Large mass flux differences for opposite flow directions of a condensable gas through an asymmetric porous membrane

Abstract

The one-dimensional, adiabatic flow of vapors through porous ceramic membranes consisting of three different layers is theoretically investigated. The individual layers have different thicknesses with pore sizes of 10nm for the separation layer, 100nm for the middle layer and 6μm for the support layer. The mass flow is calculated for values of the upstream relative pressure varying between 0.7 and 1. The relative pressure is the ratio of the actual pressure to the saturation pressure. For upstream relative pressures smaller than about 0.77, the fluid does not condense within the porous membrane, and the mass flux is a few percent larger for the flow direction from the support to the separation layer than for the other flow direction. For larger upstream relative pressures, the fluid may condense and liquid or a two-phase mixture may be transported through parts of the membrane. The mass flow can become about 10 times larger for one flow direction than for the opposite flow direction. The flow is modeled using the energy balance and accounting for capillary condensation, for the transport of the enthalpy of vaporization, and for the temperature variation due to the Joule–Thomson effect.