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1
Tribbe, Christian. "Gas/liquid flow in cylindrical and corrugated channels". Thesis, University of Surrey, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244760.
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Wu, Xuemei. "Monte-Carlo modeling of turbulent dispersion of small particles in channels". Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17389.
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Goodwin, William A. "The characteristics of reduced-density channels in NH3-N2 gas mixtures". Thesis, Monterey, California. Naval Postgraduate School, 1988. http://hdl.handle.net/10945/22941.
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A CO2 laser was used to generate reduced-density channels in various gas mixtures of ammonia and nitrogen. Interferometers were used to record the changing density resulting from the NH3 absorption of the CO2 laser radiation. One method used to determine the characteristics of the channel was based on the assumption that the resulting density profile was Gaussian shaped. The second method used the Abel Integral Transformation, requiring no pre-conditions on the density profile expect that it was cylindrically symmetric. While used extensively in plasma spectroscopy, this technique is not generally well known for analyzing interferometric data. The results show that for a fixed laser energy long, shallow reduced density channels were formed in gas mixtures of low ammonia concentration and short, deep channels were formed in gas mixtures high ammonia concentration. These results qualitatively agree with an earlier experiment in which gas mixtures of nitrogen and sulfur-hexafluoride were used. Both experiments support the concept of reduced-density channel formation and lay the foundation for future studies of relativistic electron beam propagation for application in the Strategic Defense Initiative. Keywords: Reduced density channel; Fringe data; Interferogram; Zero Fringe Line; Reference mark; Channel depth; Channel width; Carbon dioxide laser; Theses. (MGM)
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Dounia, Omar. "Numerical investigation of gas explosion phenomena in confined and obstructed channels". Phd thesis, Toulouse, INPT, 2018. http://oatao.univ-toulouse.fr/20584/1/DOUNIA_Omar.pdf.
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Mining, process and energy industries suffer from billions of dollars of worldwide losses every year due to Vapour Cloud Explosions (VCE). Moreover, explosion accidents are often tragic and lead to a high number of severe injuries and fatalities. The VCE scenario is complex and controlled by various mechanisms. The interplay among them is still not entirely understood. Understanding all these intricate processes is of vital importance and requires detailed experimental diagnostics. Coupling accurate numerical simulations to well documented experiments can allow an elaborate description of these phenomena. This thesis focuses on explosions occurring on configurations that are either semi-confined or confined. In such configurations, the explosion is generally initiated by a mild ignition and a subsonic flame front emerges from the ignition source. An important feature of self-propagating flames lies in their intrinsically unstable nature. When they propagate in an environment with high levels of confinement and congestion, which is the case in most industrial sites, a Flame Acceleration (FA) process is often observed that can give rise to very fast flames, known for their destructive potential. In some cases, the FA process can create the appropriate conditions for the initiation of detonations, which corresponds to a rapid escalation of the explosion hazard. To reproduce the confinement and congestion conditions that one can find in industrial sites, the university of Munich TUM equipped a confined chamber with a series of obstacles and analysed the influence of repeated obstructions on the propagation of hydrogen/air deflagrations. This experimental study showed a strong influence of the mixture composition on the acceleration process. A Deflagration to Detonation Transition (DDT) has also been observed for a certain range of equivalence ratio. This configuration is therefore ideal to study the mechanisms of flame acceleration as well as the intricate DDT process. A numerical study of both scenarios is performed in this thesis: -First for a lean premixed hydrogen/air mixture, a strong flame acceleration is observed experimentally without DDT. The characteristic features of the explosion are well reproduced numerically using a Large Eddy Simulation (LES) approach. The crucial importance of confinement and repeated flame-obstacle interactions in producing very fast deflagrations is highlighted. -DDT is observed experimentally for a stoichiometric hydrogen/air mixture. This thesis focuses on the instants surrounding the DDT event, using Direct Numerical Simulations (DNS). Particular attention is drawn to the impact of the chemistry modelling on the detonation scenario. The failure of preventive measures is often observed in many explosion accidents. To avoid a rapid escalation of the explosion scenario, mitigative procedures must be triggered when a gas leak or an ignition is detected. Metal salts (like potassium bicarbonate and sodium bicarbonate) have received considerable attention recently because well-controlled experiments showed their high efficiency in inhibiting fires. The last part of the thesis focused on the mechanism of flame inhibition by sodium bicarbonate particles. First, criteria based on the particle sizes are established to characterize the inhibition efficiency of the particles. Second, two dimensional numerical simulations of a planar flame propagating in a stratified layer of very fine sodium bicarbonate particles showed that under certain conditions these powders can act as combustion enhancers. These results echo a number of experimental observations on the possible counter-effects of the inhibitors.
5
Sundberg, Jenny. "Heat Transfer Correlations for Gas Turbine Cooling". Thesis, Linköping University, Department of Mechanical Engineering, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-5446.
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A first part of a ”Heat Transfer Handbook” about correlations for internal cooling of gas turbine vanes and blades has been created. The work is based on the cooling of vanes and blades 1 and 2 on different Siemens Gas Turbines. The cooling methods increase the heat transfer in the cooling channels by increasing the heat transfer coefficient and/or increasing the heat transfer surface area. The penalty paid for the increased heat transfer is higher pressure losses.
Three cooling methods, called rib turbulated cooling, matrix cooling and impingement cooling were investigated. Rib turbulated cooling and impingement cooling are typically used in the leading edge or mid region of the airfoil and matrix cooling is mostly applied in the trailing edge region.
Literature studies for each cooling method, covering both open literature and internal reports, were carried out in order to find correlations developed from tests. The correlations were compared and analyzed with focus on suitability for use in turbine conditions. The analysis resulted in recommendations about what correlations to use for each cooling method.
For rib turbulated cooling in square or rectangular ducts, four correlations developed by Han and his co-workers [3.5], [3.8], [3.9] and [3.6] are recommended, each valid for different channel and rib geometries. For U-shaped channels, correlations of Nagoga [3.4] are recommended.
Matrix cooling is relatively unknown in west, but has been used for many years in the former Soviet Union. Therefore available information in open literature is limited. Only one source of correlations was found. The correlations were developed by Nagoga [4.2] and are valid for closed matrixes. Siemens Gas Turbines are cooled with open matrixes, why further work with developing correlations is needed.
For impingement cooling on a flat target plate, a correlation of Florschuetz et al. [5.7] is recommended for inline impingement arrays. For staggered arrays, both the correlations of Florschuetz et al. [5.7] and Höglund [5.8] are suitable. The correlations for impingement on curved target plate gave very different results. The correlation of Nagoga is recommended, but it is also advised to consult the other correlations when calculating heat transfer for a specific case.
Another part of the work has been to investigate the codes of two heat transfer programs named Q3D and Multipass, used in the Siemens offices in Finspång and Lincoln, respectively. Certain changes in the code are recommended.
6
Penache, Dan Lucius. "Heavy ion beam transport in laser initiated high current gas discharge channels". Phd thesis, [S.l.] : [s.n.], 2002. http://elib.tu-darmstadt.de/diss/000245.
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Khamaj, J. A. J. "An experimental study of heat transfer in the cooling channels of gas turbine rotor blades". Thesis, Swansea University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637783.
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This thesis presents an investigation of experimental research into the effect of rotation on the convective heat transfer mechanism inside the cooling channels of turbine rotor blades. These involved the selection of eleven different channel geometries and these have been designated alphabetically by the letters 'A' through 'K' respectively. These channels involve a collection of basic geometrical duct cross sectional shapes with the incorporation of ribbed surfaces. The leading and trailing edges of the duct are fitted with in-line or staggered ribs aligned at 30° to 45° to the central axis of the duct. The leading and trailing edges are heated using electrical foil heaters bonded underneath copper plates on which a particular rib configuration was machined. The other two sides of the test sections would be deemed adiabatic. The centre lines of the heated leading and trailing edges were fitted with thirteen foil thermocouples. The coolant used was air with the flow direction in the radially outward direction. Test section A was square in cross section with 'in-line' ribs fitted to the leading and trailing edges. The ribs were inclined at 45° to the direction of coolant flow, which was radially outward. Test sections 'B', 'C' and 'D', were used to examine experimentally the effect of the aspect ratio of rectangular-sectioned ducts cross sections. The respective aspect ratios of test channels 'B', 'C' and 'D' were 0.5, 1.0 and 2.0. Each channel was fitted with staggered ribs inclined at 45° to the direction of flow. Test section 'D' was used to examine the effect of a rectangular channel having an angular inclination relative to the plane of rotation. In other words the heated leading and trailing edges of the channel were skewed to simulate the fact that, in a cambered rotor blade, these edges were inclined to the plane of rotation. Relative to the case of in line rotation, test sections 'E' and 'F' were inclined at 30° and 60° (clock wise) to the plane of rotation. Similarly test sections 'G' and 'H' had inclinations of -30° and -60° respectively.
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Siow, Erh Chang. "Numerical solution of a two-phase model for laminar film condensation of vapour-gas mixtures in channels". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ62848.pdf.
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Göhring, Michael [Verfasser]. "Numerical Investigation of Internal Two-Pass Gas Turbine Cooling Channels Under the Influence of Rotation / Michael Göhring". München : Verlag Dr. Hut, 2020. http://d-nb.info/1219470112/34.
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Liu, Yao-Hsien. "Heat transfer in leading and trailing edge cooling channels of the gas turbine blade under high rotation numbers". [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3196.
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Lamont, Justin Andrew. "Heat Transfer in Stationary and Rotating Coolant Channels Using a Transient Liquid Crystal Technique". Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/19192.
