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Dissertations / Theses on the topic 'Combustion Phenomena'
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Tutt, David Marcus. "The visual simulation of combustion phenomena." Thesis, University of East Anglia, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361489.
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Jager, Bram de. "Combustion and noise phenomena in turbulent alkane flames." Enschede : University of Twente [Host], 2007. http://doc.utwente.nl/58022.
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Graham, John Kenneth. "The preflame reactions of normal heptane in a motored engine." Thesis, City University London, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.232951.
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Giles, Karl. "Predicting abnormal combustion phenomena in highly booted spark ignition engines." Thesis, University of Bath, 2018. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760958.
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As powertrains and IC engines continue to grow in complexity, many vehicle manufacturers (OEMs) are turning to simulation in an effort to reduce design validation and calibration costs. Ultimately, their aim is to complete this process entirely within the virtual domain, without the need for any physical testing. Practical simulation techniques for the prediction of knock in spark ignition (SI) engines rely on empirical ignition delay correlations (IDCs). These IDCs are used to approximate the complex ignition delay characteristics of real and surrogate fuel compositions with respect to temperature, pressure and mixture composition. Over the last 40 years, a large number of IDCs have been put forward in the literature, spanning a broad range of fuels, operating conditions and calibration methods. However, the applicability of these tools has yet to be verified at the high brake mean effective pressure (BMEP) operating conditions relevant to highly boosted, downsized engines. Here, the applicability of 16 gasoline-relevant IDCs for predicting knock onset at high loads (BMEP > 30bar) has been investigated by comparing the knock predictions from each IDC against experimentally measured knock onset times. Firstly, a detailed investigation into cylinder pressure data processing techniques was performed to determine which knock detection and angle of knock onset (aKO) measurement methods were most appropriate at high loads. A method based on the maximum amplitude pressure oscillation (MAPO) during knock-free operation best estimated cycle classifications, whilst Shahlari’s Signal Energy Ratio technique [1] most accurately predicted knock onset. To the author’s knowledge, this is the first time that such a comprehensive study on the accuracy of these techniques at such high loads has been conducted. Importantly, these findings represent a valuable framework to inform other researchers in the field of knocking combustion on which techniques are needed to extract accurate and relevant information from measured cylinder pressure records. Secondly, the data processing techniques derived were applied to experimental data collected across a wide range of high BMEP operating conditions (up to a maximum of 32 bar) using a 1.6 litre, 4-cylinder SI engine. Trapped charge composition and temperature were predicted using a calibrated 1D model of the engine, whilst the temperature of a hypothetical hotspot in the unburned zone was estimated separately by assuming adiabatic compression from a point after intake valve closing and by mapping γ (the ratio of specific heat capacities) as a function of temperature. This revealed that none of the IDCs tested performed well at conditions relevant to modern, downsized engines. The IDC that achieved the best overall balance between aKO accuracy and cycle-classification agreement was the “cool-flame” correlation for iso-octane proposed by Ma [2]. However, this had an unacceptably high average aKO error of ±3.5° compared to the ±2°CA limit observed within the literature, and its average cycle-classification accuracy was below 60%. The main reason for this relatively modest accuracy was a large number of false-positive cycle classifications, which mainly occurred in slow or late burning cycles. Further work should therefore focus on methods to reduce the number of false positive classifications obtained with this correlation, which could be achieved using empirical correlations to describe the latest point in the cycle for which knock would be permitted to occur in terms other measureable combustion parameters. Overall, this research has generated a unique insight into combustion at very high loads, as well as an extensive dataset that can be used for future research to improve the accuracy of empirical knock modelling techniques. Furthermore, this work has demonstrated that for the purposes of virtual spark timing calibration and the avoidance of knock, the current crop of practical simulation tools is not accurate enough at the conditions relevant to modern SI engines and has provided a better understanding of their limitations. These findings represent a major contribution to the field from both a research perspective and for industrial applications.
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Singh, G. "Numerical study of the evolution of piston-driven detonation." Thesis, Cranfield University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278827.
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Koren, Chai. "Modeling conjugate heat transfer phenomena for multi-physics simulations of combustion applications." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC001/document.
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Dans un souci d’optimisation des fours industriels et de réduction des émissions de gaz à effet de serre,l’oxy-combustion est considérée comme l’une des solutions d’avenir. Les conditions existantes dans les chambres d’oxycombustion créent une interaction forte entre les différents phénomènes : Combustion,turbulence et transferts de chaleur. Pour mieux dimensionner les configurations futures il est nécessaire de pouvoir étudier la physique qui y règne, et ce pour un coût et un temps de retour raisonnables. De tels études nécessitent l’emploi d’outils de simulation de haute fidélité,et afin de modéliser les interactions inter-phénomènes à un coût acceptable le couplage de codes est utilisé. C’est avec cet objectif que les travaux présentés dans ce manuscrit se concentrent sur la mise au point d’une méthodologie de couplage entre codes d’écoulements réactifs et de transfert de chaleur dans les parois pour la réalisation de simulations de haute-fidélité massivement parallèles prédictives des chambres futuresOxycombustion is seen as one mean to attain the wished goals in terms of efficiency optimisation and Greenhouse Effect Gases emissions reduction for industrial furnaces. The extreme operating conditions, high pressure and temperature, lead to a strong interaction between the different phenomena which take place inside the combustion chambe r: Combustion, turbulence and heat transfer. To better design these futur oxyfuel processes, a mean to study the related physics with a reasonable computational cost and return time. Such studies require the use of high-fidelity numerical resolution tools, and in order to model the multi-physics interaction in a cost efficient way, code coupling. The operating conditions being extreme : High pressure and temperature, a strong interaction exists between the different phenomena occuring inside the chamber. To better understand the physics inside oxycombustion chambers,a multiphysics high-fidelity simulation methodology is developped
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内田, 正宏, Masahiro UCHIDA, 章. 梅村, Akira UMEMURA, 哲也 平田, Tetsuya HIRATA, 順一 佐藤, and Jun'ichi SATO. "微小重力場における被覆電線の燃焼の数値計算." 日本機械学会, 2001. http://hdl.handle.net/2237/9229.
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Tabbara, Hani. "Numerical investigations of thermal spray coating processes : combustion, supersonic flow, droplet injection, and substrate impingement phenomena." Thesis, University of Southampton, 2012. https://eprints.soton.ac.uk/348993/.
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The aim of this thesis is to apply CFD methods to investigate the system characteristics of high speed thermal spray coating processes in order facilitate technological development. Supersonic flow phenomena, combustion, discrete droplet and particle migration with heating, phase change and disintegration, and particle impingement phenomena at the substrate are studied. Each published set of results provide an individual understanding of the underlying physics which control different aspects of thermal spray systems. A wide range of parametric studies have been carried out for HVOF, warm spray, and cold spay systems in order to build a better understanding of process design requirements. These parameters include: nozzle cross-section shape, particle size, processing gas type, nozzle throat diameter, and combustion chamber size. Detailed descriptions of the gas phase characteristics through liquid fuelled HVOF, warm spray, and cold spray systems are built and the interrelations between the gas and powder particle phases are discussed. A further study looks in detail at the disintegration of discrete phase water droplets, providing a new insight to the mechanisms which control droplet disintegration, and serves as a fundamental reference for future developments of liquid feedstock devices. In parallel with these gas-particle-droplet simulations, the impingement of molten and semi-molten powder droplets at the substrate is investigated and the models applied simulate the impingement, spreading and solidification. The results obtained shed light on the break-up phenomena on impact and describe in detail how the solidification process varies with an increasing impact velocity. The results obtained also visually describe the freezing induced break-up phenomenon at the splat periphery.
