The first step on the way to understanding the complicated dynamics of spray is to study the behavior of isolated droplets. In many industrial and natural processes such as turbulent combustion, agricultural sprays, spray cooler, falling raindrops and cloud evolution the droplet is subjected to a chaotic unsteady external flow field. The interaction between the liquid and gaseous phases results in very intricate droplet dynamics like capillary instabilities, atomization, droplet collision and coalescence and vaporization, to name a few. In this dissertation, the focus is on shape oscillations, atomization and vaporization dynamics of pendant and sessile droplets. A droplet residing on a substrate which vibrates vertically at ultrasonic frequency will exhibit different modes of shape oscillation. The competition between capillary forces and inertia forces is basically responsible for these oscillations. However, when an acoustic force field is introduced asymmetrically around the droplet, we discover with the help of ultra high-speed imaging, a new droplet spreading phase. This new method of droplet manipulation could nd application in micro fluidics and lab-on-a-chip systems. By lading the droplet with nanoparticles, the spreading rate can be easily controlled. The spreading phase is followed by an atomization phase where surface ligaments grow to disintegrate into daughter droplets; the intensity of atomization is found to decrease with increase in fluid viscosity. The ability to control atomization characteristics of droplets by lading them with nanoparticles is a powerful technique that may be implemented in spray coolers and combustors to control the spray characteristics or combustion efficiency. Both the spreading and ligament dynamics have been theoretically simulated and the physics behind the observed trends is explained. The growth rate of the ligaments is found to be governed by Weber number modified to include the acoustic pressure level of the standing wave. The frequency of ligament breakup is found to decrease with fluid viscosity and this observation is adequately supported by a theory developed based on the evolution crater on the droplet surface. Turning now to the pendant droplets, by decomposing the droplet shape into Legendre modes, the shape oscillations exhibited by a droplet hanging from the junction of cross-wire placed at the center of an air jet is studied. Both high-speed imaging and hot-wire anemometry are employed. The driving force of oscillation of droplets subjected to the air jet is proved to be the inherent pressure fluctuations in the jet. The effect of surface tension, viscosity and Reynolds number on the shape oscillation level has been examined. The first experimental evidence of viscous attenuation of lower frequencies in a particular mode in glycerol/water mixture is reported. A theoretical model was developed to simulate the droplet shape oscillations induced by different ambient flow fields like pulsatile flow, vortical flow and flow with broadband energy spectrum. The time of interaction of the droplet with an eddy in the flow is found to be very crucial in determining the amplitude of oscillation of the droplet. The shorter the interaction time, the higher are the chances of the droplet oscillation being pushed into resonance. Finally, the heat transfer and droplet regression dynamics of pendant droplets in a hot air stream of various chemical compositions (like conventional fuels, alternative fuels and nanosuspensions) have been experimentally analyzed using high speed imaging. The droplet is deployed at the junction of cross-wire at the centre of a vertical air jet. A hybrid timescale has been proposed which incorporates the effects of latent heat of vaporization, saturation vapor pressure and thermal diffusivity. This timescale in essence encapsulates the different parameters that influence the droplet vaporization rate. The analysis further permitted the evaluation of the effect of various parameters such as surrounding temperature, Reynolds number, far-field vapor presence, impurity content and agglomeration dynamics (nanosuspensions) in the droplet.

