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K. A. Yih - One of the best experts on this subject based on the ideXlab platform.
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coupled heat and mass transfer by natural convection adjacent to a permeable horizontal cylinder in a saturated porous medium
International Communications in Heat and Mass Transfer, 1999Co-Authors: K. A. YihAbstract:Abstract The heat and mass transfer characteristics of free convection about a permeable horizontal cylinder embedded in porous media under the coupled effects of thermal and mass diffusion are numerically analyzed. The surface of the horizontal cylinder is maintained at a uniform wall temperature and uniform wall concentration. The transformed governing equations are obtained and solved by Keller box method. Numerical results for the dimensionless temperature profiles, the dimensionless concentration profiles, the Nusselt Number and the Sherwood Number are presented. Increasing the buoyancy ratio N and the transpiration parameter f w increases the Nusselt Number and the Sherwood Number. For thermally assisting flow, when Lewis Number Le increases, the Nusselt (Sherwood) Number decreases (increases). Whereas, for thermally opposing flow, both the Nusselt Number and the Sherwood Number increase with increasing the Lewis Number.
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Uniform transpiration effect on coupled heat and mass transfer in mixed convection about inclined surfaces in porous media: the entire regime
Acta Mechanica, 1999Co-Authors: K. A. YihAbstract:A boundary layer analysis is used to investigate the effect of uniform transpiration velocity on the heat and mass transfer characteristics of mixed convection about inclined surfaces in saturated porous media under the coupled effects of thermal and mass diffusion. The surfaces are maintained at variable wall temperature (VWT) and variable wall concentration (VWC). Nonsimilar governing equations are obtained by using a suitable transformation and solved by Keller box method. Numerical results are presented for the local Nusselt Number as well as the local Sherwood Number. The local Nusselt Number and the local Sherwood Number increase (decrease) due to the effect of suction (blowing). Increasing the buoyancy ratio N increases the local Nusselt Number and the local Sherwood Number. It is apparent that the Lewis Number has a pronounced effect on the local Sherwood Number than it does on the local Nusselt Number. Furthermore, increasing the Lewis Number decreases (increases) the local heat (mass) transfer rate.
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Coupled heat and mass transfer in mixed convection over a VHF/VMF wedge in porous media: The entire regime
Acta Mechanica, 1999Co-Authors: K. A. YihAbstract:Coupled heat and mass transfer in mixed convection about a wedge embedded in saturated porous media has been analyzed by nonsimilar solutions for the case of variable heat flux (VHF) and variable mass flux (VMF). The entire regime of the mixed convection is included, as the mixed convection parameter χ* varies from 0 (pure free convection) to 1 (pure forced convection). The transformed nonlinear system of equations is solved by using an implicit finite difference method. The dimensionless temperature profiles, the dimensionless concentration profiles, the local Nusselt Number and the local Sherwood Number are presented. The decay of the dimensionless temperature profiles and the dimensionless concentration profiles has been observed in all cases. The local Nusselt Number and the local Sherwood Number increase for the increase in buoyancy ratioN*, wall heat/mass flux exponents and for the decrease in wedge angle parameter λ. The variations of the local Nusselt Number and the local Sherwood Number with the increase of χ* have the phenomenon of minimum. For a positive (negative)N*, increasing the Lewis Number decreases (increases) the local Nusselt Number. On the other hand, the local Sherwood Number enhances as the Lewis Number increases. Moreover, it is observed that the Lewis Number has a more pronounced effect on the local Sherwood Number than it has on the local Nusselt Number.