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Simonetti, Marco. "Study of convective heat transfer phenomena for turbulent pulsating flows in pipes." Thesis, Orléans, 2017. http://www.theses.fr/2017ORLE2057/document.
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Dans le but de réduire la consommation en carburant et les émissions de CO2 des moteurs à combustion interne, un des leviers, qui a intéressé diffèrent acteurs dans le secteur automobile, est la récupération de l’énergie thermique disponible dans les gaz d’échappement. Malgré différents technologie ont été investigués dans le passé; les transferts de chaleur qui apparient dans les gaz d’échappement n’ont pas encore étés suffisamment étudiés. Le fait que les échanges de la chaleur apparent dans des conditions pulsatives, notamment due aux conditions de fonctionnement moteur, rende les connaissances acquis jusqu’à présent limités et ne pas exploitables. A l’état actuel on n’est pas capable de pouvoir prédire le transfert thermique convectif des écoulements pulsé. Les travaux de cette thèse s’instaurent dans la continuité de ce besoin, l’objectif principal est donc l’étude expérimentale du transfert thermique convectif des écoulements turbulent pulsés dans un conduit cylindrique. La première partie de ce travail a été consacrée à le dimensionnement d’un moyen d’essais permettant la création d’un écoulement pulsé type moteur; en suite différents méthodes de mesures ont étés développes afin de connaitre les variations instantanés de vitesse et température de l’écoulement. Plusieurs essais ont été reproduits afin de caractériser l’impact de la pulsation sur le transfert de la chaleur. Les résultats expérimentaux ont été analysés avec deux approches différentes: dans un premier temps une approche analytique 1D a permis de mettre en évidence le mécanisme principal responsable de l’amélioration du transfert thermique convectif,ainsi, il a fourni des éléments supplémentaires pour le futur développement de modèles mathématiques plus adaptés à la prédiction des transferts d’énergie. En suite une approche 2D, supporté d’une phase de modélisation numérique, a permis de caractériser le mécanisme de transport radial d’énergie thermiqueWaste Energy Recovery represents a promising way to go further in fuel saving and greenhouse emissions control for Internal Combustion Engine applications. Although several technologies have been investigated in the past few years, the convective heat transfers, playing an important role in the energy exchanges at the engine exhaust, has not receive enough attention. Heat transfers, in such applications, occur in pulsating conditions because of the engine operating conditions, making thus the actual knowledge of the heat transfer phenomena limited and not exploitable. Nowadays there is not any model capable to predict convective heat transfers for pulsating flows. In this context, the present thesis addresses the purpose to study the convective heat transfer phenomena, by an experimental approach, occurring for turbulent pulsating flows in pipes. In the first part of this work, an experimental apparatus has been designed to reproduce an exhaust type pulsating flow in fully managed conditions, as well as, several measurement techniques have been developed to know the instantaneous profiles of air temperature and velocity. Many experiments have been performed in order to characterize the impact of the flow pulsation on the convective heat transfers. In the second part of this work, the experimental results have been analyzed with two different approaches: firstly, with a 1D assumption the time-average convective heat transfers has been computed, and the major mechanism responsible of the heat transfer enhancement has been pointed out. Furthermore, it has been possible to highlight the mathematical term representative of such mechanism, which should be accounted in future to define a more adapted numerical model for the heat transfer prediction. In a second phase with a 2D assumption, and, with an energy and a fluid-mechanic computational phase, the radial transport of thermal energy has been characterized for a pulsating flow
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中村, 祐二, Yuji NAKAMURA, 陽介 恵藤, Yosuke ETOH, 博史 山下, and Hiroshi YAMASHITA. "微小重力下での固体燃料の火炎伝播に与える速度境界層の影響." 日本機械学会, 2003. http://hdl.handle.net/2237/8996.
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Maestro, Dario. "Large Eddy Simulations of the interactions between flames and thermal phenomena : application to wall heat transfer and combustion control." Thesis, Toulouse, INPT, 2018. http://www.theses.fr/2018INPT0074/document.
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Les interactions entre les flammes et les phénomènes thermiques sont le fil conducteur de ce travail. En effet, les flammes produisent de la chaleur, mais peuvent aussi être affectées par des transferts ou des sources de chaleur. La Simulation aux Grandes Echelles (SGE) est utilisée ici pour étudier ces interactions, en mettant l’accent sur deux sujets principaux: le transfert de chaleur aux parois et le contrôle de la combustion. Dans un premier temps, on étudie le transfert de chaleur aux parois dans un modèle de brûleur CH4/O2 de moteur-fusée. Dans un contexte deréutilisabilité et de réduction des coûts des lanceurs, qui constituent des enjeux majeurs, de nouveaux couples de propergols sont envisagés et les flux thermiques à la paroi doivent êtreprécisément prédits. Le but de ce travail est d’évaluer les besoins et les performances des SGEpour simuler ce type de configuration et de proposer une méthodologie de calcul permettant desimuler différentes configurations. Les résultats numériques sont comparés aux donnéesexpérimentales fournies par la Technische Universität München (Allemagne). Dans un deuxième temps, le contrôle de la combustion au moyen de décharges de plasma de type NRP (en anglaisNanosecond Repetitively Pulsed) est étudié. Les systèmes de turbines à gaz modernes utilisent en effet une combustion pauvre dans le but de réduire la consommation de carburant et les émissions de polluants. Les flammes pauvres sont connues pour être sujettes à des instabilités et le contrôle de la combustion peut jouer un rôle majeur dans ce domaine. Un modèle phénoménologique qui considère les décharges de plasma comme une source de chaleur est développé et appliqué à un brûleur pauvre avec prémélange CH4/Air stabilisé par un swirler. LesSGE sont réalisées afin d’évaluer les effets des décharges NRP sur la flamme. Les résultats numériques sont comparés aux observations expérimentales faites à la King Abdulla University ofScience and Technology (Arabie Saoudite)Interactions between flames and thermal phenomena are the guiding thread of this work. Flamesproduce heat indeed, but can also be affected by it. Large Eddy Simulations (LES) are used hereto investigate these interactions, with a focus on two main topics: wall heat transfer andcombustion control. In a first part, wall heat transfer in a rocket engine sub-scale CH4/O2 burner isstudied. In the context of launchers re-usability and cost reduction, which are major challenges,new propellant combinations are considered and wall heat fluxes have to be precisely predicted.The aim of this work is to evaluate LES needs and performances to simulate this kind ofconfiguration and provide a computational methodology permitting to simulate variousconfigurations. Numerical results are compared to experimental data provided by the TechnischeUniversität München (Germany). In a second part, combustion control by means of NanosecondRepetitively Pulsed (NRP) plasma discharges is studied. Modern gas turbine systems use indeedlean combustion with the aim of reducing fuel consumption and pollutant emissions. Lean flamesare however known to be prone to instabilities and combustion control can play a major role in thisdomain. A phenomenological model which considers the plasma discharges as a heat source isdeveloped and applied to a swirl-stabilized CH4/Air premixed lean burner. LES are performed inorder to evaluate the effects of the NRP discharges on the flame. Numerical results are comparedwith experimental observations made at the King Abdulla University of Science and Technology(Saudi Arabia)
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Cavaglieri, Marcelo Renato 1975. "Estudo experimental do fenômeno de onda em coletores de admissão para motores de combustão interna : Experimental study of the wave phenomena into the intake manifolds for internal combustion engines." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265919.
