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The paper investigates two-dimensional, steady, nonlinear laminar boundary layer heat and mass transfer MHD flow past a stretching porous surface embedded in a porous medium under the action of internal heat generation with the consideration of viscous and joules heat dissipation in the presence of a transverse magnetic field. The two-dimensional governing equations are solved by using MATLAB built in bvp4c solver technique for different values of physical parameters. The numerical values of various flow parameters such as velocity, temperature, concentration are calculated numerically and analysed graphically for various values of the non-dimensional physical parameters of the problem followed by conclusions. The study concludes opposite behaviour of transverse and longitudinal velocity under the action of suction velocity in addition to the effects of heat source on fluid velocities, temperature and concentration.

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The paper investigates two-dimensional, steady, nonlinear laminar boundary layer heat and mass transfer MHD flow past a stretching porous surface embedded in a porous medium under the action of internal heat generation with the consideration of viscous and joules heat dissipation in the presence of a transverse magnetic field. The two-dimensional governing equations are solved by using MATLAB built in bvp4c solver technique for different values of physical parameters. The numerical values of various flow parameters such as velocity, temperature, concentration are calculated numerically and analysed graphically for various values of the non-dimensional physical parameters of the problem followed by conclusions. The study concludes opposite behaviour of transverse and longitudinal velocity under the action of suction velocity in addition to the effects of heat source on fluid velocities, temperature and concentration. [ABSTRACT FROM AUTHOR]

The performance of receptor-based biosensors is often limited by either diffusion of the analyte causing unreasonable long assay times or a lack of specificity limiting the sensitivity due to the noise of nonspecific binding. Alternating current (AC) electrokinetics and its effect on biosensing is an increasing field of research dedicated to address this issue and can improve mass transfer of the analyte by electrothermal effects, electroosmosis, or dielectrophoresis (DEP). Accordingly, several works have shown improved sensitivity and lowered assay times by order of magnitude thanks to the improved mass transfer with these techniques. To realize high sensitivity in real samples with realistic sample matrix avoiding nonspecific binding is critical and the improved mass transfer should ideally be specific to the target analyte. In this paper we cover recent approaches to combine biosensors with DEP, which is the AC kinetic approach with the highest selectivity. We conclude that while associated with many challenges, for several applications the approach could be beneficial, especially if more work is dedicated to minimizing nonspecific bindings, for which DEP offers interesting perspectives. [ABSTRACT FROM AUTHOR]

Evaporation from free water surface is considered a very important constituent in both the energy and hydrologic cycles. Precise measurement of evaporation from the free water surface is almost impossible. This is why we need a calculation model for free water evaporation. In this study, a simple mass-transfer evaporation model was developed to be applicable over Lake Nasser in the hyper-arid region located in the south of Egypt. Measured meteorological data (2011–2014) at two stations, Aswan and Abu-Simbel, were used to calculate free water surface evaporation using Priestly–Taylor equation. Priestly–Taylor equation was used because it is the most appropriate equation for Lake Nasser evaporation according to the literature. Results from this model were used to develop a simple mass-transfer evaporation model. The statistical analysis for both calibration and validation periods were very good. The slope of the regression line is about 0.9, with a coefficient of determination of 0.98. The t value is 0.6, at p value of 0.544, which is much greater than 0.05. The developed model could be used with confidence at Aswan meteorological station or on the average of the two meteorological stations, while it should be used carefully on Abu-Simbel meteorological station.

In this work, the process of adhesive stamp mass-transfer of micro light-emitting diode (micro-LED) is optimized by a Support Vector Machine (SVM) model. The pick-up experiments have been performed repeatedly for hundreds of times from which the separation speed and the force between the stamp and the donor substrate are extracted as signal features. The SVM model with a Gaussian kernel function is designed to classify pick-up results into success and failure. In addition, the optimal cost parameter C as well as the Gaussian kernel function parameter gamma (γ) has been optimized, leading to the improvement of the classification by Particle Swarm Optimization (PSO) algorithm. Finally, an 85% classification accuracy is achieved based on the SVM model, implying that more sophisticated definition of signal features is demanded in future work.

