Fluid mechanics and mass transport in centrifugal membrane separation

Centrifugal membrane separation (CMS) is a novel technology proposed for the treatment of industrial process streams and waste waters. This membrane separation process benefits from inherent energy recovery and from the favorable effects of centrifugal and Coriolis acceleration in alleviating concentration polarization and membrane fouling. A numerical study of both conventional membrane separation and CMS is presented and used to quantify and analyze the effects of centrifugal and Coriolis accelerations. The numerical model consists of a 3-D flow channel with a permeable membrane surface. The membrane is modeled using a boundary condition representing the preferential removal of one component of a solution. The Navier-Stokes equations, coupled with a scaler transport equation which accounts for dissolved species, are solved for both stationary and rotating membranes. The model is validated against measurements obtained in a parallel investigation. In the case of CMS, secondary flow structures are identified and found to enhance the mixing of the feed solution and to increase the permeate flux over the non-rotating case. Modeled surface salt concentrations increase up to 28% above the feed concentration for non-rotating separations, while with CMS it is possible to keep the surface concentration within 4% of the feed. The relative effects of centrifugal and Coriolis accelerations are investigated for various membrane orientations, and it is shown that the alleviation of concentration polarization and the resulting increase in permeate production are largely due to Coriolis acceleration. (C) 2000 Elsevier Science B.V, All rights reserved.