Coalescence of bubbles in nucleate boiling on microheaters

In this paper, an experiment was performed which is based on a heating surface consisting of microheaters where the temperature of each heater can be individually controlled by an electronic feedback loop. The power consumed by the heaters throughout the cycle of individual bubble growth, coalescence, detachment and departure was measured at high frequencies, thus the heat flux and its variation were obtained. By a careful timing and control of two individual microheaters, we were able to produce two individual bubbles side-by-side. The coalescence would takes place when they grow to a certain size that allows them to touch each other. We have recorded two major heat flux spikes for a typical cycle of boiling with coalescence. The first one corresponds to the nucleation of bubbles; the second one is for the coalescence of the two bubbles. We found that the heat flux variation is closely related to the bubble dynamics and bubble-bubble interaction. By comparing with the single bubble results without coalescence, we also found that the heat transfer is highly enhanced due to the coalescence.