ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
Displaying 1 - 10 of 18
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- Creators: Wang, Robert
- Creators: Chawla, Nikhilesh
Description
As one of the most promising materials for high capacity electrode in next generation of lithium ion batteries, silicon has attracted a great deal of attention in recent years. Advanced characterization techniques and atomic simulations helped to depict that the lithiation/delithiation of silicon electrode involves processes including large volume change (anisotropic for the initial lithiation of crystal silicon), plastic flow or softening of material dependent on composition, electrochemically driven phase transformation between solid states, anisotropic or isotropic migration of atomic sharp interface, and mass diffusion of lithium atoms. Motivated by the promising prospect of the application and underlying interesting physics, mechanics coupled with multi-physics of silicon electrodes in lithium ion batteries is studied in this dissertation. For silicon electrodes with large size, diffusion controlled kinetics is assumed, and the coupled large deformation and mass transportation is studied. For crystal silicon with small size, interface controlled kinetics is assumed, and anisotropic interface reaction is studied, with a geometry design principle proposed. As a preliminary experimental validation, enhanced lithiation and fracture behavior of silicon pillars via atomic layer coatings and geometry design is studied, with results supporting the geometry design principle we proposed based on our simulations. Through the work documented here, a consistent description and understanding of the behavior of silicon electrode is given at continuum level and some insights for the future development of the silicon electrode are provided.
ContributorsAn, Yonghao (Author) / Jiang, Hanqing (Thesis advisor) / Chawla, Nikhilesh (Committee member) / Phelan, Patrick (Committee member) / Wang, Yinming (Committee member) / Yu, Hongyu (Committee member) / Arizona State University (Publisher)
Created2014
Description
In nature, it is commonly observed that animals and birds perform movement-based thermoregulation activities to regulate their body temperatures. For example, flapping of elephant ears or plumage fluffing in birds. Taking inspiration from nature and to explore the possibilities of such heat transfer enhancements, augmentation of heat transfer rates induced by the vibration of solid and well as novel flexible pinned heatsinks were studied in this research project. Enhancement of natural convection has always been very important in improving the performance of the cooling mechanisms. In this research, flexible heatsinks were developed and they were characterized based on natural convection cooling with moderately vibrating conditions. The vibration of heated surfaces such as motor surfaces, condenser surfaces, robotic arms and exoskeletons led to the motivation of the development of heat sinks having flexible fins with an improved heat transfer capacity. The performance of an inflexible, solid copper pin fin heat sink was considered as the baseline, current industry standard for the thermal performance. It is expected to obtain maximum convective heat transfer at the resonance frequency of the flexible pin fins. Current experimental results with fixed input frequency and varying amplitudes indicate that the vibration provides a moderate improvement in convective heat transfer, however, the flexibility of fins had negligible effects.
ContributorsPrabhu, Saurabh (Author) / Rykaczewski, Konrad (Thesis advisor) / Phelan, Patrick (Committee member) / Wang, Robert (Committee member) / Arizona State University (Publisher)
Created2019
Description
District heating plays an important role in improving energy efficiency and providing thermal heat to buildings. Instead of using water as an energy carrier to transport sensible heat, this dissertation explores the use of liquid-phase thermochemical reactions for district heating as well as thermal storage. Chapters 2 and 3 present thermodynamic and design analyses for the proposed district heating system. Chapter 4 models the use of liquid-phase thermochemical reactions for on-site solar thermal storage. In brief, the proposed district heating system uses liquid-phase thermochemical reactions to transport thermal energy from a heat source to a heat sink. The separation ensures that the stored thermochemical heat can be stored indefinitely and/or transported long distances. The reactant molecules are then pumped over long distances to the heat sink, where they are combined in an exothermic reaction to provide heat. The product of the exothermic reaction is then pumped back to the heat source for re-use. The key evaluation parameter is the system efficiency.
