Comparative pore and continuum-scale modeling of evaporation in mixed wettability porous media

Abstract

Evaporation in porous media plays a critical role in systems where optimizing evaporation rates and patterns is vital. Heterogeneous wettability can significantly influence evaporation dynamics by altering capillary forces and liquid connectivity; however, its specific effects on evaporation front morphology, capillary pressure–saturation relationships, and the transition to the falling-rate regime are not well understood. This study addresses this gap by using a modeling framework to simulate evaporation in mixed-wet porous media. The approach combines a three-dimensional pore-network model with a spatially-resolved non-equilibrium continuum model on an identical voxel-based domain. The porous medium is assigned random contact angles ranging from 30°to 150°. Capillary-driven flow and evaporation are simulated, and key metrics such as liquid saturation, capillary pressure, and relative permeability are monitored. Our results show a two-stage drying process. In the initial stage, a highly connected liquid network sustains capillary-driven evaporation with high flux. Over time, liquid clusters become isolated and wet pockets persist, slowing evaporation and inducing a falling-rate regime. Heterogeneous wettability produces a ramified evaporation front, alters capillary pressure dynamics, and affects the evolution of relative permeability. These findings improve our understanding of evaporation kinetics in mixed-wet porous media. They validate the use of a dynamic capillary pressure formulation in continuum models and inform improved modeling of evaporation in environmental and industrial porous materials.