A review of technology, applications, and future perspectives of thermosyphons in permafrost regions

Thermosyphons, utilizing natural convection and phase change mechanisms, offer a reliable and maintenance-free solution for heat transfer, crucial for preserving permafrost and maintaining infrastructure stability. This paper reviews the design variations and operational principles of thermosyphons, highlighting their adaptability and effectiveness in diverse applications such as transportation, energy, and infrastructures in Earth regions with low temperature. Over the past decades, the cooling performance of thermosyphons, especially two-phase closed thermosyphons, has been widely employed to save permafrost subgrades under pavements, railway embankments, pipeline foundations, transmission tower foundations, buildings, and other structures in Northern America, Russia, China, and elsewhere. These applications have been the focus of numerical simulations, laboratory experiments, and field studies. Recent innovations, including the use of nanorefrigerants, new configurations such as L-shaped and horizontal thermosyphons, and the combination of thermosyphons with other passive cooling technologies, have significantly improved their performance and efficiency. Some innovative applications, however, remain at the stage of laboratory research, numerical simulations, or conceptual modeling, with further field studies needed to assess their durability, reliability, and ease of construction. This review underscores the importance of continued research to enhance material durability, operational efficiency, and the development of advanced monitoring systems.