Enhanced vapor bubble condensation and collapse with ultrasonic vibration

Investigation was carried out concerning the effects of ultrasonic field on the condensation and collapse of vapor bubbles in a quiescent subcooled pool. Experimental results showed that the vapor bubbles were split gradually at liquid subcooling of 15-30 K, while were collapsed into many tiny bubbles when subcooling was higher than 40 K. Once the ultrasonic vibration was applied, capillary waves would arise on the bubble surface, and the threshold of liquid subcooling for collapsing the bubble was diminished to 20-26 K. Further, the presence of capillary wave increased the contacting area of the bubble with the cold bulk, and disturbs the thermal boundary layer in the vicinity of the vapor-liquid interface, resulting in the enhancement of condensation process. Therefore, the inertial shock of liquid on the vapor bubble was much stronger than that without ultrasonic vibration at the same liquid subcooling. This would also accelerate the instability of the bubble surface in turn. Based on the experimental data at liquid subcooling of 15-60 K, empirical correlations were given to predict the condensation heat transfer of vapor bubbles with and without ultrasonic, with deviations within ±30%.