Development of a Hybrid Capillary-Driven Single-Phase and Two-Phase Micro-Cooler for Power Electronics Cooling

We developed a hybrid single- and two-phase capillary-based microcooler consisting of parallel microchannels with hydrophilic wicks for power electronics. The presented approach overcomes the conventional pumped-only flow two-phase cooling limitations, such as flow instabilities and large temperature superheat in confined microchannels. We further conducted a parametric study of the microcooler and investigated the boiling dynamics of capillary flow using high-speed imaging. While the proof-of-concept microcooler is demonstrated on a copper substrate and free-form liquid supply setup, it can be easily implemented in the copper layer of a direct bonded copper (DBC) substrate of the power module package. The capillary-driven microchannel cooler demonstrates a significant performance improvement compared to conventional single/two-phase closed-microchannel coolers, achieving maximum heat flux ~700 W/cm2, superheat ~30 °C, and the target two-phase thermal resistance ~0.043 cm<inline-formula> <tex-math notation="LaTeX">$^{2}\cdot ^{\circ }\text{C}$ </tex-math></inline-formula> /W. The capillary-based microcooler achieves vapor quality > 0.9, utilizing <inline-formula> <tex-math notation="LaTeX">$50\times $ </tex-math></inline-formula> smaller flowrates compared to two/single-phase conventional microchannel coolers. Successful implementation of the capillary-driven microcooler would result in significant downsizing of the cooling system for electric vehicles.