High-frequency oscillation of coalesced vapor bubbles and resultant ambient liquid motion in microbubble emission boiling in subcooled pool

High-frequency oscillation of coalesced vapor bubbles and resultant ambient liquid motion in the microbubble emission boiling (MEB) is experimentally investigated. A new approach is introduced to detect the occurrence of MEB by monitoring the temperature fluctuations of the heating surface. Frequency and temporal irregularity of corresponding vapor bubble oscillation are evaluated by high-speed imaging over a designated range of the degree of subcooling. The resultant ambient liquid behavior around the heating surface is measured via the particle image velocimetry by detecting the emitted tiny bubbles as tracers. Through the spatial–temporal variation of the velocity field of the ambient liquid, the macroscopic liquid path around the heating surface is unveiled against the variations of MEB regime.