Influence of wettability conditions on slow evaporation in two-dimensional porous media

Abstract

We study numerically the influence of the wettability condition on slow evaporation in two-dimensional pore square networks of aspect ratio 1. We show how evaporation in a hydrophobic network can be simulated numerically by combining imbibition rules and the computation of diffusion transport in the gas phase. Then we conduct a statistical study of drying in hydrophilic or hydrophobic networks based on pore network simulations. We concentrate on the situation where the external transfer resistance and liquid film effect are negligible and the invasion is dominated by capillary effects. It is found that drying in a hydrophilic network is significantly faster than in a hydrophobic one. The dimensionless overall drying time is found to be network size dependent, approaching exponentially a limit for large size hydrophilic networks. The dimensionless average overall drying time is 0.93 and 0.75 in hydrophobic and hydrophilic large networks, respectively. Other properties, such as the overall saturation and the evaporation flux (through the concept of equivalent flat front position) are also studied. In a last part the impact of liquid film flow on the overall drying time fluctuation is briefly investigated for the case of hydrophilic networks. It is found that the films dampen the drying time fluctuations.