Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Heat transfer and flow in packed beds with nuclear magnetic resonance microscopy and computational fluid dynamics(Montana State University - Bozeman, College of Engineering, 2017) Perera, Dinal; Chairperson, Graduate Committee: Sarah L. Codd; Ryan Anderson (co-chair)Fluid flow and heat transfer characteristics in packed beds are studied extensively due to its importance in different fields. The macroscopic and continuum approaches used for analysis require a degree of empiricism and theoretical assumptions. Pore-scale models drive out the need for empiricism and theoretical assumptions but cannot be validated due the lack of accurate pore-scale experimental methods. This thesis presents a novel method that utilizes Nuclear Magnetic Resonance (NMR) techniques to map the pore scale melt fraction and velocities within packed beds, non-invasively. An initial experiment was conducted where heated Nitrogen was flowed through a packed bed filled with PCMs. The increasing signal intensities due to the melting of these PCMs were captured using a 1H tuned coil. Another experiment was conducted where heated Fluorinert was flowed through a packed bed filled with PCMs. The melt front of the PCMs and the velocity of the Fluorinert was imaged using a 1 H/19 F dual tuned coil. Discrete Element Modelling (DEM) was used for the generation of randomly packed beds that mimic the experimental packed beds. These numerical packed beds were modelled under the same inlet conditions as in experimental work to yield models that showed similarities to the processes seen in experimental results. Numerical work analyzed the effects of particle size and geometry on flow, heat transfer and pore structure. Three models were developed: a packed bed of monodisperse spheres, a bed of spherical particles with a Gaussian distribution in diameters and a bed of non-spherical particles with a Gaussian distribution in diameters. It was concluded that the beds of spherical and non-spherical particles with a Gaussian distribution in diameters yielded the best complementary results to the experimental work. These numerical models and the experimental work yielded maximum velocities in the range of 6 mm/s to 8 mm/s, while showing similar attributes such as intra-particle melt gradients, preferential flow pathways and channeling effect. Experimental work shows a melt front of 60 mm in 41 minutes while models yielded a melt front of 18 mm in the same time.Item Flow and transport studies of porous systems by magnetic resonance microscopy and Lattice Boltzmann simulations(Montana State University - Bozeman, College of Engineering, 2010) Brosten, Tyler Ryan; Chairperson, Graduate Committee: Sarah L. CoddNuclear magnetic resonance experiments and Lattice-Boltzmann simulations are powerful techniques for studying pore scale dynamics in porous media. Several applications of these methods to the study of pore scale hydrodynamics and transport are discussed. Of special interest are concepts relating to pore structure characterization. In the first application it is shown that nuclear magnetic resonance measurements of pre-asymptotic transport dynamics in random open cell foams provide a characteristic structure length scale. These measurements and Lattice-Boltzmann simulations for a model foam structure demonstrate dynamical behavior similar to lower porosity consolidated granular porous media; suggesting a generalized approach to pore structure characterization. Normalizing the data by the characteristic length collapses data for different foam samples and mono-disperse packed beds. The non-equilibrium statistical mechanics theory of pre-asymptotic dispersion is used to model the hydrodynamic dispersive dynamics. In the second application transport of hard sphere colloidal particles under flow through an open cell foam is studied using nuclear magnetic resonance. The temporal dynamics of the colloidal particles and suspending fluid phase are obtained through spectral chemical resolution. The data is interpreted in the broader context of classic hydrodynamic dispersion theory and mechanisms of transport for each phase. In the third application pore scale hydrodynamics of flow over a model porous surface are investigated using three dimensional Lattice-Boltzmann simulations and nuclear magnetic resonance. The Lattice-Boltzmann and nuclear magnetic resonance data are used to interpret classic interfacial hydrodynamic boundary conditions. Finally, in the fourth application a study of magnetic resonance microscopy to novel tape cast porous ceramics is conducted.Item Nuclear magnetic resonance microscopy of NAFION-117 proton exchange polymer membranes(Montana State University - Bozeman, College of Engineering, 2004) Howe, Daniel Trusler; Chairperson, Graduate Committee: Joseph SeymourAs the combustion of fossil fuels for the generation of energy and transportation becomes more expensive, of limited supply, and environmentally unsound, the development of viable fuel cell alternatives becomes more important. A comprehensive understanding of the proton exchange membranes (PEM's) used as electrolytes in certain types of fuel cells will play a major role in bringing the cost and reliability of PEM fuel cell systems down to a competitive level with traditional fossil fuel methods. Magnetic resonance microscopy (MRM) is well suited to the study of these membranes because it is non-invasive, and can spatially resolve material structure and give data on transport phenomena such as diffusion that cannot be determined by other methods. The goal of this research was to use magnetic resonance microscopy to study solvent mobility levels within the polymer membranes via spin-spin, T2, magnetic relaxation and diffusion mapping. The molecular