Browsing by Subject "hydrogen"

Now showing 1 - 5 of 5
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    Hydrogen Fuel Cell Cold Operation
    (2019-09) Bell, Christina
    The purpose of this project is to model the operation of a proton exchange membrane (PEM) fuel cell during operation in weather as cold as -40 °C. The fuel cell must be kept above the freezing point of water, and it is hypothesized this can be done by utilizing the heat produced in the system. The system is being designed to provide off-grid power for operation of various scientific sensors requiring power output of 20 W at a potential of 12 V. A fuel cell combines hydrogen and oxygen to form water, heat, and electricity. Process steps include generating hydrogen from the alcoholysis and/or hydrolysis of sodium borohydride, creating electricity from the fuel cell to charge a battery, and preheating feed air to provide oxygen to the fuel cell. The project explores 1) modeling of the reaction kinetics for hydrogen production, 2) modeling the efficiency and kinetics of the catalytic reaction between the generated hydrogen and oxygen from air within the fuel cell, and 3) modeling heat flow within the system to preheat the incoming air and maintain good fuel cell temperature. The reaction kinetics show sufficient hydrogen production to keep the fuel cell running as specified. The modeled efficiency gives an average efficiency just above 50% for the conversion of chemical potential energy to usable power. The heat flow, assumed to be 1-dimensional, shows sufficient heat transfer to keep the area around the fuel cell above the freezing point of water as modeled.
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    The influence of hydrogen, deformation geometry, and grain size on the rheological properties of olivine at upper mantle conditions
    (2015-09) Tielke, Jacob
    Many important geophysical processes, including mantle convection and the associated movement of Earth's tectonic plates, are strongly dependent upon the rheological properties of Earth's upper mantle. Olivine is the most abundant mineral in the upper mantle and therefore largely controls the mechanical behavior of this region of Earth's interior. Many experimental investigations have been carried out to study the rheological properties of olivine single crystals, synthetically produced aggregates, and naturally occurring mantle rocks at asthenospheric temperatures. In contrast, relatively few studies have focused on measuring the rheological properties of olivine deforming at lithospheric temperatures. Furthermore, there are several unanswered questions about the microphysical processes that control deformation of olivine at upper mantle conditions. One outstanding question in the field of rock and mineral physics is "Do different microphysical processes control the rate of deformation of olivine at asthenospheric compared to lithospheric mantle conditions?" To address this question we carried out direct shear experiments on olivine single crystals at temperatures that span the transition from lithospheric to asthenospheric mantle conditions. The results of these experiments, which are presented in Chapter 2, demonstrate that the dependence of strain rate upon stress transitions from a power-law relationship at high temperatures to an exponential dependence at lower temperatures. This transition in rheological behavior is consistent with deformation that is controlled by the climb of dislocations at high-temperature conditions and deformation that is controlled by the glide of dislocations at low-temperature conditions. Furthermore, the direct shear geometry allows for isolation of the (001)[100] and (100)[001] dislocation slip systems, which cannot be individually activated in triaxial compression. At high-temperature conditions, crystals oriented for shear on the (001)[100] slip system are observed to be weaker than crystals oriented for shear on the (100)[001] slip system. At low-temperature conditions the opposite relationship is observed: crystals oriented for shear on the (100)[001] slip system are weakest. Another important outstanding question is "Do the mechanisms of hydrolytic weakening in olivine differ at asthenospheric compared to lithospheric mantle conditions?" In Chapter 3 we report the results of experiments carried out on olivine single crystals under hydrous conditions at both asthenospheric and lithospheric temperatures. For crystals deformed at high-temperatures and under hydrous conditions, the dependence of strain rate on stress follows a power-law relationship with a stress exponent (n) of ~2.5, consistent with deformation that is rate limited by diffusion of silicon through the olivine lattice. In contrast, crystals deformed at high-temperatures and under anhydrous conditions yield n values of ~3.5, consistent with deformation that is rate limited by diffusion of silicon through the cores of dislocations. At low temperature conditions, the strain rate of both hydrous and anhydrous crystals are equally well described by the same exponential dependence of stress. These observations demonstrate significant hydrolytic weakening occurs at asthenospheric temperatures, but hydrolytic weakening cannot be resolved at lithospheric temperatures for