Basic knowledge on the hydrodynamics in the spacer-filled spiral wound membrane (SWM) channel is vital for the understanding of the formation of concentration polarization at the membrane interface. In the present study, a 3D laminar transient hydrodynamics modeling approach was used to study and optimize the spacer mesh angle for the SWM feed spacer. Based on the simulated results, the optimal spacer mesh angle that yields the minimum effective concentration polarization factor, was found to be alpha 120 beta 30. Under this optimal mesh angles, spacer alpha 120 beta 30 also demonstrated the highest magnitude of unsteady hydrodynamics (which adjacent to the membrane wall) at a moderate degree of pressure loss. (C) 2009 Elsevier B.V. All rights reserved.