Rising fluid velocity in the tubular-membrane module by inserting concentrically a steel rod has two conflicting effects. One, the decrease in resistance to permeation due to reduction in concentration polarization, is good for ultrafiltration, while the other, the decrease in average transmembrane pressure due to increase in friction pressure loss, is bad for ultrafiltration. It appears, therefore, that proper adjustment of fluid velocity as well as proper arrangement of the annular size of flow channel with a specified volumetric feed rate, might effectively suppress any undesirable resistance to permeation while still preserving an effective transmembrane pressure and thereby lead to improved performance of membrane ultrafiltration. It was found that considerable improvement in permeate flux is obtainable by employing such a modified tubular module rather than using the open tubular module without an inner tube. The enlargement of power consumption for fluid flow due to the insertion of an inner tube has been also discussed. The improved performance has been checked at same hydraulic dissipated power.
