Fluid mechanics plays an important role in pressuredriven membrane processes. This manifests itself through the convective motion of fluids and its influence on the motion of dissolved and suspended solutes. In this review, we compare impact with crossflow filtration and summarize the advantages and limitations of different membrane permeators. Then, we present results from recent theoretical studies of flow in an annulus with porous walls, and from recent experiments showing the effect of transmembrane flux on the friction coefficient of a flowing fluid inside a porous tube with suction. We also compare the porous tube with a porous twowalled slit for capturing suspended colloids. The performance of several commercial modules are compared in light of the theory. Under the assumptions of the theoretical models, and all things being equal (besides fractional recovery per unit length), tubular systems will capture more particles from dilute suspensions than slits with two porous walls. This is expected since the fractional recovery for a tube is 2.67 times that for a s