Isothermal drying on non-hygroscopic capillary-porous materials as an invasion percolation process

Abstract

Numerical simulations of drainage and drying at low capillary number are performed. Drainage is simulated by means of the standard invasion percolation algorithm. Simulations of drying are based on an invasion algorithm combining elements of the invasion percolation algorithm with the computation of the vapour flux at each elementary liquid-gas interface. The simulations show that the invasion front is the very same fractal object in drainage and in drying. Specific features of drying are investigated. It is shown that the evaporation front should be clearly distinguished from the invasion front. In the presence of gravity forces, the disconnected cluster erosion mechanism is very effective and no disconnected cluster can survive outside the invasion front region. In the absence of gravity forces, the simulations indicate that drying of an initially saturated capillary-porous medium cannot be described according to the continuum approach to porous media.