Дисертації з теми "Liquid oxygen and methane"

Utiliser le méthane comme carburant dans les moteurs fusées présente beaucoup d'avantages mais la combustion avec de l'oxygène pur à haute pression reste mal comprise. D'un point de vue thermodynamique, le méthane et l'oxygène partagent des valeurs de point critique très similaires, ce qui rend difficile la prédiction du mélange des ergols, l'accrochage, la stabilité et la structure de la flamme. De plus, quand le méthane est injecté en excès, des aérosols peuvent être produits, pouvant obstruer les lignes, endommager la turbine et réduire le rendement.Une mise à jour approfondie des connaissances sur la combustion LOX/CH4 est donc nécessaire. Ce défi est relevé au sein du consortium composé du laboratoire EM2C, de l'ONERA, du CNES et d'ArianeGroup. Deux campagnes d'essais sont menées sur le banc MASCOTTE de l'ONERA visant à étudier trois sujets centraux : la structure de la flamme, les transferts thermiques aux parois et la production d'aérosols. Dans ce but, divers diagnostics expérimentaux sont mis en œuvre simultanément pendant des essais à feu à haute pression.Différents diagnostics d'imagerie sont mis en place pour analyser la structure de la flamme et des jets liquides. Malgré les difficultés d'acquisition rencontrées dans ces conditions extrêmes, les analyses révèlent une structure de flamme complexe. En régime subcritique, les mécanismes d'atomisation et d'évaporation dominent. La flamme est alors bien plus ouverte et plus longue qu'à de plus hautes pressions, où les mécanismes de mélange diffusifs prévalent. Caractériser l'accrochage de la flamme reste un défi. En effet, un anneau de glace, probablement d'eau, entoure et masque le pied de la flamme. Des mécanismes de formation sont proposés et un cycle temporel de croissance/destruction est mis en avant. Sa présence affecte fortement la visualisation de la flamme, et peut conduire à des interprétations erronées de sa topologie.Pour la première fois à MASCOTTE, la phosphorescence induite par laser (LIP) est mise en place. Diverses méthodes LIP existent mais ne sont pas bien adaptées aux conditions de MASCOTTE : large gamme de températures, transitoires thermiques et environnement diphasique. C'est pourquoi une méthode spécifique a été mise au point (Full Spectrum Fitting method). Elle exploite la dépendance spectrale à la température, permettant des mesures instantanées de 100 à 900 K avec une précision de 17 K, sans dépendance à l'énergie d'excitation laser. Une analyse détaillée des données met en évidence les modes de transfert de chaleur prédominants, étudie l'influence des points de fonctionnement et compare les données expérimentales avec un modèle de transferts thermiques de paroi, particulièrement bien adapté pour déduire les caractéristiques convectives de l'écoulement à la paroi.Différents diagnostics sont mis en œuvre pour caractériser les aérosols. Une sonde intrusive prélève les particules et les gaz brûlés en aval de la flamme. Les particules sont prélevées sur des grilles adaptées à des analyses par microscopie électronique à transmission (TEM). Les images détaillées de leurs morphologies révèlent qu'il s'agit de suies. Les gaz sont analysés par chromatographie en phase gazeuse. Ceci permet d'identifier des molécules précurseurs des suies comme le benzène et l'acétylène. Les suies sont quantifiées temporellement par extinction laser. Des post-traitements dédiés sont développés et diverses hypothèses sont discutées pour expliquer les variations spatiales de production de suies
Using methane as a fuel in rocket engines would have many advantages but the combustion with pure oxygen at high pressure remains poorly understood. From a thermodynamic point of view, methane and oxygen share very similar critical point values, making it challenging to predict propellant mixing, flame anchoring, stability and structure. Moreover, when methane is injected in excess, aerosols can be produced, which can clog the lines, damage the turbine, and reduce the efficiency.Therefore, a thorough update of the knowledge of LOX/CH4 combustion is necessary. These challenges are tackled within the consortium composed of EM2C laboratory, ONERA, CNES, and ArianeGroup. Two test campaigns are carried out at the MASCOTTE facility from ONERA, aiming to study three central topics: the flame structure, wall heat transfers, and aerosol production. To this end, various experimental diagnostics are implemented simultaneously during high-pressure hot-fire tests.Various imaging diagnostics are implemented to analyze the flame structure and the dense liquid jets. Despite the acquisition difficulties encountered in these extreme conditions, the analyses reveal a complex flame structure. In the subcritical regime, atomization and evaporation mechanisms dominate. The flame is much more opened and longer than at higher pressures, where diffusive mixing mechanisms prevail. Characterizing flame anchoring remains a challenge. A water ice ring surrounding, and masking, the flame foot has been identified. Formation mechanisms are proposed, and a growth/destruction temporal cycle is highlighted. Its presence strongly affects flame visualizations, and may lead to misinterpretations of its topology.Laser-induced phosphorescence (LIP) is implemented for the first time at MASCOTTE. Various LIP methods exist, but they are not well suited to the MASCOTTE conditions: wide temperature range, thermal transients, and two-phase flow environment favoring laser absorption/diffusion. Therefore, a specific method, the Full Spectrum Fitting method (FSF method), has been developed. It exploits the spectral dependence on temperature, enabling instantaneous measurements from 100 to 900 K with a precision of 17 K, with no dependence on the laser excitation energy. A detailed data analysis highlights the predominant wall heat transfer modes, studies the influence of the operating points, and compares the experimental data with a wall heat transfer model, which is particularly well suited for deducing the convective properties of the flow.Three diagnostics are used to characterize aerosols. An intrusive probe samples particles and burnt gases downstream of the flame. The particles are sampled on TEM grids and analyzed by Transmission Electron Microscopy. Detailed images of the aerosol morphology reveal that the particles are soot. Combustion products are analyzed by gas chromatography. This makes it possible to identify soot precursor molecules such as benzene and acetylene. Soot are quantified temporally by laser extinction. A dedicated post-processing method is developed and various hypotheses are discussed to explain the spatial variations of the soot production downstream of the flame

Chemical kinetics is the science of modeling the steps involved in a chemical reaction at the molecular level. This investigation is concerned with the chemical reactions that occur during combustion. There is ample room for improvement in most presently accepted chemical kinetic models and many reactions are still not modeled. The key to creating and improving chemical kinetic models of combustion reactions is gathering sufficient experimental data and solidifying the foundations upon which more complicated models may be built.
The experimental apparatus that is used to gather data in this study is a stagnation flame burner. Particle image velocimetry, a laser-based flow visualization technique, is used to measure velocity in both the axial and radial directions. The results are analyzed first to confirm the validity of the one-dimensional, axisymmetric model commonly used to describe impinging-jet flow. Experimental results are found to have good agreement with theoretical approximations and numerical models. Tests are then conducted to reproduce previously published data for methane-air flames at lean, stoichiometric and rich conditions in order to prove the reliability of the experimental apparatus. There is agreement between published data and the new experimental results.
Experiments with oxygen enrichment are then conducted at equivalence ratios not normally within the flammability limits of methane-air mixtures, from the very lean, phi = 0.55, to the very rich, phi = 1.45. Results show marked disagreement between model and experiment at equivalence ratios far from stoichiometric. These experimental data will allow the chemical kinetic model for premixed methane combustion to be improved -- by correcting divergence in the model at very lean and very rich conditions, the model should be improved appreciably over the narrower range of equivalence ratios typically seen in methane-air combustion.
La cinétique chimique est la science de la modélisation des étapes d'une réaction chimique au niveau moléculaire. Ce mémoire s'interesse aux réactions chimique qui se produisent durant la combustion. Les modèles cinétique présentement acceptés sont en besoin d'amélioration et d'autres enplus, il existe plusieurs réactions qui n'ont aucun modèle. Pour mieux développer les modèles et pour en créer des nouveaux, il fault rassembler assez de données expérimentales pour produire une base solide sur laquelle des modèles de plus en plus compliqués peuvent etre construits.
Pour générer des données, cette étude utilise un appareil expérimental avec une géométrie de point d'arrêt, dans laquelle une flamme aplatie peut exister. Les vitesses dans la direction axiale et radiale sont mesurées par la vélocimétire image-particule, une technique à base de laser. Les résultats sont d'abord analisés pour vérifier que le modèle unidimensionnel est valide. Une bonne concordance est observée entre la théorie et les résultats et entre les modèles numériques et les résultats. Subséquemment, des expériences sont effectuées pour reproduire des données déjà publiées pour le méthane et l'air aux rapports d'équivalence oxydants, stoechiométriques et réducteurs, afin de prouver la fiabilité de l'appareil expérimental. Il ya une bonne concordance entre les données publiées et les résultats expérimentaux.
Des expériences dans lequelles l'air est enrichi avec de l'oxygène sont effectuées à des rapports d'équivalence de phi = 0.55 juste qu'à phi = 1.45; ces rapports d'équivalence ne sont normalement pas dans les limites d'inflammabilité des mélanges de méthane-air. Ici, les résultats montrent un désaccord marqué entre le modèle et les expériences pour les rapports d'équivalence très loin de phi = 1.0. Les données permettent le modèle cinétique chimique pour la combustion du méthane prémélangée d'être amélioré. En corrigeant les divergences entre le modèle et les resultats experimentales pour rapports d'équivalence très oxydants et très réducteurs, le modèle sera amélioré pour rapports d'équivalences généralement vus dans la combusiton de méthane dans l'air.

