Analytical Modeling and Parameter-Based Evaluation of Cooling Technologies for MW-Class High Specific Power Electric Motors in Electrified Aircraft Propulsion Systems

Power density and efficiency of electric motors in electrified drive trains are key aspects for electric aircraft propulsion. To increase both, temperature levels within electric machines must be decreased and high quantities of heat generated by electrical losses in critical components must be removed effectively. Hence, highly effective, capable and efficient cooling systems are crucial to enable electrification of aviation. A step towards an optimal cooling system for MW-class electric motors for electrified aircraft propulsion is to identify the most suitable cooling technique for each of the main heat sources within the machine. Goal of this paper is therefore to analytically model preselected cooling techniques, to define specific numerical parameters enabling their objective and reproductive evaluation and finally to perform their comparison aiming for identification of the optimal technologies in terms of high heat discharge ability and low energetic effort. Firstly, an analytical modeling of the thermal and fluid dynamical heat transfer processes for each of the preselected cooling techniques is executed. On this basis, comparative parameters are derived for each model to evaluate its effectiveness, capability and energetic efficiency of heat dissipation from the electric motor. Subsequently, identification of the optimal cooling technique for each component can be performed through comparison of the obtained comparative parameters. The results of the quantitative evaluation and comparison performed in this paper highlight the high potential of direct cooling technologies, especially in combination with forced convection and liquid coolants.