Tesi sul tema "Low pressure gas carburizing"
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1
Matamoros, Marin Fatima. "Modélisation et optimisation des fours de cémentation gazeuse basse pression". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0288.
Abstract (sommario):
Ce travail de thèse s'intéresse au développement d'une méthodologie d'optimisation des fours de cémentation gazeuse basse pression. L'objectif est de déterminer les conditions opératoires optimales qui permettent aux opérateurs exposés aux sous-produits toxiques générés (les hydrocarbures aromatiques polycycliques (HAP) et les suies en l'occurrence) de travailler dans des conditions plus sûres. Un modèle phénoménologique du procédé basé sur les équations du bilan de matière et des équations issues d'un mécanisme cinétique détaillé de pyrolyse d'acétylène en phase gazeuse, est d'abord développé. Le mécanisme cinétique est ensuite simplifié afin de réduire la taille du système différentiel, puis complété par un modèle de formation de suies, une réaction de formation de carbone pyrolytique et des phénomènes hétérogènes ayant lieu à la surface des pièces à cémenter qui sont décrits à l'aide du modèle de Langmuir-Hinshelwood-Hougen-Watson. Une première campagne expérimentale sur un réacteur tubulaire et un réacteur sphérique de laboratoire est réalisée en absence de pièces métalliques et permet de comparer les résultats expérimentaux de pyrolyse d'acétylène, de formation de suies et de carbone pyrolytique aux résultats de simulations en réacteur piston et réacteur parfaitement agité. Les résultats montrent l'importance du rôle joué par la formation de carbone pyrolytique et suies sur la formation des HAP. Une deuxième campagne expérimentale est menée sur un four industriel de cémentation gazeuse basse pression ; elle consiste à cémenter des pièces en adoptant une « recette » industrielle, c'est-à-dire en adoptant des conditions opératoires préétablies de manière empirique pour satisfaire le cahier des charges. Les résultats expérimentaux sont utilisés pour estimer les paramètres de la réaction hétérogène de surface en supposant un modèle complet de cémentation gazeuse basse pression en réacteur parfaitement agité. Le modèle est ensuite utilisé dans la formulation du problème d'optimisation dynamique sous contraintes qui vise à minimiser la production de composés toxiques tout en assurant la qualité industrielle des pièces cémentées. Des conditions opératoires optimales permettant d'obtenir des pièces de même qualité que celles obtenues avec la recette industrielle sont alors déterminées par résolution du problème d'optimisation établi et des expériences avec la recette optimisée sont menées sur le four industriel. Les résultats permettent de corroborer que la recette optimisée conduit à des pièces de même qualité que la recette classique industrielle, tout en réduisant la formation de la toxicité du procédéThis PhD work deals with the development of an optimization methodology for low-pressure gas carburizing furnaces. The objective is to determine the optimal operating conditions allowing operators exposed to the toxic by-products generated (polycyclic aromatic hydrocarbons (PAHs) and soot in this case) to work in safer conditions. A first-principles model of the process based on mass balance equations as well as equations derived from a detailed kinetic mechanism of gas-phase acetylene pyrolysis is first developed. The kinetic model is then reduced in order to reduce the size of the differential system; then completed by a model of soot formation, a pyrolytic carbon formation reaction and heterogeneous phenomena occurring on the surface of the steel parts to be cemented which are described by means of Langmuir-Hinshelwood-Hougen-Watson model. Experiments conducted on a laboratory scale tubular reactor and a jet stirred reactor are carried out without steel parts. The results are then compared to the results of simulations of acetylene pyrolysis, soot and pyrolytic carbon formation in a plug flow reactor and in a perfectly stirred tank reactor. The results show the importance of the role played by the formation of pyrolytic carbon and soot on the formation of PAH. Experiments on an industrial low-pressure gas-carburizing furnace are conducted as well; they consist in the carburization of steel parts using an industrial "recipe", i.e. predetermined operating conditions obtained by trial-and-error basis in order to meet the desired carburizing depth. The experimental results are used to estimate the parameters of the heterogeneous surface reaction by assuming a complete model of low-pressure gas carburizing in a perfectly stirred tank reactor. The model is then used in the formulation of the dynamic constrained optimization problem which aims to minimize the production of toxic compounds while ensuring the industrial quality of the carburized steel parts. Optimal operating conditions allowing to obtain steel parts of the same quality as those obtained with the industrial recipe are then determined by solving the optimization problem and experiments using the new operating conditions are conducted in the industrial furnace. The results corroborate that the optimized recipe leads to steel parts of the same quality as the industrial recipe, while reducing the process toxicity
2
Wang, Danqi. "LOW-TEMPERATURE GAS-PHASE CARBURIZING AND NITRIDING OF 17-7 PH STAINLESS STEEL". Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1386165240.
3
Weatherup, Clifford Robert. "New low pressure gas switches". Thesis, University of St Andrews, 1991. http://hdl.handle.net/10023/14040.
Abstract (sommario):
This thesis describes an investigation the aim of which was the development of low pressure gas switches with the advantages of zero standby power consumption and instant readiness. Hydrogen thyratrons use a hollow anode to give the switch a convenient reverse conduction capability. The hollow anode structure has been shown to pass a 4 kA pulse current at 500 Hz for 1010 shots. The use of the hollow anode structure as a cold cathode for a low pressure switch is proposed and triggering of the structure by ions is demonstrated. Under conditions of low gas pressure and high discharge voltage, electrons make few collisions in the cathode dark space of a glow discharge and form extensive beams which travel many centimetres in the gas. Current/voltage characteristics of this 'electron beam' type of discharge are presented for deuterium at pressures between 0.2 and 1.0 torr. The electron beam discharge was found to be space-charge limited with I V3/2 at pressures below about 0.25 torr and I V3/2 at pressures above about 0.25 torr. It is proposed that the current in the electron beam discharge is limited by the flow of positive ions in the cathode dark space. Control of the emission area of a discharge in a hollow metal cylinder is demonstrated and is used as a triggering method for a new type of low pressure gas switch. Tests in a pulse modulator at repetition rates up to 1 kHz show that the switch operates satisfactorily. The triggering mechanism is shown to depend on the properties of the cold cathode glow discharge which, in certain circumstances, leads to the unusual phenomenon of post trigger-pulse firing of the switch. The phenomenon is shown to result from the interaction of the trigger discharge cathode dark space and the geometry of the switch. The glow discharge electron beam is successfully applied as a triggering method in several new low pressure gas switches. In one arrangement, the electron beam is used to pre-ionise the switch and subsidiary grids are used to trigger main conduction. In another arrangement, the electron beam is directed into the high voltage region to trigger conduction directly. The designs of these switches are discussed and their operation is demonstrated.
4
Андріїшин, Mихайло Петрович, Костянтин Іванович Капітанчук, Назар Михайлович Андріїшин, Kostiantyn Kapitanchuk e Константин Иванович Капитанчук. "Natural gas turbine flow meters calibrations in low gas flow pressure situations". Thesis, Національний авіаційний університет, 2018. http://er.nau.edu.ua/handle/NAU/39801.
Abstract (sommario):
In the article criteria of possible turbine flow meters calibrations with natural gas, parameters fluctuations are determined Article presents experimentation results of natural gas parameters influence on processes that occur in turbine flow meters. In the article criteria of possible turbine flow meters calibrations with natural gas, parameters fluctuations are determined. It is known that metrological parameters of the turbine flow meter in operating systems will deter from certificated values. With pressure, temperature or other fluctuations of a flow physical parameters the flow meter's results will occur within of an error space determined by Reynolds number equation for current flow passing through turbine grille. With Reynolds numbers constant aspect ratio the relative error of a flow meter will stay irrelevant of type of the environment. It is suggested to use this value as a criterion that is not affected by thermodynamic parameters and physical characteristics of an environment but of turbine grille
model and mechanical state of a flow meter. Turbine flow meter SM-RI-X-KG1000, DN200 was used for experiment with flow volume varies of 80 m3/h to 1600 m3/h and pressure varies of 100 kPa to 700. Results of theoretical calculations and experimental research data for Reynolds number ratio is shown on a graph of a turbine flow meter speed on pressure dependency. It is determined that the flow meter designed for the low-pressure environment should be calibrated for actual range of operating environment pressure and temperature valuesУ статті визначено критерії калібрувань турбінних витратомірів природного газу. Запропоновано використовувати значення числа Рейнольдса як критерій, на який не впливає термодинамічні параметри та фізичні характеристики середовища, параметри турбінної решітки. модель і механічний стан витратоміра. Для експерименту використовували турбінний витратомір SM-RI-X-KG1000, DN200 з об'ємом потоку від 80 м3 / год до 1600 м3 / год, а тиск змінювався від 100 кПа до 700. Результати теоретичних розрахунків та даних експериментальних досліджень для числа Рейнольдса показано на графіку швидкості турбінного витратоміра на залежність від тиску. Встановлено, що витратомір, призначений для середовища низького тиску, повинен бути відкалібрований для фактичного діапазону тисків робочого середовища та значень температури
В статье определены критерии калибровок турбинных расходомеров природного газа. Предложено использовать значение числа Рейнольдса как критерий, на который не влияет термодинамические параметры и физические характеристики среды, параметры турбинной решетки. модель и механическое состояние расходомера. Для эксперимента использовали турбинный расходомер SM-RI-X-KG1000, DN200 с объемом потока от 80 м3 / ч до 1600 м3 / ч, а давление изменялось от 100 кПа до 700 Результаты теоретических расчетов и данных экспериментальных исследований для числа Рейнольдса показано на графике скорости турбинного расходомера в зависимости от давления. Установлено, что расходомер, предназначенный для среды низкого давления, должен быть откалиброван для фактического диапазона давлений рабочей среды и значений температуры
5
Yang, Suidong. "Diagnostics and modelling of an inductively coupled RF low-pressure low-temperature plasma". Thesis, n.p, 1998. http://oro.open.ac.uk/19841/.
