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Calibration of Jointed Tube Model for the Gas Diffusion Coefficient in Soils
Author(s) -
Freijer Jan I.
Publication year - 1994
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1994.03615995005800040010x
Subject(s) - diffusion , soil water , porosity , characterisation of pore space in soil , water content , porous medium , analytical chemistry (journal) , materials science , soil science , chemistry , mineralogy , thermodynamics , composite material , environmental science , geotechnical engineering , chromatography , geology , physics
Modeling of gas and vapor transport in soils requires knowledge of the relative gas diffusion coefficient. The relative diffusion coefficient was determined as a function of air‐filled porosity, using a pore model based on two tortuous tubes of different radii joined in series. This model was fitted to measured relative diffusion coefficients on undisturbed samples of nine soil types at a wide range of water contents. It was found that model parameters vary with the soil types studied. Combined measurements of the water retention curve, air‐filled porosity, and relative diffusion coefficient were made to evaluate the effects of water distribution in the soil pores on the relative diffusion coefficient. After the samples were saturated with water, the residual air‐filled porosity ranged from 0.051 to 0.167 m 3 m −3 and the relative diffusion coefficient was practically zero, which is due to pore blocking by soil water. At pressure heads corresponding to the air‐entry value in the water retention function, air‐filled porosity ranged from 0.095 to 0.256 m 3 m −3 and the relative diffusion coefficient ranged from 0.002 to 0.013. From this point, with increasing air‐filled porosity, the relative diffusion coefficient increased rapidly to values ranging from 0.165 to 0.383 at zero water content. It was concluded that the air‐entry value is an important parameter, which indicates a priori the water content at which pore blocking becomes relevant.