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Orientador: Rogério Gonçalves dos SantosDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-24T21:02:17Z (GMT). No. of bitstreams: 1 Cavaglieri_MarceloRenato_M.pdf: 17998120 bytes, checksum: 987df39d379a639bae4123aeab57a9d6 (MD5) Previous issue date: 2014
Resumo: Com o intuito de otimizar o Motor de Combustão Interna e encontrar aplicações que o utilizem de forma racional e eficiente, nessa dissertação estuda-se o comportamento dinâmico da pressão na cavidade dos Coletores de admissão, já que o escoamento através dele acontece de forma pulsada, devido ao movimento do pistão e modulado pelo abrir e fechar das válvulas de admissão e escapamento. Sendo o Coletor de Admissão parte desse circuito, ele consequentemente impõe uma impedância a esse escoamento intermitente, podendo ser mais ou menos acentuada, devido suas formas construtivas. Para essa avaliação busca-se um fator ou um coeficiente que quantifique como as ondas de pressão interagem com a cavidade do Coletor de Admissão, de forma metódica e confiável, para que os resultados possam ser usados como ferramenta prática de desenvolvimento desse componente. Podendo assim, os Coletores de Admissão serem ajustados adequadamente à aplicação e não apenas nos quesitos de regimes permanentes tradicionais como perda de carga e desbalanceamento no fornecimento de ar. Nessa dissertação é apresentado um aparato para medir experimentalmente a curva do Coeficiente de Transmissão de onda de pressão, seus detalhes construtivos, de configuração e operação para a obtenção de curvas de boa qualidade. É mostrado também um método para validação do aparato e por fim a comparação do Coeficiente de Transmissão com a curva de desempenho desses componentes quando instalados em um Motor de Combustão Interna. Comprovando dessa maneira, a relação entre as características dinâmicas da cavidade e sua influência no desempenho do Motor de Combustão Interna e mais, demonstrando que o método experimental de medir o Coeficiente de Transmissão é uma forma eficaz e coerente de se quantificar a influência desse componente no processo de admissão
Abstract: In order to optimize the Internal Combustion Engine and find out applications that use it rationally and efficiently, in this dissertation it is studied the dynamic behavior of the intake manifolds cavity pressure, since the flow through it happens in a pulsed manner, due to the movement of the piston and modulated by opening and closing the intake and exhaust valves. Being the intake manifold part of this circuit, it imposes impedance to the flow that may be more or less pronounced, due to its constructive design. For this evaluation it is made an experimental determination of the Transmission Coefficient of pressure waves through the Intake Manifold, methodically and reliably, so the results can be used as a practical tool for developing these components. The Intake Manifold may thus be properly adjusted to the application needs and not just in the categories of traditional patterns like permanent loss and imbalance of air supply. This dissertation presents an experimental apparatus to measure the curve of the wave pressure Transmission Coefficient, its construction details, configuration and operation to get good quality curves. It is also shown a method to calibrate the apparatus and finally, the comparison of the Transmission Coefficient with the performance curve of measured Intake Manifolds when installed on an Internal Combustion Engine. Providing this way, the correlation between the dynamic characteristics of the cavity and its influence on the Internal Combustion Engine¿s performance and demonstrating that the experimental method to measure the Transmission Coefficient is an effective and consistent way to quantify the influence of the Intake Manifold in admission process
Mestrado
Termica e Fluidos
Mestre em Engenharia Mecânica
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Yildiz, Dilek. "Experimental Investigation of superheated liquid jet atomization due to flashing phenomena." Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211018.
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The present research is an experimental investigation of the atomization of a superheated pressurized liquid jet that is exposed to the ambient pressure due to a sudden depressurization. This phenomena is called flashing and occurs in several industrial environments.Liquid flashing phenomena holds an interest in many areas of science and engineering. Typical examples one can mention: a) the accidental release of flammable and toxic pressure-liquefied gases in chemical and nuclear industry; the failure of a vessel or pipe in the form of a small hole results in the formation of a two-phase jet containing a mixture of liquid droplets and vapor, b) atomisation improvement in the fuel injector technology, c) flashing mechanism occurrence in expansion devices of refrigerator cycles etc. The interest in flashing events is especially true in the safety field where any unexpected event is undesirable. In case of an accident, flammable or toxic gas clouds are anticipated in close regions of the release because of the sudden phase change .Due to the non-equilibrium nature of the flow in these near field regions, conducting accurate data measurements for droplet size and velocity is a challenging task resulting in scarce data in the very close area.
This research has been carried out at the von Karman Institute (VKI) within the 5th framework of European Commission to fulfill the goal of understanding of source processes in flashing liquids in accidental releases. The program is carried out under name of FLIE (Flashing Liquids in Industrial Environments)(Contract no: EVG1-CT-2000-00025). The specific issues that are presented in this thesis study are the following:a) a comprehensive state of art of the jet break up patterns, spray characteristics and studies related to flashing phenomena; b)flashing jet breakup patterns and accurate characterization of the atomized jet such as droplet diameter size, velocity and temperature evolution through carefully designed laboratory-scale experiments; c) the influence of the initial storage conditions on the final atomized jet; d) a physical model on the droplet transformation and rapid evaporation in aerosol jets.
In order to characterize the atomization of the superheated liquid jet, laser-based optical techniques like Particle Image Velocimetry (PIV), Phase Doppler Anemometry (PDA) are used to obtain information for particle diameter and velocity evolution at various axial and radial distances. Moreover, a high-speed video photography presents the possibility to understand the break-up pattern changes of the simulating liquid namely R-134A jet in function of driving pressure, superheat and discharge nozzle characteristics. Global temperature measurements with an intrusive technique such as thermocouples, non-intrusive measurements with Infrared Thermography are performed. Cases for different initial pressures, temperatures, orifice diameters and length-to-diameter ratios are studied. The break-up patterns, the evolution of the mean droplet size, velocity, RMS, turbulence
intensity and temperature along the radial and axial directions are presented in function of initial parameters. Highly populated drop size and velocity count distributions are provided. Among the initial storage conditions, superheat effect is found to be very important in providing small droplets. A 1-D analytical rapid evaporation model is developed in order to explain the strong temperature decrease during the measurements. A sensitivity analysis of this model is provided.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished
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Chaussonnet, Geoffroy. "Modeling of liquid film and breakup phenomena in Large-Eddy Simulations of aeroengines fueled by airblast atomizers." Phd thesis, Toulouse, INPT, 2014. http://oatao.univ-toulouse.fr/12098/1/chaussonnet_version_publique.pdf.
