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Climate change is one of the most pervasive issues for society in the modern world. To successfully mitigate the devastating consequences of this phenomenon without sacrificing economic growth, the positive income-emissions nexus must be broken. In this paper, I asses the United States' progress along this dimension by investigating the time-varying effect of GDP on emissions from 1850-2018. I distinguish between the cyclical and trend relationship between income and emissions and utilize a Bayesian Time-Varying-Parameter (TVP) model to determine the effect of GDP on emissions over time. I find weak evidence that the United States follows the often-proposed Environmental Kuznets Curve (EKC) in the trend and base components of the nexus: the effect of GDP on emissions has significantly weakened over time but remains positive. Additionally, I present evidence that income and emissions have relatively decoupled for all components of the nexus, casting doubt on “degrowth” arguments, wherein this is only possible if economic growth slows. I find that since the 2000s, the long-run relationship of GDP and emissions has further decoupled, while the short-run relationship has intensified. I provide evidence that the United States’ increasingly green energy mix is a driver of this heterogeneity.

Functional materials, particularly metal oxides, have been the focus of much attention in solid state chemistry for many years and impact every aspect of modern life. The approach adopted in this thesis to access desirable functionality for enhanced fundamental understanding is via modifying existing materials by deploying reducing synthetic procedures. This work spans several groups of inorganic crystalline materials, but is unified by the development of new properties within host compounds of particular relevance to solid oxide fuel cell technology, which allow interstitial oxide ion conduction at elevated temperatures. The Ca₁₂Al₁₄O₃₂e₂ electride was successfully synthesized by replacing the mobile extra-framework oxygen ions with electrons acting as anions. The high concentration of electrons in the C12A7 electride gives rise to an exceptionally high electronic conductivity of up to 245 S cm⁻¹ at room temperature. Making use of the high density of electrons in Ca₁₂Al₁₄O₃₂e₂ electride, the strong N-N bonds in N₂ was found to be broken when heating Ca₁₂Al₁₄O₃₂e₂ in a N₂ atmosphere. A reaction between silicate apatites and the titanium metal yielded another completely new electride material La₉.₀Sr₁.₀(SiO₄)₆O₂.₄e₀.₂ which was found to be a semiconductor. To fully understand the role of oxygen interstitials in silicate apatites, high-resolution transmission electron microscopy (HRTEM) was employed as the main technique in probing how the oxygen nonstoichiometry is accommodated at the atomic level. Atomic-resolution imaging of interstitial oxygen in La₉.₀Sr₁.₀(SiO₄)₆O₂.₅ proved to be a success in this thesis. Substitution of oxygen in 2a and interstitial sites with fluoride ions in La[subscript(8+y)]Sr[subscript(2- z)](SiO₄)₆O[subscript(2+(3y-2z)/2)] (0

This thesis explores the synthesis and characterization of novel hybrid halide Ruddlesden–Popper compounds, which are derivatives of three-dimensional AMX3 perovskites, where A represents a monovalent cation, M a divalent metal cation, and X a halogen. The focus is on compounds with the general formula (L)2(CH3NH3)n−1PbnI3n+1, where L is a monovalent spacer cation, showcasing a layered crystal structure with perovskite-like layers separated by organic cation spacers. Two specific Ruddlesden–Popper compounds, incorporating a conjugated cation, 2-(4- biphenyl)ethylammonium (BPEA), were synthesized using solvothermal and solvent evaporation techniques.The structural elucidation of these compounds, (BPEA)2PbI4 and (BPEA)2(CH3NH3)Pb2I7, was achieved through X-ray crystallography. The ambient stability of these compounds was confirmed over time using powder X-ray diffraction. The investigation extended to the photoelectronic properties of these compounds, where transient photoconductance was measured by time-resolved microwave conductivity. Band-gap calculations of these two compounds was determined from absorption spectra, resulting in optical properties comparable to those of simpler alkyl ammonium cation-based Ruddlesden–Popper compounds.The comprehensive study presented herein not only advances the understanding of hybrid halide Ruddlesden–Popper compounds but also contributes to the development of materials with potential applications in optoelectronics, highlighting the synthesis methods, structural analysis, and functional characterization as essential tools in the material scientist’s toolkit.

