The effect of humidity in ambient gas on HTWs in volatile drops

The objective of this study is to clarify the effect of ambient gas on hydrothermal waves (HTWs) in the evaporation of a volatile droplet by understanding the relation between local thermal information at the solid-liquid interface and the bulk heat transfer. Experiments are conducted in a controlled environment. The gas environment was changed to pure nitrogen and humidified nitrogen. An infrared (IR) camera and a CCD camera are used to determine the temperature/heat flux distribution at the solid/liquid interface and the profile of evaporating droplet, respectively. The liquid used here is HFE-7100. The evaporation of HFE- 7100 droplets where HTWs occur was found to become increasing dependent on the liquid-vapor interface area as the substrate temperature was increased, indicating that HTWs enhance the evaporation through the liquid-vapor interface rather than the perimeter of a droplet where the liquid layer is thinnest. Similarly humidity present in the ambient gas was found to enhance the dependence on evaporation through the liquidvapor interface area. When the substrate is heated the effect of humidity on the evaporation is not observed since the evaporation process becomes thermally dominated.