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Heat transfer inside rotating coolant channels have a significant impact in design of gas turbine airfoils and other rotating components such as generator windings. The effects of the Coriolis acceleration and centrifugal buoyancy have a significant impact on heat transfer behavior inside such rotating coolant channels due to the complex flow patterns of coolant. Detailed heat transfer knowledge greatly enhances the designers\' ability to validate numerical models of newly designed channels. A rotating experimental rig was designed and built to model scaled up coolant channels at speeds up to 750 rotations per minute (rpm). A camera is mounted onto the rotating test section and a transient liquid crystal technique is used to measure detailed heat transfer coefficients on a surface of interest. The experimental set-up is innovative, as it involves no surface heating of the test section, very little instrumentation beyond a few thermocouples and a spray coating of thermochromic liquid crystals on the test surface. To validate the test rig and the experimental method, multipass coolant channels with rib turbulators, large diameter radially outward channels with rib turbulators, and jet impingement cooling schemes are studied during rotation. 90deg, W, and M-shaped rib enhancements are studied and detailed heat transfer measurements clearly capture the heat transfer enhancement mechanisms with and without rotation. Jet impingement schemes with single and double rows, normal and off-angle jets, and a cross flow outlet condition are all studied under rotation. Non-rotating studies are also performed for baseline comparisons to rotating conditions. Large aspect ratio, diverging channels with dimple and rib turbulators are studied in a stationary condition. Results for all different test geometries show good comparisons with published studies indicating that the rotating rig and experimental method are valid. Jet impingement schemes produce higher heat transfer compared to the two-pass channels with ribs, however pressure losses are significantly higher. The fewer the jets and H/d=1 produces the highest pressure losses with no significant gain in heat transfer. Off angle jets at H/d=1 produces very high pressure losses with no heat transfer advantage. A final study with radially outward coolant channels is performed with the highest rotation speeds. The structure, test section, and camera are thoroughly designed to withstand the exceptional g-forces. Heat transfer in the radial channels with and without rotation show very little effect of rotation due to the small rotation number.Ph. D.
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Yang, Lixia. "Local investigations of gas-liquid mass transfer around Taylor bubbles flowing in straight and meandering millimetric channels using a colorimetric method". Thesis, Toulouse, INSA, 2017. http://www.theses.fr/2017ISAT0027/document.
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Les réacteurs-échangeurs à plaques (HEX) sont une technologie clé en intensification des procédés. Cependant, la plupart des recherches existantes portant sur ce type d'équipement ont été réalisées dans le cas d’écoulements monophasiques. Pour les réactions gaz-liquide, peu d'études ont été conduites. Cette thèse a pour objectif d’étudier localement le transfert de matière gaz-liquide autour de bulles de Taylor en écoulement dans des canaux millimétriques droits et ondulés par une méthode dite colorimétrique. Ceci constitue une étape préliminaire indispensable avant la mise en œuvre de systèmes réactifs diphasiques. Il a d’abord déterminé si une possible accélération du transfert de matière gaz-liquide pouvait avoir lieu en présence de la réaction chimique utilisée. La deuxième phase de ce travail s’est focalisée sur l'étape de formation des bulles de Taylor dans un microréacteur. Ensuite, l'hydrodynamique gaz-liquide a été caractérisée et les effets des coudes sur le mécanisme de transfert de masse ont été étudiés localement dans un canal carré millimétrique ondulé. Enfin, une comparaison rigoureuse a pu être effectuée entre les différentes géométries de canaux (ondulé et droit). Elle a permis de montrer comment et pourquoi une géométrie ondulé permet d’intensifier le transfert de masse gaz-liquide (notamment en terme d’efficacité de transfert). L’ensemble de ces résultats ont conduit à la formulation une loi d'échelle, exprimée en termes de nombres de Sherwood, de Graetz et de Péclet, capable de décrire l'évolution du transfert de matière gaz-liquide en fonction de la position axiale dans le canal et des conditions opératoires mises en œuvreCompact Heat-EXchanger reactors (HEX) are an important part of process intensification technology. However, most of the existed research dealing with such type of equipment has been focused on the application of one-phase reactive flows. For gas-liquid reactions, few investigations have been out carried. This thesis aims at locally studying gas-liquid mass transfer around Taylor bubbles flowing in straight and meandering millimetric channels using a colorimetric method; this is a preliminary step essential before implementing two-phase reactive systems. Firstly, the occurrence of a possible enhancement of the gas-liquid mass transfer by the chemical reaction involved was investigated. Secondly, the gas-liquid mass transfer occurring in Taylor flows right after the bubble formation stage in a microreactor was studied. Thirdly, the gas-liquid hydrodynamics were characterized and the effects of bends on the mass transfer mechanism were locally investigated in a millimetric meandering channel. At last, a rigorous comparison could be made between the meandering and straight channels. It showed how and why the meandering geometry leads to intensify gas-liquid mass transfer. All these findings enabled to formulate a scaling law, expressed in terms of Sherwood, Graetz and Péclet numbers, able to describe the evolution of gas-liquid mass transfer as a function of axial position and operating conditions
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Tyagi, Kartikeya. "Detailed Experimental Measurements of Heat Transfer Augmentation in Internal Channels Using a Thermochromic Liquid Crystal Technique". Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/52990.
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Design of internal cooling channels for gas turbine blade is critical to system performance. To achieve maximum efficiency, i.e. maximum cooling with minimum coolant usage, intensive research is required to optimize heat transfer enhancement features. The present study aims at experimental and numerical investigation of two heat transfer augmentation techniques for internal cooling, viz. dimple and swirl induced jet impingement. Dimples are suitable candidates for high performance enhancement as they impose a low pressure drop penalty. The present study aims at experimentally measuring heat transfer on all the walls of diamond, triangular, square and cylindrical shaped dimples in a staggered configuration at three flow conditions in a high aspect ratio channel. A thermal-hydraulic performance factor was evaluated to characterize each dimple shape. Numerical simulations were conducted to visualize flow patterns which was correlated with heat transfer distribution. The results were in good agreement with previous studies. Triangular dimples showed the highest overall performance due to lowest pressure drop penalty, but heat transfer was low inside the dimples. In rotating channels, Coriolis Effect and centrifugal buoyancy significantly affect heat transfer distribution. There is a need to develop a cooling geometry that benefits from rotation and provides consistent cooling. A new geometry was derived from a past study, consisting of two channels divided by a wall with angled holes to provide jet impingement from inlet to outlet channel. Liquid crystal technique was used for heat transfer measurements. It was found that at high rotational speeds, heat transfer increased in the inlet channel, while it decreased in the outlet channel. Additional testing at even higher speeds may provide insight into replacing a traditional U-bend channel in a turbine blade.Master of Science
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Miao, Sha Ph D. Massachusetts Institute of Technology. "Mechanistic study of slug formation and evolution in high-viscosity-liquid/High-density-gas multiphase flows in channels/pipes". Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118725.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 165-176).
Rapidly rising global energy demand coupled with dwindling conventional oil resources has pushed unconventional oil, such as heavy oil, to become one of the most important future energy resources. However, design and operation of pipelines to transport heavy-oil/gas flows have raised new challenges associated with remarkably different flow regime transitions compared to conventional low-viscosity-oil/low-density-gas flows. Many traditional flow regime models for these oil/gas flows result in O(1) prediction errors when applied to high-viscosity-oil/high-density-gas flows because they fail to account for the complex change in physics and scales that occur as the fluid properties substantially change. Therefore, understanding the mechanisms that cause flow-regime transition for these types of flows is of critical importance to the development of physics-based models allowing for the creation of more robust and cost effective designs. The work described in this thesis focuses on investigating the fundamental mechanisms governing the initial growth and nonlinear evolution of interfacial waves leading to slugging in concurrent high-viscosity (laminar) liquid/high-density(turbulent) gas two-phase flows in horizontal channels/pipes. We first develop a Fully-Coupled Immersed Flow (FCIF) solver for the three-dimensional simulation of fluid-fluid interaction by coupling two distinct flow solvers using an Immersed Boundary (IB) method. The FCIF solver captures dynamic interactions between two fluids with disparate flow properties, while retaining the desirable simplicity of non-boundary-conforming grids. For the application of slug development with turbulent gas and laminar liquid, we couple an IB-based unsteady Reynolds Averaged Navier Stokes (uRANS) simulator with a depth-integrated (long-wave) solver in FCIF. We perform a series of validations on this method. The results demonstrate that the FCIF solver effectively captures the essential physics of gas-liquid interaction and can serve as a useful tool for the mechanistic study of slug generation in two-phase gas/liquid flows in channels and pipes.
by Sha Miao.
Ph. D.
15
Alrahmani, Mosab. "A numerical study on the effects of surface and geometry design on water behaviour in PEM fuel cell gas channels". Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/16245.
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Water management is a serious issue that affects the performance and durability of PEM fuel cells. It is known, from previous experimental investigations, that surface wettability has influence on water behaviour and fuel cell performance. This finding has lead researchers to develop numerical tools for further investigation of the liquid water behaviour in gas channels. The Volume-of-Fluid (VOF) method has been used in a wide range of studies for its advantage of showing the multi-phase interface in a Computational Fluid Dynamics (CFD) simulation to understand liquid water behaviour in gas channels. In this thesis, numerical study has been carried out to examine the behaviour of liquid water in gas channels. The dynamic movement of the liquid water in the channel and the associated pressure drop, water saturation and water coverage of the GDL have been investigated. Firstly, flow diffusion into the GDL was examined to determine its effect on liquid droplet behaviour in a small section of a gas channel. Furthermore, the effects of the percentage of flow diffusion, GDL wettability, pore size, and water inlet velocity were investigated. Fluid diffusion into GDL found to have insignificant impact on liquid water behaviour so further investigations has been carried with a solid GDL surface. Secondly, gas channel geometry effect on liquid water behaviour was studied. Square, semicircle, triangle, trapezoid with a long base and trapezoid with a short base were compared to find suitable cross section geometry to carry wall wettability investigations. Among the examined geometries, the square cross section showed reasonable results for both scenarios of geometry design, fixed Reynolds number and fixed GDL interface. The effect of wall wettability was assessed by comparing nine different wall/GDL wettability combinations for straight and bend channels. Wall wettability found to have an impact on liquid water behaviour but not as much as GDL wettability. It affects liquid water saturation in the channel by a great deal by accumulating water in the channel edges affecting water behaviour. This was also proven in the last test case of a long channel where water accumulation was investigated by running the calculation until the percentage of water saturation is stabilized. It is also concluded that changing wall wettability from hydrophobic to hydrophilic doubles the percentage of channel occupied by liquid water and increases the time to reach steady state.