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Aeronautical gas turbines need to satisfy growingly stringent demands on pollutant emission. Pollutant emissions are directly related to the quality of fuel air mixing prior to combustion. Therefore, their reduction relies on a more accurate prediction of spray formation and interaction of the spray with the gaseous turbulent flow field. Large-Eddy Simulation (LES) seems an adequate numerical tool to predict these mechanisms. The objectives of this thesis is to develop phenomenological models describing the liquid phase, in particular the film and its atomization at the injector atomizing lips, in the context of LES. These models are validated or calibrated on the academic experiment performed at Institut für Thermische Strömungsmaschinen (ITS) from the Karlsruhe Institute of Technology (KIT), and applied to a helicopter engine real configuration. In a first step, the thin liquid film is described by a Lagangian approach. Film particles represent an elementary volume of liquid at the wall surface. The equation of motion is given by integrating the Saint-Venant equations over the film thickness. The film dynamics derives from the pressure gradient, the interfacial shear and gravity. In a second step, the film breakup is characterized by the drop size distribution of the spray. The former one is described by a Rosin-Rammler distribution, whose coefficients depend on the gas velocity, the liquid surface tension and the atomizing edge thickness of the injector. The model, labelled PAMELA, is calibrated from the KIT-ITS experiment. The simulation of the KIT-ITS experiment allows to validate the film model, to check PAMELA robustness, and to compare qualitatively the spray angle. The application of these models in a real configuration allows to check PAMELA robustness without constants modification, and to study their impact on the flame structure, in comparison with usual methods of liquid injection.
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Perkins, Gregory Martin Parry Materials Science & Engineering Faculty of Science UNSW. "Mathematical modelling of underground coal gasification." Awarded by:University of New South Wales. Materials Science and Engineering, 2005. http://handle.unsw.edu.au/1959.4/25518.
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Mathematical models were developed to understand cavity growth mechanisms, heat and mass transfer in combination with chemical reaction, and the factors which affect gas production from an underground coal gasifier. A model for coal gasification in a one-dimensional spatial domain was developed and validated through comparison with experimental measurements of the pyrolysis of large coal particles and cylindrical coal blocks. The effects of changes in operating conditions and coal properties on cavity growth were quantified. It was found that the operating conditions which have the greatest impact on cavity growth are: temperature, water influx, pressure and gas composition, while the coal properties which have the greatest impact are: the thermo-mechanical behaviour of the coal, the coal composition and the thickness of the ash layer. Comparison of the model results with estimates from field scale trials, indicate that the model predicts growth rates with magnitudes comparable to those observed. Model results with respect to the effect of ash content, water influx and pressure are in agreement with trends observed in field trials. A computational fluid dynamics model for simulating the combined transport phenomena and chemical reaction in an underground coal gasification cavity has been developed. Simulations of a two-dimensional axi-symmetric cavity partially filled with an inert ash bed have shown that when the oxidant is injected from the bottom of the cavity, the fluid flow in the void space is dominated by a single buoyancy force due to temperature gradients established by the combustion of volatiles produced from the gasification of carbon at the cavity walls. Simulations in which the oxidant was injected from the top of the cavity reveal a weak fluid circulation due to the absence of strong buoyancy forces, leading to poor gasification performance. A channel model of gas production from underground coal gasification was developed, which incorporates a zero-dimensional cavity growth model and mass transfer due to natural convection. A model sensitivity study is presented and model simulations elucidate the effects of operating conditions and coal properties on gas production.
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Tea, Gabrielle [Verfasser], and Christof [Akademischer Betreuer] Schulz. "Development and exploitation of optical diagnostic techniques for simultaneous 2D temperature and equivalence ratio measurements for the understanding of combustion phenomena in reciprocating engine / Gabrielle Tea. Betreuer: Christof Schulz." Duisburg, 2015. http://d-nb.info/1066206333/34.
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Nair, Suraj. "Acoustic Characterization of Flame Blowout Phenomenon." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10413.
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Combustor blowout is a very serious concern in modern land-based and aircraft engine combustors. The ability to sense blowout precursors can provide significant payoffs in engine reliability and life. The objective of this work is to characterize the blowout phenomenon and develop a sensing methodology which can detect and assess the proximity of a combustor to blowout by monitoring its acoustic signature, thus providing early warning before the actual blowout of the combustor. The first part of the work examines the blowout phenomenon in a piloted jet burner. As blowout was approached, the flame detached from one side of the burner and showed increased flame tip fluctuations, resulting in an increase in low frequency acoustics. Work was then focused on swirling combustion systems. Close to blowout, localized extinction/re-ignition events were observed, which manifested as bursts in the acoustic signal. These events increased in number and duration as the combustor approached blowout, resulting an increase in low frequency acoustics. A variety of spectral, wavelet and thresholding based approaches were developed to detect precursors to blowout.
The third part of the study focused on a bluff body burner. It characterized the underlying flame dynamics near blowout in greater detail and related it to the observed acoustic emissions. Vorticity was found to play a significant role in the flame dynamics. The flame passed through two distinct stages prior to blowout. The first was associated with momentary strain levels that exceed the flames extinction strain rate, leading to flame holes. The second was due to large scale alteration of the fluid dynamics in the bluff body wake, leading to violent flapping of the flame front and even larger straining of the flame. This led to low frequency acoustic oscillations, of the order of von Karman vortex shedding. This manifested as an abrupt increase in combustion noise spectra at 40-100 Hz very close to blowout. Finally, work was also done to improve the robustness of lean blowout detection by developing integration techniques that combined data from acoustic and optical sensors.
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Abdoli, Abas. "Optimization of Cooling Protocols for Hearts Destined for Transplantation." FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1579.
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Design and analysis of conceptually different cooling systems for the human heart preservation are numerically investigated. A heart cooling container with required connections was designed for a normal size human heart. A three-dimensional, high resolution human heart geometric model obtained from CT-angio data was used for simulations. Nine different cooling designs are introduced in this research. The first cooling design (Case 1) used a cooling gelatin only outside of the heart. In the second cooling design (Case 2), the internal parts of the heart were cooled via pumping a cooling liquid inside both the heart’s pulmonary and systemic circulation systems. An unsteady conjugate heat transfer analysis is performed to simulate the temperature field variations within the heart during the cooling process. Case 3 simulated the currently used cooling method in which the coolant is stagnant. Case 4 was a combination of Case 1 and Case 2. A linear thermoelasticity analysis was performed to assess the stresses applied on the heart during the cooling process.
In Cases 5 through 9, the coolant solution was used for both internal and external cooling. For external circulation in Case 5 and Case 6, two inlets and two outlets were designed on the walls of the cooling container. Case 5 used laminar flows for coolant circulations inside and outside of the heart. Effects of turbulent flow on cooling of the heart were studied in Case 6. In Case 7, an additional inlet was designed on the cooling container wall to create a jet impinging the hot region of the heart’s wall. Unsteady periodic inlet velocities were applied in Case 8 and Case 9. The average temperature of the heart in Case 5 was +5.0oC after 1500 s of cooling.
