Bubble Behaviors in Quasi-steady Pool Boiling in Microgravity

Bubble behaviors, particularly the number density, size and velocity of bubbles and other relevant factors, in quasi-steady pool boiling on a plain plate in microgravity aboard the Chinese recoverable satellite SJ-8 were reported and analyzed in the present paper. Degassed FC-72 was used as the working liquid in the space experiments. The heating voltage was controlled to increase exponentially with time to achieve quasi steady state of pool boiling process. It's found that primary bubbles generated continually, slid on the surface, and coalesced with each other to form a larger coalesced bubble. The coalesced bubble engulfed small bubbles around it, and oscillated on the heating surface throughout the boiling process in microgravity. Generation of primary bubbles was also observed underneath the coalesced bubble. The growth rate of bubbles decreased with the increase of subcooling, which is caused by the strong condensation near the top of the coalesced bubble.