<p> The use of gamma radiation to initiate the iodination of methane in liquid phase was studied using a semi-batch technique whereby the methane was bubbling through a column of iodine solution in a reactor. Yields of CH3I and CH2I2 lower than 10% and G < 500 were obtained as contrasted with the 60% yield and G=7xl0^7 reported in the gas-phase reaction. In view of the propensity of the iodine as a radical scavenger and the endothermic nature of the reaction, various attempts to improve the low yields were carried out. Results are eiven that indicate the chances of achieving a laree G value for liquid-phase reaction are very low even if the operating conditions are optimized. </p> / Thesis / Master of Engineering (MEngr)

This dissertation examined the phenotypic plasticity of endothermic, flight and respiratory physiology in response to developmental oxygen exposure in the moth Manduca sexta. Development in both 10% O2 hypoxia and 30% O2 hyperoxia treatments were used to look at the physiological consequence on both ends of the oxygen spectrum. Hypoxic insects reached smaller sizes as adults and had longer pupation lengths than controls. Hyperoxic insects were larger at the end of the larval stage, had increased larval growth rates, but also had longer developmental larval developmental times and pupation lengths than controls. There was a decrease in both metabolic rate and thorax temperatures of hypoxic reared insects at normoxic levels. In flight trials hypoxic insects had the lowest critical flight PO2, and the hyperoxic insects had the highest PO2. There was an increase in hypoxic insect flight muscle mitochondria oxygen consumption in permeabilized fibers, but this did not translate to the isolated flight muscle mitochondria metabolic rates. Rearing oxygen level did not significantly affect mitochondrial density and size; myofibril density and size, or tracheal density and size in flight muscle. Overall, I found that higher levels of organization were more susceptible to the effects of chronic oxygen exposure and found more effects of hypoxia than hyperoxia.

No description available.

No description available.

Managing the thermal loads inside a non-airbreathing hypersonic vehicle is particularly difficult. The heat generated by the power electronics, avionics, etc. must be removed so that the components do not exceed their maximum temperatures. These vehicles cannot dump the waste heat into fuel or ram air because they carry no fuel and do not have provisions for ram air. This means that the thermal energy resulting from the heat generated must be dumped into an onboard heat sink. Existing solutions to this problem have been passive systems based on solid-liquid phase change materials (PCMs), which store thermal energy as they melt. Since space is at a premium, a heat sink must store a lot of energy per unit volume, while keeping components below their maximum temperature. In this project, three heat sink concepts are tested, i.e., one based on PCMs, a second on thermal to chemical (TTC) energy storage, and a third on a hybrid combination of the first two. For the first, three different PCMs are tested and for the second a single endothermic chemical reaction. The hybrid PCM/TTC concept consists of a single PCM which plays the dual role of PCM and reactant in the endothermic chemical reaction of the TTC energy storage. To enhance heat sink performance, the use of thermoelectric generators (TEGs) and a local coolant loop are investigated. The advantage of the former is that they transform waste heat into usable electricity, reducing the amount of thermal energy that needs to be stored by the heat sink. The advantage of the latter is that it results in a more uniform cooling of the heat source and more uniform heating of the heat sink. Prototypes of each of the heat sink concepts and the coolant loop are designed, built, and tested. Experimental results indicate that all the solutions tested in this project outperform widely used paraffin heat sink technologies on an energy per unit volume basis. Our experiments also show that a local coolant loop is indeed advantageous and that current off-the-shelf thermoelectric generators do not generate enough power to offset the power requirements of the coolant loop. Significant improvements in the ZT factor of the thermoelectric materials used by the TEG would be required. / Master of Science / All electronics produce waste heat and have a maximum operating temperature above which they fail due to overheating. Heat sinks absorb the waste heat and prevent overheating. Non-airbreathing hypersonic vehicles do not have natural heat sinks like intake air or liquid fuel which are commonly used as heat sinks in airbreathing vehicles. Heat cannot be transferred to the environment due to the high temperatures caused by the friction of hypersonic air travel. This means that all waste heat must absorbed by an onboard heat sink. Existing heat sinks in non-airbreathing hypersonic vehicles use paraffin based solid-liquid phase change materials (PCMs) which store thermal energy as they melt. Three novel heat sink options are evaluated in this project, hydrated salt PCMs which absorb energy as they melt, a chemical reaction which absorbs heat as it reacts, and a hybrid system which incorporates one of the hydrates salt PCM as a reactant in the chemical reaction. Because space is at a premium, these options are evaluated by the amount of energy they can absorb (kilojoules) per unit volume (in3) while keeping the electronics below their maximum temperature. To enhance heat sink performance, the use of thermoelectric generators (TEGs) and a local coolant loop are investigated. The advantage of the former is that they transform waste heat into usable electricity, reducing the amount of thermal energy that needs to be stored by the heat sink. The advantage of the latter is that it results in a more uniform cooling of the electronics and more uniform heating of the heat sink. Prototypes of each of the heat sink concepts and the coolant loop are designed, built, and tested. Experimental results indicate that all the solutions tested in this project outperform widely used paraffin heat sink technologies on an energy per unit volume basis. Our experiments also show that a local coolant loop is indeed advantageous and that current off-the-shelf thermoelectric generators do not generate enough power to offset the power requirements of the coolant loop. Significant improvements in the state of the art of thermoelectric materials would be required for TEGs to generate enough electricity from our waste heat load to power the local coolant loop.

