Doctor of Philosophy, Case Western Reserve University, 2022, Macromolecular Science and Engineering

Energy and electricity are vital to modern society and our daily life. However, environmental pollution and global warming caused by fossil fuels have also become highly problematic in recent years. Hydrogen has the highest energy density, it can be produced directly from water, and the only by-product during the power generation is water. Therefore, hydrogen is considered to be the key to solving the current energy problem. However, the current mainstream hydrogen production methods also result in significant carbon emissions. In the meantime, the chemical reactions performed in water electrolysis and fuel cells rely heavily on expensive noble metal catalysts. Consequently, there is an urgent need to develop cheap and efficient catalysts to replace noble metals. Since 2009, nitrogen-doped carbon nanotubes have been proved to have a similar catalytic activity to platinum for oxygen reduction reactions (ORR) and better stability. Heteroatom-doped carbon materials have been developed rapidly over recent years and are now considered a promising alternative to noble metal catalysts. In addition to ORR, carbon materials can also catalyze hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with comparable performance to the commercialized noble metal catalysts while being cheaper to produce and more stable. This dissertation will be divided into several sections to discuss the application of functionalized carbon materials in various energy conversion and storage devices. Chapter 2 explore the potential application of functionalized graphene in the transport layer and active material for perovskite solar cells. Chapter 3 introduces a small project which combines perovskite material with electrospun fiber into a flexible photodetector. Chapters 4 and 5 investigate the multifunctional catalytic performance of nitrogen and sulfur co-doped 3D graphite networks (N, S-3DPG) in water splitting, fuel cells, dye-sensitized solar cells, and zinc-air batt (open full item for complete abstract)

Committee: Gary Wnek (Committee Chair); Lei Zhu (Committee Member); Hatsuo Ishida (Committee Member); Clemens Burda (Committee Member); Liming Dai (Advisor) Subjects: Chemistry; Energy; Nanotechnology

Master of Science, Miami University, 2019, Computational Science and Engineering

The main advantages of electric vehicles (EVs) are reducing the production of greenhouse gases, reducing society's reliance on fossil-fuel-based energy infrastructure, and the ability to achieve high-efficiency energy conversion. Super-capacitors (SCs) are introduced into EV's energy storage system to supplement the primary power source, which improves the vehicle's performance. A low-voltage, high-current bidirectional DC/DC converter serves as an intermediary between the SCs and the primary power source connected to the motor drive. Current-fed CLLC converters are characterized by: a lower input current ripple then voltage source converters, extended input voltage range, reduced transformer size, and the ability to achieve soft switching across the entire input voltage range. This research evaluates the performance of a CF-CLLC converter designed with paralleled Si MOSFETs and compares the performance of a CF-CLLC converter, CLLC converter, and cascaded CF-CLLC converter. A hardware prototype was built for an input voltage of 24 V to 96 V and an output voltage of 400 V with a rated power of 2 kW.

Committee: Mark Scott PhD (Advisor); Chi-Hao Cheng PhD (Committee Member); Miao Wang PhD (Committee Member) Subjects: Electrical Engineering

Master of Science, The Ohio State University, 2017, Food, Agricultural and Biological Engineering

A Microbial Fuel Cell (MFC) is a device used to harvest electrons from living microorganisms to generate electrical power. After decades of development, new architectures have been developed and new materials have been applied to MFC systems. Improvements to this promising technology have been extensively reported. However, scientists and engineers are still facing difficulties on enhancing energy output and increasing the MFC system efficiencies. In addition to physical resistances caused by MFC materials, there are still many unknown factors affecting the electron transfer pathway used by microorganisms in MFC environments. To increase the performance, a series of technologies have been integrated into MFCs. For instance, MFC technology has been combined with other technologies such as algae pounds, anaerobic digesters and constructed wetlands, to increase substrate utilization efficiency. As one example, CW-MFCs have already been studied for wastewater treatment and electricity generation. However, the system efficiencies presented by current models are low, and new designs need be explored to reduce the energy cost during installation and operation of CW-MFC systems. The first objective of this thesis research was to review the development of MFCs and relevant technologies, then to evaluate the energy loses and efficiencies in MFC systems, leading to a comprehensive understanding of MFC system from a thermodynamic viewpoint. The second objective was to design and construct a down-flow Constructed Wetland-Microbial Fuel Cell combined system with a semi-air cathode and analyze its performance. This innovative design will be able to enhance the system efficiencies of CW-MFCs by reducing external energy requirements, and this research will provide foundational work for further CW-MFC explorations

