Effect of varying incidental angles of a wire-rod insert on the performance of tubular ultrafiltration membranes

Increasing the fluid velocity in cross-flow membrane ultrafilter 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 ultrafiltration, 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.

The effect of hydraulic behavior on membrane UF in a wire-rod tubular module was investigated by varying the wire spiral angle at a uniform rate along the flow channel. Increasing the wire spiral angle reduced the cross section of flow channel, as well as increased the fluid velocity. Actually, raising the fluid velocity in the flow channel of a cross-flow membrane ultrafilter has two conflicting effects: the desirable effect of decreasing the CP layer and the undesirable effect of decreasing transmembrane pressure. Along the flow channel of a wire-rod tubular membrane, the CP resistance increased while the transmembrane pressure decreased. It is concluded that for the devices of the same average wire-spiral angle 2, the best manner of wire-angle variation is such that the wire angle should increase gradually from 0° along the flow channel, while for the modules of different average values of wire angle, 2, the order of per6 formance within the operating conditions of present interest is (2 = 15°) > (2 = 20°) > (2 = 25°) > (2 = 30°C).