Lorsqu'une goutte impacte une surface chaude dont la température est bien plus élevée que la température d'ébullition du liquide, une couche de vapeur se forme et elle lévite au dessus de la surface: ce phénomène est appelé "Effet Leidenfrost". Dans cette étude, un nouvel algorithme permettant de modéliser les régimes d'évaporation et d'ébullition à l'interface liquide/gaz a été développé. En effet, dans certaines situations où les conditions thermodynamiques à l'interface sont très hétérogènes, la distinction entre les régimes d'évaporation et d'ébullition n'est pas toujours possible. C'est le cas de l'impact d'une goutte sur une surface chaude en régime de Leidenfrost. Dans ce cas, l'ébullition se produit dans le film de vapeur saturée piégé entre la goutte et la paroi, tandis que sur le dessus la goutte s'évapore au contact de l'air ambiant. De ce fait, l'ébullition et l'évaporation peuvent survenir simultanément dans différentes régions de la goutte. Les méthodes numériques classiques ne sont pas en mesure de prendre en compte ce régime transitoire. Par conséquent, un nouvel algorithme a été développé pour y parvenir. Cet algorithme a été utilisé pour simuler le rebond d'une goutte axisymétrique en régime de Leidenfrost. Les résultats sont ensuite comparés à des données expérimentales. / When a liquid droplet impacts on a heated surface at a temperature much higher than the liquid's boiling point, it floats above the surface due to a vapor layer formation: this phenomenon is called the Leidenfrost effect. In this study, we propose a novel numerical method which allows dealing both with evaporation and boiling regimes at the interface between a liquid and a gas. Indeed, in some specific situations involving very heterogeneous thermodynamic conditions at the interface, the distinction between boiling and evaporation is not always possible. It can occur when a droplet impacts a hot surface in the Leidenfrost regime. In this case, boiling occurs in the film of saturated vapor which is entrapped between the bottom of the drop and the plate, whereas the top of the liquid droplet evaporates in the contact of the ambient air. Thus, boiling and evaporation occur simultaneously on different regions of the droplet when it impacts a heated surface. Usual numerical methods are not able to perform computations in this transient regimes, therefore, we propose in this study a new numerical method to achieve this challenging task. This algorithm is used to simulate an axisymmetric impact of a liquid droplet in the Leidenfrost regime for different Weber numbers and the results of this simulations are compared with experimental data.

With the slow but ineluctable depletion of fossil fuels, several avenues are currently being explored in order to define the strategic boundaries for a clean and sustainable energetic future, while accounting for the specificities of each sectors involved. In regard to transport applications, alternative fuels may represent a promising solution, at least at short or middle term, such as the International Energy Agency foresees that their share could account for 9% of the road transport fuel needs by 2030 and 27 % by 2050, with the potential resources to reach 48% beyond. If they have already been included in significant blending proportions with conventional fossil fuel in most of the occidental countries, their introduction also coincides with a long-time established program of continuously more drastic standards for engine emissions of NOX and PM, now even further demanding by the seek for combustion efficiency aiming at reducing CO2 emissions. While several works discuss the alternative fuels effect on exhaust emissions when used directly in production Diesel engines, results and analysis are sometimes contradictory, depending sometimes on the conditions in which they were obtained, and the causes of these results remain unclear. Therefore, in order to better understand their effect on the combustion processes, and thus extract the maximum benefits from these fuels in the optimization of engine design and calibration, a detailed comprehension of their spray and combustion characteristics is essential. The approach of this study is mostly experimental and based on an incremental methodology of tests aiming at isolating injection and combustion processes with the objective to identify and quantify the role of both fuel physical and chemical properties at some key stages of the Diesel combustion process. After obtaining a detailed characterization of their properties, five fuels have been injected in an optical engine enabling a sharp control of the thermodynamic e / Nerva, J. (2013). An Assessment of fuel physical and chemical properties in the combustion of a Diesel spray [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/29767 / Palancia

Detailed investigation of the vaporization of an isolated of ethanol and 1-propanol droplet was carried out in this experimental study. The experimental set-up consists of a heated chamber with a cross quartz fibers configuration as droplet support. An alcohol droplet is located at the intersection of the cross quartz fibre with a controlled initial diameter (300-600µm). Ambient temperature is varied from 298 to 973K at atmospheric pressure. The quasi-steady theory has been used to compare and to explain all experimental results. The real impact of the water concentration on the vaporization rate of an ethanol droplet is also examined, where two 'quasi-steady' periods are observed on the d2-curves, clearly showing that the vaporization of an ethanol droplet is accompanied by the simultaneous condensation of water vapour on the droplet surface and thus the temporal evolution of the droplet squared diameter exhibits an unsteady behavior. The histories of the instantaneous vaporization rates of both 1-propanol and ethanol droplets confirm this phenomenon. The autoignition experimental study of ethanol, 1-propanol and blends of ethanol and water have been carried out in a rapid compression machine at a compressed pressure of 30bar over a temperature range of 750-860K for stoichiometric mixture of fuel and air. The ignition delay times recorded show a significant decrease with increasing temperature. 1-propanol is more reactive than ethanol, which results in shorter ignition delay times. However, water addition to ethanol increases the reactivity of the mixture and results in a shorter ignition delay times than 1-propanol

