High reliability piezoelectric fan cooling for electric machine thermal management

Electric machine thermal management is critical for the correct operation of high power density aerospace electrical machines. However, with increasing power density, a reliable, fault tolerant cooling mechanism needs to be developed. Piezoelectric fans are presented here as a potential, fault tolerant, forced cooling convective system that may further enhance the overall cooling of electric machines. Particle Image Velocimetry (PIV) techniques were implemented to map and quantify the flow fields generated by one such fan along the fin base and fin side walls of a vertical straight finned motor heat sink. Common fluid flow governing parameters (vibration amplitude, separation distance, and fin length) were investigated; the optimum fin/fan geometry of which resulted in mean flows in excess of 2.48m/s and turbulence values in excess of 2.00m/s. Detailed thermal results indicate that an average convective heat transfer coefficient enhancement of 340% on the fin base and an enhancement of 36% on each of the fin side walls are attainable. This in turn resulted in a 64% reduction in the electric machine heat sink cooling mass relative to natural convection cooling.