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Göhring, Michael [Verfasser] y Jens von [Akademischer Betreuer] Wolfersdorf. "Numerical investigation of internal two-pass gas turbine cooling channels under the influence of rotation / Michael Göhring ; Betreuer: Jens von Wolfersdorf". Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2020. http://d-nb.info/1219905801/34.
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Duarte, Henrique Canto e. Castro Guerreiro. "High-resolution seismic reflection investigation of gas accumulation and seepage in the tidal channels of the Ria of Aveiro barrier lagoon (Portugal)". Doctoral thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/2752.
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Doutoramento em GeociênciasO metano é um gás de estufa potente e uma importante fonte de energia. A importância global e impacto em zonas costeiras de acumulações e escape de gás metano são ainda pouco conhecidas. Esta tese investiga acumulações e escape de gás em canais de maré da Ria de Aveiro com dados de cinco campanhas de reflexão sísmica de alta resolução realizadas em 1986, 1999, 2002 e 2003. Estas incluem três campanhas de Chirp (RIAV99, RIAV02 e RIAV02A) e duas campanhas de Boomer (VOUGA86 e RIAV03). O processamento dos dados de navegação incluíram filtros de erros, correcções de sincronização de relógios de sistemas de aquisição de dados, ajuste de “layback” e estimativa da posição de “midpoint”. O processamento do sinal sísmico consistiu na correcção das amplitudes, remoção de ruído do tipo “burst”, correcções estáticas, correcção do “normal move-out”, filtragem passabanda, desconvolução da assinatura e migração Stolt F-K. A análise da regularidade do trajecto de navegação, dos desfasamentos entre horizontes e dos modelos de superfícies foi utilizada para controlo de qualidade, e permitiu a revisão e melhoria dos parâmetros de processamento. A heterogeneidade da cobertura sísmica, da qualidade do sinal, da penetração e da resolução, no seu conjunto constrangeram o uso dos dados a interpretações detalhadas, mas locais, de objectos geológicos da Ria. É apresentado um procedimento para determinar a escolha de escalas adequadas para modelar os objectos geológicos, baseado na resolução sísmica, erros de posicionamento conhecidos e desfasamentos médios entre horizontes. As evidências de acumulação e escape de gás na Ria de Aveiro incluem turbidez acústica, reflexões reforçadas, cortinas acústicas, domas, “pockmarks” e alinhamentos de “pockmarks” enterradas, horizontes perturbados e plumas acústicas na coluna de água (flares). A estratigrafia e a estrutura geológica controlam a distribuição e extensão das acumulações e escape de gás. Ainda assim, nestes sistemas de baixa profundidade de água, as variações da altura de maré têm um impacto significativo na detecção de gás com métodos acústicos, através de alterações nas amplitudes originais de reflexões reforçadas, turbidez acústica e branqueamento acústico em zonas com gás. Os padrões encontrados confirmam que o escape de bolhas de gás é desencadeado pela descida da maré. Há acumulações de gás em sedimentos Holocénicos e no substrato de argilas e calcários do Mesozóico. Evidências directas de escape de gás em sondagens em zonas vizinhas, mostraram gás essencialmente biogénico. A maioria do gás na área deve ter sido gerado em sedimentos lagunares Holocénicos. No entanto, a localização e geometria de estruturas de escape de fluidos em alguns canais de maré, seguem o padrão de fracturas do substrato Mesozóico, indicando uma possível fonte mais profunda de gás e que estas fracturas funcionam como condutas preferenciais de migração dos fluidos e exercem um controlo estrutural na ocorrência de gás na Ria.
Methane is a powerful greenhouse gas and an important energy source. The global importance and impact in coastal zones of methane gas accumulation and seepage in sediments from coastal lagoon environments is still largely unknown. This Ph.D. investigates gas accumulation and seepage in tidal channels of the Ria of Aveiro with data from five high resolution seismic surveys carried out in 1986, 1999, 2002 and 2003. These include three Chirp surveys (RIAV99, RIAV02, RIAV02A) and two Boomer surveys (VOUGA86 and RIAV03). The navigation data processing included instrumental error filters, system clock synchronization corrections, layback adjustment and trace midpoint position estimate. The seismic signal processing consisted in amplitude corrections, burst noise removal, static corrections, normal move-out corrections, band-pass filtering, spike deconvolution and Stolt F-K migration. The analysis of the track line regularity, the horizon misties and the first-break surface models were applied as quality control procedures, and allowed the revision and improvement of the processing parameters. The heterogeneity of the seismic coverage, signal quality, penetration and resolution all constrain the use of the data to mostly local but detailed interpretations and modeling of the geological objects of the Ria of Aveiro. A procedure is presented to determine adequate choice of scales of these geological models based on the seismic resolution, known positioning errors and mean mistie values. Evidence of extensive gas accumulation and seepage in tidal channel sediments from the “Ria de Aveiro” barrier-lagoon includes acoustic turbidity, enhanced reflections, acoustic blanking, domes, pockmarks and buried aligned pockmarks, disrupted horizons and acoustic plumes in the water layer (flares). The stratigraphy and the structural framework control the distribution and extent of the gas accumulations and seepage in the study area. However, in these shallow systems, tidal altitude variations have a significant impact on gas detection with acoustic methods, by changing the raw amplitude of the enhanced seismic reflections, acoustic turbidity and acoustic blanking in gas-prone areas. Amplitudes are clearly stronger during low tide with maxima during ebb, decreasing with flood with minima during high tide; this pattern confirms that bubbling and gas escape is triggered mainly by the falling tide. There are accumulations of gas both in the Holocene sediments and in the Mesozoic bedrock of marls and clays. Direct evidence of gas escape from drill-holes in the surrounding area has shown that the gas recovered in the “Ria de Aveiro” consists of biogenic methane. Most of the gas in the study area was probably mainly generated in Holocene lagoon sediments. Nevertheless, the location and geometry of fluid escape features in some channels follows the fracture pattern affecting the Mesozoic bedrock, indicating a possible deeper source of gas and that these fractures function as preferential pathways for fluid migration and exert a structural control on gas occurrences in the Ria of Aveiro.
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Tran, Lucky. "Development of Full Surface Transient Thermochromic Liquid Crystal Technique for Internal Cooling Channels". Master's thesis, University of Central Florida, 2014. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6371.
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Proper design of high performance industrial heat transfer equipment relies on accurate knowledge and prediction of the thermal boundary conditions. In order to enhance the overall gas turbine efficiency, advancements in cooling technology for gas turbines and related applications are continuously investigated to increase the turbine inlet temperature without compromising the durability of the materials used.
For detailed design, local distributions are needed in addition to bulk quantities. Detailed local distributions require advanced experimental techniques whereas they are readily available using numerical tools. Numerical predictions using a computational fluid dynamics approach with popular turbulence models are benchmarked against a semi-empirical correlation for the friction in a circular channel with repeated-rib roughness to demonstrate some shortcomings of the models used. Numerical predictions varied widely depending on the turbulence modelling approach used. The need for a compatible experimental dataset to accompany numerical simulations was discussed.
An exact, closed-form analytical solution to the enhanced lumped capacitance model is derived. The temperature evolution in a representative 2D turbulated surface is simulated using Fluent to validate the model and its exact solution. A case including an interface contact resistance was included as well as various rib sizes to test the validity of the model over a range of conditions. The analysis was extended to the inter-rib region to investigate the extent and magnitude of the influence of the metallic rib features on the apparent heat transfer coefficients in the inter-rib region. It was found that the thermal contamination is limited only to the regions closest to the base of the rib feature.
An experimental setup was developed, capable of measuring the local heat transfer distributions on all four channel walls of a rectangular channel (with aspect ratios between 1 and 5) at Reynolds numbers up to 150,000. The setup utilizes a transient thermochromic liquid crystals technique using narrow band crystals and a four camera setup. The setup is used to test a square channel with ribs applied to one wall. Using the transient thermochromic liquid crystals technique and applying it underneath high conductivity, metallic surface features, it is possible to calculate the heat transfer coefficient using a lumped heat capacitance approach. The enhanced lumped capacitance model is used to account for heat conduction into the substrate material. Rohacell and aluminum ribs adhered to the surface were used to tandem to validate the hybrid technique against the standard technique. Local data was also used to investigate the effect of thermal contamination. Thermal contamination observed empirically was more optimistic than numerical predictions.
Traditional transient thermochromic liquid crystals technique utilizes the time-to-arrival of the peak intensity of the green color signal. The technique has been extended to utilize both the red and green color signals, increasing the throughput by recovering unused data while also allowing for a reduction in the experimental uncertainty of the calculated heat transfer coefficient. The over-determined system was solved using an un-weighted least squares approach. Uncertainty analysis of the multi-color technique demonstrated its superior performance over the single-color technique. The multi-color technique has the advantage of improved experimental uncertainty while being easy to implement.M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Thermo-Fluids Track
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Larsson, David. "Gaskunders informationsbehov. : En studie i Stockholm Gas AB:s olika kundsegments behov av information och önskade informationskanaler". Thesis, KTH, Skolan för teknikvetenskap (SCI), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93447.