This thesis examines the collision induced, far-infrared absorption of homonuclear diatomic molecules. These molecular processes are relevant in the astrophysical environments of planetary atmospheres and galactic molecular clouds, and a brief survey of far-infrared measurements of these regions is presented. The theory of collision induced absorption by molecular rotational transitions is reviewed and a calculation is made of the quadrupolar induced, single rotational transition absorption line intensities of the nitrogen and oxygen molecules. The far-infrared absorption spectra of liquid nitrogen and liquid oxygen at 77K, over the frequency range 5 to 70 cm⁻¹ , have been measured. The far-infrared spectrum of liquid oxygen has not previously been reported. The present work includes the design of a low temperature, multiple pass, far-infrared absorption cell intended for low temperature, low density gas measurements. The effect of diffraction on the cell's maximum attainable optical path length, and a model used to estimate the anticipated liquid helium consumption are discussed.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

The selective oxidation of methane, which is the primary component of natural gas, isone of the most important challenges in catalysis. While the search for catalysts capable of converting methane to higher value commodity chemicals and liquid fuels such as methanol has been ongoing for over a century, an industrially viable process has not yet been developed. Currently, large scale upgradation of natural gas proceeds indirectly employing high temperature conversion to syngas which is then processed to synthesise fuels and chemicals. Different catalysts are currently being studied for direct low temperature selective oxidation of methane to liquid oxygenates primarily methanol. One of the systems studied is based on gold-palladium supported nanoparticles using hydrogen peroxide. Though the catalyst was shown to be active, high wastage of hydrogen peroxide was observed along with low productivities. The work in this thesis shows the removal of support can be used to increase the activity and efficiency of the reaction. By tuning the amount of hydrogen peroxide, high productivities and selectivities were observed. Further optimisation of catalyst preparation and methane oxidation were also performed. A theoretical study based on density functional theory into interactions between metal particles, such as gold and palladium and substrates such as oxygen, hydrogen and water was also carried out to identify the active sites and reaction mechanism underway with hydrogen peroxide and these metal particles.

This work takes a closer look at ceria catalyst synthesis through micelle self-assembly. We compare surfactants, precursors, solvent systems, and doping. The surfactants are the building blocks upon which the ceria can crystallize. The samples are calcinated to test their thermal stability. Characterization is performed using pXRD as well as physisorption. The samples that exhibited a higher thermal stability were characterized to have a high surface area as well as low fluctuations in crystallite size, pore volume, and pore size. Ceria synthesized with cerium (III) nitrate hexahydrate and CTAB in a water:ethanol mixture using sodium hydroxide showed to be the most effective at providing a thermally stable product. Doping the catalyst with titanium increased the thermal stability significantly. Select samples were run in a variety of fuel to oxygen ratios to determine the best conditions in which we could perform partial methane oxidation to recuperate hydrogen gas. Most of the experiments show oxygen depletion with minor changes in other gas levels indicating that there is no oxidation occurring. Curiously the oxygen levels do decrease. There is a possibility that there is a reaction occurring initially at room temperature and being exacerbated with further temperature increase.

Rocketry employs cryogenic refrigeration to increase the density of propellants, such as oxygen, and stores the propellant as a liquid. In addition to propellant liquefaction, cryogenic refrigeration can also conserve propellant and provide propellant subcooling and densification. Previous studies analyzed vapor conditioning of a cryogenic propellant, which occurred by either a heat exchanger positioned in the vapor or by using the vapor as the working fluid in a refrigeration cycle. This study analyzes the refrigeration effects of a heat exchanger located beneath the vapor-liquid interface of liquid oxygen. This study predicts the mass liquefaction rate and heat transfer coefficient for liquid oxygen using two different models, a Kinetic Theory Model and a Cold Plate Model, and compares both models to experimental data. The Kinetic Theory Model overestimated the liquefaction rate and heat transfer coefficient by five to six orders of magnitude, while the Cold Plate Model underestimated the liquefaction rate and heat transfer coefficient by one to two orders of magnitude. This study also suggested a model to predict the densification rate of liquid oxygen, while the system is maintained at constant pressure. The densification rate model is based on transient heat conduction analysis and provides reasonable results when compared to experimental data.
ID: 029049996; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.M.E.)--University of Central Florida, 2010.; Includes bibliographical references (p. 127-129).
M.S.M.E.
Masters
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering

Non-thermal plasmas are considered to be very promising for the initiation of chemical reactions and a vast amount of experimental work has been dedicated to plasma assisted hydrocarbon conversion processes, which are reviewed in the fourth chapter of the thesis. However, current knowledge and experimental data available in the literature on plasma assisted liquid hydrocarbon cracking and gaseous hydrocarbon decomposition is very limited. The experimental methodology is introduced in the chapter that follows the literature review. It includes the scope and objectives section reflecting the information presented in the literature review and the rationale of this work. This is followed by a thorough description of the design and construction of the experimental plasma reformer and the precise experimental procedures, the set-up of hydrocarbon characterization equipment and the development of analytical methods. The methodology of uncertainty analysis is also described. In this work we performed experiments in attempt the cracking of liquid hexadecane into smaller liquid hydrocarbons, which was not successful. The conditions tested and the problems encountered are described in detail. In this project we performed a parametric study for methane and propane decomposition under a corona discharge for COx free hydrogen generation. For methane and propane a series of experiments were performed for a positive corona discharge at a fixed inter-electrode distance (15 mm) to study the effects of discharge power (range of 14 - 20 W and 19 – 35 W respectively) and residence time (60 - 240 s and 60 – 303 s respectively). A second series of experiments studied the effect of inter-electrode distance on hydrogen production, with distances of 15, 20, 25, 30 and 35 mm tested. The analysis of the results shows that both discharge power and residence time, have a positive influence on gaseous hydrocarbon conversion, hydrogen selectivity and energy conversion efficiency for methane and propane decomposition. Longer discharge gaps favour hydrogen production for methane and propane decomposition. A final series of experiments on corona polarity showed that a positive discharge was preferable for methane decomposition.

Quantitative chemical and scanning electron microscopical techniques have been employed to investigate the deoxidation kinetics and changes in oxidation product morphology in low carbon steel melts. The techniques have been used to study the deoxidation processes associated with aluminium, titanium, silicon, zirconium and a calcium-aluminium alloy. After the addition of the deoxidant, the total oxygen concentrations of all melts rapidly decreased corresponding with a decrease in the size and number of inclusions observed. This continued to a plateau level of total oxygen concentration and mean inclusion diameter. Samples removed from the melts prior to deoxidation were found to contain globular MnO-FeO inclusions. It was discovered that the morphological sequence for single element deoxidants involved a progressive evolution from liquid globular to solid spherical inclusions followed by polyhedral, dendritic and coralline morphologies. Finally, sintered agglomerates were formed when inclusion clusters collapsed. The extent to which the oxidation products went down the sequence depended on: the dissolution characteristics of the deoxidant; the thermodynamic affinity of the deoxidant for oxygen in the melt; the inclusion/melt interfacial energy characteristics; the refractoriness of the oxidation products and intermediate compounds; and the degree of turbulence experienced by the melt. Explanations have been postulated which elucidate the behaviour of the different deoxidants, as not all displayed the whole morphological sequence. Silicon deoxidation produced spherical silicates, whereas the zirconia inclusions were either spherical or dendritic and the titanium oxidation products had spherical or polyhedral morphologies. Aluminium exhibited all morphologies in the sequence. Deoxidation with the calcium-aluminium alloy was found to have preceded by a two stage process. The initial stage was dominated by the formation of aluminium rich solid oxides followed by the progressive reduction by calcium, resulting in an adhesive liquid calcium-aluminate surface coating. The role of refractory crucible as a collecting surface for the capture and removal of deoxidation products from the melt was investigated, which confirmed that the inclusions were generally incorporated into the low melting point matrix phases. Turbulence also increased the probability that emergence would take place at these capture sites.

Thesis (M.S.)--Case Western Reserve University, 2009
Abstract Department of Mechanical & Aerospace Engineering Title from PDF (viewed on 20 April 2009) Available online via the OhioLINK ETD Center

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau Mestre em Engenharia Biomédica
The last decade of the 20th century has yielded a remarkable progress in the field of first generation artificial blood substitutes. Emulsions based on perfluorocarbons (PFCs) became one of the main candidates for a safe and reliable artificial blood substitute. The final objective of the present work is to study the fluorinated ionic liquids (FILs) with the purpose of replacing, partially or totally, the PFCs actually used as artificial blood substitutes, thus providing new fluids with tailored advanced properties. With this goal in mind, the thermophysical and thermodynamic characterization of several FILs, was carried out with the aim to select the most appropriate candidate. This characterization involves the measurement and analysis of the decomposition and melting temperature, density, viscosity, refractive index, and ionic conductivity at atmospheric pressure in a temperature range from 298.15 to 353.15 K. Furthermore, the liquid-liquid equilibria of binary mixtures of PFCs and FILs were studied, at atmospheric pressure in a temperature range usually from 293.15 to 343.15 K. The knowledge of the phase behaviour is crucial to the formulation of emulsions used nowadays as suitable oxygen carriers. Finally, Non-Random Two Liquid (NRTL) thermodynamic model was successfully applied to correlate the behaviour of the binary mixtures of PFCs and FILs

Abstract The present thesis deals with the nuclear magnetic resonance (NMR) spectroscopy of small solutes applied to the studies of liquid crystals and molecular sieves. In this method, changes induced by the investigated environment to the static spectral parameters (i.e. nuclear shielding, indirect and direct spin-spin coupling and quadrupole coupling) of the solute are measured. The nuclear shielding of dissolved noble gases is utilized for the studies of thermotropic liquid crystals. The relation between the symmetry properties of mesophases and the nuclear shielding is described. The different interaction mechanisms perturbing the observed noble gas nuclear shielding are discussed, particularly, the role of long-range attractive van der Waals interactions is brought out. The suitability of the noble gas NMR spectroscopy to the studies of lyotropic liquid crystals is investigated in terms of nuclear shielding and quadrupole coupling interactions. In molecular sieve systems, the effect of inter- and intracrystalline motions of solutes on their NMR spectra is discussed. A novel method for the measurement of the intracrystalline motions is developed. The distinctions in the 13C shielding of methane adsorbed in AlPO4-11 and SAPO-11, two structurally similar molecular sieves differing in composition, are indicated.