6
Parkinson, J. S. "Control system design for low pressure gas distribution networks". Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378367.
7
Ingram, S. G. "Investigations of low pressure RF discharges in argon". Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.480534.
8
Schirlin, Julien T. "Targeting low vapour pressure compounds in gas-phase electron diffraction". Thesis, University of Edinburgh, 2004. http://hdl.handle.net/1842/11377.
Abstract (sommario):
Gas-phase electron diffraction (GED) has remained the most valuable technique for the collection of structural information in the gas phase, for the last 70 years. Unfortunately, this structural technique had reached a limiting factor: the volatility of chemicals. Therefore this work aims to provide new ways to overcome both the kinetic and thermodynamic aspects of this problem by the adoption of a new nozzle design and by the use of a reservoir. The new nozzle extends the capabilities of gas electron diffraction to compounds with lower vapour pressures or with vaporisation rates not adequate for the existing GED experimental conditions. The shape of the new nozzle allows the user to operate at a lower vapour pressure by increasing the diffraction area. The design investigated is the slit type. It allows the electron beam diameter to be kept small, but permits the gas to emerge from a slit running parallel to the beam. Collected and simulated data have confirmed our intuition that the amplitudes will be affected slightly by the slit nozzle. Superimposing simulated and collected data allowed us to establish the profile of the gaseous output from the new design nozzle and shows that the count of electrons being diffracted increase 5.5 fold, with respect to the conventional nozzle. Gas-phase electron diffraction data have been collected and analysed for 2,5-dichlorothiophene and 3,4dichloro-1,2,5-thidiazole. An extensive series of ab initio calculations has also been undertaken on these molecules, together with 2,5-difluoro and 3,4-dichlorothiophene, allowing the accurate determination of their gas-phase molecular structures. The structures are compared to those of their parent compounds in order to assess the effects of halogen substitution on the rings.
9
Craig, G. "Thomson scattering measurements in low pressure inert and molecular gas plasmas". Thesis, Queen's University Belfast, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403450.
10
Moss, Graham James. "A time-dependent collisional-radiative model of low pressure gas discharges". Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269399.
11
Justo, Hernandez Ruiz. "Low differential pressure and multiphase flow measurements by means of differential pressure devices". Diss., Texas A&M University, 2004. http://hdl.handle.net/1969.1/1077.
Abstract (sommario):
The response of slotted plate, Venturi meter and standard orifice to the presence of two phase, three phase and low differential flows was investigated. Two mixtures (air-water and air-oil) were used in the two-phase analysis while a mixture of air, water and oil was employed in the three-phase case. Due to the high gas void fraction (α>0.9), the mixture was considered wet gas. A slotted plate was utilized in the low differential pressure analysis and the discharge coefficient behavior was analyzed. Assuming homogeneous flow, an equation with two unknowns was obtained for the multi-phase flow analysis. An empirical relation and the differential response of the meters were used to estimate the variables involved in the equation. Good performance in the gas mass flow rate estimation was exhibited by the slotted and standard plates for the air-water flow, while poor results were obtained for the air-oil and air-water oil flows. The performance of all the flow meter tested in the analysis improved for differential pressures greater than 24.9 kPa (100 in_H2O). Due to the tendency to a zero value for the liquid flow, the error of the estimation reached values of more than 500% at high qualities and low differential pressures. Air-oil and air-water-oil flows show that liquid viscosity influences the response of the differential pressure meters. The best results for high liquid viscosity were obtained in the Venturi meter using the recovery pressure for the gas flow estimation at differential pressures greater than 24.9 kPa (100 in_H2O). A constant coefficient Cd was used for the low differential pressure analysis and results did show that for differential pressure less than 1.24 kPa (5 inH2O) density changes are less than 1% making possible the incompressible flow assumption. The average of the computed coefficients is the value of Cd.
12
Malmberg, Andreas. "The influence of carbonitriding on hardness, retained austenite and residual stress in 52100 steel". Thesis, KTH, Materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-173804.
Abstract (sommario):
High rolling contact fatigue parts are vital for the long service life of fuel pumps. Cummins Fuel Systems are currently using an M2 tool steel for one of the most important roller bearing application in their pumps, namely the cam follower. The future design of the cam follower is a pin-less tappet roller. The wear and fatigue properties of the roller is vital to ensure reliability of the fuel system. M2 tool steel is an expensive material and becomes even more so if diamond like coating (DLC) is needed to decrease the friction coefficients. To cut costs of the fuel pump it might be possible to replace the M2 tool steel with 52100 steel (100Cr6). Competitive methods have proven that carbonitrided 52100 can reach excellent wear and fatigue properties making it a candidate to replace M2 tool steel. How the properties of hardness, toughness and compressive residual stresses are developed in 52100 and how they affect the fatigue and wear resistance has been researched from the literature. A big part of this project was to do an extensive analysis of a roller bearing that was believed to have gone through one of these competitive methods that produce excellent wear and fatigue resistance. The analysis was done with background to the knowledge gathered from the literature. Finally process trials were set up to carbonitride 52100 steel samples. The trials were done to develop a better understanding of how adding carbon together with nitrogen to the surface of 52100 steel will influence the metallurgical parameters that results in good wear and fatigue resistance. From this analysis Cummins hope to create a process recipe that can be used for carbonitriding the cam follower and maybe other components in their fuel systems.
13
Jayasuriya, Jeevan. "Experimental Investigations of High Pressure Catalytic Combustion for Gas Turbine Applications". Doctoral thesis, KTH, Kraft- och värmeteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-134445.
Abstract (sommario):
This work is devoted to generate knowledge and high quality experimental data of catalytic combustion at operational gas turbine conditions. The initial task of the thesis work was to design and construct a high pressure combustion test facility, where the catalytic combustion experiments can be performed at real gas turbine conditions. With this in mind, a highly advanced combustion test facility has been designed, constructed and tested. This test facility is capable of simulating combustion conditions relevant to a wide range of operating gas turbine conditions and different kinds of fuel gases. The shape of the combustor (test section) is similar to a “can” type gas turbine combustor, but with significant differences in its type of operation. The test combustor is expected to operate at near adiabatic combustion conditions and there will be no additions of cooling, dilution or secondary supply of air into the combustion process. The geometry of the combustor consists of three main zones such as air/fuel mixing zone, catalytic reaction zone and downstream gas phase reaction zone with no difference of the mass flow at inlet and exit. The maximum capacity of the test facility is 100 kW (fuel power) and the maximum air flow rate is 100g/s. The significant features of the test facility are counted as its operational pressure range (1 – 35 atm), air inlet temperatures (100 – 650 °C), fuel flexibility (LHV 4 - 40 MJ/m3) and air humidity (0 – 30% kg/kg of air). Given these features, combustion could be performed at any desired pressure up to 35 bars while controlling other parameters independently. Fuel flexibility of the applications was also taken into consideration in the design phase and proper measures have been taken in order to utilize two types of targeted fuels, methane and gasified biomass. Experimental results presented in this thesis are the operational performances of highly active precious metal catalysts (also called as ignition catalysts) and combinations of precious metal, perovskites and hexaaluminate catalysts (also called as fully catalytic configuration). Experiments were performed on different catalytic combustor configurations of various types of catalysts with methane and simulated gasified biomass over the full range of pressure. The types of catalysts considered on the combustor configurations are palladium on alumina (Pd/AL2O3), palladium lanthanum hexaaluminate (PdLaAl11O19), platinum on alumina (Pt/AL2O3),and palladium:platinum bi-metal on alumina (Pd:Pt/AL2O3). The influence of pressure, inlet temperature, flow velocity and air fuel ratio on the ignition, combustion stability and emission generation on the catalytic system were investigated and presented. Combustion catalysts were developed and provided mainly by the project partner, the Division of Chemical Technology, KTH. Division of Chemical Reaction Technology, KTH and Istituto di Ricerche sulla Combustione (CNR) Italy were also collaborated with some of the experimental investigations by providing specific types of catalysts developed by them for the specific conditions of gas turbine requirements.QC 20131125
14
O'Connor, Gavin Thomas. "Development of a low pressure-inductively coupled plasma-ion source for mass spectrometry". Thesis, University of Plymouth, 1998. http://hdl.handle.net/10026.1/1764.
