Nanofluids as Coolants to Improve the Thermal Management System of a High-Power Aircraft Electric Motor

Electrification has become increasingly common in aerospace due to climate change concerns. After successful applications in general aviation aircraft, electrification is now addressing subregional (<= 19 pax) and regional aircraft (~ 80 pax). Megawatt-class electric motors are needed both to drive propellers and to act as high-power generators in hybrid-electric propulsion systems. Although the efficiency of these electric machines is very high, the power levels require the design of heat management systems capable of dissipating a much higher quantity of heat than that dissipated by traditional cooling systems. Coolants also deserve renewed attention as their associated physical properties need to be improved to ensure greater heat removal than conventional coolants. The technical solution here explored is the addition of nanoparticles into a base liquid. Nanoparticles, in fact, have unique properties such as high thermal conductivity and large surface area that enhance the heat transfer capacity of base liquids. However, the addition of nanoparticles into a base liquid induces new challenges to be faced, such as stability, thermal and electrical conductivity properties of nanofluids, cleaning and erosion of equipment. The Italian Aerospace Research Centre (CIRA) has developed, as part of the European research initiative ORCHESTRA, a thermal management system (TMS) based on impinging jets technology for a 1 MW electric motor. This work presents the subsequent activities that CIRA has carried out to demonstrate the enhancements achievable from nanofluids. In particular, two different nanoparticles were added to the base liquid of the cooling system of the aforementioned 1 MW electric motor: alumina and graphite in two distinct molecular structure configurations, each with different concentrations between 1% and 10% (volume fraction of diathermic oil). The application of nanofluids to the reference TMS is shown to increase heat transfer at a fixed mass flow rate.