Multi-objective constrained optimization was performed for Case 5. Inlet velocities for two internal and one external coolant circulations were the three design variables for optimization. Minimizing the average temperature of the heart, wall shear stress and total volumetric flow rates were the three objectives. The only constraint was to keep von Mises stress below the ultimate tensile stress of the heart’s tissue.
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Korremla, Shiva K. Sainoju. "Experimental investigation of steady state heat transfer phenomenon in Pontiac G6 vehicle exhaust system." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2007. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Davuluri, Raghava Sai Chaitanya. "Modeling of spallation phenomenon in an arc-jet environment." UKnowledge, 2015. https://uknowledge.uky.edu/me_etds/63.
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Space vehicles, while entering the planetary atmosphere, experience high loads of heat. Ablative materials are commonly used for a thermal protection system, which undergo mass removal mechanisms to counter the heat rates. Spallation is one of the ablative processes, which is characterized by the ejection of solid particles from the material into the flow. Numerical codes that are used in designing the heat shields ignore this phenomenon. Hence, to evaluate the effectiveness of spallation phenomenon, a numerical model is developed to compute the dynamics and chemistry of the particles. The code is one-way coupled to a CFD code that models high enthalpy flow field around a lightweight ablative material. A parametric study is carried out to examine the variations in trajectories with respect to ejection parameters. Numerical results are presented for argon and air flow fields, and their effect on the particle behavior is studied. The spallation code is loosely coupled with the CFD code to evaluate the impact of a particle on the flow field, and a numerical study is conducted.
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BOUTRIF, MOHAMED-SAID. "Caracterisation energetique des phenomenes de transport instantane des gaz d'echappement a la sortie des cylindres des moteurs alternatifs a combustion interne." Paris 6, 1990. http://www.theses.fr/1990PA066426.
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Une methodologie de mesure de la pression, de la vitesse et de la temperature dans l'echappement d'un moteur alternatif par capteur en quartz, par velocimetrie laser a effet doppler et par thermocouple lineaire fin a ete developpee. La temperature reelle des gaz a ete reconstituee en tenant compte de l'inertie thermique de ce dernier grace a la mesure de la vitesse. Les valeurs de (p, u et t reconstituee) dans deux sections distantes de 90 cm, d'un tube d'echappement d'un cylindre, nous ont servi dans un premier temps pour decrire le mecanisme de la vidange du cylindre en deux phases: periode de la bouffee et periode de refoulement des gaz brules par le piston. Dans un deuxieme temps ces valeurs ont permis d'evaluer les niveaux energetiques dans deux sections de travail: 70% de la puissance cedee a l'echappement est localisee principalement dans la periode de la bouffee et 30% de la puissance est perdue entre les deux sections. Deux codes numeriques: simulation de l'ecoulement entre les deux sections (methode des caracteristiques) et modelisation des pertes thermiques au travers de la paroi du tube d'echappement ont ete crees et valides en les alimentant avec des conditions aux limites reelles. Nous avons ainsi reproduit des profils de pression et de vitesse globalement identiques a ceux mesures et mis en evidence que 75% du flux perdu etait d'origine radiative
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Liu, Chao-Pin, and 劉朝斌. "Numerical Study on the Combustion Phenomena in Micro Combustor." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/95425209138561491041.
Full textAbstract:
碩士逢甲大學
航太與系統工程所
94
In this study, three-dimensional combustion phenomena in ethylene fueled micro-combustors with different fuel-injection type, combustor inlet area, and flame holder geometry are simulated by using commercial computational fluid dynamics software (CFD-ACE+). Effects of the key parameters including equivalence ratio (Φ), mass flow rate (mf), and heat transfer coefficient (h) are explored in details. The simulation results reveal that upstream burning may happen under large Φ and the flame can be blown out/quenched causing by less residence time/heat release rate for high/low mf. The above phenomena reflect similar qualitative trends with experimental data and past numerical results. It is also found that proper heat loss is crucial for micro-combustors to operate at better combustion efficiency. Different fuel-injection type has less effect on micro-combustor efficiency, and different combustor inlet area has more obvious effects on combustor efficiency. In addition, micro-combustor with slotted flame holder had better combustor efficiency than the one with annular flame holder.
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Wei, Yih-Wen, and 韋育文. "Group Combustion Phenomena on a Diesel Engine." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/29246235636850966411.
Full textAbstract:
碩士國立成功大學
航空太空工程學系
86
The major objective is to examine the nature of the "Group Combustion Phenomena in a Diesel Engine". The numerical simulation of combustion phenomena, adopt Kive3 code which modified by "Renormalized Combustion Theory" to account for drop-drop interaction during gasification. The first part of the thesis is to study relationship between the number density of oil droplet in the cloud and the evaporation rate in combustion chamber. The result of the study reveals that the evaporation and combustion processes inside the diesel engine follows closely these of the group combustion configuration. Part two of the study is to examine whether the anomalous group combustion phenomena exist inside the diesel engine during transient combustion. Because the effect of ignition delay the oil vapor mixes with the air in droplet cloud before ignition, and thus initiate the premixed flame, which burns at inside and outside of the cloud. Subsequently, the inner flame extinct when the initial oxidizer is consumed the outer flame transforms into a diffusion flame.
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YANG, YI-PEI, and 楊屹沛. "Combustion phenomena inside an internal gun ballistics." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/52930907912101161259.
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Rosyadi, Basthiyan Sidqi Fidari, and 貝璽嚴. "Bio-fuel Droplet Combustion: Burning Rate Constants and Microexplosion Phenomena Measurements." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/84390695526398273851.
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碩士國立中央大學
機械工程學系
102
論文探討兩種不同生質燃料(生質柴油和葵花油)，以及它們分別與柴油混合燃料(生質燃料體積濃度比從5%到75%)，在常壓靜止條件下之液滴燃燒實驗。對稱球形微小液滴可由自製的壓電驅動液滴產生器所產生，液滴直徑(d)範圍從0.45 mm到0.60 mm，將小液滴懸浮在兩條非常細水平定位且相互垂直呈十字狀直徑為20 μm之陶瓷纖維上。加熱器為一對直徑為0.2 mm 之Khantal 導線，呈半橢圓形狀並將其水平地置放於懸浮小液滴的兩側邊，用來點燃液滴。一旦點燃後當火焰包圍液滴時，加熱器即斷電移開，此時液滴的直徑訂為初始直徑(d0)，由高速攝影機所決定。由液滴燃燒過程所攝之時序圖，我們以(d/d0)2對時間t的最佳擬合斜率(即d2-law)，來決定液滴的燃燒率常數(K)。研究結果顯示，當 d0值下降時，K值會上升，對所有本研究所使用之燃料均如是。100%生質柴油比一般商用柴油有較高的K值。後者沒有微爆現象，而前者在燃燒後期即將完成液滴燃燒前，有弱微爆現象，這可能是由於少量的甲基亞油酸(4.92wt%)存在於生質柴油中所導致。此外，複雜但有趣的微爆現象，可以在純葵花油和其與柴油之混合生質燃料中被觀察到，我們找到兩個不同K值於液滴燃燒的過程中。當葵花油在混合燃料中體積比超過50%時，混合液滴會經歷一轉變，從第一階段的規律燃燒(K1)到第二階段液滴燃燒後期(K2)的強膨脹和微爆現象，其中K1 < K2。但是當混合燃料中含有較少量葵花油(< 50%)時，前述轉變順序正好相反，換句話說，在液滴燃燒開始不久的第一階段，強微爆即發生，其中K1 > K2。這種微爆的反向過程，可能可以歸因於在葵花油中，具有不同揮發成分的脂肪酸所致。我們發現在液滴燃燒中，擴散過程為主導因素，因為具有不同(d/d0)2 vs. t曲線可以被擬合成單一的曲線，當時間(t)以無因次tdiff = d02/α，其中α為液滴燃料的熱擴散係數。前述結果，有助我們對生質燃料燃燒之了解，其對未來汽車和航空工業上使用生質燃料替代化石液體燃料，將有所助益。
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Wu, Chung-Wei, and 吳仲偉. "Analysis of Combustion Phenomena of Wood-Materials in Solid-Fuel Bed." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/19741854881366521601.
