Flow and convective heat transfer in disk-type electric machines with coolant flow

Thermal design and management of electric machines is important for achieving higher specific power outputs and, the heat transfer in the air gaps within them require further study. Research into convective heat transfer in the gaps between the rotor and the stator has generally centered on the rotor due to interest from turbomachinery applications. This paper focuses on rotating electric machines by investigating the stator heat transfer for an idealised disk type electric machine geometry. Experiments were carried out using a thin film heating system to provide radially resolved, steady-state heat transfer data for a number of gap ratios, rotational speeds and superposed in- and out-flow rates. Results were used to provide correlations for use in analytical models and were compared with a 2D axisymmetric CFD model using the SST turbulence model. Predictions were found to agree well with local heat transfer measurements, but did not well predict the effects of ingress at the periphery.