Coupled bubble dynamics and interaction mechanisms of adjacently nucleated vapor bubbles under subcooled pool boiling regime

The present work investigates the plausible modes of interaction between two adjacently located vapor bubbles growing on high wettability surface during subcooled nucleate pool boiling. The study becomes important as the phenomenon of bubble interaction has a significant impact on the resulting bubble dynamic parameters as well as on microlayer dynamics of the respective vapor bubbles. As against the symmetric growth of microlayer in the case of isolated pool boiling, microlayers of mutually interacting vapor bubbles no longer remain symmetric and tend to deplete relatively faster, thereby influencing the resulting wall heat transfer rates. Toward this, the microlayers and dynamics of adjacently located interacting vapor bubbles have been mapped in a simultaneous manner using thin-film interferometry and high-speed rainbow schlieren deflectometry as a function of varying subcooling levels. Results of the experiments revealed that parameters such as non-dimensional spacing between the two vapor bubbles, supplied heat flux, and degree of subcooling have a strong impact on the mechanism of bubbles' interaction, which, in turn, influence the bubble departure frequency, bubble diameter, and microlayer dynamics. Three dominant modes of bubble interaction, hydrodynamic interaction (HI), thermal interaction (TI), and coalescence (C), were identified as a function of the level of subcooling. Quantification of the experimental data showed that the equivalent diameter of the vapor bubble increases with an increase in the level of heat flux, while it decreases with an increase in the subcooling level. Additionally, the secondary nucleation affects the liftoff time and movement of the primary bubble and can hydrodynamically deplete the microlayer of the first bubble even when the bubbles are far apart, with the depletion rates showing a strong dependence on the growth rate and location of the secondary nucleation.