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Coupled heat and mass transfer by free convection over a truncated cone in porous media: VWT/VWC or VHF/VMF
Acta Mechanica, 1999Co-Authors: K. A. YihAbstract:The heat and mass transfer characteristics of natural convection about a truncated cone embedded in a saturated porous medium subjected to the coupled effects of thermal and mass diffusion is numerically analyzed. The surface is maintained at variable wall temperature/concentration (VWT/VWC) or variable heat/mass flux (VHF/VMF). The transformed governing equations are solved by Keller box method. Numerical data for the dimensionless temperature profiles, the dimensionless concentration profiles, the local Nusselt Number and the local Sherwood Number are presented for wide range of dimensionless distance ξ, the Lewis Number Le, the exponent λ, and buoyancy ratioN (orN*). In general, it has been found that when the buoyancy ratio is increasing both the local Nusselt Number and the local Sherwood Number increase. Increasing the value of λ and ξ increases the local surface heat and mass transfer rates. The local Nusselt (Sherwood) Number increases (decreases) with decreasing the Lewis Number. Furthermore, it is shown that the local Nusselt Number and the local Sherwood Number of the truncated cone approach those of inclined plate (full cone) for the case of ξ=0 (ξ→∞).
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Free convection effect on mhd coupled heat and mass transfer of a moving permeable vertical surface
International Communications in Heat and Mass Transfer, 1999Co-Authors: K. A. YihAbstract:The purpose of this paper is to consider numerically the free convection effect on magnetohydrodynamic heat and mass transfer of a continuously moving permeable vertical surface. The surface is maintained at linear temperature and concentration variations. The similar equations were solved by using a suitable variable transformation and employing an implicit finite difference method. Numerical results were graphically given for the Nusselt Number and the Sherwood Number for various parameters. Generally, it is found that the Nusselt Number and the Sherwood Number increase for the suction case, increasing the buoyancy ratio N and the buoyancy parameter GrT/Re2 and for the decrease of magnetic parameter M. Furthermore, the Nusselt (Sherwood) Number increases for the decrease (increase) of Schmidt Number Sc.
Ching-yang Cheng - One of the best experts on this subject based on the ideXlab platform.
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Double-Diffusive Free Convection over Arbitrarily Inclined Plates with Nonuniform Surface Temperature and Concentration in Porous Media
2014Co-Authors: Ching-yang ChengAbstract:This work studies the double-diffusive free convection over arbitrarily inclined plates in fluid saturated porous media with nonuniform surface temperature and concentration. The governing equations are transformed into a set of nonsimilar differential equations, and the obtained boundary layer equations are then solved by the cubic spline collocation method. The heat and mass transfer characteristics are presented as functions of surface temperature exponent, surface concentration exponent, inclination variable, Lewis Number, and buoyancy ratio. Results show that an increase in the Lewis Number leads to a decrease in the local Nusselt Number and an increase in the local Sherwood Number. Moreover, increasing the buoyancy ratio tends to increase both the local Nusselt Number and the local Sherwood Number. For the positive inclination, as the inclination variable increases, the local Nusselt Number and the local Sherwood Number first decrease, reach minima, and then increase. The minima are where the tangential and normal components of buoyancy force are comparable.
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soret and dufour effects on heat and mass transfer by natural convection from a vertical truncated cone in a fluid saturated porous medium with variable wall temperature and concentration
International Communications in Heat and Mass Transfer, 2010Co-Authors: Ching-yang ChengAbstract:This work studies the Soret and Dufour effects on the natural convection heat and mass transfer near a vertical truncated cone with variable wall temperature and concentration in a fluid-saturated porous medium. A coordinate transform is used to obtain the nonsimilar governing equations, and the transformed boundary layer equations are solved by the cubic spline collocation method. Results for local Nusselt Number and the local Sherwood Number are presented as functions of Soret parameters, Dufour parameters, surface temperature and concentration exponents, buoyancy ratios, and Lewis Numbers. Results show that increasing the Dufour parameter tends to decrease the local Nusselt Number, while it tends to increase the local Sherwood Number. An increase in the Soret Number leads to an increase in the Nusselt Number and a decrease in the Sherwood Number from a vertical truncated cone in a fluid-saturated porous medium. The local Nusselt Number and the local Sherwood Number of the truncated cones with higher surface temperature and concentration exponents are higher than those with lower exponents.
