Mass Transport in Osmotically Driven Membrane Processes.

Forward osmosis (FO) and pressure retarded osmosis (PRO) are the two operational modes for osmotically driven membrane processes (ODMPs). ODMPs have gained increasing popularity in the laboratory over the years; however, OMDPs have not been applied in very many cases at full scale because they are still emerging technologies that require further development. Computational fluid dynamics (CFD) modeling coupled with solute transport evaluation provides a tool to study hydrodynamics and concentration polarization in FO and PRO. In this study a series of models were developed to predict water flux. The simulation results of empty-channel (with no feed spacer) membrane cells were verified by comparison with experimental results, showing that CFD simulation with solute transport is a reliable tool. Ensuing 2D and 3D models were built to study the impact of feed spacers on the velocity and concentration distribution inside the flow channels, and investigate whether the presence of spacers would enable enhancement of water flux. The results showed that spacers could change the concentration and velocity profile and they could reduce or enhance water flux depending on the inlet flow velocity and distance between the membrane and spacer.