Impact of power density on heat and mass transfer in porous media under continuous wave laser irradiation

This paper establishes a heat and mass transfer model within an unsaturated porous media under laser irradiation to elucidate the intrinsic mechanisms of continuous wave laser soil remediation. Simulated studies were conducted under four different laser power densities (62.24, 77.15, 90.08, and 109.91 W/cm2), and the model's reliability was experimentally verified. The results indicate that the model can predict the experimental outcomes effectively. Under laser irradiation, the temperature of the solid surpasses the boiling point of water and continues to rise. The temperature and mass transfer of the gas are highly coupled with the temperature of the solid. The heat and mass transfer intensities within the porous media increase with rising power density. To further clarify the efficiency relationship between energy input and remediable depth, an energy management evaluation function (E-function) was constructed. It was found that the E-function distribution for both solid and gas phases is parabolic and exhibits similar properties. Although higher power densities can reach the peak more quickly, the rate of decline is also faster. The decline ratios in the solid phase are 1:2.23:2.72:3.02, while in the gas phase, they are 1:1.99:2.45:3.31. This indicates that simply increasing the laser power density is not conducive to improving remediation efficiency or control costs. The findings of this study provide a solid theoretical basis and reliable experimental foundation for efficient laser soil remediation.