Abstract (sommario):
A low pressure-inductively coupled plasma (LP-ICP) ion source has been investigated for the production of atomic and molecular ions for mass spectrometry (MS). A dedicated LPICP- MS was constructed, by modifying a Hewlett Packard mass selective detector, to detect ions from the LP-ICP. The ion sampling interface and ion optics were designed using established theory and the use of a computer simulation program. Perfluorotributylamine was continuously introduced into the LP-ICP, via a molecular leak, and the ion sampling interface, plasma forward power, and plasma gas flow rates, were optimised. When the LP-ICP ion source was sustained at 6W with a gas flow of 6 ml min'* helium, and iodobenzene and dibromobenzene, introduced via GC, only atomic signals for iodine and bromine were observed. Detection limits were 4 and 76 pg for iodobenzene and dibromobenzene respectively. The addition of nitrogen to a LP helium ICP increased the molecular signal for chlorobenzene, resulting in a detection limit of 2 pg. However, the addition of nitrogen did not aid the production of molecular ions of iodobenzene and dibromobenzene. When 0.07 ml min' of isobuiane was added to the LP-ICP mass spectra similar to those obtained by an electron impact source were observed. However, on the addition of more isobutane only the molecular ions (M*) for chlorobenzene, iodobenzene and dibromobenzene were observed. The detection limits for the instrument operating in the molecular mode were 100, 140 and 229 pg for chlorobenzene, iodobenzene and dibromobenzene respectively. Langmuir probe measurements were used to asses the effect of plasma forward power and gas flow rate on the local plasma potential, ion number density, electron temperature and electron number density within the LP-ICP. The local plasma potential varied from +50 V to -20 V depending on the plasma conditions used. The ion and electron number densities increased with increasing plasma power, with ion number densities of approximately 10^ cm' ^ and electron number densities of approximately at 10* cm ^ The effect of extra plasma gas had a less distinct affect on the plasma excited species. A plasma sustained at 6 W, 7 ml min'' helium and 1.8 ml min'* isobutane was used to provide both quantitative and qualitative information of tetraethyllead in the standard reference friel (NBS SRM 1637 II), with .the determined value of 13.06 ± 0.91 being in good agreement with the certified value of 12.9 ± 0.07 expressed as total lead.
15
Kalitan, Danielle Marie. "A Study of Syngas Oxidation at High Pressures and Low Temperatures". Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2422.
Abstract (sommario):
Ignition and oxidation characteristics of CO/H2, H2/O2 and CO/H2/CH4/CO2/Ar fuel blends in air were studied using both experimental and computer simulation methods. Shock-tube experiments were conducted behind reflected shock waves at intermediate temperatures (825 < T < 1400 K) for a wide range of pressures (1 < P < 45 atm). Results of this study provide the first undiluted fuel-air ignition delay time experiments to cover such a wide range of syngas mixture compositions over the stated temperature range. Emission in the form of chemiluminescence from the hydroxyl radical (OH*) transition near 307 nm and the pressure behind the reflected shock wave were used to monitor reaction progress from which ignition delay times were determined. In addition to the experimental analysis, chemical kinetics calculations were completed to compare several chemical kinetics mechanisms to the new experimental results. Overall, the models were in good agreement with the shock-tube data, especially at higher temperatures and lower pressures, yet there were some differences between the models at higher pressures and the lowest temperatures, in some cases by as much as a factor of five. In order to discern additional information from the chemical kinetics mechanisms regarding their response to a wide range of experimental conditions, ignition delay time and reaction rate sensitivity analyses were completed at higher and lower temperatures and higher and lower pressures. These two sensitivity analyses allow for the identification of the key reactions responsible for ignition. The results of the sensitivity analysis indicate that the ignition-enhancing reaction H + O2 = O + OH and hydrogen oxidation kinetics in general were most important regardless of mixture composition, temperature or pressure. However, lower-temperature, higher-pressure ignition delay time results indicate additional influence from HO2- and CO- containing reactions, particularly the well-known H + O + M = HO2 + M reaction and also the CO + O + M = CO2 + M and CO + HO2 = CO2 + OH reactions. Differences in the rates of the CO-related reactions are shown to be the cause of some of the discrepancies amongst the various models at elevated pressures. However, the deviation between the models and the experimental data at the lowest temperatures could not be entirely explained by discrepancies in the current rates of the reactions contained within the mechanisms. Additional calculations were therefore performed to gain further understanding regarding the opposing ignition behavior for calculated and measured ignition delay time results. Impurities, friction induced ionization, static charge accumulation, boundary layer effects, wall reaction effects, and revised chemical kinetics were all considered to be possible mechanisms for the model and measured data disparity. For the case of wall-reaction effects, additional shock-tube experiments were conducted. For the remaining effects listed above, only detailed calculations were conducted. Results from this preliminary anomaly study are at this time inconclusive, but likely avenues for future study were identified. Additional kinetics calculations showed that the large difference between the experimental data and the chemical kinetics models predictions at low temperatures can be explained by at least one missing reaction relevant to low-temperature and high-pressure experimental conditions involving the formation of H2O2, although further study beyond the scope of this thesis is required to prove this hypothesis both theoretically and experimentally.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering PhD
16
McCluney, Peter. "Development of a small natural gas fuelled two stroke cycle engine using low pressure injection". Thesis, Queen's University Belfast, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241433.
17
Leimkuehler, Thomas O. "Investigation of low-pressure laser induced fluorescence for measuring temperature profiles in a rarefied gas /". free to MU campus, to others for purchase, 2000. http://wwwlib.umi.com/cr/mo/fullcit?p9999301.
18
Heath, Melissa. "Heat Transfer Regimes during Charging of Pressure Vessels with Compressed Gas at Low Reynolds Numbers". Thesis, Griffith University, 2018. http://hdl.handle.net/10072/378153.
Abstract (sommario):
Over the past decade signi cant interest in heat transfer during lling of pressure
vessels has arisen due to overheating and under- lling when utilizing compressed
hydrogen gas as a practical storage solution for clean energy sources. The problem
is most clearly evident when hydrogen is stored as compressed gas for use in the
automotive industry since carbon bre reinforced plastic (CFRP) vessels are used
for their low weight. The low thermal conductivity of the plastic component of the
vessel wall has an insulating e ect on the stored gas. During lling, the gas undergoes
heating due to compression work, particularly during lling rates comparable to that
of a traditional vehicle. As the CFRP material can be damaged by overheating, it
is important to be able to predict the temperature of the gas, and the temperature
distribution in the vessel wall. Key to this is understanding the heat transfer between
the gas and the wall during lling. While signi cant progress has been made with
larger vessels, few studies have considered the lower Reynolds number regimes.
The aim of the PhD is to ll the gap in the literature for lower Reynolds number
regimes by providing knowledge and fundamental data required for accurately
predicting heat transfer during lling of gas pressure vessels. The methodologies
being used include experimental work, numerical simulation and analytical methods.
The thesis addresses understanding the heat transfer by experimentally producing
benchmark quality temperature measurements for validation. Experiments
have been undertaken which provide detailed measurements of thermal elds and
heat transfer and the thermal response in the vessel. Computational
uid dynamics
(CFD) is used to determine local Nusselt numbers and understand the development
of boundary layers within the vessel. An analytical solution has been developed
by neglecting convection, essentially treating the vessel as a solid with and evenly
distributed heat source. This model has provided an upper limit on the temperature
rise within the vessel and lower limit on the heat transfer.
The developed analytical solution elucidates the e ect of near wall compression
heating and provides a theoretical limit for the minimum Nusselt number and maximum gas temperature rise in the vessel. The minimum Nusselt number limit is
approached in the case of low Reynolds number. Taking the limit of small Reynolds
number for a vessel being lled with compressed gas, the energy equation was found
to asymptote to the unsteady heat conduction equation with heat generation and
variable density. This equation was solved analytically for cylindrical and spherical
geometry. Assuming the density changes linearly with time, a solution is obtained
which can become identical in form to the constant density solution if the Fourier
number is de ned using a log-mean density rather than the instantaneous density.
For a constant energy input rate the Nusselt number was found to approach a
constant value after an initial transient period. At such 'steady state' conditions, the
Nusselt number based on the diameter for cylinders with aspect ratios larger than 1
rapidly approaches an integer solution of NuD = 8. For cylinders with aspect ratios
less than 1, the Nusselt number based on the cylinder length (height) characteristic
dimension rapidly approaches NuL = 6. It is shown experimentally and numerically
that during compression lling, the heat transfer asymptotically approaches this
analytical solution at low Reynolds numbers.
Four distinct regimes were identi ed during the lling of the vessel. At the
very beginning of lling, heat transfer is dominated by heat conduction and can be
described by the analytical solution. Following this there is a period dominated by
forced convection from the jet of gas entering the vessel. A signi cant temperature
di erence and increased density of the gas causes natural convection currents to
develop as the Rayleigh number increases. Both free and forced convection play an
important role for a period of time which can be described as a mixed convection
regime. As the lling rate and jet penetration into the
ow eld decays forced
convection e ects diminish leaving only free convection which continues after gas
has stopped entering the vessel until thermal equilibrium is reached.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text
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Vancko, Jr Robert M. "Effect of a drag reducing agent on pressure drop and flow regime transitions in multiphase horizontal low pressure pipelines". Ohio University / OhioLINK, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1184354301.
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Mrosek, Matthias. "Model-based control of a turbocharged diesel engine with high- and low-pressure exhaust gas recirculation". Phd thesis, VDI Verlag, 2017. https://tuprints.ulb.tu-darmstadt.de/6960/1/Dissertation_Mrosek_TUprints.pdf.
