Study on the start-up performance of a high-temperature sodium heat pipe with a large aspect ratio

High-temperature sodium heat pipes with a large aspect ratio are widely used for heat dissipation in nuclear reactors. This study investigated high-temperature sodium heat pipes with a large aspect ratio (210) and an ultra-long length (4 m). Hot air was used to preheat the condensation section of the heat pipes to avoid the frozen start-up limit during the starting process of the heat pipes. The experimental results indicated that the start-up time in the horizontal state reached 105 min, and the temperature of the adiabatic section in the preheating stage increased significantly. The condensation section of the heat pipes was then tilted to provide an additional capillary force with the assistance of gravity. Experiments conducted at inclinations of 2° and 5° shortened the start-up time to within 90 min. During the experiments, the sodium heat pipes exhibited the single-point heating lag phenomenon at the front end of the evaporation section. Moreover, the vacuum degree was found to have a significant influence on the starting performance of the heat pipes. Through comparative experiments, this study proved that sufficient wetting time was beneficial to improving the start-up isothermal performance of the heat pipes and prolonging the start-up length. In addition, this study analyzed the reasons for the periodic fluctuations of heat pipes, providing pioneering insights for the stable start-up of high-temperature sodium heat pipes with a large aspect ratio.