Numerical Investigation of High-Temperature Heat Pipes With Different Wick Structures Under Non-Uniform Heating Boundary Conditions

Abstract High-temperature heat pipe is an ideal technical solution for microreactors applied for space missions, planet surface, and the small electricity markets on the ground. However, the internal fluid flow state and the effects of key parameters such as permeability, porosity, and capillary force of wick structure on the distribution of working fluid inside the heat pipe are difficult to measure experimentally. In this study, a general CFD model for heat pipe with wick structure that can predict the thermal behavior at different steady-state conditions was carried out. The thermal conduction through heat pipe shell, liquid film on the inner surface, and the formation of liquid reservoir at the bottom of heat pipe were considered in this model. A high-temperature heat pipe model considering the flow of liquid working fluid inside the wick structure was developed based on the Star-CCM+ numerical simulation software. The model used a combination of the liquid film model and the Volume of Fluid (VOF) model to simulate the effects of fluid flow and collection behavior inside the wick structure on the heat transfer characteristics of the heat pipe. The method included models for flow resistance and capillary driving force under steady-state conditions, centrifugal force and time-varying gravitational field under motion conditions, and mixed convective heat transfer caused by motion conditions. The accuracy of the numerical simulation was validated using typical potassium high-temperature heat pipe experiments. The effects of different permeability and capillary force characteristics of the wick structure on heat transfer and internal fluid distribution in the heat pipe were studied. Based on the current method, high-temperature heat pipes with different inclinations (0°, 90 °and 45°) were investigated. Additionally, non-uniform heating boundary conditions were added to the high-temperature heat pipe evaporator section to investigate its heat transfer performance under real reactor axial power input. This investigation lays the foundation for the design and analysis of the heat transfer characteristics of high-temperature heat pipes.