Thermosyphon systems are passive refrigeration devices, helping to protect the permafrost to support buildings, pipelines, railroad embankments and highways (Wagner (2014)). They are charged with a working fluid circulating between an evaporator and a condenser/radiator due to the natural convection. A schema operation example of a thermosyphon system is in Figure 1.1. In the winter, the ground temperature is higher than the air temperature, so the fluid at the base of the thermosyphon warms up, vaporises and moves upward to the radiator where the liquid cools down by colder air, condenses and moves downward again. This loop transfers heat from the ground to the air as long as the appropriate temperature difference prevails; otherwise, the system stops working. Therefore, the cycle ceases in the summer, and the cold is stored in the ground.
Figure 1.1 Thermosyphon operation (after Wagner (2014))
This report illustrates the thermal analysis of thermosyphon-ground systems in Geotechnical engineering using PLAXIS 2D finite element software. A typicalengineering application of thermosyphon foundation subjected to yearly air temperature variation and a permanent heated building is presented. A theoretical background of thermosyphon is briefly introduced. The key factors influencing the ground response are performance characteristics (thermal conductance) of thermosyphon, air temperature, soil thermal properties and evaporator pipe size. All these factors can be modelled by different flexible functionalities in PLAXIS, including time-dependent temperature and heat transfer functions and especially Thermosyphon boundary condition. The obtained results are consistent with physically-expected ground responses, showing the permafrost protection by a thermosyphon system.