Vapor emission from porous materials with diffusive transport in the solid-phase

摘要

A mathematical model for the transport of a chemical species in a porous medium consisting of a rigid solid-phase polymer with a gas in the pores is developed in which the species can permeate the solid-phase via molecular diffusion. A volume averaging approach is used to develop macroscale transport equations where nonequilibrium of species between the two phases is allowed. The effective transport properties for the macroscale equations are obtained by solving the closure problem on the pore-scale using both a periodic unit cell containing circular solid particles and ten different configurations of an asymmetric unit cell containing randomly placed and oriented elliptical solid particles. The computed effective transport properties are used to study the influence of pore-scale configuration on the macroscale vapor emission flux from an initially saturated porous material. Specifically, the effects of partition coefficient, solid-phase diffusivity, porosity, particle size and shape, and pore-scale variability are considered. It is found that the pore-scale configuration can have a dramatic influence on the time scale over which the surrounding environment experiences measurable effects from the vapor emission process.