POTENTIAL APPLICATIONS OF PULSED FLOW FOR MINIMIZING CONCENTRATION POLARIZATION IN ULTRAFILTRATION

Various methods have been proposed to control or minimize concentration polarization and membrane fouling. A brief review of these alternatives is presented in this paper. Flow pulsation as a means of improving transmembrane flux has been studied experimentally by a few investigators. A mathematical model is developed to evaluate the performance of a tubular membrane module under oscillatory flow conditions. Besides the effect of osmotic pressure and axial pressure variation, the model considers the convective-diffusive mass transport without decoupling the momentum equation from the solute continuity equation. Model equations are solved by a finite difference method as part of an iterative solution. Model predictions of transmembrane flux with experimental data are found to be in good agreement. By flow pulsing, it is possible to improve the transmembrane flux by more than 68% at pulsing frequency of 60 cycles.min-1. An analysis of extra power requirement for flow oscillation shows that the gain in transmembrane flux outweighs the cost of extra power, which is a minute fraction of the power required to maintain steady flow.