Energy storage within hypersonic aircraft is becoming increasingly important with the development of more sophisticated electronic components and is an integral piece of expanding their overall capabilities. Hypersonics not only produce large external thermal loads, but also an abundance of internal thermal loads from components such as power electronics, avionics, and batteries. Additionally, limited volume within such vehicles introduces additional constraints. Thus, having efficient heat sinks that are capable of storing much of these heat loads is imperative. Passive thermal management systems, i.e., heat sinks, are preferable in most applications because they do not require power input to operate, and they are typically smaller than active systems such as coolant loops. In identifying and developing heat sinks with increased energy storage capability, an exhaustive search of available phase change materials (PCMs) is conducted. PCMs have been used in hypersonic vehicles in the past as a means of energy storage. Additionally, the use of energy-consuming endothermic reactions is considered. An innovative PCM-endothermic reaction hybrid approach is also developed. Both thermodynamic and transient/quasi-stationary models are developed for each of these proposed heat sink technologies. Prototypes are then developed for the best candidates to validate the models and draw conclusions on each heat sink's performance. Both the thermodynamic modeling and experimental results presented in this paper suggest that PCMs, endothermic reactions, and, especially, the hybrid system show greater energy storage capabilities than what is being used in hypersonic vehicles currently. / Master of Science / Hypersonic vehicles are an important topic of interest in the aerospace and defense industries. To be classified as hypersonic, a vehicle must travel at or above Mach 5, which is at least five times the speed of sound. Hypersonic vehicles often travel at high altitudes and a common application of the technology is in missiles. One major hurdle in developing hypersonic technologies at lower altitudes is that because of the high speeds, the outside skin temperature of the vehicle can reach thousands of degrees. Clearly, these temperatures can affect the heat load on the inside of the vehicle as can the thermal energy release of internal components such as the power electronics, the avionics, etc. To deal with these internal heat loads, innovative energy storage solutions are needed to efficiently and effectively store the thermal energy released internally. One approach considered here is the use of phase change materials (PCMs) as a storage medium. Melting such a material requires large amounts of energy and occurs at constant temperature. This is much more advantageous than heating a material in which only the temperature rises. Another approach considered in this thesis is that of using a chemical reaction, which requires energy input to proceed. Such a reaction is called an endothermic reaction and often results in a temperature decrease. Thus, simply mixing a set of reactants and adding energy helps cool the system. A final approach considered is a hybrid one, which combines a PCM material and an endothermic reaction. Such an approach combines the advantages of both. Each of these approaches are modeled thermodynamically to better understand how devices based on them work. Physical prototypes are then designed, built, and tested to confirm their performance. Both the modeling and experimental results presented in this thesis suggest that these devices show significantly improved energy storage capabilities over the devices currently used in hypersonic vehicles.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-06-13T19:56:21Z No. of bitstreams: 1 FRANCISCO PINTO FILHO – TESE (PPGEP) 2016.pdf: 2405186 bytes, checksum: d7b5b1d68600f138fc5134159b39d6fc (MD5) / Made available in DSpace on 2018-06-13T19:56:21Z (GMT). No. of bitstreams: 1 FRANCISCO PINTO FILHO – TESE (PPGEP) 2016.pdf: 2405186 bytes, checksum: d7b5b1d68600f138fc5134159b39d6fc (MD5) Previous issue date: 2016-08-29 / Capes / A busca por inovações tecnológicas nos últimos anos cada vez mais se intensifica. Neste contexto, dois importantes grupos, os lantanídeos e as hidantoínas se destacam com importantes contribuições em diversas áreas de pesquisas apresentando vasto campo de aplicações. Nesses termos, esta pesquisa teve como objetivo sintetizar e caracterizar nanocomplexos dos íons lantanídicos: Eu +3, Er+3 e Nd+3 com 5-(4-metilfenil)-3-fenil-2-tioxo-imidazolidin-4-ona (HPA) e um segundo ligante, 1,10-fenatrolina (Phen), almejando obter complexos com propriedades biológicas. Partindo da reação entre os cloretos dos respectivos lantanídeos com os ligantes orgânicos, sob refluxo de aproximadamente 8 horas e temperatura de 60°C, foram obtidos os complexos de európio, érbio e neodímio. Os nanocomplexos em pó foram caracterizados utilizando técnicas de análises espectroscópicas, térmicas e estrutural. Os complexos de íons lantanídicos apresentaram resultados da análise elementar conforme a estequiometria proposta (1:3:1). A coordenação dos ligantes com os íons lantanídicos ocorreu através dos átomos de oxi gênio e enxofre da estrutura do 5-(4-metilfenil)-3-fenil-2-tioxo-imidazolidin-4-ona (HPA) e dos átomos de nitrogênio (C=N) da 1,10’- fenantrolina, que podem ser observados nos espectros de infravermelho, através dos deslocamentos dessas bandas presentes nos ligantes livres e coordenados. Os espectros UV-Vis apresentaram discretos deslocamentos e mudanças nas intensidades das bandas de absorção dos complexos em relação ao ligante HPA. As curvas TG/DTG do ligante HPA apresentou 3 etapas de decomposição, enquanto, que os complexos apresentaram 4 etapas. O nanocomplexo de Eu+3 apresentou menor estabilidade térmica, o que possibilita o uso destes pós como fármacos. As curvas DSC dos nanocomplexos apresentaram uma série de eventos endotérmicos e exotérmicos correspondentes a processos de decomposição, desidratação, fusão e volatilização que corroboram com as curvas termogravimétricas. Todos os complexos lantanídicos obtidos apresentaram dimensões nanométricas, e o complexo de neodímio apresentou a estrutura mais cristalina. / The search for technological innovations in recent years increasingly intensifies. In this context, two major groups, the lanthanides and hydantoins stand out with important contributions in many areas of research showing wide field of applications. In these terms, this research aims to synthesize and characterize complex of lanthanide ions: Eu+3, Ho+3, Er+3 and Nd+3 with 5-(4-methyl-phenyl)-3-phenyl-2-thioxo-imidazolidin-4-one (HPA) and a second linker, 1,10-fenatrolina (Phen), aiming to obtain complexes with biological properties. From the reaction between the chlorides of lanthanides with the respective organic ligands under reflux for approximately 8 hours and 60°C, were obtained complexes of europium, holmium, erbium and neodymium. The powder complexes were characterized using spectroscopic techniques, thermal and structural analyzes. The complexes of lanthanide ions showed elemental analysis results according to the proposed stoichiometry (1:3:1). The coordination of the ligands with lanthanide ions occurred through oxygen and sulfur atoms in the structure of 5 - (4-methylphenyl) -3-phenyl-2-thioxo-imidazolidin-4-one (HPA) and nitrogen atoms (C = N) of 1,10'- phenanthroline, which can be observed in the infrared spectra, through the displacement of these bands present in free and coordinated ligands. UV-Vis spectra showed discrete displacements and changes in the intensities of the absorption bands of the complex compared to the HPA binder. The TG/ DTG curves HPA binder 3 had decomposition steps, while the complexes showed 4 and 5 steps. The complex synthesized Er+3 showed higher thermal stability. The DSC curves of the complexes showed a series of endothermic and exothermic events corresponding to decomposition processes, dehydration, fusion and volatilization, corroborating the thermogravimetric curves. All lanthanide complexes obtained showed nanometric dimensions, and neodymium complex presented the most crystalline structure.

