Organizational Unit:
George W. Woodruff School of Mechanical Engineering

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Now showing 1 - 10 of 4870
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    Development and characterization of novel reduction-oxidation active materials for two-step solar thermochemical cycles
    (Georgia Institute of Technology, 2019-05-21) Bush, Hagan E. ; Loutzenhiser, Peter G. ; Jeter, Sheldon ; Kumar, Satish ; Orlando, Thomas ; Ranjan, Devesh ; Mechanical Engineering
    Solar thermochemistry enables concentrating solar technologies to store or produce energy and materials in new, more versatile ways. In this work, binary and perovskite metal oxide candidates for high-temperature reduction-oxidation (redox) thermochemical cycles were synthesized and characterized to determine their potential for solar applications. First, the experimental infrastructure required to study rapidly reacting, high temperature metal oxides was developed. A high flux solar simulator (HFSS) capable of rapid heating was coupled to an upward flow reactor (UFR) to thermally reduce oxide samples, and O2 product gas flows were measured to calculate thermal reduction rates. The radiative input from the HFSS was characterized and coupled to computational models of the UFR to predict gas dynamics and redox sample heating. Dispersion modeling was used to correct temporal O2 measurements downstream of reducing samples. Thermal reduction experiments with the well-studied binary oxide pair Co3O4/CoO were performed to validate the computational models. Next, the UFR and a thermogravimetric analyzer (TGA) were used to evaluate candidate materials. Fe2O3/Fe3O4 were kinetically characterized via TGA and evaluated in thermodynamic cycle models. The results suggested the oxides were promising candidates for solar thermochemical electricity production. Al-doped SrFeO3-δ was synthesized and reaction models were developed with TGA to predict equilibrium nonstoichiometry and redox thermodynamics. The results were incorporated into a thermodynamic cycle model, and redox cycling experiments were performed in the UFR. The analyses determined that the oxides were well-suited to air separation for NH3 production.
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    Using magnetic resonance imaging to track inflammatory cells in a murine myocardial infarction model
    (Georgia Institute of Technology, 2009-04-08) Yang, Yidong ; Hu, Tom ; Cho, Sang Hyun ; Wang, Chris ; Yanasak, Nathan ; Mechanical Engineering
    In cellular MRI, micrometer-sized iron oxide particles (MPIO) are a more sensitive contrast agent for tracking inflammatory-cell migration compared to ultra-small superparamagnetic iron oxide particles (USPIO). Inflammation, which promotes adverse tissue remodeling, is known to occur in the viable myocardium adjacent to the necrosed area after a myocardial infarction (MI). This study investigated the temporal relationship between inflammatory cell infiltration and cardiac function during tissue remodeling post-MI using MPIO-enhanced MRI. The MPIO were injected into 7 C57Bl/6 mice (MI+MPIO group) via intravenous administration. The MI was induced 7 days post-MPIO injection. As control groups, 7 mice (Sham+MPIO group) underwent sham-operated surgery without myocardial injury post-MPIO injection and another 6 mice (MI-MPIO group) underwent MI surgery without MPIO injection. MRIs performed post-MI showed a significant signal attenuation at the MI zone in the MI+MPIO group compared to the control groups. The findings suggested that the inflammatory cells containing MPIO infiltrated into the myocardial injury site. Cardiac function was also measured and correlated with the labeled-cell infiltration at the MI site. This study demonstrated a noninvasive technique for monitoring inflammatory cell migration using the MPIO contrast agent. This MPIO-enhanced MRI technique could provide additional insight concerning cardiac disease progression that would improve therapeutic treatment for MI patients.
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    Thermomechanical modeling of porous ceramic-metal composites accounting for the stochastic nature of their microstructure
    (Georgia Institute of Technology, 2009-11-24) Johnson, Janine ; Qu, Jianmin ; Garmestani, Hamid ; Gokhale, Arun ; Johnson, W. Steven ; Lara-Curzio, Edgar ; Sitaraman, Suresh ; Mechanical Engineering
    Porous ceramic-metal composites, or cermets, such as nickel zirconia (Ni-YSZ), are widely used as the anode material in solid oxide fuel cells (SOFC). These materials need to enable electrochemical reactions and provide the mechanical support for the layered cell structure. Thus, for the anode supported planar cells, the thermomechanical behavior of the porous cermet directly affects the reliability of the cell. Porous cermets can be viewed as three-phase composites with a random heterogeneous microstructure. While random in nature, the effective properties and overall behavior of such composites can still be linked to specific stochastic functions that describe the microstructure. The main objective of this research was to develop the relationship between the thermomechanical behavior of porous cermets and their random microstructure. The research consists of three components. First, a stochastic reconstruction scheme was developed for the three-phase composite. From this multiple realizations with identical statistical descriptors were constructed for analysis. Secondly, a finite element model was implemented to obtain the effective properties of interest including thermal expansion coefficient, thermal conductivity, and elastic modulus. Lastly, nonlinear material behaviors were investigated, such as damage, plasticity, and creep behavior. It was shown that the computational model linked the statistical features of the microstructure to its overall properties and behavior. Such a predictive computational tool will enable the design of SOFCs with higher reliability and lower costs.