The oxidation of lower alkanes especially methane to methanol under mild reaction conditions is one of the most challenging task for industry and academia. At present, indirect utilisation via synthesis gas is the only commercially viable process for methanol production. Therefore, this study intends to investigate the direct oxidation of methane to methanol using a novel low temperature approach. Recently, gold based supported catalysts have been found to be highly effective oxidation catalysts where a number of important discoveries have been made such as in hydrogen peroxide synthesis and selective oxidation of alcohols to aldehydes. Due to these recent advances, further work into the oxidation of carbon-hydrogen bonds especially methane by gold and gold-palladium alloyed nanoparticles was the central topic of this study. As a proof of concept for the following studies, oxidation of primary C-H bonds in toluene and toluene derivatives were carried out in a high pressure stirred autoclave with molecular oxygen as oxidant. It was evident that Au-Pd supported catalyst is capable in oxidising primary C-H bonds on toluene and toluene derivatives at lower temperature with high catalytic activity based on turnover number (TON) compared to available heterogeneous catalysts reported in literature. However, these catalysts are ineffective in the oxidation of methane with oxygen under mild conditions with water as solvent and temperature below 90 °C. In view of this, hydrogen peroxide has been used as oxidant and it was shown that Au-Pd supported nanoparticles are active for the oxidation of methane giving high selectivity to methanol especially in the reactions carried out with hydrogen peroxide generated using an in-situ approach. Methane oxidation reactions were carried out in aqueous medium. The main products were methanol, methyl hydroperoxide and only carbon dioxide as overoxidation product. Investigations of reaction conditions such as concentration of oxidant, reaction time, reaction temperature and pressure of methane were investigated. It was found that the activity and selectivity of the catalyst was highly dependant on these variables. Oxygenate productivity was found to increase by increasing the H₂O ₂ or H₂/O₂ concentration and methane pressure. Longer reaction times were detrimental to the methanol selectivity where overoxidation reaction occurred. Interestingly, the Au-Pd catalytic system was able to oxidise methane to methanol at temperatures as low as 2 °C. The applicability of the developed catalytic system was tested on ethane oxidation reaction and it successfully produced ethanol as the major product. The oxygenate productivity was higher as compared to methane due to the solubility factor and the difference in the strength of carbon-hydrogen bonds. The catalyst preparation method and pretreatment were shown to be very important in the formation of active catalysts. The Au-Pd alloy having Au core-palladium shell structure with PdO dominance on the surface and bigger particle size was preferred than analogue catalyst consists of Au and Pd in metallic state with smaller particle size. In addition to that, the choice of support is crucial and this study discovered TiO: as a preferred support where it could assist in stabilising the active hydroperoxy species. The Au:Pd ratio was also found to be an important variable, and equal weight ratio between Au and Pd was shown to be the optimised ratio for methane oxidation either using addition of H₂O₂ or in-situ H₂O₂ approach. The synergistic effect of Au and Pd was confirmed by superior catalytic activity compared to monometallic catalysts. Reaction mechanism was proposed and it was based on catalytic evaluation data, stability of the products and oxidation with radical scavengers. The proposed mechanism was in line with the theoretical modelling studies on similar catalytic systems. Optimisation of Au based supported catalyst with copper as co-metal supported on TiO₂ was shown to improve the oxygenate productivity and methanol selectivity as well as enhanced the H₂O ₂ utilisation. In particular, trimetallic 5wt%AuPdl.0wt%Cu/TiO ₂ synthesised via impregnation method and calcined in static air gave more than double turn over frequency (TOF = 1.404) with methanol selectivity around 83% as compared to bimetallic 5wt%Au-Pd/TiO₂ catalyst (TOF = 0.692, methanol selectivity = 49%). It was suggested in this study that copper is responsible in enhancing the formation of intermediate methyl hydroperoxide species and in some extent to block the non-selective sites for hydrogen peroxide decomposition and hydrogenation by disrupting the surface structure of Au-Pd alloy whilst at the same time maintaining the active sites (Au-Pd alloy) responsible for selective formation of methanol. The oxidation state of copper was shown to be the main factor in controlling the catalytic activity and selectivity. Copper in a combination of multiple oxidation states was preferred than single oxidation state.

The combustion behavior of methane and ethane is important to the study of natural gas and other alternative fuels that are comprised primarily of these two basic hydrocarbons. Understanding the transition from methane-dominated ignition kinetics to ethane-dominated kinetics for increasing levels of ethane is also of fundamental interest toward the understanding of hydrocarbon chemical kinetics. Much research has been conducted on the two fuels individually, but experimental data of the combustion of blends of methane and ethane is limited to ratios that recreate typical natural gas compositions (up to ~20% ethane molar concentration). The goal of this study was to provide a comprehensive data set of ignition delay times of the combustion of blends of methane and ethane at near atmospheric pressure. A group of ten diluted CH4/C2H6/O2/Ar mixtures of varying concentrations, fuel blend ratios, and equivalence ratios (0.5 and 1.0) were studied over the temperature range 1223 to 2248 K and over the pressure range 0.65 to 1.42 atm using a new shock tube at the University of Central Florida Gas Dynamics Laboratory. Mixtures were diluted with either 75 or 98% argon by volume. The fuel blend ratio was varied between 100% CH4 and 100% C2H6. Reaction progress was monitored by observing chemiluminescence emission from CH* at 431 nm and the pressure. Experimental data were compared against three detailed chemical kinetics mechanisms. Model predictions of CH* emission profiles and derived ignition delay times were plotted against the experimental data. The models agree well with the experimental data for mixtures with low levels of ethane, up to 25% molar concentration, but show increasing error as the relative ethane fuel concentration increases. The predictions of the separate models also diverge from each other with increasing relative ethane fuel concentration. Therefore, the data set obtained from the present work provides valuable information for the future improvement of chemical kinetics models for ethane combustion.
M.S.A.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Aerospace Engineering MSAE

In this thesis, combustion processes in a laboratory-scale methane based low pressure rocket motor (LPRM) is studied experimentally and numerically. Experiments are conducted to measure flame temperatures and chamber temperature and pressure. Single reaction-four species reacting flow of gaseous methane and gaseous oxygen in the combustion chamber is also simulated numerically using a commercial CFD solver based on 2-D, steady-state, viscous, turbulent and compressible flow assumptions. LPRM geometry is simplified to several configurations, i.e. Channel and Combustion Chamber with Nozzle and FWD. Flow in a Bunsen burner is simulated inside Channel geometry in order to validate the reaction model. Grid independence study is also conducted for reacting as well as non-reacting flows. Numerical model is calibrated based on experimental results. Results of the computational model are found in a good agreement with the experimental data after calibrating specific heats of the products. Parametric study is conducted in order to investigate the effects of different mass flow rates and chamber pressures on flow and combustion characteristics of a LPRM to provide insight to future studies.

A study of two the sequential displacement of gas and liquid phases in microchannels for eventual application in temperature swing adsorption (TSA) methane purification systems was performed. A model for bulk fluid displacement in 200 m channels was developed and validated using data from an air-water flow visualization study performed on glass microchannel test sections with a hydraulic diameter of 203 m. High-speed video recording was used to observe displacement samples at two separate channel locations for both the displacement of gas by liquid and liquid by gas, and for driving pressure gradients ranging from 19 to 450 kPa m-1. Interface velocities, void fractions, and film thicknesses were determined using image analysis software for each of the 63 sample videos obtained. Coupled 2-D heat and mass transfer models were developed to simulate a TSA gas separation process in which impurities in the gas supply were removed through adsorption into adsorbent coated microchannel walls. These models were used to evaluate the impact of residual liquid films on system mass transfer during the adsorption process. It was determined that for a TSA methane purification system to be effective, it is necessary to purge liquid from the adsorbent channel. This intermediate purge phase will benefit the mass transfer performance of the adsorption system by removing significant amounts of residual liquid from the channel and by causing the onset of rivulet flow in the channel. The existence of the remaining dry wall area, which is characteristic of the rivulet flow regime, improves system mass transfer performance in the presence of residual liquid. The commercial viability of microchannel TSA gas separation systems depends strongly on the ability to mitigate the presence and effects of residual liquid in the adsorbent channels. While the use of liquid heat transfer fluids in the microchannel structure provides rapid heating and cooling of the adsorbent mass, the management of residual liquid remains a significant hurdle. In addition, such systems will require reliable prevention of interaction between the adsorbent and the liquid heat transfer fluid, whether through the development and fabrication of highly selective polymer matrix materials or the use of non-interacting large-molecule liquid heat transfer fluids. If these hurdles can be successfully addressed, microchannel TSA systems may have the potential to become a competitive technology in large-scale gas separation.