Le refroidissement actif par endocarburant permet d’assurer la tenue thermique d’un superstatoréacteur pour le vol hypersonique. Néanmoins, l’utilisation de cette technologie de refroidissement passe par la maitrise du couplage combustion – pyrolyse, qui fait de la définition d’une stratégie de contrôle du moteur un véritable défi. Une étude expérimentale a été réalisée afin d’analyser l’effet du paramètre de commande principal, le débit de combustible, sur des paramètres de sorties pertinents, à l’aide d’un dispositif de test spécifiquement conçu pour appréhender le couplage combustion – pyrolyse. Ceci a permis d’étudier la dynamique d’un circuit régénératif par rapport à ce paramètre de commande. Une étude cinétique paramétrique sur la pyrolyse du carburant a été conduite en parallèle de celle expérimentale afin d’affiner l’analyse et améliorer l’interprétation des expériences. La décomposition du carburant utilisé pour les tests (éthylène) a été prise en compte grâce à un mécanisme cinétique détaillé (153 espèces, 1185 réactions chimiques). / Regenerative cooling is a well-known cooling technique, suitable to ensure scramjets thermal protection. The development of regeneratively cooled engines using an endothermic propellant is a challenging task, especially because of the strong coupling between fuel decomposition and combustion, which makes the definition of an engine regulation strategy very hard. An experimental study, aiming at identifying the effect of fuel mass flow rate variations on a fuel cooled-combustor in terms of system dynamics has been carried out. A remotely controlled fuel-cooled combustor, designed by means of CDF calculations and suitable for the experimental analysis of combustion-pyrolysis coupling, has been used. In order to improve tests results analysis, a parametric study to characterize fuel decomposition has also been realized. The pyrolysis has been modeled by using a detailed kinetic mechanism (153 species, 1185 chemical reactions).

