Comparison of Two Hollow-Shaft Liquid Cooling Methods for High Speed Permanent Magnet Synchronous Machines

The rotor cooling poses a significant challenge for high speed permanent magnet synchronous machines (PMSMs). This paper presents a recirculating hollow-shaft liquid cooling structure. Through the computational fluid dynamics (CFD) method, its convective heat transfer coefficient (CHTC) and friction loss are studied in depth. Besides, the recirculating hollow-shaft is compared with the direct-through hollow-shaft. Based on the CFD analysis, it is found that the recirculating hollow-shaft has higher friction loss. But the CHTC of the recirculating hollow-shaft is higher than that of the direct-through hollow-shaft, which can be as high as 32%. Finally, the cone-shaped structure and blade structure are used to optimize the recirculating hollow-shaft, increasing its CHTC by 49%. The cooling effect of the optimized recirculating hollow-shaft structure is more prominent, especially when the rotor loss is large.