Las baterías de litio-oxigeno (Li-O2 o litio-aire) son un campo de gran interés y reciente actualidad ya que su densidad energética es teóricamente similar a la de la gasolina. Esta tecnología es potencialmente una de las mejores soluciones para el diseño y la construcción de vehículos eléctricos. Sin embargo, esta nueva tecnología seguirá sujeta a investigación al menos durante los próximos 20 años, debido a su baja ciclabilidad, su eficiencia eléctrica limitada y la dificultad para montar una celda real, segura, y capaz de funcionar en condiciones atmosféricas tan bien como a escala de laboratorio donde las condiciones son controladas. Recientemente, el uso de líquidos iónicos como disolventes verdes está captando la atención de muchos investigadores por características físico-químicas, tales como su casi nula inflamabilidad, su baja presión de vapor y su amplia ventana de potencial. En este sentido los líquidos iónicos ofrecen una alternativa interesante a los disolventes orgánicos tradicionales utilizados para los electrolitos de baterías de Li-O2. En la presente tesis doctoral, se determinan las propiedades químico-físicas de varios líquidos iónicos para diseñar un electrolito adecuado basado en los mismos. El estudio de estos parámetros, comparados con las prestaciones electroquímicas de la batería, permite encontrar una correlación entre la viscosidad, la solvatación de litio en el electrolito y la capacidad de la batería. Dado que la viscosidad de los líquidos iónicos es demasiado alta para tener una cinética de reacción adecuada en la batería, se estudian mezclas con disolventes orgánicos. Posteriormente, se caracterizan estos electrolitos compuestos de dimetilsulfóxido (DMSO), 1-etil-3-metilimidazolio bis(trifluorometilsulfonil)imida (EMI TFSI) y LiClO4, evaluando la idoneidad de cada formulación. La concentración óptima de EMI TFSI permite reducir el sobrepotencial de 1.43 V a 1.06 V, con una ciclabilidad de 69 ciclos, con una capacidad limitada a 200 mAh g-1. Con estos resultados, se utiliza la difracción de rayos X en tiempo real con un sincrotrón, con el objetivo de analizar la oxidación/reducción de los derivados de óxidos de litio en una batería en funcionamiento. Este estudio demuestra que el litio utilizado como material anódico, reacciona con el líquido iónico, formando LiOH en continuo, independientemente del estado de carga. La comparación entre los diferentes electrolitos, permite incrementar el conocimiento sobre el funcionamiento interno de la batería, para futuras investigaciones sobre el desarrollo de electrolitos para baterías de Li‑O2.
The lithium-oxygen (Li-O2) battery has received much interest in the last few years as global energy demand is growing and availability of fossil energies becomes limited. With its high theoretical energy density approaching that of gasoline, this technology is potentially one of the best solutions for electric vehicles (EV). However, this new technology will remain a research topic for at least the next 20 following years, due to the low cyclability, the limited electrical efficiency, the low rate capability and the difficulty of assembling a safe practical cell working in ambient atmosphere as good as at the laboratory scale under well-controlled conditions. Recently, Room Temperature Ionic Liquids (RTILs) attracted much attention. Indeed, their high thermal stability, non-flammability, low vapor pressure and wide potential window can offer an interesting alternative to the traditional organic solvents for Li-O2 battery electrolyte. In this context, the chemical and physical properties of RTILs are determined in order to design a suitable RTIL-based electrolyte. The study of these parameters, compared to the electrochemical performance of the battery, enables to find a correlation between the viscosity, the lithium solvation of the electrolyte and the capacity of the battery. Given that RTILs viscosity is too high for adequate battery reaction kinetics, a mixture of an organic solvent and a RTIL is then studied. Electrolytes composed by dimethylsulfoxide (DMSO), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI TFSI) and LiClO4 are characterized, evaluating the suitability of such electrolyte. The optimum concentration of EMI TFSI enables to reduce the overpotential from 1.43 V to 1.06 V, with a cyclability of 69 cycles with 200 mAh g-1 of limited capacity. Thereafter, a real-time synchrotron X-ray diffraction technique is applied to analyze the oxidation/reduction of lithium oxide derivatives in an operating battery cell. Four different electrolytes composed of DMSO, a RTIL and LiClO4 are tested. This study proves that the lithium used as anode material is reacting with the RTIL, forming continuously LiOH, independently of the cycling stage. The comparisons between the different electrolytes provide insights for future investigation on the improvement of electrolyte design of this technology.

The present work was initiated to investigate runnerrefractory corrosion by molten steel. The aim was to understandthe mechanism of inclusion formation during ingot casting. Thework is also of interest to other unit processes in steelmaking, where refractory corrosion and erosion are seriousproblems. The oxides investigated in the present work werealumina, silica and mullite, which are the main components inrunner refractory. In addition, industrial refractory materialwas investigated.

Two types of experiments were conducted. The first, "rodexperiments", involved dipping a rod of the oxide into an ironbath containing varying amounts of oxygen. After quenching, therods were examined through SEM/EDS analysis. In the second setsof experiments, the wetting behaviour of molten iron onrefractory oxides was investigated by means of the sessile-dropmethod. The reactions were followed in static as well asdynamic modes through contact angle measurements. Temperatureand oxygen partial pressure were, besides time the parametersthat were investigated in the present study. Oxygen partialpressure was defined by introducing a gas mixture of CO-CO₂-Ar into the furnace.

The experimental studies were preceded by a thermodynamicinvestigation of the refractory systems, in order to get afundamental understanding of the reactions that occurred. Phasestability diagrams for the systems were constructed based onthe data available in literature. The diagrams showed that thereaction between alumina and oxygen containing iron would leadto the formation of hercynite at a critical oxygen level in themetal. With silica, the reaction would lead to the formation offayalite. In the mullite case, the reaction products would behercynite at moderate oxygen levels in the melt and hercynitetogether with fayalite at slightly higher oxygenpotentials.

For all substrates, the contact angles started decreasing asthe surface-active oxygen came into contact with the iron drop.At a critical level of oxygen in the metal, a reaction productstarted forming at the drop/substrate interface. The reactionproducts were identified through SEM/EDS analysis and werefound to be in agreement with thermodynamic predictions. In thecase of SiO₂substrate, there were also deep erosion tracksalong the periphery of the drops, probably due to Marangoniflow.

Alumina-graphite refractory reactions with molten iron werealso investigated through Monte Carlo simulations. The resultsshowed that, with increased alumina content in the refractory,the carbon dissolution into the melt decreased. Further, thewetting behaviour at the interface was found to be an importantfactor to considerably reduce the carbon dissolution fromalumina-graphite refractories.

The experimentation was extended to the commercialrefractories used in the ingot casting process at UddeholmTooling AB, Sweden. The analysis of the plant trial samplesindicates that there is less likelihood of a strong corrosionof the refractories that could lead to a significant populationof inclusions in the end product. The impact of the presentexperimental results on refractory erosion is discussed. Theimportance of the results to clean steel processing anddevelopment of new generation refractories are alsopresented.

Superoxide (O2•-) is the key discharge intermediary driving many non-aqueous metal-oxygen (M-O2) battery chemistries.1–4 Characteristic dioxygen (O2x, where x = -2, -1, 0, +1) stretching vibrations (νO-O) have been well documented spectroscopically in numerous chemically unique systems.5–8 Therefore, the O2•- intermediary can be used as a diagnostic molecule to spectroscopically probe electrolyte effects on O2 reduction-evolution reaction (OR/ER) processes at the electrode/electrolyte interface, providing fundamental insight into non-aqueous M-O2 reaction mechanisms. However, it is first important to understand the vibrational spectra of O2x, though a concise overview of the large amount of empirical data in different chemical environments is lacking. Herein, reviewing the spectroscopy of O2•- and other O2x species gave a good spectroscopic grounding that supported in situ spectroscopic studies of OR/ERs in novel ionic liquid (IL) based electrolytes. Fundamental studies of OR/ERs at the roughened gold (rAu) model electrode interface in a variety of IL electrolytes using in situ surface enhanced Raman spectroscopy (SERS) were performed to study IL cation and anion effects on the chemical nature of O2•-. Analysis of νO-O and IL vibrational peak intensities and Stark shifts provided valuable information about electrolyte interactions. Furthermore, IL:solvent (IL:sol) blended electrolytes were studied to determine the effect of the solvent and salt additives on the properties of the IL electrolyte. Overall, four key parameters were shown to affect the chemical nature of O2•- at the electrode/electrolyte interface, the: (1) IL cation, (2) IL anion, (3) solvent additive Gutmann acceptor/donor number (AN/DN) and (4) the electrode potential. To optimise various physicochemical properties of the electrolyte, A general heuristic methodology for “tailoring”, screening and optimising the electrolyte was developed and a series of novel electrolytes were formulated. These novel electrolytes showed improved O2 reduction reaction (ORR) electrochemistry and exceptional stability in contact with lithium metal (Li-metal) with good physicochemical properties. Our study provides valuable information for the design and tailoring of novel IL based electrolytes for Li and other M-O2 batteries.