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碩士國立臺灣大學
機械工程學研究所
89
This paper discusses the temperature variations and phenomena of wood-materials combustion in a small-scale solid-fuel bed furnace experimentally. We provide the same burning situation and analyze the fuel burning states at different stages by quenching. If we gain the number of experiment times, we can get each transitory state of the fuel. If we combine each transitory state, we can get the whole burning process of the fuel material. As a result, we obtain a well burning rate by using wood-materials in the upward burning mode. The combustion phenomena in upward burning mode are simpler than that in the downward burning mode. The agreement between the theoretic model predictions and the experimental phenomena in upward burning mode are reasonably good. The different ignition time influences the experimental accuracy. The average burning rate of early ignition time is faster than that of late ignition time.
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Lee, Ming-tsang, and 李明蒼. "A Numerical Study of The Thermofluid Phenomena in An Internal Combustion Engine." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/31540391970298494718.
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碩士中原大學
機械工程學系
87
With the recent progress of computer technology, numerical analysis method and software have been wildly used in most engineering problems. For predicting and analysis the thermofluid phenomena inside the cylinder of internal combustion (IC) engine, computational fluid dynamic (CFD) models are becoming powerful tools. The KIVA code, originally developed at the US Los Alamos National Laboratory, is one of the advanced computer programs for optimizing IC engine research. It can calculate the transient, two- and three-dimensional, chemically reactive fluid flows with sprays and turbulence. The numerical scheme is based on the Arbitrary Lagrangian-Eulerian (ALE) [1,2,5] method and finite volume technique. An implicit scheme similar to SIMPLE rule is also been used in the procedure of gas-phase solution. A stochastic particle method is used to calculate the evaporation rate of liquid sprays. The effect of droplet oscillation, distortion, breakup, collision and coalescence are also considered during the computation. In this case, we used the version of KIVA-3V, which is modified to simulate the vertical or canted valves as moving solid boundary by using the "snapper" technique which is already used for piston motion in KIVA-3 [3] and retaining all previous features of KIVA family. There are two turbulence models available in the KIVA-3V code and have been used in this study, the standard k-e turbulence model and the RNG (Renormalization Group) variant k-e turbulence model. The calculation result will be compared with the results among these two turbulence models and experimental data.
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Su, Ding-jie, and 蘇鼎傑. "A Study on the Phenomena of the Flow Field in an Internal Combustion Engine." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/69191818402892744756.
Full textAbstract:
碩士中原大學
機械工程研究所
90
Internal combustion engines are the primary power source for cars and motorcycles. It is the production of mechanical power from the chemical energy contained in the fuel. Because the importance of the phenomena of the flow field in internal combustion engines, this study uses the KIVA-3V code to analyze the flow field. The KIVA-3V code, which was developed at the US Los Alamos National Laboratory, is a powerful tool to analyze the transient, two- and three-dimensional, chemically reactive fluid flows with sprays and turbulence. In general, the study of the flow field in internal combustion engines uses two methods: the experimental technique and the numerical simulation. Because the experimental technique cannot measure the overall flow field in the cylinder, this study uses the KIVA-3V code to simulate it. Besides, due to the tremendous computing capability available, people usually use numerical simulation for the study. The KIVA-3V code is a computational fluid dynamic program that uses the finite volume method with Arbitrary Lagrangian-Eulerian (ALE) algorithm. The Monte Carlo-based discrete-particle technique used in the fuel sprays model was implemented to describe the behavior of the droplets. The KIVA-3V code is capable of calculating the effects of droplet oscillation, distortion, breakup, collision and coalescence. The study uses the RNG (Renormalization Group) turbulence model to study the phenomena of the flow field in an internal combustion engine. The engine performance parameters investigated are tumble ratio, swirl ratio, turbulence intensity, and turbulence kinetic energy. In addition, volumetric efficiency and the in-cylinder pressure behavior during the intake and compression stroke were obtained and compared with the experimental data. Their differences are within 5%, using the experimental values as the reference. Furthermore, the volumetric efficiencies for the three sets of intake valve lifts under study appear to be reasonable.
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Xu, Guo-Zhi, and 許國治. "The combustion synthesis reaction mechanism and ignition phenomena of the Ti-C-Sn system." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/61246447799707543067.
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碩士國立成功大學
化學工程學系
86
In this research, the combustion synthesis reaction mechanism of the Ti-C-Snsystem was experimentally investigated . We try to understand the reactionmechanism in detail according to the ignition temperature, ignition phenomena,XRD spectrums and SEM photographs of the products. When the addition of tin was less than 50wt%, the ignition temperature wasnot significantly decreased compare with the Ti-C system .i.e. due to theformation of SnTi2C before the ignition of reaction .As a result ,the ignitionof combustion reaction was controlled by the rate of surface reaction (relatedto the melting of Ti),which ,in turn ,was controlled by the melting of Sncontained Ti spreading over the surface of graphite (related to the formationof SnTi2C ). Ti+C→TiC is the major igniting mechanism.When the addition oftin was more than 50wt%,the ignition temperature was significantly decreasingas the addition of Sn increasing. It was explained by the fact that themelting of tin contained Ti spreading over(or almost) the surface of graphite,thus increasing the formation rate of SnTi2C.Therefore , SnTi2C+C→2 TiC+Sn isthe major igniting mechanism.So,the ignition of reaction was controlled by thereaction rate of solid-liquid interface ,which,in turn,was controlled by theinterfacial area between solid and liquid phase or the concentration of Tiin Sn . The addition of tin not only affected the ignition temperature but alsochanged the morphology of the product .When the addition of tin attained50wt%, more tin was added ,more SnTi2C was formed in the product . Besides,due to the difference of the interior and exterior temperature inside thepellet during the combustion reaction , the inner products of the pelletwas TiC and the outer products of the pellet was SnTi2C. From the above analysis, possible reaction mechanisms have been proposed onthe basis of the experimental observations of the ignition phenomena and theproduct morphology.
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Cheng, Tzn-Shan, and 鄭子善. "An Action Research about Developing an Elementary Science Story Course: Stories about Combustion Phenomena." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/08494954351653846569.
