Influence of Membrane Sealing in Pressure-Driven Test Cells on Their Performance

This communication demonstrates the relevance of membrane sealing in a test cell to its performance. Membranes need to be sealed, and therefore a more or less signifcant (depending on the test cell design) peripheral part of the membrane is supported directly by the cell body (instead of a permeate spacer). Although it may seem that there should be no fltration through the membrane when it is supported by an impermeable surface, this communication demonstrates that this is not generally true due to fltration along the membrane porous support. To confrm this, experiments were performed with a cross-flow test cell (GE SEPA™ CF II), blocking the membrane hydraulically from beneath in order to simulate the effect of having the membrane supported by an impermeable surface. The results show that the trans-membrane volume flux obtained in all cases is only slightly affected by the membrane blocking. In view of this, in the cell design, care should be taken to reduce such peripheral parts of the membrane to a minimum because it may be technically very difcult to have there the same conditions of concentration polarization as over the membrane part supported by the permeate spacer.