Shear stresses and mass transfer at the base of a stirred filtration cell and corresponding conditions in narrow channels with spacers

This study aims to adequately characterize shear stresses and mass transfer coefficients at the membrane surface of a high pressure stirred filtration cell, and to determine equivalent conditions for flow in narrow channels with spacers. Employing electro-chemical techniques, measurements were made of local wall stresses and transfer coefficients, and of space-average mass transfer rates, at various Schmidt numbers and Reynolds numbers 6500–39,000. The local measurements revealed salient features of momentum and mass transfer at the cell base, and the average quantities were successfully correlated with the respective Reynolds numbers. Furthermore, from detailed numerical and experimental studies of cross-flow in narrow spacer-filled channels (simulating conditions in spiral-wound membrane modules), relevant data on wall shear stress and mass transfer were selected for comparison with the new results from the stirred-cell. This comparative data analysis allows estimation of the stirrer rotational speed ω which corresponds to equal area-average shear stress (or mass transfer coefficient) at the membrane surface of stirred cell and of spacer-filled channel (for specific cross flow velocity U). The range of ω values, corresponding to a certain U range, is different for the cases of matching mean shear stress or mass transfer rates in the two flow systems.

► Conditions at the membrane surface of high pressure stirred cell are investigated.
► Local shear stress and mass transfer radial profiles are measured and interpreted.
► Measured space-average wall stress and mass transfer coefficients are correlated.
► Appropriate correlations of same quantities for spacer-filled channels are selected.
► Relations are suggested of equivalent channel velocity and stirrer rotation speed.