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| Titel |
A New Method For Accurate In Situ Concentration Measurements In Packed Columns |
| VerfasserIn |
J. M. Thomas, C. V. Chrysikopoulos |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022061
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| Zusammenfassung |
| Columns packed with glass beads or quartz sand are commonly used in the laboratory as a
model porous medium for groundwater hydrological experiments. In a typical experiment
water flows through the packed column in one direction, a chemical, tracer, or colloidal
suspension is injected at the influent, and the effluent is sampled at various times and
analyzed to determine concentration. Column parameters (e.g., porosity and dispersivity),
chemical reactions or dissolution, and hydrodynamic parameters (e.g., interstitial velocity and
dispersion) can be determined from effluent concentrations (i.e., break-through curves). This
method has two inherent weaknesses. First, for experiments involving seismic or
acoustic wave vibration, the packing material can settle, leading to preferential
flow paths that develop over time and lead to inconsistent and inaccurate results.
Second, measurements of the concentration of a tracer as it flows through the column
(in situ) cannot be determined. A new method for accurately measuring in situ
conservative tracer and colloid concentrations in packed columns is presented. The
method includes fabricating clear sintered glass-bead-packed columns, taking digital
photographs of the column under black light, and determining concentrations by
measurement of the fluorescence in the photographs using MATLAB’s® Image Processing
Toolbox-¢. The sintering prevents changes in the geometry of the porous medium
making it particularly useful for seismic or acoustic vibration experiments. Since
fluorescence is measured, the method is limited to fluorescent solute tracers and
fluorescent polystyrene microspheres (colloidal suspensions). The method is shown to
be as accurate as effluent sampling and allows for accurate in situ measurement
of tracer concentrations at multiple times. However, the method is not useful for
decaying chemical species since each time must be scaled to the known injected mass. |
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