Increasing the fluid velocity in cross-flow membrane ultrafllter has two conflicting effects: one, the decrease in concentration polarization resistance, which is good for ultrafiltration; while the other, the decrease in average transmembrane pressure is bad for performance. Along the flow channel of a cross-flow membrane ultraflltration, concentration polarization increases while transmembrane pressure decreases. Therefore, proper adjustment of the convection strength along the flow channel might effectively suppress the undesirable concentration polarization resistance while still preserving effective transmembrane pressure, and thereby lead to improved permeate recoveries. The effect of hydraulic behavior on membrane ultrafiltration in a tubular module inserted concentrically with a steel rod wrapped by a wire spiral with a wire angle varied at a uniform rate along the flow channel was investigated, and the appropriate manner of wire-angle variation along the tube discussed. It was concluded that for the modules of fixed average wire-spiral angle, the best manner of wire-angle variation is such that the wire angle should increase gradually from 0 � along the flow channel.