Comparison of Nanoparticle-Enhanced and Centrifugally Pumped Dielectric Oil Cooling Techniques for High-Power Aircraft Electric Motors

Aircraft electrification requires high performance thermal management systems able to cool-down power-plants with increasing power densities in electric aircraft motors. The demanding mission profiles and the request for compact electric components, in fact, induce high temperatures in power-plant system that must be cooled by proper thermal management systems, to assure systems efficiency and reliability. This paper investigates and compares two promising approaches for the cooling of megawatt order electric motor for aviation applications: nanofluid based liquid cooling and radial tube systems. Nanofluids are an innovative approach to system cooling leveraging on the physic properties of the coolant; radial tubes, conversely, represent a structural solution aimed at improving the heat removal. In particular, nanofluids are composed by colloidal suspensions of nanoparticles in a base fluid, enabling enhanced thermal conductivity and convective heat transfer coefficients compared to conventional coolants. Radial tubes improve heat removal through optimized conduction paths and increased surface to volume ratios without altering the working fluid. Through numerical analysis carried out by using state of the art Computational Fluid Dynamic (CFD) tools, results highlight the main advantages of the two systems: nanofluids provide a significant average heat transfer enhancement on the tooth, while the radial tubes involve a strong increase in the global heat exchange despite a larger oil flow rate.