SUMMARY

Dielectric fluids, including refrigerants, are electrically inert and are a good candidate as working fluid in two-phase microsystem cooling applications. In this study, R245fa is investigated for flow boiling in a microgap of height 200 μm. Circular cylindrical pin fins of spacing 200 μm (dense device) and 400 μm (sparse device) are studied. For heat fluxes up to 498 W/cm2, mass flux values ranging from 789 kg/m2s to 7896 kg/m2s and inlet temperatures of 13 oC and 18 oC, average two phase heat transfer coefficient up to 60 kW/m2K are measured. High speed flow visualizations at frame rate of 2229 fps elucidate the flow boiling patterns inside the microgaps. The visualizations have shown different two flow regimes including bubbly and foggy that are generated in the pin finned area. The surface temperatures are obtained for a wide range of heat flux.