Advances in power density and efficiency — Circumferentially vs. conventionally cooled electric motors

Circumferential cooling as inexpensive but highly effective cooling technique for machines with high torque density is compared to water jacket cooling in terms of compactness and power efficiency of the resulting motor. Technological aspects are discussed, and simple mathematical introduction to this comparison is given. A particular traction motor with water jacket cooling is then compared to a circumferentially cooled machine with the same torque and same total volume. Constant torque density is validated by thermal FEM simulations. Material properties, heat sources and boundary conditions are calculated analytically and by the use of FEM flow simulations.