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    Experimental determination of the feasibility of waste heat recovery in data centers using ejector based refrigeration
    (Georgia Institute of Technology, 2011-05-04) Sharp, Joshua Glenn ; Joshi, Yogendra ; Mostafa Ghiaasiaan ; Pramod Kumar ; Sheldon Jeter ; Mechanical Engineering
    The purpose of this thesis is to experimentally determine the feasibility of an ejector based, waste heat recovery driven refrigeration system applied to the data center environment in order to reduce operational cooling costs. A comprehensive literature review is detailed to determine the current state of the ejector refrigeration research and assess the initial direction of this thesis. A simplified model was created to perform preliminary performance estimations and system sizing before constructing an experimental system apparatus to evaluate the model predictions. The pressures and temperatures used in the model and instituted in the experimental system are based on the maximum temperatures typically observed in computing servers (50-75°C). Precision controlled heaters are used to simulate the computer server heat, and R245fa is used as the working fluid. Performance results ranged from 0.06 to 0.13.
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    Experimental and theoretical thermal analysis of microelectronic devices
    (Georgia Institute of Technology, 1988-08) Heng, Stephen Fook-Geow ; Black, William Z. ; Mechanical engineering
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    An analysis of the full floating textile spindle bearing
    (Georgia Institute of Technology, 1953-12) Williams, James Frederick ; Vidosic, Joseph P. ; Mechanical engineering
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    Concept development of a product design algorithm: an aid to increase designer productivity
    (Georgia Institute of Technology, 1992-05) McCullough, John Patrick, III ; Lee, Kok-Meng ; Mechanical engineering
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    Determining the environmnetal impact of disposal, recycling and remanufacturing strategies
    (Georgia Institute of Technology, 2007-12-06) Govetto, Sophie ; Bras, Berdinus A. ; Beril Toktay ; Melkote, Shreyes N. ; Mechanical Engineering
    In the past few decades, globalization has led to a world economy with unbounded consumption. In addition to the consequential impoverishment of natural resources, this large consumption produces copious amounts of waste and requires high energy use. Proper end-of-life strategies can help to reduce the global impact of these inefficiencies. The objective of this thesis is to demonstrate, through life-cycles analyses of an automotive transfer case and a gear, the positive environmental impact of remanufacturing strategies compared to recycling and disposal end-of-life strategies. In this study, the energy consumption, the air emissions and the wastes resulting from the entire supply chain s engineering processes will be quantitatively evaluated through calculations and also industrial or governmental data. In disposal end-of-life strategies, the analysis will begin with the ore mining phase, will go through material refining and processing; and eventually end with the final parts machining. In recycling scenarios and remanufacturing scenarios, the analysis will begin with the used material collection, will go through material s reprocessing or refurbishing and will finally end with the new or renewed parts machining. This study will show the significant impact of high energy consumption processes such as electrolysis of aluminum and metal melting. It will also show how shipping and collection phases can dramatically change or annihilate the advantage of sustainable reuse scenarios depending on the sorting strategies adopted in the supply chain. To conclude, the goal of this research is to demonstrate how remanufacturing strategies can reduce the energy consumption, air emissions and waste. This thesis will also show how inappropriate supply chain management can negate the impact of these savings.
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    Consistent energy treatment for radiation transport methods
    (Georgia Institute of Technology, 2012-03-30) Douglass, Steven James ; Rahnema, Farzad ; Lubinsky, Doron ; Morley, Tom ; Petrovic, Bojan ; Zhang, Dingkang ; Nuclear Engineering
    A condensed multigroup formulation is developed which maintains direct consistency with the continuous energy or fine-group structure, exhibiting the accuracy of the detailed energy spectrum within the coarse-group calculation. Two methods are then developed which seek to invert the condensation process turning the standard one-way condensation (from fine-group to coarse-group) into the first step of a two-way iterative process. The first method is based on the previously published Generalized Energy Condensation, which established a framework for obtaining the fine-group flux by preserving the flux energy spectrum in orthogonal energy expansion functions, but did not maintain a consistent coarse-group formulation. It is demonstrated that with a consistent extension of the GEC, a cross section recondensation scheme can be used to correct for the spectral core environment error. A more practical and efficient new method is also developed, termed the "Subgroup Decomposition (SGD) Method," which eliminates the need for expansion functions altogether, and allows the fine-group flux to be decomposed from a consistent coarse-group flux with minimal additional computation or memory requirements. In addition, a new whole-core BWR benchmark problem is generated based on operating reactor parameters in 2D and 3D, and a set of 1D benchmark problems is developed for a BWR, PWR, and VHTR core.
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    An evaluation of time dependent numerical methods applied to a rapidly converging nozzle
    (Georgia Institute of Technology, 1973-05) Giles, Garland Eldridge ; Shelton, Samuel V. ; Mechanical engineering