Tesi: "High temperature"

1

Wu, Xu. "Development of high temperature PEMFC and high temperature PEMWE". Thesis, University of Newcastle Upon Tyne, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555981.

Testo completo

Abstract (sommario):

Polymer electrolyte membrane fuel cells (PEMFC) and polymer electrolyte membrane water electrolysers (PEMWE) are promising electrochemical energy conversion devices. This thesis describes research carried out on high temperature PEMFC and PEMWE. High temperature (> 100 QC) operation is one of the most topical research trends of PEMFC and PEMWE, because of the operational and kinetic advantages it can provide. In this research, an anhydrous solid electrolyte, Sb-doped SnP207 was prepared and characterized. The synthesis parameters, microstructure, and conductivity of Sb-doped SnP207 were studied. The Sbo.2Sno.gP207 exhibited good conductivity (0.01-0.l S cm") in the temperature range 100-300 QC, and was initially applied in PEMFCs at intermediate temperatures (200-300 QC). Research into development of polymer acid complex membranes for high temperature PEMFCs, including phosphoric acid and sulphuric acid - doped polybenzimidazole membranes, was also carried out. The maximum power density of high temperature PEMFCs achieved was 0.5-0.7 W cm-2. For high temperature PEMWEs, firstly, Sn and Ir stabilized RU02 nanopartic1es were synthesized and studied as catalysts for the oxygen evolution reaction (OER). Iro.7RUo.302 nanopartic1es were found to be the most stable and active catalysts for OER. Research to develop a catalysts coated membrane (CCM) method for PEMWE membrane electrode assembly (MEA) fabrication is described. A high performance PEMWE was developed by studying fabrication parameters of the CCM method and optimizing electrode compositions of MEAs. High temperature (> 1 00 QC) PEMWE was eventually realized, using a perfluorinated silica composite membrane. The voltage achieved at 1 A cm-2 current density of PEMWE was 1.51 V at 140 QC and 4 bar pressure. The final part of this thesis describes work on catalyst support materials, which are essential for reducing noble metal loading in PEMWEs. Although the costs of PEMFCs and PEMWEs are still high, which is due to noble metal catalysts and expensive membranes, high temperature operation (> 100 QC) can help both devices be more competitive for energy conversion applications.

Gli stili APA, Harvard, Vancouver, ISO e altri

2

Patterson, Peter A. "High temperature cyclones". Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75974.

Testo completo

Abstract (sommario):

Gas-solids separation was studied in a 102 mm diameter conventional cyclone operated with air heated to temperatures between 300 K and 2 000 K. Cyclone pressure drops, fractional and overall collection efficiencies were measured as functions of temperature, gas throughput, dust loading and cyclone geometry. Alumina and silica of 100% less than 44 $ mu$m mass median diameter were used as test dusts. Inlet velocities ranged from 3 to 42 m/s and inlet dust loadings were between 0.3 and 235 g/m$ sp3$.
Empirical models were derived to correlate the experimental results for the cyclone collection efficiency, pressure drop, tangential velocity and 50% cut size. The performance of the cyclones at very high temperatures was not significantly different from the room temperature behavior, provided that the effect of temperature on particle, gas and flow properties was adequately treated.

Gli stili APA, Harvard, Vancouver, ISO e altri

3

Black, Victoria J. "High temperature supercapacitors". Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12490.

Testo completo

Abstract (sommario):

The scientific objective of this research program was to determine the feasibility of manufacturing an ionic liquid-based supercapacitor that could operate at temperatures up to 220 °C. A secondary objective was to determine the compatibility of ionic liquids with other cell components (e.g. current collectors) at high temperature and, if required, consider means of mitigating any problems. The industrial motivation for the present work was to develop a supercapacitor capable of working in the harsh environment of deep offshore boreholes. If successful, this technology would allow down-hole telemetry under conditions of mechanical vibration and high temperature. The obstacles, however, were many. All supercapacitor components had to be stable against thermal decomposition up to T ≥ 220 °C. Volatile components had to be eliminated. If possible, the finished device should be able to withstand voltages greater than 4 V, in order to maximise the amount of stored energy. The internal resistance should be as low as possible. Side reactions, particularly faradaic reactions, should be eliminated or suppressed. All liquid components should be gelled to minimise leakage in the event of cell damage. Finally, any emergent problems should be identified.