Computational Fluid Dynamics (CFD) simulations are presented within this study for super-cooled liquid oxygen atomisation and gasification in a subcritical chamber operating at 1MPa. Relatively low cost simulation techniques have been used and their accuracy evaluated. Gasification efficiency expected from theory is compared with simulation results and physical limitation in addition to modelling limitations are discussed. Impinging jets have been used within the simulations with the intent of atomising the incoming liquid oxygen, followed by injection of hot water vapour perpendicularly, to increase turbulent mixing, residence time and in turn expected gasification efficiency. A computational fluid dynamics heating analysis is also included in order to highlight constraints on the chamber geometry imposed by transient rapid oxidation material limits. 316 stainless steel and 3D printed Inconel 718 were investigated experimentally to identify their transient macroscopic rapid oxidation limits. This information supplements existing published literature for operation at high temperatures for a transient period of time in oxygen rich environments. ANSYS Fluent 2020R1, and its newly included Volume of Fluid to Discrete Particle (VOF-DPM) Model, is used for CFD simulation of LOx atomisation and vaporisation. The CFD simulation technique is discussed in detail in order to allow the reader to gain knowledge into areas where computational power can be saved while still allowing assessment of trends for conducting relatively quick feasibility reviews e.g. for different chamber configurations. The CFD simulation results are compared with published experimental data and its accuracy when extended to this application is discussed. Results indicate that gasification of LOx within a compact chamber may be feasible if sufficient turbulence, resulting in longer residence times is present providing sufficient time for heat and mass transfer from the continuous phase. Simulations indicate that due to the mixing and gasification process the LOx particles within the chamber that have not entered the gaseous phase are smaller than that from pure atomisation and therefore more susceptible to gasification if injected into the main motor combustion chamber. Results hint at the potential benefit of swirl injection of hot gases to increase residence time and in turn the gasification efficiency, therefore, this is recommended for the topic of future research.
Computational Fluid Dynamics (CFD) simuleringar presenteras i denna studie för superkyld flytande syreförstoftning och förgasning i en underkritisk kammare som arbetar vid SI 1 MPa. Relativt billiga simuleringstekniker har använts och deras noggrannhet utvärderats. Förgasningseffektivitet som förväntas från teorin jämförs med simuleringsresultat och fysisk begränsning utöver detta diskuteras modelleringsberäkningarna. Stötstrålar har använts inom simuleringarna med avsikt att finfördela det inkommande flytande syret, följt av injektion av varm vattenånga vinkelrätt, för att öka turbulent blandning, uppehållstid och i sin tur förväntad förgasningseffektivitet. En beräkningsenhetsanalys för uppvärmningsdynamik ingår också för att belysa begränsningar för kammargeometri som införs genom övergående gränser för snabb oxidation. 316 rostfritt stål och 3D-printad Inconel 718 undersöktes experimentellt för att identifiera deras övergående makroskopiska snabba oxidationsgränser. Denna information kompletterar befintlig publicerad litteratur för drift vid höga temperaturer under en kort tid i syrgasrika miljöer. ANSYS Fluent 2020R1, och dess nyligen inkluderade volym av vätska till diskret partikel (VOF-DPM) -modell, används för CFD-simulering av LOxatomisering och förångning. CFD-simuleringstekniken diskuteras i detalj för att göra det möjligt för läsaren att få kunskap om områden där beräkningskraft kan sparas medan man fortfarande tillåter bedömning av trender för att göra relativt snabba genomförbarhetsgranskningar, t.ex. för olika kammarkonfigurationer. CFD-simuleringsresultaten jämförs med publicerade experimentella data och dess noggrannhet när den utvidgas till denna applikation diskuteras. Resultaten indikerar att förgasning av LOx i en kompakt kammare kan vara möjlig vid tillräcklig turbulens, vilket resulterar i längre uppehållstider är närvarande som ger tillräcklig tid för värme och massöverföring från den kontinuerliga fasen. Simuleringar indikerar att på grund av blandnings- och förgasningsprocessen är LOx-partiklarna i kammaren som inte har gått in i gasfasen mindre än den från ren förgasning och därför mer mottagliga för förgasning om de injiceras i huvudmotorns förbränningskammare. Resultat antyder den potentiella fördelen med virvelinjektion av heta gaser för att öka uppehållstiden och i sin tur förgasningseffektivitet, därför rekommenderas detta för ämnet för framtida forskning.

Improved catalytic routes could help to transform the exploitation of the large worldwide natural gas reserves, whose principal component is methane. They transform methane into more valuable chemicals and fuels through carbon dioxide reforming of methane (CDRM), steam reforming of methane (SRM) and partial oxidation of methane (POM). These reactions facilitate the formation of syngas, which is subsequently converted to fuels through the Fischer-Tröpsch synthesis. Mixed Ionic and Electronic Conducting (MIEC) membrane reactors are of interest because they have the potential to produce high purity oxygen from air at lower costs and provide a continuous oxygen supply to reactions or/and industrial processes, and hence avoid sourcing the pure oxygen from air by conventional cryogenic separation technology. In addition, the MIEC ceramic membrane shows the ability to carry out simultaneous oxygen permeation and hydrocarbons oxidation into single compact ceramic membrane reactor at high temperature. This can reduce the capital investment for gas-to-liquid (GTL) plants and for distributing hydrogen. This study compares the oxygen release and oxygen uptake obtained through a LaSrCoFeO hollow fibre membrane (referred as LSCF6428-HFM) under an 0.60.40.20.83-δ Air/He gradient at 850°C and 900°C. The separation and quantification of these two processes permitted the determination of the oxygen incorporated into LSCF6428 structure and the development of a model for apparent overall rate constant using the molar flow of the oxygen at the inlet and outlet in different side of membrane (i.e. shell side and lumen side). The results show that the oxygen flux is enhanced by rising helium flow rates, this is due to an increased driving force for oxygen migration across the membrane and also the air flow determines the oxygen amount that permeates across the membrane. In addition, the oxygen flux improves at higher temperatures, due to its dependence on bulk oxygen diffusion and the oxygen surface reaction rates. The temperature increase improves the mobility of the lattice oxygen vacancies and also the concentration of lattice oxygen vacancies in the perovskite. The impact of surface modification was also studied by coating CoO and 5%Ni-LSCF6428 34 catalysts on the shell side surface of the LSCF6428 hollow fibre membrane for oxygen permeation. It was found that the oxygen flux significantly improved under Air/He gradient for catalyst-coated LSCF6428-HFM. However, under continuous operation conditions over a long time both the unmodified and the modified perovskite LSCF6428-HFM reactors suffered segregation of metal oxides or redistribution of metal composition at the surface membrane, although the bulk LSCF6428 membrane stoichiometry did not change. The apparent overall rate constants for oxygen permeation of the CoO/LSCF6428-HFM and 34 5%Ni/LSCF6428-HFM were enhanced 3-4 fold compared to unmodified LSCF6428-HFM. Comparison of both modified HFM reactors revealed that the apparent overall rate constants for CoO/LSCF6428-HFM were 2 fold higher than those obtained for 5%Ni- 34 LSCF6428/HFM. According to the distribution of total oxygen permeation residence for unmodified and modified LSCF6428-HFM reactor, the oxygen permeation rate is limited by surface exchange on the oxygen lean side or lumen side (R) at 850°C and 900°C and the ex contribution of bulk diffusion on the oxygen permeation rate increased with a rise in the temperature (900°C). The methane oxidation reaction was studied in unmodified and modified 5%Ni- LSCF6428/LSCF6428 hollow fibre membrane in reactors at 850°C. The results suggest that catalytic pathways in methane oxidation depended upon flow operation modes, oxygen concentration, Htreatment and on the type of catalyst. The performances in methane conversion of LSCF6428-HFM and 5%Ni/LSCF6428-HFM modules facilitated the formation of SrCO3 because of the reaction of CO2 with segregated strontium oxide.

A constant volume cylindrical combustion bomb of 100 mm diameter, and of variable length (from 250 mm to 1000 mm) has been built. The effect of charge stratification on the ignitability and subsequent flame propagation of lean (1 > 6) methane-oxygen mixtures has been investigated. The test mixtures were quiescent with initial conditions of 25°C and 1.5 bar absolute. The stratified charge was created by injecting small quantities of a relatively rich (λ = 4.57) premixed methane-oxygen mixture through a modified commercially available spark plug so that an easily ignitable mixture formed in the vicinity of the spark electrodes. The injector used was a commercially available Bosch gasoline injector, suitably modified for gas operation. The injection pressure was 5 bar gauge. The size of the injected puff could be altered by adjusting the duration (from 0-100 ms) for which the injector was opened, and the timing of the spark could be adjusted so that it occurred either before, after or at the end of injection. Results show that the injected premixed puff is an efficient high energy ignition source for very lean methane-oxygen mixtures. For the most reliable ignition performance a delay of 10 ms between the end of injection and the occurrence of the spark has been found to be desirable. This is attributed to the decay of the turbulence produced by the puff. Long injection durations (greater than 20 ms) also improved ignition reliability, due to the larger puff size. The use of charge stratification did not enable combustion to continue below the ideal flammability limit. It did extend the equipment lean limit of flammability from λ = 7.3 (spark alone) to λ = 8.35, and thus demonstrated that it could be useful as a limit extender in non-ideal combustion situations. Results from the longest bomb used (1000 mm) show that the flame dies out after successful ignition has been achieved, and that a distinct lean flammability limit does not exist. Experimental evidence suggests that the flame is generating turbulence as it propagates, and this turbulence causes the flame to become self accelerating. Further, it is thought that the flame generated turbulence is the primary cause of flame extinction (in the form of turbulence induced gas phase quenching) after successful ignition in the 1000 mm bomb.

