Thermal impact of integrated bore cooling with impinging jets and turbulators in rotating shaft of interior permanent magnet electric motor

Thermal failures limit power density of an electric motor and having effective cooling schemes is vital. The oversights in cooling of rotating components through compound heat transfer enhancement (HTE) methods led present study to devise novel shaft cooling schemes that integrate impinging-jets and turbulated annular-flows using pin-fins and spiral rib. The empirical correlations of cooling attributes and flow resistances in rotating shaft with three innovative cooling arrangements are devised for defining thermal boundary conditions during thermal simulations of an interior permanent magnet electric motor using the validated tridimensional model. With rotations, jets in shaft are distorted and diffused by Coriolis forces and crossflows, attenuating cooling efficacy over impinging-jet regime. Heat transfer elevations afforded by annular flows with turbulators in shaft with slow rotations are depressed by further increasing rotor speed until threshold speeds, above which the rotation-induced heat transfer deprivations are recovered. Turbulators in shaft augment flow resistances, reducing flow rates at constant pumping powers; but their HTE benefits still leverage overall cooling efficacies. The maximum coil (magnet) temperatures are reduced by 30.16–35.2% (69.73–75.7%) of those without shaft cooling at three sets of operating conditions with rotor speeds of 1000, 2000, and 3000 rev/min.