Flowfields on feed and permeate sides of tubular molecular sieving silica (MSS) membranes

We present a novel computational fluid dynamic approach to integrate diffusion through inorganic molecular sieve silica (MSS) membranes and continuum flows on the feed/retentate and permeate sides of these membranes. In this approach, we model the membrane by creating a bounded region separating the feed/retentate side from the permeate side in which only the phenomenological equations of the activated gas transport model apply. Continuum flows on both sides of this region are described by the Navier-Stokes equations and gas-through-gas diffusion is modelled using the Stefan-Maxwell model only. The phenomenological equations are applicable exclusively to diffusion through the membrane. By coupling these equations we obtain complete flowfields on the feed/retentate and permeate sides of MSS membranes. The complete model characterises the flow Of CO, CO2, He, H-2, and N-2 and gas mixtures of CO2 and H-2 on both sides of tubular MSS membranes and is validated by comparing flow rates with single gas experiments. We found that partial pressure axial distributions in the feed/retentate and permeate streams of the membrane are constant. In the permeate stream, the radial variation of axial velocity across the flow is nearly the same for all axial locations. There is a linear increase of axial velocity (and total flow rate) with axial coordinate. (c) 2007 Elsevier B.V. All rights reserved.