An Investigation of Laminar Flow in the Rotor Windings of Directly-Cooled Electrical Machines

Abstract

A theoretical and experimental investigation aimed at gaining an insight into the effect of rotation on flow and heat transfer in the cooling channels of rotors for electrical machines. Specifically, the flow geometry considered is that of a circular tube constrained to rotate about an axis parallel to its axis of symmetry, this being the main component in the coolant circuit for the internal cooling of rotor windings. The theoretical work treats the case of laminar flow well removed from entrance effects. The governing conservation equations were solved numerically and solutions are presented for the velocity and temperature fields when the tube wall is uniformly heated. Subsequently, the influence of rotation on heat transfer and flow resistance was derived from these solutions. Comparison of the theoretical prediction with experimental data obtained with air and water demonstrated that the theoretical model is, in general, capable of predicting the effect of rotation.