio diminished the interaction energy between particles but enlarging particles would strengthen the interaction energy. In addition, the orientation angle of ellipsoidal particles would affect their interaction. [ABSTRACT FROM AUTHOR]

• A clouded bubble-based drag model is developed for bubbling fluidization. • The non-uniformity of drag force caused by bubble cloud is considered. • The feasibility of the clouded bubble-based drag model is validated. • Application of the modified drag model for Geldart A/B and A particle. A clouded bubble-based (CBB) drag model is developed in view of gas flow patterns around the clouded bubble. The bubble cloud is taken as the inter-phase between the bubble phase and emulsion phase based on the muti-scale resolution of the heterogeneous system. Moreover, the non-uniform distributions of drag force in the bubble crown and wake as well as the bubble sides are considered. The structure parameters are obtained by solving a series of equations including the mass conservation equations and empirical or semi-empirical correlations. The heterogeneous drag model is implemented into the two-fluid model (TFM) for 2D & 3D simulations of bubbling fluidized beds with Geldart A/B and A particles. The results demonstrate that the simulated results using the CBB drag model agree better with the experimental results compared to the homogeneous drag model and the structure-based drag model without the bubble cloud effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • An equilibrium model for catalytic pyrolysis of light hydrocarbons was presented. • Effects of temperature, pressure, and weight dilution ratio were studied. • A simulation process to predict experimental yield was built with Aspen Plus. • The simulation process was successfully validated with the experimental data. • The adiabatic temperature and reaction heat were estimated by the reaction extent. The catalytic pyrolysis of light hydrocarbons has been regarded as a promising route for satisfying the growing demand for light olefins. This study established a thermodynamic equilibrium model based on one set of independent reactions in the catalytic pyrolysis process, for predicting the thermodynamic equilibrium yield and analyzing the effects of the operating conditions on the equilibrium yields. The trend of the equilibrium yields was consistent with the trend of the experimental yields. Thus, under the present operating conditions, determined by applying the thermodynamic equilibrium model, the production of light olefins was increased and the propylene/ethylene (P/E) ratio could be tailored to meet market demands. Then, an actual reaction degree model based on independent reactions was established and incorporated in Aspen Plus to simulate the catalytic pyrolysis process, and the reliability was validated experimentally. The thermodynamic equilibrium model and process simulation are easy to implement and can help to optimize the operating conditions and to predict the product yields for the catalytic pyrolysis of light hydrocarbons. [ABSTRACT FROM AUTHOR]

Conversion and temperature distributions in a tubular reactor with an inner diameter of 1 mm were numerically calculated for a second order exothermic reaction in laminar flow of homogeneous liquid. Based on the resulting radial temperature profiles, the local Nusselt numbers and bulk mean temperatures were determined along the reactor tube. Strong effects of the homogeneous reaction on the heat transfer can be observed in the entrance region of the reactor, where a hot spot emerges. Due to the large radial temperature gradients in vicinity of the reactor wall, heat transfer coefficients are significantly higher compared to a non-reactive system. The consequences of this effect on the design and control of exothermic reactions in reactor/heat exchangers are demonstrated by comparison with a simple one-dimensional plug flow model. In the simplified model, neglecting thermal influence of the exothermic reaction results in a significant underestimation of the required reactor length for defined conversion. Accordingly, numerical simulation of both axial and radial transport in the hot spot region can be essential to precisely predict the bulk temperatures and conversion rates in the reaction mixture, even with the small length scales of milli- and micro-structured reactors. [ABSTRACT FROM AUTHOR]

