The Effect of Vortices Induced by Baffles on Concentration Polarization

Abstract

A numerical analysis was performed to investigate the effect of recirculations formed by rectangular or triangular baffles on depolarization of concentration in a flat sheet membrane module. The k-[;turbulent model was used to predict the flow field in the flat channel. Control-volume-based finite difference methods were employed to solve for the two-dimensional fluid velocity and solute concentration distribulions. We examined rigorously the effect of various parameters including the velocity, diffusivity, perrneate flux, baffle size, baffle shape, and interbaffle spacing in an effort to find optimum operating conditions which may provide enhanced mass transfer. The vortices induced by the baffles on the membrane are found to be extremely effective in depolarizing the retained solutes at the membrane surface. The predictions show that baffle configurations and flow conditions have a great influence on depolarization of concentration. To achieve effective concentration depolarization, the baffle height should be greater than 0.5h (h = half the channel height) and the interbaffle spacing around 2h to 3h for the Reynolds number from 1,250 to 25,000. The simulated results indicate that the optimal Reynolds number is around 5,000 to 8,000 in view of both concentration polarization and energy consumption.