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=0.040degC-cm²/W for 0.144 cm² die at a peak heat flux of 1180 W/cm² and 55 Amps and 0.11degC-cm²/W for 1.46 cm² die at a peak heat flux of 550 W/cm² and 305 Amps. A technique for automatic in situ degassing that would reduce manufacturing cost and permit field servicing of immersion systems that reach sub-ambient pressure when idle showed fluid loss rates of 0.3 g per 100 cc of air vented, roughly 1/100^th that expected from an HFC-134a air conditioning system with a similar leak. Experiments to quantify packaging density and fluid requirements suggest that 100cc of fluid is required to dissipate 1kW and packaging density is limited only by the electrical bus geometry.