This work is aimed at obtaining a better understanding of transport phenomena in membrane elements, where feed-flow spacers (employed to separate membrane sheets and create flow channels) tend to enhance mass transport characteristics, possibly mitigating fouling and concentration polarization phenomena, while augmenting pressure drop. A model flow geometry is considered consisting of a plane-channel, where a regular array of cylinders is inserted, acting as turbulence promoters. Direct numerical simulations using the Navier-Stokes equations are performed over a range of Reynolds numbers typical of such membrane modules. The results show that the flow becomes unstable at a critical Reynolds number of 60, and progressively tends to a chaotic state. Qualitative flow features, such as the development and separation of boundary layers, vortex formation, the presence of high-shear regions and recirculation zones, and the underlying mechanisms are examined. In addition. quantitative statistical characteristics such as time-averaged velocities, Reynolds stresses, wall-shear rates and pressure drop are obtained, which are directly related to mass transport enhancement. (C) 2003 Elsevier B.V. All rights reserved.