Heat Transfer and Thermal Design of Finned Frames for TEFC Variable-Speed Motors

This paper addresses the evaluation of the heat transfer capability of a finned frame for different velocities of the cooling fan and different numbers and dimensions of the fins. As the heat transfer is highly dependent on the air speed and turbulence, separate evaluations are done in four axial sectors of four different frames. For each frame, each sector is thermally isolated and evenly heated by an internal cylindrical heater with controlled losses. The experimental results allow computing the local transfer coefficient on each axial sector in terms of the fin dimensions and cooling air velocity, and using these empirical coefficients, it is possible to evaluate the thermal capability of the frames and/or to compute the temperature gradient needed to dissipate certain losses. Based on these results, a simple and accurate method to size finned frames is proposed.