### Abstract

The structure of an aggregated soil or a dual-porosity medium is characterized by a function called the generalized surface-area-to-volume ratio, which can be measured as a distance distribution. For an isotropic structure the distance measurements may be done in the digitized image of a cross-section. A diffusion-reaction process in the soil matrix can be described by means of an equivalent cylinder system which preserves the generalized surface-area-to-volume ratio of the structure. The contribution of each cylinder radius is described by a weight function, which is obtained by transforming the measured cross-sectional distance distribution. In order to test the method, a diffusion-reaction model from the literature has been applied to spheres with a lognormal radius distribution and to an irregular, generated structure. Both geometries can be represented by just a few cylinder radii and cylinder weights. The method works best for dual-porosity structures with a convex shape. Deviations occur if parts of the matrix structure have a concave shape.

Original language | English |
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Pages (from-to) | 1-24 |

Journal | Transport in Porous Media |

Volume | 37 |

DOIs | |

Publication status | Published - 1999 |

### Keywords

- soil texture
- soil structure
- diffusion

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## Cite this

Rappoldt, C., & Verhagen, J. H. G. (1999). Equivalent cylinder systems representing the soil matrix in diffusion-reaction models.

*Transport in Porous Media*,*37*, 1-24. https://doi.org/10.1023/A:1006675326508