(407f) CFD Analysis of Flow in Tubular Zeolite Membrane Modules

It is necessary to analyze the flow in membrane modules for optimizing module structure and operation conditions and developing scale-up rules of membrane module. In this study, the flow in a single element zeolite membrane module was simulated numerically using a thermal flow analysis software, RFLOW, as for vapor permeation through a zeolite membrane. A flow analytical model taking into account the effects of both molecular and turbulent diffusion of flow was developed.

The numerical analysis using the k-epsilon model was conducted with Navier-Stokes equations for incompressible fluid, equations of continuity, convection-diffusion equations. The validity of our model was also investigated by comparing with the experimental results of vapor permeation separation through a zeolite membrane. In this experiment, a mixture of ethanol and water was fed and water was permeated selectively. In order to elucidate the contribution of turbulent and molecular diffusion to the flow in the module and the fluxes of ethanol and water, the numerical analyses were carried out by taking into accounts the effects of both turbulent and molecular diffusion and only the effect of turbulent diffusion. The discrepancy between calculated and experimental data became smaller when both turbulent and molecular diffusion were taken into account. The magnitude of the effects of turbulent and molecular diffusion would depend on the flux, i.e. the Re number of the flow. The effects of turbulent and molecular diffusion on the water concentration of the outlet could be evaluated by changing the flux of the flow. When the Re number of the flow exceeded 5000, the fluxes were so large that the effect of turbulent diffusion on the flow was more significant than that of molecular diffusion. In these cases, i.e. the turbulent diffusion controlled region, the values of the water concentrations at the outlet were not affected by molecular diffusion. On the other hand, molecular diffusion became significant with decreasing Re number, explaining the experimental results well. These results obtained in this study illustrated that this analysis model can be applied for the flow in the wide range of Re number.