The effect of mixing promoters on the performance of forward osmosis membrane systems: Computational fluid dynamics simulations

Computational fluid dynamics simulations are performed to study the desalination process in forward osmosis modules. Concentration polarization phenomenon is responsible for lowering the water flux permeation through the membrane. It is desired to mitigate the external concentrative and dilutive concentration polarizations by proper mixing of both the feed and the draw solutions. Chevron-type of corrugation with a single triangular shape is used for membrane corrugation. The peak of the corrugation is oriented toward the feed channel. This type of corrugations produces dips in the membrane in the draw side. The dips will not mix the draw solution properly. Net-type spacers of 45° will be placed in the middle of the draw channel. The spacers will work as mixing promoters and add extra support for the membrane. All configurations will have the same Reynold number of 1500 in both channels. K - ?SST turbulence model is used with modules containing mixing promoters, and the laminar model is used with the module without corrugation and spacers. The results indicate that a 14% increase in the water flux is attained with the presence of spacers and membrane corrugation compared with a flat membrane and no spacers. Also, the dilutive concentration polarization has been mitigated significantly compared with the empty case.