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Nonsimilar solutions for double diffusive convection near a frustum of a wavy cone in porous media
Applied Mathematics and Computation, 2007Co-Authors: Ching-yang ChengAbstract:A nonsimilar boundary layer analysis is presented for double diffusive convection flow near a vertical frustum of a sinusoidal wavy cone in a porous medium with constant wall temperature and concentration. A coordinate transformation is employed to transform the complex wavy conical surface to a smooth conical surface, and the transformed nonsimilar boundary layer governing equations are then solved by the cubic spline collocation method. Effects of the Lewis Number, buoyancy ratio, half cone angle and wavy geometry on the Nusselt and Sherwood Numbers for a frustum of a sinusoidal wavy cone in porous media are studied. The harmonic curves for the local Nusselt Number and those for local Sherwood Number as functions of streamwise coordinate have a frequency twice the frequency of the wavy conical surface. Moreover, an increase in the amplitude-wavelength ratio raises the amplitude of the local Nusselt Number and the local Sherwood Number. Further, the average Sherwood Number and the average Nusselt Number for a frustum of a wavy cone are found to be smaller than those for the corresponding smooth frustum cone.
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An integral approach for hydromagnetic natural convection heat and mass transfer from vertical surfaces with power-law variation in wall temperature and concentration in porous media☆
International Communications in Heat and Mass Transfer, 2005Co-Authors: Ching-yang ChengAbstract:This work uses the integral method to study the heat and mass transfer by natural convection from vertical plates with variable wall temperature and concentration in porous media saturated with an electrically conducting fluid in the presence of a transverse magnetic field. The surface temperature and concentration are assumed to vary as a power of the axial coordinate measured from the leading edge of the plate. The approximate solutions are found to be in reasonable agreement with the similarity solutions. Results are plotted for the local Nusselt Number, the local Sherwood Number, and the reciprocal of the ratio of the thermal boundary-layer thickness to the concentration boundary-layer thickness. Increasing the power-law exponents tends to increase the local Nusselt Number and the local Sherwood Number. Increasing the magnetic parameter decreases the local Nusselt Number and the local Sherwood Number. Moreover, the ratio of the thermal boundary-layer thickness to the concentration boundary-layer thickness increases with the Lewis Number, and it also increases with the buoyancy ratio when the Lewis Number is not equal to one.
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Natural convection heat and mass transfer near a vertical wavy surface with constant wall temperature and concentration in a porous medium
International Communications in Heat and Mass Transfer, 2000Co-Authors: Ching-yang ChengAbstract:Abstract This paper reports a study of the phenomenon of natural convection heat and mass transfer near a vertical wavy surface embedded in a fluid-saturated porous medium. The buoyancy effect is due to the variation of temperature and concentration across the boundary layer. A simple coordinate transformation is employed to transform the complex wavy surface to a flat plate, and the obtained boundary layer equations is then solved by the local nonsimilarity method and the cubic spline collocation method. Effects of the Lewis Number, the buoyancy ratio, and the wavy geometry on the local Sherwood Number and the local Nusselt Number are studied. The harmonic curves for the local Sherwood Number and the local Nusselt Number have a frequency twice the frequency of the wavy surface. Moreover, increasing the amplitude-wavelength ratio tends to increase the amplitude of the local Sherwood Number and the local Nusselt Number. Further, the average Sherwood Number and the average Nusselt Number for a sinusoidal wavy surface are found to be constantly smaller than that of the corresponding flat plate.
Dimitri Gidaspow - One of the best experts on this subject based on the ideXlab platform.
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Computation and measurements of mass transfer and dispersion coefficients in fluidized beds
Powder Technology, 2010Co-Authors: Mayank Kashyap, Dimitri GidaspowAbstract:Abstract Conventional design of circulating fluidized beds requires the knowledge of dispersion and mass transfer coefficients, expressed in dimensionless forms as Sherwood Numbers. However, these are known to vary by five or more orders of magnitude. Furthermore, the Sherwood Numbers for fine particles reported in the literature are several orders of magnitude lower than the Sherwood Number of two for diffusion to a single particle. We have shown that by replacing the particle diameter in the conventional Sherwood Number with cluster or bubble diameter, the modified Sherwood Number is again of the order of two. We have also shown that the kinetic theory based computational fluid dynamics codes correctly compute the dispersion and mass transfer coefficients. Hence, the kinetic theory based computational fluid dynamics codes can be used for fluidized bed reactor design without any such inputs.
