Influence of contact angle on slow evaporation in two-dimensional porous media

TL;DR

This study numerically investigates how contact angle influences slow evaporation patterns and times in 2D porous media, revealing a transition from fractal to flat front patterns and identifying a critical contact angle where drying time peaks.

Contribution

It introduces a combined model linking invasion percolation and diffusive transport to predict evaporation patterns and times based on contact angle variations.

Findings

Drying pattern transitions from fractal to flat front at a critical contact angle.

Drying time is minimized at low contact angles and peaks at the critical angle.

Fluctuations in drying time are significant below the critical angle and vanish afterward.

Abstract

We study numerically the influence of contact angle on slow evaporation in two-dimensional model porous media. For sufficiently low contact angles, the drying pattern is fractal and can be predicted by a simple model combining the invasion percolation model with the computation of the diffusive transport in the gas phase. The overall drying time is minimum in this regime and is independent of contact angle over a large range of contact angles up to the beginning of a transition zone. As the contact angle increases in the transition region, the cooperative smoothing mechanisms of the interface become important and the width of the liquid gas interface fingers that form during the evaporation process increases. The mean overall drying time increases in the transition region up to an upper bound which is reached at a critical contact angle \Theta_c. The increase in the drying time in the transition region is explained in relation with the diffusional screening phenomenon associated with the Laplace equation governing the vapor transport in the gas phase. Above \Theta_c the drying pattern is character- ized by a flat traveling front and the mean overall drying time becomes independent of the contact angle. Drying time fluctuations are studied and are found to be important below \Theta_c, i.e., when the pattern is fractal. The fluctuations are of the same order of magnitude regardless of the value of contact angle in this range. The fluctuations are found to die out abruptly at \Theta_c as the liquid gas interface becomes a flat front.