Professor Bulent Sarlioglu, CEME Collaborator, University of Wisconsin-Madison

This research project presents an additively manufactured heat exchanger for rapid prototyping and active cooling of an electric machine. A rectangular in-slot heat exchanger with a coolant is used to cool the winding. The heat exchanger is optimized for a high heat-transfer coefficient, high-temperature operation, water tightness, and additive manufacturing capability. Two different 3D printing materials, which can withstand a maximum temperature of 110°C and 200°C, respectively, have been considered for the heat exchanger. The winding thickness is calculated using these maximum temperature limits for the desired slot-current density. A copper thickness of 1.3 mm corresponds to a peak slot-current density of 27 Arms/mm2 for a heat-transfer coefficient of 3000 W/m2K. This winding is realized by a flat wire on each side of the heat exchanger, shown in Figure 32a and b. A preliminary mock-up unit is shown in Figure 33  with the flat wire, a dummy heat exchanger, and black cubes that hold the assembly in place temporarily.

Another winding alternative is presented using printed circuit boards (PCBs). The heat exchanger remains the same, but a PCB is used as the winding rather than a flat wire, as shown in Figure 1c and d. PCBs make the fabrication easy but reduce the slot-current density to around 13 Arms/mm2, which requires double the slot area for the same machine. The hotspot temperature for the flat wire winding is kept around 190°C, and for the PCB winding, around 110°C, which is the limit for materials used. If PCBs are mass-produced and assembled automatically, this can be a lower-cost option than flat winding. These concepts were published and presented at the 2022 IEEE ITEC conference and at the 2022 IEEE EPE conference.

A complete system is under fabrication with the following characteristics that were established in accordance with the test setup available.

This research is funded by the Grainger Center for Electric Machinery and Electromechanics.

Table I:

Machine topology 12/10 spoke type IPM
Rated speed 3000 rpm
Max. Continuous torque 20 N-m
Phase current 30 Arms
Fill factor 42 %
Max. Winding temperature 190 °C
Targeted copper current density 67 Arms/mm2
Targeted slot current density 28 Arms/mm2


Figure 32(a): Flat wire winding with heat exchanger and stator core

Figure 32(b): b. Cross section

Figure 32(c): PCB winding with heat exchanger and stator core

Figure 32(d): Cross section

Figure 33: Hardware prototype for flat-wire winding