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Abstract
An unsteady-state mass transfer model has been developed which takes into account the variation of diffusivity with solute concentration in the boundary layer. The main aim of this model is to study the effect of variation of diffusivity on membrane surface concentration as well as on the concentration profile prevailing within the boundary layer. Experimental data generated in this study have been used to validate the model. The resulting complex nonlinear partial differential equation has been solved by a numerical technique. The developed model is also capable of simulating volumetric flux and the permeate volume collected at any time under specified operating conditions. The simulated results show excellent fitting of the present model with variable diffusivity consideration when compared with experimental data. On the other hand, prediction based on constant diffusivity deviates considerably, indicating the importance of consideration of variable diffusivity in unsteady-state batch ultrafiltration.