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Stockholm Gas AB säljer i huvudsak två olika produkter. Den ena är stadsgas och den andra är fordonsgas. Båda produkterna skall på sikt i huvudsak ha biogas som råvara. I dagsläget är det dock så att stadsgasen till största delen består av naturgas blandad med luft.Stockholm Gas AB har genomgått stora förändringar och står inför nya. År 2011 togs ett stort steg i Stockholm Gas klimat- och miljöriktiga utveckling. Den tidigare stadsgasen baserad på lättbensin ersattes med en stadsgaskvalité bestående av naturgas och/eller biogas blandad med luft. Utöver denna förändring har Stockholm Gas också utvecklat sin roll som leverantör av biogas som fordonsbränsle. Nya rörnät för leverans av biogas är under uppbyggnad för att knyta ihop biogasens produktionsplatser med olika tankställen. Genom att Stockholm Gas AB är ett relativt ungt företag i kombination med de stora förändringar som nämns ovan anser sig Stockholm Gas AB ha ett behov av att utveckla sin kommunikation gentemot sina kunder. Denna studie är ett led i utvecklingen av kommunikationen.Studiens övergripande syfte är att ge Stockholm Gas AB ett underlag för att utveckla och förbättra sin kommunikation med sina olika kundsegment vad det gäller såväl informationskanaler som informationsinnehåll rörande Stockholm Gas AB:s båda produkter samt råvaran biogas. Strävan är att rapporten skall kunna fungera som ett underlag och en vägledning för Stockholm Gas AB vid framtagande av informationsmaterial rörande sina båda produkter och råvaran biogas, samt hjälpa Stockholm Gas AB:s marknadsavdelning att bättre kunna kommunicera med Stockholm Gas AB:s kunder. Det centrala i studien är att ta reda på vilken typ av information som Stockholm Gas AB:s kunder är intresserade av och vilka informationskanaler som föredras och jämföra detta med de uppfattningar som de anställda på Stockholm Gas AB har. Kunderna har i studien delats in i fyra segment. Dessa segment är fordonsgasstorkunder (främst taxibolag), fordonsgasprivatkunder, stadsgasstorkunder (främst krögare) och stadsgasprivatkunder. Studien utfördes genom att kvalitativa intervjuer har genomförts med anställda på Stockholm Gas AB och med vart och ett av kundsegmenten. Intervjusvaren på varje fråga har kategoriserats och utifrån detta har slutsatser dragits och ett resultat utformats. Ett resultat presenteras för vart och ett av kundsegmenten i form av venndiagram samt i en mer diskuterande resultatdel.Stockholm Gas AB sells essentially two different products. One is the town gas and the other vehicle gas. Both products will eventually have substantially the biogas as a feedstock. In the current situation though, the city gas consists mainly of natural gas mixed with air. Stockholm Gas AB has undergone major changes and facing new ones. The year 2011 marked a major step in Stockholm Gas climate and environmentally friendly development. The former town gas is based on light petroleum was replaced with a town gas quality consisting of natural gas and / or biogas is mixed with air. In addition to this change, the Stockholm Gas also developed its role as a supplier of biogas as vehicle fuel. New mains for the supply of biogas are under construction to link up biogas production locations with different filling stations. Stockholm Gas AB being a relatively young company, combined with the significant changes mentioned above, Stockholm Gas AB have a need to develop their communication to their customers. This study is a part of that development of communication. The study's overall purpose is to provide Stockholm Gas AB with a basis to develop and improve its communications with its various customer segments in terms of both information channels and the information contents regarding Stockholm Gas AB's both products and the raw material biogas. The aim is that the report should serve as a basis and a guide to Stockholm Gas AB in the preparation of information material relating to its products and raw material biogas, as well as helping Stockholm Gas AB's marketing department to better communicate with the Stockholm Gas AB's customers. Central to this study is to determine what type of information that Stockholm Gas AB's customers are interested in and their channels of choice, and compare this with the views of the staff at Stockholm Gas AB. The customers have in the study been divided into four segments. These segments are vehicle gas key accounts, (mainly taxi companies), vehicle gas private customers, town gas key accounts (primarily chefs) and town gas private customers. The study was conducted through qualitative interviews with employees at the Stockholm Gas AB, and with each of the customer segments. Interview responses to each question have been categorized and from this conclusions have been drawn and results been designed. A result is presented for each of the segments in the form of a Venn diagrams, and in a more deliberative part of the result.
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Oliveira, Bruna Gonçalves de. "Emissão de metano e microbiota funcional associadas a vinhaça de cana-de-açúcar em sistemas de armazenamento e transporte". Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/11/11138/tde-13052015-160145/.
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Esta pesquisa teve como objetivo quantificar a emissão de metano (CH4) proveniente da vinhaça presente em diferentes sistemas de armazenamento e transporte e, adicionalmente, avaliar, por técnicas independentes de cultivo, a microbiota funcional relacionada à produção deste gás. Para atingir esta meta foram realizados três estudos complementares. O primeiro abordou a caracterização dos sistemas de armazenamento e transporte de vinhaça encontrados no Brasil baseado em um questionário aplicado às usinas produtoras de etanol. O segundo visou quantificar as emissões de CH4 em condições de campo provenientes da vinhaça nos canais e tanques e também em laboratório em um estudo de incubação. O terceiro estudo avaliou a microbiota funcional associada à emissão de CH4 através de técnicas independentes de cultivo, como PCR em tempo real (qPCR) e pirosequenciamento. As análises microbiológicas indicaram que as emissões de CH4 são produzidas, preferencialmente, através da decomposição anaeróbia do material orgânico dissolvido da vinhaça depositados no fundo dos sistemas. Estas emissões não são desprezíveis e devem ser consideradas nos cálculos de pegada de carbono do etanol. Nos canais sem revestimento a emissão média em dois anos safras consecutivos apresentou valor de 0,75 kg CO2 eq m-3 de vinhaça, aproximadamente 5 vezes superior às emissões na parte revestida. Nos tanques a emissão foi aproximadamente setenta vezes inferior quando comparada ao canal revestido. O experimento de incubação auxiliou no entendimento de que a vinhaça sozinha não produz quantidades significativas de CH4. Entende-se que os nichos microbianos metanogênicos provavelmente são formados no sedimento, enquanto que a vinhaça mantém as condições de anaerobiose do sedimento necessárias à metanogênese e fornece nutrientes para acelerar a reação. O gênero Methanobrevibacter se mostrou dominante na comunidade microbiana metanogênica, conforme demonstrado pelo pirosequenciamento do gene 16S rRNA. Houve correlação positiva entre a abundância do gene 16S rRNA de Arquéia e dos genes funcionais mcrA e mba com a emissão de CH4. As informações sobre produção e emissão de CH4 e das características da vinhaça constituem informações importantes para tomada de decisão sobre a mitigação e/ou aproveitamento do CH4 gerado para fins econômicos e ambientais.This research aimed to quantify methane (CH4) emissions from the vinasse in different storage and transportation systems and, additionally, to evaluate the functional microbiota associated with the production of this gas by molecular biology approaches. Three complimentary studies were performed to reach this goal. The first one was related to the characterization of main vinasse storage and transportation systems adopted in Brazil based on a survey administered to the mills, in south-central region of Brazil, producing sugarcane etanol. The second aimed to quantify the CH4 emissions from vinasse in both, field - channels and thanks - and laboratory conditions. The third study evaluated the functional microbiota associated with the CH4 emission by molecular biology approaches like real time PCR ans pyrosequencing. Microbial analysis indicated that CH4 emissions are produced preferably by anaerobic decomposition of the organic material dissolved in the vinasse and deposited on the bottom of the systems. These emissions are not negligible and should be considered in ethanol\'s carbon footprint calculations. At the uncoated part of the channel, the average emission from two crop years was 0.75 kg CO2 eq m-3 of vinasse, about 5 times greater than the emissions at the coated part. Methane emissions from the tank were about seventy times lower than from the uncoated channel. The laboratory experiment supported the understanding that the vinasse alone produces no significant emission of CH4. The microbial methanogenic niches were probably formed in the sediment, while the vinasse keeps sediment anaerobic conditions necessary for methanogenesis and provides nutrients to speed up the reaction. The Methanobrevibacter genus showed dominant in methanogenic microbial community, as demonstrated by pyrosequencing of the 16S rRNA gene. There was a positive correlation between the abundance of 16S rRNA gene Archaea and the functional mcrA and mba genes with the emission of CH4. Information on production and emission of CH4 and vinasse characteristics are important for decision making on mitigation and/or use of gas generated for economic and environmental purposes.
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Gomez, de Leija Rodrigo [Verfasser] y R. [Akademischer Betreuer] Stieglitz. "Measurement and qualification of the local heat transfer and pressure losses in high turbulent gas flows in channels with different artificial surface structures / Rodrigo Gomez de Leija ; Betreuer: R. Stieglitz". Karlsruhe : KIT-Bibliothek, 2018. http://d-nb.info/117235166X/34.
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Carter, Rachel C. "Submarine Channel Evolution Linked to Rising Salt Dome, Mississippi Canyon, Gulf of Mexico". ScholarWorks@UNO, 2015. http://scholarworks.uno.edu/td/2060.
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By examining halokinetics and channel evolution in a deep-water system, we investigate how submarine channel morphology is affected by changing seascape linked to diapirism. The study area is located in Mississippi Canyon, Gulf of Mexico (GOM), situated directly off the continental slope in a prominent salt dome region. Interactions of salt domes with submarine channels in the GOM are poorly documented. Utilizing 3D seismic data and seismic geomorphology techniques, a long-lived Plio-Pleistocene submarine channel system has been investigated to develop a relationship between variable phases of salt movement and plan-form morphology of preserved channels.
We suggest that halokinetics acts as a driver for topographic-channel evolution in the study area. We show how submarine channel morphology can be directly controlled by halokinetics, where salt movement can act as a structural control on both location and morphology of meandering channel complexes. Channels are able to move towards an equilibrium state only when holokinetics decreases.