The performance of receptor-based biosensors is often limited by either diffusion of the analyte causing unreasonable long assay times or a lack of specificity limiting the sensitivity due to the noise of nonspecific binding. Alternating current (AC) electrokinetics and its effect on biosensing is an increasing field of research dedicated to address this issue and can improve mass transfer of the analyte by electrothermal effects, electroosmosis, or dielectrophoresis (DEP). Accordingly, several works have shown improved sensitivity and lowered assay times by order of magnitude thanks to the improved mass transfer with these techniques. To realize high sensitivity in real samples with realistic sample matrix avoiding nonspecific binding is critical and the improved mass transfer should ideally be specific to the target analyte. In this paper we cover recent approaches to combine biosensors with DEP, which is the AC kinetic approach with the highest selectivity. We conclude that while associated with many challenges, for several applications the approach could be beneficial, especially if more work is dedicated to minimizing nonspecific bindings, for which DEP offers interesting perspectives.

A general and efficient method, involving sand‐milling pretreatment and base‐catalyzed transesterification of sucrose and fatty acid methyl ester (FAME), was presented for the solvent‐free synthesis of sucrose esters. A metastable homogeneous paste with a solid particle size of 13 μm (D50) was obtained by milling at 1000 rpm for 1 h. This reaction mixture generated a total SE yield of 88.2% with a methyl stearate (MS) conversion of 91.4% using K2CO3 as a catalyst at 135 °C for 3 h at a stirring rate of 500 rpm, while those without milling (D50, 153 μm) yielded a total sucrose fatty acid esters (SE) of 49.3% with a MS conversion of 83.1% under the same reaction conditions. The reaction kinetics revealed that the reaction mixture with milling pretreatment displays a shorter induction time and a faster reaction rate for the formation of SE. The promotion of the solvent‐free synthesis of SE in the current study could be attributed to the reduction of solid particle sizes and the increased compatibility of solid–liquid phases. We believe that this strategy could be used as a general way for strengthening other heterogeneous reactions in the organic synthesis. [ABSTRACT FROM AUTHOR]

• A model for NH 3 -SCR based on kinetics and computational fluid dynamics (CFD). • Model validation with SCR by monolithic Cu-ZSM-5. • Inhibition of effect of hydrocarbons in engine emission tests. A simple kinetic model for the standard NH 3 -SCR reaction by Cu-ZSM-5 catalysts has been developed by assuming three reaction steps: NH 3 adsorption (desorption), reactions of adsorbed NH 3 with O 2 (NH 3 oxidation) and NO (NH 3 -SCR). The model is based on Arrhenius parameters for NH 3 -SCR and NH 3 oxidation by a powder catalyst, combined with models for heat and mass transport and parameters of monolithic catalysts. The model is validated with the experimental results, not included in the estimation of the model, for NH 3 -SCR by monolithic catalysts with different parameters (catalyst loading and cell density). NOx removal from diesel exhaust, generated by engine bench, was also carried out by using monolithic Cu-ZSM-5 and Cu-AFX catalysts. The results suggest the poisoning effect of hydrocarbons in the exhaust emissions on NOx conversion is more significant for Cu-ZSM-5 than Cu-AFX. [ABSTRACT FROM AUTHOR]

• An open source algorithm was validated with theoretical and experimental results. • The analogy between mass and momentum transfer was successful. • RDE: the uniformity of mass-transfer is lost for turbulent conditions. • RCE: the interelectrode gap is the critical parameter on the mass-transfer conduct. Results of numerical calculations and their comparison with analytical expressions or experimental data under laminar and turbulent flow conditions are reported. It is predicted the transient and steady-state behaviour of mass-transfer coefficients and shear stresses in electrochemical reactors composed of rotating electrodes. Computational fluid dynamics (CFD) simulations were performed for both the rotating disc electrode (RDE) and the rotating cylinder electrode (RCE) considering the laminar or Reynolds-Averaged Navier-Stokes (RANS) equations. In this last case, it was assumed the Shear Stress Transport (SST) k-ω turbulence model sensitised by a correction term that accounts for streamline curvature and rotation. The hydrodynamics, coupled to the averaged diffusion-convection equation under transient conditions, was solved using the open source software OpenFOAM. A good agreement was attained between simulations and experimental or analytical results. In both rotating systems, a steady-state can be reached with an oscillatory behaviour that can be periodic in the case of laminar flow; depending on the Schmidt number, the interelectrode gap and the hydrodynamics. Also, the uniformity of the mass-transfer coefficient is lost under some circumstances. Finally, the full numerical code and a tutorial on how to use it, in order to perform simulations for the RDE or RCE, are supplied. [ABSTRACT FROM AUTHOR]

