Theses and Dissertations at Montana State University (MSU)
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Item Controlling the area expansion of a backwards centrifugal fan blade passage using the principles of a diffuser and computational fluid dynamics(Montana State University - Bozeman, College of Engineering, 2021) Michalson, Adam Jeffrey; Chairperson, Graduate Committee: Erick JohnsonCentrifugal Fans are widespread in today's modern built environment. While a few variations of these fans exist, backward centrifugal fans are an efficient economical option capable of producing the pressure and airflow required for many modern building systems. Even though fans have become necessary piece of building engineering to facilitate occupant health and comfort, fan design almost exclusively relies on approximations to equations that have not changed since the 1950s and can consume, on average, 15% of a building's electrical consumption. Additionally, the approximations made support the ease and low cost of manufacturability. The traditional centrifugal fan design is made from stamped metal parts creating a fan blade sandwich with the blades held between an inlet shroud and a backplate. This rectangular blade passage is where the fluid flows through and picks up tangential acceleration. However, since the 1950s, nearly all advancements in fan design have been through incremental changes that are made by individual companies, and these resulting designs and performance data remain proprietary. This research revisits the foundations of centrifugal fan design with more modern tools and utilizes the concept of the diffuser to strictly control the expansion of the blade passage to improve centrifugal fan efficiency. Computational fluid dynamics was used to evaluate the performance of the new design against a traditionally manufactured fan. Combining the diffuser concept with an elliptical profile for the blade passage better controls the uniformity of the velocity field and pressure gradients through the passageway, while also reducing turbulence. Simulations of the new design against the traditional approach to fan design show an increase of nearly 10% in total efficiency.Item The development of superresolution spectroscopic techniques and characterization of microscale exciton diffusion in organic semiconducting polymers(Montana State University - Bozeman, College of Letters & Science, 2018) Massaro, Eric Stephen; Chairperson, Graduate Committee: Erik Grumstrup; Andrew H. Hill and Erik M. Grumstrup were co-authors of the article, 'Superresolution structured pump-probe microscopy' in the journal 'ACS Photonics' which is contained within this thesis.; Andrew H. Hill, Casey L. Kennedy and Erik M. Grumstrup were co-authors of the article, 'Imaging theory of structured pump-probe microscopy' in the journal 'Optics Express' which is contained within this thesis.; Erik M. Grumstrup was a co-author of the article, 'Label-free saturated structured excitation microscopy' in the journal 'Photonics' which is contained within this thesis.; Erik M. Grumstrup was a co-author of the article, 'Exceptionally fast nanoscale exciton diffusion in donor-acceptor polymer thin films' which is contained within this thesis.; Erik M. Grumstrup was a co-author of the article, 'Toward direct imaging of sub-10 nm carrier diffusion lengths by differential detection pump-probe microscopy' which is contained within this thesis.Disordered semiconducting materials offer cost effective, solution processable alternatives to highly crystalline semiconducting materials for utilization in a variety of optoelectronic devices. However, characterization of these complex materials systems using bulk spectroscopic methods is heavily influenced by chemical and morphological heterogeneity inherent to the material. The experiments described in this thesis are designed to improve the fundamental understanding of the photophysical processes in disordered solution processed semiconducting materials by developing and utilizing high spatial resolution spectroscopic methods. Chapters 2-4 will outline the experimental and theoretical development of two superresolution spectroscopic techniques. First (chapters 2 & 3), structured pump-probe microscopy (SPPM) utilizes a structured excitation profile along with a diffraction limited probe pulse to achieve ~100 nm spatial resolution. Using SPPM it is also possible to collect time resolved spectroscopic data from a sub-diffraction limited volume. Second (chapter 4), label-free saturated structured excitation microscopy (LF-SSEM) is theoretically developed. LF-SSEM is experimentally similar to SPPM but exploits the saturation of the absorption process to achieve even greater resolution enhancement. Here, simulated LF-SSEM is shown to achieve ~33 nm spatial resolution. Chapter 5 demonstrates the utilization of PPM to investigate exciton transport in the organic semiconducting polymer (OSP), poly [N-9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT). Although OSPs have shown great promise for use in a variety of optoelectronic applications, much remains un-known about their excited state dynamics. The data reported here represents a significant contribution to the rapidly growing wealth of knowledge pertaining to OSP systems. Specifically, the microscale exciton diffusivity observed in PCDTBT thin films using PPM is found to reach 3.2 cm 2/s. Chapter 6 examines a technique in the early stages of development and optimization that is able to detect excited state carrier diffusion with increased sensitivity and accuracy compared to PPM. Differential detection pump-probe microscopy (DDPPM) uses two probe pulses to selectively eliminate the signal of carriers that have not diffused beyond the boundaries of the initial excitation. The experiments described within this dissertation are diverse, yet the common goal is to increase and improve the knowledge of photophysical properties in disordered semi-conducting materials. This goal takes two forms in the development of novel spectroscopic methodology and the characterization of complex materials using PPM. The singular result is the advancement of basic science pertaining to complex semiconducting materials systems.