The results demonstrate that with heat recovery, the system efficiency can be up to 77% when the sink temperature equals 25 C. The results also indicate that the appropriate chemical reaction candidates should have large reaction enthalpy and small reaction entropy. Further, the design analyses of two district heating systems, Direct District Heating (DDH) system and Indirect District Heating (IDH) system using the solvated case shows that the critical distance is 106m. When the distance is shorter than 1000,000m, the factors related to the chemical reaction at the user side and factors related to the separation process are important for the DDH system. When the distance is longer than 106m, the factors related to the fluid mechanic become more important. Because the substation of the IDH system degrades the quality of the energy, when the distance is shorter than 106m, the efficiency of the substation is significant. Lastly, I create models for on-site solar thermal storage systems using liquid-phase thermochemical reactions and hot water. The analysis shows that the thermochemical reaction is more competitive for long-duration storage applications. However, the heat recovery added to the thermochemical thermal storage system cannot help improving solar radiation absorption with high inlet temperature of the solar panel.
ContributorsZhang, Yanan (Author) / Wang, Robert (Thesis advisor) / Milcarek, Ryan (Committee member) / Parrish, Kristen (Committee member) / Phelan, Patrick (Committee member) / Rykaczewski, Konrad (Committee member) / Arizona State University (Publisher)
Created2022
Description
Energy storage technologies are essential to overcome the temporal variability in renewable energy. The primary aim of this thesis is to develop reactor solutions to better analyze the potential of thermochemical energy storage (TCES) using non-stoichiometric metal oxides, for the multi-day energy storage application. A TCES system consists of a reduction reactor and an insulated MOx storage bin. The reduction reactor heats (to ~ 1100 °C) and partially reduces the MOx, thereby adding sensible and chemical energy (i.e., charging it) under reduced pO2 environments (~10 Pa). Inert gas removes the oxygen generated during reduction. The storage bin holds the hot and partially reduced MOx (typically particles) until it is used in an energy recovery device (i.e., discharge). Irrespective of the reactor heat source (here electrical), or the particle-inert gas flows (here countercurrent), the thermal reduction temperature and inert gas (here N2) flow minimize when the process approaches reversibility, i.e., operates near equilibrium. This study specifically focuses on developing a reduction reactor based on the theoretical considerations for approaching reversibility along the reaction path. The proposed Zigzag flow reactor (ZFR) is capable of thermally reducing CAM28 particles at temperatures ~ 1000 °C under an O2 partial pressure ~ 10 Pa. The associated analytical and numerical models analyze the reaction equilibrium under a real (discrete) reaction path and the mass transfer kinetic conditions necessary to approach equilibrium. The discrete equilibrium model minimizes the exergy destroyed in a practical reactor and identifies methods of maximizing the energy storage density () and the exergetic efficiency. The mass transfer model analyzes the O2 N2 concentration boundary layers to recommend sizing considerations to maximize the reactor power density. Two functional ZFR prototypes, the -ZFR and the -ZFR, establish the proof of concept and achieved a reduction extent, Δδ = 0.071 with CAM28 at T~950 °C and pO2 = 10 Pa, 7x higher than a previous attempt in the literature. The -ZFR consistently achieved > 100 Wh/kg during >10 h. runtime and the -ZFR displayed an improved = 130 Wh/kg during >5 h. operation with CAM28. A techno-economic model of a grid-scale ZFR with an associated storage bin analyzes the cost of scaling the ZFR for grid energy storage requirements. The scaled ZFR capital costs contribute < 1% to the levelized cost of thermochemical energy storage, which ranges from 5-20 ¢/kWh depending on the storage temperature and storage duration.
ContributorsGhotkar, Rhushikesh (Author) / Milcarek, Ryan (Thesis advisor) / Ermanoski, Ivan (Committee member) / Phelan, Patrick (Committee member) / Wang, Liping (Committee member) / Wang, Robert (Committee member) / Arizona State University (Publisher)
Created2023
Description
Radiation heat transfer can surpass blackbody limit when distance between the hot emitter and cold receiver is less than the characteristic wavelength of electromagnetic radiation. The enhanced radiation heat transfer achieved is also called near-field radiation heat transfer. Several theoretical and experimental studies have demonstrated enhancement in near-field radiation heat transfer for isotropic materials such as silicon carbide (SiC), undoped and doped Si. The enhancement achieved however is narrow-banded. Significant improvement in radiation heat transfer is necessary to satisfy some of the energy demands. So, there is a growing interest to use hyperbolic materials because of its enhancement due to propagating modes. The main objective of the current thesis project is to investigate the control of hyperbolic bands using boron nitride nanotubes (nanostructure of hexagonal boron nitride) for near-field radiative heat transfer. Optical properties of boron nitride nanotubes are calculated using Maxwell-Garnet’s effective medium theory and its corresponding hyperbolic bands are identified. It is observed that the boron nitride nanotubes have only one hyperbolic band located at higher frequencies. Preliminary comparisons of the near-field radiative heat flux calculations with literature are performed using a more general 4×4 transfer matrix method. Due to its high computational time, anisotropic thin film optics is used to calculate near-field radiative heat transfer. Factors contributing to enhancement is investigated. In the end, Spectral allocation ratio, the ratio of heat flux contributed from higher frequencies to the heat flux contributed from lower frequencies is calculated to assess the contribution of each hyperbolic band to total heat flux.
