Research on key factors and mechanisms influencing geyser boiling in sodium heat pipes using a novel multiphase model

Heat pipes, known for their high efficiency in heat transfer, often experience significant periodic temperature oscillations during operation, with amplitude exceeding 100 K. A multiphase model is developed to analyze the complex bubble dynamics of geyser boiling, a form of temperature oscillation, in high-temperature heat pipes. The model considers surface evaporation and nucleation boiling based on the degree of overheating. The capillary force in the wick region is simulated using a user-defined function. Various factors are thoroughly examined, including surface tension, contact angle, gravity, nucleation superheat degree, filling ratio, and length-to-diameter ratio. Results indicate that lower surface tension could mitigate or prevent geyser boiling, while a smaller contact angle increases its intensity but reduces frequency. Gravity plays a critical role in inducing geyser boiling, which does not occur in zero-gravity conditions. Higher nucleation superheat delays its onset, while higher filling ratios worsen the severity and extent of geyser boiling. Additionally, a greater lengthto-diameter ratio amplifies both the intensity and range of the phenomenon. These findings provide valuable insights for designing and operating high-temperature heat pipes and offer practical guidance for mitigating geyser boiling challenges.