Pore-scale SPH simulations of diffusive tortuosity in 3-D porous media

The diffusive tortuosity is an important measurement of the diffusion rate of pollutants in porous media. Determining the diffusive tortuosity of porous media is of great significance for studying the migration of pollutants. Based on the Smooth particle hydrodynamics (SPH) method, the effective diffusion coefficient and the values of diffusive tortuosity can be obtained conveniently and accurately by simulating the diffusive experiment on 3-D reconstructed soil columns. The particle fluid code (PFC) and the Monte Carlo method are used to generate 3-D soil columns by stacking spherical particles and by filling random layered elements, respectively. The calculated results show that for the layered porous media, the angle between the layer and the concentration gradient direction has a significant influence on the diffusive tortuosity. The values of diffusive tortuosity generally grow with the increasing included angle. When the orientation of layers consists with the concentration gradient direction, the diffusive tortuosity is minimized and may even be less than the tortuosity value of the spherical particle packing media with the same porosity.