Resistance-in-series analysis of the permeate flux for ultrafiltration in a tubular membrane inserted concentrically with a solid rod, having rod radius varied linearly along the tube axis with rod volume kept unchanged, was carried out by mass and momentum balances under various feed solution concentrations and transmembrane pressures. The correlation predictions qualitatively confirm with the experimental results, especially for the device with rod radius increased linearly, and for the operations under lower transmembrane pressure and smaller volumetric flow rate. Both theoretical predictions and experimental results show that considerable improvement in performance is obtained if the rod radius increases along the tube axis of a solid-rod tubular-membrane module.
