Heat transfer characteristics of a rotating heat pipe integrated into an electric motor rotor

The increasing power density of electric motors, particularly in electric vehicle and aerospace applications, presents a critical thermal management challenge for the rotor. A rotating heat pipe (RHP) offers a promising passive cooling solution, but comprehensive experimental data on fully integrated rotor-RHP systems remain scarce. This study systematically investigates an RHP concentrically embedded in a motor rotor under controlled heat loads of 20-35 W and rotational speeds from 0 to 2000 RPM. The RHP configuration consistently outperforms the solid rotor baseline across all tested conditions. At 35 W and 0 RPM, the RHP achieves a minimum thermal resistance of 0.114 °C/W, compared with 0.539 °C/W for the solid rotor, corresponding to nearly a four-fold improvement in heat transfer effectiveness. Even at 2000 RPM, the RHP maintains a maximum thermal resistance of 0.354 °C/W. This value remains substantially lower than the non-RHP baseline of 0.608 °C/W measured 35 W and 250 RPM. These results show that the optimal performance is obtained at static or very low speeds, where capillary forces in the wicked RHP dominate liquid return. At higher speeds, centrifugal instabilities degrade two-phase transport and reduce the effective thermal conductivity by nearly 70% relative to the non-rotating state. Overall, this work establishes validated benchmarks for RHP-based cooling in high-power-density rotating machinery. It also challenges the assumption that higher speeds are inherently beneficial for rotating two-phase devices. In addition, the results provide practical design guidance for RHP integration in electric vehicles, robotics, and aerospace systems.