CFD simulations of net-type turbulence promoters in a narrow channel

The most common spacers or turbulence promoters for membrane processes are net-like materials which enhance mass transfer as well as provide passage f or feed solutions. The enhanced membrane performance of spacer-filled chann els is determined by the fluid how patterns induced by the spacer filaments . Insight into the effect of spacer characteristics can be obtained by comp utational fluid dynamics. In this research, the commercial finite volume pa ckage FLUENT was used to visualise the flow pattern in a rectangular membra ne channel. Three transverse filament arrangements were simulated. The resu lts show that both high shear stress regions and eddies are present in the channel due to the spacer cylinders. The mass transfer enhancement on the w all/membrane surface is directly related to the high sheer stress value, ve locity fluctuation, and eddy formation. The peak shear stress and velocity fluctuation are repeated after each spacer cylinder, while the eddies are g enerally found before and after each cylinder. The CFD simulation also sugg ests that reducing the transverse filament distance will reduce the distanc e between sheer stress peaks and consequently introduce larger shear stress regions near the wall region and increase the number of eddies, which will benefit membrane mass transfer. However, the penalty for this is that ener gy losses will also be significantly increased. The selection of optimum sp acer geometry design involves a trade-off between these competing effects. (C) 2001 Elsevier Science B.V. All rights reserved.