  Recently, next-generation vehicles such as electric vehicles (EV) and fuel cell vehicles (FCV) are attracting attention from the viewpoint of environmental protection.  One of the key electronic devices in the next-generation vehicles is an automotive inverter that controls a motor.  Compact and energy-saving type of inverters are expected using SiC semiconductor that can significantly reduce power loss.  There is, however, an issue that the cooling system needs much larger pumping power because the heat generation form the SiC chip drastically increases due to downsizing the SiC chip and also increase in local current.  The heat from the inverter is generally removed by a liquid-cooled system that circulates coolant such as LLC with a pump.  Such a system is not preferable from the viewpoint of energy-saving.  In that sense, completely new cooling technology, which enables small pumping power operation or pumpless operation, becomes a breakthrough technology toward the spread of the next generation vehicles.

  Against such a background, our group has proposed a new two-phase immersion cooling in which a lotus type of porous copper is jointed onto a grooved heat transfer surface.  This boiling surface utilizes breathing phenomenon that can supply liquid toward the heat transfer surface by vapor discharge and that can suppress generation of coalesced bubbles.  In previous studies, the effect of the groove size on the critical heat flux was verified, and the critical heat flux of 534 w/cm^2^ was achieved at the maximum \[1\].  It was confirmed that the cooling liquid was sucked from the top of the lotus copper in the process of injecting the vapor from the groove.  If this phenomenon can be promoted further, it is expected that the critical heat flux also increases.  The purpose of this study is to improve the critical heat flux by controlling the breathing phenomenon.  

  The experimental apparatus is mainly composed of a heated copper block, a glass vessel, and a condenser.  Square grooves with the width of 1.0 mm are fabricated at the heat transfer surface, and a lotus copper plate is soldered onto the grooves.  The lotus copper plate is 10 mm ×10 mm, which is the same size as the heat transfer surface, and the thickness is 2.0 mm.  The average hydraulic diameter of the pore of the lotus copper is 0.56 mm, and the porosity is 66 %.  In order to control the breathing phenomenon, a 1.0 mm cube of insulating material is embedded at the center of each groove.  By plugging the center of each groove, we expect the breathing phenomenon to be symmetrical toward each exit of the groove.  The coolant is distilled water, and a saturated pool boiling test is performed under atmospheric pressure condition.  The results show that the critical heat flux is improved by 83 W/cm^2^ up to 531 W/cm^2^ by plugging the groove, while the critical heat flux is 448 W/cm^2^ before plugging the groove, which proves that it is sufficiently possible to increase the critical heat flux by controlling the breathing phenomenon.


Critical Heat Flux Improvement of Two-Phase Immersion Cooling by Controlling Breathing Phenomenon

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

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