In today's political and ecological climate, there is a growing demand for the Biden Administration to invest in renewable energy sources. Particularly, along the Atlantic, and Pacific coasts, and in the Gulf of Mexico, offshore wind is gaining traction as a viable alternative to fossil fuels. This is due to its technical capability to supply electricity beyond consumptive needs, and its availability to major cities in these regions. Yet, in the United States, there are just seven offshore wind turbines. Thus, to meet the national demand for renewable energy it is clear the US is going to need a lot more offshore wind capital. With this, offshore wind has come to the forefront of the energy economy to help meet demand. The Bureau for Ocean Energy Management (BOEM) is working with the National Oceanic and Atmospheric Administration (NOAA) to lease and permit tracts of the ocean for offshore wind development. Although it is an exciting time to be looking into the potential of offshore wind, there are many considerations that should be addressed to ensure the offshore wind industry develops with minimum possible negative impacts to the environment and is part of a responsible and just transition to a renewable energy economy. These considerations include: · protections and mitigations for marine mammals during offshore wind development’s pre-construction, construction, and operation phase, and decommissioning · the impact of the cost of those mitigations on the economic viability of offshore wind · policies that determine what measures should be taken, and · the social justice implications of offshore wind development. In this report we hope to shed light on these and other considerations. We have conducted an analysis of: • existing mitigation measures that are industry standard • the impacts of construction on the North Atlantic Right Whale (NARW) • Impact of mitigation measures on economic viability • policies that can improve protecting for NARW • the estimated cost of these protections, • the economic potential of offshore wind energy (OSW) • areas where OSW would be best suited • future job potential • and social justice implications. These areas have been investigated in order to determine the best course forward for OSW develop in the United States. There is an emphasis on ensuring greatest possible protections for NARW and creating a just transition to renewables to reach President Biden’s energy goals. Since policy change to improve marine mammal protections at the federal level is unlikely at this time, we have investigated potential avenues for policy action on the State level. We have also determined where OSW development is best suited in the US given available data layers.

Hydrogen (H2) combustion and Solid Oxide Fuel Cells (SOFC) have the potential to mitigateaviation-induced greenhouse emissions in comparison to kerosene propulsion. This thesis describes a methodology to assess the performance and emissions trade-offs of retrofitting a short, medium, and long haul aircraft employing conventional kerosene powered propulsion, with H2-combustion and SOFC hybrid powered lower emission alternatives. The proposed framework employs a constant range approach analysis to design a liquid hydrogen fuel tank that meets insulation, sizing, center of gravity, and power constraints. These liquid hydrogen tanks are utilized to compare the performance of H2-combustion powered and SOFC hybrid powered aircraft, all flying the same range. A lifecycle assessment is conducted to evaluate the potential mitigation of carbon footprints through greenhouse gas emissions and contrail formation effects. Additionally, a cost analysis is modeled to examine the implications of implementing such retrofitting. In this thesis, three sample cases are presented to demonstrate the proposed framework on different aircraft models: Embraer 170LR (representing short haul), Boeing 737-800 (medium haul), and Boeing 777-300ER (long haul). The advantages of adopting the mentioned alternative fuel sources are evident, with an overall reduction in aircraft mass observed for medium and long haul configurations. However, for the short haul case, there is a slight increase in overall weight of 1.13% for H2-combustion and 1.39% for the SOFC hybrid system. Conversely, the medium haul case shows a substantial 27.73% decrease in overall weight for H2-combustion and a 0.4% decrease for the SOFC hybrid configuration. For long haul flights, H2-combustion and SOFC cases yield weight reductions of 38.51% and 2.85%, respectively, compared to conventional kerosene-powered aircraft. Moreover, considering the trade-off of removing cargo compartments to maintain fixed passenger capacity and range by making refueling stops, the lifecycle analysis of green hydrogen in H2-combustion and SOFC hybrid configurations results in an average reduction of 40% and 68% in CO2 lbs of emissions, respectively, compared to conventional Jet-A fuel emissions across all haul configurations. Fuel costs increase by 45% when replacing kerosene combustion with SOFC hybrid power using gray H2 for the short haul configuration, considering one refueling stop. In the case of long haul flights using green H2-combustion, the cost increases by 58.18% compared to conventional kerosene powered aircraft. However, for the long haul SOFC green H2-combustion case (ii), which includes 50% of passengers and their luggage, the total cost is estimated to be close to 33 million USD, representing a 98.90% increase compared to the cost of the long haul kerosene-powered aircraft. The results obtained through this methodology indicate that retrofitting all three aircraft to operate with these alternative fuels can significantly lower carbon emissions at a higher total cost, considering the trade-off of removing cargo compartments and making refueling stops to maintain the same fixed range as specified for each aircraft.

