INVESTIGATION ON BEHAVIOR OF BUBBLES GENERATION IN A DROPLET IMPINGING ON A HEATING SURFACE

Abstract

Cooling method in which fine water droplets are sprayed onto a high-temperature surface has been considered as a method that has a higher heat transfer coefficient than a cooling method in which cooling water is circulated over a high-temperature surface. The purpose of this study is to observe and clarify the mechanism of generation behaviors of bubbles in the center of droplet when a water droplet collided with a heating surface. A transparent sapphire was used as the heating surface in order to clearly catch the bubble which arises at the solid-liquid contact surface. Boiling behavior was photographed by a high-speed video camera from the backside direction of the surface. Bubbles’ fluctuation was measured in order to determine the behavior during boiling process. Also, two different heating surfaces were used to determine the effect of surface wettability. Alas, the sapphire heated surface pretreated with hydrogen peroxide plasma had better wettability and increased bubble point density than the original sapphire surface.