Boundary layer phenomena during ultrafiltration of dextran and whey protein solutions

Abstract

The osmotic pressure and viscosity of dextran and whey protein solutions were measured at concentrations up to 50 wt%. It is shown that the flux-pressure data for ultrafiltration at varying concentrations and circulation velocities can be explained by the increased osmotic pressure of the concentrated boundary layer. Experiments with colored macromolecules in a transparent thin channel system, show that dissipative structures are formed on the membrane surface. In certain areas of the flow channel, the concentrated boundary layer is moving in thin stripes along the membrane surface in the flow direction. In these areas the concentrated boundary solution can be skimmed off through small holes in the skin layer of the membrane.