Thermal Characterization of Two-Phase Cooling using Embedded Microchannels in a High Current Density Electric Motor

The transportation sector is rapidly transitioning from fossil fuels to hybrid and fully electric propulsion alternatives. Aviation presents a challenging application in this transition, in part due to the strict power density (kW/kg) targets required for propulsion using electric motors. Scaling of traditional motor designs to higher powers increases the component weight as well as that of auxiliary infrastructure, specifically, the thermal management system that must also increase in capacity. Integration of advanced cooling methods within the motor windings has the potential to enable operation at increased powers without compromising the overall system weight. In this study, an additively manufactured stator section prototype with embedded microchannels for cooling is constructed to demonstrate the high current density operation of Litz wire coils. The cooling performance is characterized using two-phase flow of a dielectric refrigerant (R1233zdE) and tested under steady-state conditions. Wall-embedded thermocouples inserted along the flow length of the channels, as well as an electrical-resistance-based average coil temperature measurement, enable characterization of the flow boiling heat transfer coefficient and ground insulation thermal resistance. Under this cooling configuration, a peak current density of 30.4 A/mm² was achieved at a safe operating peak coil temperature of 128 °C with a heat transfer coefficient of 2530 W/m²K. This thermal performance allows for high electric loading of machines to meet the propulsion power density requirements of electrified aviation.