Fluid mechanics and mass transport in centrifugal membrane separation

Centrifugal membrane separation (CMS) is a novel technology proposed for th e treatment of industrial process streams and waste waters. This membrane s eparation process benefits from inherent energy recovery and from the favor able effects of centrifugal and Coriolis acceleration in alleviating concen tration polarization and membrane fouling. A numerical study of both conven tional membrane separation and CMS is presented and used to quantify and an alyze the effects of centrifugal and Coriolis accelerations. The numerical model consists of a 3-D flow channel with a permeable membran e 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 diss olved species, are solved for both stationary and rotating membranes. The m odel is validated against measurements obtained in a parallel investigation . In the case of CMS, secondary flow structures are identified and found to e nhance the mixing of the feed solution and to increase the permeate flux ov er the non-rotating case. Modeled surface salt concentrations increase up t o 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 invest igated for various membrane orientations, and it is shown that the alleviat ion of concentration polarization and the resulting increase in permeate pr oduction are largely due to Coriolis acceleration. (C) 2000 Elsevier Scienc e B.V, All rights reserved.