Visual studies on film boiling

Abstract

The purpose of this research is to study and examine the droplet bounding phenomena on carbon heated surface during film-boiling period, which occur when a water droplet collided with the heated surface at a very high temperature (400ºC-500ºC). When the surface temperature reaches a maximum value, the critical superheated surface is suddenly covered with a vapor layer. Because of the vapor layer’s lower thermal conductivity, this vapor layer insulates the surface. This condition of vapor film insulating the surface from the liquid characterizes film-boiling. The carbon boiling curve that obtained from the experiment is examined in order to study the relation between carbon boiling curve and the evaporation lifetime curve of a droplet. According to the Leidenfrost phenomena, liquids cannot touch a surface with a temperature above their boiling point because evaporation forms a cushion of vapor preventing contact. The higher the surface’s temperature above the boiling point of the liquid, the more rapid evaporation occurs. The carbon material was heated in order to study this bounding phenomenon in the droplet collision boiling system.