Study on heat and mass transfer mechanism of unsaturated porous media under CW laser irradiation: with and without carrier gas

Abstract

The use of laser irradiation to remove contaminants from soil is an emerging soil remediation technology with broad application prospects. The mechanisms of temperature field variations, moisture transport, evaporation, and condensation under conditions with or without a carrier gas during laser soil remediation are still unclear. This paper utilizes a heat and mass transfer model under continuous wave (CW) laser irradiation, established based on local non-thermal equilibrium, to analyze the variation characteristics of the physical field within the soil, with or without introducing a carrier gas. The results show that CW laser irradiation can rapidly heat the soil to the expected remediation temperature (90 °C–560 °C). However, the gas transport speed induced solely by CW laser irradiation within the soil is very limited (on the order of 0.01 mm/s), making it ineffective at removing vapor from the soil. In contrast, using a carrier gas significantly improves gas flow (on the order of 10 mm/s), enhancing both heat and mass transfer processes and assisting in removing contaminants during laser soil remediation. This study elucidates the coupled heat and moisture transfer process in unsaturated porous media under conditions with and without a carrier gas, providing theoretical support for applying laser soil remediation.