A Systematic Investigation of the Effects of Microchannel Width, Depth, and Aspect Ratio on Convective Boiling Heat Transfer and Flow Regimes in Parallel Microchannels

Experiments are conducted with a perfluorinated dielectric fluid, Fluorinert FC-77, to investigate the effects of channel width, depth, and aspect ratio on flow boiling heat transfer and flow patterns in microchannels. Experiments are performed for a fixed mass flux of 630 kg/ms with eleven different silicon test pieces containing parallel microchannels of widths ranging from 100 μm to 5850 μm and depths ranging from 100 μm to 400 μm. Flow visualizations are performed using a high-speed digital video camera to determine the flow regimes, with simultaneous local measurements of the heat transfer coefficient and pressure drop. In recent work by the authors [1], it was shown that for a fixed channel depth, the heat transfer coefficient was independent of channel width for microchannels of width 400 μm and larger, with the flow regimes in these microchannels being similar; nucleate boiling was also found to be dominant over a wide range of heat fluxes. The aim of the present study is to expand the range of the microchannel dimensions considered, and specifically to investigate as independent parameters the effects of channel width and depth as well as the aspect ratio and cross-sectional area on boiling heat transfer in microchannels. Flow visualizations and heat transfer results show that the channel cross-sectional area is the important governing parameter determining boiling mechanisms and heat transfer in microchannels.