High power density two-phase cooling in microchannel heat exchangers

This paper reports two-phase cooling in compact cross-flow microchannel heat exchangers with high power density up to 180 W/cm³. The performance is enabled by high-speed air flow through microchannels and two-phase condensation of refrigerant R245fa. The heat exchangers were realized in 1 cm³ blocks of copper alloy, using micro-electrical-discharging machining. Two heat exchanger designs were analyzed, fabricated, and tested. The first device has 150 air-side channels of diameter 520 μm, and the second device has 300 air-side channels of diameter 355 μm. In both cases the refrigerant channels are 2.0 × 0.5 mm². The heat exchangers were operated with Reynolds number between 7500 and 20,500 for the air flow and with mass flux between 330 and 750 kg/m² s for the refrigerant flow. The refrigerant temperature at the channel entrance was 80 °C, which is near the maximum operating temperature for some electronic devices. For comparison purposes, the devices were also tested with single-phase refrigerant flows. This work demonstrates the potential of high power density heat exchangers that leverage advanced manufacturing technologies to fabricate miniature channels.