Committee: Ann Christy (Advisor); Olli Tuovinen (Committee Member); Lingying Zhao (Advisor) Subjects: Agricultural Engineering

Master of Science in Engineering (MSEgr), Wright State University, 2014, Mechanical Engineering

Over the last few years, fuel cell technology has significantly advanced and has become a mode of clean power generation for many engineering applications. Currently the dominant application for fuel cell technology is with stationary power generation. Very little has been published for applications on mobile platforms, such as unmanned aerial vehicles. With unmanned aerial vehicles being used more frequently for national defense and reconnaissance, there is a need for a more efficiency, longer endurance power system that can support the increased electrical loads onboard. It has already been proven by others that fuel cell gas turbine hybrid systems can achieve higher system efficiencies at maximum power. The integration of a solid oxide fuel cell combustor with a gas turbine engine has the potential to significantly increase system efficiency at off-design conditions and have a higher energy density compared to traditional heat based systems. This results in abilities to support larger onboard electrical loads and longer mission durations. The majority of unmanned air vehicle mission time is spent during loiter, at part load operation. Increasing part load efficiency significantly increases mission duration and decreases operational costs. These hybrid systems can potentially have lower power degradation at higher altitudes compared to traditional heat based propulsion systems. The purpose of this research was to analyze the performance of a solid oxide fuel cell combustor hybrid gas turbine power system at design and off-design operating conditions at various altitudes. A system level MATLAB/Simulink model has been created to analyze the performance of such a system. The hybrid propulsion system was modeled as an anode-supported solid oxide fuel cell integrated with a commercially-available gas turbine engine used for remote control aircraft. The design point operation of the system was for maximum power at sea-level. A steady-state part load performance analysi (open full item for complete abstract)

Committee: Rory Roberts Ph.D. (Advisor); Scott Thomas Ph.D. (Committee Member); Hong Huang Ph.D. (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2001, Medicine : Environmental Health Sciences

Jet fuel is a common occupational exposure among commercial and military maintenance workers. JP-8 jet fuel, a military formulation, has been found to have immunotoxic effects in mice but little data exists for humans. The aim of this cross-sectional study was to determine if the number of immune cells in the peripheral blood was altered among tank entry workers, a group which has been determined in previous studies to have the highest exposure to JP-8 in the U.S Air Force. A total of 123 volunteers (45 tank entry workers) from three Air Force bases participated in the study. After adjusting for a number of covariates, tank entry workers were found to have higher numbers of white blood cells (p=0.01), neutrophils (p=0.05), and monocytes (p=0.02) and no differences in the numbers of total lymphocytes, T-cells, T-helper cells, T-suppressor cells, Natural Killer cells, and B-cells when compared with a low exposure group. Tank entry workers did not show any clinical effects of the increased immune cell counts. Although there were no differences in the number of lymphocytes among study groups, further investigations are needed to evaluate the functional ability of these cells to produce lymphokines and cytokines and modulate the immune system.

Committee: Grace Lemasters (Advisor) Subjects:

MS, University of Cincinnati, 2010, Engineering and Applied Science: Aerospace Engineering

In this study, a fuel system controller for a gas turbine engine was examined. Controller design in this application is challenging due to nonlinearities in the closed loop system, as well as uncertainties associated with hardware components from part variation or degradation. Current closed loop design methodologies are discussed, as are the limitations or challenges facing these systems. Details on fuzzy logic control and its benefits in this type of application are explored. Information on genetic algorithms is presented, along with a study on how this optimization approach can be utilized to enhance the fuzzy logic controller process. A fuzzy logic controller structure was developed for providing closed loop fuel control in the gas turbine application, using a genetic algorithm to tune the system to provide an accurate and fast response to changing input demands. With a genetic fuzzy controller in place, closed loop analysis was performed, along with a stochastic robustness analysis to assess controller performance in an uncertain environment. Results show that the genetic fuzzy system performed well in this application, resulting in a system with fast rise and settling times to stepping inputs, while also minimizing overshoot and steady state error. Robustness characteristics of the fuzzy controller were also demonstrated, as the stochastic robustness analysis yielded acceptable performance in each simulation of the closed loop system with uncertainties included.