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Carrara, Brent. "Air-Gap Covert Channels". Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35103.
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A fresh perspective on covert channels is presented in this work. A new class, air-gap covert channels, is defined as an unintentional communication channel established between systems that are physically and electronically isolated from one another. A specific class of air-gap covert channel is studied in depth, out-of-band covert channels (OOB-CCs), which are defined as policy-breaking communication channels established between isolated, physically unmodified systems. It is shown that OOB-CCs can be categorized by the physical channel that they communicate over: acoustic, light, seismic, magnetic, thermal, and radio-frequency, and the hardware that is required at the transmitter and receiver to make covert communication possible. In general, OOB-CCs are not as high-bandwidth as conventional radio-frequency channels; however, they are capable of leaking sensitive information that requires low data rates to communicate (e.g., text, recorded audio, cryptographic key material). The ability for malware to communicate information using a specific type of OOB-CC, the covert-acoustic channel, is also analyzed. It is empirically demonstrated that using physically unmodified, commodity systems (e.g., laptops, desktops, and mobile devices), covert-acoustic channels can be used to communicate at data rates of hundreds of bits per second, without being detected by humans in the environment, and data rates of thousands of bits per second when nobody is around to hear the communication. Defence mechanisms to counter covert-acoustic channels are also proposed and evaluated, and, as a result, best practices for the designers of secure systems and secure facilities are presented. Additionally, the covertness of OOB-CCs, i.e., the amount of data that can be leaked before the channel is detected, is also determined for classical communication channels as well as for covert-acoustic channels.
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Pouliquen, Benoît. "Two phase, gas liquid flow through a vertical channel". Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63182.
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Jerome, Tiphaine. "Stratégie(s) de diffusion volontaire d’informations sur les gaz à effet de serre : Le cas du Carbon Disclosure Project". Thesis, Jouy-en Josas, HEC, 2013. http://www.theses.fr/2013EHEC0010/document.
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Le réchauffement climatique représente un enjeu prégnant auquel les entreprises répondent, entre autres, par la diffusion volontaire d’informations sur leurs émissions de gaz à effet de serre (GES). Trois études empiriques, traitant pour chacune d’elle une dimension de la stratégie mise en place par les firmes à cet égard, sont menées. Elles sont toutes trois réalisées à partir du programme Carbon Disclosure Project. La première étude identifie deux étapes séquentielles conduisant à la diffusion d’informations sur les GES : la production puis la diffusion sélective. À partir d’un échantillon mondial, une analyse coûts-bénéfices identifie les différents déterminants de ces deux décisions et invite à considérer de manière plus fine le processus de diffusion volontaire. La deuxième étude examine l’influence de la gouvernance interne sur la qualité des informations carbones diffusées, en distinguant la gouvernance spécifiquement dédiée à l’environnement de la gouvernance générale. Les analyses mettent en évidence, dans le contexte américain, le rôle contingent de la gouvernance spécifique puisque son rôle ‒ positif ‒ est modéré par la gouvernance générale dans laquelle elle s’insère. La troisième étude s’intéresse finalement à l’utilisation concomitante de deux canaux de diffusion. Il s’avère qu’une partie des entreprises françaises étudiées adapte les indicateurs diffusés sur les GES au canal et à l’audience ciblée. Afin d’assurer la crédibilité des données, la traçabilité de l’information est par ailleurs renforcée. L’ensemble de ces résultats contribue à la compréhension de la façon dont les besoins des parties prenantes sont gérés par les entreprises. Notre connaissance de l’environnement informationnel créé par ces dernières autour du changement climatique s’en trouve ainsi amélioréeGlobal warming is nowadays a significant issue. Firms respond to this challenge by, among others, voluntarily disclosing information about their greenhouse gas (GHG) emissions. Three empirical studies, each dealing with one dimension of the disclosure strategy, are conducted. They are all based on the Carbon Disclosure Project program. The first study identifies two sequential steps leading to information disclosure: information production and selective disclosure. A costs-benefits analysis is performed on a global sample in order to identify the different determinants of the two decisions and calls for a finer consideration of the disclosure process. The second study examines the influence of internal corporate governance on the quality of carbon information disclosed. Environmental-specific governance is distinguished from general governance. In the American context, analyses show that the role of the environmental-specific governance is contingent: its positive influence is moderated by the general governance context. The third study focuses on the concurrent use of two disclosure channels. It appears that French firms adapt the content of their GHG emissions indicator to the channel and the target audience. To ensure data credibility, information traceability is sustained in this case.Overall, this dissertation contributes to our understanding of the way stakeholders’ needs are managed by companies. Our knowledge of the informational environment created by firms about global warming is thus improved
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Wang, Fei. "Gas-Solid Fluidization: ECVT Imaging and Mini-/Micro-Channel Flow". The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1290390285.
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Banerjee, Arindam. "Statistically steady measurements of Rayleigh-Taylor mixing in a gas channel". Texas A&M University, 2006. http://hdl.handle.net/1969.1/4183.
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A novel gas channel experiment was constructed to study the development of
high Atwood number Rayleigh-Taylor mixing. Two gas streams, one containing air
and the other containing helium-air mixture, flow parallel to each other separated by
a thin splitter plate. The streams meet at the end of a splitter plate leading to the
formation of an unstable interface and of buoyancy driven mixing. This buoyancy
driven mixing experiment allows for long data collection times, short transients and
was statistically steady. The facility was designed to be capable of large Atwood
number studies of ABtB ~ 0.75. We describe work to measure the self similar evolution
of mixing at density differences corresponding to 0.035 < ABtB < 0.25. Diagnostics
include a constant temperature hot-wire anemometer, and high resolution digital
image analysis. The hot-wire probe gives velocity, density and velocity-density
statistics of the mixing layer. Two different multi-position single-wire techniques
were used to measure the velocity fluctuations in three mutually perpendicular
directions. Analysis of the measured data was used to explain the mixing as it
develops to a self-similar regime in this flow. These measurements are to our knowledge, the first use of hot-wire anemometry in the Rayleigh-Taylor community.
Since the measurement involved extensive calibration of the probes in a binary gas
mixture of air and helium, a new convective heat transfer correlation was formulated
to account for variable-density low Reynolds number flows past a heated cylinder. In
addition to the hot-wire measurements, a digital image analysis procedure was used
to characterize various properties of the flow and also to validate the hot-wire
measurements. A test of statistical convergence was performed and the study
revealed that the statistical convergence was a direct consequence of the number of
different large three-dimensional structures that were averaged over the duration of
the run.
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Welsh, Susan A. "Hydrodynamic characteristics of countercurrent gas-pseudoplastic liquid two-phase channel flow". Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/16923.
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Stinson, Michael J. "Interphase transfer processes in cocurrent two phase channel flow". Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/17215.
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Shimoura, Susumu. "VARIOUS INTERMEDIATE CHANNELS IN 12C+12C→12C[g.s.]+α+8Be[g.s.] REACTION". 京都大学 (Kyoto University), 1986. http://hdl.handle.net/2433/212050.
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Zhou, Gang. "Relationship marketing strategies at distribution channel in gas appliance market in Guangdong". Thesis, University of Macau, 2000. http://umaclib3.umac.mo/record=b1636678.
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Tanaka, Futoshi. "Study on boiling heat transfer in narrow gap channels". Kyoto University, 2007. http://hdl.handle.net/2433/135594.
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Kyoto University (京都大学)0048
新制・論文博士
博士(エネルギー科学)
乙第12068号
論エネ博第49号
新制||エネ||37(附属図書館)
UT51-2007-H623
京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻
(主査)教授 三島 嘉一郎, 教授 代谷 誠治, 教授 功刀 資彰
学位規則第4条第2項該当
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APPASWAMY, ARAVIND C. "SIMULATION OF SHORT CHANNEL AlGaN/GaN HEMTs". University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1109277211.
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Conteau, Delphine. "Développement d’outils pour l’étude des écoulements diphasiques dans les canaux d’une pile à combustible de type PEM". Thesis, Vandoeuvre-les-Nancy, INPL, 2011. http://www.theses.fr/2011INPL036N/document.
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Parmi les nombreuses problématiques liées à la PEMFC, l'eau est un point crucial car elle est à la fois indispensable et indésirable dans le coeur de pile. En effet, les flux gazeux qui alimentent le système en réactifs sont humidifiés pour que la membrane soit convenablement hydratée afin de faciliter le transport des protons de l'anode vers la cathode. Mais à cet apport initial vient s'ajouter l'eau produite par la réaction électrochimique. Des gouttes d'eau liquide peuvent alors se former dans les pores des couches actives et peuvent grossir jusqu'à boucher les canaux des plaques d'alimentation en gaz. Ce travail de thèse est centré sur l'étude des écoulements gaz-liquide dans ces canaux, dont le diamètre hydraulique est de l'ordre du millimètre. Dans un premier temps, des micro-capteurs ont été mis au point pour détecter la présence d'eau liquide. Après une phase de tests en maquette froide, ces micro-capteurs ont été insérés dans une cellule de 25 cm2 de surface active, identique à celles étudiées au LRGP. Ceci a permis de montrer que dans une pile en fonctionnement, les fluctuations de tension sont liées à la présence d'eau liquide. Par ailleurs, des corrélations existantes ont été utilisées pour prédire les pertes de charge engendrées par la présence de deux phases dans les mini-canaux. Ces calculs ont été comparés aux mesures expérimentales, mettant en évidence l'influence de la couche de diffusion des gaz, située entre les canaux et la membrane, et l'importance des conditions opératoires.Ces méthodes originales viennent compléter les outils de diagnostic existants sans demander d'appareillage complexe et coûteux, ni nécessiter le développement de matériel spécifique, non optimisé pour une utilisation commercialeWater management is a critical issue in the operation of proton exchange fuel cells (PEMFC). On one hand, the membrane must be sufficiently hydrated to allow the transport of protons from the anode side to the cathode side. But on the other hand, supersaturation of water vapour in the gas phase results in liquid water formation, which can be detrimental to the fuel cell operation. Liquid water can clog up the porous structure of the gas diffusion layer (GDL) and hinder the transport of gases in the catalyst layer. Liquid accumulation can also lead to the formation of water columns inside the gas flow channels, thus preventing the fuel gas from flowing into the reaction area.Micro-sensors have been designed to detect the presence of liquid water. Three of them were inserted inside the gas distribution channels of a 25 cm2 cell. The tests run with this equipped cell highlighted the link between the presence of liquid water and the variations of the cell voltage. Besides, existing correlations were used to calculate the pressure drop between the inlet and the outlet of the cathode channel due to two-phase flow during the cell operation. The results of this calculation were compared with experimental results. This part of the study highlighted the influence of the GDL and of the operating conditions on the flows inside the channels
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Krishnamurthy, Nagendra. "Investigation of Fouling in Wavy-Fin Exhaust Gas Recirculators". Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/32012.