ContributorsRajan, Vishwa Krishna (Author) / Wang, Liping (Thesis advisor) / Phelan, Patrick (Committee member) / Wang, Robert (Committee member) / Arizona State University (Publisher)
Created2022
Description
Thermal management of electronics is critical to meet the increasing demand for high power and performance. Thermal interface materials (TIMs) play a key role in dissipating heat away from the microelectronic chip and hence are a crucial component in electronics cooling. Challenges persist with overcoming the interfacial boundary resistance and filler particle connectivity in TIMs to achieve thermal percolation while maintaining mechanical compliance. Gallium-based liquid metal (LM) capsules offer a unique set of thermal-mechanical characteristics that make them suitable candidates for high-performance TIM fillers. This dissertation research focuses on resolving the fundamental challenges posed by integration of LM fillers in polymer matrix. First, the rupture mechanics of LM capsules under pressure is identified as a key factor that dictates the thermal connectivity between LM-based fillers. This mechanism of oxide “popping” in LM particle beds independent of the matrix material provides insights in overcoming the particle-particle connectivity challenges. Second, the physical barrier introduced due to the polymer matrix needs to be overcome to achieve thermal percolation. Matrix fluid viscosity impacts thermal transport, with high viscosity uncured matrix inhibiting the thermal bridging of fillers. In addition, incorporation of solid metal co-fillers that react with LM fillers is adopted to facilitate popping of LM oxide in uncured polymer to overcome this matrix barrier. Solid silver metal additives are used to rupture the LM oxide, form inter-metallic alloy (IMC), and act as thermal anchors within the matrix. This results in the formation of numerous thermal percolation paths and hence enhances heat transport within the composite. Further, preserving this microstructure of interconnected multiphase filler system with thermally conductive percolation pathways in a cured polymer matrix is critical to designing high-performing TIM pads. Viscosity of the precursor polymer solution prior to curing plays a major role in the resulting thermal conductivity. A multipronged strategy is developed that synergistically combines reactive solid and liquid fillers, a polymer matrix with low pre-cure viscosity, and mechanical compression during thermal curing. The results of this dissertation aim to provide fundamental insights into the integration of LMs in polymer composites and give design knobs to develop high thermally conducting soft composites.
ContributorsUppal, Aastha (Author) / Rykaczewski, Konrad (Thesis advisor) / Wang, Robert (Thesis advisor) / Kwon, Beomjin (Committee member) / Choksi, Gaurang (Committee member) / Phelan, Patrick (Committee member) / Arizona State University (Publisher)
Created2022
Description
Solid Oxide Fuel Cells (SOFCs) generate electricity using only hydrogen and oxygen and they form H2O as the only byproduct, giving them the potential to significantly reduce carbon emissions and the impacts of global warming. In order to meet the global power demands today, SOFCs need to significantly increase their power density and improve robustness in startup and cycling operations. This study explores the impact of decreasing the anode thickness to improve the mass transport of the fuel through the anode of a micro-tubular (mT) SOFC because few studies have reported the correlation between the two. Decreasing the thickness decreases the chance for concentration overpotential which is caused by not enough of the reactants being able to reach the reaction site while products are not able to be removed quickly enough. Experiments were performed in a split tube furnace heated to 750°C with nickel-yttria stabilized zirconia (Ni-YSZ) supported cells. Pure hydrogen was supplied to the cell at rates of 10, 20, 30, and 40 mL/min while the cathode was supplied air from the environment. The cell's performance was studied using the current-voltage method to generate polarization curves and electrochemical impedance spectroscopy to create Bode and Nyquist plots. The results from the electrochemical impedance spectroscopy show a lower impedance for the frequencies pertaining to the gas diffusion in the anode for the thinner cells. This suggests that decreasing the anode thickness increases the mass transport of the gas. Additionally, through a distribution of relaxation times (DRT) analysis, the peaks vary between the two cell thicknesses at the frequencies pertaining to gas diffusion in anode-supported cells, implicating the decreased resistance created by thinning the anode layer.
