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Mathieu Lamandé

Gas Dispersion in Granular Porous Media under Air-Dry and Wet Conditions

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Subsurface gaseous-phase transport is governed by three gas transport
parameters: the air permeability coefficient (ka), gas diffusion coefficient
(DP), and gas dispersion coefficient (DH). Among these, DH is the least
understood due to hitherto limited research into the relationship between
gas dispersion and soil physical characteristics. In this study, a series of
advection–dispersion experiments was performed on granular porous media
to identify the effects of soil column dimensions (length and diameter),
particle size and shape, dry bulk density, and moisture content on the
magnitude of gas dispersion. Glass beads and various sands of different
shapes (angular and rounded) with mean particle diameters (d50) ranging
from 0.19 to 1.51 mm at both air-dry and variable moisture contents
were used as granular porous media. Gas dispersion coefficients and gas
dispersivities (a = DH/v, where v is the pore-gas velocity) were determined
by fitting the advection–dispersion equation to the measured breakthrough
curves. For all test conditions, DH increased linearly with v. The test results
showed that neither soil column length nor diameter had significant effect
on gas dispersivity. Under air-dry conditions, higher gas dispersivities were
observed for media with wider particle size distribution and higher dry bulk
density. The minor effect of particle shape on gas dispersivity was found
under both air-dry and wet conditions. Under wet conditions, the variations
in gas dispersivity were mainly controlled by the air-filled porosity. An
empirical model was also proposed for the prediction of gas dispersivity in
granular, unsaturated porous media.
Original languageEnglish
JournalSoil Science Society of America Journal
Pages (from-to)845-852
Number of pages8
Publication statusPublished - 2012

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