Air Channel Formation, Size, Spacing, and Tortuosity During Air Sparging |
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| Authors: | Carl R. Elder Craig H. Benson |
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| Affiliation: | Carl R. Elder is a doctoral student in the Department of Civil and Environmental Engineering at the University of Wisconsin-Madison (Madison, WZ53706). He receceived a B.S. in civil engineering from the University of Massachusetts-Amherst, and an MS. from the University of Wisconsin-Madison.;Craig H. Benson is an associated professor of civil and environmental engineering and geological engineering at the University of Wisconsin-Madison. He has a B.S. from Lehigh University, and M.S. and Ph.D. degrees from the University of Texas-Austin. All three degrees are in civil engineering, with the M.S. and Ph.D. degrees focused on geotechnical engineering. Dr. Benson's research is on waste containment and remediation, with emphasis on statistical data analysis, characterization and simulation of heterogeneity, geophysical methods, and flow and transport modeling in saturated and unsaturated soils. Dr. Benson has received the following research awards: Presidential Young Investigator Award fvom the National Science Foundation, the Distinguished Young Faculty Award from the U.S. Department of Energy, and the Collingwood, Middlebrooks, Croes, and Casagrande awards from the American Society of Civil Engineers. He teaches courses in geotechnical engineering for waste containment, geotechnical engineering for site remediation, probabilistic methods, unsaturated flow and transport, and geosynthetics engineering. He is currently an editor for the ASCE/G-1 Journal of Geotechnical and Geoenvironmental Engineering. |
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| Abstract: | Characterizing mass transfer during in situ air sparging requires knowledge of the size, shape, and interfacial area of air channels. These characteristics were determined by analysis of digital images of air channels passing through submerged glass beads having particle size in the sand range. Pore-scale channeling occurred in all cases. The analysis showed that the air channels were narrower, more tortuous, more closely spaced, and moved nearly vertically through the coarser media. In the finer media, air channels had larger diameter, were spaced further apart, and passed nearly horizontally through the media. The mean diameter of the channels varied between 2.8 and 8.1 mm, and the mean spacing varied between 8.3 and 19.4 mm. Estimates of the area of the air-water interface per unit volume of soil (a0), computed using data from the digital images and an assumed arrangement of channels, ranged from 0.02 to 0.2 mm2/mm3. Larger a0 were obtained for coarser media and uniformly graded media. These estimates of a0 compare well with published values for common packed-column materials and for unsaturated soils. |
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