No description available.

<p dir="ltr">The chemical industry faces unprecedented pressure to reduce its carbon footprint while meeting growing global demand. As a major contributor to greenhouse gas emissions, accounting for approximately 7% of global carbon release, the sector plays a crucial role in achieving net-zero goals. This challenge is further compounded by projections suggesting that demand for chemicals could increase up to four-fold by 2050, and by the sector's role in producing several raw materials for other industries.</p><p dir="ltr">Within this context, endothermic reactors are of particular concern. The production of ethylene, propylene, and hydrogen alone accounts for around 3.6% of global CO2 emissions, representing over half of the chemical industry's total release. This situation underscores the need for alternatives in reactor design and operation.</p><p dir="ltr">To address these challenges, we introduce novel decarbonized process schemes and unit operations. The research centers around the development of Electric Reaction Towers (ERTs), a novel reactor configuration designed to ensure consistent product composition despite intense process fluctuations, such as those associated with Variable Renewable Energy (VRE). This is achieved by creating Custom Non-linear Heat Profiles (CNHPs) that maintain the key dimensionless groups of the system under dynamic conditions.</p><p dir="ltr">We present the concept of ERTs, explore their key principles, and the intuition behind their design. Additionally, we introduce Modular Reaction Towers (MRTs), which retain the benefits of handling fluctuations while addressing the investment and logistical challenges of adopting electric reactors.</p><p dir="ltr">The research employs a combination of Dimensional Analysis, Process Simulations, and Computational Fluid Dynamics (CFD) to evaluate these novel designs. Using ethylene production as a case study, we demonstrate that ERTs can enhance output by up to 4.2 times compared to state-of-the-art industrial designs.</p><p dir="ltr">The study further explores several additional concepts: Intermediate Cooling Zones (ICZs) and their potential to optimize complex reaction systems; the application of MRTs in the decentralized production of liquid hydrocarbons from shale gas to reduce flaring; and TurboQuenching, a novel approach to rapidly cool reaction products without a cooling agent while co-producing power. Finally, we discuss the broader implications of these innovations for the chemical industry's transition to more sustainable and efficient production methods.</p><p dir="ltr">By fundamentally re-thinking reactor design, this research contributes to the development of more efficient and sustainable production methods in the chemical industry, supporting the transition to a Net-Zero future.</p><p><br></p>