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/cm ² , superheat ~ 30 °C and the target two-phase thermal resistance ~ 0.043 cm ² -°C /W. The capillary-based microcooler achieves vapor quality >0.9, utilizing 50× 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.