Effect of sessile binary droplet evaporation at different ambient temperatures on interfacial profile near the triple line

Abstract

Heat and mass transfer near the triple line of an evaporating droplet contains complex physics, while the mechanisms of evaporation influenced by the ambient temperature remain unclear. This paper describes an experimental study of interfacial profile near the triple line during evaporation of pure water and binary mixtures including dilute aqueous ethanol and n-butanol solutions at different ambient temperatures. The difference of interfacial profile between single and multi-component sessile evaporative droplets were experimentally demonstrated. The result shows that the thin film evaporation of the binary droplets is greatly suppressed when the ambient temperature drops. The thin film thickness reduces with the time under various ambient temperature conditions which are below 25 °C. The thickness difference at between 0 s and 40 s decreases in the order of water, ethanol solution and n-butanol solution. For water droplet, the critical thin film thickness at which the evaporation mode changes decreases with increasing ambient temperature, which is opposite to the binary droplets. Meanwhile, the rate of change of thin film thickness increases with increasing ambient temperature for water or ethanol solution, while it decreases with increasing temperature for n-butanol solution, which is attributed to the contact line energy barrier that decreases with increasing ambient temperature.