Steady three dimensional flow and mass transfer analyses for brackish water desalination by reverse osmosis membranes

Reverse osmosis has been emerged as one of the most used technologies to desalinate water. Present study investigates steady three dimensional flows and mass transfer in the feed channel for a brackish water desalination process by using reverse osmosis membranes. Flow and the mass transfer in the feed channel are governed by Navier-Stokes and mass transport equations. The channel containing cylindrical shaped spacers is bounded by membranes. Computational fluid dynamics simulations are conducted for the range of the Reynolds number 100 ⩽Re⩽ 800. The laminar flow model is employed when Re=100 while SST k-ω turbulence model is employed when Re⩾400. Membranes are treated as a functional surface where water flux is determined from local concentration and pressure by employing the solution-diffusion model of the reverse osmosis. The influence of three dimensional flow structures on the concentration polarization and the potential fouling over the membrane surface is discussed. It is shown that high water flux regions and low concentration regions coincide with low wall shear regions. The high intensity concentration polarization sites correlates directly with the high potential fouling sites. Spacers enhance the membrane performance and they help to alleviate concentration polarization.