ContributorsPhillips, Kristina (Author) / Milcarek, Ryan (Thesis advisor) / Wang, Robert (Committee member) / Phelan, Patrick (Committee member) / Arizona State University (Publisher)
Created2023
Description
Gallium based room-temperature liquid metals (LMs) have special properties such as metal-like high thermal conductivity while in the liquid state. They are suitable for many potential applications, including thermal interface materials, soft robotics, stretchable electronics, and biomedicine. However, their high density, high surface tension, high reactivity with other metals, and rapid oxidation restrict their applicability. This dissertation introduces two new types of materials, LM foams, and LM emulsions, that address many of these issues. The formation mechanisms, thermophysical properties, and example applications of the LM foams and emulsions are investigated.LM foams can be prepared by shear mixing the bulk LM in air using an impeller. The surface oxide layer is sheared and internalized into the bulk LM as crumpled oxide flakes during this process. After a critical amount of oxide flakes is internalized, they start to stabilize air bubbles by encapsulating and oxide-bridging. This mechanism enables the fabrication of a LM foam with improved properties and better spreadability.
LM emulsions can be prepared by mixing the LM foam with a secondary liquid such as silicone oil (SO). By tuning a few factors such as viscosity of the secondary liquid, composition, and mixing duration, the thermophysical properties of the emulsion can be controlled. These emulsions have a lower density, better spreadability, and unlike the original LM and LM foam, they do not induce corrosion of other metals.
LM emulsions can form by two possible mechanisms, first by the secondary liquid replacing air features in the existing foam pores (replacement mechanism) and second by creating additional liquid features within the LM foam (addition mechanism). The latter mechanism requires significant oxide growth and therefore requires presence of oxygen in the environment. The dominant mechanism can therefore be distinguished by mixing LM foam with the SO in air and oxygen-free environments. Additionally, a comprehensive analysis of foam-to-emulsion density change, multiscale imaging and surface wettability confirm that addition mechanism dominates the emulsion formation. These results provide insight into fundamental processes underlying LM foams and emulsions, and they set up a foundation for preparing LM emulsions with a wide range of fluids and controllable properties.
ContributorsShah, Najam Ul Hassan (Author) / Rykaczewski, Konrad (Thesis advisor) / Wang, Robert (Thesis advisor) / Phelan, Patrick (Committee member) / Green, Matthew D. (Committee member) / Kwon, Beomjin (Committee member) / Arizona State University (Publisher)
Created2023
Description
The objective of this dissertation is to study the use of metamaterials as narrow-band and broadband selective absorbers for opto-thermal and solar thermal energy conversion. Narrow-band selective absorbers have applications such as plasmonic sensing and cancer treatment, while one of the main applications of selective metamaterials with broadband absorption is efficiently converting solar energy into heat as solar absorbers.
This dissertation first discusses the use of gold nanowires as narrow-band selective metamaterial absorbers. An investigation into plasmonic localized heating indicated that film-coupled gold nanoparticles exhibit tunable selective absorption based on the size of the nanoparticles. By using anodized aluminum oxide templates, aluminum nanodisc narrow-band absorbers were fabricated. A metrology instrument to measure the reflectance and transmittance of micro-scale samples was also developed and used to measure the reflectance of the aluminum nanodisc absorbers (220 µm diameter area). Tuning of the resonance wavelengths of these absorbers can be achieved through changing their geometry. Broadband absorption can be achieved by using a combination of geometries for these metamaterials which would facilitate their use as solar absorbers.
Recently, solar energy harvesting has become a topic of considerable research investigation due to it being an environmentally conscious alternative to fossil fuels. The next section discusses the steady-state temperature measurement of a lab-scale multilayer solar absorber, named metafilm. A lab-scale experimental setup is developed to characterize the solar thermal performance of selective solar absorbers. Under a concentration factor of 20.3 suns, a steady-state temperature of ~500 degrees Celsius was achieved for the metafilm compared to 375 degrees Celsius for a commercial black absorber under the same conditions. Thermal durability testing showed that the metafilm could withstand up to 700 degrees Celsius in vacuum conditions and up to 400 degrees Celsius in atmospheric conditions with little degradation of its optical and radiative properties. Moreover, cost analysis of the metafilm found it to cost significantly less ($2.22 per square meter) than commercial solar coatings ($5.41-100 per square meter).
