TED-AJ03-413 Bubble Coalescence and Its Heat Transfer Effects

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A boiling heat transfer study with controlled coalescence of bubbles has been performed by producing dual individual bubbles from microheaters (0.27mm×0.27mm). The effects of separation distances between the bubbles were investigated with various heater configurations. Each heater was kept at a nominally constant temperature during the experiment so that the time-and space-resolved heat flux could be measured at a frequency of about 4,500 times per second. In each case, the heaters were set at the same superheat, which was varied from 35℃ to 85℃. We have recorded two major heat flux spikes for a typical cycle of boiling with coalescence. The first one corresponds to the departure and nucleation of bubbles; the second one is to 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 coalescence. Based on the heat fluxes measured by the data acquisition system, we found that the heat transfer enhancement rate becomes higher as the separation distances among bubbles increase. The heat transfer enhancement is attributed to rewetting of the dry heater surface and turbulent mixing effects.
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