DEAN VORTICES WITH WALL FLUX IN A CURVED CHANNEL MEMBRANE SYSTEM - 3 - CONCENTRATION POLARIZATION IN A SPIRAL REVERSE-OSMOSIS SLIT

Numerical solutions of the 3-dimensional convective diffusion equation are used to obtain a quantitative measure of concentration polarizati on for Dean vortex flow of an aqueous salt solution in a spiral revers e osmosis system, The velocity fields for total spanwise, radial and s treamwise directions are incorporated into the convective-diffusion eq uation to obtain the concentration profiles. The concentration polariz ation for flow in spiral (with Dean vortices) and flat (without Dean v ortices) membrane channels are calculated under similar non; condition s. The rate of concentration build-up in a spiral membrane channel wit h axial distance is significantly inhibited when Dean vortices are pre sent. Dean vortex non promotes rapid mixing and inhibits the growth of the solute concentration boundary layer, hence a module with Dean vor tices is more productive at larger downstream distances than one witho ut such instabilities.