Two-scale modeling of solute dispersion in unsaturated double-porosity media: Homogenization and experimental validation

Abstract : A two-scale modeling of solute transport in double-porosity (DP) media under unsaturated water flow conditions is presented. The macroscopic model was developed by applying the asymptotic homogenization method. It is based on theoretical and empirical considerations dealing with the orders of magnitude of characteristic quantities involved in the process. For this purpose a physical model that mimics the behavior of DP medium was built. The resulting two-equation model relies on a coupling exchange term between micro- and macro-porosity subdomains associated with local non-equilibrium solute concentrations. The model was numerically implemented (Comsol Multiphysics®) to simulate the macroscopic one-dimensional physical process taking place into the porous medium of 3D periodic microstructure. A series of dispersion experiments of NaCl solution under unsaturated steady-state flow conditions were performed. The experimental results were used first to calibrate the dispersion coefficient of the model, and second to validate it through two other independent experiments. The excellent agreement between the numerical simulations and the measurements of the time evolution of the non-symmetrical breakthrough curves provides a proof of predictive capacity of the developed model. Copyright © 2010 John Wiley & Sons, Ltd.