(653b) CFD Analysis of Transport in a Forward Osmosis System

A systematic approach to modeling and analyzing the performance data of a laboratory forward osmosis system was evaluated via the application of a detailed CFD transport model of the coupled fluid flow and solute mass transfer equations. The detailed modeling approach was compared with analysis based on the classical film model with the goal of assessing the impact of various model assumptions and associated implications regarding the significance of the FO membrane support layer to water and salt permeation. The analysis revealed that water permeability and solute transport parameter values that are determined from FO operation performance data in the RO operational mode (FO-RO) are of significantly higher magnitude relative to transport parameter values directly extracted from CFD analysis of FO experimental data. Moreover, the magnitude of the porous layer resistivity (K), when determined based on the FM model in which the transport parameters are extracted from FO-RO operational data, implies tortuosity/porosity ratio that is a factor ~2-5 higher than physically realizable with typical membrane porous supports. Comparative analysis of experimental FO data with the FM and CFD models showed that the former overestimates the permeation resistance of the FO membrane support layer by up to about an order of magnitude. Accordingly, the present study suggests that enhancement of FO membrane water permeability would in fact benefit from developing higher permeability membrane skin and improved channel hydrodynamics (to decrease external concentration polarization) as opposed to developing thinner ad higher permeability FO membrane support layers.