Evaluation of Coupled Thermal and Hydraulic Relationships Used in Simulation of Thermally-Induced Water Flow in Unsaturated Soils

摘要

This paper focuses on the role of coupling between the thermal and hydraulic properties of soils on simulations of the distribution in temperature and degree of saturation surrounding a geothermal heat exchanger in an unsaturated soil deposit. This information is relevant to the simulation of geothermal heat storage systems in unsaturated soil layers. The simulations involved heat transfer coupled with water flow in both liquid and vapor forms, and were performed considering the properties of sand, silt, and clay. A water table was fixed at a depth of 20 m below the extent of the heat exchanger, which means that the different soils considered have different initial hydraulic conditions along the length of the heat exchanger. After heat injection for 90 days at the same heat injection rate, the ground temperatures varied significantly with the soil type, with the clay showing the greatest changes in temperature despite having a lower thermal conductivity than the sand. The clay layer also experienced the greatest changes in degree of saturation and had the highest heat transfer due to latent heat transfer, likely because the initial degree of saturation was higher in this soil. The results indicate that a larger change in degree of saturation may occur in soils with a higher initial hydraulic conductivity.