Hydrogen production and storage play a critical role in energy transformation from fossil fuels to green energy. To realize the carbon neutralization target by increasing the competitiveness of hydrogen as an energy vector, production and storage of hydrogen must be made more efficient, safer, and cheaper, which is essential for future energy security and economic development. Water splitting via electrolysis holds great promise for hydrogen production, due to its simplicity, sustainability, and high purity for industrial hydrogen production. Recently, despite tremendous efforts have been devoted, platinum (Pt)-based catalysts are still considered to be the most effective electrocatalysts for hydrogen evolution reaction (HER). However, the high cost and low reserves of platinum-based catalysts greatly limit their commercial application. To make hydrogen derived from water splitting more cost-competitive, it is thus highly desirable to exploit low-cost, highly efficient electrocatalysts to replace the expensive Pt-based catalysts. Furthermore, after hydrogen production, the gaseous hydrogen needs to be stored safely and efficiently for utilization by end-users. The current mainstream methods of solid-state hydrogen storage including molecular physisorption and atomic chemisorption, both possess either too high or too low enthalpy of hydrogen adsorption, which are not suitable for practical application. The ideal hydrogen storage materials should be reversibly ab-/desorbing hydrogen under mild temperatures with high hydrogen capacities. To this end, it is extremely essential to design and construct new solid-state hydrogen storage materials at atomic levels. Recently, the atomic metal-site (AMS) nanomaterials are found to be promising catalysts and solid-state media for both the H2 production and storage, which is not only ascribed to the maximized atomic metals utilization but also the unique electronic structure of various metal-site coordination motifs at atomic scales. The aim of this project is to develop efficient and inexpensive AMS nanomaterials that are expected to create new knowledge of atomic interface catalysis and develop practical applications of solid-state hydrogen storage materials, reducing carbon dioxide emissions and alleviating the air pollution. In summary, this thesis mainly focusses on designing and fabricating cost-effective, efficient , and scalable AMS nanomaterials for both hydrogen production and storage, and the reaction mechanisms of atomic metal sites in hydrogen production and storage are also systematically studied.

Abstract: Microbial lipids are a promising feedstock to produce renewable fuels. Lignocellulosic feedstocks can provide multiple carbon sources for microbial growth, such as hexoses (C6) and pentoses (C5). Oleaginous yeasts can convert C5 and C6 sugars to microbial lipids that can be further processed into renewable fuels and value-added chemicals. The major challenge to the production of microbial lipids for biofuel production using mixed sugar streams is the inability of oleaginous yeasts and many other microbes to utilize the C5 and C6 sugars simultaneously. The challenge is caused by carbon catabolite repression (glucose repression), which is characterized by the global regulatory mechanism that prevents the transcription of genes responsible for the expression/synthesis of enzymes responsible for secondary carbon (C5) utilization in the presence of preferred primary carbon (C6). Many preliminary screening research reports have identified some oleaginous microbes that can simultaneously utilize xylose and glucose for microbial lipid production. However, further studies to explore comparatively these non-conventional oleaginous yeasts endowed with the ability to simultaneously use C5 and C6 sugars for lipid production will add more knowledge to our understanding of the behavior of these oleaginous yeasts, and improve their industrial application in the renewable energy sector. The present study investigates the mixed sugar (i.e. C5 and C6) utilization abilities of Pseudozyma tsukubaensis, Pseudozyma hubeiensis, and Cystobasidium iriomotense in both shake flask and 5 L scale. The lipids extracted from biomass grown using nitrogen-limiting medium and fully automated 5 L bioreactors were subjected to lipid pyrolysis to generate renewable hydrocarbons. The products of lipid pyrolysis were then characterized. Comparative studies of P. tsukubaensis, P. hubeiensis, and C. iriomotense grown in shake flasks and bioreactors using the fermentation strategy deployed in this study confirmed the gradual simultaneous assimilation of the xylose and glucose sugars, rather than the preferential utilization of glucose that is typically observed. This research revealed that P. tsukubaensis and P. hubeiensis efficiently utilized the mixed C5 and C6 carbon sources within 240 h. Conversely, C. iriomotense could not completely utilize both sugars within the same cultivation period. P. hubeiensis and P. tsukubaensis produced higher lipid levels, 59.0 ± 2.3% and 58.1 ± 0.1%, respectively, than C. iriomotense, which displayed lipid yields of 27.0 ± 07%. The n-hexane soluble extracts (recovered fatty acids) when derivatized were abundant in unsaturated fatty acid methyl esters (FAMEs): 86.8% for P. tsukubaensis, 64.8% for P. hubeiensis, and 56.4% for C. iriomotense. The composition of the renewable hydrocarbon products generated from lipid pyrolysis was identified. n-alkanes, 1-alkenes, internal alkenes, branched hydrocarbons, aromatics, cyclics, and some fatty acids were present. These classes of hydrocarbons had a high C to H ratio indicating that some of the lipid feedstocks were subjected to saturation, decarbonylation, and/or decarboxylation reactions. The most abundant hydrocarbon was the n-alkanes series in both the gaseous and liquid fractions. The observed composition of renewable hydrocarbons in this research is consistent with fossil fuels and thus can be used in existing infrastructure where fossil fuels are already in operation. Thus, the hydrocarbon products generated in these studies are promising alternatives to fossil fuel towards reduced/zero carbon emissions, sustainability, and cost-effectiveness. Taken together, this study provides a comparative study of three oleaginous yeasts and demonstrated that they could simultaneously use xylose and glucose in nitrogen-limiting (C: N = 100:1) fermentation conditions to generate large amounts of lipids. Pyrolysis experiments yielded liquid renewable hydrocarbons that could potentially be used as drop-in fuels. Finally, this research demonstrated that the microbes that are best candidates for simultaneously using C5 and C6 sugars from lignocellulosic feedstocks to generate lipids for biofuel applications were P. tsukubaensis and P. hubeiensis.