mobility can quantify membrane swelling and spatial heterogeneity of the membrane material. A key aim of the research is to correlate these findings with previous bulk MRM studies of solvent within polymer membranes. Prior bulk MRM studies of solvent molecular mobility at different hydration levels were unable to study the membranes fully submersed in solvents, as the free solvent signal would dominate the nuclear magnetic resonance (NMR) signal from the solvent within the membrane. In this study spatial resolution of the MRM data provides the means to study fully saturated membranes, a condition of interest since the degree of hydration is related to membrane operational efficiency. The material homogeneity of the polymer in the thickness and surface directions of the membrane, an important factor in the reliable performance of fuel cells, was studied via T2 mapping. Nafion®-117 was the proton exchange membrane studied because it is currently the most popular electrolyte used in the PEM fuel cell industry and several bulk MRM studies have been conducted. Results indicate that both solvent mobility and membrane swelling are highly dependant on the concentration of methanol used to prepare the samples, as seen in the bulk studies, and that solvent mobility can vary on the 20 micron level within the polymer in both the thickness and surface directions. This research establishes MRM as an important tool for the study of individual proton exchange polymer membrane samples and provides a basis for extension to the study of membranes during operation.Item Supercritical fluids, oscillatory flow, and partially saturated porous media by magnetic resonance microscopy(Montana State University - Bozeman, College of Engineering, 2011) Rassi, Erik Michael; Chairperson, Graduate Committee: Sarah L. Codd; Joseph D. Seymour (co-chair)The research presented in this dissertation used Magnetic Resonance (MR) techniques to study fluid dynamics in complex systems. The systems investigated were critical and supercritical fluids, partially saturated porous media, and oscillatory flow. Supercritical fluids (SCF) are useful solvents in green chemistry and oil recovery and are of great current interest in the context of carbon sequestration. Flow in partially saturated porous media and the resultant hydrodynamics are important in fields including but not limited to hydrology, chemical, medical, and the petroleum industry. Lastly, Pulsatile and oscillatory flows are prevalent in many biological, industrial, and natural systems. Displacement propagators were measured at various displacement observation times to quantify the time evolution of dynamics in critical and supercritical fluid flow. In capillary flow, the critical phase transition fluid C2F6 showed increased compressibility compared to the near critical gas and supercritical fluid. These flows exhibit large variations in buoyancy arising from large changes in density due to very small changes in temperature. Ensemble averaged MR measurements were taken to observe the effects on a bead pack partially saturated with air under flowing conditions of water. Air was injected into the bead pack as water flowed simultaneously through the sample. The initial partially saturated state was characterized with MR imaging density maps, free induction decay (FID) experiments, propagators, and velocity maps before the water flow rate was increased. After the maximum flow rate, the MR imaging density maps, FID experiments, propagators, and velocity maps were repeated and compared to the data taken before the maximum flow rate. The work performed here showed that a partially saturated single phase flow had global flow dynamics that returned to characteristic flow statistics once a steady state high flow rate was reached. A system was constructed to provide a controllable and predictable oscillatory flow in order to gain a better understanding of the impact of oscillatory flow on Newtonian and non-Newtonian fluids, specifically water, xanthan gum (XG), polyacrylamide (PAM) colloidal suspensions. The oscillatory flow system coupled with MR measured the velocity distributions and dynamics of the fluid undergoing oscillatory flow at specific points in the oscillation cycle.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 flow and transport behavior in small channels by magnetic resonance microscopy(Montana State University - Bozeman, College of Engineering, 2007) Brown, Jennifer Ruth; Chairperson, Graduate Committee: Joseph D. Seymour; Sarah Codd (co-chair)The research presented addresses colloidal transport issues in small channel systems using Magnetic Resonance Microscopy techniques. In transport phenomena, the interaction between convection or deterministic motions and diffusion or random motions is important in many engineering and natural applications, especially relating to multiphase flows. Magnetic Resonance methods have the ability to separate coherent from incoherent motion, as well as measure spatially resolved velocity, probability distributions of displacement, and microstructure on the pore scale, even within a multiphase colloidal system. A dilute (f < 0.10) suspension of ~2.5 mm Brownian particles under shear flow in a 1 mm diameter glass capillary was investigated using spectrally resolved Pulsed Gradient Spin Echo techniques. The results indicate particle migration inward towards the capillary center. In addition, dispersion coefficients measured via flow-compensated Pulsed Gradient Spin Echo techniques as a function of observation time indicate the onset of irreversible dynamics with increasing total strain. Particle migration and irreversible dynamics are generally not expected to occur in dilute Brownian suspensions and are therefore not considered in the modeling of flow systems.