A Comprehensive Model on Convective Flows During Sessile Drop Evaporation

A sessile drop evaporates when it is deposited on a heated or non-heated substrate. Then, as the three phases solid, liquid, and gas interact, several effects can occur. These include thermo-capillarity, strong evaporation near the triple line and thermal buoyancy that may induce the liquid motion inside the drop, and thermo-solutal buoyancy that causes motion in the surrounding gas. The combination of all these effects generates complex flow patterns, which affect heat and mass transfer phenomena. In the present study, all these effects are taken into account for developing a numerical model which allows analyzing the contribution of each one to the evaporation of the drop. The numerical predictions show an important increase of heat and mass transfer at the drop edge due to thermo-capillarity and thermo-solutal buoyancy in the surrounding air. Furthermore, the cooling effect resulting from evaporation depends much more on the thermal compensation provided by the substrate. The kinetics of evaporation is highly influenced by the wall temperature and the substrate thermal conductivity rather than by the variation of the drop surface area and the fluid motion.