The complex, stratified seaweeds within kelp forests provide habitat to a multitude of organisms and can alter the physical and chemical parameters of their surrounding environment. It is unclear, however, how patterns in the architecture of these beds change as the tide ebbs and floods. We investigate biomass distribution of floating and stipitate canopies within a kelp bed during low and high slack tides to determine how biomass interacts with common environmental parameters (nutrients, light, and mass-transfer). Floating canopy biomass remained consistent despite differences in depth, likely driven by an interaction between stipe density and individual biomass. Biomass was distributed inconsistently throughout the water column, in which biomass at the surface roughly doubled at low tide relative to high. Despite an increase in kelp biomass at the surface of the water column during low tide, more light reached the benthos than at high tide, suggesting that seawater optical properties independent of algal canopy better explain light attenuation. Seawater nutrients were consistent throughout the bed. Rates of mass-transfer decreased from the exterior to the interior of the bed and also attenuated with depth. This study highlights the structural complexity of kelp beds and the localized effects on important environmental variables. [ABSTRACT FROM AUTHOR]

Gassed biochemical reactor called Gassed reactor from now on is equipped by pneumatic mixing device per substitution of the electric motors and magnetic drivers or the aseptic mechanical seal to warrant asepsis and isolation conditions in biochemical applications; in particular, Gassed reactor is distinguished by higher mass-transfer rates in aerobic biochemical processes that take place under the enriched gas atmosphere of the reactor’s chamber. A maximum working gas-flow expands to the set allowable levels of liquid turbulence of the reactor’s chamber by experimental tests and the maximum reactor-scale to the set allowable value is found by mathematical simulation. The software and the user-interface are conceived to accomplish the reactor’s design and estimate the technical performance to the mixing processes on gas-liquid systems. Gassed reactor supports different geometrical rates to the standard reactor with single impeller at the slender vessels showing arrangements of impellers of different sizes; the sterile gas for the reactor’s operation is produced to the compression unit itself per substitution of the regular sterilization procedures. Gassed reactor is distinguished by mechanical breaking of the unwanted foams to avoiding the use of chemicals, the safe extraction of samplings and yields pressurizing the reactor’s chamber and the supply of suspensions on the working gas-stream; the reactor constitutes a new technological alternative of low-cost for small pharmaceutical productions, the works on labs and research purposes; significant technical and economical profits at reactors layouts are foreseen.

A useful aerosol model must be able to adequately resolve the chemical complexity and phase state of the wide particle size range arising from the many different secondary aerosol growth processes to assess their environmental and health impacts. Over the past two decades, significant advances in understanding of gas-aerosol partitioning have occurred, particularly with respect to the role of organic compounds, yet aerosol representations have changed little in air quality and climate models since the late 1990s and early 2000s. The gas-aerosol partitioning models which are still commonly used in air quality models are separate inorganics-only thermodynamics and secondary organic aerosol (SOA) formation based on absorptive partitioning theory with an assumption of well-mixed liquid-like particles that continuously maintain equilibrium with the gas phase. These widely used approaches in air quality models for secondary aerosol composition and growth based on separated inorganic and organic processes are inadequate. This review summarizes some of the important developments during the past two decades in understanding of gas aerosol mass transfer processes. Substantial increases in computer performance in the last decade justify increasing the process detail in aerosol models. Organics play a central role during post-nucleation growth into the accumulation mode and change the hygroscopic properties of sulfate aerosol. At present, combined inorganic-organic aerosol thermodynamics models are too computationally expensive to be used online in 3-D simulations without high levels of aggregation of organics into a small number of functional surrogates. However, there has been progress in simplified modeling of liquid-liquid phase separation (LLPS) and distinct chemical regimes within organic-rich and inorganic-rich phases. Additional limitations of commonly used thermodynamics models are related to lack of surface tension data for various aerosol compositions in the small size limit, and lack of a comprehensive representation of surface interaction terms such as disjoining pressure in the Gibbs free energy which become significant in the small size limit and which affect both chemical composition and particle growth. As a result, there are significant errors in modeling of hygroscopic growth and phase transitions for particles in the nucleation and Aitken modes. There is also increasing evidence of reduced bulk diffusivity in viscous organic particles and, therefore, traditional secondary organic aerosol models, which are typically based on the assumption of instantaneous equilibrium gas-particle partitioning and neglect the kinetic effects, are no longer tenable.

