Pore-scale investigation on nonaqueous phase liquid dissolution and mass transfer in 2D and 3D porous media

Fluid fluid interphase mass transfer in porous media plays an important role in the remediation of soil and groundwater contaminated by nonaqueous phase liquid (NAPL). In this study, we experimentally elucidated the pore-scale dissolution process and the macroscopic interphase mass transfer coefficient inside the porous media. Further, the local characteristics of the residual phase, including saturation and interfacial area, were determined during the dissolution process using nondestructive visualization technologies. The dynamic dissolution process indicated that not all blobs are equally exposed to flowing water and the dead-end pores considerably decreased the dissolution rate. According to the linear driving force model, the NAPL concentration in mobile water was predicted from the residual saturation. Further, the local and overall mass transfer coefficients corrected with concentration and interfacial area were estimated. The results showed that the NAPL concentration in mobile water increased along the water injection direction because of the NAPL dissolved in water. The local mass transfer coefficient exhibited a uniform distribution along the sample, indicating that the mass transfer coefficient is independent of the concentration difference. The effect of pore structure on the dissolution process of entrapped NAPL was studied by comparing a two-dimensional (2D) micromodel and a three-dimensional (3D) packed bed. The overall mass transfer coefficient was higher in the 3D packed bed under Darcy flow conditions. The major differences between the 3D packed bed and 2D micromodel can be attributed to the heterogeneity of pore geometry and the differences in pore connectivity. (C) 2021 Elsevier Ltd. All rights reserved.