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 Diffusion and diffusive exchange are sensitive to the structure of cartilage as measured by nuclear magnetic resonance(Montana State University - Bozeman, College of Engineering, 2017) Mailhiot, Sarah Elizabeth; Chairperson, Graduate Committee: Ronald K. June II; Nathan H. Williamson, Jennifer R. Brown, Joseph D. Seymour, Sarah L. Codd and Ronald K. June were co-authors of the article, 'T1-T2 correlation and biopolymer diffusion within human osteoarthritic cartilage measured with nuclear magnetic resonance' in the journal 'Applied magnetic resonance' which is contained within this thesis.; Sarah L. Codd, Jennifer R. Brown, Joseph D. Seymour and Ronald K. June were co-authors of the article, 'Pulsed gradient stimulated echo (PGSTE) NMR shows spatial dependence of fluid diffusion in human stage IV OA cartilage' submitted to the journal 'Magnetic resonance in medicine' which is contained within this thesis.; Fangrong Zong, James E. Maneval, Ronald K. June, Petrik Galvosas and Joseph D. Seymour were co-authors of the article, 'Quantifying NMR relaxation correlation and exchange in articular cartilage with time domain analysis' submitted to the journal 'Journal of magnetic resonance' which is contained within this thesis.; James E. Maneval, Ronald K. June and Joseph D. Seymour were co-authors of the article, 'Relaxation exchange in human OA cartilage impacts the observable T 2 relaxation rates' submitted to the journal 'Magnetic resonance in medicine' which is contained within this thesis.Osteoarthritis (OA) is the deterioration of the tissue on the surface of the articulating joints in mammals. OA is the progression loss of articular cartilage. OA affects 50% of people over age 65 and is the leading cause of workplace disability. There is no cure for OA and the state of the art treatment is joint replacement. One limitation for treating OA is the difficulty of diagnosing OA before tissue failure. Magnetic Resonance Imaging (MRI) is capable of detecting early pathologic changes to cartilage but challenges remain. The goal of this work is to evaluate how parameters, specifically relaxation and diffusion, used for creating imaging contrast in MRI are affected by disease in naturally occurring human osteoarthritis. Nuclear Magnetic Resonance (NMR) is utilized to measure the diffusion and magnetic relaxation in human OA cartilage samples. Diffusion Weighted Imaging (DWI) is a proposed imaging mechanism for diagnosing OA. The hypothesis is that fluid diffusion is faster in diseased tissue than in healthy tissue. We show that diffusion of fluid increases when cartilage is damaged by enzymes, such as during OA. We also show that the diffusion of fluid is donor specific in human OA cartilage. Diffusion of proteins in cartilage is also sensitive to enzyme degradation and donor as well as to the size and structure of the proteins in cartilage. These are complementary measures of the fluid and solid phase of cartilage. Relaxation weighted imaging is the most common way to image cartilage and is capable of measuring small structure changes due to OA. One limitation of this method is that reported relaxation rates vary between studies. We show that exchange, or motion of fluid, between the two sites of relaxation in cartilage alters the observed relaxation. Further, we show that the exchange rate is sensitive to donor and enzyme degradation. The results suggest that exchange rate is a sensitive measure of structure in cartilage and that relaxation should be cautiously interpreted when exchange occurs. Overall, this work shows that NMR and MRI are sensitive to the structure of cartilage and capable of detecting pathological damage to cartilage.Item A numerical study of diffusion of nanoparticles in a viscous medium during solidification(Montana State University - Bozeman, College of Engineering, 2016) Rahman, Kazi Mizanur; Chairperson, Graduate Committee: M. Ruhul AminIn the field of additive manufacturing process, laser cladding is widely considered due to its cost effectiveness, small localized heat generation and full fusion to metals. Introducing nanoparticles with cladding metals produces metal matrix nanocomposites which in turn improves the material characteristics of the clad layer. The strength of the laser cladded reinforced metal matrix composite are dependent on the location and concentration of the nanoparticles infused in metals. Hence, investigating the nanoparticle diffusion characteristics during solidification of laser cladding process is of prime interest. The governing equations that controls the fluid flow are standard incompressible Navier-Stokes and heat diffusion equation whereas the Euler-Lagrange approach has been considered for particle tracking. The mathematical formulation for solidification is adopted based on enthalpy porosity method. During the solidification process of liquid titanium, particle flow and distribution has been observed until the entire geometry solidified. A two dimensional numerical analysis has been performed to identify and track the silicon carbide nanoparticle diffusion in titanium. A numerical model implemented in a commercial software based on control volume method has been developed that allows to simulate the fluid flow during solidification as well as tracking nanoparticles during this process. The influence of the free surface of the melt pool has a high importance on the fluid flow as well as the influence of pure natural convection. Thus both buoyancy and Marangoni convection have been considered in terms of fluid flow in the molten region. A detailed parametric study has been conducted by changing the Marangoni number, convection heat transfer coefficient, different initial distribution of particles, and thermal boundary condition of bottom wall to analyze the behavior of the nanoparticle movement. Variation in particle's initial distribution along with different Marangoni number and solidification time results in a high concentration of nanoparticles in some portion of the geometry and lack of particles in rest of the geometry. High concentration of nanoparticles decrease with a decrease in Marangoni number. Furthermore, an increase in the rate of solidification time limits the nanoparticle movement from its original position which results in different distribution patterns with respect to the solidification time.Item Time-dependent Monte Carlo studies of surface diffusion(Montana State University - Bozeman, College of Letters & Science, 1990) Bowler, Ann MarieItem 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.