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Ceramic 3-D Printed Direct Winding Heat Exchangers for Thermal Management of Concentrated Winding Electric Machines

Direct cooling of the windings in a motor using oil offers more effective thermal management than conventional alternatives and can therefore increase the torque density of electric machines; however, this technique is limited by the thermophysical properties of the oil. The use of a direct winding heat exchanger allows a glycol-water coolant mixture to be used, which leads to a significant improvement in heat transfer and a reduction in the pumping losses compared to direct oil cooling. This article proposes ceramic 3-D printed direct winding heat exchangers (3D-DWHX), which can significantly improve the cooling of windings in electric machines due to the unique geometries enabled by 3-D printing. Ceramics are also capable of withstanding extremely high temperatures, which extends the application of the proposed 3D-DWHX. A closed-form analytical thermal model incorporating the temperature dependence of winding losses is proposed and used with empirical heat transfer correlations to design a microfeature enhanced 3D-DWHX. The ceramic 3D-DWHX was built and tested in a motorette that demonstrated a continuous current density of 35.7 ARMS/mm2, corresponding to a continuous specific power in the reference electric machine of at least 12.1 kW/kg while keeping the maximum winding temperature below 200 °C.