A numerical study of the effect of channel spacers on the performance of cross-flow forward osmosis membrane modules

In this paper, we perform two-dimensional simulations of cross-flow forward osmosis (FO) membrane modules in the presence of draw and feed channel spacers. For this purpose, the equations corresponding to the conservation of mass, momentum, and convection-diffusion for the mass fraction of solute are solved using a commercial finite volume flow solver. We consider six configurations of channel spacers being constructed by the symmetric and asymmetric placement of cavity, submerged, and zigzag arrangements. We will study the effect of the spacers’ geometrical parameters such as diameter and relative distance in these configurations as well as the solute resistivity of the porous support layer on the performance of the FO membrane modules in terms of water flux, external concentration polarization (ECP) factors, and pressure drop per unit length of the membrane. Our results reveal that increasing the solute resistivity of the porous support layer has an adverse effect on the water flux, whereas the impact on the ECP factors is positive. In addition, it turns out that the submerged configurations, where the spacer filaments are not in direct contact with the membrane surface, produce the highest water flux through the membrane; however, they have an adverse effect on the pressure drop along the membrane surface.

Keywords:

Forward osmosis , concentration polarization , Channel Spacer , Computational fluid dynamics