our experimental conditions. Lastly, we address a question about polycrystalline deformation: "What deformation mechanism is responsible for grain-size sensitive (GSS) power-law creep of olivine aggregates?" In Chapter 4 we compare strain rates measured during deformation experiments on olivine aggregates to strain rates calculated from a micromechanical model of intragranular slip. The micromechanical model uses the measured stress from deformation experiments and grain orientations determined from post-deformation electron backscatter diffraction measurements to approximate the contribution of dislocation creep to the strain rate. Olivine aggregates deform up to a factor of 4.6 times faster than the maximum possible rates determined from the micromechanical model of intragranular slip. The ratio of experimentally determined strain rates to those from the micromechanical model is strongly dependent upon grain size, but is independent of stress and strength of lattice-preferred orientation. These observations indicate that GSS power-law creep occurs in both weakly and strongly textured olivine aggregates at the studied conditions. We consider three explanations for the observed rheological behavior, (1) a combination of diffusion and dislocation creep, (2) the operation of dynamic recrystallization creep, and (3) the operation of dislocation-accommodated grain-boundary sliding. Our analyses indicate that the microstructural and mechanical behavior of olivine aggregates deforming in the grain-size sensitive power-law regime are most consistent with the operation of dislocation-accommodated grain-boundary sliding at the studied experimental conditions.
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    A modular technology for fermentative hydrogen production and capture from wastewater
    (2014-11) Sigtermans, Louis
    Despite the inherent chemical energy in wastewater, current wastewater treatment practices expend a considerable amount of energy to aerobically remove organic pollutants. Anaerobic fermentation of these dissolved organics to produce hydrogen could instead provide a positive energy output while delivering the ancillary benefit of lessening aeration demands for downstream treatment processes. A scalable and modular technology, based on the membrane-encapsulation of hydrogen-producing mixed consortia onto hollow fiber membranes for efficient hydrogen collection, was developed to produce and capture hydrogen from dissolved phase organics in wastewater. The membranes were tested in a continuously stirred tank reactor (CSTR) and monitored for hydrogen production and capture. The results showed that two different membrane polymer chemistries were successful in producing and capturing hydrogen from high-strength synthetic wastewater, with maximum captured yields of 25-50 mL/g hexose. Low available carbohydrate content, pH conditions, and leakage of microorganisms into and out of the membranes may have contributed to the failure of hydrogen production in trials using municipal wastewater. Batch tests of dairy manufacturing waste demonstrated the potential for future application of this technology for producing hydrogen from a real industrial wastewater.
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    Optimization of Ammonium and Biohydrogen Production from Mutant Strains of Azotobacter vinelandii Deregulated for Nitrogen Fixation
    (2018-05) Plunkett, Mary
    The increase in demand for food and fuel as a result of an increasing population must be sustainable and renewable in the face of global climate change. Azotobacter vinelandii, an aerobic nitrogen fixing bacterium, has the potential to supplement or replace a major consumer of global energy, which is the production of ammonium (NH4+) for use in fertilizers. A requisite by-product of nitrogen fixation includes the production of hydrogen gas (H2), which can be used for many applications, including renewable hydrogen fuel cells. A. vinelandii produces both of these in a biochemical process which takes place at ambient temperatures and pressures using renewable carbon sources for energy. Within this research, improvement of the conditions needed for higher NH4+ and H2 production from a strain deregulated for the production of nitrogenase was explored and H2 output was characterized as a result of multiple genetic modifications and changes to culture conditions.
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    Solar Synthesis Gas Production via the Thermochemical Cerium Oxide Redox Cycle: Inert-Swept and Methane-Hybridized Reduction
    (2016-01) Krenzke, Peter
    The cerium oxide (ceria) redox cycle is evaluated as a means for producing synthesis gas from carbon dioxide and water using solar energy. Two options are considered for facilitating oxygen removal during ceria reduction: inert gas sweeping and reaction with methane to produce synthesis gas. Thermodynamic process analyses are developed to ascertain the viability of the cycle and identify requirements for high efficiency under the assumption of equilibrium chemistry. A parametric experimental study is conducted to determine the impact of temperature and methane flow rate on methane conversion, syngas selectivity, oxidizer conversion, and the solar-to-fuel efficiency.