Date of Thesis

5-20-2017

Thesis Type

Honors Thesis

Degree Type

Bachelor of Science

Department

Geology

First Advisor

Ellen K. Herman

Abstract

Flow and contaminant transport in karstic aquifers differs drastically from porous media. Little work has been done to quantify the transport dynamics of non-aqueous phase liquids (NAPLs) in karst in the lab. Some studies have 3-D printed fractures to evaluate multiphase transport at the core scale, but examination of conduit flow using this technique is lacking in the literature. This project illustrates some of the strengths and limitations of 3-D printing and using X-ray computed tomography (XRCT) to characterize flow. After testing prints made from stereolithographic resin (SLA) and polyactic acid (PLA) plastic, we decided to use acrylonitrile butadiene styrene (ABS) plastic to construct flow cells to image turbulent water-NAPL-analog flow in conduits using XRCT. To mimic conduit flow transport dynamics, printed conduit apertures are elliptical and measure more than 1 cm in cross sectional area to promote turbulent flow. Fused filament fabrication, a type of 3-D printing process used during construction, produces permeable prints. To minimize communication between the conduit and surrounding support matrix allowing reuse of flow cells, we moderately melted cores using acetone vapor. This allows dissolved plastic to fill and harden between layers making the walls impermeable. Flow of water and hydrogel beads, a potential non-toxic NAPL analog tracer candidate, was imaged with a modified XRCT scanner. XRCT images were stitched together to identify conduit irregularities, and to image beads as they move through the conduit. Future work aims to develop hydrogel beads that behave like NAPLs in the lab. As a novel technique in karst modeling, printing and imaging requires further validation. Our images do not differentiate between beads, epoxy, and plastic, making validation difficult. Future work should involve radiologic agents added to water and NAPL-analogs during experimentation to increase the contrast between water and hydrogel beads in order to clarify flow paths.

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