Microbubble Formation in Abrupt Condensation of Vapor Bubble Exposed to Subcooled Pool

Microbubble emission boiling (MEB) has been recognized for a potential phenomenon to be applied to devices such as next-generation heat exchanger for cooling small but high-power CPU and for long-duration exploring in the space/deep ocean; the MEB realizes higher heat flux than the critical heat flux known as ‘CHF’ accompanying with blowing out microbubbles smaller than 100 μm from the heated surface under highly subcooled condition. Invaluable information on characteristics of heat transfer and occurring condition of the MEB has been indicated by several research groups. Little knowledge on the mechanism of the MEB, however, has been accumulated; one of the reasons must be an immense complexity of the phenomenon of the boiling itself with interaction among solid-liquid-gas phases. In the present study, the authors focus on the condensing process of a vapor bubble in order to comprehend the mechanism of the microbubble formation and emitting processes in the MEB. In order to extract an interaction between the vapor and the liquid from a complex boiling phenomenon, a series of experiments of injection of superheated vapor to a subcooled pool are carried out. Comparison of the condensing process of the vapor and microbubble formation is made between the present vapor-injection experiment and conventional on-wire pool boiling experiment.