Performance analysis of cross-flow forward osmosis membrane modules with mesh feed spacer using three-dimensional computational fluid dynamics simulations

Abstract

This study presents a three-dimensional computational fluid dynamics (CFD) model to characterize the effect of mesh feed spacer's geometry on the performance of cross-flow forward osmosis (FO) membranes. The performance of FO membranes against various spacer's geometrical parameters are investigated in terms of permeate water flux, reverse solute flux, concentrative external concentration polarization (CECP) on the membrane, mass transfer coefficient, and longitudinal pressure drop of the feed channel. Also, the membrane support layer is explicitly modeled as a porous medium; the relation between the internal and external concentration polarization phenomena, under different spacer's geometrical variables, is exhibited for different porosities. Our results reveal that the feed spacer's geometrical parameters affect the performance of FO membranes by influencing the volume of the low-circulation or dead zones, and the shear rate on the membrane active layer. The CECP modulus is mainly dominated by the reverse solute flux and the volume of the dead zone on the membrane, while the mass transfer coefficient and the longitudinal pressure drop are more impacted by the exerted shear stress on the membrane. Furthermore, the results of our model demonstrates that the reduction of internal concentration polarization results in an increase in CECP and a magnified impact of the spacer's geometry on the CECP modulus.