Investigation of the Flattening Effect on Heat Pipe Thermal Conductivity and Motor Performance

Heat pipes (HPs) are increasingly applied in electrical machines to improve their cooling effectiveness. Due to spatial constraints within motors, cylindrical HPs are commonly flattened into flat pipes to accommodate confined spaces such as interlayer gaps in windings. This alteration in cross-sectional geometry may reduce HP thermal conductivity and thereby impair motor cooling performance. However, the intrinsic degradation mechanism and flattening effect remain unclear, which could potentially diminish HP cooling benefits in motors. Therefore, this study aims to address the above knowledge gap from both theoretical and experimental sides. Initially, the flattening effect on HP thermal conductivity is quantitatively investigated via analytical modeling and experimental measurements. Further, the impact of flattened HPs on motor additional losses and thermal performance is comprehensively evaluated and verified. Finally, practical guidelines for the application of flattened HPs in electrical machines are proposed considering requirements for high efficiency and high power density.