Three-Dimensional Numerical Simulation of Effective Thermal Conductivity and Fractal Dimension of Non-Aqueous Phase Liquid-Contaminated Soils at Mesoscopic Scale

In situ thermal desorption is one of the most promising remediation techniques for soils contaminated with non-aqueous phase liquids (NAPLs), but its remediation efficiency is limited by the thermal conductivity (k) of NAPL-contaminated soils. The fractal dimension is an important factor affecting k. To systematically study the influence of the fractal dimension on k, firstly, this research establishes a three-dimensional numerical model of NAPL-contaminated soils and calculates its k. Subsequently, the reliability of the numerical simulation results is verified through experiments. Combining the numerical simulation method with Hausdorff fractal theory, we explored the relationship between the fractal dimension and k. This research shows that k decreases with increasing porosity and increases with increasing saturation. The liquid phase can form a “liquid bridge” between solid phases, greatly shortening the path of heat flux and increasing k. k is more affected by porosity. With the increase in porosity, the pore fractal dimension and liquid phase fractal dimension of NAPL-contaminated soils increase, while the solid phase fractal dimension and pore curvature fractal dimension decrease. The fractal dimension of the liquid phase increases with the increase in NAPL content. k increases with the increase in the solid phase fractal dimension, liquid phase fractal dimension, and pore curvature fractal dimension and decreases with the increase in the pore fractal dimension. This study provides a basis for the investigation of the thermal conductivity of NAPL-contaminated soils and the development of in situ thermal desorption technology.