On the Measurement and Modeling of the Heat Transfer Coefficient of a Hollow-Shaft Rotary Cooling System for a Traction Motor

This paper addresses the heat transfer coefficient (HTC) associated with the hollow-shaft rotor cooling of a traction motor. In such a hollow-shaft cooling system, the coolant is made to flow through the shaft hole in order to cool the rotor. The HTC is estimated using computational fluid dynamics (CFD), where the effect of rotational velocity as well as the coolant flow rate has been accounted for. Experiments are then used to validate the accuracy of CFD models with the assistance of an analytical lumped-parameter thermal network approach. On the basis of CFD simulations and the experimental prototype testing, it is concluded that the rotational speed can significantly increase the convective heat transfer of the shaft hole about 3.8 times at 4500 r/min above the level of the stationary condition. As a result of such analysis, a new dimensionless correlation of the Nusselt number with the Reynolds number is derived.