Thesis supervisor: Albert Ratner. Includes bibliographical references (p. 117-126).

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Thesis (M. S.)--Aerospace Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Tim Lieuwen; Committee Member: Jeff Jagoda; Committee Member: Suresh Menon. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Studies on the effect of transport properties coupled with the interaction of fluid dynamics and combustion in acoustically forced laminar hydrogen jet diffusion flames have been performed using the planar laser-induced fluorescence (PLIF) technique. These unsteady diffusion flames are of particular interest because they are reproducible turbulent-like events that can be investigated to gain insight into turbulent combustion. Results reported herein add to the ongoing effort of understanding the complex transport processes taking place in the flames encountered in most modern heat-producing and power-producing devices. Fuel transport properties (i .e. fuel Lewis number, LeF) were varied by fuel dilution with various levels of helium (He) or argon (Ar). The fuel stream ofBurkeSchumann type hydrogen flames was acoustically excited by using a loudspeaker and the two-dimensional OH and temperature fields were measured. PLIF measurements were performed using an intricate two-laser, two-camera system; digital image analysis was implemented to reduce the large image data set obtained. The temperature of the unsteady flames departed significantly from the steadystate temperature as predicted by previous researchers. It was found that, regardless of LeF, unsteady He-diluted flames had maximum flame temperatures at some point during the speaker -oscillation that were always higher than the maximum temperatures of the H2-Ar flames. This was contrary to the trends seen in steady flames. An increased H2 mass flux to the flame zone in the unsteady H2-He flames was the reason for this observation since mass diffusion becomes important in the driven flames due to increased mass gradients and the difference in diffusivity of hydrogen in the diluents used. Low turbulence intensities (i.e.low frequency) allowed the flames to respond steadily to the changing flowfield. The structure of the reaction zone of unsteady flames at this low frequency was altered (i.e. stretched or compressed) slightly and, in general, these flames resembled the steady flames structurally. At high frequency, however, the flames responded to the imposed flow oscillation by considerable reaction zone stretch/compression. Results obtained from the present experiments suggest that, depending on the Lewis number, the flame temperature responds differently to the stretch imparted on the flame by the unsteady flowfield. These Lewis number effects were evidenced by both the low and high frequency flames, however, they were most obvious in the high frequency cases. The temperature of flames with LeF ~ l increased/decreased when the reaction zone thickened/thinned. On the other hand, flames with LeF < l increased/decreased in temperature when the reaction zone thinned/thickened. These trends competed with the thermal and mass transport processes present in the high-curvature regions of the flames.

Acoustic instabilities in a combustion chamber arise due to the coupling of acoustic pressure with in-phase heat-release, and are characterized by large amplitude oscillations of one or more natural modes of combustor. Even though an array of studies, both theoretical and experimental, has been conducted by a number of authors in this field to extract the flame response, most of these are based on kinematic flame models. In this dissertation, an experimental study of a subsonic flame's intrinsic response to acoustic pressure perturbations is performed for the case of a tube closed at one end and the other end opened to the atmospheric conditions. Pressure fluctuations inside the tube are measured for hot and cold side flows, and their varying trend is explained. The frequencies obtained from Fourier transform analysis exhibit a strong dependence with the distance between the stabilized flame position and open end of the tube. For different values of flame position (xf ), the values of growth constant 's' are calculated from the pressure versus time data readings procured from acoustic pressure transducer and dominant frequencies are analyzed from windowed FFT of the same. The expression for obtaining response function from the measured pressure fluctuations has been derived from the 1-D linearized conservation equations. The undamped response function plot is obtained by adding the decay rates at different frequencies inside the tube to the corresponding growth rates. Finally, the effect of blockage of pre-mixed flow on the growth rates inside the tube and consequently, the flame response values, is studied by repeating the experiment with different types of flame holders. A large number of theoretical flame-response models have been developed in modern literature, and some of these models are compared with the experimentally obtained response. Suggestions are also cited in this study so as to account for the observed deviations in trends. This includes a revisit of the intrinsic flame model by incorporating the effect of flame-area perturbations, with the aid of analyzed steady flame images.