Mass transfer was studied at the external electrode of a cylindrical electrochemical reactor with decaying swirling flow using a single phase electrolyte and also a dispersion of a gas phase in the solution. The local mass-transfer coefficients were measured with a segmented cathode using the reduction of ferricyanide as test reaction. Two strategies were used to introduce the gas phase. In the first case the gas was fed by three holes symmetrically drilled at the bottom of the central anode tube and in the second one by means of a tee fitting at the reactor inlet. The best performance was obtained with the single phase electrolyte giving 0.78 as the exponent of the Reynolds number and the mass-transfer distribution along the reactor length is more uniform than that reported for a parallel plate electrochemical reactor under laminar flow conditions. The mass-transfer enhancement factor related to an annular duct with axial developing flow ranges from 8 to 11. This high value is the consequence of two factors: (i) the intensive forced convection produced by the swirling flow at the outer electrode and (ii) the sudden expansion of the flow at the entrance due to the small tangential inlet. The fed of a gas phase in the reactor has scarce influence on the mass-transfer performance. A comparison of mass-transfer results with previous studies is made. [ABSTRACT FROM AUTHOR]

Ultrasonic is well-known to be helpful for the improvement of chemical reactions due to its acoustic cavitation. This work reports for the first time the use of ultrasonic to enhance micromixing and mass-transfer in a rotating packed bed (RPB) reactor. The ultrasonic probes were installed as stators on the cover of the RPB reactor. Comparisons of micromixing efficiency, effective interfacial area, and volumetric liquid-side mass-transfer coefficient in the RPB reactor with and without ultrasonic were investigated systematically. A discussion for the micromixing and mass-transfer improvement in the RPB reactor was given. Feasibility studies indicated that the relative segregation index decreasing, the relative effective interfacial area increasing, and the relative volumetric liquid-side mass-transfer coefficient increasing are 13.8%, 3.7%, and 5.5%, respectively. [ABSTRACT FROM AUTHOR]

This work presents a two-dimensional analytical solution of the governing differential equation for falling film vapour-absorption around a plain horizontal tube. The solution of the species transport equation gives the LiBr mass fraction distribution within the liquid absorptive film flowing along the tube surface and can be used to characterize the mass transfer performance of falling film absorbers or generators. By means of the inclusion of partial wetting effects at reduced solution mass flowrates, this study obtains an analytical expression of the mass transfer coefficient of these devices applicable over an extended range of operative conditions. The hypotheses of small penetration for physical absorption and constant heat flux condition are applied at the film interface to reach a closed-form solution. Fourier method is used to solve the problem and the eigenvalues obtained from the characteristic equation depend on Lewis number, Biot number and the dimensionless heat of absorption. Given the boundary condition at the wall, the two-dimensional mass fraction field of the laminar film can be expressed analytically as a function of Schmidt, Reynolds numbers, the tube dimensionless diameter and the ratio of the wetted area to the total exchange surface. Finally, mass transfer coefficient and absorbed mass flux are locally and globally investigated as functions of the influent dimensionless groups to clarify their effects on the physical process and screen the potentiality of the model. Results show notable qualitative and quantitative agreement with previous numerical solutions and experimental results from previous literature. This model constitutes a widely applicable and time-saving tool for actual system simulations, design and control. [ABSTRACT FROM AUTHOR]

