Coalescence of dual bubbles on micro heaters

This experiment is based on a heating surface consisting of micro heaters where the temperature of each heater can be individually controlled by an electronic feedback loop similar to those used in hot-wire anemometry. The power consumed by the heaters throughout the cycle of individual bubble growth, coalescence and departure was measured at high frequencies, thus the heat flux and its variation were obtained. At the same time, visualization of bubbles' behaviour by a fast CCD camera has been performed to gather more information. By combining the heat flux data closely with the visualization result, we have found that the single bubble's heat flux variation correlates with the separate stages of its life cycle: nucleation, growth, detachment and departure. By careful timing and control of two individual heaters, we were able to grow two individual bubbles side-by-side. The coalescence of these two bubbles would take 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. 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.