Flow Boiling Instabilities in Microchannels and Means for Mitigation by Reentrant Cavities

The ability of reentrant cavities to suppress flow boiling oscillations and instabilities in microchannels was experimentally studied. Suppression mechanisms were proposed and discussed with respect to various instability modes previously identified in microchannels. It was found that structured surfaces formed inside channel walls can assist mitigating the rapid bubble growth instability, which dominates many systems utilizing flow boiling in microchannels. This, in turn, delayed the parallel channel instability and the critical heat flux (CHF) condition. Experiments were conducted using three types of 200×253μm2 parallel microchannel devices: with reentrant cavity surface, with interconnected reentrant cavity surface, and with plain surface. The onset of nucleate boiling, CHF condition, and local temperature measurements were obtained and compared in order to study and identify flow boiling instability.