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kinetic theory based computation of psri riser part ii computation of mass transfer coefficient with chemical reaction
Chemical Engineering Science, 2009Co-Authors: Benjapon Chalermsinsuwan, Pornpote Piumsomboon, Dimitri GidaspowAbstract:Abstract The design of circulating fluidized bed systems requires the knowledge of mass transfer coefficients or Sherwood Numbers. A literature review shows that these parameters in fluidized beds differ up to seven orders of magnitude. To understand the phenomena, a kinetic theory based computation was used to simulate the PSRI challenge problem I data for flow of FCC particles in a riser, with an addition of an ozone decomposition reaction. The mass transfer coefficients and the Sherwood Numbers were computed using the concept of additive resistances. The Sherwood Number is of the order of 4 × 10 −3 and the mass transfer coefficient is of the order of 2 × 10 −3 m/s, in agreement with the measured data for fluidization of small particles and the estimated values from the particle cluster diameter in part one of this paper. The Sherwood Number is high near the inlet section, then decreases to a constant value with the height of the riser. The Sherwood Number also varies slightly with the reaction rate constant. The conventionally computed Sherwood Number measures the radial distribution of concentration caused by the fluidized bed hydrodynamics, not the diffusional resistance between the bulk and the particle surface concentration. Hence, the extremely low literature Sherwood Numbers for fluidization of fine particles do not necessarily imply very poor mass transfer.
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kinetic theory based computation of psri riser part i estimate of mass transfer coefficient
Chemical Engineering Science, 2009Co-Authors: Benjapon Chalermsinsuwan, Pornpote Piumsomboon, Dimitri GidaspowAbstract:Abstract The PSRI benchmark challenge problem one is modeled using kinetic theory based CFD with the energy minimization multi-scale (EMMS) drag law. These computations give a better comparison than the previous models to measured solids mass flux, solids density and pressure drop. The computer model was also used to calculate axial and radial normal Reynolds stresses, energy spectra, power spectra, granular temperatures, the FCC viscosity and axial and radial dispersion coefficients. The computed cluster sizes agreed with the published empirical correlations. Then, the mass transfer coefficients and the Sherwood Numbers are estimated based on particle cluster sizes. The conventional Sherwood Number is scaled with the particle cluster diameter. The Sherwood Number is the order of 10 - 2 and the mass transfer coefficient is the order of 10 - 3 m / s . This Sherwood Number is two orders of magnitude smaller than the diffusion controlled limit of two based on particle diameter, in agreement with the experimental data for fluidization of fine particles.
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Kinetic theory based computation of PSRI riser: Part I—Estimate of mass transfer coefficient
Chemical Engineering Science, 2009Co-Authors: Benjapon Chalermsinsuwan, Pornpote Piumsomboon, Dimitri GidaspowAbstract:Abstract The PSRI benchmark challenge problem one is modeled using kinetic theory based CFD with the energy minimization multi-scale (EMMS) drag law. These computations give a better comparison than the previous models to measured solids mass flux, solids density and pressure drop. The computer model was also used to calculate axial and radial normal Reynolds stresses, energy spectra, power spectra, granular temperatures, the FCC viscosity and axial and radial dispersion coefficients. The computed cluster sizes agreed with the published empirical correlations. Then, the mass transfer coefficients and the Sherwood Numbers are estimated based on particle cluster sizes. The conventional Sherwood Number is scaled with the particle cluster diameter. The Sherwood Number is the order of 10 - 2 and the mass transfer coefficient is the order of 10 - 3 m / s . This Sherwood Number is two orders of magnitude smaller than the diffusion controlled limit of two based on particle diameter, in agreement with the experimental data for fluidization of fine particles.
