The thermal budget evaluation of the two-phase closed thermosyphon embankment of the Qinghai–Tibet Highway in permafrost regions

The two-phase closed thermosyphon (TPCT) is a passive high-performance thermal transfer device that can efficiently decrease the ground temperature. However, only a few studies focus on the quantization of working efficiency of thermosyphons. Thus, in this study, based on data obtained from an experimental TPCT embankment on the Qinghai–Tibet Highway from 2004 to 2012, the ground temperature fields of the TPCT embankment were obtained, and the horizontal and vertical ground temperature characteristics were analysed. The results showed that the TPCT embankment exhibited better thermal stability than that of a traditional embankment. The artificial permafrost table was elevated to or maintained at the original natural level due to the cooling effect of the TPCT. To quantitatively analyse the cooling effect of the TPCT embankment, a thermal budget evaluation method is proposed. The calculated results revealed the dynamic working state of the thermosyphon during its service period. The annual average energy of the TPCT transferred in a year was generally determined to be between 1500 MJ and 2000 MJ. The results of this study could provide a method to evaluate the TPCT embankments and provide technological support in designing the TPCT embankments in permafrost regions.