THE EFFECT OF VORTICES INDUCED BY BAFFLES ON CONCENTRATION POLARIZATION

A numerical analysis was performed to investigate the effect of recirc ulations formed by rectangular or triangular baffles on depolarization of concentration in a flat sheet membrane module. The k-epsilon turbu lent model was used to predict the how field in the flat channel. Cont rol-volume-based finite difference methods were employed to solve for the two-dimensional fluid velocity and solute concentration distributi ons. We examined rigorously the effect of various parameters including the velocity, diffusivity, permeate flux, baffle size, baffle shape, and interbaffle spacing in an effort to find optimum operating conditi ons which may provide enhanced mass transfer. The vortices induced by the baffles on the membrane are found to be extremely effective in dep olarizing the retained solutes at the membrane surface. The prediction s show that baffle configurations and flow conditions have a great inf luence on depolarization of concentration. To achieve effective concen tration 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 result s indicate that the optimal Reynolds number is around 5,000 to 8,000 i n view of both concentration polarization and energy consumption.