Pore network model of evaporation in porous media with continuous and discontinuous corner films

TL;DR

This paper develops a pore network model that incorporates continuous and discontinuous corner films to better understand evaporation in porous media, highlighting the roles of corner films and geometrical effects on evaporation rates.

Contribution

A novel pore network model that explicitly includes both continuous and discontinuous corner films and their effects on evaporation thresholds in porous media.

Findings

Model agrees well with experimental evaporation data.

Continuous corner films sustain high evaporation rates.

Gas invasion and capillary scissors effect interrupt corner films.

Abstract

During evaporation in porous media, two types of corner films are distinguished. A continuous corner film is connected to the bulk liquid, while a discontinuous one is not. To disclose their effects on evaporation in porous media, a pore network model with both continuous and discontinuous corner films is developed, which considers the capillary and viscous forces as well as the effects of corner films on the threshold pressures of pores. The capillary valve effect induced by the sudden geometrical expansion between the small and large pores is also taken into account in the model. The developed pore network model agrees well with the evaporation experiment with a quasi 2D micro model porous medium, in terms of not only the variation of the liquid saturation in each pore but also the variation of the total evaporation rate. The pore network models that neglect the corner films or the liquid viscosity are also compared with the experiment so as to shed light on the roles of the corner films. The continuous corner films, which contribute to sustain the high evaporation rate, can be interrupted to be the discontinuous ones not only by the gas invasion into pores but also by the capillary scissors effect due to the local convex topology of the solid matrix.