Numerical evaluation of the cooling performance of a composite L-shaped two-phase closed thermosyphon (LTPCT) technique in permafrost regions

The use of two-phase closed thermosyphons (TPCTs) is an effective energy control technique in permafrost regions due to the specific energy transport process and climate conditions. Under the scenarios of climate warming and engineering activities increasing, how to sufficiently cool permafrost ground to ensure the environmental and engineering stabilities is an important issue. In this paper, the cooling effects of several cooling techniques combined with L-shaped TPCT (LTPCT), innovatively used in an embankment with strong heat-absorption asphalt pavement, are assessed based on a developed 3-D heat transfer model considering the climate warming. The model includes coupled air-LTPCT-soil heat transfer, convective heat transfer and conductive heat transfer with phase change. The numerical results show that the embankment combined with LTPCTs, crushed-rock revetment and insulation is the optimized technique to adjust the thermal exchange process between permafrost ground and ambient. The composite LTPCT technique can effectively cool underlying permafrost mainly during the first few years after construction, and then control permafrost degradation rate by reducing heat absorption in warm seasons and enhancing the ambient energy utilization in cold seasons. Consequently, the technique should be considered for application in low-temperature permafrost regions and other thermal control engineering.