This study is a step toward integrated modeling of the evolving (in space and time) flow and concentration fields during water desalination in membrane spacer-filled channels. Such detailed model predictions are of practical significance, leading to improved understanding of spiral wound membrane (SWM) module operation. Submerged and zigzag spacer filament 2-dimentional configurations are employed, as they create geometric flow-channel features (contact lines, flow constrictions, etc) encountered in SWM modules. The numerical study, performed in a Reynolds number range typical for desalination modules, is focused on the evolution of local mass transfer coefficient k and concentration polarization, which significantly affect SWM module performance. A detailed quantitative prediction is obtained of these parameters, which are linked to the variation of wall shear stress, static pressure and permeation flux. By focusing on a typical region of the membrane channel (adequately capturing the evolving flow characteristics), it is predicted that increasing average k values (with the concomitant reduction of concentration polarization) are associated with the undesirable increase of pressure drop; these conflicting requirements can be balanced through the selection of appropriate spacer geometry. The negative effect of membrane filament contact lines on concentration polarization is well documented. An assessment is made of the two spacer filament configurations, from this perspective, and directions for future research are outlined. (C) 2014 Elsevier B.V. All rights reserved.