Gli stili APA, Harvard, Vancouver, ISO e altri

4

Hernandez, Sinuhe. "High Temperature Wear Processes". Licentiate thesis, Luleå tekniska universitet, Maskinelement, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16827.

Testo completo

Abstract (sommario):

Moving machine assemblies are increasingly exposed to extreme operating conditions involving high temperatures owing to demands on higher power densities, high performance/efficiency and extreme environments. The changes in surface and near surface properties of contacting surfaces caused by exposure to high temperature and deformation govern the occurrence of friction, wear and material transfer of the tribological system. However, these changes have not been thoroughly investigated. In order to enable development of new products and processes, there is a need for new knowledge pertaining to tribological phenomena occurring at elevated temperatures.One of the most commonly used engineering materials is steel as it offers a good compromise between performance and cost even at high temperatures. For example, prehardened (quenched and tempered) tool steels are commonly used in hot forming dies can also be employed in other technological applications involving elevated temperatures. Although the research pertaining to hot stamping, and high temperature tribology in general, has significantly grown during the last years there are still knowledge gaps that need to be bridged. Adhesion and abrasion have been identified as the most dominant wear mechanisms in high temperature tribological systems but the detailed understanding of the mechanisms is still inadequate.The objective of this work is therefore to obtain a deeper understanding of the tribological phenomena associated with adhesion and abrasion that takes place at high temperatures. Unidirectional sliding wear tests have been conducted in order to investigate the influence of contact pressure and temperature on the wear and friction characteristics of tool steel and boron steel pair. Tribological studies involving boron steel, tool steels and heat-treated high-Si steels in a three body abrasive environment were also carried out with a view to explore the effect of temperature on the wear rate, wear mechanisms and to correlate this with material properties like hot hardness and toughness.The results from the unidirectional sliding tests showed that the frictional behaviour of tool steel and boron steel is load and temperature dependent. In general the friction coefficient decreases as both temperature and load are increased as a result of the formation of oxide layers. At temperatures above 200 °C, the compaction and sintering of these layers led to the formation of a wear protective glaze layer. Consequently, the wear rate for both materials decreased at elevated temperatures. Additionally, a friction and wear mechanisms map was developed for the investigated materials.In the case of abrasive wear tests, the results showed that the main wear mechanism presented for each material varied with temperature. In general, a transition from micro-ploughing to a combination of micro-cutting and micro-ploughing was present. The tool steels and boron steel showed a decrease in wear rate in the range of 100 to 400 °C compared to that at room temperature. This was attributed to the toughness in case of the tool steel and the formation of a protective tribolayers for the boron steel. Above 400 °C the wear rate increased for these three materials mainly due to the recovery and recrystallization processes. The wear rate of the high-Si steels increased with testing temperature. At 500 °C, these steels had the same hardness and the differences in wear were attributed to the changes in the material toughness.
Godkänd; 2014; 20140408 (sinher); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Sinuhe Hernandez Ämne: Maskinelement/Machine Elements Uppsats: High Temperature Wear Processes Examinator: Professor Braham Prakash, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: Assoc. Prof. Ph.D; Head, Metallic Materials and Tech. Dept. Bojan Podgornik, Institute of Metals and Technology, Ljubljana, Slovenia Tid: Fredag den 16 maj 2014 kl 10.00 Plats: E231, Luleå tekniska universitet

Gli stili APA, Harvard, Vancouver, ISO e altri

5

Lev, Leonid C. (Leonic Charles). "High temperature ceramic composites". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38078.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

6

Heczko, Milan. "High Temperature Deformation Mechanisms". Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-391818.