Droplets as precursor are extensively applied in diverse fields of science and engineering. Various contributions are provided previously towards analysis of single phase and multi-phase droplets of single and multiple components. This thesis describes modelling of multi-phase (nano fluid) droplet vaporization. The evaporation of liquid phase along with migration of dispersed particles in two-dimensional plane within droplet is detailed using the governing transport equations along with the appropriate boundary and interface conditions. The evaporation model is incorporated with aggregate kinetics to study agglomeration among nano silica particles in base water. Agglomeration model based on population balance approach is used to track down the aggregation kinetics of nano particles in the droplet. With the simulated model it is able to predict different types of final structure of the aggregates formed as observed in experimental results available in literature. High spatial resolution in terms of agglomeration dynamics is achieved using current model. Comparison based study of aggregation dynamics is done by heating droplet in convective environment as well as with radiations and using different combination of heating and physical parameters. The effect of internal flow field is also analysed with comparative study using levitation and without levitation individually. For levitation, droplet is stabilized in an acoustic standing wave. It is also attempted to study the transformation of cerium nitrate to ceria in droplets when heated under different environmental conditions. Reaction kinetics based on modified rate equation is modelled along with vaporization in aqueous cerium nitrate droplet. The thermo physical changes within the droplet along with dissociation reaction is analysed under different modes of heating. The chemical conversion of cerium nitrate to ceria during the process is predicted using Kramers' reaction velocity equation in a modified form. The model is able to explain the kinetics behind formation of ceria within droplet at low temperatures. Transformation of chemical species is observed to be influenced by temperature and configuration of the system. Reaction based model along with CFD (computational fluid dynamics) simulation within the droplet is able to determine the rate of chemical dissociation of species and predict formation of ceria within the droplet. The prediction shows good agreement with experimental data which are obtained from literature.

In this dissertation, different approaches have been employed to address the quest of understanding the formation and growth mechanisms of carbon-containing molecular ions with relevance to astrochemistry. Ion mobility mass spectrometry and DFT computations were used to investigate how a second nitrogen in the pyrimidine ring will affect the formation of a covalent bond between the benzene radical cation and the neutral pyrimidine molecule, after it was shown that a stable covalent adduct can be formed between benzene radical cation and the neutral pyridine. Evidence for the formation of a more stable covalent adduct between the benzene radical cation and the pyrimidine is reported here. The effect of substituents on substituted-benzene cations on their solvation by an HCN solvent was also investigated using ion mobility mass spectrometry and DFT computations were also investigated. We looked at the effect of the presence of electron-withdrawing substituents in fluorobenzene, 1,4 di- fluorobenzene, and benzonitrile on their solvation by up to four HCN ligands, and compared it to previous work done to determine the solvation chemistry of benzene and phenylacetylene by HCN. We report here the observed increase in the binding of the HCN molecule to the aromatic ring as the electronegativity of the substituent increased. We also show in this dissertation, DFT calculations that reveal the formation of both hydrogen-bonded and electrostatic isomers, of similar energies for each addition to the ions respectively. The catalytic activity of the 1st and 2nd row TM ions towards the polymerization of acetylene done using the reflectron time of flight mass spectrometry and DFT calculations is also reported in this dissertation. We explain the variation in the observed trend in C-H/C-C activity of these ions. We also report the formation of carbide complexes by Zr+, Nb+, and Mo+, with the acetylene ligands, and show the thermodynamic considerations that influence the formation of these dehydrogenated ion-ligand complexes. Finally, we show in this dissertation, a novel ionization technique that we employed to generate ions that could be relevant to the interstellar and circumstellar media using the reflectron time of flight mass spectrometry.

The theoretical part of my thesis at first introduces the most common benign neoplasm in men over fifty, a non cancerous prostate gland enlargement called the benign prostate hyperplasia (BPH). The main focus of this section will be on BPH's anatomy, etiology, symptomatology, complications, diagnosis and therapy. I will also describe four cost analyses used in health services: CMA, CEA, CUA and CBA. In the practical section of my thesis I will analyze the therapy effectiveness of transurethral resection of the prostate and photoselective vaporization of the prostate with the use of cost-effectiveness analysis.

