L’atmosphère est un milieu oxydant au sein duquel les réactions en phase homogène, initiées par des espèces radicalaires (OH notamment), sont prépondérantes. Le chlore atomique peut être l'oxydant le plus important de la couche limite marine à l'aube lorsque la concentration en radicaux OH est faible. L’atmosphère est aussi chargée en particules d’aérosol où des collisions réactives peuvent se produire à l’interface gaz/solide ou gaz/liquide. Il est donc important de prendre en compte les mécanismes élémentaires de chimie hétérogène pour une meilleure description des processus physico-chimiques atmosphériques. L’objectif de cette thèse est d’étudier la réactivité entre le chlore atomique et des particules représentatives des sels marins (NaCl et sels marins synthétiques). Des mesures ont également été effectuées avec du sulfate et du nitrate d’ammonium, composés majoritaires dans les particules secondaires issues de la condensation d’espèces gazeuses d’origine anthropique. Le principe consiste à mettre une phase gazeuse en contact avec une phase solide au sein d’un réacteur à écoulement à parois recouvertes couplé à un spectromètre de masse. Nous cherchons à mesurer la vitesse de réaction et à déterminer le coefficient de capture de ces réactions ainsi que les produits formés. Nous avons fait varier un certain nombre de paramètres : concentration des réactifs, température, présence ou non de vapeurs d’eau. L’analyse de la surface solide après réaction a été réalisée par des techniques de microscopie avancée (XPS, TOF SIMS). / The atmosphere is an oxidizing environment in which the homogeneous phase reactions initiated by radical species (OH in particular) are dominant. Atomic chlorine could be the most important oxidant in the marine boundary layer at dawn when the concentration of OH radicals is low. The atmosphere is loaded with aerosol particles, on the surface of which reactive collisions can occur at the gas / solid or gas / liquid interfaces. It is therefore important to take into account the basic mechanisms of heterogeneous chemistry for a better description of atmospheric chemical and physical processes. The objective of this thesis is to study the reactivity between chlorine atoms and particles representative of sea salts (NaCl and synthetic sea salts). Measurements have also been carried out with ammonium sulfate and nitrate particles, the major components in the secondary particles formed by the condensation of gaseous species of anthropogenic origin. The principle is to put a gas phase in contact with a solid surface in a coated wall flow tube reactor and microwave discharge coupled to a quadrupole mass spectrometer. The contact time between the two phases can be varied inside the reactor. In this work, we have measured the reaction rate and determined the uptake coefficient of these reactions and the possible products formed. Several parameters have been studied: the concentration, the temperature and the presence or absence of surface adsorbed water. The solid surface was analyzed after reaction by advanced microscopy techniques (XPS, TOF SIMS) during this study.

Des études cinétiques et des analyses de surface ont été effectuées sur la réaction multiphasique entre le gaz NO2 et des cristaux de NaCl en présence de molécules tensio-actives sous air humide. Ces études de laboratoire contribuent à la validation de processus de chimie atmosphérique suggérés par des campagnes de mesure sur des aérosols d’origine marine. Les vents provoquant des vagues à la surface des océans propulsent de nombreuses gouttelettes d’eau de mer dans la troposphère où elles se déshydratent partiellement et forment l’aérosol marin, constitué de particules de taille micrométrique comportant du NaCl et de nombreux composés mineurs dont des acides gras (stéarique, oléique). Les concentrations en particules peuvent dépasser 20 µg/m3 dans l’air des zones côtières. Des quantités énormes d’oxydes d’azote (NO, NO2) sont émises actuellement par les transports et le chauffage et leur concentrations peuvent dépasser 100 µg/m3 dans les zones fortement antropisées. Le passage de masses d’air d’origine marine dans des zones fortement urbanisées a des impacts négatifs sur la qualité des eaux continentales par des pluies chargées en nitrates et sur la qualité de l’air par des dégagements de gaz chlorés. La cinétique de la réaction montre que la capture de NO2 par NaCl est favorisée a des fortes humidités. Par contre un revêtement d’acides gras réduit peu la production de NaNO3 et l’émission de NOCl. Les études de surfaces par microimagerie Raman polarisée et microscopie à force atomique mettent en évidence des processus de précipitation et de migration de surface dans la production de nanocristaux de NaNO3 et le faible rôle protecteur des molécules tensio-actives. / In this laboratory work we studied an important atmospheric process typical of polluted costal regions: the heterogeneous reaction of a gaseous pollutant of mainly anthropogenic origin, NO2, on NaCl(100), taken as a surrogate for marine aerosol. Evidence of the presence of a native organic coating on field-collected marine aerosol particles inspired us to investigate the effect of insoluble fatty acids on the heterogeneous removal reaction of NOx in the marine boundary layer. The originality of this work consists in coupling reactivity studies with high spatial resolution surface analysis. The surface is followed, before and after reaction, via Raman micro-spectrometry and AFM techniques. Significant modifications in the morphology and orientation of the formed NaNO3 crystals on the surface are found as a function of humidity during the reaction. A thin organic coating on the salt surface is prepared and characterized. The reactivity of the coated/uncoated salt is measured in a static reactor where the gaseous phase composition can be monitored by FTIR spectrometry in different humidities (RH=0-80%). From NO2 and ClNO kinetics we can independently estimate both the uptake and the reaction probability coefficients. The presence of a palmitic or oleic acid coating slightly hinders the reactivity, especially in some humidities. By coupling all experimental information to a simple reactivity model which fits the experimental data well, we can conclude that the NO2/NaCl reaction directly releases a precursor of active chlorine atoms (ClNO) into the atmosphere, even at high humidities.