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This dissertation presents a detailed account of the study undertaken on the subject of fouling of Exhaust Gas Recirculator (EGR) coolers. The fouling process in EGR coolers is identified to be due to two primary reasons â deposition of fine soot particles and condensation of hydrocarbons known as dry soot and wet soot fouling, respectively. Several numerical simulations are performed to study the fouling process. Preliminary analysis of the particle forces for representative conditions reveal that drag, thermophoresis and Brownian forces are the significant transport mechanisms and among them, the deposition process is dominated by thermophoresis. Soot deposition in a representative turbulent plain channel shows a direct relationship of the amount of deposition with the near-wall temperature gradient. Subsequently, periodic and developing flow simulations are performed on a wavy channel geometry, a common EGR design for various Reynolds numbers and thermal boundary conditions. Constant heat flux boundary condition is used in the periodic fully-developed calculations, which assist in establishing various deposition trends. The wavy nature of the walls is noted to affect the fouling process, resulting in specific deposition patterns. For the lower Reynolds number flows, significantly higher deposition is observed due to the higher particle residence times. On the other hand, the developing flow calculations facilitate the use of wall temperature distributions that typically exist in EGR coolers. The linear dependence of the amount of deposition on the near-wall temperature gradient or in other words, the heat flux, is ascertained. It is also observed in all the calculations, that for the sub-micron soot particles considered, the deposition process is almost independent of the particle size. In addition, the nature of the flow and heat transfer characteristics and the transition to turbulence in a developing wavy channel are studied in considerable detail. Finally, a study on the condensation of heavy hydrocarbons is undertaken as a post-processing step, which facilitates the prediction of the spatial distribution and time-growth of the combined fouling layer. From the calculations, the maximum thickness of the dry soot layer is observed to be near the entrance, whereas for the wet soot layer, the peak is found to be towards the exit of the EGR cooler. Further, parametric studies are carried out to investigate the effect of various physical properties and inlet conditions on the process of fouling.Master of Science
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Talbot, Krystle. "Zebrafish (Danio rerio) Aquaporin 1a as a Multi-functional Transporter of Water, CO2, and Ammonia". Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31076.
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Previous in vitro studies have demonstrated that AQP1, traditionally viewed as a water channel, also facilitates the passage of CO2 and ammonia across cell membranes. This thesis summarizes the first in vivo studies confirming a physiologically-relevant role for AQP1 in acid-base balance and nitrogenous waste excretion. Zebrafish embryos were microinjected with a translation-blocking morpholino oligonucleotide targeted to the zebrafish AQP1 paralog, AQP1a. Closed-system respirometry, total CO2 analysis, tritiated water fluxes and measurement of ammonia excretion were performed on larvae at 4 days post-fertilization (dpf). Knockdown of AQP1a significantly reduced rates of water, CO2 and ammonia excretion. Use of phenylhydrazine, a haemolytic agent, provided evidence that the yolk sac epithelium AQP1a (and not erythrocyte AQP1a) is the major site of CO2 and ammonia movements. Further, the hypothesis that AQP1a and the Rh glycoprotein Rhcg1, another multi-functional gas channel, act in concert to regulate CO2 and ammonia excretion was explored. Exposure to conditions impairing ammonia excretion (such as high external ammonia (HEA) or alkaline water) modulated AQP1a protein expression in 4 dpf zebrafish larvae experiencing knockdown of Rhcg1. Chronic HEA exposure triggered a significant compensatory increase in AQP1a protein abundance in Rhcg1 morphants. Exposure of Rhcg1 morphants to pH 10 water, however, caused a significant decrease in AQP1a protein expression. Interestingly, when AQP1a mRNA and protein levels were examined in Rhcg1 morphants and vice versa, no changes were observed. Overall, zebrafish AQP1a was found to be a multi-functional transporter of water, CO2 and ammonia, though the exact relationship it holds with other such gas channels bears further exploration.
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Miller, Hennessy Felicia y Hennessy Felicia Miller. "Assessment of Ephemeral Channel Cross-Section Morphology Following Pipeline Construction in Southern Arizona". Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/624133.
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Morphologic change of ephemeral stream cross-sections is a natural component of fluvial geomorphology but disruptions to natural erosion and deposition by anthropogenic disturbances has the potential for cascading impacts down the channel corridor. The proximal impact of a natural gas pipeline construction on ephemeral stream cross-section geometry in southern Arizona was evaluated from July 2014 (pre-construction) to July 2016 (two years post construction). Cross-sections at three locations (upstream the pipeline Right-Of-Way (ROW)), through the middle of the ROW, and downstream of the ROW) were measured using Light Detection And Ranging (LIDAR) and field methods for 16 ephemeral streams. Results of both the LIDAR and field measurements indicated insignificant difference in cross-sectional area change between upstream, across, and downstream-ROW cross-sections [(F 2,64) = 0.341, p = 0.73; (F2,18)= 0.980, p = 0.395]. Sediment generated during pipeline construction appeared to have moved beyond the physical confines of the study site, which limited the assessment of larger-scale geomorphic impacts. Furthermore, the 2014-2016 study period experienced only small (high-recurrence frequency) precipitation events, indicating the absence of large flows capable of significant morphologic change. To further explain differences in cross-section area change between LIDAR datasets, a linear regression model was used to assess the predictive value of nine variables: year of measurement, drainage area, drainage density, basin slope, upstream-, across-, downstream-ROW cross-section locations, percent bare soil in basin, percent mesquite in basin, total precipitation, and number of storms with average precipitation above 25 mm/hour. Though the amount of bare soil in the basin and the second study period (February 2015-July 2016) at least partially explained the changes in cross-section area, the model was not a strong predictor of morphologic change during the 2014-2016 study period. The majority of the variability in cross-sectional area change in the study basins remained unexplained.
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Leung, Ho Wing. "Theoretical and numerical analysis of high-explosive channel detonation using real-gas models". Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:8881/R/?func=dbin-jump-full&object_id=92306.
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Grünker, Ronny, Irena Senkovska, Ralf Biedermann, Nicole Klein, Martin R. Lohe, Philipp Müller y Stefan Kaskel. "A highly porous flexible Metal–Organic Framework with corundum topology". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-138599.
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A flexible Metal–Organic Framework Zn4O(BenzTB)3/2 (DUT-13) was obtained by combination of a tetratopic linker and Zn4O6+ as connector. The material has a corundum topology and shows the highest pore volume among flexible MOFsDieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
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Haapala, A. (Antti). "Paper machine white water treatment in channel flow:integration of passive deaeration and selective flotation". Doctoral thesis, Oulun yliopisto, 2010. http://urn.fi/urn:isbn:9789514263682.
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Abstract
Gas removal from the papermaking process is currently a standard practice, whereas purification of the internal water circulation has become common only recently. Both unit processes have progressed greatly during recent decades and new concepts are constantly being developed. The aim of this thesis was to analyse the efficiency and applicability of a channel flow design introduced by Metso for passive white water deaeration and to study the dynamics of passive bubbly gas removal. In addition, separation of the detrimental process water components by selective flotation during deaeration was studied to add further functionality to the channel flow design.
Turbulent mixing at the flow discharge and the consequent air entrainment were seen to limit the gas separation efficiency. Also, the properties of different white waters notably affect their deaeration through viscous forces, the concentration of surface active components and bubble-particle interactions. Thus similar levels of gas separation cannot be achieved with all process waters. The analysis showed that the drag of small microbubbles is mostly caused by hydrophobic contamination and the dispersed particles that readily attach to the bubbles. Correlations were derived based on experimental data to provide new information on the drag force experienced by small bubbles in white waters.
Chemically unaided flotation of white water in the channel flow was shown to be efficient in separating hydrophobic contaminants that have adverse effects on paper machine production and product quality. Both good reductions in contaminant content and high selectivity in their removal were achieved. Channel flow with an overflow can be considered well suited for the first stage of froth separation, while further treatment of the channel flow reject may consist of a secondary flotation or other process that enables the recirculation of fines and fillers. Although a certain level of losses of fines and fillers must be expected, substantial fraction of these solid components can be returned to the process stream.
The proposed multifunctional process, channel flow deaeration and frothing of white water, was seen to be straightforward, economical and feasible while also providing benefits in terms of total process efficiency that are not delivered by any current process scheme. The experimental parameters presented here regarding bubble dynamics and flotation efficiency can be used to achieve better models of these processes.
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Calvanese, Giordano. "Volumetric deep learning techniques in oil & gas exploration". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20556/.
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This work consisted in the study and application of volumetric Deep Learning (DL) approach to seismic data provided by Eni S.p.A., with an industrial utility perspective.