Chromium is an important alloying element in stainless steel but also environmentally harmful element. A number of mineralogical phases present in the slag matrix can contain chromium and lead to chromium leaching. Chromium in slag if not stabilized, could oxidize to the cancerogenic hexavalent state, and leach out if exposed to acidic and oxygen rich environment. Other environmental concerns are slag dusting and chromium escape to the atmosphere. Despite the fact that there is a certain risk of Cr-emission from slags at operating conditions, still very little is known regarding the emission of the oxides of chromium during the slag tapping. Spinel phase is known to be important for controlling the leaching properties of chromium from the slag. The objective of the present study was to get an understanding of the phase relationships and chromium partition in the chromium-containing industrial slags and synthetic slags with a view to control the chromium stabilization in spinel phase. The impact of slag basicity, heat treatment, oxygen partial pressure and Al2O3 addition, on the phase relationships and chromium partition has been determined. The experimental results were compared with the phase equilibrium calculations. It was found that the oxygen partial pressure in the gas phase had a strong impact on chromium partition. The experimental results show that the impact of the slag basicity on chromium partition at lower oxygen partial pressures was negligible in contrast to that in air. The amount of spinel phase was found to increase with increased Al2O3 content. Slow cooling of slag and soaking at low oxygen partial pressure would improve the spinel phase precipitation. This treatment will also lead to less Cr dissolved in the unstable matrix phases. Chromium oxide was found to be emitted when chromium containing slags were exposed to oxidizing atmosphere. The results indicate that chromium oxide evaporation increases with increase in temperature and oxygen partial pressure, but decreases with slag basicity and sample thickness. / <p>QC 20131114</p> / Steel Eco-Cycle

La vaporisation explosive, ou flashing, par dépressurisation rapide du C6F14 au travers d'une vanne à boisseau sphérique est analysée expérimentalement sur une grande plage de surchauffe. Les visualisations rapides montrent un jet s’ouvrant très largement en aval, preuve de l'existence d'un fort gradient de pression. Des mesures locales par sonde optique et par vélocimétrie phase Doppler ont permis de caractériser tailles, vitesses, concentration et flux numérique des gouttes en fonction de la surchauffe. La faible influence du degré de surchauffe sur la remontée en pression et sur les tailles et flux de gouttes suggère que le champ de pression s’adapte, et que par conséquent le liquide est soumis à une surchauffe locale bien plus faible que la surchauffe globale imposée. Différents scenarii sont discutés pour expliquer les observations, dont le fait que les tailles de gouttes sont peu sensibles à la surchauffe. Celui basé sur l’existence d’un front d’ébullition est le plus probable. / Depressurization (flashing) experiments through a ball valve were conducted with C6F14 for a large range of superheat. High-speed imaging shows a rapid and wide expansion of the jet, which evidences strong pressure gradients. Local measurements with phase detection optical probes and phase Doppler velocimetry were used to characterize size, speed, concentration and volumetric flux of drops as a function of superheat. The level of superheat has little influence on the vaporized fraction and on drop size and flux: this suggests that due to strong pressure gradients the liquid sees a much weaker level of superheat than the global superheat imposed on the system. Different scenarii are discussed to explain observations, in particular the fact that drop size remains approximately constant independent of the superheat. A scenario based on the existence of a boiling front seems to be the most consistent.

Ziel der Arbeit war die Nutzbarmachung von Bioethanol zur Wandlung in Strom und Wärme in einer Hochtemperaturbrennstoffzelle. Dazu waren neben der Entwicklung eines langzeitstabilen, effektiven Katalysators zur Synthesegaserzeugung und dessen Testung sowie der Übertragung gewonnener Erkenntnisse auf in einem Reformer einsetzbare Konzepte die Verifizierung kommerzieller Katalysatorsysteme für die partielle Oxidation von Ethanol notwendig. Außerdem ist für die Entwicklung eines ethanolbetriebenen SOFC-Systems eine pulsations- und ablagerungsfreie Verdampfung von unvergälltem und vergälltem Ethanol – welche nicht Stand der Technik ist – erforderlich, für die ein geeignetes Verdampferkonzept entwickelt und getestet wurde. Experimentell konnte die Betreibbarkeit eines SOFC-Systems mit Ethanol an einem für den Betrieb mit LPG ausgelegten System nachgewiesen werden.