Abstract (sommario):
Modern Diesel engines fulfil challenging requirements for emission limits, fuel consumption and ride comfort by numerous modular combinable components and mechatronical actuators. These components are utilised for precondition and aftertreatment of air, fuel and exhaust gas, which is involved in the combustion process. In this dissertation a methodology for a model-based function development with semi-physical engine models for control of air path quantities of an exemplary Diesel engine with high-pressure (HP-EGR) and low-pressure exhaust gas recirculation (LP-EGR) is developed. In this framework for function development black-box models for stationary and dynamical emission formation are utilised to optimise reference values for the air path control and to rate the developed control scheme with regard to the cumulated driving cycle emissions of the new European driving cycle (NEDC).
A combination of HP-EGR and LP-EGR represents a novel approach to significantly lower the particulate and NOx emissions of Diesel engines. A semi-physical mean value engine model with lumped parameters is the base to analyse the system properties of the complex air path. In doing so, the additional LP-EGR shows only minor influences to the quantities charge air pressure and HP-EGR, while there are significant influences of these quantities on the LP-EGR mass flow rate. Furthermore, the LP-EGR is characterised by significant gas propagation times in the intake and exhaust system. These delays are modelled by a gas composition model, which is incorporated into the control scheme.
NOx and particulate emissions as well as engine torque are stationary modelled by local polynomial models with input quantities of the combustion process. These quantities are air mass flow rate, charge air pressure, intake temperature and crank angle of 50% mass fraction burned. A bilinear interpolation between engine speed and injection quantity transforms local polynomial models into global models. Models for the dynamical emission formation are given by considering the combustion as a batch process. Consequently all dynamics are included in the quantities of the cylinder charge at intake valve closing and the emission measurement dynamics. Thus, a combination of a dynamical gas composition model, stationary emission models and models for the emission measurement dynamics yield the dynamical course of the engine emissions.
The investigated system properties and the emission models deliver the control variables charge air pressure, air content and intake temperature for the engine with VGT-turbocharger, HP- and LP-EGR. A stationary optimisation with regard to emissions and engine torque delivers reference values for the air path control and further shows the potential of the LP-EGR to lower the emissions. Due to the multi-variable characteristics of the air path with different dynamics, there are increased dynamical emissions at engine transients. These dynamical emissions are lowered by dynamical optimised reference values for the air path control.
Generally, the air path is a strongly nonlinear process and the multitude of engine variants and engine operation modes result in a trade-off between achievable control quality, control robustness and number of control parameter sets. A semi-physical feedforward control, which is based upon parameterised model relationships of the mean value engine model delivers a good response to setpoint changes. Thus, the disturbance rejection can be achieved by relatively simple controllers. This results in an significantly lower application effort of control parameters and allows by its modular structure to exchange engine components without the drawback to completely re-parameterise the control parameters. A reference value transformation with modelled states of the gas composition model compensates long gas propagation times in the intake and exhaust system and delivers an optimal air content in the cylinder charge. All control concepts are validated with measurements at the engine test bench. Finally, the derived control concepts for the LP-EGR are compared to the classical HP-EGR control with regard to the cumulated driving cycle emissions. In this investigation the proportion of stationary and dynamical emissions is clearly quantified.
In a nutshell this dissertation is an important contribution for model-based optimisation and function development for the air path control of Diesel engines. The given combination of models for dynamical emission formation, dynamically optimised reference values for the air path control and semi-physical control design are a holistic framework to master the complexity and variance of future Diesel and gasoline engines.
21
Le, Thi Kim Cuong. "Raman spectroscopy of soot produced in low pressure flames : ex situ Analyses and Online Gas Phase Studies". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS068/document.
Abstract (sommario):
Chaque année, une quantité de 107tonnes de suie est produite à l'échelle mondiale. Le carbone-suie dans l'atmosphère a des effets graves sur le changement climatique et la santé humaine. Les impacts dépendent de nombreux facteurs comme les composés organiques adsorbés, le vieillissement et les processus de mélange. Par conséquent, afin de réduire la quantité de suie émise, outre l'examen des facteurs mentionnés, les études de la cinétique de formation, de la structure et des propriétés optiques des suies sont également essentielles. Il existe plusieurs méthodes optiques dans les études sur la suie. La spectroscopie Raman occupe un rôle particulier puisqu'elle est un outil puissant pour l'étude structurale des matériaux carbonés grâce à sa sensibilité aux structures à l’échelle moléculaire. Dans ce travail, des sections Raman différentielles de suies et quelques autres particules carbonées ont été mesurées pour progresser vers la spectroscopie Raman quantitative de ces particules. Les suies produites par des flammes d'éthylène pré-mélangées à basse pression ont été étudiées par mesure Raman ex-situ sur des films déposés et des mesures Raman in-situ (enligne) dans la phase gazeuse. La combinaison de la spectroscopie Raman de suies échantillonnées sur substrat avec les spectroscopies infrarouge et optique et la microscopie électronique en transmission a permis de progresser sur l'interprétation des spectres Raman de suie. Les mesures en phase gazeuse, obtenues pour la première fois, fournissent de nouvelles informations sur la naissance des suies et leurs structures dans les flammes à basse pression avec, par exemple, la détection d'une grande quantité d'atomes de carbones hybridés sp lors de la formation et de la croissance des premières suies. Ces étude s’ouvrent la voie à la détection et à l'analyse des suies directement en phase gazeuse et à leur détection quantitative dans l’atmosphère au travers de leurs spectres RamanEvery year, an amount of 107 tons of soot is produced on the world scale. Soot, as part of atmospheric black carbon, has serious impacts on climate change and human health. The impacts depend on many factors including adsorbed compounds, aging and mixing processes. Therefore in order to reduce the soot amount, besides considering these mentioned factors, the study of formation kinetics, structure and optical properties is also essential. There are several methods applied in soot investigations. Raman spectroscopy plays a particular role as it is a powerful tool for structural investigation of the carbon-based materials because it is sensitive to molecular structures. In this work, differential Raman cross sections of soot and some other carbonaceous particles were measured to progress toward quantitative Raman spectroscopy. Soot particles produced by premixed ethylene flames at a low pressure were investigated by ex-situ Raman measurement on deposited films and in-situ(online) Raman measurement in the gas phase. Combination of the Raman spectroscopy of soot sampled on substrates with infrared and optical spectroscopy and transmission electron microscopy allowed progressing on the interpretation of soot Raman spectra. The online gas phase measurements provided a novel view on soot birth and structures in low pressure flames with, for instance, the detection of a large amount of sp hybrized carbon atoms during nascent soot growth. These studies pave the way to soot detection and analysis directly and quantitatively in the atmosphere
22
Zhang, Kaiyi. "CO2 Minimum Miscibility Pressure and Recovery Mechanisms in Heterogeneous Low Permeability Reservoirs". Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/93728.
Abstract (sommario):
Benefited from the efficiency of hydraulic fracturing and horizon drilling, the production of unconventional oil and gas resources, such as shale gas and tight oil, has grown quickly in 21th century and contributed to the North America oil and gas production. Although the new enhancing oil recover (EOR) technologies and strong demand spike the production of unconventional resources, there are still unknowns in recovery mechanisms and phase behavior in tight rock reservoirs. In such environment, the phase behavior is altered by high capillary pressure owing to the nanoscale pore throats of shale rocks and it may also influence minimum miscibility pressure (MMP), which is an important parameter controlling gas floods for CO2 injection EOR. To investigate this influence, flash calculation is modified with considering capillary pressure and this work implements three different method to calculate MMP: method of characteristics (MOC); multiple mixing cell (MMC); and slim-tube simulation. The results show that CO2 minimum miscibility pressure in nanopore size reservoirs are affected by gas-oil capillary pressure owing to the alternation of key tie lines in displacement. The values of CO2-MMP from three different methods match well.
Moreover, in tight rock reservoirs, the heterogeneous pore size distribution, such as the ones seen in fractured reservoirs, may affect the recovery mechanisms and MMP. This work also investigates the effect of pore size heterogeneity on multicomponent multiphase hydrocarbon fluid composition distribution and its subsequent influence on mass transfer through shale nanopores. According to the simulation results, compositional gradient forms in heterogeneous nanopores of tight reservoirs because oil and gas phase compositions depend on the pore size. Considering that permeability is small in tight rocks and shales, we expect that mass transfer within heterogeneous pore size porous media to be diffusion-dominated. Our results imply that there can be a selective matrix-fracture component mass transfer during both primary production and gas injection secondary recovery in fractured shale rocks. Therefore, molecular diffusion should not be neglected from mass transfer equations for simulations of gas injection EOR or primary recovery of heterogeneous shale reservoirs with pore size distribution.Master of Science
The new technologies to recover unconventional resources in oil and gas industry, such as fracturing and horizontal drilling, boosted the production of shale gas and tight oil in 21st century and contributed to the North America oil and gas production. Although the new technologies and strong demand spiked the production of tight oil resources, there are still unknowns of oil and gas flow mechanisms in tight rock reservoirs. As we know, the oil and gas resources are stored in the pores of reservoir formation rock. During production process, the oil and gas are pushed into production wells by formation pressure. However, the pore radius of shale rock is extremely small (around nanometers), which reduces the flow rate of oil and gas and raises capillary pressure in pores. The high capillary pressure will alter the oil and gas phase behavior and it may influence the value of minimum miscibility pressure (MMP), which is an important design parameter for CO2 injection (an important technology to raise production). To investigate this influence, we changed classical model with considering capillary pressure and this modified model is implemented in different methods to calculate MMP. The results show that CO2 -MMP in shale reservoirs are affected by capillary pressure and the results from different methods match well. Moreover, in tight rock reservoirs, the heterogeneous pore size distribution, such as fractures in reservoirs, may affect the flow of oil and gas and MMP value. So, this work also investigates the effect of pore size heterogeneity on oil and gas flow mechanisms. According to the simulation results, compositional gradient forms in heterogeneous nanopores of tight reservoirs and this gradient will cause diffusion which will dominate the other fluid flow mechanisms. Therefore, we always need to consider molecular diffusion in the simulation model for shale reservoirs.
