Analysis of mass transfer in unstirred batch ultrafiltration: Effect of variation of diffusivity in boundary layer

An unsteady-state mass transfer model has been developed which takes into a ccount the variation of diffusivity with solute concentration in the bounda ry 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 concentrat ion profile prevailing within the boundary layer. Experimental data generat ed in this study have been used to validate the model. The resulting comple x nonlinear partial differential equation has been solved by a numerical te chnique. The developed model is also capable of simulating volumetric flux and the permeate volume collected at any time under specified operating con ditions. The simulated results show excellent fitting of the present model with variable diffusivity consideration when compared with experimental dat a. On the other hand, prediction based on constant diffusivity deviates con siderably, indicating the importance of consideration of variable diffusivi ty in unsteady-state batch ultrafiltration.