Microtomographic Imaging of the Air-Water Interface in Unsaturated Porous Media Molly S. Costanza-Robinson, Middlebury College, VT The air-water interface in porous media serves as a two-dimensional retention domain for solutes and colloids and also governs the dynamics of interphase mass- and energy transfer. Advances in synchrotron X-ray microtomography (µCT) provide direct visualization of the air-water interfacial area, from which quantitative porescale information is extracted. Accusand medium Accusand coarse Granusil fine Granusil coarse Granusil mix
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-1
Ai (cm )
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Acknowledgements Microtomographic imaging was performed at GeoSoilEnviroCARS Beamline, Advanced Photon Source, Argonne National Laboratory, which is supported by NSF, the State of Illinois, and DOE.
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40 60 % water saturation
Measured air-water interfacial areas depend on the size of the imaged region. The small samples typically imaged by µCT may not always satisfy representative elementary volume (REV) requirements with regard to air-water interfacial areas (e.g., yellow and blue lines).
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REV achieved
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Ai (cm-1)
µCT visualization of the air-water interface for glass beads (left) and two natural sands (Accusand and Granusil). Total imaged volumes are 4×4×6-mm cuboids.
Measured airwater interfacial areas for various size fractions of two natural media as a function of water saturation. Ai varies linearly with Sw for all media examined.
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15.8%
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39.9%
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57.2% 70.5%
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REV not achieved
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1 2 3 Index of imaged volume (-)
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