DYNAMICS OF CONTACT ANGLE DURING GROWTH AND LIFTOFF OF BUBBLES AT A SINGLE NUCLEATION SITE IN FLOW BOILING

摘要

Contact angle is a critical parameter needed in the mechanistic models for the prediction of flow boiling heat transfer. In this paper, variations of upstream and downstream contact angles for a single vapor bubble in flow boiling on horizontal and vertical surfaces were investigated experimentally. The nucleation site is a well-characterized cavity, which was etched on a highly polished silicon wafer surface using micro-fabrication techniques. Water at one atmosphere pressure was used as the working fluid. Photographic images of the bubble were recorded during its inception, growth and liftoff by using high-speed video system and analyzed by an image-processing program. The results provide clean data on the dependence of upstream and downstream contact angles on surface orientation and flow velocity.