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碩士國立花蓮師範學院
國小科學教育研究所
88
Many science educators argued that elementary school is the place where students enthusiasm of science is extinguished. The researcher thus proposed that a course of science stories may play a cure. Therefore, the major purpose of this study is to develop a 6-8 week course and to see what impacts it may have upon students attitude toward science and their understanding about science. The topic researcher selected for investigation is stories about combustion and the source of stories comes from the history of science and the story books. This study is an action research and has been conducted in accordance with the cycle of planning, execution, analysis, and planning again. With such a continuous feedback mechanism, researcher kept revising the content of this course and finding effective ways for teaching it. Videos of teaching, student interview, field notes, and student assignment for each unit were collected. The results of this study indicate that the implementation of such a science story course in elementary school is doable yet challenging. In terms of the views of teacher-as-researcher, six units of final teaching plan and the whole revising process of having ideas, insistence when facing difficulties and fighting for proper implementation will be reported. As to the impacts of this course upon students, no significant change of students attitude toward science and their understanding about science was identified. Yet, by human touch, researcher did observe signs of change from the process of interviewing students. Many difficulties merged during the implementation process such as presenting stories without right skills, no appropriate teaching tools which can be used, the necessity of heavy research for seeking out proper content, classroom management and the restriction of time. Some of the difficulties were conquered and the strategies will be discussed. Most of all, the professional growth of researcher in teaching is tremendous and impressive, which in turn signifies the value of this research.
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Lee, Jou-Hong, and 李昭宏. "Combustion Synthesis:Reverse Burning Phenomena in Synthesis of ZrB2 and Synthesis of Titanium Carbide Cascade." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/27591428472373611201.
Full textAbstract:
碩士國立中正大學
化學工程研究所
84
The thesis contains two parts. The first part describes the reverse burningphenomenon in combustion synthesis of ZrB2. In general, using SHS to produce fine ceramics has a property: the reaction(ignition) always starts at the heatedend , i.e. the ignited hot spot always appears first at that place. But,in theexperiments of ZrB2 reaction, under some reaction conditions , the ignited hotspot first appeared at the opposite of the heated end , or at themiddle of thepellet . This may be due to the nonuniformly distribution of thepellet density,and resulted in the heat transfers within the pellet. The second part studiesies combustion synthesis of pellet-train TiC. Pellet cascades were ignited by the tungsten coil in the glove box. After the firstpellet reacted, heat of re-action of the first pellet was utilized by the secondpellet.Because the effectof interface, the combustion wave velocity of the first pellet was faster thanthat of the second pellet , and the reaction time of the reaction was proport-ional to the total length of the pellet-train. We also studies the influences of interface by varying the physical properties of the interface.
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Pa, Han-Chuan, and 巴漢川. "Combustion Synthesis of High-Performance Materials:Ignition Phenomena and Reaction Mechanisms of the Ti-C-Sn System." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/60438630818067446283.
Full textAbstract:
碩士國立成功大學
化學工程學系
84
Based on Ti-C-Sn ternary system,this thesis was aimed at the research ofmechanism of combustion synthesis(or SHS). In order to know what role Snplay in combustion synthesis of Ti-C, various weight ratios of Sn were addedto powder mixture with an atomic ratio of 1:1. The amounts of Sn powder affected the ignition temperature and morphologies of the products duringthe heating and combustion reaction. In the course of reaction,Ti3Sn wasformed firstly, so that the ignition temperature raise to the melting pointsof Ti or Ti3Sn. Obviously, the surface reaction and contacting ares betweenparticles directly controlled ignition of the combustion reaction. Thediffusion of carbon atom through Sn2Ti4C2 layer produced product which ledto the growth of carbide layer and the reactions of dissolving/ precipitatingoccured simultaneously to form Ti6Sn5 and TiC which covered graphite or withmorphology of Sn2Ti4C2 on. As mentioned above, this was the reactionmechanism with little Sn powder added(less than 40wt%). When a large amountof Sn powder was added(more than 40wt%), more Ti could be dissolved in Snmelt in the course of reaction. The Sn-Ti melt spreading on graphiteparticle formed Sn2Ti4C2, and then, the diffusion of carbon through Sn2Ti4C2layer reacted with Ti which contained in Sn-Ti melt. Obviously, the ignition of the combustion reaction depended on the rate of solid-liquidinterfacial reaction, the area of solid-liquid interface, the mole fractionof Ti in the Sn melt and the thickness of ternary carbide Sn2Ti4C2. In thecase, the mechanism of reaction could be distinguished two types. If the rate of dissolution of Sn2Ti4C2 was less than that formation, carbon atom diffusion through Sn2Ti4C2 was main reaction and to form the morphologies ofSn2Ti4C2 platelets and graphite particles coated with Sn2Ti4C2 layer. On the contrary, if the rate of dissolution of Sn2Ti4C2 was greater than that of formation, the reaction of dissolving/precipitating occured simultaneouslyto form the morphologies consisting Sn2Ti4C2 plateled, granular TiC and graphite particles coated with Sn2Ti4 C2 layer.
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Tsao, Jen-Chieh, and 曹仁杰. "The Study of Spray Combustion on Transport Phenomea in a Bluff-body Combustor." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/50312645540410173082.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
84
Responses of CBF to NMDA were inhibited after the pretreatment with MK-801 (0.5 mg/kg iv) or tetrodotoxin (10-6 M; topical application) . MK-801 or tetrodotoxin, however, had no effect on acetylcholine (ACh; 10-7 M and 10-6 M)-induced increases in CBF. The selective inhibitor of neuronal nitric oxide synthase, 7-nitroindazole (7-NI; 50 mg/kg ip) also significantly inhibited the increases in CBF produced by NMDA, but not by ACh.
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Panse, Shreyas S. "Background and Available Potential Energy in Numerical Simulations of a Boussinesq Fluid." 2013. https://scholarworks.umass.edu/theses/1002.
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In flows with stable density stratification, a portion of the gravitational potential energy is available for conversion to kinetic energy. The remainder is not and is called “background potential energy”. The partition of potential energy is analogous to the classical division of energy due to motion into its kinetic and internal components. Computing background and available potential energies is important for understanding stratified flows. In many numerical simulations, though, the Boussinesq approximations to the Navier-Stokes equations are employed. These approximations are not consistent with conservation of energy. In this thesis we re-derive the governing equations for a buoyancy driven fluid using Boussinesq approximations. Analytical and stochastic approaches to partitioning potential energy are developed and analyzed in simplified 1-D cases. Finally, ambient and deviatoric potential energies, quantities analogous to background and available potential energy are introduced. Direct Numerical Simulations are used to formulate an energy budget. The actual and surrogate potential energies are compared based on the simulation results.
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Tzeng, Ming-Sung, and 曾明松. "Combustion Transitory-Phenomenal Analysis in Solid -Fuel Bed." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/39932284957446504349.
Full textAbstract:
碩士國立臺灣大學
機械工程研究所
84
Proper air manipulation is key to the achievement of good combustion efficiency and reduction of pollutant emissions. Experiments, using a small fix-gate laboratory furnace with cylindrical combustion chamber, were performed to investigate the influence of undergrate/sidewall air distribution on the combustion of beds of wood cubes. The experimental results indicated that the combustion rates are higher when the fuel beds have small voidages. Air jets supplied from side walls, provide efficient combustion and lower co emissions. A simple one-dimension model was constructed to derive correlations of combustion rate as functions of fuel gas temperature and oxygen concentration. The agreement between the model predictions and the experiments are reasonably good.
