Effect Of Mass Transfer Coefficient Research Articles

Evaporation From Six Water Bodies of Various Sizes in East Asia: An Analysis on Size Dependency

AbstractOne pond and five lakes in East Asia with area from 0.05 to 3,000 km2 were comparatively investigated to reveal the size‐dependency of the evaporation and its radiation and aerodynamic contributions. The available energy controls on the annual evaporation are independent on the sizes of the six water bodies, but the ratio of evaporation to Penman's open water evaporation decreases with areas from almost unity at the small pond to around 0.8 at the two large lakes. The aerodynamic related parameters of three combination equations can be well represented by the water body areas with a power law, which is attributed to the decreasing mass transfer coefficient with the fetch of the water body. The increasing size‐dependent wind speed offsets the effect of mass transfer coefficient, making the energy partitioning and evaporation rate size independent. Results imply that the energy‐based equations can be used for evaporation without considering the water body size in the study area. The size‐dependent parameters of the combination equations are required to be further investigated with more lakes.

Modeling Study of Steel–Slag–Inclusion Reactions During the Refining of Si–Mn Killed Steel

Complex deoxidation by Si and Mn is beneficial for certain steel long products since it leads to the formation of low‐temperature melting manganese silicates. However, the introduction of Al via steel–slag reactions can lead to unwanted inclusion formation, which can cause nozzle clogging down the process line. To simulate steel–slag–inclusion reactions during the refining of steel, a kinetic model based on the mass transfer of steel species has been developed for inclusions and integrated with a previously developed steel/slag coupled reaction model. Using the model, the rate‐determining step for inclusion transformation is clarified, and the effect of slag–metal reactions on inclusions is investigated. The model calculations are validated using experimental data reported in the literature. Subsequently, the influence of slag compositions on the chemistry of inclusions and the effect of mass transfer coefficient on deoxidation characteristics is examined through a parametric study. The results are helpful for understanding inclusion dynamics during ladle refining of Si–Mn killed steel.

Semi Analytic Investigation of Heat and Mass Transfer Modelling in Solidification

Objectives: The objective of this study is to develop a mathematical model to describe the heat and mass transfer of the solidification process with surface ice sublimation, in a square section, considering conduction and convection mode of heat transfer in the medium. Methods/Statistical analysis: The basic equations that describe the process are non-linear PDE. With semi analytical techniques the model turns in to a system of ODE and these equations are solved using finite difference method, and numerical simulations are carried out using MATLAB software. Findings: Temperature distributions in the active regions are discovered along with the sublimation front temperature. Also position of the advancing moving fronts at any time t is traced out. The results of numerical calculations are used to find the effect of mass transfer coefficient, frozen mass, and sublimated mass on the dehydrated front, sublimation front, and also on the sublimation and frozen temperature are investigated. Mass transfer coefficient shows significant influence on the sublimation front evolution and on the dehydrated front temperature. Whereas the increase of frozen mass volume increases the dehydrated front evolution and decreases the freezing front evolution. Many phase change problems deal with only active frozen region for consideration. In this paper along with the frozen part, sublimation region is also considered, with which the effect of frozen mass volume on the movement of sublimation front is studied. Application/Improvements: Freezing with surface ice sublimation is an important phenomenon to study the characteristics of the frozen tissues, final quality of the food. Diffusion of water vapor through the sublimation plays an important role in the freezing process of moving boundary problems. These models can be used to optimize the productivity, minimize the solidification time in food processing techniques.

Effects of mass transfer coefficient on pore shape in solid

The shape of a pore resulting from a nucleated bubble entrapped by a solidification front for different mass transfer coefficients is predicted in this work. Mass transfer coefficient associated with different reference concentrations is used to determine different characteristics of solute transfer rate across the cap of the pore or bubble responsible for the pore shape in solid. Pore formation and its shape in solid influence contemporary issues of biology, engineering, foods, geophysics and climate change, etc. This work extends previous models, accounting for mass and momentum transport of solute across a self-consistently determined shape of the bubble cap whose surface is satisfied by physico-chemical equilibrium beyond the solidification front, to study different mechanisms for pore formation. Mechanism of pore formation can be Case 1, which is subject to solute transport from the pore across an emerged cap through the concentration boundary layer on the solidification front into surrounding liquid in the early stage. Cases 2a and 2b are referred to opposite directions of solute transport across a submerged cap in the concentration boundary layer. In contrast to the former, the latter exhibits stronger effects of pore volume expansion on solute gas pressure in the pore than solute transport. The results show that an increase in mass transfer coefficient decreases pore radius and time for bubble entrapment in Case 1. An isolated pore cannot be found in Cases 2a and 2b, since solute concentration at the cap increases and decreases rapidly in the late stage, respectively. The predicted pore shape in solid agrees with experimental data. Mass transfer coefficient associated with solidification rate can be used to control the pore shape, which strongly depends on directions and magnitudes of solute transport.

