Flow-Assisted Evaporative Cooling for Electric Motor

Abstract

This article examines a novel concept of flow-assisted latent heat-driven two-phase evaporative cooling (EC) confined in-between slot liner and active-winding of electric motor. Wicking microstructure-enhanced PDMS liner axially sucks coolant in the form of thin film between the PDMS liner and active-winding and eventually enables thin-film evaporation on the outer surface of the active-winding. Therefore, EC-based thermal management eliminates a major thermal resistance between the winding and the coolant and enhances the heat extraction from the winding without compromising the electromagnetic (EM) performance. Two-way coupled EM—computational fluid dynamics/heat transfer (CFD/HT) and EM—lumped parameter thermal network (LPTN) models have been developed to assess the electrothermal performance of the EC for steady and transient conditions. Taking a case study of a 125-kW jacket-cooled BMW i3 motor and dielectric coolant FC-84, EC is shown to be capable of handling a maximum steady-state rms current density of 26 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at an evaporative HT coefficient of 5000 W/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{2}\cdot \text {K}$ </tex-math></inline-formula> , which is about 78.7% higher compared to the traditional jacket cooling (JC). In the case of EC, a maximum steady-state and transient rms current density of 30 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (106.2% higher compared to the JC) and 40.8 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, have been realized by using high thermal conductivity epoxy (1.9 W/m.K) impregnation material. The thermal performance of the EC is also assessed and compared with JC over a dynamic drive cycle. Finally, a motorette testing has been performed to demonstrate the applicability of the proposed EC method and validate the developed modeling framework.