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Lin, Yu-Chun, and 林佑俊. "A Study on the Phenomena of Ignition and Flame Spread in a Sudden-Expansion Combustor." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/18430944330258887900.
Full textAbstract:
碩士國立清華大學
動力機械工程學系
93
This research work is to study the ignition process of a PMMA slab installed in a sudden-expansion chamber, simulating that occurring in a solid fuel ramjet (SFRJ) combustor. The subject was rarely published in the combustion community before and has long been considered essential to practical application of solid fuel. For the study a hot flow wind tunnel with a sudden-expansion test section has been fabricated. The slab is set immediately downstream of a backward-facing step, and a high-temperature oxidizing stream is provided to flow over the slab. To date the wind tunnel is fully operational and its performance has been extensively evaluated. For a given step height and prescribed velocity, temperature and oxygen concentration of the oxidizing stream, distinct ignition and flame spread phenomena have been observed. Data show that the ignition features are determined by the competition between two dominant variables, the residence time and temperature. As pyrolysis of the solid fuel proceeds, dominance of residence time is gradually replaced by high temperature, which is induced by the premixed flame formed downstream. Thus, instead of occurring within the recirculation zone, ignition is found more likely to take place near the rear end of the fuel slab. Images acquired via high-speed photography reveal interesting, however, unrecognized “rolling” behavior of flame kernels that remains to be further identified. Both concurrent and opposed flame spread are observed if ignition occurs downstream of the reattachment zone. The opposed flame spread is noticed to occur later than the concurrent mode since it suffers more severe convective heat loss. Besides the establishment of a reliable SFRJ simulation platform and corresponding diagnostic techniques, this research provides more physical insights into combustion features of solid fuel in a sudden-expansion combustor, which is commonly seen in industrial applications. Further investigation into this subject is believed to be critical for future development of power and high-speed aero-propulsion systems.
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Tsao, Jiun-Fann, and 曹君範. "A Study on the Numerical Simulation of the Thermo-fluidic Phenomena in the Fluidized Bed Combustor." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/23gtr3.
Full textAbstract:
碩士中原大學
機械工程研究所
91
To prevent the spread of contaminants, the waste of detection and decontamination is not to be disposed in place; nor is packaging and local burying suggested. The best option, therefore, falls on incinerator, by virtue of its performance in decomposing biochemical toxicity. Among various equipments, the movable incinerator, with its high efficacy and mobility, will be demanded in the foreseeable future. Incinerators vary, while available documents inform us of better model of fluidized bed incinerator, capable of saving energy and protection environment. As people have been hatching plans on movable fluidized bed incinerator, the research is based on applying the model in burning the assigned protection equipment of chemical corps – the protective clothes. Upon completing theoretical analysis, we follow by using the simulation software, PHOENICS. By means of controlling different secondary-air and baffle, we discuss the change of velocity and heat-flow fields, in an attempt to provide some reference for continuing incinerator development and design. We discover from our research results some problems in addition to the limitation of simulating function by non-linear variables. These problems are the location of feed, the secondary-air and cooling water input and output, the improvement of incinerator structure, and the stronger effect of removing heat of secondary-air than the effect imposed by the vortex strength. All of them will be further investigated in the future.
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Bai, Jia-Hong, and 白嘉浤. "The Study on the Variation of Neutral Planes and Combustion Phenomenon of Fire Whirls in High-rise Buildings." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/26358291858822118416.
Full textAbstract:
碩士國立高雄第一科技大學
環境與安全衛生工程研究所
103
The safety of evacuation people and rescue personnel will be influenced by the neutral plane position when a fire occurred in the vertical space of the high-rise building. Moreover, the fire whirl will be formed and lead to serious damage due to the characteristic of space constraints. The purpose of this study is to investigate the possibility whether a fire whirl generate and to observe height variation of the neutral plane at different boundary conditions in the vertical space of the high-rise building. Schlieren Photography were used in a model with 35 cm (L) x 34 cm (W) x 145 cm (H) and the width of 3.6 cm(W) gap to measure the height of the neutral plane. Four different roof types of vertical shafts, fully open, fully covered, the front covered and rear covered, were executed to observe the formation of a fire whirl. Secondly, the flame phenomenon was analyzed in various lengths baffles and obstruction region at the gap of the model. The results showed that the fire whirl are formed when no baffle mounted at the gap. The study found that the formation time of a fire whirl is linked with the combustion phenomenon of the fuel tray. The recorded images indicated the same trend with measured data . The results show the fire whirl obviously been delayed or destroyed when the baffle mounted at the bottom of the gap. The study found the formation procedure of a fire whirl possess regularity in the vertical space of high-rise buildings.
39
Caffery, Grant A. "Analysis of transport phenomena in a combusting sulfide particle cloud : with implications to the flash smelting of high-grade copper concentrates." Thesis, 2002. http://hdl.handle.net/2429/12969.
Full textAbstract:
High-grade copper concentrates are becoming increasingly important as feed
materials for flash smelting furnaces. Escondida concentrate from Chile is one of the
most important of these high-grade concentrates. When smelting concentrate blends with
Escondida loadings in excess of approximately 20 wt-%, BHP's San Manuel furnace
observed unreacted concentrate accumulating at the bottom of the reaction shaft. This
limited the quantity of Escondida concentrate that could be smelted by the furnace and
therefore increased its treatment costs.
The objective of this project was to suggest operational improvements to optimise
furnace performance at high Escondida loadings by gaining an understanding of the
influence of high-grade concentrate on the flash smelting behaviour of concentrate
blends. This objective was achieved by conducting experimental and Computational
Fluid Dynamics (CFD) studies on the flash smelting process.
Results from the experimental study show that sulfide flash smelting can be
described using group combustion theory. Furthermore results suggest addition of highgrade
concentrate to the blend reduces the oxygen-to-concentrate ratio and increases the
oxygen enrichment. This lowers the heat transfer effectiveness factor of the particles
within the'cloud and the burner exit velocity, in turn reducing the cloud heat transfer
coefficient. The lower rate of heat transfer to the particles increases the distance required
for them to reach their ignition temperature. At some Escondida loading, the heat-up
time of the particles becomes so large that there is insufficient residence time for particles
to react with the available oxygen, leading to the observed operational problems.
To overcome these problems requires that the heat transfer characteristics of the
concentrate burner be improved. Therefore experimental and CFD studies were
conducted to compare the performance of a swirl burner to a bluff-body burner. The
bluff-body burner was used to approximate the concentrate burner used in industry.
Some differences between the bluff-body burner investigated in this study and the
industrial concentrate burner may cause the observed results for the bluff-body burner to
differ from those of the industrial concentrate burners. It was found that the swirl burner
gives superior performance to the bluff body burner due to two effects:
1) formation of an internal re-circulation zone which transfers heat from the
combustion zone to the fresh mixture, increasing the heat transfer rate to the
concentrate particles; and
2) reduction of the volume of the stagnant zone within the shaft, increasing the
average particle residence time.