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Flux and Resident Injection in Gaseous Advection Experiments
Author(s) -
Gimmi T.,
Flühler H.
Publication year - 1996
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/95wr02719
Subject(s) - flux (metallurgy) , inlet , advection , mechanics , diffusion , dispersion (optics) , molecular diffusion , flow (mathematics) , materials science , porosity , environmental science , thermodynamics , geology , physics , composite material , metallurgy , metric (unit) , operations management , geomorphology , economics , optics
The occurrence of gaseous pollutants in soils has stimulated many experimental activities, including forced ventilation in the field as well as laboratory transport experiments with gases. The dispersion coefficient in advective‐dispersive gas phase transport is often dominated by molecular diffusion, which leads to a large overall dispersivity γ. Under such conditions it is important to distinguish between flux and resident modes of solute injection and detection. The influence of the inlet type on the macroscopic injection mode was tested in two series of column experiments with gases at different mean flow velocities υ. First we compared infinite resident and flux injections, and second, semi‐infinite resident and flux injections. It is shown that the macroscopically apparent injection condition depends on the geometry of the inlet section. A reduction of the cross‐sectional area of the inlet relative to that of the column is very effective in excluding the diffusive solute input, thus allowing us to use the solutions for a flux injection also at rather low mean flow velocities υ. If the whole cross section of a column is exposed to a large reservoir like that of ambient air, a semi‐infinite resident injection is established, which can be distinguished from a flux injection even at relatively high velocities υ, depending on the mechanical dispersivity of the porous medium.