Dean Vortices with Wall Flux in a Curved Channel Membrane System: 3. Concentration Polarization in a Spiral Reverse Osmosis Slit.

Abstract

Numerical solutions of the 3-dimensional convective diffusion equation are used to obtain a quantitative measure of concentration polarization for Dean vortex flow of an aqueous salt solution in a spiral reverse osmosis system. The velocity fields for total spanwise, radial and streamwise directions are incorporated into the convective-diffusion equation to obtain the concentration profiles. The concentration polarization for flow in spiral (with Dean vortices) and flat (without Dean vortices) membrane channels are calculated under similar flow conditions. The rate of concentration build-up in a spiral membrane channel with axial distance is significantly inhibited when Dean vortices are present. Dean vortex flow promotes rapid mixing and inhibits the growth of the solute concentration boundary layer, hence a module with Dean vortices is more productive at larger downstream distances than one without such instabilities.