Practical Considerations Relating to Immersion Cooling of Power Electronics in Traction Systems

Junction-to-fluid thermal resistivities R^´´jf, of two dual-side-soldered insulated gate bipolar transistor (IGBT) modules immersion cooled in a hydrofluoroether C₃F₇OCH₃ liquid were measured experimentally. R^´´jf = 0.040°C·cm²/W for 0.144 cm² die at a peak heat flux of 1180 W/cm² and 55 A, and 0.11 ^°C· cm²/W for 1.46 cm² die at a peak heat flux of 550 W/cm² and 305 A. A technique for automatic in situ degassing that would reduce manufacturing cost and permit field servicing of immersion systems that reach subambient pressure when idle showed fluid loss rates of 0.3 g per 100 cm³ of air vented, roughly 1/100th that expected from an HFC-134a air conditioning system with a similar leak. Experiments to quantify packaging density and fluid requirements suggest that 100 cm³ of fluid is required to dissipate 1 kW and packaging density is limited only by the electrical bus geometry.