Geotemperature control performance of two-phase closed thermosyphons in the shady and sunny slopes of an embankment in a permafrost region

Heat pipes are a widely-used technology for energy exchange in the world. One of the important issues in the future is how ground heat control can meet the demands of the environmental and engineering stabilities in cold regions. In this paper, a low-temperature gravity assisted heat pipe (two-phase closed thermosyphon, TPCT) is innovatively installed in an embankment with shady and sunny slopes to adjust the geotemperature of the underlying permafrost stratum. The geothermal conditions for three cases-an embankment without TPCTs, an embankment with unilateral TPCTs (UTPCTs), and an embankment with bilateral TPCTs (BTPCTs)-are assessed based on a three-dimensional heat transfer model considering the global warming. The model includes coupled air-TPCT-soil heat transfer and conductive heat transfer with phase change. The numerical results show that: (1) both the UTPCTs and BTPCTs can cool the permafrost stratum, but the UTPCTs aggravate the asymmetric geotemperature caused by the shady-sunny slope effect; and (2) the BTPCTs are better to alleviate the asymmetric geotemperature by controlling the working time and efficiency of the TPCTs under the two slopes. Consequently, the BTPCTs are a more effective engineering measure for embankments affected by the shady-sunny slope effect.