Mass transfer in forward osmosis with hollow fiber membranes

The recent development of high performance thin film composite membrane has been a major technological thrust in the research of forward osmosis (FO). While most of the recently developed FO membranes are of flat sheet (FS) geometry, hollow fiber (HF) FO membranes have attracted significant attention in recent years due to their promising prospect in full-scale applications. Existing studies on HF FO membrane fabrication and characterization exclusively apply the mass transfer equations developed for FS membranes. Whether or not these mass transfer equations for FS membranes are applicable for membranes with HF geometry remains theoretically unclear. In this paper, accurate analytical equations are derived to describe mass transfer of water and solute across an HF membrane. These equations take into account the curvature effect of the HF membranes and thus have very different mathematical forms from those for FS membranes. A systematic comparison of the mass transfer equations between HF and FS membranes was also conducted using both simulated and experimentally measured flux data. The results from such a comparison suggest that the mass transfer equations for FS membranes are in general applicable for an HF geometry, which provides the theoretical basis for the application of the well-established FS mass transfer equations in characterizing HF membranes. (C) 2016 Elsevier B.V. All rights reserved.