Selecting cooling methods for electric motors

• Cooling methods for electric motors are reviewed and quantitatively compared. • The heat transfer coefficient and the maximum heat flux are used as key performance indicators. • Suggestions are provided for the selection of cooling methods for electric motors. • Challenges and the future direction of cooling method development are analysed. Electric motors (EMs) are the key component for electric vehicles (EVs) and electric aircrafts (EAs). To achieve high performance, the working temperature of EMs has to be well controlled as high temperature can accelerate the motor degradation and even cause failure. Although many methods have been developed for EM cooling, there lacks guidance about how to select the cooling methods to meet the requirements. This review provides a comprehensive analysis about the existing technologies using the heat transfer coefficient (HTC) and the maximum heat flux (MHF) as key performance indicators (KPIs), including indirect and direct air-based cooling, liquid jacket-based cooling, spray cooling, heat pipe-based cooling, potting cooling, immersion cooling, inter-winding cooling, intra-winding cooling, and PCM cooling. Based on performance comparisons, suggestions are provided to facilitate the selection of cooling methods when designing EMs and optimizing the configuration of EVs and EAs.