After a series of fruitful meetings with the Upstream & Technical Services team, we clearly defined the final objective of this approach: the automatic search for geological structures such as turbidite channel-bases, as potential regions of interest for the Oil & Gas industry. Therefore, we defined a workflow based on the training of volumetric DL models over seismic horizons containing channel bases providing “windrose” input patches, i.e. a planar approximation of a three-dimensional volume.
All components and sources of criticality were systematically analyzed. For this purpose we studied: the effect of preprocessing, the contribution of the dataset augmentation, the sensitivity for the channel-base manual segmentation, the effect of the spatial expansion of the input patches. Evaluating both qualitatively and quantitatively through K-fold cross-validation.
This work showed: how an appropriate preprocessing of the original data substantially helps DL models, how the dataset augmentation is fundamental for good model generalization given the poor representativity of the accessible examples compared to all possible configurations, how this DL approach is susceptible to the channel-base segmentation imposing to invest sufficient effort in the generation of reliable labels, how the size of input patches must be large enough to allow models to perceive around each voxel the structure concavity and the texture of any sediment infill.
We conclude that the volumetric DL approach developed in this work has proved to be very promising.
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Ayash, Ahmed. "Counter-current gas-liquid contacting in a rotating spiral channel : experimental and theoretical study". Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/21622/.
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Controlled counter-current contacting between a gas and a liquid forms the basis for a wide range of chemical separation operations, including absorption, stripping and distillation. A radical technique based on the rotating of a spiral channel can achieve segregation of any two immiscible phases into two parallel layers, allowing for a detailed control of phase flow rates and phase layer thicknesses. This work experimentally and theoretically studied the mass transfer process of gas-liquid contacting in this novel contactor, aiming for understanding, evaluating and demonstrating its performance. In order to establish the spiral performance, experiments were conducted over a wide range of contacting conditions. In the experiments, desorption of four different organic solutes from water was studied separately at dilute concentrations, using air as a sweeping gas. The solutes were ethanol, acetonitrile, acetone and 2-butanone (MEK). This collection of solutes at different spiral temperatures (24, 30 and 49°C) gives a range of solute equilibrium distributions (f) from 0.232 to 5.5 (the mole fraction ratio of solute in the two phases). Thus, the performance of the rotating spiral channel was explored using phase and solute systems having different equilibrium characteristics (f) and solute transferring properties. The other contacting conditions were the pressure and the rotation rate, which were fixed to 1.8 bara and 3200 rpm, respectively. For each phase and solute system (f), the amount of solute desorbed was measured over a range of phase flow rates. Interestingly, the results showed that a fixed channel design can process a variety of systems at any desired conditions, producing solute-free water when operating at the appropriate phase flow rate ratio. Furthermore, the experimental results showed a universal peak in the mass transfer coefficient at a liquid layer thickness between 80-90 μm. The peak occurred independently of the gas phase flow rate and appeared prominently for the systems with large f, where the mass transfer was much affected by the liquid phase. This finding indicates that independent adjustment of the liquid phase flow rate could determine the optimum contacting and this optimum can be tailored to occur at any desired phase flow rates ratio by changing only the gas phase flow rate. Thus, simultaneously, the optimal contactor size and solvent usage could be achieved with rotation spiral contacting. In addition, the spiral performance, based on the extensive data of the current work, was compared to the performance for the conventional packed column, rotating packed beds and the membrane microchannel using data from the literature for these contactors. The normalised total specific throughput (molar flow rate of the treated stream divided by the contactor volume) was developed here and used as the comparison criterion. The maximum of this measure corresponds to a minimum contactor volume to achieve a given separation task. The comparison showed that the rotating spiral was able to operate in the appropriate range of phase flow rate ratios and gave the highest specific throughput. This suggests that the contactor size for this method can be many times smaller than that of the other methods considered. A two-dimensional (2-D) computational model was adopted in this work to study the detail of the flow and species fields that determine the mass transfer process. This model is based on a novel combination of the governing equations and an existing interface model to capture accurately the Coriolis acceleration effects and phase interactions. The 2-D model effectively predicted a wide range of experimental conditions, demonstrating that Coriolis secondary motion could double the mass transfer performance. A parametric study was also conducted using the 2-D model, where desorption of acetone was taken as a reference case. The purpose of this study was to examine the role of three key parameters (rotation rate, channel aspect ratio and flow rate of both phases) that were not tested experimentally. The results demonstrated that by adjusting the rotation rate, the contacting process could be optimised. For a range between 1000 and 20,000 rpm, it was found that the rotation rate of 16,000 rpm gave a maximum mass transfer coefficient. Furthermore, the data showed that the spiral performance was enhanced considerably by changing the channel aspect ratio. Reducing the channel width from 4 mm to 1 mm increased the mass transfer coefficient by a factor of two. Finally, at a given rotation rate and channel aspect ratio, an improvement in mass transfer was observed by adjusting the flow rates of the contacting phases. Increasing the flow rate of both phases increased the mass transfer coefficient also by a factor of two. In general, the experimental and theoretical work in this thesis demonstrates the potential of rotating spiral contacting and establish a useful foundation underpinning its future development.
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Lee, Jeongik. "Gas heat transfer in a heated vertical channel under deteriorated turbulent heat transfer regime". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/41296.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007.Includes bibliographical references (p. 283-289).
Passive cooling via natural circulation of gas after a loss of coolant (LOCA) accident is one of the major goals of the Gas-cooled Fast Reactor (GFR). Due to its high surface heat flux and low coolant velocities under natural circulation in post-LOCA scenarios, the capability of turbulent gas flow to remove heat from the GFR core can be impaired by either a buoyancy effect or an acceleration effect. These phenomena lead to a Deteriorated Turbulent Heat Transfer (DTHT) regime. To predict accurately the cladding temperature at the hot spot, reliable heat transfer correlations that account correctly for these effects are needed. This work addresses this need by experimentally obtaining heat transfer data and developing new heat transfer correlations that can be used in system analysis codes, such as RELAP5-3D, to reduce uncertainties of predictions in these DTHT regimes. An experimental facility was designed and built using similitude analysis to match key experimental loop parameters to the GFRs' Decay Heat Removal (DHR) system operating conditions to the largest extent possible. Through a thorough literature survey two non-dimensional numbers namely (1) the buoyancy parameter (Bo*) and (2) the acceleration parameter (K,) were identified as important indicators of the DTHT regime. The experimental data was collected for a range of (1) inlet Reynolds number from 1800 to 42,700, (2) inlet Bo* up to 1X10-5 (3) and inlet Kv up to 5x10-6. The data showed significantly higher reduction of the Nusselt number (up to by 70%) than previously reported (up to 50%). Also, the threshold at which DTHT regime occurs was found to be at smaller non-dimensional numbers than previously reported. A new phenomenon "re-turbulization", where the laminarized heat transfer recovers back to turbulent flow along the channel, was observed in the experiment.
(cont.) A new single phase gas flow heat transfer map is proposed based on the non-dimensional heat flux and the Reynolds number in our data, and is shown to compare well with data in the literature. Three sets of new correlations were developed, which reflect both the buoyancy and acceleration effects and have better accuracy as well as ease of numerical implementation than the existing correlations. The correlations are based on the Gnielinski correlation and replace the Reynolds number subtracting constant by a functional form that accounts for the buoyancy and acceleration effects separately, or in the combined form through a newly introduced non-dimensional "DTHT" number. The three correlation types have different complexity level, with the first being the most complex and the third being the most simple and easy to apply without any need for iterations. Additional runs with natural circulation showed that the friction factor in the DTHT regime could be significantly higher than predicted by conventional friction factor correlations, although more experiments will be needed to develop reliable correlations for pressure drop in these regimes. Overall, it is concluded that due to the low heat transfer coefficient and increased friction factor in the DTHT regime, the GFR DHR system should be ideally designed to operate outside the DTHT regime to (1) avoid reduction of heat transfer capability, (2) avoid increase of pressure drop, and (3) reduce uncertainties in predictions of the cladding temperature.
by Jeongik Lee.
Ph.D.
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Slabaugh, Carson. "HEAT TRANSFER AUGMENTATION IN A NARROW RECTANGULAR DUCT WITH DIMPLES APPLIED TO A SINGLE WALL". Master's thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2172.
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Establishing a clean and renewable energy supply is the preeminent engineering challenge of our time. Turbines, in some form, are responsible for more than 98 percent of all electricity generated in the United State and 100 percent of commercial and military air transport. The operation of these engines is clearly responsible for significant consumption of hydrocarbon fuels and, in turn, emission of green house gases into the atmosphere. With such wide-scale implementation, it is understood that even the smallest increase in the operating efficiency of these machines can lead to enormous improvements over the current energy situation. These effects can extend from a reduction in the emission of greenhouse gases to lessening the nation s dependence of foreign energy sources to lower energy prices for the consumer. The prominent means of increasing engine efficiency is by raising the  Turbine Inlet Temperature  the temperature of the mainstream flow after combustion, entering the first stage of the turbine section. The challenge is presented when these temperatures are forced beyond the allowable limits of the materials inside the machine. In order to protect these components, active cooling and protection methods are employed. The focus of this work is the development of more efficient means of cooling  hot turbine components. In doing so, the goal is to maximize the amount of heat removed by the coolant while minimizing the coolant mass flow rate: by removing a greater amount of heat with a lower coolant mass flow rate, more compressed air is left in the mainstream gas flow for combustion and power generation. This study is an investigation of the heat transfer augmentation through the fully-developed portion of a narrow rectangular duct (AR=2) characterized by the application of dimples to the bottom wall of the channel. Experimental testing and numerical modeling is performed for full support and validation of presented findings. The geometries are studied at channel Reynolds numbers of 20000, 30000, and 40000. The purpose is to understand the contribution of dimple geometries in the formation of flow structures that improve the advection of heat away from the channel walls. Experimental data reported includes the local and Nusselt number augmentation of the channel walls and the overall friction augmentation throughout the length of the duct. Computational results validate local Nusselt number results from experiments, in addition to providing further insight to local flow physics causing the observed surface phenomena. By contributing to a clearer understanding of the effects produced by these geometries, the development of more effective channel-cooling designs can be achieved.M.S.M.E.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering MSME
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Choueiri, George H. "Experimental Investigations of Flow Development, Gap Instability and Gap Vortex Street Generation in Eccentric Annular Channels". Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31017.
