Realizing highly coordinated, rapid and sustainable nucleate boiling in microchannels on HFE-7100

Abstract Flow boiling in microchannels using dielectric fluids is one of the most desirable cooling solutions for high power electronics. However, it is challenging to promote the flow boiling performances, particularly critical heat flux (CHF), due to their unfavorable thermophysical 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) starting 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 rapid switch on–off harmonically coordinated nucleate boiling in the neighboring channels creates a highly desirable periodic rewetting mechanism to substantially delay CHF conditions and enhance heat transfer rate. Flow boiling in this innovative microchannel configuration has been systematically characterized with mass flux ranging from 462 kg/m 2 ∙s to 1617 kg/m 2 ∙s. Compared to plain-wall microchannels with inlet restrictors (IRs), flow boiling heat transfer coefficient (HTC) is enhanced up to ∼172% at a mass flux of 462 kg/m 2 ·s primarily owing to the enhanced latent heat transfer including nucleate boiling and thin film evaporation. The peak value of effective HTC is ~60 kW/m 2 ·K in the fully developed boiling regime. Moreover, CHF is substantially enhanced by ∼76% at a mass flux of 1155 kg/m 2 ·s owing to the rapid and periodic rewetting enabled by these micro-slots. Such drastic enhancements have been achieved without compromising two-phase pressure drop.