Experimental investigation on critical heat flux measurement in parallel microchannel heat sink at low mass fluxes

Flow boiling experiments in microchannels under low mass fluxes have rarely been reported in the literature. In this study, flow boiling critical heat flux (CHF) for a parallel straight copper microchannel heat sink with 41 channels and hydraulic diameter of 420 µm (width: 300 µm; height: 700 µm) is reported under low mass fluxes(< 100 kg/m 2 s). The flow patterns reveal that the inertial force will be too low to flush the bubble downstream. The heat transfer coefficient was observed to decrease with an increase in the heat flux or vapor quality, which pointed toward convective boiling dominancy inside the channels. When approaching the CHF, the vapor flowed back to the heat sink’s inlet plenum, resulting in a flow blockage, which is the main factor for the CHF occurrence.