Finally, this dissertation concludes with recommendations for further studies like using these selective metamaterials and metafilms as absorbers and emitters and using the aluminum nanodiscs on glass as selective filters for photovoltaic cells to enhance solar thermophotovoltaic energy conversion.
This dissertation first discusses the use of gold nanowires as narrow-band selective metamaterial absorbers. An investigation into plasmonic localized heating indicated that film-coupled gold nanoparticles exhibit tunable selective absorption based on the size of the nanoparticles. By using anodized aluminum oxide templates, aluminum nanodisc narrow-band absorbers were fabricated. A metrology instrument to measure the reflectance and transmittance of micro-scale samples was also developed and used to measure the reflectance of the aluminum nanodisc absorbers (220 µm diameter area). Tuning of the resonance wavelengths of these absorbers can be achieved through changing their geometry. Broadband absorption can be achieved by using a combination of geometries for these metamaterials which would facilitate their use as solar absorbers.
Recently, solar energy harvesting has become a topic of considerable research investigation due to it being an environmentally conscious alternative to fossil fuels. The next section discusses the steady-state temperature measurement of a lab-scale multilayer solar absorber, named metafilm. A lab-scale experimental setup is developed to characterize the solar thermal performance of selective solar absorbers. Under a concentration factor of 20.3 suns, a steady-state temperature of ~500 degrees Celsius was achieved for the metafilm compared to 375 degrees Celsius for a commercial black absorber under the same conditions. Thermal durability testing showed that the metafilm could withstand up to 700 degrees Celsius in vacuum conditions and up to 400 degrees Celsius in atmospheric conditions with little degradation of its optical and radiative properties. Moreover, cost analysis of the metafilm found it to cost significantly less ($2.22 per square meter) than commercial solar coatings ($5.41-100 per square meter).
Finally, this dissertation concludes with recommendations for further studies like using these selective metamaterials and metafilms as absorbers and emitters and using the aluminum nanodiscs on glass as selective filters for photovoltaic cells to enhance solar thermophotovoltaic energy conversion.
ContributorsAlshehri, Hassan (Author) / Wang, Liping (Thesis advisor) / Phelan, Patrick (Committee member) / Rykaczewski, Konrad (Committee member) / Wang, Robert (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2018
Description
Thermodynamic development and balance of plant study is completed for a 30 MW solar thermochemical water splitting process that generates hydrogen gas and electric power. The generalized thermodynamic model includes 23 components and 45 states. Quasi-steady state simulations are completed for design point system sizing, annual performance analysis and sensitivity analysis. Detailed consideration is given to water splitting reaction kinetics with governing equations generalized for use with any redox-active metal oxide material. Specific results for Ceria illustrate particle reduction in two solar receivers for target oxygen partial pressure of 10 Pa and particle temperature of 1773 K at a design point DNI of 900 W/m2. Sizes of the recuperator, steam generator and hydrogen separator are calculated at the design point DNI to achieve 100,000 kg of hydrogen production per day from the plant. The total system efficiency of 39.52% is comprised of 50.7% hydrogen fraction and 19.62% electrical fraction. Total plant capital costs and operating costs are estimated to equate a hydrogen production cost of $4.40 per kg for a 25-year plant life. Sensitivity analysis explores the effect of environmental parameters and design parameters on system performance and cost. Improving recuperator effectiveness from 0.7 to 0.8 is a high-value design modification resulting in a 12.1% decrease in hydrogen cost for a modest 2.0% increase in plant $2.85M. At the same time, system efficiency is relatively inelastic to recuperator effectiveness because 81% of excess heat is recovered from the system for electricity production 39 MWh/day and revenue is $0.04 per kWh. Increasing water inlet pressure up to 20 bar reduces the size and cost of super heaters but further pressure rises increasing pump at a rate that outweighs super heater cost savings.
ContributorsBudama, Vishnu Kumar (Author) / Johnson, Nathan (Thesis advisor) / Stechel, Ellen (Committee member) / Rykaczewski, Konrad (Committee member) / Phelan, Patrick (Committee member) / Wang, Robert (Committee member) / Arizona State University (Publisher)
Created2018