A series of axially-coordinated aluminum(III) porphyrins were synthesized and evaluated as potential photosensitizers of a ruthenium-based water oxidation catalyst. The porphyrins themselves are 5,10,15,20-tetraphenylporphyrins, and differ in the degree of fluorination on the peripheral phenyl groups. These aluminum(III) porphyrins readily assemble into catalytic dyads through formation of a covalent ester linkage between the central aluminum atom of the porphyrin and a terminal carboxyl group on the ruthenium catalyst. The aluminum center is also able to act as a Lewis acid, forming the final triad by way of a coordinate bond with a suitable Lewis base. Catalytic dyads were successfully synthesized from all three porphyrins in the series; a set of control compounds were also prepared. The dyads and reference molecules were then characterized, with molecular structure and successful formation of the dyads being confirmed with proton NMR spectroscopy, optical properties assessed with respect to UV-Vis absorption and fluorescence spectroscopy, and redox potentials being assessed by both cyclic and differential pulse voltammetry. Formation of the final triad was achieved by titration of the catalytic dyads with a C60 fullerene functionalized to act as a Lewis base; absorption and fluorescence spectra were monitored during titration, allowing for confirmation of the triad formation, as well as calculation of binding constants. The characterization data were used to construct energy level diagrams, laying the groundwork for a theoretical abstraction of these molecule’s functioning. the catalytic systems as synthesized, as well as how they might function in a prototypical photochemical cell. ii Analysis of the results reveal these materials to be promising candidates as photoactivated water oxidation catalysts. The absorption and electrochemical data demonstrate that, when the catalytic dyads are formed, the electronic structure of the constituent parts is preserved. The fluorescence spectra of the dyads show significant quenching relative to the reference porphyrins. Control studies allowed for the exclusion of intermolecular processes as being the source of this quenching, and therefore the optically excited porphyrin must be able to interact with the attached ruthenium catalyst, either through energy or electron transfer. Based on the negligible overlap of the spectra of the catalyst with that of the porphyrins, energy transfer is unlikely. The most likely source of the fluorescence quenching is therefore electron transfer across the ester-bond. The formation and persistence of such a radical ion pair is a fundamental prerequisite for the material to function as a water oxidation catalyst, as it is on this charge-separated species that water oxidation proceeds. Coordination of the dyads with a fullerene ligand was similarly demonstrated, with the resulting triad exhibiting complete fluorescence quenching. The fullerene ligand itself was chosen specifically for its suitability as an electron acceptor, and once again the most likely cause of this quenching is intramolecular electron transfer.