Estimation of effect of diffusion and dispersion parameters on VAPEX process

Abstract Recent developments in heavy oil extraction have heightened the need for a promising vapor extraction process in problematic reservoirs. Due to the high energy efficiency and suitability for the latter reservoirs, it is believed that VAPEX has had a great deal of interest compared to the thermal methods in recent years. The present study aims to develop a method based on a compositional simulation in the VAPEX process to study the effect of mass transfer coefficients on production rate. This model can simulate VAPEX with different diffusion and dispersion coefficients and is validated against the experimental data. Simulation results show a challenge between mass transfer and gravity drainage process; hence, if drainage is the dominant step, a high diffusion coefficient has a reverse impact on production rate. Instead, a high dispersion coefficient almost has a positive effect on oil production.

Theoretical estimation of semi-permeable membranes leading to development of forward osmosis membranes and processes as a future seawater desalination technology

Recently, forward osmosis (FO) process has been expected for the future seawater desalination method. In this study, the estimation of semi-permeable membranes leading to development of FO membranes and processes was investigated from the theoretical calculation view point. It is common to apply multivalent ionic materials to draw solution in FO membrane process. MgCl2, one of the common multivalent ionic materials, was used for calculating the relationship between pure water permeability (A value) and required FO membrane length. Two cases were assumed—one as an ideal condition which was without any concentration polarization (CP), the other as an actual condition which was with external concentration polarization. In the case of non-CP condition, the membrane length decreased with increase the A value. On the other hand, in the case of CP condition, the membrane length converged to constant value with increase of the A value. From this phenomenon, there was the optimized relationship between A value and membrane length. For instance, under the condition of MgCl2 concentration at 12.9 wt%, the A value over 2.0 × 10−11 [m s−1 Pa−1] was required while the membrane length was equal to eight elements. Moreover, the effect of mass transfer coefficient was estimated. It was suggested that the estimation was possible for the A value and the membrane length with any given mass transfer coefficients.

Pressure swing adsorption modeling of acetone and toluene on activated carbon

A five steps pressure swing adsorption process was designed for acetone and toluene mixtures separation and recovery. Dynamic distributions of gas phase content and temperature were investigated. Based on the theory of Soret and Dufour, a non-isothermal mathematical model was developed to simulate the PSA process. Effects of heat and mass transfer coefficients were studied. The coupled Soret and Dufour effects were also evaluated. It is found that the heat transfer coefficient has little effect on mass transfer in adsorption stage. However, it has some impacts in desorption stage. The maximum value of C/C0 increases by about 25% as heat transfer coefficient decreases. The temperature variation is less than 0.05 K with the change of mass transfer coefficient, so that the effect of mass transfer coefficient on heat transfer can be ignored. It is also concluded that the Soret and Dufour coupled effects are not obvious in pressure swing adsorption compared with fixed-bed adsorption.

Mass transfer studies on the biodegradation of phenols in up-flow packed bed reactors

A quantitative analysis of the effect of mass transfer coefficients on the operating parameters namely, flow rate, bed height, particle and column diameter, voidage and initial concentration of phenols, etc. is carried out for the biodegradation of phenols in an up-flow packed bed reactor. A mass transfer correlation of the type, j D= K ( Re′) n−1 is developed to represent the present experimental data obtained using activated carbon– Pseudomonas pictorum–alginate, celite– P. pictorum–alginate and P. pictorum–alginate beads for the continuous biodegradation of phenol. The overall reaction rate was found to be of the first order with the mass transfer as the rate-limiting step. For mass transfer with biochemical reaction, a correlation of experiment with theory is made. A realistic estimate of the effects of external mass transfer coefficients is also made in this present work.

Enhanced naphthalene solubility in the presence of sodium dodecyl sulfate: effect of critical micelle concentration

Surfactants can increase the solubility of non-polar compounds, and have been applied in areas such as soil washing and treatment of non-aqueous phase liquids (NAPLs). This investigation explored the feasibility of removing vapor phase polycyclic aromatic hydrocarbon (PAH) from gases using an anionic surfactant. The solubility of vapor phase naphthalene was measured herein using gas chromatograph (GC) with a photon ionization detector (PID). The measurement results indicated that surfactant molecules were not favorable to micelle formation when temperatures increased from 25°C to 50°C. Regardless of whether solutions were quiescent or agitated, equilibrium naphthalene apparent solubility increased linearly with surfactant concentrations exceeding critical micelle concentration (CMC). The pH effects on naphthalene apparent solubility were small. Agitation increased naphthalene apparent solubility and lumped mass transfer coefficients. Furthermore, lumped mass transfer coefficients decreased with increasing surfactant concentration owing to increase in interfacial resistance and viscosity and decreased spherical micelle diffusion coefficients. Finally, the net absorption rate increased because the solubilization effects of micelles exceeded the reduction effects of mass transfer coefficient above the CMC. The enhanced naphthalene apparent solubility from the addition of surfactant can be expressed by an enrichment factor (EF). The EF value of naphthalene for the surfactant solution at 0.1 M with agitation at 270 rpm relative to quiescent water could reach 18.6. This work confirms that anionic surfactant can improve the removal efficiency of hydrophobic organic compound (HOC) from the gas phase.

