Interface behavior and void formation during infiltration of liquids into porous structures

Abstract

A numerical approach was proposed to simulate time-dependent evolution of the liquid front during the pore-level infiltration of liquids into porous structures. It considers the multiphase problem of liquid penetration into the pore(s) initially occupied with air and the simultaneous escaping of air. The Volume-of-Fluid (VOF) method was employed using a two-dimensional model of the graphite pore structure. The proposed method is capable of tracking the evolution of liquid front and yields the infiltration criteria for wetting and non-wetting liquids. Contribution of various driving forces (resulting from pressure gradient, gravity and interfacial effects) to infiltration and interface behavior including the liquid front shape, position and velocity was investigated. Interface pinning (temporary and permanent) and wicking flow through the pore(s) were investigated during infiltration of wetting liquids, whereas pore-level fingering and void formation (entrapment of air within the pore) were observed for non-wetting liquids. The results were verified against the results of coupled VOF level-set method, known to be more accurate for interface tracking. Moreover, the results of liquid penetration length during the wicking flow through a network of pores in series were validated with good agreement against the experimental results of unidirectional horizontal infiltration of graphite foam, and a modified Washburn equation.