Testo completo

Abstract (sommario):

Dvě pokročilé vysoce legované austenitické oceli s Fe-Ni-Cr matricí byly studovány za podmínek nízkocyklové únavy jak za pokojové tak vysoké teploty. Široká škála experimentálních a charakterizačních nástrojů byla použita ke studiu vzájemně souvisejících aspektů zahrnujících chemické složení slitin, mikrostrukturu, deformační mechanismy a celkovou odezvu materiálů na externě působící zatížení. Klíčové mechanismy a faktory definující mechanické vlastnosti a výkonnost v reálném provozu byly analyzovány a diskutovány v souvislosti s materiálovým designem. • Standardní únavové experimenty byly provedeny za pokojové teploty a teploty 700°C. Byly získány křivky cyklického zpevnění/změkčení, cyklické deformační křivky, Coffin-Manson a Wöhlerovy křivky. • Ke studiu změn mikrostrukturního stavu slitin v důsledku cyklického zatěžování za pokojové a zvýšené teploty byla použita široká škála technik charakterizace pomocí elektronové mikroskopie. • Únavové chování, pevnost a cyklická plastická odezva studovaných materiálů byla vysvětlena v souvislosti s mikrostrukturními změnami a mikrostrukturními aspekty deformačních mechanismů jak za pokojové tak za zvýšených teplot. • Bylo zjištěno, že Sanicro 25 vykazuje nejvyšší pevnostní charakteristiky ze všech materiálů stejné třídy. Výjimečné vlastnosti této slitiny jsou spojeny s populacemi dvou typů nanočástic, koherentními precipitáty bohatými na měď a nanočásticemi typu MX s charakteristikou disperzoidu. Tyto nanočástice mají klíčový vliv na pevnost a celkovou cyklickou odezvu. V důsledku interakcí s precipitáty způsobujících zachytávání je pohyb dislokací v Sanicro 25 významně zpomalen, což vede k potlačení normálních procesů zotavení obvykle vedoucích ke změně uspořádání dislokační struktury tak, aby byla celková vnitřní energie systému co nejnižší. Takové uspořádání je tvořeno například dislokačními buňkami. Jelikož jsou procesy zotavení potlačeny, dislokační struktura za vysokých teplot je charakteristická homogenní distribucí dislokací o vysoké hustotě s velkou mírou vzájemných interakcí. V kombinaci s dalšími mechanismy zpevnění jako jsou precipitáty a substituční prvky v tuhém roztoku, tyto deformační mechanismy vedou k významnému zvýšení cyklické pevnosti za vysokých teplot.

Gli stili APA, Harvard, Vancouver, ISO e altri

7

Hout, S. R. in't. "High-temperature silicon sensors". Delft, the Netherlands : Delft University Press, 1996. http://books.google.com/books?id=dApTAAAAMAAJ.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

8

Ohi, Shugo. "High temperature orthorhombic pyroxene --Phase transition between low and high temperature orthorhombic pyroxene and phase relation in enstatite-diopside system at high temperature--". 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124430.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

9

Xu, Juncheng. "High Temperature High Bandwidth Fiber Optic Pressure Sensors". Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/25988.

Testo completo

Abstract (sommario):

Pressure measurements are required in various industrial applications, including extremely harsh environments such as turbine engines, power plants and material-processing systems. Conventional sensors are often difficult to apply due to the high temperatures, highly corrosive agents or electromagnetic interference (EMI) noise that may be present in those environments. Fiber optic pressure sensors have been developed for years and proved themselves successfully in such harsh environments. Especially, diaphragm based fiber optic pressure sensors have been shown to possess advantages of high sensitivity, wide bandwidth, high operation temperature, immunity to EMI, lightweight and long life. Static and dynamic pressure measurements at various locations of a gas turbine engine are highly desirable to improve its operation and reliability. However, the operating environment, in which temperatures may exceed 600 Â°C and pressures may reach 100 psi (690 kPa) with about 1 psi (6.9kPa) variation, is a great challenge to currently available sensors. To meet these requirements, a novel type of fiber optic engine pressure sensor has been developed. This pressure sensor functions as a diaphragm based extrinsic Fabry-PÃ©rot interferometric sensor. One of the unique features of this sensor is the all silica structure, allowing a much higher operating temperature to be achieved with an extremely low temperature dependence. In addition, the flexible nature of the sensor design such as wide sensitivity selection, and passive or adaptive temperature compensation, makes the sensor suitable for a variety of applications An automatically controlled CO2 laser-based sensor fabrication system was developed and implemented. Several novel bonding methods were proposed and investigated to improve the sensor mechanical ruggedness and reduce its temperature dependence. An engine sensor testing system was designed and instrumented. The system generates known static and dynamic pressures in a temperature-controlled environment, which was used to calibrate the sensor. Several sensor signal demodulation schemes were used for different testing purposes including a white-light interferometry system, a tunable laser based component test system (CTS), and a self-calibrated interferometric-intensity based (SCIIB) system. All of these sensor systems are immune to light source power fluctuations, which offer high reliability and stability. The fiber optic pressure sensor was tested in a F-109 turbofan engine. The testing results prove the sensor performance and the packaging ruggedization. Preliminary laboratory and field test results have shown great potential to meet not only the needs for reliable and precise pressure measurement of turbine engines but also for any other pressure measurements especially requiring high bandwidth and high temperature capability.
Ph. D.