Committee: Kelly Cohen PhD (Committee Chair); Bruce Walker ScD (Committee Member); Manish Kumar PhD (Committee Member) Subjects: Aerospace Materials

Master of Science in Mechanical Engineering, University of Toledo, 2009, Mechanical Engineering

Hydraulic hybrid vehicle (HHV) is a new technology being developed in order to improve fuel economy for road vehicles. This technology also has limitations for example: low energy density, no power grid plug-in capability. This research is on the evaluation of a new concept for improving the HHV technology. With an added air system to HHV, the air system can be charged through grid plug-in or by the internal combustion engine (ICE). The new scheme has the potential to significantly improve the energy density of the hydraulic hybrid vehicles and also provide plug-in capability for these vehicles.Basing on a symbolic program developed in MATLAB/Simulink, a parallel hybrid simulation model for the new system is developed in this thesis. The simulation model includes all the system components such as the vehicle, the air tank, the accumulators, the pressure exchangers, the hydraulic pump/motor, the compressor and the ICE. The power management is implemented based on using all the available hydraulic power. The main objective of this model is to evaluate the average fuel economy (FE) for the HHV with the added compressed-air system. This model is tested basing on the federal urban drive schedule (FUDS). The simulations results with various configurations have not shown significant improvement in the fuel economy. This thesis provides a detailed analysis about the results from the system structure and the energy loss. In this system, there are two alternating accumulators. Every time the accumulator switches to reservoir, energy will be lost. When the engine drives the compressor to recharge the air system, a large engine would be needed to power such a compressor. These are the main reasons for the poor fuel economy of the proposed HHV system.

Committee: Mohammad Elahinia (Advisor); Walter Olson (Committee Member); Maria Coleman (Committee Member) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 2009, Electrical and Computer Engineering

In this dissertation, a proton exchange membrane (PEM) fuel cell-based distributed generation (DG) system is analyzed by modeling various units of the DG system, performing mathematical analyses, and simulation studies. The suitable control strategies are designed for the specific units of the DG system in order to achieve the desired operating performance. First, the nonlinear state space model of a 500-W PEM fuel cell is developed by modeling an open-circuit output voltage of the PEM fuel cell, irreversible voltage losses in the PEM fuel cell, formation of a charge double-layer in the PEM fuel cell, along with a mass balance and thermodynamic energy balance in the PEM fuel cell system. The state space model is validated, and then used to study the dynamic behavior of the PEM fuel cell under different input conditions. The modeling of the PEM fuel cell is also performed using the neural network approach, and the nonlinear autoregressive moving average model of the PEM fuel cell with external inputs (NARMAX) is developed using the recurrent neural network. It is shown that the two-layer neural network with a hyperbolic tangent sigmoid function, as an activation function, in the first layer, and a pure linear function, as an activation function, in the second layer can effectively model the nonlinear dynamics of the PEM fuel cell. The sizing of the lead-acid battery bank, which is the energy storage element required for the DG system, is performed using the model of a 12 V, 4Ah lead-acid battery. The discharge characteristics of the battery model are studied, and the model is appropriately scaled to perform the design of the battery bank. Using the battery and dc/dc boost converter model, the charging of the battery bank is simulated in MATLAB/Simulink. A sliding mode control law is designed for the dc/dc converter to control its output voltage. The application of two different control strategies to a single-phase and three-phase inverter is analyzed. The objective (open full item for complete abstract)

Committee: Ali Keyhani PhD (Advisor); Donald Kasten PhD (Committee Member); Betty Lise Anderson PhD (Committee Member) Subjects: Electrical Engineering; Energy