Three volatile organic compounds (VOC) with no acidic or basic function (butanol, butyraldehyde, methylethylketone), encountered at low concentrations in odorous effluents, were absorbed in water in a compact wet scrubber. This gas-liquid contactor consisted of a wire mesh packing structure where the gas phase flows at high velocity (>12 m s −1 ). A very turbulent two-phase downward flow could be observed in the scrubber with dispersed fine droplets (around 10 μm). For compounds showing a good affinity for water, such as butanol, removal efficiencies up to 90% were measured for a short contactor length of 32 cm leading to a gas residence time of 20 ms. However, the removal efficiency of butyraldehyde, which is poorly soluble in water, ranged between 10 and 30%. Mass-transfer modeling was achieved and underlined that working with several small scrubbers in series, fed with an unloaded solution, is effective to improve the removal efficiency. The influences of the VOC/solvent affinity, the contactor length, and the mass-transfer and hydrodynamic parameters on the removal efficiency were evaluated through a sensitivity analysis. [ABSTRACT FROM AUTHOR]

Mass transfer of light non-aqueous phase liquids (LNAPLs) trapped in porous media is a complex phenomenon. Water table fluctuations have been identified as responsible for generating significant variations in the concentration of dissolved hydrocarbons. Based on field evidence, this work presents a conceptual model and a numerical solution for mass transfer from entrapped LNAPL to groundwater controlled by both LNAPL saturation and seasonal water table fluctuations within the LNAPL smear zone. The numerical approach is capable of reproducing aqueous BTEX concentration trends under three different scenarios – water table fluctuating within smear zone, above the smear zone and partially within smear zone, resulting in in-phase, out-of-phase and alternating in-phase and out-of-phase BTEX concentration trend with respect to water table oscillation, respectively. The results demonstrate the model's applicability under observed field conditions and its ability to predict source zone depletion. [ABSTRACT FROM AUTHOR]

• Mass-transfer in bubbly flows is simulated in OpenFOAM. • Absorption and desorption as well as co- and counter-current flows are considered. • Comparison is made with literature data including concentration measurements. • Constant bubble size and mass transfer coefficient are taken from the experiment. • A demonstration of a polydisperse simulation is given. Mass transfer in bubbly flows is important in many engineering applications. Simulation of such processes on technical scales is feasible by the Euler-Euler two-fluid model, which relies on suitable closure relations describing interfacial exchange processes. In comparison with the pure fluid dynamics of bubbly flows however, modeling and simulation of bubbly flows including mass transfer is significantly less developed. In particular, previous studies have focused entirely on absorption in upward vertical flows, whereas the present study considers a larger variety of conditions including desorption and counter-current (downward) flow. Suitable experimental data for comparison are available from the classic work of Deckwer et al. [Canadian Journal of Chemical Engineering 56 (1978) 43–55]. In line with previous studies on the co-current absorption cases from that work, a monodisperse approximation is made. In addition, a class method to treat bubble shrinkage and growth is implemented in the OpenFOAM code and tested by showing the crossover between two monodisperse cases. [ABSTRACT FROM AUTHOR]

The kinetic modeling of NH 3 -SCR with a Cu-ion-exchanged chabazite (Cu-CHA) catalyst in steady-state reactions was investigated by a combination of flow reactor experiments and kinetic modeling with an in-house computational code. Here H-CHA and Cu-CHA monolith cylindrical catalyst specimens were used to identify the reactions at both Brønsted (H+) acid sites and Cu sites. Based on the proposals in the literature for NH 3 -SCR mechanism, a scheme for SCR and side reactions incorporating 17 reactions is proposed, and some of the reactions were verified by the experimental results here for the adsorption/desorption of NH 3 , unsteady-state reactions of the adsorbed NH 3 with NO 2 over the Cu-CHA and H-CHA, and NH 3 oxidation over Cu-CHA. The Arrhenius parameters for Standard, Fast, and Slow SCR reactions, NH 3 oxidation, NO oxidation to NO 2 , NO 2 decomposition to NO, and NH 3 desorption were obtained by kinetic experiments. This report develops a quantitative simulation model for SCR and side reactions, and the model was validated by experimental data for adsorption/desorption of NH 3 and NO 2 , steady-state SCR reactions (Standard, Fast, and Slow SCR), and side reactions (NH 3 and NO oxidation). The simulation model developed in this study can predict the steady-state SCR data and adsorption/desorption of NH 3 and NO 2 under unsteady-state. [Display omitted] • Investigations of reactions over Brønsted and Lewis acid sites by Cu-CHA and H-CHA catalysts. • The identified 17 kinds of important reactions were suggested through experiments. • Ammonia nitrate (NH 4 NO 3) production in Fast and Slow SCR reactions. • The developments of a kinetic SCR model considering energy transport, mass transport, diffusion, and chemical reactions. [ABSTRACT FROM AUTHOR]