Gli stili APA, Harvard, Vancouver, ISO e altri

10

Giordano, Valentina. "High-pressure high-temperature phases of carbon dioxide". Paris 6, 2006. http://www.theses.fr/2006PA066529.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

11

Norrby, Niklas. "High pressure and high temperature behavior of TiAlN". Licentiate thesis, Linköpings universitet, Nanostrukturerade material, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-78830.

Testo completo

Abstract (sommario):

This licentiate thesis mainly reports about the behavior of arc evaporated TiAlN at high pressures and high temperatures. The extreme conditions have been obtained in metal cutting, multi anvil presses or diamond anvil cells. Several characterization techniques have been used, including x-ray diffraction and transmission electron microscopy. Results obtained during metal cutting show that the coatings are subjected to a peak normal stress in the GPa region and temperatures around 900 °C. The samples after metal cutting are shown to have a stronger tendency towards the favorable spinodal decomposition compared to heat treatments at comparable temperatures. We have also shown an increased anisotropy of the spinodally decomposed domains which scales with Al composition and results in different microstructure evolutions. Furthermore, multi anvil press and diamond anvil cell at even higher pressures and temperatures (up to 23 GPa and 2200 °C) also show that the unwanted transformation of cubic AlN into hexagonal AlN is suppressed with an increased pressure and/or temperature.

Gli stili APA, Harvard, Vancouver, ISO e altri

12

Palmer, C. J. "High temperature creep of copper". Thesis, Swansea University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638403.

Testo completo

Abstract (sommario):

The key observations that have underpinned traditional power law approaches to creep mechanism identification have been re-evaluated using information obtained for pure copper and aluminium, and also for various other metals and alloys. Specifically, data is presented which show stress/creep rate plots for copper and aluminium over extended stress ranges to be well represented by continuous curves, contradicting the common assumption that a transition in mechanisms occurs as the stress is reduced. Data is also presented from a series of stress interruption tests on pure copper, with strain/strain rate responses which also suggest that essentially the same mechanism dominates creep behaviour at high and low stresses. Furthermore, results for copper single crystals and polycrystals are shown which contradict the assumption that dislocation creep processes are grain size independent so the creep rate increases rapidly with decreasing grain diameter only when diffusional mechanisms are dominant at low stresses. Evidence is also introduced to demonstrate that the theoretical and practical limitations of power-law descriptions of steady-state creep rates can be overcome by quantifying the shapes of normal creep curves and the variations in curve shape with changing stress conditions. The superior predictive capabilities of curve shape analysis are then illustrated by results showing accurate predictions of creep behaviour in the low stress region may be obtained from data generated experimentally at far high stresses. Finally, results are presented showing the effects of a range of room temperature prestrains which illustrate the importance of distinguishing between the contributions made by the grain interiors and the grain boundary zones to the overall rates of strain accumulation during creep.

Gli stili APA, Harvard, Vancouver, ISO e altri

13

Miles, Bryan Ernest. "High Temperature Nuclear Reactor Dynamics". Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520877.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

14

Saran, Mohinder. "High temperature strengthening of zirconia". Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504522.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

15

Kale, K. S. "High temperature superconducting microwave devices". Thesis, University of Oxford, 1996. http://ora.ox.ac.uk/objects/uuid:85481181-0e9f-41e4-8f26-71cb51fe7ca8.

