Research progress and prospects on heat transfer characteristics of high-temperature heat pipes with nanostructured wicks

High-temperature heat pipes, as highly efficient and passive phase-change heat transfer devices, play an irreplaceable role in nuclear reactor core cooling, spacecraft thermal management, and advanced energy systems. One of the key factors limiting their heat transfer performance lies in the capillary driving force and liquid-phase transport capability of the wick structure. Conventional wick designs suffer from an inherent trade-off between capillary pressure and permeability, which constrains the performance of high-temperature heat pipes under extreme heat fluxes and complex operating conditions. In recent years, nanostructure modification technologies have provided new pathways to overcome this bottleneck. This review systematically summarizes the research progress on high-temperature heat pipes with nanostructured wicks, covering the full research chain from microstructural fabrication and characterization, evaporation heat transfer mechanisms of alkali metals, macroscopic heat transfer performance experiments, to multiscale numerical simulations. Studies indicate that nanoscale structures constructed on wick surfaces via methods such as oxidation-reduction and sol-gel processing can simultaneously and significantly enhance capillary pressure and permeability, effectively reducing the thermal resistance of the evaporating meniscus. As a result, the startup speed, isothermal performance, and heat transfer limit of heat pipes can be improved by approximately 10%~40%. Molecular dynamics and lattice Boltzmann simulations reveal the critical influence of surface wettability on liquid sodium evaporation dynamics and flow spreading behavior, and experimentally correlated relationships for the contact angle as functions of temperature and pressure have been obtained. Moreover, multiscale numerical models based on computational fluid dynamics have been developed to predict the transient response and limiting behavior of heat pipes, further validating the heat transfer enhancement mechanisms induced by nanostructures. Finally, experimental studies on the adaptability of nanostructured-wick high-temperature heat pipes under complex operating conditions such as bending, motion, and thermal mismatch, are summarized, and future research challenges and development trends are discussed, including liquid metal flow and heat transfer mechanisms, the effects of non-condensable gases, strong transient and impact responses, high-fidelity code development, and data-driven predictive methodologies. This review aims to provide systematic theoretical insights and technical guidance for the design and application of next-generation high-performance high-temperature heat pipes.