▼ JP-8 fuel is easily accessible, transportable, and has hydrogen content essential to solid oxide fuel cell (SOFC) operation. However, this syngas has sulfur content which results in a poisonous hydrogen sulfide that degrades electrochemical activity and causes complete SOFC failure in some cases. The goal is to synthesize and verify a cost-effective, catalyst supported on cerium oxide that either stabilizes ionic conductivity in the presence of hydrogen sulfide and/or is highly sulfur-resistant. After thorough computational analysis, it was concluded that the platinum-copper skin catalyst was the most cost-effective, sulfur-resistant catalyst. Experimental synthesis of copper, platinum, and platinum-copper skin catalysts supported on cerium oxide was verified. Further experimentation must be performed to establish the platinum-copper skin catalyst supported on cerium oxide operational affects on the SOFC system in a sulfur environment. Advisors/Committee Members: Huang, Hong.

▼ The use of the earth's thermal energy to heat and cool building space is nothing new; however, the heat transfer approximations used in modeling geothermal systems, leave uncertainty and lead to over sizing. The present work is part of a Wright State effort to improve the computer modeling tools used to simulate ground loop geothermal heating and cooling systems. The modern computer processor has equipped us with the computation speed to use a finite volume technique to solve the unsteady heat equation with hourly time steps for multi-year analyses in multiple spatial dimensions. Thus we feel there is more need to use approximate heat transfer solution techniques to model geothermal heating and cooling systems. As part of a DOE funded project Wright State has been developing a ground loop geothermal computer modeling tool that uses a detailed heat transfer model based on the governing differential energy equation. This tool is meant to be more physically detailed and accurate than current commercial ground loop geothermal computer codes. The Wright State code allows the geothermal designer to optimize the system using a number of outputs including temperature field outputs, existing fluid temperature plots, heat exchange plots, and even a histogram of the COP data. Careful attention to the algorithm speed allows for multi-year simulations with minimal computation cost. Once the thermal and heat transfer computations are complete, a payback period calculator can compare any conventional heating and cooling system to the designed geothermal system and payback periods are displayed. The work being presented as part of this thesis deals with five issues that were required to make the Wright State geothermal computer code a reality. The five aspects of this modeling tool addressed by this thesis work are: energy load calculations, GUI (graphical user interface) development, turbulence model development, heat pump model development, and two-dimensional numerical grid development. The energy load, or heating and cooling load, calculations are handled using the sophisticated DOE program called EnergyPlus. This thesis work developed a technique for coupling EnergyPlus to the Wright State geothermal code and devising a way for novice users to obtain energy loads quickly and easily, while still allowing expert users to utilize the full strength of EnergyPlus. The GUI for the Wright State computer program was developed with the novice and expert users in mind. The GUI offers ease of use while maintaining the ability for the expert users to setup unique designs for simulation. A unique way of modeling the effects of turbulent flow in the ground tube has allowed the Wright State code to maintain low computation times, while having small errors for a wide range of Reynolds numbers. To make the Wright State ground loop computer model more complete, a heat pump was developed as part of this work. The heat pump model uses the performance characteristics of commercial heat pumps to determine the performance of the geothermal system. The energy transport in the fluid is determined and used to select one of eighteen water-to-air heat pumps that calculate hourly COP's for all system conditions. The calculated heat pump efficiencies are used in an energy balance with hourly building loads to calculate the next iteration's bulk temperature entering the ground loop. Additional details are provided in this thesis on each of these five, important, computer modeling issues. Advisors/Committee Members: Menart, James.

▼ Nanosensors, i.e., sensors based on nanomaterials, have the potential of superior performance owing to their size effect, and can have significant effects on detection of pollutants in the environment. Various nanowires have been used in this context. Here we investigate the possibility of NO2 and Li detection using the quantum conductance change in graphene nanoribbon. Quantum conductance modification in graphene nanoribbon upon NO2/Li adsorption was calculated using ab initio methods. The optimized structures of the adsorbed NO2 indicated two different geometries where either nitrogen or oxygen was closer to the graphene lattice. The former resulted in charge transfer from NO2 to graphene, while the latter caused charge to be transferred in the reverse direction. As for Li, the optimized adsorption location was at the zigzag edge and above the center of a hexagon (hollow site). The charge transfer in the Li case was smaller compared to the NO2 case. The quantum conductance calculations for NO2 adsorption showed semiconductor-to-metal transformation and gap modification for the two adsorption geometries. In the case of Li adsorption, the gap remained almost the same as that of pristine graphene nanoribbon, however, the pseudo-gap was widened upon Li adsorption. These effects are detectable and explain the basis for nanosensor effect in graphene nanoribbons, with superior sensitivity and selectivity Advisors/Committee Members: Farajian, Amir.

