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Item Analysis of water transport phenomena in thin porous media of a polymer electrolyte membrane fuel cell(Montana State University - Bozeman, College of Engineering, 2018) Battrell, Logan Robb; Chairperson, Graduate Committee: Ryan Anderson; Aubree Trunkle, Erica Eggleton, Lifeng Zhang and Ryan Anderson were co-authors of the article, 'Quantifying cathode water transport via anode humidity measurements in a polymer electrolyte membrane fuel cell' in the journal 'Energies' which is contained within this thesis.; Ning Zhu, Lifeng Zhang and Ryan Anderson were co-authors of the article, 'Transient, spatially resolved desaturation of gas diffusion layers measured via synchrotron visualization' in the journal 'International journal of hydrogen energy' which is contained within this thesis.; Virat Patel, Ning Zhu, Lifeng Zhang and Ryan Anderson were co-authors of the article, '4-D imaging of the desaturation of gas diffusion layers by synchrotron radiography' submitted to the journal 'Journal of power sources' which is contained within this thesis.This thesis explores and quantifies water transport related to the desaturation of the thin porous layer known as the Gas Diffusion Layer (GDL) associated with Polymer Electrolyte Membrane (PEM) fuel cells. The proper management of water within this layer is critical to optimal fuel cell performance. If there is not enough water, the membrane can become dehydrated, which leads to poor cell performance, but if too much water accumulates or becomes flooded, gas transport is restricted, which also lowers performance and can potentially lead to total cell failure. Understanding the desaturation of this layer is thus key to obtaining and maintaining optimal fuel cell performance. This behavior is explored both at the macroscale, through the quantification of the removal of excess water from an active fuel cell, as well as at the micro-scale, through the use of synchrotron X-ray computed tomography (X-ray CT) to visualize and quantify the desaturation of an initially flooded GDL. The macro-scale investigation extends the previously developed qualitative Anode Water Removal (AWR) test, which functions to identify when poor PEM fuel cell performance is due to excess water, to a diagnostic protocol that quantifies the amount of water being removed by the test through an analysis of the anode pressure drop. Results show that the protocol can be applied to a variety of fuel cell setups and can be used to quickly quantify water management capabilities of novel GDL materials. The microscale investigations show that while both convection and evaporation play a role in the desaturation, evaporation is required to fully desaturate the GDL. Additionally, the microscale investigation allows for the spatial segmentation of the GDL to identify local desaturation rates and temporal saturation profiles, which show that the overall desaturation of the GDL is a heterogeneous process that depends on initial conditions, flow field geometry and the natural anisotropy of the material. Results show that future control strategies and modeling studies will need to expand their investigated domains in order to accurately capture the fully heterogeneous nature of this process.Item Knudsen diffusion in beds of monodisperse silica spheres(Montana State University - Bozeman, College of Engineering, 1984) Huizenga, David GaryItem A study of new methods for the simultaneous measurement of diffusion and pore structure in catalyst supports(Montana State University - Bozeman, College of Engineering, 1984) Drake, Mark ClaytonItem Theoretical investigation of biofilm detachment and protection from killing using a bacterium level automata model(Montana State University - Bozeman, College of Engineering, 2004) Hunt, Stephen Michael; Chairperson, Graduate Committee: Philip S. Stewart.This dissertation presents a three-dimensional dynamic, stochastic computer model of biofilm development, BacLAB, created to theoretically explore conjectures associated with biofilms. BacLAB simulates the life cycle of a biofilm by mimicking the physical and biological behavior of a system with a simple set of experimentally determined "rules" applied to the smallest possible biofilm unit (the cell). These rules, however, lead to patterns on a larger scale. Much as bacterial cells organize themselves in a biofilm as a response to individual spatial conditions, the resulting model structure is produced in a process of self-organization rather than by some predetermined plan for biofilm development. Detachment of cells from a mature biofilm is an important process determining the accumulation of attached cells and allowing for dissemination of the organism. The mode by which cells detach is, therefore, a critical stage in the life cycle of biofilms. Initial simulation studies with BacLAB were used to investigate conjectures associated with detachment resulting from either the accumulation of a metabolic product or the depletion of a metabolic substrate. Results demonstrated that the typical simulated biofilm eventually attains a steady state where biofilm growth was counterbalanced by detachment with cell areal densities comparable to those in laboratory biofilms. Some of the phenomena predicted by BacLAB include sloughing, hollow cell clusters and gradients in solute concentration and growth rate. BacLAB was also adapted to simulate the protection from killing by antimicrobial agents afforded to microorganisms in the biofilm state. It is believed that the reduced susceptibility of bacteria in biofilms is an important factor in the persistence of some chronic infections and the mechanisms of protection are only moderately understood. Because antimicrobials are thought be more effective in killing actively growing bacteria, the rate of killing was assumed to be proportional to the local concentration of the substrate. The results suggest that substrate limitation has the potential to contribute to the reduced antimicrobial susceptibility found in biofilms, but is not adequate by itself in explaining the log-term persistence of biofilm viability observed experimentally.Item Magnetic resonance microscopy studies of biofilms : diffusion, hydrodynamics and porous media(Montana State University - Bozeman, College of Engineering, 2009) Hornemann, Jennifer Ann; Chairperson, Graduate Committee: Sarah