There have been growing concerns over global warming, and this has increased the awareness towards the reduction of Greenhouse gas (GHG) emissions. Many countries including Australia have signed the “Paris Agreement” to try and combat global climate change. This agreement aims to restrict global temperature rise under 2ºC above pre-industrial levels and further limit the temperature rise to 1.5ºC. In December 2018, the United Nations Climate Change conference was held in Katowice, Poland and a framework called the United Nations Framework Convention on Climate Change (COP24) was agreed upon to help in implementing regulations of 2015 Paris Agreement. The agreement also ensures boosting support to developing countries to counter this threat. In order to help the developing and the most vulnerable countries achieve these rather ambitious goals, this new framework will focus on technology, financial flows and capacity improvement. The global reliance on fossil fuels, which contributes approximately 80% of primary energy, has resulted in the rise of global temperatures. Several countries have begun to reduce their reliance on fossil fuels and thus GHG emissions, by shifting their focus towards Renewable Energy (RE). Thus, RE has become a “go to” energy source to solve the aforementioned global issues with a pronounced focus on the guiding energy policies Energy, economics and environment play a crucial role in ensuring the sustainability of a country. Adoption of RE would be the key to ensuring energy sustainability and also reducing the environmental impact, thus helping RE to reach the citizens. Having acknowledged these global challenges and thus relying on RE for the energy needs, sustainability can be achieved by modernising the present micro-grids by integrating RE into them. In order to integrate RE into the existing micro-grid, sizing of Distributed Energy Resources (DERs) using RE sources are investigated to improve their energy production mechanism and enhance the overall efficiency. There are several approaches to size the RE sources into a micro-grid. Two approaches are followed for sizing HRES based on analysing the electricity consumption of the area of interest relying on: (i) Hybrid Optimisation of Multiple Energy Resources (HOMER) software and (ii) improved Hybrid Optimisation using Genetic Algorithm (iHOGA) software. This study highlights the issues related to the optimal sizing of the DERs by investigating their use of the novel application in micro-grids, using both photovoltaic (PV), wind turbine (WT) as the RES for supplying power to the grid for residences and commercial building at Aralvaimozhi, India and Warrnambool, Australia. These two chosen locations are bestowed with good sunlight and wind. The average solar radiation in Warrnambool 4.16kWh/m2/day and annual average wind velocity 5.96m/s. The wind speed and the average solar radiation at Aralvaimozhi are 7.16m/s and 5.05kWh/m2/day respectively. Aralvaimozhi has been spotted as a potential wind farm location according to the Government of Tamil Nadu. India being a developing country and Australia, a developed country, their respective energy policies are scrutinised to understand their energy policies status. Suggestions to improve RE adoption by understanding the energy policies laid by other RE developed counties like Germany, USA, etc. have been conducted. Triple Bottom Line (TBL) analysis is conducted to understand the feasibility of adopting RE into a micro-grid. It focuses on the Techno-economic, environmental and social perspectives to understand the feasibility of RE adoption from the perspective of a developed country (Australia) versus a developing country (India). In this respect, a prototype model of the micro-grid is studied and used at Victoria University, Footscray Campus for various scenarios.

As renewable energy becomes more prevalent across the United States and the world, solar energy investment has also grown. There have been many studies done on photovoltaic (PV) systems in terms of energy payback and efficiency, but little research done to understand a PV system as a financial investment specific to South Carolina. This study aims to understand the return on investment that a PV system can achieve. More specifically whether PV systems in areas of South Carolina that uses Duke Energy achieve a favorable return on investment and what affects the profitability. This study uses the PVwatts calculator provided by NREL as well as an investment simulation to calculate the Internal Rate of Return (IRR) and Net Present Value on 1024 simulated 5kW PV arrays and evaluates their profitability. It then uses this information to apply it to real case studies for houses in South Carolina. This study found that shade has a significant impact on profitability of investment. At 30% shading, profitability drops near 0% IRR or below. Orientation impacts profitability significantly as well. Panels that are facing south, southeast, and southwest yielded the best return. While north, northeast and northwest orientations yielded very low or negative IRR. East and west facing panels can yield positive financial return, but this return is lower than panels orientated to the south. PV systems oriented towards the east or west must have optimal conditions to remain efficient. This study found that tilt had minimal impact on financially return. Incentives also significantly impacted profitability of investment. For a PV system to be profitable, federal, state, and Duke Energy incentives needed to be applied to the investment. When homes with PV systems are sold also has a great impact on profitability. Research has shown that there is a housing premium for homes with PV systems (Adomatis, 2015). This premium is highest when first installed and declines as the PV systems age. People also associate premiums with houses with PV systems even if the system is not adding much value to the home. This study has also found that the price of the PV system impacts investment. Premium grade panels had significantly less return compared to standard grade panels because prices per watt were higher.

