Internal flow patterns of an evaporating multicomponent droplet on a flat surface

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.Evaporation processes of droplets with different ethanol/water volume ratios (0% ethanol/100% water, 5% ethanol/95% water and 10% ethanol/90% water, respectively) on a hydrophobic silicon dioxide surface covered by a layer of FAS were investigated by PIV method. It was found that the evaporation process of heated two-component droplets can be divided into three stages, downward vortex stage, transition stage and upward vortex stage sequentially, while for a pure water droplet only the upward vortex stage exists. The mechanism of those three stages was analysed in detail, combining previous theories of Marangoni effects, buoyancy effect and experiment results. Besides, it was also found that initial composition and input power affected the duration of the three stages, especially the downward vortices and transition stage which are related to ethanol evaporation: In low input power, the transition stage of the high ethanol fraction droplet occurred earlier and lasted a shorter time than the low ethanol fraction droplet, while, in high input power, the transition stage of the low ethanol fraction droplet occurred earlier and lasted a shorter time than the high ethanol fraction droplet. That phenomenon was also analysed with ethanol evaporation in different thermal and solutal conditions.