23
Cheng, An-jen Tzeng Y. "Cold cathodes for application in poor vacuum and low pressure gas environments carbon nanotubes versus zinc oxide nanoneedles /". Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Spring/master's/CHENG_AN-JEN_7.pdf.
24
Bolduc, Mathieu. "Deposition of Commercially Pure Titanium Powder Using Low Pressure Cold Spray and Pulsed Gas Dynamic Spray for Aerospace Repairs". Thesis, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24249.
Abstract (sommario):
The objective of this study is to investigate the feasibility of depositing 1.5 mm thick titanium coatings, as a repair method for aerospace Ti-6Al-4V substrates, using two new commercially available processes: Low Pressure Cold Spray (LPCS) and Pulsed Gas Dynamic Spray (PGDS). The coatings produced were examined and characterized by their porosity level, microhardness, adhesion strength, particle flattening ratio, wipe tests, fracture surface type and wear tests. Phases and chemical composition were determined using X-Ray diffraction analysis and energy dispersive spectroscopy, respectively. It was found that both spraying processes are capable of producing dense, hard and oxide-free coatings using specific parameters. Finally, as a first step towards repair implementation of these processes, damages were simulated on Ti-6Al-4V samples, which were successfully repaired with low porosity and high hardness levels. The feasibility of repairs was confirmed, the next step will consist in qualification testing to assess coating performances under real life application.
25
Moore, Myles Thomas. "An Integrative Geochemical Technique to Determine the Source and Timing of Natural Gas Formation in Gas Hydrates". The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1577959057433697.
26
Lui, Samson Sze-Sang. "A Data Acquisition System Experiment for Gas Temperature and Pressure Measurements on a Liquid-Nitrogen-Powered Vehicle". Thesis, University of North Texas, 1998. https://digital.library.unt.edu/ark:/67531/metadc278790/.
Abstract (sommario):
A data acquisition system was set up to measure gas temperatures and pressures at various points on a liquid-nitrogen-powered vehicle. The experiment was attempted to develop a data acquisition method for applications on engines that use liquid air as the fuel. Two thermocouples and a pressure transducer were connected using data acquisition instruments interfaced to a laptop computer to acquire data.
27
Pelletier, Jean-Louis. "Development of Ti-6Al-4V Coating onto Ti-6Al-4V Substrate Using Low Pressure Cold Spray and Pulse Gas Dynamic Spray". Thesis, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24239.
Abstract (sommario):
The objective of this study is to successfully deposit Titanium Ti-6Al-4V layers onto Ti-6Al-4V substrate using two new commercially available Cold Spray processes such as Low Pressure Cold Spray (LPCS) and Pulsed Gas Dynamic Spray (PGDS). The second objective of this work is to develop a technique to repair Titanium parts since there is currently no repair technique commercially available. It is envisioned that commercial cold spray systems could be used to repair gashes on Titanium components. The examination of both feedstock powders and coatings were performed by different techniques such as optical microscopy and Scanning Electron Microscopy (SEM). Porosity, hardness, adhesion strength, flattening ratio, wipe test, fracture surface, wear test, XRD and chemical composition of the coatings using EDS have been evaluated. Cold spray has shown to be a promising technique for the deposition of heat sensitive particles such as titanium. LPCS and PGDS both produced high quality coatings. Low porosity, high hardness, adhesion strength over 40 MPa, metallurgical bonding, similar to bulk material wear rate, no oxide and nitride phases inside coating were measured.
28
Cotton, Dominique. "Etude de formation d'hémicarbure de tantale (Ta2C) par l'intermédiaire d'un procédé de cémentation sous pression réduite". Thesis, Dijon, 2015. http://www.theses.fr/2015DIJOS010/document.
Abstract (sommario):
Le tantale est un métal très dense (d = 16,6) et fond à très haute température (2996°C), ce qui en fait un matériau potentiellement utilisable pour des creusets utilisés en pyrochimie. La littérature montre qu'il est possible de renforcer encore ces propriétés anti-corrosion par un traitement de cémentation. En effet, la corrosion intergranulaire du tantale est stoppée par la présence de précipités de Ta2C aux joints de grains. L'obtention du Ta saturé carbone avec Ta2C aux joints de grains en surface (Ta(C) + Ta2C), très pauvre en carbone, demande une bonne compréhension et une maitrise de la cémentation du tantale.La réalisation d'un cycle de cémentation sur des échantillons de tantale provoque l'apparition à la surface du tantale d'une couche de TaC (en surface) et d'une couche de Ta2C sous jacente. Un travail sur la réduction du flux de carbone à la surface du tantale a permis d'étudier les premiers stades de formation des couches de carbures de tantale. Ces conditions particulières de cémentation favorisent la croissance en épitaxie des couches de carbures sur le substrat Ta. Les analyses EBSD ont permis de mettre en évidence les relations cristallographiques entre chaque phase.Lors d'un cycle de cémentation, la croissance des couches de carbures doit être contrôlée du fait que celles-ci soient très riches en carbone. Plusieurs types de paramètres peuvent influer sur la croissance des couches : les paramètres de cycles (temps et température de cémentation) et des paramètres extérieurs aux cycles de cémentation, tels que la surface des échantillons. L'influence de ces paramètres sur la cinétique de croissance des couches a été étudiée. En complément des essais, la simulation numérique avec le logiciel CASTEM© a été utilisée afin d'étudier la diffusion du carbone dans le tantale. Les données expérimentales permettent d’ajuster les variables du modèle comme le coefficient de diffusion du carbone dans le tantale.La réalisation d'un recuit sous vide après cémentation permet d'obtenir en surface des microstructures autres que le TaC. Le recuit fait diffuser le carbone contenu en surface vers le coeur du tantale. Une étude a permis de déterminer les paramètres du traitement de recuit, pour obtenir en surface, au choix : du TaC, ou du Ta2C, ou du Ta(C) + Ta2CTantalum is a very dense metal (d = 16.6) and has a very high melting temperature of 2996°C. This material is particularly required for crucibles used for pyrochemical applications. Early studies show that a carburizing treatment enhances corrosion resistance from liquid metals. Indeed, the intergranular attack of tantalum is stopped by Ta2C precipitates, which occupy the grain boundary regions. The production of the carbon saturated tantalum with Ta2C precipitates requires a good understanding of tantalum carburizing.A carburizing treatment on tantalum sample causes the emergence of a TaC layer on surface and Ta2C layer just below. A reduction of carbon flow has enabled the study of the first steps of tantalum carbides formation. This specific condition of carburizing leads to an epitaxic growth of carbide layers on tantalum substrate. EBSD analysis highlights the crystallographic relations between each phase.Tantalum carbide layers are highly carbon concentrated. So the growth of carbide layers has to be controlled during the carburizing treatment. Several parameters may affect carbide layers growth : process parameters (time and temperature of carburizing treatment) and external parameters such as the reactive surface of the samples. The influence of these parameters on tantalum carbide growth kinetics has been studied. In addition, the diffusion of carbon in tantalum has been modeled with CASTEM© software. Experimental data are used to compute parameters of the model, such as carbon diffusion coefficient in tantalum.Other microstructures than TaC can be obtained on surface by applying an annealing treatment after carburizing. With this treatment, the carbon contained on surface diffuses to the bulk of the metal. Annealing treatment parameters have been determined to get on surface TaC, or Ta2C, or carbon saturated tantalum with Ta2C precipitates
29
Beule, Caroline de [Verfasser], e Gerhard [Akademischer Betreuer] Wurm. "Lifting grains from a dust bed by interaction with optical radiation and gas at low ambient pressure / Caroline de Beule. Betreuer: Gerhard Wurm". Duisburg, 2016. http://d-nb.info/1090785550/34.
30
Robin, Frisk. "Distortion Analysis of Low Pressure Carburized Components : A heat treatment distortion comparison of transmission gear components for truck and automobile". Thesis, KTH, Materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193539.
Abstract (sommario):
During the last 10 years, low pressure carburizing and high pressure gas quenching has become more popular since it is a “new” process and researchers reports that the distortion characteristics gained from these processes is improved in relation to conventional processes. The aim of this work was to investigate the distortions gained from three different heat treatment processes on main shaft gears and crown wheels. Experiments with atmospheric carburization with oil quenching and low pressure carburization with nitrogen gas quenching or oil quenching were made and distortion characteristics gained from these processes were then measured and compared. It was found that components treaded in the relatively new LPC-HPGQ process are similar and often even better than the conventional method. The larger main shaft gear improves the most with newer method but instead gets a lower core hardness and systematic diametrical shrinkage. Some measurements on the crown wheel were also improved but others were affected negatively.
