The simulations are based on the numerical solution of the Navier-Stokes and local species balance equations on the three dimensional domain representing quite closely the selected module geometry. The membranes are modelled as a selective layer, which allows the permeation of different components as a function of the transport mechanism and the driving force.

The computational approach, previously devised for the simulation of a simple ceramic membrane only, has been further implemented to improve the predictions accuracy and to describe also the case of commercial Pd/Ag membrane modules. Three membranes have been investigated: a ceramic, and two ceramic supported palladium-silver membranes. Since the selected membranes contain a ceramic structure whose behavior is extremely complicated to predict theoretically, the diffusion coefficients of all the membranes have been experimentally evaluated. The experimental data available at different working conditions (pressure and feed flow rate) and different hydrogen concentration in the feed stream have allowed to strictly evaluate the CFD results.

The different membranes have been modelled with simple approach considering four different transport mechanisms: molecular diffusion (self and mutual), Knudsen diffusion, Poiseuille flow and Sieverts' law. The excellent agreement between the experimental and the predicted data suggests that CFD can be considered an useful and reliable tool for designing new modules or optimizing existing ones. In practice, for instance, a CFD simulation allows to evaluate accurately the convective mass transfer resistance thus guiding the module geometry selection. In any case, for industrial applications the CFD simulations may be useful also to identify the influence of some internals on the mass transfer performances, to correctly estimate the driving force across the membrane taking into account the concentration polarization effect, and to identify the effect of different working conditions as the adoption of sweep streams.