Experimental research on subcooled flow boiling heat transfer performance and associated bubble characteristics under pulsating flow

An experimental research was conducted to study the effects of non-reversing pulsating flow on subcooled boiling heat transfer performance on a chip using FC-72 in a horizontal rectangular narrow channel with a hydraulic diameter of 8.57 mm. The associated bubble characteristics were also analyzed. In the experiment, the pulsating period varied from 3 s to 20 s with the pulsating amplitude changing from 20% to 50% for the inlet liquid subcooling of 35 K. The result indicates that time-average boiling curves under pulsating flow overlapped with that under steady flow, and the heat transfer coefficient was not affected by flow pulsation. The critical heat flux (CHF) decreased compared with that under time-average steady flow, and the decrease would be further aggravated with the increases of the pulsating amplitude or the decrease of the pulsating period. The CHF under pulsating flow was limited by the lowest flow rate. Bubble behavior changed periodically with the flow rate, and bubble accumulation effect under pulsating flow was found. There was no slide process during bubble growth, and the bubbles near the CHF tended to be bigger and more round-like with no obvious deformation. This phenomenon was caused by the virtual mass force acting on the bubble due to fluid acceleration.