Recent developments have indicated high oxygen consumption rates of about 35 g-mole/m³-min during oxidative pressure leaching. At such high oxygen consumption rates the mass transfer of dissolved oxygen at the gas-liquid interface may become rate-limiting. The objective of this study was to obtain an understanding of the gas-liquid mass transfer processes that take place in mechanically agitated pressure leaching systems. The classical reaction between sodium sulphite and dissolved oxygen to form sulphate at atmospheric pressure was used to determine the oxygen mass transfer rates in a 200-liter asymmetrical plastic tank, modelled after the shape of the first compartment of the zinc pressure leach. The effect of this asymmetry was compared with the work of Swiniarski who used a cylindrical symmetrical tank of similar volume. A number of process variables such as the impeller type and size, the impeller speed, the impeller immersion depth and the effect of full baffles that affect mixing were investigated. Also, the volumetric power consumption associated with the mass transfer rates were measured. The results indicate that the asymmetrical tank is at least 3.6 times more efficient in mass transfer than the symmetrical tank. There is a critical speed below which the mass transfer parameter, K[formula omitted], is almost zero and above which K[formula omitted] increases almost linearly with impeller tip speed. A simple energy balance model for bubble creation can predict the critical tip speed. It is shown that K[formula omitted] is enhanced at shallow depths, with a corresponding high mass transfer to energy ratio. The relative effectiveness of impeller types and sizes with regard to the use of power for gas-liquid mass transfer was established. Full baffles degrade the mass transfer rate at increased depth of impeller immersion. The results also add substantial support to the findings provided by DeGraaf [5] that: (i) The dimensionless correlations used in liquid mixing systems do not accurately predict dispersion rates by agitators. (ii) The optimum conditions for gas dispersion and the consequent generation of gas-liquid interfacial area are different from fluid mixing. (iii) The classical mixing power equations for impellers markedly overestimate power requirements during impeller gas dispersion.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

Hydrogen can be adopted as a clean alternative to hydrocarbons fuels in the marine sector. Liquid hydrogen (LH2) is an efficient solution to transport and store large amounts of hydrogen, thus it is suitable for the maritime field. Additional safety knowledge is required since this is a new application and emerging risk might arise. Recently, a series of LH2 large-scale release tests was carried out in an outdoor facility as well as in a closed room to simulate spills during a bunkering operation and inside the ship’s tank connection space, respectively. The extremely low boiling point of hydrogen (-253°C) can cause condensation or even solidification of air components, thus enrich with oxygen the flammable mixture. This can represent a safety concern in case of ignition of the flammable mixture of LH2 and solid oxygen, since it was demonstrated that the resulting fire may transition to detonation. In this study, the abovementioned LH2 release experiments were analysed by using an advanced machine learning approach. The aim of this study was to provide critical insights on the oxygen condensation and solidification during an LH2 accidental spill and to evaluate whether the hydrogen concentration within the gas cloud formed due to the LH2 evaporation would reach the lower flammability limit. In particular, a model was developed to predict the possibility and the location of the oxygen phase change and of the hydrogen concentration above the lower flammability limit depending on the operative conditions during the bunkering operation (e.g. LH2 flow rate). The model demonstrated accurate and reliable predicting capabilities. The outcomes of the model can be exploited to select effective safety barriers and adopt the most appropriate safety measures in case of liquid hydrogen leakage.

A magnetic fluid system could potentially replace mechanically moving parts in a satellite as a means of increasing system reliability and mission lifetime, but rather than a standard ferrofluid with magnetic particles, liquid oxygen (LOX) may be a more adequate working fluid. As a pure paramagnetic cryogen, LOX is already heavily used in space, but still requires basic research before being integrated into system development. The objectives of the research conducted were to verify LOX as a magnetic working fluid through experiment and establish a theoretical model to describe its behavior. This dissertation presents the theoretical, experimental, and numerical results of a slug of LOX being pulsed by a 1.1 T solenoid in a quartz tube with an inner diameter of 1.9 mm. The slug oscillated about the solenoid at 6-8 Hz, producing a pressure change of up to 1.2 kPa. System efficiency based on the Mason number was also studied for various geometric setups, and, using a one-dimensional, finite-differenced model in Matlab 2008a, the numerical analyses confirmed the theoretical model. The research provides groundwork for future applied studies with complex designs.

In order to reduce the amount of pollution that is generated by burning fossil fuels alternative energy sources should be explored. Hydrogen has been identified as the most promising replacement for fossil fuels and can be produced by using the Hybrid Sulphur (HyS) cycle. Currently the SO2/O2 separation step in the HyS process has a large amount of knock out drums. The aim of this study was to investigate new technology to separate the SO2 and O2. The technology that was identified and investigated was to separate the SO2 and O2 by absorbing the SO2 into an ionic liquid. In this study the maximum absorption, absorption rate and desorption rate of SO2 from the ionic liquid [BMIm][MeSO4] with purities of 95% and 98% was investigated. These ionic liquid properties were investigated for pure O2 at pressures ranging from 1.5 to 9 bar(a) and for pure SO2 at pressures from 1.5 to 3 bar(a) at ambient temperature. Experiments were also carried out where the composition of the feed-stream to the ionic liquid was varied with compositions of 0, 25, 50, 75 and 100 mol% SO2 with O2 as the balance. For each of these compositions the temperature of the ionic liquid was changed from 30oC to 60oC, in increments of 10oC. The absorption rate of SO2 in the ionic liquid increased when the mole percentage SO2 in the feed stream was increased. When the temperature of the ionic liquid was decreased the maximum amount of SO2 that the ionic liquid absorbed increased dramatically. However, the absorption rate was not influenced by a change in the absorption temperature. The experimental results for the maximum SO2 absorption were modelled with the Langmuir absorption model. The model fitted the data well, with an average standard deviation of 17.07% over all the experiments. In order to determine if the absorption reaction was endothermic or exothermic the Clausius-Clapeyron equation was used to calculate the heat of desorption for the desorption step. The heat of desorption data indicated that the desorption of SO2 from this ionic liquid was an endothermic reaction because the heat of desorption values was positive. Therefore the absorption reaction was exothermic. From the pressure-change experiments the results showed that the mole percentage of O2 gas that was absorbed into the ionic liquid was independent of the pressure of the O2 feed.On the other hand, there was a clear correlation between the mole percentage SO2 that was absorbed into the ionic liquid and the feed pressure of the SO2. When the feed pressure of the SO2 was increased the amount of SO2 absorbed also increased, this trend was explained with Fick’s law. In the study the effect of the ionic liquid purity on the SO2 absorption capacity was investigated. The experimental results for the pressure experiments showed that the 95% and 98% pure ionic liquid absorbed about the same amount of SO2. During the temperature experiments the 95% pure ionic liquid absorbed more SO2 than the 98% pure ionic liquid for all but two of the experiments. However the 95% pure ionic liquid also absorbed small amounts of O2 at 30 and 40oC which indicated that the 95% pure ionic liquid had a lower selectivity than the 98% pure ionic liquid. Therefore, the 95% pure ionic liquid had better SO2 absorption capabilities than the 98% pure ionic liquid. These result showed that the 98% pure ionic liquid did not absorb more SO2 than the 95% pure ionic liquid, but it did, however, show that the 98% pure ionic liquid had a better selectivity towards the SO2. Hence, it can be concluded that even with the O2 that is absorbed it would be economically more advantageous to use the less expensive 95% pure ionic liquid rather than the expensive 98% pure ionic liquid, because the O2 would not influence the performance of the process negatively in such low quantities.
Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013

The oxyfuel cutting method is still widely used nowadays, even though it is not a fully autonomous process. Thisthesis presents a computational model to study ion and electron transport and current-voltage characteristics inside a methane-oxygen flame. By finding the relationship between current-voltage characteristics and critical parameters,such as standoff, fuel oxygen ratio, and flow rate, a control algorithm could be implemented into the system and make it autonomous. Star CCM+ software is used to develop preheat phase computational models by splitting the simulations into the combustion and electrochemical transport parts. Both the laminar and turbulent flows are considered. Several laboratory experiments are used to compare test data with the numerical results generated using this model. The initial and boundary conditions used in the simulation were to the extent possible similar to the experimental conditions in the laboratory experiment. In the combustion part, the general GRI3.0 mechanism plus three additional ionization reactions are applied, and the combustion part results are then used as input into the electrochemical transport part. A particular inspection line inside the domain is created to analyze the results of the electrochemical transport part. Ions, electrons number density, and current density are studied in the interval from -40V to 40V electric potential. The ions are heavier and more challenging to move than electrons. The results show that at both the torch and work surfaces, charged sheaths are formed, which cause three different regions of current-voltage relations to form in a similar manner as observed in the tests.
Master of Science
Oxyfuel cutting is essential to numerous industries, such as shipbuilding, rail, earth moving equipment, commercial building construction, etc. Tuning the process parameters and diagnosing problems with the oxyfuel process still relies on experienced operators. The main obstacles to the automation of the oxyfuel process come from the limitations of the sensing suites currently in use. Since typical sensors are highly unreliable in the harsh environment near the high-temperature flame, an alternate method is proposed to find the co-dependence between the flame's electrical characteristics and critical parameters of the oxyfuel cutting system (standoff, flow rate, F/O ratio, etc.). The relevant electrical characteristics are the electrical potential and distribution of ions and electrons. Two-dimensional models are created to analyze the combustion of methane-oxygen flame and transport of ions and electrons. The models allow the derivation of the current-voltage characteristic between the torch and work surface. Also, the way sheath phenomena of ions and electrons on the surface affect the current-voltage relationship can be analyzed from ions and electrons distribution. The electric field is added to the model by applying a constant voltage to the torch tip surface. To validate the models, a laboratory experiment with a similar geometry arrangement is used as a comparision. The models' results reveal three different regimes in the current-voltage relationship.

