Study on the effect of flow maldistribution on the performance of the hollow fiber modules used in membrane distillation

Abstract

This paper investigates the effects of flow maldistribution on the performance of hollow fiber module used in membrane distillation (MD). As a base of this work, the mathematical model for ideal hollow fiber module was established. To get the flow maldistribution mathematically, sub-division of the module was employed to divide the fiber bundle into a number of sub-regions with different characteristics. The regional behavior was obtained from the analysis of ideal module, and the overall performance of a practical module was obtained by the combination of its sub-regions. At lumen side, the flow maldistribution is caused by the polydispersity of fiber inner diameter, and a Gauss distribution was introduced to divide the fiber bundle. At the shell side, the flow maldistribution is caused by the non-uniformity of fiber packing, and the Voronoi tessellation technique was adopted to determine the distribution of polygonal cell area. The effects of flow maldistribution at the two sides of the membrane were assessed individually. The result shows that the polydispersity of fiber inner diameter has some negative effect on the module permeate flux at the conditions considered, and the negative influence of the non-uniformity of fiber packing on the module performance seemed to be more important. More studies were focused on the shell side, the module flux was found increasing with the increase of packing fraction and flowrates at the two sides of the membrane.