Orientation dependent permeability in asymmetric composite membranes

Abstract

Asymmetric composite membranes, consisting of a dense polymer layer coated on a porous substrate layer, are widely used in devices such as Energy Recovery Ventilators (ERVs). The permeability of membranes typically depends on water vapour concentration and temperature. Due to the asymmetry of the composite membrane, the orientation of the membrane (i.e., which layer of the membrane experiences a higher water vapour concentration) can also affect the permeability. In this study, the permeability of two asymmetric composite membranes (commercial names “T4 (MX4)" and “HP2″) is measured at temperatures ranging from 5 °C to 50 °C and water vapour activities ranging from 0.2 to 0.95 and the orientation-dependent behaviour of permeability is investigated. Consistent with other studies, the permeability of the membranes increases with increasing water vapour concentration and decreases with increasing temperature. The permeability of the membrane is also a function of the membrane orientation and the sweep flow water vapour concentration as well as the feed flow water vapour concentration. However, the computed permeability is shown to be independent of orientation and sweep flow water vapour concentration when results are plotted against the water vapour concentration at the dense coating layer.