Design of liquid-liquid extraction columns for the possible test system Zn/D2EHPA in n-dodecane

A simple simulation study of the design of a liquid-liquid extraction column for the possible test system Zn/D2EHPA has been carried out. The results show the behaviour of different reaction kinetic models and the effect of the mass transfer coefficients on the column design. A contamination factor has also been used to determine the effect of changing mass transfer coefficients on the liquid-liquid extraction performance. A sensitivity analysis has been carried out to determine which factors significantly influence the column design for a particular range of conditions.

Separation of enantiomers of 1 a,2,7,7 a-tetrahydro-3-methoxynaphtha-(2,3 b)-oxirane by liquid chromatography: laboratory-scale elution chromatography and modelling of simulated moving bed

The separation of enantiomers of 1 a,2,7,7 a-tetrahydro-3-methoxynaphtha-(2,3 b)-oxirane (Sandoz epoxide) on cellulose triacetate HPLC columns was investigated on the laboratory scale. The performance of the columns was calculated by HEPT measurements and the slopes of the adsorption equilibrium isotherms and effective diffusivities were calculated from elution chromatographic experiments. Multi-component adsorption equilibrium isotherms were calculated from single isotherms by using the ideal adsorbed solution (IAS) model. Simulation of continuous chromatographic separation of the racemic mixture of Sandoz epoxide in a simulated moving bed was carried out and the effect of mass transfer coefficient on process performance was analysed.

Effect of mass-transfer coefficients on the elution of a binary mixture in nonlinear liquid chromatography

A procedure for calculating numerical solutions of the nonlinear, nonequilibrium model of chromatography for a two-component mixture is described. Solutions are presented and discussed for a series of numerical values corresponding to a wide range of mass-transfer kinetics for either component. When the mass-transfer kinetics is not very slow, the band profiles are controlled by the thermodynamic effects and the solutions are identical with those obtained by solution of the corresponding semiideal model. When the kinetics becomes slow, the nonlinear thermodynamic effects decrease and vanish. The retention time of the maximum of the band profile first increases, then decreases, and eventually a bimodal band appears, with the second maximum eluted with nonretained compounds. When the mass-transfer kinetics of the two components are very different, elution profiles are complex. The coupling effect between the two bands disappears rapidly if the component which has the larger concentration is the one with the very slow kinetics. As the opposite of the semiideal model, previously discussed, this model permits an accurate prediction of the elution profiles of the components of a mixture when their mass-transfer coefficients are different.

Effect of mass transfer coefficient on the elution profile in nonlinear chromatography

The kinetic model of chromatography includes a mass balance equation and a mass transfer rate equation. A numerical analysis of the system of partial differential equations obtained is presented, and the characteristics of the finite difference method used to solve it are described. The results obtained are discussed, and the influence of the value of the mass transfer coefficient on the chromatographic elution profile is analyzed. In the limit case of linear chromatography (linear equilibrium isotherm), the result is very similar to the result obtained from the solution of the ideal nonequilibrium equation. In the other limit case, at large values of the rate constant, the result is very similar to the one obtained by solving numerically the equations of nonlinear equilibrium chromatography.

20 Absorption of nitrogen oxides into water

Absorption of NO 2 and NONO 2 mixture into weak alkaline solutions are studied. Emphasis is put on the concentration level ranging from 5000 down to 5 ppm. The absorption rates and the stoichiometric relations are determined by simultaneously measuring the gas and liquid phase compositions. Flat-liquid-level absorber and bubbling type absorber are employed for testing the effects of mass transfer coefficient. The absorption rates of NO 2 depend on the concentration of NO 2 in second order at the concentrations above around 800 ppm. At the lower concentrations, the rate dependency changes to 1 1/2 order in NO 2 and, in the case of rather large mass transfer coefficients, it further changes to 1'st order. The absorption rates from NO and NO 2 mixtures change in 3/4 order with respect to the product of NO and NO 2. A model is constructed by postulating the equilibrations between NO, NO 2, N 2O 3 and N 2O 4 and the hydration reactions of N 2O 3 and N 2O 4 in the liquid film. The computational results based on the model agree well with the all present experiments as well as those in literature. The parameters required for predicting the absorption, including the solubilities of NO 2 and N 2O 4, the hydration rates of N 2O 3 and N 2O 4 and the equilibrium constants, have been established.