Benjapon Chalermsinsuwan - One of the best experts on this subject based on the ideXlab platform.
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kinetic theory based computation of psri riser part ii computation of mass transfer coefficient with chemical reaction
Chemical Engineering Science, 2009Co-Authors: Benjapon Chalermsinsuwan, Pornpote Piumsomboon, Dimitri GidaspowAbstract:Abstract The design of circulating fluidized bed systems requires the knowledge of mass transfer coefficients or Sherwood Numbers. A literature review shows that these parameters in fluidized beds differ up to seven orders of magnitude. To understand the phenomena, a kinetic theory based computation was used to simulate the PSRI challenge problem I data for flow of FCC particles in a riser, with an addition of an ozone decomposition reaction. The mass transfer coefficients and the Sherwood Numbers were computed using the concept of additive resistances. The Sherwood Number is of the order of 4 × 10 −3 and the mass transfer coefficient is of the order of 2 × 10 −3 m/s, in agreement with the measured data for fluidization of small particles and the estimated values from the particle cluster diameter in part one of this paper. The Sherwood Number is high near the inlet section, then decreases to a constant value with the height of the riser. The Sherwood Number also varies slightly with the reaction rate constant. The conventionally computed Sherwood Number measures the radial distribution of concentration caused by the fluidized bed hydrodynamics, not the diffusional resistance between the bulk and the particle surface concentration. Hence, the extremely low literature Sherwood Numbers for fluidization of fine particles do not necessarily imply very poor mass transfer.
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kinetic theory based computation of psri riser part i estimate of mass transfer coefficient
Chemical Engineering Science, 2009Co-Authors: Benjapon Chalermsinsuwan, Pornpote Piumsomboon, Dimitri GidaspowAbstract:Abstract The PSRI benchmark challenge problem one is modeled using kinetic theory based CFD with the energy minimization multi-scale (EMMS) drag law. These computations give a better comparison than the previous models to measured solids mass flux, solids density and pressure drop. The computer model was also used to calculate axial and radial normal Reynolds stresses, energy spectra, power spectra, granular temperatures, the FCC viscosity and axial and radial dispersion coefficients. The computed cluster sizes agreed with the published empirical correlations. Then, the mass transfer coefficients and the Sherwood Numbers are estimated based on particle cluster sizes. The conventional Sherwood Number is scaled with the particle cluster diameter. The Sherwood Number is the order of 10 - 2 and the mass transfer coefficient is the order of 10 - 3 m / s . This Sherwood Number is two orders of magnitude smaller than the diffusion controlled limit of two based on particle diameter, in agreement with the experimental data for fluidization of fine particles.
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Kinetic theory based computation of PSRI riser: Part I—Estimate of mass transfer coefficient
Chemical Engineering Science, 2009Co-Authors: Benjapon Chalermsinsuwan, Pornpote Piumsomboon, Dimitri GidaspowAbstract:Abstract The PSRI benchmark challenge problem one is modeled using kinetic theory based CFD with the energy minimization multi-scale (EMMS) drag law. These computations give a better comparison than the previous models to measured solids mass flux, solids density and pressure drop. The computer model was also used to calculate axial and radial normal Reynolds stresses, energy spectra, power spectra, granular temperatures, the FCC viscosity and axial and radial dispersion coefficients. The computed cluster sizes agreed with the published empirical correlations. Then, the mass transfer coefficients and the Sherwood Numbers are estimated based on particle cluster sizes. The conventional Sherwood Number is scaled with the particle cluster diameter. The Sherwood Number is the order of 10 - 2 and the mass transfer coefficient is the order of 10 - 3 m / s . This Sherwood Number is two orders of magnitude smaller than the diffusion controlled limit of two based on particle diameter, in agreement with the experimental data for fluidization of fine particles.
Sirshendu De - One of the best experts on this subject based on the ideXlab platform.
