Hydrothermal waves in droplet evaporation

Abstract

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.The hydrothermal waves (HTWs) have been investigated on the evaporation of ethanol, novec-7100 and pure water sessile droplets forming at the top of a cone-shaped container under the steady state. For ethanol and novec-7100, the temperature along the droplet diameter is higher near the triple line than in the middle section, within which the temperature shows slight oscillations representing instability of the thermal motion. Behaving inversely, the temperature of the water droplet is higher in the middle section than at the periphery, and no evident oscillation is observed. The results show that with the increase of the imposed voltage, the thermal motion is more rapid and the number of HTWs is increased in ethanol and novec-7100. The relation between the number of HTWs and the imposed voltage is fitted by an empirical equation for novec- 7100. With analysis of the origin of HTWs, the droplets evaporation belongs to the category of HTWs type 1 with gravity prevails over the surface tension.