This diploma thesis is focused on combination of experimental study and computer modelling of diffusion processes in gel phases. The aim of experimental part of the diploma thesis was to test and optimize the setting of the diffusion coefficient in gel medium by using the method of horizontal diffusion cells, commonly used for study of diffusion processes through membranes. Specific description of experiments was to determinate the impact of presence of reactive component in inert hydro-gel carrier on final value of diffusion coefficient of low-molecular model diffusion probe. The defined dependencies were subsequently combined with computer simulation of diffusion process in a properly designed model in order to determinate the experimentally unavailable system parameters. The stated combination of both approaches was proved to be an appropriate instrument for studying of hydro-gels with a wide potential especially in the field of preparation of hydro-gel carriers with controlled release of active substances.

Calcium carbonate minerals (CaCO3) are important for our understanding of past marine conditions as well as tools for constructing paleoclimate. However, very little experimental work has been done to determine the influence of oxygen depletion on the geochemistry of CaCO3. To determine how oxygen depletion affects elemental incorporation and partitioning, aragonite was grown inorganically in artificial seawater at pressures of 1 atm and 5 bars (0.1%CH4-N2 mixture). Solution of Na2CO3 was used to induce aragonite precipitation. N2 was bubbled through solution in order to minimize oxygen content and iron powder was used to trap remaining O2. Experimental products (aragonite and fluid) were analyzed with ICP-MS, and isotope ratio mass spectrometer. Results suggest that Eh affects incorporation of Mn, S, Cu, and V into aragonite. No methane oxidation was observed.

Previous work has systematically and numerically demonstrated feasibility and performance benefits of the tension-element concept in golf club heads; however, higher fidelity models needed to be created and validated for this concept. There is a need for more accurate models for this concept to further investigate its performance benefits. Performance is measured in terms of impact efficiency of the ball and head and is referred to as coefficient of restitution (COR). COR is affected by the dynamic effective face stiffness and mass properties of the club. This thesis creates and validates high-fidelity, non-linear, dynamic finite element models for the tension-element golf club concept. These models predicted COR with less than one percent error when compared to dynamic experimentation results.

Numerical approaches have been conducted to investigate the effect of droplet deformation and internal circulation on droplet dynamics. Although droplet drag is a classical area of study, there are still theoretical gaps in understanding the motion of large droplets. In applications such as spray combustion, droplets of various sizes are generated and move with the flow. Large droplets tend to deform in the flow, and they have complex interactions with the flow because of this deformation. To better model spray, the physical understanding of droplets needs to be improved. Under spray conditions, droplets are subjected to a high-temperature-and-pressure environment, and the coupling between liquid and gas is enhanced. Therefore the deformation and internal circulation will affect the droplet drag coefficient more significantly than they would under atmospheric conditions. To study the mechanism of how droplet shape and internal circulation influence droplet dynamics, we have used direct numerical simulation (DNS) to simulate a droplet falling at its terminal velocity in high-pressure air. An in-house code developed for interface-capturing DNS of multiphase flows is employed for the simulation. The drag coefficient is calculated, and the results are consistent with the existing literature for slightly deformed droplets. The results show that the drag coefficient is directly related to the droplet deformation and droplet internal circulation. This paper also develops an analytical theory to account for the effect of the Weber number and fluid properties on droplet deformation. / Master of Science / This study investigates how larger droplets interact with airflow in spray conditions. Classical droplet drag models are not accurate under extreme conditions due to the neglect the droplet deformation and droplet internal circulation. To better understand droplet dynamics and to improve the accuracy of droplet models, direct numerical simulations were conducted. In our simulations, a non-evaporating falling droplet in high-pressure air was modeled. Results show a direct link between drag coefficient and droplet shape and internal flow. We also derived an analytical scaling law to explore the parameters related to droplet deformation. This research enhances our understanding of droplet dynamics in spray conditions.

No description available.

