Microchannel Cooling of Electric Drive Motors

Technical Objectives

Heat exchangers are used in a wide variety of applications, from heat transfer between two or more fluids to removing heat from objects. This project involves the application of microchannels to remove heat from u-core electro-magnets used in a new type of electric motor developed by Apex Drives Laboratories. The motor has the potential for developing a very high torque and power density, which translates into compact motors for electric vehicles and other mobile and stationary uses. Management and removal of the generated heat in the motor is critical to sustained, reliable operation. In this motor, power is dissipated in a confined space leading to thermal management issues. In order to, for example, double the motor’s sustained torque density, a microchannel liquid cooling device has been proposed as a solution.

Results to Date

A microchannel heat exchanger in the form of an enveloping jacket was proposed to fit over the u-core assembly as shown in Figure 1. Reasons for pursuing a microchannel device include overcoming the compact arrangement in the motor as well as providing a liquid cooling solution to enhance performance.

The design parameters that were considered in the jacket-style heat exchanger included flow direction and flow distribution. The first design was a proof-of-concept, and footprint was not considered a primary design characteristic. It was considered in later designs. The two flow directions that were considered included flow parallel to the windings as well as perpendicular to the windings. These designs are shown with flow direction in Figure 2.

The parallel flow cooling jacket was developed further for experimental work. Polymeric material was used for construction with temperature limits of 100+ C for the upper coolant range expected. The assembled device was used to verify extended operation at the upper temperature design limit with internal pressures of 5 psig. Also, experiments were performed where the windings were powered by an AC signal at over 2x the design current for the air-cooled version of the motor. Windings and core assembly remain at an operational temperature lower than that of the air-cooled version.

Implications

The project is on-going with the development of a design where the cooling solution is built into the motor. Space constraints dictate a very compact design. Testing will progress with the liquid-cooled motor once fabrication of parts and assembly of the motor has been completed. The implications of this work include the development of high torque, high power density motors that can operate at much improved performance factors over air-cooled designs.

For Additional Information

Contact project manager Richard Peterson for additional details about the project.