Ceramic 3D Printed Direct Winding Heat Exchangers for Improving Electric Machine Thermal Management

Direct winding oil cooling offers more effective cooling 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 (DWHX) 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 paper proposed ceramic 3D printed direct winding heat exchangers (3D-DWHX) which can significantly improve the cooling of concentrated windings in electric machines due to the unique geometries enabled by 3D printing. Ceramics are also capable of withstanding extremely high temperatures. 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 micro-feature enhanced 3D-DWHX. The ceramic 3D-DWHX was built and tested in a motorette and shown to enable a continuous current density of 30.7 A(RMS)/mm(2) while keeping the maximum winding temperature below 132 degrees C.