MODELING OF ULTRAFILTRATION - PREDICTIONS OF CONCENTRATION POLARIZATION EFFECTS

This paper essentially deals with modeling of the concentration polari zation effects on solute separation in ultra-filtration. Laminar tange ntial flow in a rectangular section channel is considered. The concent ration polarization phenomenon in ultrafiltration has been studied by different authors who used different approaches for the finite-differe nce discretization of the mass transport differential equation. Two of those approaches are examined in detail. It is shown how numerical co nvergence can be reached, with a small number of increments, when an a ppropriate choice of the discretized mass transport equation is done. It is also shown why erroneous results have been obtained even with a large number of increments. Parametric studies show a strong influence of the true separation and of the permeation velocity on the separati on profile along the tangential flow channel. A comparison between a f inite-difference solution and an analytical solution for the mass tran sport differential equation is presented. Good agreement between the t wo methods is shown for the limiting case of high separation.