Numerical model using a Volume-Of-Fluid method for the study of evaporating sessile droplets in both unpinned and pinned modes

We propose a numerical study of the evaporation of sessile droplets using a Volume-Of-Fluid (VOF) method in the free-software Basilisk. We consider pure liquid droplets forming a spherical-cap onto a smooth or rough substrate and we investigate two different modes of evaporation: the unpinned mode where the contact angle is constant and the pinned mode where the wetting area is constant. The numerical method used to implement the contact angle and for the reconstruction of the interface is fully described, especially for the pinned mode for which we present a new VOF implementation. In the unpinned mode, the parametric studies predict that the volume decreases in time according two phases, which matches the signature behavior of evaporating unpinned droplets, irrespective of the geometrical parameters. In the pinned mode, the volume follows a linear decrease for the whole evaporation time and the contact angle analysis indicates a linear decrease in time which was expected according to the theory and validated with some experiments we performed. (C) 2021 Elsevier Masson SAS. All rights reserved.