Contact vaporization of an impacting drop on heated surfaces

Abstract

Contact vaporization phenomena including violent nucleate boiling, gentle nucleate boiling and film evaporation during a liquid drop impact on heated surfaces are experimentally presented. Also the bubble behaviors are discussed with respect to different phenomena. Secondary droplets in violent nucleate boiling originate from not only the jets on pagoda-like bubbles, but also the cracking of both plain and pagoda-like bubbles. While in gentle boiling, bubbles undergo the expansion and receding processes due to influences of evaporating and condensing. In film evaporation, there still exist small growing bubbles within the drop on account of the initial bubble entrainment. In the second part, the drop geometric parameters are mainly provided. Results suggest that the divided stages during film evaporation including a constant wetting area in the literature are only appropriate for water and its critical contact angle corresponding to the sharp diminution of the contact diameter is about 5–8°. The impact process has minor effects on the drop evaporation and the evaporation rate as well as the average heat flux increase linearly with the surface temperature.