Flow boiling of HFE-7100 in microchannels: Experimental study and comparison with correlations

The main objective of this research was the design and test of a multi-microchannels heat sink for electronics cooling applications, which operates at system pressure near atmospheric and low mass flow rates. HFE-7100, a dielectric and eco-friendly coolant, was chosen as the working fluid. Twenty five rectangular microchannels, of width 0.7 mm and height 0.35 mm giving a hydraulic diameter of 0.46 mm, were fabricated from oxygen-free copper with a base area of 500 mm2. The channels in-between wall was 0.1 mm thick. Five mass fluxes ranging from 50 to 250 kg/m2 s were tested at fixed inlet sub-cooling near 5 K. The effect of heat flux, mass flux and vapour quality on the local heat transfer coefficient was investigated. Four flow patterns namely; bubbly, slug, churn and annular flow, were visualized using a high-speed camera mounted on a microscope. In this study, the maximum flow boiling heat transfer coefficient was 12.71 kW/m2 K at mass flux of 250 kg/m2 s. A comprehensive comparison with experimental results was conducted including flow pattern maps, heat transfer and pressure drop correlations. Some of the correlations, proposed for conventional channels and microchannels, showed good agreement with the present results.