Experimental characterization of immersion-cooled devices at elevated ambient temperatures

Immersion cooling of power electronic equipment can avoid device derating at elevated ambient temperatures and thereby increase power density. In this paper, a test bench is presented that can be used to characterize the heat transfer from fluid-immersed electrical components inside cylindrical volumes. Since the thermal properties of coolants are themselves temperature dependent and vary locally, the temperature on the perimeter of the enclosure must be controlled independently from the power dissipation inside in order to establish realistic operating conditions. Ceramic heater elements enable continuous ambient temperatures up to 120°C. The test bench has been used for the characterization of two different heatsink arrangements and two different coolants (pentaeryt tetraester and fluorpercarbon). Results are presented and compared with a simplified analytical model. Modelling results are furthermore extended to mineral oil, silicone oil, and silicate ester.