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Victor Obi_ Masters_Thesis.pdf (4.32 MB)

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Investigating the Transition from Non-Fickian to Fickian Dispersion With Increasing Length Scale and Flow Rate In Sand Packs: An Experimental Approach

Obi, Victor Chizoba
http://orcid.org/0009-0000-2714-722X
http://rave.ohiolink.edu/etdc/view?acc_num=kent1689685563350926

Abstract Details

2023, MS, Kent State University, College of Arts and Sciences / Department of Earth Sciences.
Numerous experimental and theoretical studies have explored the length-scale dependence of dispersion and dispersivity in different sedimentary porous media, revealing asymptotic dispersion but also a linearly increasing dispersivity with transport length scale. Albeit these transport behavior, defining the Representative Elementary Volume (REV) required to achieve Fickian dispersion in homogeneous porous media remains ambiguous, with very few experimental studies addressing this issue. Additionally, there is insufficient data about the relationship between longitudinal dispersivity (α_L) and flow rate or Peclet number (Pe). In contrast, dispersion is known to depend on Pe through a power law, but we do not know if the reported power-law exponents are impacted by various amounts of non-Fickian characteristics, i.e., Fickian transport characteristics are not ensured in determining the power-law exponents. In this laboratory study, we analyze Breakthrough Curves (BTCs) and Residence Time Distribution (RTD) curves from 900 tracer experiments conducted on a set of two well-sorted homogeneous column packs and a set of three two-layer heterogeneous column packs each of which includes seven different length columns between 0.6 ft and 6 ft. Our analysis shows that when the transport length scale increases, there is a distinct transition from non-Fickian to Fickian transport characteristics. From transport in different length columns, we determine power-law exponents of Pe-dependent dispersion and dispersivity highlighting how the exponents are affected by various degrees of non-Fickian transport characteristics., i.e., from the pre-asymptotic to the asymptotic regime. The power-law exponents exhibit a decreasing trend with an increase in transport length. For example, the well-sorted sand exhibit exponent of 1.55 in the non-Fickian regime at 0.6ft and converges to a value of 1.0 in the Fickian regime from the 6ft column. In the well-sorted media, the inclusive graphical skewness (Sg) decreases with L as the dispersion becomes Fickian but increases in the layered heterogeneous media. In the well-sorted media, we demonstrate that a power-law relation holds for dispersivity with Pe at each length scale, with the scaling exponents decreasing from 0.43 in the non-Fickian regime to 0 in the Fickian regime. Thus, we show dispersivity is independent of Pe when it reaches a Fickian transport scale. Overall, this study thoroughly accounts for Fickian dispersion and determines unique power-law exponents that can be used to predict the fate of contaminant transport.
Kuldeep Singh (Advisor)
Timothy Gallagher (Committee Member)
Anne Jefferson (Committee Member)
89 p.
Environmental Geology; Experiments; Fluid Dynamics; Geology; Hydrologic Sciences
Breakthrough Curve, Representative Elementary Volume, Fickian Dispersion, Non-Fickian Dispersion, Peclet number, Power law exponents.

Recommended Citations

Citations

  • Obi, V. C. (2023). Investigating the Transition from Non-Fickian to Fickian Dispersion With Increasing Length Scale and Flow Rate In Sand Packs: An Experimental Approach [Master's thesis, Kent State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=kent1689685563350926

    APA Style (7th edition)

  • Obi, Victor. Investigating the Transition from Non-Fickian to Fickian Dispersion With Increasing Length Scale and Flow Rate In Sand Packs: An Experimental Approach. 2023. Kent State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=kent1689685563350926.

    MLA Style (8th edition)

  • Obi, Victor. "Investigating the Transition from Non-Fickian to Fickian Dispersion With Increasing Length Scale and Flow Rate In Sand Packs: An Experimental Approach." Master's thesis, Kent State University, 2023. http://rave.ohiolink.edu/etdc/view?acc_num=kent1689685563350926

    Chicago Manual of Style (17th edition)

kent1689685563350926
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© 2023, all rights reserved.
This open access ETD is published by Kent State University and OhioLINK.