Impact of Flow Dynamics on the Heat Transfer of Bubbly Flow in a Microchannel

Abstract

During nucleate flow boiling, the bubble dynamics affect the liquid flow field and the corresponding heat transfer process through several distinct mechanisms. At the microscale, this effect is different than at the macro scale partly because the bubble dimensions are comparable to the characteristic length scale of the channel. Since the process involves several mechanisms, an attempt to isolate and study them independently from one another is desired in order to extend knowledge. To remove the evaporation effect from the heat transfer process, noncondensable gas bubbles were introduced upstream of a 1 mm أ— 1 mm heater into a 220 خ¼m deep and a 1.5 mm wide microchannel and the heat transfer coefficient was measured and compared to singlephase liquid flow. High speed imaging and micro particle image velocimetry (خ¼PIV) measurements were used to elucidate the bubble dynamics and the liquid velocity field. This, in turn, revealed mechanisms controlling the heat transfer process. Acceleration and deceleration of the liquid flow due to the presence of bubbles were found to be the main parameters controlling the heat transfer process.