Heat Transfer and Bubble Behaviors in Microgravity Pool Boiling in ESA Parabolic Flight Experiment

To clarify the relation between local heat transfer and bubble behaviors in pool boiling under microgravity conditions, a transparent heating surface, which has multiple array of heaters and temperature sensors, and experimental apparatus were developed to make the measurement of local heat transfer characteristics and the observation of liquid-vapor behavior simultaneously possible. In this paper, preliminary results of the microgravity pool boiling experiments conducted in ESA 49th parabolic flight campaign were reported. It was found that the bubble behaviors were strongly affected by the fluctuation of gravity in low-gravity period, and the effect of gravity on the bubble behaviors and heat transfer was dependent on the liquid subcooling. In the case of high subcooling, boiling bubbles were pushed on to the heating surface during positive low-g, and heat transfer due to microlayer evaporation was enhanced. On the other hand, during negative low-g period, bubbles detached from the heating surface, and the heat transfer rate was decreased. This trend, however, completely inverted at low subcooling. In positive low-g, the heat transfer was deteriorated because the dry patch was extended on the heating surface.