This paper focuses on the CFD simulation of a CFB pilot-scale carbonator of a 1 MW th DFB installation located at TU Darmstadt (TUD). The carbonator riser height and diameter are 8.661 m and 590 mm, respectively. The state-of-the-art TFM approach is applied while the inter-phase drag coefficient is simulated using a new configuration of the sub-grid EMMS drag model. This configuration incorporates a new approach for the determination of the clusters diameter taking into account the geometrical limitations that the riser diameter poses to the meso-scale structures. The conventional Gidaspow model and the EMMS scheme are tested simultaneously along with the grid density effect. Two mesh densities, one coarse, and one dense are applied, i.e. 31,207 and 285,369 hexahedral elements. The mean ratio of the equivalent cell size to particles diameter ( D cell / D p ) is 465.64 and 222.67, respectively. Except for the grid density effect on the solution results, the wall treatment boundary conditions are investigated, as far as particulates are concerned, through a parametric study on the specularity coefficient values (0.01, 0.1, 0.6 and 0.99) implemented in the partial slip model. Finally, the heterogeneous carbonation reaction is incorporated to the model and a study of the influence of the hydrodynamics on the carbon dioxide capture is investigated. Simulation results are averaged over a time period of 15 s, while the pressure measurements are compared with the corresponding experimental data. Results for pressure converge well with the experimental results for pressure measurements along the riser, when the EMMS model is applied, while it is worth mentioning that this drag model reproduced an almost grid independent solution. For the CO 2 concentration at the riser exit, the averaged for 65 s value converges well with the respective measured value. [ABSTRACT FROM AUTHOR]

Recent experimental investigations have found that the rate and conversion of the photopolymerization of 1-vinylimidazole (VIm) can be significantly accelerated with the addition of lithium bistriflimide (LiTf 2 N). However, the underlying molecular-level interactions responsible for this phenomenon are unclear. The two components, VIm and LiTf 2 N, are miscible over a wide range of concentrations and form liquid phases at ambient temperature, and if the fundamental behavior of this mixture can be clearly quantified, there are significant opportunities for tuning the polymerization dynamics, polymer structure, and properties. In this work, molecular dynamics (MD) simulations are used to model the underlying pre-polymerization structure of VIm+LiTf 2 N mixtures at several different concentrations. It is found that the Li + enhances the site–site interactions of key functional groups involved in the polymerization, and this is suggested to play a major role in the experimentally-observed enhancement of the polymerization behavior. [ABSTRACT FROM AUTHOR]

A method for determining the steady states in tubular reactors with biofilm on their inner walls is presented. The proposed method is general and can be used for modeling and design of aerobic processes in vertical and horizontal co-current tubular bioreactors. The proposed model can be extended for multi-substrate processes, aerobic as well as anaerobic. It was shown that bioreactor diameter strongly influences the degree of conversion of substrates. A new phenomenon was discovered, namely switching of profiles of concentrations of reagents in the biofilm. Interpretation of this phenomenon was given. It has been shown that by appropriate selection of the bioreactor diameter, it is possible to achieve high degrees of conversions of substrates at much lower residence times than in the continuous tank bioreactors. [ABSTRACT FROM AUTHOR]

The nonlinear frequency response (NFR) method is applied for evaluation of possible improvement through simultaneous periodic modulation of two inputs of a non-isothermal continuously stirred tank reactor (CSTR) in which homogeneous n th order reaction A→product(s) takes place. The two modulated inputs are the concentration of the reactant in the feed steam and the temperature of the feed stream. The cross asymmetrical second order FRF which correlates the outlet concentration with both modulated inputs is derived and analyzed. The optimal phase difference which should be used in order to maximize the conversion is determined. The method is tested on three numerical examples of non-isothermal CSTRs: (a) one which is oscillatory stable with strong resonant behavior, (b) one which is oscillatory stable with weak resonant behavior and (c) one which is nonoscillatory stable. Good agreement between the results of the approximate NFR method and the results of “exact” numerical integration is obtained except for the reactor with strong resonance for forcing frequencies which are close to the resonant frequency and for the reactor with weak resonant behavior for forcing frequency equal to the resonant one in case of high forcing amplitudes. [ABSTRACT FROM AUTHOR]