Thermal Performance Study of an Electric-Motor Using Innovative Indirect Cooling Methods

Abstract

A 70 kW Permanent Magnet Synchronous Motor (PMSM) is selected for the present thermal management study, where detailed loss calculations including stator iron losses, copper losses, rotor and magnet losses are applied as distributed heat sources in the simulation. A mesh sensitivity analysis is performed, and an optimized mesh configuration with 14 prism layers is adopted to accurately resolve near-wall heat transfer. The numerical model is validated using an energy balance, ensuring the accuracy and reliability of the thermal predictions. Two indirect liquid-cooling strategies helical and meander cooling channels are evaluated using 3D steady state CFD simulations. Although the Helical channel demonstrates approximately 20% higher thermal performance (TPF), the Meander channel is selected for further analysis due to its lower pressure drop, improved flow uniformity, and better suitability for practical motor integration. Thermal enhancement is further explored using BN and CNT nanofluids dispersed in an ethylene-glycol (EG) base fluid. Increasing the BN and CNT nanoparticle concentrations leads to a marked decrease in average temperatures across stator, windings, rotor, and magnets, indicating enhanced heat removal capability. For both nanofluids, the representative maximum reductions achieved are 8.6% at the stator, 7.7% at the slot windings, 7% at the end windings, and approximately 3.2% across the rotor and magnets. An optimal concentration range is observed for both nanofluids. BN shows a clear and substantial improvement up to 6% concentration, beyond which temperature reduction becomes marginal. Similarly, CNT exhibits strong improvement up to 1% concentration, after which further increases result in minimal additional thermal benefit. These results demonstrate that nanofluids significantly enhance PMSM cooling performance, with well-defined saturation limits guiding their effective usage in next-generation EV motor thermal management.