Evaporative Cooling of High Power Density Motors: Design and Analysis

Abstract

This study presents the design and thermal analysis of a 25kW high-power-density electric motor prototype. The design employs a capillary flow-assisted evaporative cooling system, resulting in a lightweight and power-dense architecture suitable for high-performance electric automobiles and electric aviation applications. The cooling system proposed in this study significantly reduces motor mass by eliminating the need for an external cooling jacket. This design differs from traditional internally cooled motors since a highly wetting dielectric coolant is used to facilitate evaporation within the stator core windings. Furthermore, in place of the usual slot liner material, wicking structures are used to aid coolant flow into the stator core slots. In this way, two-phase flow can be maintained around the stator windings. Novec-7200 dielectric coolant with a saturation temperature of 76 °C at atmospheric pressure is used as the working fluid within the electric motor. The motor is semi-flooded with coolant; therefore, the end windings are also cooled via evaporation. A thin composite sleeve separating the rotor and stator cores of the electric motor was used to prevent coolant from entering the air gap, thus preventing inefficiencies due to friction against the rotor as well as damage to the permanent magnets.