Oxygen Transport Membranes (OTMs) can drastically reduce the energy and cost demands of processes that require pure oxygen, as they offer the possibility to combine a separation unit with a chemical reactor. One of the most commercially viable applications of OTMs is the partial oxidation of hydrocarbons for syngas production. A typical OTM configuration is a sequential arrangement of layers, i.e. an inactive support, a fuel oxidation layer, a dense layer and an oxygen reduction layer. However, one of the limitations of the OTM system is the low catalytic activity and stability of the materials currently used for the fuel oxidation layer. Moreover, the traditional deposition techniques that are used for the catalysts preparation are difficult to perform, as the fuel oxidation layer is buried deeply in the structure of the OTM. To simplify the OTM fabrication and improve the catalysts activity and stability, this thesis explores the exsolution of Ni nanoparticles from two different host lattice compositions, as potential materials for the fuel oxidation layer of OTMs. The (La₀.₇₅Sr₀.₂₅)(Cr₀.₅Mn₀.₄₅Ni₀.₅)O₃ (LSCMNi5) perovskite was selected, as the first candidate material for the OTMs. During reduction, the exsolution of Ni nanoparticles from the perovskite lattice took place and enhanced significantly the catalytic activity of the material regarding methane conversion. However, these nanoparticles were oxidised during the first hours of the testing and slowly reincorporated into the perovskite structure, leading to drop in the performance. Thereafter, the (La₀.₇₅Sr₀.₂₅)(Cr₀.₅Mn₀.₄₅Ni₀.₅)O₃ (LSCMNi5) perovskite was selected as an alternative composition. When the oxide lattice was sufficiently reduced, the exsolution of Fe-Ni alloy nanoparticles occurred. The catalytic testing suggested that the Fe-Ni alloy nanoparticles on LSCFNi5 presented lower activity for methane conversion comparing to the Ni nanoparticles on LSCMNi5, but higher stability in oxidising conditions. By increasing the Ni doping on the B-site of LSCF to 15 mol%, the catalytic activity of the material regarding methane conversion was increased and exceeded that of LSCMNi5. A CH₄ conversion of 70% was achieved, which was 20 times higher than that of the initial LSCF perovskite. Therefore, by tailoring the perovskite composition and the exsolution of the Fe-Ni alloy nanoparticles, it was possible to synthesize a material for the fuel oxidation layer of OTMs, which combined the high catalytic activity of Ni and the good redox stability of Fe.

This study introduces an evaluation of the downstream utilization of oxygen produced by the hybrid sulfur process (HYS). Both technical and economic aspects were considered in the production of primarily synthesis gas and hydrogen. Both products could increase the economic potential of the hybrid sulfur process. Based on an assumed 500MWt pebble bed modular nuclear reactor, the volume of hydrogen and oxygen produced by the scaled down HYS was found to be 121 and 959 ton per day respectively. The partial oxidation plant (POX) could produce approximately 1840 ton synthesis gas per day based on the oxygen obtained from the HYS. The capital cost of the POX plant is in the order of $104 million (US dollars, Base year 2008). Compared to the capital cost of the HYS, this seems to be a relatively small additional investment. The production cost varied from a best case scenario $9.21 to a worst case scenario of $19.36 per GJ synthesis gas. The profitability analysis conducted showed favourable results, indicating that under the assumed conditions, and with 20 years of operation, a NPV of $87 mil. and an IRR of 19.5% could be obtained, for the assumed base case. The economic sensitivity analysis conducted, provided insight into the upper and lower limitations of favourable operation. The second product that could be produced was hydrogen. With the addition of a water gas shift and a pressure swing adsorption process to the POX, it was found that an additional 221 ton of hydrogen per day could be produced. The hydrogen could be produced in the best case at $2.34/kg and in the worst case at $3.76/kg. The investment required would be in the order of $50 million. The profitability analysis for the base case analysis predicts an NPV of $206 million and a high IRR of 23.0% under the assumed conditions. On financial grounds it therefore seemed that the hydrogen production process was favourable. The thermal efficiency of the synthesis gas production section was calculated and was in good agreement with that obtained from literature. The hydrogen production section’s thermal efficiency was compared to that of steam methane reforming of natural gas (SMR) and it was found that the efficiencies were comparable but the SMR process was superior. The hydrogen production capacity of the HYS process was increased by a factor of 1.83. This implied that for every 1 kg of hydrogen produced by the HYS an additional 1.83 kg was produced by the proposed process addition. This lowers the cost of hydrogen produced by the HYS from $6.83 to the range of approximately $3.93 - $4.85/kg. In the event of a global hydrogen economy, traditional production methods could very well be supplemented with new and innovative methods. The integration of the wellknown methods incorporated with the new nuclear based methods of hydrogen production and chemical synthesis could facilitate the smooth transition from fossil fuel based to environmentally friendly methods. This study presents one possible integration method of nuclear based hydrogen production and conventional processing methods. This process is technically possible, efficient and economically feasible.
Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

