REALIZE HIGHLY COORDINATED, RAPID AND SUSTAINABLE NUCLEATE BOILING IN MICROCHANNELS ON HFE7100
Flow boiling in microchannels on dielectric fluids is one of the most desirable cooling solutions for high power electronics. However, it is challenging to promote flow boiling performance due to their unfavorable thermal/hydraulic properties. Flow boiling in parallel and isolated microchannels has been extensively studied. In this study, five parallel microchannels (W=200 µm, H=250 µm, L=10 mm) are interconnected by 4×28 micro-slots (20 µm wide and 250 µm deep) from the middle section to the channel outlet. Our visualization study shows that these micro-slots designed as artificial nucleation sites can enable high frequency nucleate boiling by drastically reducing the bubble waiting time and remaining fully activated simultaneously. More importantly, such unique nucleate boiling phenomenon was observed to rapidly switch on and off coordinately in the neighboring channels, creating a highly desirable periodic rewetting mechanism to substantially delay CHF conditions and enhance heat transfer rates. Flow boiling in the innovative microchannel configuration has been systematically characterized with mass flux ranging from 462 kg/m2·s to 1617 kg/m2·s. Compared to plain-wall microchannels with inlet restrictors, flow boiling heat transfer coefficient (HTC) is enhanced up to ~172% at a mass flux of 462 kg/m2·s owing to the sustainable high frequency nucleate boiling. The peak value of effective HTC is ~60 kW/m2·K in the fully developed boiling regime. Moreover, CHF is substantially enhanced by ~76% at a mass flux of 1155 kg/m2·s because of the rapid and periodic rewetting enabled by these micro-slots. Note that drastic enhancements have been achieved without compromising two-phase pressure drop.