Rotating membrane disk filters: design evaluation using computational fluid dynamics

Computational fluid dynamics is used to investigate designs for rotating me mbrane disk filters. Simulations have been run for the case of water permea ting through a membrane disk rotating in a pressurized housing. The water w as assumed to be Newtonian, incompressible, non-fouling and isothermal. A k -epsilon model was used to describe turbulent how in the vessel surrounding the rotating disk. Similar to a nonporous disk, the rotation of the membra ne disk induces a recirculating flow pattern of the fluid within the vessel . However, the centrifugal force acting on the permeate may locally increas e the permeate side pressure above the feed side pressure resulting in a ne gative local transmembrane pressure. Hence, a portion of the membrane is su bject to a reversed flow of permeate which reduces effectiveness of membran e area and may damage the membrane. This 'back pressure' phenomenon can be avoided by a careful choice of the operating conditions and design paramete rs. The propensity for 'back pressure' is higher when the membrane is more permeable but can be reduced by increasing the feed flow rate or decreasing the disk diameter (i.e. the membrane area). (C) 1999 Elsevier Science S.A. All rights reserved.