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an analytical solution of Sherwood Number in a stirred continuous cell during steady state ultrafiltration
Journal of Membrane Science, 2012Co-Authors: Suvrajit Banerjee, Sirshendu DeAbstract:Abstract Sherwood Number relationship was developed for gel controlled steady state ultrafiltration in a stirred cell from the first principles, under the framework of boundary layer analysis. A developing mass transfer boundary layer was considered and the governing equation was solved using an integral method. Variation of viscosity in the mass transfer boundary layer was included as proposed by Aimar and Field (1992) [29] . Polyvinyl alcohol, having molecular weight of 14,000, was used as the gel forming material. A weak dependence of mass transfer coefficient on transmembrane pressure drop was observed. The final expression of Sherwood Number was obtained using 50% of the experimental data of the steady state. Permeate flux values were calculated for the rest 50% of the experiments using the developed relation in the predictive mode. In all cases, the predictions lie within ±10% of the experimental data. Using the expression of Sherwood Number, the transient profile of flux decline was also estimated.
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Sherwood Number in porous microtube due to combined pressure and electroosmotically driven flow
Chemical Engineering Science, 2011Co-Authors: Nallapusa Vennela, Subir Bhattacharjee, Sirshendu DeAbstract:Abstract Mass transfer of a neutral solute in a porous microtube is quantified in this study. An analytical expression of the Sherwood Number is developed from first principles for combined flow of pressure driven and electroosmotic flow. Similarity solution method is adopted for solution of convective-diffusive species balance equation with coupled velocity profile, within the mass transfer boundary layer. It is observed that the Sherwood Number increases with decrease in the Debye length (as the electric double layer becomes more compact) and it becomes constant beyond scaled Debye length of 60. Effects of the Reynolds Number, dimensionless suction velocity, ratio of driving force and scaled Debye length have been investigated in detail. The analysis is useful for efficient design of microfluidic devices and flow through porous media.
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Sherwood Number in flow through parallel porous plates (Microchannel) due to pressure and electroosmotic flow
Aiche Journal, 2011Co-Authors: Nallapusa Vennela, Sourav Mondal, Sirshendu De, Subir BhattacharjeeAbstract:An expression for Sherwood Number is developed from first principles for combined pressure-driven and electroosmotic flow in a porous rectangular microchannel. This quantifies the mass transfer of an electrically neutral solute in the microchannel and is useful for designing microfluidic devices and porous media flows. The convective-diffusive species balance equation, coupled with the velocity field, is solved within the mass transfer boundary layer utilizing similarity method. From the simulations, it is observed that the Sherwood Number increases as the electric double layer near the channel wall becomes more compact (as manifested through a decrease in the Debye length), and it reaches a constant value around the scaled Debye length of 40. The Sherwood Number becomes constant at higher Debye lengths as electrokinetic effects become negligible. A detailed analysis of dependence of Reynolds Number, dimensionless permeation velocity, ratio of driving force and scaled Debye length on Sherwood Number is presented. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1693–1703, 2012
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Sherwood Number in flow through parallel porous plates (Microchannel) due to pressure and electroosmotic flow
Aiche Journal, 2011Co-Authors: Nallapusa Vennela, Sourav Mondal, Sirshendu De, Subir BhattacharjeeAbstract:An expression for Sherwood Number is developed from first principles for combined pressure-driven and electroosmotic flow in a porous rectangular microchannel. This quantifies the mass transfer of an electrically neutral solute in the microchannel and is useful for designing microfluidic devices and porous media flows. The convective-diffusive species balance equation, coupled with the velocity field, is solved within the mass transfer boundary layer utilizing similarity method. From the simulations, it is observed that the Sherwood Number increases as the electric double layer near the channel wall becomes more compact (as manifested through a decrease in the Debye length), and it reaches a constant value around the scaled Debye length of 40. The Sherwood Number becomes constant at higher Debye lengths as electrokinetic effects become negligible. A detailed analysis of dependence of Reynolds Number, dimensionless permeation velocity, ratio of driving force and scaled Debye length on Sherwood Number is presented. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1693–1703, 2012