31
Mrosek, Matthias Patrick Alexander [Verfasser], Rolf [Akademischer Betreuer] Isermann e Ulrich [Akademischer Betreuer] Konigorski. "Model-based control of a turbocharged diesel engine with high- and low-pressure exhaust gas recirculation / Matthias Patrick Alexander Mrosek ; Rolf Isermann, Ulrich Konigorski". Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1145141935/34.
32
Simiema, de Freitas Barbosa Gustavo [Verfasser], Bernd [Akademischer Betreuer] Mayer, Bernd [Gutachter] Mayer e Jürgen [Gutachter] Meichsner. "Construction and Evaluation of Gas Feed-in System, Electrodes and Gas Exhaustion System applied to Low Pressure Plasma Coating Processes / Gustavo Simiema de Freitas Barbosa ; Gutachter: Bernd Mayer, Jürgen Meichsner ; Betreuer: Bernd Mayer". Bremen : Staats- und Universitätsbibliothek Bremen, 2018. http://d-nb.info/1165772302/34.
33
Loukota, Martin. "Návrh dvoutlakého vertikálního kotle na odpadní teplo za plynovou turbínou na zemní plyn". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-319280.
Abstract (sommario):
This master‘s thesis deals with design of vertical heat recovery steam generators (HRSG). In the introduction part is performed description and distribution HRSG, thermal calculation, proposal of a heat transfer surfaces and choice of materials. Finally is executed aerodynamic calculation, hydraulic calculation and then are suggested dimensions of the drums. Thesis also includes technical documentation of the boiler.
34
Bongers, Marian David Verfasser], Astrid [Akademischer Betreuer] Pundt, Astrid [Gutachter] Pundt, Michael [Gutachter] Seibt, Hans Christian [Gutachter] Hofsäss, Reiner [Gutachter] [Kirchheim, Vasily [Gutachter] Moshnyaga e Martin [Gutachter] Wenderoth. "In situ studies on palladium/rutile titanium dioxide exposed to low pressure hydrogen gas environments / Marian David Bongers ; Gutachter: Astrid Pundt, Michael Seibt, Hans Christian Hofsäss, Reiner Kirchheim, Vasily Moshnyaga, Martin Wenderoth ; Betreuer: Astrid Pundt". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2018. http://d-nb.info/1171521464/34.
35
Ngeleka, Tholakele Prisca. "Sulphur dioxide capture under fluidized bed combustion conditions / Tholakele Prisca Ngeleka". Thesis, North-West University, 2005. http://hdl.handle.net/10394/1416.
Abstract (sommario):
An investigation was undertaken to determine the feasibility of increasing the hydrogen
production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process
(HyS). This investigation also involved the technical and economical analysis of the water gas
shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical
analysis of the water gas shift reaction was determined under the operating conditions selected
on the basis of some information available in the literature. The high temperature system (HTS)
and low temperature system (LTS) reactors were assumed to be operated at temperatures of
350ºC and 200ºC, respectively. The operating pressure for both reactors was assumed to be 30
atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was
242T/D, which is approximately two times the amount produced by the HyS process alone. The
PSA was used for the purification process leading to a hydrogen product with a purity of
99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2
is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with CO2
and traces of CH4, CO, and saturated H2O. The estimated capital cost of the WGS plant with
PSA is about US$50 million. The production cost is highly dependent on the cost of all of the
required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2
based on the input cost of synthesis gas as produced by the POX process. In this case the
production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen
was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the
corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg.Thesis (M.Sc. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.
36
Ngeleka, Tholakele Prisca. "An investigation into the feasibility of applying the watergas shift process to increase hydrogen production rate of the hybrid sulphur process / T.P. Ngeleka". Thesis, North-West University, 2008. http://hdl.handle.net/10394/4108.
Abstract (sommario):
An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350°C and 200°C, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with C02 and traces of CH4, CO, and saturated H20. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg.Thesis (M.Sc. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.
37
Malbois, Pierre. "Analyse expérimentale par diagnostics lasers du mélange kérosène/air et de la combustion swirlée pauvre prémélangée, haute-pression issue d’un injecteur Low-NOx". Thesis, Normandie, 2017. http://www.theses.fr/2017NORMIR25/document.
Abstract (sommario):
Les motoristes aéronautiques misent sur le développement de systèmes d’injection de carburant innovants pour réduire la consommation de carburant et les émissions de polluants. L’objectif de la thèse est de contribuer à l’étude expérimentale d’un injecteur « Lean Premixed » par le développement de diagnostics lasers couplant des approches basées sur la diffusion de Mie et l’émission fluorescente de traceurs. Les mesures ont été réalisées sur le banc de combustion haute pression HERON. Une approche novatrice avec l’imagerie de fluorescence du kérosène a permis d’obtenir une quantification du mélange kérosène/air. La structure de flamme a été mesurée simultanément par PLIF-OH et des mesures PIV de vitesse ont complété cette analyse. Un développement préliminaire de la PLIF-CO a également été mené. Les nombreuses mesures permettent de fournir une analyse détaillée des interactions flamme/spray/aérodynamique lors d’une combustion swirlée stabilisée kérosène/air à haute pressionAeronautical engine manufacturers are banking on the development of innovative fuel injection systems to reduce fuel consumption and pollutant emissions. The aim of the thesis is to contribute to the experimental investigation of a "Lean Premixed" injector by developing laser diagnostics coupling approaches based on Mie scattering and fluorescent emission of tracers. Measurements are performed at high pressure on the HERON combustion test bench. An innovative approach with fluorescence imaging of kerosene has resulted in the quantification of the kerosene/air mixture. The flame structure was analyzed simultaneously by OH-PLIF and velocity PIV measurements were performed to complete this analysis. A preliminary development of CO-PLIF was also conducted. The numerous measurements provided a detailed analysis of the mechanisms of flame/spray/aerodynamic interactions during a swirl-stabilized kerosene/air combustion at high pressure
38
Filoušová, Natálie. "Parní turbína v paroplynovém cyklu". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318750.
Abstract (sommario):
Diploma thesis named Steam turbine in the combi cycle deals with design of low pressure part of three-body turbine and it’s lateral outlet throat to the air condenser. Before the design itself, the thermal schema of entire turbine is calculated. Than follows the detail draft, the strength calculations are included as well. Turbine has any technological consumption of steam or any regenerativ consumption. Turbine will be suplly to Panama. The thesis includes following drawings: cut of flowing part, design of outlet throat and fixing of inner body in outer body of low pressure part. The diploma thesis is created for Doosan Škoda Power company.
39
Biggs, Timothy James. "Studies of crystalline organic molecular materials under extreme conditions". Thesis, University of Oxford, 2006. http://ora.ox.ac.uk/objects/uuid:51dae806-2954-4ea7-a3cb-1980ecb53e98.
Abstract (sommario):
This thesis describes investigations into the properties of -phase BEDT-TTF charge transfer salts. Charge transfer salts are mainly studied as they are very useful test beds for fundamental physics due to the tuneability of their proper- ties and ground states. The effects of temperature and pressure on such systems have been studied, as these allow access to a wide range of different states and properties. Transport properties of these systems have been studied to obtain information about the Fermi surface and effective mass, and the effect of deuter- ation and also change of pressure media will be discussed. The interaction of infrared radiation with these systems has also been investigated and simultaneous pressure and temperature measurements will be presented, something not greatly studied due to the large technical challenges. The techniques and approaches for overcoming these are also discussed. Chapter 1 provides an introduction to the organic materials themselves with particular emphasis on the actual compounds studied. Chapter 2 provides the necessary theoretical background for studying organic charge transfer salts using magnetic quantum oscillations and their infrared re- ectivity. Chapter 3 covers the experimental techniques and also discusses some of the challenges encountered and their solutions to aid others working in this area. Chapter 4 describes an investigation into the transport properties of - (ET)2Cu(SCN)2 by studying Shubnikov-de Haas oscillations using both deuter- ated and normal samples and using two different pressure media, and comparing it to work done using a third. Chapter 5 presents an investigation into the pressure dependence of selected phonon modes in -(ET)2Cu(SCN)2 using infrared radiation on a deuterated sam- ple. Chapter 6 presents what is believed to be the first pressure and temperature dependent infrared study of an organic molecular material. In this case the or- ganic molecular material is d8--(ET)2Cu[N(CN)2]Br, but the techniques should be readily transferable to other materials.
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Fletcher, Nathan James. "Design and Implementation of Periodic Unsteadiness Generator for Turbine Secondary Flow Studies". Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright1560810428267352.
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Fernandes, Hipolito Ana Isabel. "Étude des phénomènes de transport dans un réacteur catalytique pilote de type filaire". Thesis, Lyon 1, 2010. http://www.theses.fr/2010LYO10285/document.
