CEME Collaborator Bulent Sarlioglu with Research Assistant William Sixel at University of Wisconsin-Madison
Increasing the power density of electric machines operating in high ambient temperatures is a challenge as all the materials involved must be rated for operation at those temperatures. To improve cooling in electric machines exposed to temperatures greater than 400°C, a 3D-printed direct-winding heat exchanger (3D-DWHX) manufactured with ceramics is investigated in this project supported by the Grainger Center for Electric Machinery and Electromechanics. The 3D-DWHX has coolant channels in close contact with the windings and is electrically insulating. Therefore, a non-dielectric coolant (such as water mixtures) can be used as coolant. The T-shaped cross-section of the 3D-DWHX cools both the windings and the stator iron. As a result, cooling performance is improved compared to the water jacket, direct oil-cooled and air-cooled methods. A prototype ceramic 3D printed direct winding heat exchanger was designed and manufactured and is shown in Figure 11. The alumina ceramic material from Ceramco can withstand temperatures of 1650°C and is therefore suitable for very high temperature electric machines.
Motorette tests are used to experimentally verify various parts of the electric machine design, and in this case refers to two slots of a stator of an electric machine used to verify the thermal design of the ceramic 3D-DWHX. The key reasons for the test are to determine whether the 3D-DWHX has good thermal contact with the windings after being encapsulated and to verify the thermal analysis of the convection enhancing internal fins. Silicone encapsulation material is used to create a good thermal contact between the 3D-DWHX and the windings. The ceramic 3D-DWHX was tested at varying current densities and shown to enable a continuous current density of 33ARMS/mm2 while keeping the winding temperature below 132°C when used with a 30°C inlet temperature coolant (see Figure 12). With its performance validated in a motorette test, the ceramic 3D-DWHX concept can now be further explored for high temperature and high power density applications.