For concrete, a sustainable design requires considering both mechanical properties and durability. One of the major deterioration modes of reinforced concrete structures is the entry of chloride ions and corrosion of embedded metals, which is mainly controlled by diffusion as the mass transport mechanism. Therefore, it is pivotal to quantify the chloride diffusion coefficient of concrete, which controls the rate of chloride ingress. Several testing methods exist for quantifying diffusivity of concrete. However, the current test methods are time consuming and demanding. The primary goal of this study is to develop models for quantifying the chloride diffusion coefficient of concrete. As such, initially, the most recent and prevailing analytical models proposed in the scientific literature were critically reviewed and the parameters controlling the chloride diffusion coefficient of concrete were identified. Then, the cement degree of hydration of concrete – as a key parameter which controls the properties of concrete – its measurement methods, and the uncertainties associated with different quantification methods were scrutinized. Finally, three models were developed to quantify the chloride diffusivity of concrete. The first model quantifies the chloride diffusivity of concrete in terms of its electrical resistivity based on the modified Nernst-Einstein equation. The model accounts for the ionic concentration of the pore solution through the alkalis released due to hydration of cementing materials and the alkali uptake of hydration products, the pore solution conductivity, and the interaction between the ions in the pore solution. The second model, which provides a phenomenological relationship for chloride diffusivity of concrete in terms of its compressive strength, accounts for the tortuosity factor of the mixture, aggregate volume fraction, porosity, compressive strength, and cementing materials content and composition. The third model is developed based on the mixture constituents and the cement degree of hydration of concrete. The model accounts for tortuosity factor through the volume fraction of aggregate particles, the interfacial transition zone thickness and diffusivity, cementing materials type and chemical composition, bulk cement paste transport properties through water to cementing materials ratio, cement degree of hydration, supplementary cementing materials type and replacement levels. In order to assess the accuracy and precision of the proposed models, an experimental program was developed and conducted. The following variables were considered for the experimental program: the volume fraction of coarse aggregate, water to cementing materials ratio, total cementing materials content, and supplementary cementing materials type and replacement levels. The experimental results along with the reported data in the scientific literature were used to validate the proposed models. The results revealed the capability of the models to capture the documented observations, as well as the high accuracy and precision of the proposed models for quantifying the chloride diffusivity of concrete in a wide range of concrete mixtures composition and age. The developed models provide designers, practicing engineers and standard/code developers with accurate, precise and consistent models for quantifying the chloride diffusion coefficient of concrete as a direct measure of its durability. / Thesis / Doctor of Philosophy (PhD)

Many gas turbine engines operate in harsh environments where the engine can ingest solid particles. Particles can accelerate the deterioration of an engine and reduce the engine’s service life. Understanding particle interactions with the materials used in gas turbines, at representative engine conditions, can improve the design and development of turbomachinery operating in particle laden environments. Coefficient of Restitution (COR) is a measure of the particle/wall interactions and is used to study erosion and deposition. This study presents data taken using the Virginia Tech Aerothermal Rig. Arizona Road Dust (ARD) of 20-40 μm is injected into a flow field to measure the effects of temperature and velocity on particle rebound from a polished high temperature material coupon. The high temperature coupon was tested at different temperatures of ambient (300K), 873K, 1073K, 1173 K, 1223 K, 1273 K, and 1323 K while the velocity of the flow field was held constant at 28 m/s or 70 m/s. The impingement angle of the coupon was varied from 30° to 80° for each temperature tested. The results show an increase in deposition as the temperature approaches the melting temperature of sand. The results have also been compared to previously published literature. / Master of Science

Most real-world networks exhibit a high clustering coefficient— the probability that two neighbors of a node are also neighbors of each other. We propose four algorithms CONF-1, CONF-2, THROW-1, and THROW-2 which are based on the configuration model and that take triangle degree sequence (representing the number of triangles/corners at a node) and single-edge degree sequence (representing the number of single-edges/stubs at a node) as input and generate a random graph with a tunable clustering coefficient. We analyze them theoretically and empirically for the case of a regular graph. CONF-1 and CONF-2 generate a random graph with the degree sequence and the clustering coefficient anticipated from the input triangle and single-edge degree sequences. At each time step, CONF-1 chooses each node for creating triangles or single edges with the same probability, while CONF-2 chooses a node for creating triangles or single edge with a probability proportional to their number of unconnected corners or unconnected stubs, respectively. Experimental results match quite well with the anticipated clustering coefficient except for highly dense graphs, in which case the experimental clustering coefficient is higher than the anticipated value. THROW-2 chooses three distinct nodes for creating triangles and two distinct nodes for creating single edges, while they need not be distinct for THROW-1. For THROW-1 and THROW-2, the degree sequence and the clustering coefficient of the generated graph varies from the input. However, the expected degree distribution, and the clustering coefficient of the generated graph can also be predicted using analytical results. Experiments show that, for THROW-1 and THROW-2, the results match quite well with the analytical results. Typically, only information about degree sequence or degree distribution is available. We also propose an algorithm DEG that takes degree sequence and clustering coefficient as input and generates a graph with the same properties. Experiments show results for DEG that are quite similar to those for CONF-1 and CONF-2. / Master of Science