Abstract (sommario):
L’extrapolation des réacteurs catalytiques nécessite l’acquisition des données cinétiques sur des réacteurs à petite échelle dans les conditions opératoires industrielles. Le critère de dimensionnement utilisé lors de la réduction d’échelle est la conservation de la vitesse volumique horaire, ce qui conduit à des vitesses de circulation très faibles dans les réacteurs pilotes à lit-fixe. A ces vitesses, les flux de transfert de matière externes peuvent devenir limitant par rapport au flux de réaction. Dans ce contexte, une nouvelle géométrie de réacteur a été imaginée pour intensifier les transferts de matière et chaleur et pour augmenter les vitesses de circulation des fluides : le réacteur "filaire". Il s’agit d’un réacteur dont le diamètre est égal ou proche de celui des grains de catalyseur et avec un ratio longueur sur diamètre très élevé. Le principal objectif de cette thèse est de caractériser ce réacteur en termes d’hydrodynamique et de transferts de matière externes pour définir ses limites d’utilisation. En écoulement diphasique, ce réacteur est relativement piston et la rétention liquide est élevée, ce qui permet d'assurer un mouillage total du catalyseur. En ce qui concerne les vitesses des transferts de matière externe, celles-ci sont proches de celles d'un réacteur agité avec panier et sont supérieures à celles caractéristiques d'un réacteur pilote à lit-fixe conventionnel. Cette observation est liée à l’augmentation des vitesses locales du liquide et à la présence d'un écoulement du type Taylor modifié. En conclusion, le réacteur "filaire" constitue une alternative efficace aux réacteurs pilotes à lit-fixe pour l’étude de catalyseurs mis en formeSmall size fixed-bed reactors are a common choice for testing industrial supported catalyst under industrial operating conditions. The most common criterion for reactor’s scale-down is based on the conservation of the liquid hourly space velocity which leads to a very low fluid flow velocity at the laboratory scale. Under these conditions, the external mass transfer flux can become the limiting step of the process. In this context, a new reactor geometry was proposed to intensify mass and heat transfers and to increase fluid flow velocities: the single pellet string reactor. This reactor is composed of a tube with an internal diameter close to that of the catalyst particles and with a high length over diameter ratio. The main goal of this thesis is to characterise the hydrodynamic and external mass transfer performances of this new reactor in order to define its application domain. In two-phase gas-liquid flow, the reactor flow is plug flow and the liquid hold-up values are high, which insures a complete wetting of the catalyst particles. The mass transfer coefficients were quantified and the measured rates are much higher than those observed in conventional pilot fixed-bed reactors, which can be explained by the increased local liquid velocities and by the modified Taylor flow regime. Catalytic tests with a very fast model reaction revealed that the external mass transfer performances of the single pellet string reactor are close to those measured in a stirred tank reactor equipped with a catalytic basket. In conclusion, the single pellet string reactor represents a new and efficient alternative to fixed-bed pilot reactors to study shaped catalysts
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TERNER, MATHIEU. "Innovative materials for high temperature structural applications: 3rd Generation γ-TiAl fabricated by Electron Beam Melting". Doctoral thesis, Politecnico di Torino, 2014. http://hdl.handle.net/11583/2527509.
Abstract (sommario):
In the aeronautics industry, the propulsion systems stand among the most advanced and critical components. Over the last 50 years, gas turbine aeroengines were subjected to intensive research to increase efficiency and reduce weight, noise and harmful emissions. Together with design optimization, breakthrough in materials science for structural applications triggered the development of the most advanced gas turbine engines. For low temperatures, basically ahead of the combustion section, lightweight Ti alloys are preferred for their good mechanical properties. For high temperatures instead, Ni-based superalloys exhibit outstanding properties up to very high temperatures despite a rather high material’s density.
Research have focused on enhancing to the maximum the potential of materials in gas turbine engines. According to the application, the components experience various mechanical and environmental constraints. Special designs, manufacturing process, material compositions and protective coatings have been developed to push the limits of advanced materials. Nowadays, the attention is focused on innovative materials to replace the existing Ti and Ni based alloys leading to substantial benefits. Light weight composite materials in particular were found very attractive to replace some components’ Ti alloys. At higher temperatures, it is of great interest to replace Ni-based superalloys by materials with lower density and/or higher temperatures applications, which in turn would lead to substantial weight reduction and increase efficiency.
At the highest temperatures range, in particular in the combustion chamber and high pressure turbine sections, ceramic based materials offer promising balance of properties. Research are dedicated to overcome the drawbacks of ceramics for such structural applications, and in particular their brittle fracture behavior, by addition of reinforcing fibers. At lower temperatures range, TiAl based intermetallics emerged as very promising materials at half the density of Ni-based superalloys. Significant weight reduction could be achieved by the introduction of TiAl based alloys for rotating components of the compressor and low pressure turbine. 2nd generation γ-TiAl alloys were lately introduced in GE’s GEnx and CFM’s LEAP engines.
The present work concerns the fabrication by the additive manufacturing technique Electron Beam Melting of 3rd generation γ-TiAl alloys for high temperatures application in gas turbine aeroengines. EBM, building parts layer by layer according to CAD, offers many advantages compared to other manufacturing processes like casting and forging. Reported by Avio, 2nd generation γ-TiAl alloys have been successfully fabricated by EBM. To increase the material’s potential, the production of 3rd generation γ-TiAl alloys Ti-(45-46)Al-2Cr-8Nb was therefore studied. The optimization of the EBM parameters led to high homogeneity and very low post-processing residual porosity ≤ 1%. The fine equiaxed microstructure after EBM could be tailored towards the desired mechanical properties by simple heat treatment, from equiaxed to duplex to fully lamellar. In particular, a duplex microstructure composed by about 80 % lamellar grains pinned at grain boundaries by fine equiaxed grains was obtained after heat treatment slightly over the α transus temperature.
The study showed that addition of a higher amount of Nb significantly increased the oxidation resistance of the material, thus increasing the application temperature range of these γ-TiAl alloys.
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Gicquel, Alix. "Etude des processus catalytiques heterogenes dans les milieux plasmas basse pression hors-equilibre". Paris 6, 1987. http://www.theses.fr/1987PA066396.
Abstract (sommario):
Etude des reacteurs tubulaires a plasma basse pression dans le cas de reactions consecutives cinetiquement controlees par une etape endothermique. Le role catalytique d'une feuille de tungstene se traduit par une augmentation de l'excitation vibrationnelle des molecules dans la couche limite; a contrario, le transfert d'energie vers le solide est d'autant moins important que le solide est meilleur catalyseur. L'excitation vibrationnelle se communique aux molecules reactives au cours de transfert vibration-vibration. Les especes reactives sont alors susceptibles de franchir les verrous reactionnels soit en phase gazeuse (etape endothermique) soit en phase heterogene (etape de chimisorption)
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Tobek, Miroslav. "Řešení dopravy v centru Havlíčkova Brodu". Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-225922.
Abstract (sommario):
The aim of this diploma thesis is the solution of the traffic situation in the city center of Havlíčkův Brod. Mainly the ground road number II/150 adjustment, which consist in the modification of the two-way traffic to one-way traffic organization in the streets Dolní, Žižkova and Na Ostrově by using the analogy of a roundabout layout, is solved within this thesis. All mentioned modifications simplify the traffic situation, improve the orientation and increase the security and the traffic flow mainly in relation to pedestrians and cyclists. Another part of this thesis is focused on revitalization of the public spaces in front of the community center called Ostrov and junction of existing cycle tracks situated on the both banks of the Sázava river. In relation to this topic the adjustment of rainwater sewerage system, low-voltage above ground network, public lighting, communication electric cables, fire brigade signal lights and low-pressure gas pipeline is also solved.
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Mallardeau, Catherine. "L'hydrogène atomique polarisé : interaction avec les films d'Helium : expérience de compression". Paris 6, 1986. http://www.theses.fr/1986PA066186.
Abstract (sommario):
Etude expérimentale de certains mécanismes de recombinaison de H| afin de comprendre les limites à l'obtention de la condensation de Bose Einstein. Mesure de l'énergie d'adsorption de H sur une couche mince 4He en fonction de l'épaisseur de la couche, paramètre qui donne les limites de stabilisation de H à basse température; obtention de la stabilisation sur des couches biomoléculaires. Construction d'un dispositif expérimental pour comprimer le gaz H| en champ magnétique de 20t, pour étudier le taux de recombinaison à 3 corps de H à haute densité et en champ magnétique intense.
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Quichaud, Viviane. "Etude des processus elementaires : de synthese de la molecule no, en post-decharge en ecoulement, de collisions titane-gaz rares, titane-molecules, par perturbation laser resolue en temps". Paris 6, 1987. http://www.theses.fr/1987PA066135.
Abstract (sommario):
I. Etude de la preparation des etats excites de no dans un dispositif de post-decharge en ecoulement a partir de n::(2) excite (prepare par transfert d'excitation a partir d'atomes ar metastables dans une decharge basse pression) et de o (obtenu par dissociation de o::(2) dans une decharge de he). Observation d'une emission intense des bandes gamma de no, qui implique un etat a courte duree de vie (b) de n::(2) et le premier etat metastable de o. Ii. Analyse des processus d'extinction et de transfert d'excitation a partir d'etats a courte duree de vie de ti (crees dans un dispositif a cathode creuse) lors de collisions avec des gaz rares (ar, ne, he) et des molecules (n::(2),h::(2)). Ces experiences permettent l'etude de cinetiques de reactions elementaires au sein d'un plasma basse pression ensemence de vapeurs metalliques, a l'aide du dispositif de post-decharge en ecoulement
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Hsu, Shuo-Han, e 徐碩韓. "Study on Low-temperature Carburizing of Austenitic Stainless Steel by the Gas Carburizing Method". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/11375772547653487334.
