Evaporation of a sessile water droplet during depressurization

Abstract

This paper reports an experimental and theoretical study of sessile water droplet evaporation during depressurization. During the experiments, three kinds of surfaces were used: copper, slide glass and Teflon. The change in droplet shape with ambient pressure was recorded. The experimental results showed that the water droplet evaporated the fastest on the slide glass surface and the lowest on the Teflon surface, due to the different wettability of substrates. Bubbles were easily formed on the Teflon surface, and the existence of bubbles hindered the contraction of the contact line. A mathematical model was then developed to simulate droplet evaporation on the copper surface and the slide glass surface during depressurization, which combined the effects of air flow, the substrate thermal properties, evaporative cooling, internal circulation and the Stefan flow for the first time. The calculated results matched well with the experimental results, and the deviations between them were within 30%. A significant difference between sessile droplet evaporation under reduced pressure and under atmospheric pressure was that the droplet height did not follow the linear change with time, which was related to the change of droplet surface temperature. And then, the changes of droplet surface temperature and substrate surface temperature with time were analyzed based on calculations. Finally, the main factors affecting the accuracy of present model were proposed.