Water vapor permeability in heterogeneous porous membranes: Analytical modeling and experimental characterization

Abstract

In this study, an analytical fractal model was established to simulate water vapor permeability in porous membranes with uneven pore size distribution. The permeability of the membrane was expressed analytically as a function of pore size distribution fractal dimension, tortuosity fractal dimension, porosity and pore size based on the fractal theory. Three mass transfer mechanisms namely Knudsen diffusion, Poiseuille flow and transition flow, were considered for different membrane pore sizes. The water vapor permeability of different porous membranes was tested on a specially designed test bench to experimentally characterize the permeable mass transfer performance, and the experimental results were compared with the model results. It shows that considering Poiseuille flow without Knudsen diffusion will significantly overestimate the mass permeability of membranes with small pore size. When the maximum pore diameter is >1.15 μm, the large pore where only Poiseuille flow regime occurs begins to take on the task of mass transfer rapidly, and finally the Poiseuille flow permeability value begins to exceed the transition flow permeability value when the maximum pore diameter is about 2.32 μm. This analytical model provides an accurate and convenient method for predicting the mass permeability of heterogeneous porous membranes.