Different values describing both the efficiency of rectification column and the efficiency of mass-transfer are represented in the brief literature review. It is also showed that the approach used for the calculation of mass-transfer efficiency characteristics in binary mixtures is not very acceptable for multi-component mixtures.

• available models for the mass transfer coefficient are assessed. • a rather complete set of measurements from the literature is used. • fluid dynamical properties are predicted quite well. • prediction of mass transfer still has some deficiencies. • pressure is found to have a significant effect which has not been highlighted before. Mass transfer in bubbly flows is a field of obvious technological importance. On industrially relevant scales it may be studied by simulations based on the Euler-Euler two-fluid model, which however requires closure models for the interfacial exchange processes. Despite recently increased efforts, modelling of the exchange of mass between the phases is still much less developed than the corresponding exchange of momentum. The present study compares several proposed models for the mass transfer coefficient using a previously established set of closure relations for the purely fluid dynamical part of the problem. A set of experimental data for the absorption of O 2 into water in a bubbly mixing layer from the literature is used to assess their relative merits. A model for the pertinent material properties of this system has been assembled from available measurements. A rather sensitive dependence of the amount of absorbed O 2 is found on the pressure, which varies with the hydrostatic head above the test section. [ABSTRACT FROM AUTHOR]

• New Swell-Cavity Ratio parameter was used to characterize transport channel changes. • A model was built about the Hansen solubility parameter and Swell-Cavity Ratio. • Membrane mass transfer mechanism greatly affects the trend of the Swell-Cavity Ratio. • The model can accurately calculate the membranes pore changes in organic solvents. • The model is instructive for the application agility of membrane in organic solvents. The relationship between swelling, the difference (Δδ) in theoretical Hansen solubility parameters (HSP) between the two substances, and the change of membrane mass-transfer channel has been controversial. In this work, a completely new parameter, Swell-Cavity Ratio (SCR), defined as the ratio of membrane molecular weight cut off (MWCO), was introduced to characterize the changes in mass transfer channels before and after membrane swelling. Models of the relationship between Δδ and SCR were successfully constructed for nanoporous glassy (SCR = 0.19 × Δδ0.40) and rubbery (SCR = 17.7 × Δδ-0.93) membranes, using the swelling as a bridge. Based on this contradiction in models, we speculate that SCR variation is strongly related to the separation mechanism of the membranes. The theoretical model accurately calculates the influence of the solvent on the membrane mass transfer channel, allowing for the selection of the best membrane material and pretreatment process to maximize treatment efficiency. [ABSTRACT FROM AUTHOR]

For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. Concerning pure fluid dynamics of dispersed gas-liquid multiphase flow, an ongoing effort has led to a validated set of closures that is applicable under a rather broad range of conditions. Similar results for the technologically even more important field of mass transfer remain to be achieved. Progress so far has been hampered by a lack of spatially resolved data including measurements of concentration, which are suitable for CFD model validation. In addition, correlations proposed to describe the mass transfer coefficient differ widely. Here, a preliminary study of axial concentration profiles in a bubble column is given, based on the available experimental data found in the literature. For this purpose the simplified assumption of a constant mass transfer coefficient throughout the column is made and experimentally determined values are used. New measurements will be needed to come to a final conclusion. [ABSTRACT FROM AUTHOR]

Models proposed to describe the liquid side mass transfer coefficient in absorption processes differ widely in such basic questions as on which of the local flow variables they are based. Comparison of different alternatives with experimental data taken from the literature suggests that there are two basic mechanisms, a laminar and a turbulent one, each of which dominates under suitable conditions. A dimensionless number that allows to identify the corresponding regimes is suggested together with a preliminary model encompassing both. New experiments will be needed to come to a final conclusion. [ABSTRACT FROM AUTHOR]