Implementation of heat transfer techniques for an axial flux permanent magnet generator design

Abstract

Heat transfer problem is explored for a new-designed low power generator. A self-cooling mechanism of the generator is designed and implemented for the forced convection via a fan being on the generator rotor. In addition, air is naturally directed towards the lateral parts of the machine in air gaps between stator and rotors. The designed fan has 16 blades with 65 degrees. The CFD and experimental self-cooling analyses are performed to focus on the flow velocities and temperature measurements. In this study, it has been aimed to compare heat transfers by the natural convection and by the forced convection. For this reason, besides Rayleigh ( Ra), Nusselt ( Nu), Grashof ( Gr) and Reynolds ( Re) numbers, heat transfer terms on the small winding coil, which is important heat source for the generator, are calculated for natural and forced convection. They are also clarified experimentally and theoretically. The heat transfer at 300 rpm varies between 0.04 W and 0.30 W by time for forced convection and varies between 0.21 W and 0.30 W by time for natural convection, whereas, it increases up at 1000 rpm from 0.50 W to 1.49 W by time for forced convection and from 0.02 W to 0.45 W by time for natural convection. It is proven that the proposed cooling system operates efficiently and the proposed self-cooling method can be used for other axial flux machines, too.