Mechanism of Critical Heat Flux for Convective Boiling of FC-72 in a Diverging Microchannel Heat Sink

The present study explores experimentally the mechanism of critical heat flux (CHF) of FC-72 in a 10 parallel diverging microchannel heat sink with different distributions of artificial nucleation sites (ANS). The effects of mass flux and number of ANS with or without degassing on CHF of FC-72 are investigated. During CHF, flow visualization shows that the dryout of liquid film in annular flow appears near the outlet region with frequent rewetting of liquid film with slug bubble or rewetting of liquid column on the dryout surface. The results demonstrate that diverging microchannels with ANS distributed uniformly along the whole channel (Type-2 system) shows better flow boiling performance and higher CHF and can be recommended as a high-heat-flux microchannel heat sink. Moreover, five CHF correlations in the literature for flow boiling in microchannels are compared, which generally underpredict the CHF data of the present study. This suggests that the present diverging design with ANS enhances the CHF. The comparison also reveals that Bowers and Mudawar correlation predicts the present data best with MAE of 15.8% for the type-2 system.