Stator heat transfer prediction of disk-type electrical machines

This work describes an analytical modeling for predicting the stator heat transfer in a discoidal system of an electrical machine. The configuration consists of a rotor-stator system surrounded by a cylindrical cover. We aim to fully predict the stator heat transfer taking into account variable parameters namely the rotational Reynolds number, the gap size ratio and the surface temperatures. In the range of 4.19×104 ≤ Re≤ 4.19×105 and 0.00333 ≤ G ≤ 0.08, CFD simulations are implemented. Unlike the studies in the literature with the ambient temperature being considered as the reference temperature to evaluate the convective heat transfer coefficient, the average bulk temperature in the air gap is considered here. In this way, the mean Nusselt number correlation becomes independent of the ambient temperature. After that, a linear correlation between the bulk fluid temperature in the air gap and the surface temperature of the rotor, the stator and the cover is constructed. On the other hand, CFD simulations are carried out for different ranges of the rotational Reynolds number and the gap size ratio at various surface temperature values. Subsequently, with the aid of the least squares method together with the curve fitting procedure, the appropriate formulations for the mean Nusselt number of the stator surfaces are derived. It is found that the proposed correlation is quite versatile in predicting the convective heat transfer of the stator surface in the disk type electrical machines. The results show that there is a gap size ratio for which the average convective heat transfer for the stator facing rotor in the gap reaches a minimum.