Abstract (sommario):
碩士國立臺灣大學
機械工程學研究所
100
Austenitic stainless steel is an alloy steel containing large amounts of nickel, chromium and other alloying elements. The surface will form a thin layer of Cr2O3 passive film, which is resistant to corrosion, so that this type of stainless steel can be applied in petroleum engineering, chemical engineering, medical equipment, and the food industry etc. However, this stainless steel will easily be scratched due to its low hardness; therefore in the application of mechanical parts, its wear resistance often fails to meet the requirements of the users. Carburization is one of the surface hardening techniques commonly used in industries, but the traditional high temperature carburization (800℃~1100℃) will lead to the precipitation of chromium carbides (Cr7C3) onto the grain boundaries, which will significantly reduce the corrosion resistance of the stainless steel. To prevent the precipitation of the chromium carbides, this research focuses on utilizing a carburization technique with long duration at low temperature, lower than or at 520°C, to increase the surface hardness of the stainless steel. At low temperatures, substitutive chromium atoms are not easy to move, but interstitial carbon atoms can move more easily. Therefore, carbon atoms can dissolve into the stainless steel, which can increase its surface hardness and wear resistance. In addition, the chromium atoms within the stainless steel cannot precipitate to form carbides; therefore, preventing from the decreasing of the corrosion resistance of the stainless steel. This research utilizes the mixture of nitrogen and methanol dissociation gas to carburize the surface of the stainless steel. Before the carburization process, the passive film on the surface of the stainless steel should be removed through the so-called activation treatment. This research uses a pre-oxidation process with hydrochloric acid vapor to replace the conventional activation treatment, so that the former can save more time than the latter. Within ten minutes, the passive film will be completely removed, and then the stainless steel can be carburized. After the stainless steel is pre-oxidized by the hydrochloric acid vapor under appropriate conditions, and then carburized at a low temperature, the effects of the carburization on the stainless steel are evaluated from the microstructure, hardness distribution, wear resistance and corrosion resistance of the carburized layer.The results are as follow: 1. The carburized layer created at a carburizing temperature of 470°C mainly consists of a super saturated solid solution of carbon atoms and only a minute amount of carbide; On the contrary, the carburized layer created at a carburizing temperature of 520°C is a mixture which consists of a super saturated solid solution and a noticeable amount of carbides. 2. Major carbides generated from AISI 304 in the carburized layer are Cr7C3. In addition to Cr7C3, another type of carbide generated from AISI 316 is Mo2C. 3. When comparing the carburizing rate and the carburized layer’s thickness of both stainless steels, AISI 316 is better than AISI 304, overall. 4. When the stainless steel is carburized at low temperatures, the deterioration of its corrosion resistance is not significant. The carburizing of AISI 304, on the contrary, will increase the corrosion resistance to the hydrochloric acid. When closely observing the effect of carburizing temperature on the corrosion resistance, the higher carburizing temperature of 520°C produces more carbides, which results in poor corrosion resistance. As opposed to a lower carburizing temperature of 470°C, less carbides are produced, resulting in better corrosion resistance. 5. When the low temperature carburized specimen is compared with the raw one, its wear resistance is improved significantly. The main reason is due to a large amount of compressive stress generated on the surface of the carburized specimen because of the super saturation of carbon atoms, therefore resulting in significant improvement in surface hardness and wear resistance.
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Tinashe, Sanyangare Edwin. "Conceptual design of a low pressure cold gas dynamic spray (LPCGDS) system". Thesis, 2010. http://hdl.handle.net/10539/8398.
Abstract (sommario):
Low Pressure Cold Gas Dynamic Spray (LPCGDS) is a coating process that utilises kinetic
energy instead of thermal energy to deposit powder particles (1-50 μm) to substrates at low
temperatures (<400 oC) without going through melting. The deposited coatings provide
improved wear and corrosion protection to underlying surfaces while maintaining the
original phase structure of the particles and minimising oxide formation and residual
stresses associated with conventional thermal spray processes such as flame, arc and
plasma spraying. Bonding occurs when particles impact velocities on the substrates exceed
a certain critical velocity. This critical velocity depends on the propellant gas and particles
characteristics, and the spray system components (gas supply, gas heater, powder feeder
and the supersonic nozzle) design. Consequently, design optimisation of these parameters is
a key to improve the coating quality and reduce the spraying costs.
This study develops an effective and efficient conceptual design of a LPCGDS system.
Requirements for both the overall LPCGDS system and its individual components or subsystems
are established. Components variants that include off-the-shelf, customised and
innovative solutions are generated. An evaluation of these variants is then carried out to
determine components that best performs LPCGDS functions. Subsequently, an optimal
spray system that meets the specifications of the LPCGDS system is assembled from these
best components. Finally, a complete spray set-up that includes the spraying chamber, a gas
and particle recovery system, the data acquisition and control system and, coating quality
measurement equipment is established.
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(7038164), Gayathri Shivkumar. "Coupled plasma, fluid and thermal modeling of low-pressure and microscale gas discharges". Thesis, 2019.
Abstract (sommario):
Large scale and cost-efficient synthesis of carbon nanostructured materials has garnered tremendous interest over the last decade owing to their plethora of engineering and bio-science applications. One promising method is roll-to-roll radio frequency chemical vapor deposition and this work presents a computational investigation of the capacitively coupled radio frequency plasma in such a system. The system operates at moderate pressures (less than 30 mbar) with an 80 kHz square wave voltage input. The computational model aids the understanding of plasma properties and α-γ transition parameters which strongly influence the nanostructure deposition characteristics in the system. One dimensional argon and hydrogen plasma models are developed to characterize the effects of input voltage, gas pressure, frequency, and waveform on the plasma properties. A hybrid mode which displays the characteristics of both α and γ discharges is found to exist for the low cycle frequency 80 kHz square wave voltage input due to the high frequency harmonics associated with a square waveform. The threshold voltage at which the transition between the different regimes occurs is higher for hydrogen than for argon owing to its diatomic nature. Collision radiative modeling is performed to predict the argon emission intensity in the discharge gap. The results are found to lie within 16% of the optical emission spectroscopy measurements with better agreement at the center of the discharge, where the measurement uncertainty is low and the emission by ions is not significant. A quasi-zero dimensional steady state chemistry model which uses the hydrogen plasma properties as inputs predicts high concentrations of C2H, C2H2, C2H3+, C2H4+ and C2H6+ during carbon nanostructure deposition.
Carbon nanostructures are popularly used as field emitters. Field emission based microplasma actuators generate highly non-neutral surface discharges that can be used to heat, pump, and mix the flow through microchannels and offer an innovative solution to the problems associated with microcombustion. They provide a constant source of heat to counter the large heat loss through the combustor surface, they aid in flow transport at low Reynolds numbers without the use of moving parts, and they provide a constant supply of radicals to promote chain branching reactions. This work presents two actuator concepts for the generation of field emission microplasma, one with offset electrodes and the other with planar electrodes. They operate at input voltages in the 275 to 325 V range at a frequency of 1 GHz which is found to be the most suitable value for flow enhancement. The momentum and energy imparted by the charged particles to the neutrals as modeled by 2D Particle-In-Cell with Monte Carlo Collisions (PIC/MCC) are applied to actuate flow in microchannels using 2D Computational Fluid Dynamics modeling. The planar electrode configuration is found to be more suitable for the purpose of heating, igniting and mixing the flow, as well as improving its residence time through a 10 mm long microcombustor. The combustion of hydrogen and air with the help of 4 such actuators, each with a power consumption of 47.5 mW/cm, generates power with an efficiency of 28.8%. Coating the electrode surface with carbon nanostructures improves the combustion efficiency by a factor of 2.5 and reduces the input voltage by a factor of 6.5. Such microcombustors can be applied to all battery based systems requiring micropower generation with the ultimate goal of “generating power on a chip'”.
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Amato, Giorgio. "Design Solutions for Reducing Losses in Aeronautical Low-Pressure Turbines". Doctoral thesis, 2021. http://hdl.handle.net/2158/1235154.
Abstract (sommario):
The present thesis deals with the generation of innovative design solutions for reducing aerodynamic losses in Low-Pressure Turbines through the combined use of Artificial Neural Networks and CFD (Computational Fluid Dynamics). In particular, a lean model for optimizing blade airfoils in a multi-row environment and the development of a passive control device for reducing secondary losses are presented.
The first procedure allows building a 1.5 stage by starting from a single blade profile, which is one of the main focuses of low TRL (Technology Readiness Level) design activities. In the obtained setup, two airfoil aerodynamic optimizations are performed by considering steady and unsteady conditions separately. The evaluation of the unsteady phenomena proves to be critical already at the considered blade design stage. Indeed, such practice allows achieving better aerodynamic performance and reducing the blade count per row.
The second part of the thesis explains the blade fence development, which has been performed in collaboration with Avio Aero and Università degli Studi di Genova (UniGE). Such shelf-like devices are applied onto the blade surface to hinder the generation of secondary flows. The blade fence shape is the result of numerical aerodynamic optimizations so that the devices determine the reduction not only of the secondary loss but also of the flow turning deviation at the vane outlet. Such beneficial effects are also confirmed by the results of the experimental campaign conducted by UniGE on linear cascades.