Numerical modeling and cooling performance evaluation of a pressure-driven two-phase closed thermosyphon with a long horizontal evaporator

In the quest to improve thermal regulation within permafrost embankments, the permafrost thermosyphons equipped with horizontal evaporators remains underexplored in scholarly discourse in open. This study delineates the design and numerical evaluation of a pressure-driven two-phase closed thermosyphon (PD-TPCT), featuring a horizontal evaporator exceeding 100 m. A half-theory heat transfer model, borne from a synergy of monitoring data and the thermal resistance method, was derived from an outdoor experimentation. Considering the growing global focus on the sustainable development of the Arctic and the Third Pole, we employ this heat transfer model to analyze the long-term thermal stabilities of a PD-TPCT embankment, a PD-TPCT embankment with insulated boards, and an unprotected embankment (as a control) in the Siberian Arctic (SA) and Qinghai Tibet Plateau (QTP). This study reveals that the horizontal installation of the evaporator can mitigate the shady sunny slope effect and improve the thermal stability of the underlying permafrost. The SA's climate allows the PD-TPCT embankment to protect permafrost for 50 years, while in the QTP, the PD-TPCT embankment with insulated boards is needed for the same protection. The insights garnered herein offer references to both the theoretical exploration and pragmatic implementation of advanced thermosyphon with ultra-long horizontal evaporators.