Enhanced Motor Performance via Two-Phase Thermal Management

Thermal management presents a significant constraint on the achievable efficiency and power density of MW-scale electric motors for aircraft propulsion. High temperatures within the windings limit the maximum power density, reduce the lifetime of the winding insulation, and increase electrical losses resulting in lower efficiency. Innovative thermal management strategies can significantly enhance the performance of motors for electrified aircraft propulsion. In this SBIR program, Advanced Cooling Technologies, Inc. (ACT) is developing an innovative two-phase thermal transport system for high power electric motors that will augment traditional cooling solutions by efficiently extracting heat from difficult to cool areas. The two-phase thermal transport system will be fully passive, lightweight and scalable. The proposed technologies will improve waste heat rejection from motor windings allowing for increased power density and efficiency. The Phase I program successfully demonstrated the feasibility of the concept and presented an electric motor with a 60% increase in power density over a conventional design with comparable thermal performance. In the Phase II program, ACT will continue to lead the development and maturation of an innovative two-phase heat-transfer-based thermal management solution for electric motors. The goal of the Phase II program is to demonstrate an optimized design of an enhanced motor capable of power density of 20 kW/kg and efficiency of at least 98%. Enabling ultra-efficient electric aircraft requires the weight and efficiency to be improved beyond the state-of-the-art. Thermal management significantly constrains the achievable power density and efficiency of electric motors. In high-power electric motors a significant thermal management bottleneck is the large thermal resistance between critical heat sources and heat sinks. For example, copper losses in the windings must conduct through the stator iron to reach a water jacket heat sink. In this Phase II, ACT will continue to develop innovative pulsating heat pipe (PHP) based thermal transport technology for high power electric motors. Hollow windings containing a two-phase fluid will operate as a PHP and to passively transfer heat generated by the windings to an area where cooling can be easily applied. By increasing the effective thermal conductivity of the windings by an order of magnitude, the effectiveness of direct cooling applied locally to easily accessible locations will be increased. This technology will enable efficient higher power electric motors of MW scale. The goal of this SBIR is to demonstrate the enhanced power density and efficiency of electric motors for electrified aircraft propulsion, enabled by the innovative pulsating heat pipe winding concept. The Phase I program successfully demonstrated concept feasibility. PHP windings enabled a 60% increase in power density compared to a baseline motor design with comparable thermal performance. The goal of the Phase II program is to demonstrate an electrically and thermally optimized motor design incorporating PHP windings to achieve power density of 20 kW/kg, and experimentally demonstrate a relevant PHP winding motor prototype. The electromagnetic design and analysis will be refined and expanded to identify the optimum stator and rotor topology to fully benefit from the PHP windings. The thermal performance and reliability of the PHP winding will be optimized and modeling capabilities will be expanded. Trade studies will be conducted to identify optimum thermal management strategies to utilize the benefits of PHP windings. An optimized design of a MW-scale electric motor and thermal management system utilizing the PHP windings will be developed to maximize power density and efficiency with acceptable thermal performance. Finally, a reduced-scale prototype of the motor and PHP windings geometry along with integrated thermal management system will be fabricated and tested.
Benefits: The two-phase thermal management technology proposed is relevant to several strategic thrusts outlined by NASA's Aeronautics Research Mission Directorate: “Ultra-Efficient Commercial Vehicles” and “Transition to Low-Carbon Propulsion”. NASA envisions a significant shift in commercial aircraft to ultra-efficient airframes and propulsion concepts utilizing electric or hybrid electric propulsion. Improved thermal management resulting from the proposed technology will enable significant increase in the power and torque density of electric motors. The proposed technology is applicable to various motor architectures and sizes. It will find use in passenger aircraft, unmanned aircraft, and electric vertical takeoff and landing aircraft. In addition to the aviation industry, the need for high-performing motors in electric automobiles is rapidly growing as nearly all sectors of the transportation industry begin to electrify.