Experimental investigation on evaporation dynamics of sessile ethanol droplets on a heated substrate

Abstract

In order to understand the evolution of thermal patterns and the effect of the thermal convection in the sessile droplet on the evaporation processes, a series of experimental investigations on evaporation dynamics of sessile ethanol droplets on a heated substrate were carried out based on the steady state evaporation method. The contact radius of the droplet on the substrate is fixed at 2.5 mm and the droplet height varies from 0.4 to 1.2 mm. Results indicate that with the decrease of the droplet height, the temperature distribution near the droplet center becomes nonuniform, and hydrothermal waves and Bénard-Marangoni cells appear in sequence. The effect of liquid supplementation on the thermal patterns can be neglected. With the raise of the substrate temperature, both the wave number of the thermal waves and the frequency of the temperature fluctuation near the contact line increase. Moreover, the evaporation rate decreases first, and then increases with the decrease of the droplet height. The enhancing thermal convection in the droplet can promote the evaporation process at a high substrate temperature.