▼ Progress in commercializing renewable energy technologies is being advanced by developments in Zinc Oxide material science. The photovoltaic cell, for example, generates electricity by receiving solar energy into the cell, generating electrons, and simultaneously transporting electrical charge out of the cell. Metals are capable of removing electrical charge but block transmission of sunshine. Glass and plastics are capable of transmitting sunshine but block the removal of electrical charge. Therefore an exterior layer that is both optically transparent and electrically conductive is desirable. Transparent conductive oxides (TCOs) are the ideal material for such applications since they are capable of both functions. In addition, the unique opto-electronic properties of TCOs make them suitable for many other applications such as dye sensitized solar cells and sensor devices. Zinc oxide is a non-toxic and inexpensive TCO material in comparison with the state-of-the-art tin-doped indium oxide (ITO). Therefore, optimizing the fabrication of high-quality zinc oxide thin films at low cost plays a significant role in the advancement of solar technology commercialization. The sol-gel process has advantages over other techniques in terms of low-cost, feasible mass production. In this work, key variables affecting zinc oxide sol-gel processing were investigated. Resulting films were characterized for optical transparency by UV-VIS spectrophotometry. Chemical reaction mechanisms within the sol-gel process and Zinc Oxide film crystalline properties were analyzed using Raman spectroscopy. Key variables affecting final film quality were explored. Advisors/Committee Members: Huang, Hong.

▼ The rise in fossil fuel consumption and green house gas emissions has driven the need for alternative energy and energy efficiency. At the same time, ground loop heat exchangers (GLHE) have proven capable of producing large reductions in energy use while meeting peak demands. However, the initial cost of GLHEs sometimes makes this alternative energy source unattractive to the costumer. GLHE installers use commercial programs to determine the length of pipe needed for the system, which is a large fraction of the initial cost. These commercial programs use approximate methods to determine the length of pipe mainly due to their heat transfer analysis technique, and as a result, sometimes oversize the systems. A more accurate GLHE sizing program can simulate the system correctly, thus, reducing the length of pipe needed and initial cost of the system. We feel a more accurate GLHE sizing program is needed. As part of a DOE funded project Wright State University has been developing a ground loop geothermal computer modeling tool, GEO2D, that uses a detailed heat transfer model based on the governing differential energy equation. This tool is meant to be more physically detailed and accurate than current commercial ground loop geothermal computer codes. The specific work of this Master's thesis first includes a detailed literature search of GLHE sizing techniques. Secondly, this work contains a detailed description of commercial GLHE sizing codes currently available and compares some results to GEO2D. Additionally, this work has developed a g-function program; a GLHE sizing technique used by many commercial programs, and compared results to GEO2D. Next, this work has developed subroutines to develop a three-dimensional grid system for a horizontal and vertical GLHE. Lasty this work has developed computer code for the boundary conditions and material property allocation used in GEO3D. Advisors/Committee Members: Menart, James.

▼ The energies and temperature-dependent dynamics of hydrogen and lithium chemisorption on a silicon nanosheet, called silicene, were studied using density functional theory and molecular-dynamics (MD) simulations. Silicene has a buckled honeycomb structure, and has been fabricated as suspended monolayer sheets and nanoribbons in recent experiments. We calculated the adsorption energies of hydrogen and lithium on silicene for different adsorption ratios between 3.1% and 100%. The studies will clarify the characteristics of these novel and promising nanomaterials, and pave the way for their applications. For Hydrogen, the adsorption energy had a maximum of 3.01 eV/H for complete hydrogenation, and decreased by 24.5 % to 2.27 eV/H for single atom adsorption on a 32-silicon-atom supercell. It was determined that the preferred hydrogen adsorption patterns were clusters. Molecular dynamics simulations revealed the stability of adsorption configurations at 300K. The electronic structure of these stable configurations could be modified and controlled through partial and complete hydrogenations, and a transformation from zero-gap semiconductor to insulator was observed. For lithium on silicene, the adsorption energy had a maximum of 2.23 eV/Li for 50% lithiation and decreased by 29.6% to 1.57 eV/Li for 100% lithiation. For partial Lithium adsorptions up to 50%, the preferred adsorption sites were hollow sites on top of silicon hexagons. This preference changed as more lithium atoms were introduced. At a 100 % adsorption ratio, the lithium atoms adsorbed to sites directly above or below the silicon atoms. Unlike hydrogenated silicene, the band structure of each partially lithiated structure was shown to be that of a metal. Combining hydrogen and lithium adsorptions, it was shown that silicene-Li nanocompounds can be considered for hydrogen storage. Advisors/Committee Members: Farajian, Amir.