Temperature and Consumed Energy Predictions for Air-Cooled Interior Permanent Magnet Motors Driving Aviation Fans—Part 1: Mathematical Analytical Solutions for Incompressible Air Cases

The increase in worldwide awareness of environmental issues has necessitated the air transport industry to drastically reduce carbon dioxide emissions. To meet this goal, one solution is the electrification of aircraft propulsion systems. In particular, single-aisle aircraft with partial turboelectric propulsion with approximately 150 passenger seats in the 2030s are the focus. To develop a single-aisle aircraft with partial turboelectric propulsion, an air-cooled interior permanent magnet (IPM) motor with an output of 2 MW is desired. In this article, mathematical system equations that describe heat transfer inside the target air-cooled IPM motor are formulated, and their mathematical analytical solutions are obtained. From the results, the following predictions are made. (1) In the heat exchanger, the external air should flow between a stator and the internal air, and the flow direction of the external air should be opposite to that of the internal air. (2) The internal air mass flow rate should be chosen to maintain the turbulent internal flow through the heat exchanger. (3) The internal air mass flow rate has the optimum value to minimize the rotor temperature. (4) The rotor temperature increases with decreasing internal air mass flow rate below the optimum value. (5) The rotor temperature increases with increasing internal air mass flow rate beyond the optimum value. (6) The rotor and stator temperatures are linearly proportional to the ambient temperature. (7) The rotor temperature increases with decreasing ambient pressure. (8) An increase in altitude causes a decrease in power consumption for both the external air and internal air. (9) The most severe condition is the top-of-climb condition, and the external and internal air mass flow rates should be chosen to make the rotor temperature less than the maximum limit temperature of 100°C and the stator temperature less than the maximum limit temperature of approximately 250°C.