Improved dual-permeability model for characterizing the mass transfer process inside matrix blocks

The dual-permeability model (DPM) is highly efficient for describing bimodal transport in heterogeneous porous media. However, it uses only one domain to describe the matrix blocks, and it therefore ignores the impact of the mass transfer process inside the matrix blocks at the microscale. Therefore, in this study, to investigate the effect of the mass transfer process in dual-permeability media and the computational accuracy when considering it, the dual-permeability model with a transition domain (DPMTD) is proposed based on the DPM. Comparison of the DPMTD with the DPM by applying them to a sand column experiment with the same concept as the model reveals that the DPMTD captures the bimodal transport (especially the first peak) more effectively because it calculates the rapid exchange of solute in the early stage more accurately. Subsequently, the same conclusion is reached when both models are applied to a reported solute displacement experiment for an Andisol. In short, we suggest ..., To verify the rationality of the new model and compare the DPMTD with the DPM, an experiment is designed. It is similar to the experiment of Köhne and Mohanty (2005), which used a cylindrical macropore filled with coarse sand crossing through a sand column. Although the experimental sand column is artificially filled, it is not meaningless. It can reflect the microscopic idea of the DPM at the macroscopic level. In essence, this experiment is designed based on the concept of the DPM, and this approach has been widely used by researchers. In this way, a macropore filled with coarse sand can be considered to represent the preferential flow path, and some parameters in the conceptual model can be obtained directly from the experimental conditions to prevent the fitting parameters from being inconsistent with actual values in the numerical simulation. In this experiment, two kinds of sand (fine sand and coarse sand) are used as filling materials. A cylindrical container made of acrylic with...,