Study on thermal conductivity of non-aqueous phase liquids-contaminated soils

Purpose This paper studies the effects of non-aqueous phase liquids (NAPLs) content and soil structural anisotropy on the thermal conductivity of NAPLs-contaminated soils, providing theoretical support for selecting heating methods and parameters in in situ thermal desorption remediation technology for NAPLs-contaminated soils. Materials and methods The feasibility of establishing the NAPLs-contaminated soil model using a random four-parameter generation method and calculating its thermal conductivity based on lattice Boltzmann method (LBM) is verified by testing the thermal conductivity of remolded soil samples with different porosities and diesel content. Then, the numerical simulation method is extended to study the thermal conductivity of NAPLs-contaminated soils with an anisotropy structure. Results The thermal conductivity of NAPLs-contaminated soils increases with the increase in the diesel content and decreases with porosity increase. The diesel content and effect of "liquid bridges" significantly impact the thermal conductivity of NAPLs-contaminated soils with large porosity and a high degree of anisotropy. According to the angle between the direction of soil pore connection and heat conduction, the S-r-k(y) : k(x) curves are divided into two types of trend lines with the included angle of 45 degrees as the boundary. Conclusions Porosity, saturation, and anisotropy significantly affect the thermal conductivity of NAPLs-contaminated soils. The thermal conductivity of NAPLs-contaminated soils is largest when the heat conduction direction is consistent with the pore connection direction of NAPLs-contaminated soils. The thermal conductivity of anisotropic NAPLs-contaminated soils with high NAPLs content tends to be isotropic. The porosity, NAPLs content, and anisotropy of soil structure should be fully considered in the in situ thermal desorption remediation of NAPLs-contaminated soils.