Influence mechanism of thermally enhanced phase change on heat transfer and soil vapour extraction.

Thermal enhanced soil vapour extraction (T-SVE) is a remedial technique involving gas, aqueous, solid and nonaqueous phases along with mass and heat transfer. Interphase mass transfer of contaminants and water evaporation/condensation will cause the redistribution of phase saturation, eventually affecting the performance of T-SVE. In this study, a multiphase, multicompositional and nonisothermal model was developed to simulate the T-SVE treatment of contaminated soil. The model was calibrated using published data from the SVE laboratory and T-SVE field experiments. The temporal and spatial distributions of the contaminant concentrations in the four different phases, the mass transfer rates and the temperatures are presented to reveal the coupling interactions that occur between multiple fields during T-SVE. A series of parametric studies were carried out to investigate the effect of water evaporation and adsorbed/dissolved contaminants on the T-SVE performance. It was found that endothermic evaporation, exothermic condensation and the interaction between different removal paths of a contaminant played critical roles in the thermal enhancement of SVE. Ignoring them can result in significant differences in the removal efficiency values.