Thesis (MEng)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: The expansion of the global fuels industry has caused an increase in the quantity of hydrocarbons produced as a by-product of refinery gas-to-liquid processes. Conversion of hydrocarbons to higher value products is possible using bioprocesses, which are sustainable and environmentally benign. Due to the deficiency of oxygen in the alkane molecule, the supply of sufficient oxygen through aeration is a major obstacle for the optimization of hydrocarbon bioprocesses. While the oxygen solubility is increased in the presence of hydrocarbons, under certain process conditions, the enhanced solubility is outweighed by an increase in viscosity, causing a depression in overall volumetric oxygen transfer coefficient (KLa). The rate at which oxygen is transferred is defined in terms of a concentration driving force (oxygen solubility) and the overall volumetric oxygen transfer coefficient (KLa). The KLa term comprises an oxygen transfer coefficient (KL) and the gas-liquid interfacial area (a), which are dependent on the uid properties and system hydrodynamics. This behaviour is not well understood for hydrocarbon bioprocesses and in a bubble column reactor (BCR). To provide an understanding of oxygen transfer behaviour, a model hydrocarbon bioprocess was developed using a BCR with a porous sparger. To evaluate the interfacial area, the Sauter mean bubble diameter (D32) was measured using an image analysis algorithm and gas holdup (ϵG) was measured by the change in liquid height in the column. Together the D32 and ϵG were used in the calculation of interfacial area in the column. The KLa was evaluated with incorporation of the probe response lag, allowing more accurate representation of the KLa behaviour. The probe response lag was measured at all experimental conditions to ensure accuracy and reliability of data. The model hydrocarbon bioprocess employed C14-20 alkane-aqueous dispersions (2.5 - 20 vol% hydrocarbon) with suspended solids (0.5 - 6 g/l) at discrete super ficial gas velocity (uG) (1 - 3 cm/s). For systems with inert solids (corn our, dp = 13.36 m), the interfacial area and KLa were measured and the behaviour of KLa was described by separation of the in uences of interfacial area and oxygen transfer coefficient (KL). To further the understanding of oxygen transfer behaviour, non-viable yeast cells (dp = 5.059 m) were used as the dispersed solid phase and interfacial area behaviour was determined. This interfacial area behaviour was compared with the behaviour of systems with inert solids to understand the differences with change in solids type. In systems using inert solids, a linear relationship was found between G and uG. An empirical correlation fo rthe prediction of this behaviour showed an accuracy of 83.34% across the experimental range. The interfacial area showed a similar relationship with uG and the empirical correlation provided an accuracy of 78.8% for prediction across the experimental range. In inert solids dispersions, the KLa increased with uG as the result of an increase in interfacial area as well as increases in KL. An increase in solids loading indicated an initial increase in KLa, due to the in uence of liquid-film penetration on KL, followed by a decrease in KL at solids loading greater than 2.5 g/l, due to diffusion blocking effects. In systems with yeast dispersions, the presence of surfactant molecules in the media inhibited coalescence up to a yeast loading of about 3.5 g/l, and resulted in a decrease in D32. Above this yeast loading, the fine yeast particles increased the apparent viscosity of the dispersion sufficiently to overcome the in uence of surfactant and increase the D32. The behaviour of G in yeast dispersions was similar to that found with inert solids and demonstrated a linear increase with uG. However, in yeast dispersions, the interaction between alkane concentration and yeast loading caused a slight increase in dispersion viscosity and therefore G. An empirical correlation to predict G behaviour with increased uG was developed with an accuracy of 72.55% for the experimental range considered. Comparison of yeast and inert solids dispersions indicated a 37.5% lower G in yeast dispersions compared to inert solids as a result of the apparent viscosity introduced by finer solid particles. This G and D32 data resulted in a linear increase in interfacial area with uG with no significant in uence of alkane concentration and yeast loading. This interfacial area was on average 6.7% lower than interfacial area found in inert solid dispersions as a likely consequence of the apparent viscosity with finer particles. This study provides a fundamental understanding of the parameters which underpin oxygen transfer in a model hydrocarbon bioprocess BCR under discrete hydrodynamic conditions. This fundamental understanding provides a basis for further investigation of hydrocarbon bioprocesses and the prediction of KLa behaviour in these systems.
AFRIKAANSE OPSOMMING: Die uitbreiding van die internasionale brandstofbedryf het 'n toename veroorsaak in die hoeveelheid koolwaterstowwe geproduseer as 'n deur-produk van raffinadery gas-tot-vloeistof prosesse. Omskakeling van koolwaterstowwe na hoër waarde produkte is moontlik met behulp van bioprosesse, wat volhoubaar en omgewingsvriendelik is. As gevolg van die tekort aan suurstof in die alkaan molekule, is die verskaffing van voldoende suurstof deur deurlugting 'n groot uitdaging vir die optimalisering van koolwaterstof bioprosesse. Terwyl die suurstof oplosbaarheid verhoog in die teenwoordigheid van koolwaterstowwe, onder sekere proses voorwaardes is die verhoogde oplosbaarheid oortref deur 'n toename in viskositeit, wat 'n depressive veroorsaak in die algehele volumetriese suurstofoordragkoëffisiënt (KLa). Die suurstof oordrag tempo word gedefinieer in terme van 'n konsentrasie dryfkrag (suurstof oplosbaarheid) en KLa. Die KLa term behels 'n suurstofoordragkoëffisiënt (KL) en die gas-vloeistof oppervlakarea (a), wat afhanklik is van die vloeistof eienskappe en stelsel hidrodinamika. Hierdie gedrag is nie goed verstaan vir koolwaterstof bioprosesse nie, asook in kolom reaktors (BCR). Om 'n begrip van suurstof oordrag gedrag te voorsien, is 'n model koolwaterstof bioproses ontwikkel met 'n BCR met 'n poreuse besproeier. Om die oppervlakarea te evalueer, is die gemiddelde Sauter deursnit (D32) gemeet deur 'n foto-analise algoritme en gas vasvanging ( G) is gemeet deur die verandering in vloeibare hoogte in die kolom. Saam is die D32 en G gebruik in die berekening van die oppervlakarea in die kolom. Die KLa is geëvalueer met insluiting van die meter se reaksie sloering, om n meer akkurate voorstelling van die KLa gedrag te bereken. Die meter reaksie sloering was gemeet op alle eksperimentele toestande om die akkuraatheid en betroubaarheid van data te verseker. Die model koolwaterstof bioproses gebruik n-C14-20 alkaan-water dispersies (2.5 - 20 vol% koolwaterstof) solide partikels (0.5 - 6 g/l) op diskrete oppervlakkige gas snelhede (1 - 3 cm/s). Vir stelsels met inerte solides (koring meel, dp = 13.36 m), is die oppervlakarea en KLa gemeet en die gedrag van KLa beskryf deur skeiding van die invloede van oppervlakarea en KL. Om die begrip van suurstof oordrag se gedrag te bevorder, is nie-lewensvatbare gisselle (dp = 5.059 m) gebruik as die verspreide solide fase en oppervlakarea is bepaal. Hierdie oppervlakarea gedrag is vergelyk met die van stelsels met inerte solides om die verskille met verandering in solide tipes te verstaan. In stelsels met inerte solides, is 'n line^ere verwantskap gevind tussen G en uG. 'n Empiriese korrelasie vir die voorspelling van hierdie gedrag is opgestel met 'n akkuraatheid van 83.34% in die eksperimentele reeks. Die oppervlakarea het 'n soortgelyke verhouding met uG en die empiriese korrelasie verskaf 'n akkuraatheid van 78,8% vir die voorspelling van oppervlakarea oor die eksperimentele reeks. In inerte solide dispersies, het die KLa toegeneem met uG as die gevolg van 'n toename in grens oppervlak asook stygings in KL. 'n Toename in solides belading het n aanvanklike styging in KLa aangedui, as gevolg van die invloed van die vloeistof-film penetrasie op KL, gevolg deur 'n afname in KL op vastestowwe ladings groter as 2.5 g/l, te danke aan diffusie blokkeer effekte. In stelsels met gis dispersies, het die teenwoordigheid van benattings molekules in die media samesmelting geïnhibeer tot 'n gis lading van ongeveer 3.5 g/l, en het gelei tot 'n afname in D32. Bo hierdie gis lading, het die fyn gis partikels die skynbare viskositeit van die verspreiding verhoog genoegsaam om die invloed van benattings molekules te oorkom en die D32 te verhoog. Die gedrag van G in gis dispersies was soortgelyk aan die van inerte solides en dui op 'n lineêre toename met uG. Maar in gis dispersies, het die interaksie tussen alkaan konsentrasie en gis lading 'n effense toename veroorsaak in die verstrooiing viskositeit en dus in G. 'n Empiriese korrelasie is ontwikkel om G gedrag te voorspel en het 'n akkuraatheid van 72,55% vir die eksperimentele verskeidenheid beskou. Vergelyking van gis en inerte patrikel dispersies wys 'n 37.5% laer G in gis dispersies in vergelyking met inerte vaste stowwe as 'n gevolg van die skynbare viskositeit bekendgestel deur fyner vastestowwe partikels. Hierdie G en D32 data het gelei tot 'n linere toename in grens oppervlak met uG met geen beduidende invloed van alkaan konsentrasie en gis lading nie. Die oppervlakarea was gemiddeld 6.7% laer as oppervlakarea gevind in inerte partikel dispersies as 'n waarskynlike gevolg van die skynbare viskositeit met fyner partikels. Hierdie studie bied 'n fundamentele begrip van die veranderlikes wat die suurstof oordrag definieer in 'n model koolwaterstof bioproses BCR onder diskrete hidrodinamiese voorwaardes. Hierdie fundamentele begrip bied n basis vir verdere ondersoek van koolwaterstof bioprosesse en en die voorspelling van KLa gedrag in hierdie stelsels.

This study presents the first attempt to combine the fields of ultraviolet (UV) photobiology, plant cell wall biochemistry, aerobic methane production and reactive oxygen species (ROS) mechanisms to investigate the effect of UV radiation on vegetation foliage. Following reports of a 17% increase in decomposition rates in oak (Quercus robur) due to increased UV, which were later ascribed to changes in cell wall carbohydrate extractability, this study investigated the effects of decreased UV levels on ash (Fraxinus excelsior), a fast-growing deciduous tree species. A field experiment was set up in Surrey, UK, with ash seedlings growing under polytunnels made of plastics chosen for the selective transmission of either all UV wavelengths, UV-A only, or no UV. In a subsequent field decomposition experiment on end-of-season leaves, a significant increase of 10% in decomposition rate was found after one year due to removal of UV-B. However, no significant changes in cell wall composition were found, and a sequential extraction of carbohydrate with different extractants suggested no effects of the UV treatments on cell wall structure. Meanwhile, the first observations of aerobic production of methane from vegetation were reported. Pectin, a key cell wall polysaccharide, was identified as a putative source of methane, but no mechanism was suggested for this production. This study therefore tested the effect of UV irradiation on methane emissions from pectin. A linear response of methane emissions against UV irradiation was found. UV-irradiation of de-esterified pectin produced no methane, demonstrating esters (probably methyl esters) to be the source of the observed methane. Addition of ROS-scavengers significantly decreased emissions from pectin, while addition of ROS without UV produced large quantities of methane. Therefore, this study proposes that UV light is generating ROS which are then attacking methyl esters to create methane. The study also demonstrates that this mechanism has the potential to generate several types of methyl halides. These findings may have implications for the global methane budget. In an attempt to demonstrate ROS generation in vivo by UV irradiation, radio-labelling techniques were developed to detect the presence of oxo groups, a product of carbohydrate attack by ROS. Using NaB3H4, the polysaccharides of ash leaflets from the field experiment were radio-labelled, but did not show any significant decrease in oxo groups due to UV treatments. However, UV-irradiation of lettuce leaves showed a significant increase in radio-labelling, suggesting increased UV irradiation caused an increase in the production of ROS. The study shows that the use of this radio-labelling technique has the potential to detect changes in ROS production due to changes in UV levels and could be used to demonstrate a link between ROS levels and methane emissions.

When conducting a chemistry experiment, reactions are often completed in a liquid solvent. This thesis investigates the outcome of using liquid metals as a new reaction environment. Galinstan is an alloy comprised of 68.5% gallium, 21.5% indium and 10% tin that can remain a liquid at room temperature and is extremely useful due to its flexibility and conductivity. This thesis shows that liquid metals can be used to synthesise new 2D materials that catalyse oxygen production during water splitting, form new materials that can catalyse ammonia production from abundant nitrate sources and facilitate the degradation of organic dye pollutants.