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Isothermal flow development, gap instability, and gap vortex street generation in eccentric annular channels have been studied experimentally. A representative paradigm of a flow in a highly eccentric annular channel was examined for a channel having an inner-to-outer diameter ratio d/D = 0.50 and an eccentricity e = 0.8 for a Reynolds number Re = 7300. Observation of the flow development has identified three distinct regions: the entrance region, the fluctuation-growth region and the rapid-mixing region. Weak quasi-periodic velocity fluctuations were first detected in the downstream part of the entrance region, and grew into very strong ones, reaching peak-to-peak amplitudes in the narrow gap that were nearly 60% of the bulk velocity. The dependence on inlet conditions, d/D, e and Re on the development and structure of flows was also investigated. Experimental conditions covered the ranges: 0 ≤ Re ≤ 19000, 0 ≤ e ≤ 0.9 and d/D = 0.25, 0.50 and 0.75. For Re < 7000, the Strouhal number, the normalized mid-gap axial flow velocity and the axial and cross-flow fluctuation intensities at mid-gap were found to increase with increasing Re and to depend strongly on inlet conditions. At higher Re, however, these parameters reached asymptotic values that were only mildly sensitive to inlet conditions. A map was constructed for the various stages of periodic motions vs. e and Re and it was found that, for e < 0.5 or Re < 1100, the flow was unconditionally stable as far as gap instability is concerned. For e ≤ 0.5, transition to turbulence occurred at Re ≈ 6000, whereas, for 0.6 ≤ e ≤ 0.9, the critical Reynolds number for the formation of periodic motions was found to increase with eccentricity from 1100 for e = 0.6 to 3800 for e = 0.9. The use of an empirically derived "mixing layer Strouhal number" permitted a universal description of gap vortex street periodicity in eccentric annular channels. This study has contributed to our understanding of the physical mechanisms that lead to gap instability and the development of a gap vortex street and the dependence of these flow phenomena on the channel geometry and the dynamic conditions of the flow.
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Wu, Mo. "AlGaN/GaN Dual Channel HFETs and Realization of GaN Devices on different substrates". VCU Scholars Compass, 2012. http://scholarscompass.vcu.edu/etd/403.
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GaN-based HFETs demonstrate ubiquitous high power and high frequency performance and attract tremendous research efforts. Even though significant advances have been achieved, there still exist some critical issues needed to be investigated and solved. In particular, high defect densities due to inhomogeneous growth and operation under high power conditions bring many unique problems which are not so critical in the conventional Si and GaAs materials systems. In order to reduce the defect density and heat dissipation of GaN-based HFETs, research work on the realization of GaN-based HFETs on bulk GaN substrate has been carried out and the key problems have been identified and solved. Hot phonon scattering is the bottleneck which limits the enhancement of electron velocity in the GaN 2DEG channel. It is found that the plasmon-phonon coupling is the mechanism for converting of hot phonons into high group velocity acoustic phonons. In order to push more electrons into the GaN 2DEG channel in the plasmon-phonon coupling regime and to further reduce the hot phonon lifetime, a novel AlGaN/GaN dual channel HFET structure has been proposed. The growth, fabrication and characterization of such a AlGaN/GaN dual channel HFET structure has been carried out. Conventionally GaN-based light emitting diodes and laser diodes are grown and fabricated using the c-plane III-nitride expitaxy layers. In c-plane III-nitride epi-layers, the polarization-induced electric field introduces spatial separation of electron and hole wave functions in quantum wells (QW)s used LEDs and laser diodes LDs and degrades quantum efficiency. As well, blueshift in the emission wavelength becomes inevitable with increasing injection current unless very thin QWs are employed. The use of nonpolar orientations, namely, m-plane or a-plane GaN, would solve this problem. So far, m-plane GaN has been obtained on LiAlO2 (100), m-plane SiC substrates, and m-plane bulk GaN, which all have limited availability and/or high cost. Silicon substrates are very attractive for the growth of GaN due to their high quality, good thermal conductivity, low cost, availability in large size, and ease with which they can be selectively removed before packaging for better light extraction and heat transfer when needed To realize the low cost and improve the internal quantum efficiency of GaN based light emitting diodes, the process for m-plane GaN growth on Si (112) substrates has been studied and optimized. The continuous m-plane GaN film is successfully grown on Si (112) substrates.
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Roclawski, Harald. "PIV Measurements of Channel Flow with Multiple Rib Arrangements". UKnowledge, 2001. http://uknowledge.uky.edu/gradschool_theses/303.
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A model of a gas turbine blade cooling channel equipped with turbulators and a backward facing step geometry was examined. Up to four turbulators oriented cross-stream and inclined 45° to the flow direction were mounted in the channel. The blockage ratio b/H of the turbulators and the height h/H of the backward facing step was 0:125 and 0:14 respectively. The number of turbulators as well as their size was varied. In a preliminary investigation, hot-wire and pressure measurements were taken for three different Reynolds numbers (5,000, 12,000, 18,000)in the center plane of the test section. Subsequently, particle image velocimetry (PIV) measurements were made on the same geometries. Results of PIV measurements for a Reynolds number range of Reb=600 to 5,000 for the turbulators and Reh=1,500 to 16,200 for the backward facing step are presented, where Reynolds numbers are based on turbulator height b and step height h, respectively. Plots of the velocity field, vorticity, reverse flow probability and RMS velocity are shown. The focus is on the steady flow behavior but also the unsteadiness of the flow is discussed in one section. Also reattachment lengths were obtained and compared among the various turbulator arrangements and the backward facing step geometry. It was found that the flow becomes periodic after three or four ribs. For one turbulator, a very large separation region was observed. The magnitude of the skin friction factor was found to be the highest for two ribs. If the first rib is replaced by a smaller rib, the skin friction factor becomes the lowest for this case. Compared to the backward facing step, the flow reattaches earlier for multiple turbulators. A dependency of reattachment length on Reynolds number was not observed.
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Achike, Francis Ifejika. "The cardiovascular responses to calcium channel blockers in rats subjected to blood gas/pH changes". Thesis, [Hong Kong] : University of Hong Kong, 1990. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12937095.
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Semeraro, Emanuele. "Experimental investigation on hydrodynamic phenomena associated with a sudden gas expansion in a narrow channel". Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066516/document.
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La vaporisation rapide du sodium liquide surchauffé est supposée être à l’origine des arrêts automatiques pour réactivité négative du réacteur Phénix.Un dispositif expérimental a été mis en œuvre pour reproduire la détente d'un gaz pressurisé, repoussant un liquide dans un canal de section rectangulaire très allongée.L’interface qui sépare les deux fluides, initialement plate, ondule du fait d'instabilités de Rayleigh-Taylor dont le caractère 2D est garanti par le rapport d'aspect de la section du canal. L’aire interfaciale augmente d'un facteur 50.L’expansion du gaz peut être divisée en deux phases principales : une phase dite « de Rayleigh-Taylor » (linéaire et non-linéaire) et une phase dite « à multi-structures » (transitionnelle et chaotique). La première est caractérisée par la dynamique de l'interface et l’aire interfaciale qui en résulte est proportionnelle à l’amplitude des ondulations. La deuxième est influencée par le comportement des structures liquides, dispersées dans la matrice gazeuse et l’aire interfaciale est alors proportionnelle au nombre de structures.La distribution de fraction volumique suggère un modèle d’écoulement composé de trois régions : une région où la frontière des bulles est clairement définie et régulière, une région compartimentée par des membranes liquides issues des frontières des bulles, une région diphasique formée de la queue de ces structures. L’analyse de sensibilité à la tension superficielle confirme que plus la tension est faible, plus les interfaces sont instables. Les ondes sont plus prononcées et plus de structures sont produites, ce qui conduit à une majoration du taux de production de l’aire interfacialeThe sharp vaporization of superheated liquid sodium is investigated. It is suspected to be at the origin of the automatic shutdown for negative reactivity, occurred in the Phénix reactor at the end of the eighties.An experimental apparatus has been designed and operated to reproduce the expansion of overpressurized air, superposed to water in a narrow vertical rectangular section channel.When expansion begins, the initial flat interface separating the two fluids becomes corrugated under the development of two-dimensional Rayleigh-Taylor instabilities. The interface area increases significantly and becomes even 50 times larger than the initial value. Since the channel is very narrow, instabilities along the channel depth do not develop.The gas expansion in a narrow channel can be divided into two main phases: Rayleigh-Taylor (linear and non-linear) and multi-structures (transition and chaotic) phases. The former is characterized by the dynamic of corrugated profile and the interface area results proportional to the amplitude of corrugation The latter is influenced by the behavior of the liquid structures dispersed in gas matrix and the interface area is mainly proportional to the number of liquid structures.The distribution of volume fraction suggests a model of channel flow consisting of three regions: the regular profile of peaks, the spike region and the structures tails. The analysis of sensibility to surface tension confirms that, with a lower surface tension, the fluids configuration is more unstable. The interface corrugations are more pronounced and more structures are produced, leading to a higher increment of the interface area
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Gürkaynak, Frank Kağan. "GALS system design side channel attack secure cryptographic accelerators". Konstanz Hartung-Gorre, 2006. http://e-collection.ethbib.ethz.ch/ecol-pool/diss/fulltext/eth16351.pdf.
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