Comprehensive efficiency analysis of air-cooled vs water-cooled electric motor for unmanned aerial vehicle

The efficiency of an electric motor for an unmanned aerial vehicle can reduce when its temperature exceeds the working temperature. In this paper, air- and water-cooling methods for electric motors in unmanned aerial vehicles are proposed and comprehensively compared. The effects of fan speed, water flow speed, and convection heat transfer coefficient on the outer surface of the electric motor on the cooling capacity of the electric motor are discussed. A comprehensive performance evaluation factor for the cooling method of the motor is proposed. Results show that when the fan speed increased from 800 to 2000 rpm, the cooling efficiency increased by 27.78% for the air-cooled motor, whereas when the inlet flow rate of cooling water increased from 0.1 to 0.9 m/s, the cooling efficiency increased by 67.47% for the water-cooled motor. The comprehensive performance of the water-cooled motor reached the highest level with a velocity of 0.7 m/s. The convection heat transfer coefficient increased from 5 to 25 W/(m2·K), and the cooling efficiency increased by 22.93% and only 2.77% for the air- and water-cooled motors, respectively. These findings can provide guidance for designing highly efficient electric motor cooling equipment for unmanned aerial vehicles.