The objectives of this paper focus upon composing recommendations with respect to burners design while observing aerodynamic, together with present and advanced developments in the field of flame technology principles. Specifically the aims are set at flame stability and pollutions. Important part of this paper is a novel design procedure dealing with premixed burners. Further, by exploiting the results of testing program enabled one to design burners exhibiting low level of nitrogen oxides emissions. On the basis of aerodynamic analysis of premixed burners flow path several recommendations on the geometry resulted in proposing two ejectors, which transport the combustion air. In the first ejector the fuel jet, generated by flow through a nozzle, draws the specified part of the combustion air, and then the mixture is a driving agent of the second ejector. The remaining part of combustion air flows first through the radial curved vanes, and second its tangential velocity component is augmented by axial vanes prior it enters mixing part of the second ejector. For the additional contribution to the rotating motion the inclined axial vanes built inside the nozzle of the second ejector are responsible. The resulting swirling number reaches the values up to 2.6. For the burner so arranged fire stability and low NOx emissions in the wide operating conditions can be expected. Within the frame of extensive testing program in the field of diffusion burners several modifications have been carried out such as setting of axial vanes which secure the swirling motion, changes of combustion air flows path, and modifications of secondary nozzles, these resulted in extending zone of stabilized flame and reducing the formation of NOx, e.g. NOx emissions of 70 ppm, prior the modifications, have dropped to 30 ppm (dry flue gas 3% O2). The main contribution of this paper stands in applications of development activities results in aerodynamic and flame within their implementation in the field of burners design. Further, it is the proposed design of burners which are capable of simultaneously firing products of the biomass microwave pyrolysis, namely syngas and bio-oils.

A novel flame spray collar called the Coanda Assisted Spray Manipulation collar (CSM) has been tested for use on the Sulzer Metco 5P II combustion flame spray gun. A comparison study of the stock nozzle and the CSM has been performed by evaluating the porosity, surface roughness, microhardness, tensile strength and microscopy of normal and off-normal sprayed NiAl deposits. The use of the CSM collar resulted in the need to position the sprayed coupons closer to the gun, which in turn affected the particle impact energy and particle temperatures of the NiAl powder. For the CSM, porosities had a larger scatterband, surface roughness was comparably the same, microhardness was lower, and tensile strength was higher. The microscopy analysis revealed a greater presence of unmelted particles and steeper intersplat boundaries for the CSM. For both processes, the porosity and surface roughness increased and the microhardness decreased as the spray angle decreased.

Ce travail de thèse porte sur le développement de films diamantés pour des applications de dissipation de chaleur dans les circuits électroniques de puissance. Dans le cadre d’un accord de cotutelle franco-américain, une approche duale a été adoptée. En France, la fabrication de films composites à matrice cuivre et renforts diamant par métallurgie des poudres a été privilégiée. Aux Etats-Unis, les efforts se sont concentrés sur la croissance de films de diamant par une méthode de combustion de flamme assistée laser. Dans chacune des approches, les corrélations entre microstructure et interfaces (microscopies à balayage et à transmission), composition chimique (spectroscopies Auger, Raman, XPS), et propriétés thermiques (radiométrie flash laser, radiométrie photothermique infrarouge, dilatométrie, cyclage thermique) ont été établies. Enfin, la simulation du comportement des matériaux en situation de fonctionnement opératoire à été abordée. / This PhD work deals with the development of diamond-based heat-spreading films for power electronic packaging applications. In the frame of a French-American dual PhD agreement, a double research approach was adopted. In France, the fabrication of copper-matrix diamond-reinforced composite films through tape casting and hot pressing has been endeavoured. In the US, the efforts were focused on the growth of diamond films through laser-assisted combustion synthesis. In both cases, relationships between the microstructure and the interfaces (scanning and transmission electron microscopy), the chemical composition (Auger, Raman, and XPS spectroscopy), and the thermal properties (flash laser radiometry, infrared photothermal radiometry, dilatometry, thermal cycling) of the final materials were established. Finally, the behaviour of the materials in operating environment was simulated.