L. Codd; Joseph D. Seymour (co-chair)Due to the complicated nature of studying living bacterial communities, Magnetic Resonance Microscopy (MRM) is a necessary tool providing unique data that is complementary to other techniques such as confocal microscopy and microelectrodes. MRM has the ability to probe an opaque system non-invasively and collect velocity measurements, imaging data, diffusion, and relaxation values and is an asset in the quest to learn how biofilms establish, grow, and die. The goal of these studies was to extend current biofilm research using MRM to enhance our understanding of transport phenomena over a hierarchy of scales, from the microscopic diffusion level to the macroscopic bulk flow. Staphylococcus epidermidis was the bacteria chosen for the biopolymer diffusion and the secondary flow studies due to its common identification in opportunistic biofilm infections. This diffusion study was the first Pulse Gradient Spin Echo (PGSE) MRM measurements of the impact of environmental and chemical challenges on the biomacromolecular dynamics in medically relevant S. epidermidis biofilm material demonstrating the ability to characterize molecular dynamics in biofilms, providing a basis for sensors which can indicate the state of the biofilm after thermal or chemical treatment and provide information to further understand the molecular level mechanisms of such treatments. The secondary flow data clearly support the conclusion that reactor size impacts studies of spatially distributed biological activity, and the idea that, scaling of transport models in biofilm impacted devices is possible but requires more study. Additionally, due to the increasing amount of CO 2 in the earth's atmosphere and the need to understand the options of sequestering this CO 2 to combat the impacts of global warming, studies were conducted to understand how biofilms grow in porous media. The resilience of Bacillus mojavensis biofilms to super critical CO 2 is documented, and thus, this bacteria was chosen. Results indicate that by varying exchange times, T 2-T 2 experiments can determine the extent of biofilm growth in an opaque porous media as demonstrated in multiple glass bead pack configurations. Using MRM as a tool to study these biofilm systems over a wide range of environmental conditions is the focus of the research presented in this dissertation.Item Colloidal suspension hydrodynamics and transport processes in microcapillary and porous media flows studied using dynamic nuclear magnetic resonance(Montana State University - Bozeman, College of Engineering, 2010) Fridjonsson, Einar Orn; Chairperson, Graduate Committee: Joseph D. Seymour; Sara L. Codd (co-chair)The research presented in this dissertation uses Magnetic Resonance Microscopy (MRM) to investigate complex fluid dynamics systems. The systems investigated are colloidal transport in a microcapillary, bifurcation and porous medium, reactive transport in porous medium, transport through beta-lactoglobulin gels and the effect of peptide surfactants on droplet deformation in a Taylor-Couette device. Complex transport phenomena underlies many applications in engineering and thorough understanding of convective and diffusive motion in multiphase systems is important. MRM allows for the investigation of multi-phase transport phenomena noninvasively and can be used to investigate different moments of motion by sequence of the application of magnetic field gradients. The measurement of coherent and incoherent motion separately and the simultaneous measurement of multiple phases (colloids or suspending fluid) is possible. The colloidal flow studies show the effects shear induced migration, deposition, incoherent and coherent motion have on the macro- and microscopic structure of the fluids. Results show the direct effect increased shear has on the onset of secondary and chaotic fluid motion due to microscopic particle-particle and macroscopic fluid-structure interactions indicating the presence of shear thresholds. Reactive transport in porous media is important for understanding the spread of contaminants in the Earth's subsurface. The effect of calcium carbonate precipitation in a model porous medium due to Sporosarcina pasturii growth on the hydrodynamics was measured using MRM. These measurements show an increase in mechanical mixing causing a more rapid asymptote to Gaussian dynamics than for the same system without precipitation. The transport measurements of water with and without NaCl flowing through a homogeneous (pH 7.0) and heterogeneous (pH 5.2) beta-lactoglobulin gels quantifies the hydrodynamic dispersion in the gels and provided direct information on the gel structure noninvasively. Droplet deformation of (36/64)%wt toluene/chloroform droplets in a continuous phase of glycerol inside a Taylor-Couette device with and without surfactants (2%wt Tween60, AM1 and AFD4 peptide surfactants) is measured using a rapid MRM sequence (ROTACOR) which compensates for system rotation. MRM measurements show a restriction to droplet deformation due to the presence of the peptide surfactants.Item A 3D computer model investigation of biofilm detachment and protection mechanisms(Montana State University - Bozeman, College of Engineering, 2008) Chambless, Jason Daniel; Chairperson, Graduate Committee: Philip S. Stewart.A biofilm is a dense aggregation of microorganisms attached to each other and a supporting surface. Biofilms are ubiquitous in industrial environments and are also frequently recognized as the source of persistent infections. Biofilm invasions and biofilm-induced infections are often difficult or impossible to remedy. This dissertation presents the results of a 3D hybrid computer model, BacLAB, which was used to simulate detachment and protection mechanisms of biofilms in a cellular automata framework. Protection against antimicrobials afforded by each of four hypothesized protective mechanisms was investigated in order to examine population survival versus antimicrobial exposure time, and the spatial patterns of chemical species and cell types. When compared to each other, the behaviors of the slow penetration, adaptive stress response, substrate limitation, and persister mechanisms produced distinct shapes of killing curves, non-uniform spatial patterns of survival and cell type distribution, and anticipated susceptibility patterns of dispersed biofilm cells.