The need for a reduced dependence on fossil fuels is motivated by a wide range of factors: from increasing fuel costs, to national security implications of supply, to rising concern for environmental impact. Although much focus is given to terrestrial systems, over 90% of the world's freight is transported by ship. Likewise, naval warfighting systems are critical in supporting U.S. national interests abroad. Yet the vast majority of these vessels rely on fossil fuels for operation. The results of this thesis illustrate a common theme that hybrid mechanical-electrical marine propulsion systems produce substantially better fuel efficiency than other technologies that are typically emphasized to reduce fuel consumption. Naval and commercial powertrains in the 60-70 MW range are shown to benefit substantially from the utilization of mechanical drive for high speed propulsion; complemented by an efficient electric drive system for low speed operations. This hybrid architecture proves to be able to best meet the wide range of performance requirements for each of these systems, while also being the most easily integrated technology option. Naval analyses evaluate powertrain options for the DDG-51 Flight III. Simulation results using actual operational profile data show a CODLAG system produces a net fuel savings of up to 12% more than a comparable all-electric system, corresponding to a savings of 37% relative the existing DDG-51 powertrain. These results prove that a mechanical linkage for the main propulsion engine greatly reduces fuel consumption and that for power generation systems requiring redundancy, diesel generators represent a vastly superior option to gas turbines. For the commercial application it is shown that an augmented PTO/PTI hybrid system can better reduce cruise fuel consumption than modern sail systems, while also producing significant benefit with regard to CO2 emissions. In addition, using such a shaft mounted hybrid system for low speed electric drive in ports reduces NOx emissions by 29-43%, while CO is reduced 57-66% and PM may be reduced up to 25%, depending on the specific operating mode. As an added benefit, fuel consumption rates under these conditions are reduced 20-29%.

This thesis focuses on China’s wind energy development, focusing on data pertaining to effects of wind energy development on economic, environmental, and social issues. It also reviews the Chinese government’s Wind Energy development policy, laws that encourage the development of wind energy, as well as wind energy development problems and future development plans. I will also address current trends in China’s wind energy development, as well as present the results of my field research.

Texas – the energy center of the world – is emerging as a pioneer in algae biodiesel research and production. There are a number of reasons for this. Texas is the largest emitter of CO₂ in the country, and efforts are being made to reduce the state's dependence on fossil fuels. Also, algae – robust and promising organisms – need non-arable land, lots of sunlight and brackish/waste water, along with CO₂. Texas has all of these in abundance, plus universities and algae start-ups that are doing crucial R

This project entails a study of a wind energy recovery system that utilizes a unique three-dimensional spiral structure to amplify wind speed and direct it toward pluralities of turbines. The system is comprised of an outer spiral shell, internal support structure, turbines, and mechanisms for positioning the turbines to face the prevailing wind. Computational Fluid Dynamics (CFD) analyses were conducted to determine the wind speed amplification factors as a result of a simulated wind flow around the spiral structure. To ensure accuracy of the results, state of the art CFD techniques were applied using Gambit 2.2.30 and Fluent 6.2.16. Specifically, wind speed amplification factors were determined for 25ft and 30ft radius spiral shells. The velocity profiles of the wind flow around both spiral structures were obtained under a postulated 10mph wind speed. This resulted in a turbulent flow with a Reynolds number of 5,596,819. All analyses were run using “standard k-ε” turbulence model with the “near wall treatment” option “standard wall function”. A “y+” value of 50 was held constant in all vi simulations. The affect of the grid size on the accuracy of the results was examined. Convergence criterion was satisfied in each case. The 25ft radius spiral structure yielded an average velocity amplification factor of 1.524; while the 30ft radius resulted in an average amplification factor of 1.539. This particular information can help the designer of the system to select an appropriate overall shell size based not only on the mechanical efficiency, but also considering the cost and economical factors.