Influences of geometry and flow pattern on hydrogen separation in a Pd-based membrane tube

The abatement of concentration polarization in a membrane tube is of the utmost importance for improving the efficiency of hydrogen separation. In order to enhance the performance of hydrogen separation, the characteristics of hydrogen permeation in a Pd-based membrane system under various operating conditions and geometric designs are studied numerically. The effects of Reynolds numbers, shell size, baffle, and pressure difference on hydrogen mass transfer across the membrane are evaluated. The predictions suggest that a larger shell deteriorates concentration polarization, stemming from a larger H2 concentration boundary layer. Baffles equipped in the shell are conducive to disturbing H2 concentration boundary layer and reducing concentration polarization at the retentate side, thereby intensifying H2 permeation. The more the number of baffles, the less the increment of improvement in H2 permeation is. The installation of one baffle is recommended for enhancing H2 separation and it is especially obvious under the environments of high pressure difference. Within the investigated ranges of Reynolds number at the permeate side and the retentate side, the feasible operating conditions are suggested in this study.