Testo completo

Abstract (sommario):

This thesis describes investigations into the application of high temperature superconductoR_s(HTS) for microwave devices. The ultimate aim of this research was to produce HTS components that would demonstrate the commercial potential of their use in spacecraft such as satellites or in base stations for terrestrial cellular communication systems. During the course of this research the surface resistance (R_s) of HTS thick and thin films deposited onto different substrates has been measured by a variety of techniques. These have been compared and contrasted with each other. There has been a particular emphasis upon the use of dielectric resonators as characterization tools and this thesis describes their use to measure the R_sof films and the loss tangents of the materials used in them. Consideration has been given to losses in the walls of the enclosures that surround dielectric resonators which is an area that has been neglected in previous work. Many of the films characterized had R_s values lower than normal conductoR_sat the same temperature and frequency including a thick film which had an R_sof 2.7mΩ±8.0% at 77K and scaled to 10 GHz which represents the second lowest result achieved in a thick film to date. Using such high quality films a number of devices have been made including microstrip resonatoR_soperating at 1.7-8.4 GHz, 5.58 GHz, 23 GHz and 24.75 GHz dielectric resonatoR_sand filteR_swith centre frequencies from 5.58-13 GHz. Such devices have shown performance enhancements of up to 700% over their normal conductor equivalents. Benefits have been delivered in light, low volume packages which is of particular advantage to the satellite communications industry. Finally, there has been a demonstration, for the first time, of a tunable HTS thin film filter.

Gli stili APA, Harvard, Vancouver, ISO e altri

16

Lee, Te-Hao. "Silicon Carbide High Temperature Logic". Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1283437983.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

17

Marsh, M. G. "The effect of a temperature gradient on high temperature fretting wear". Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267625.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

18

Bloom, Scott Harris. "Superconducting and normal compounds : some high field/high pressure effects /". Thesis, Connect to Dissertations & Theses @ Tufts University, 1989.

Cerca il testo completo

Abstract (sommario):

Thesis (Ph.D.)--Tufts University, 1989.
Submitted to the Dept. of Physics. Includes bibliographical references (leaves 192-204). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Gli stili APA, Harvard, Vancouver, ISO e altri

19

Xia, Xiangjun. "Theoretical investigation of high-Tc cuprate superconductors using t-J model : transport properties /". View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202005%20XIA.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

20

Fang, Yue. "Interfacial studies of high temperature superconducting Bi₂Sr₂Can-₁Cun 0₂n+₄ and Ag". Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/17890.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

21

Vanpeteghem, Carine B. "High-pressure high-temperature structural studies of binary semiconductors". Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/11496.

Testo completo

Abstract (sommario):

The last decade has seen a tremendous improvement in high-pressure diffraction techniques. Among other things, this has led to a completely new understanding of the structural systematics of the group IV, III-V and II-VI semiconductors. Many phases have been shown to have more complex, lower-symmetry, high-pressure structures than previously thought. One of the most surprising discoveries has been the non-existence of the diatomic b-tin structure, long believed to be one of the principal high-pressure phases of the III-V and II-VI systems. However, most of the work to date has been performed at room temperature and in fact, very little is yet known about the high-pressure phases of these systems above room temperature. The work presented in this thesis centres on the use of high temperature under pressure to investigate further the absence of the diatomic, site-ordered, b-tin or b-tin-like phases have been found but appear to be site-disordered. Additionally, the P-T phase diagrams of these systems are explored above room temperature. This work has required the development the existing high-pressure facilities on the SRS synchrotron source of Daresbury Laboratory to allow routine high-pressure high-temperature (hp/ht) experiments. These technical developments are described. High-temperature studies of GaSb under pressure reveal a new, previously unknown phase. A detailed study of the structural ordering in the hp/ht phases of GaSb is performed by combining two different experimental techniques. It is shown, by x-ray powder-diffraction, that all the hp and hp/ht phases of GaSb are site-disordered over about two unit cells or less. A complementary high-pressure EXAFS study demonstrates the absence of complete order over nearest-neighbour distances.

Gli stili APA, Harvard, Vancouver, ISO e altri

22

Sphicas, Panagiotis. "High pressure and high temperature measurements on diesel sprays". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/18063.

Testo completo

Abstract (sommario):

Environmental, financial and legal reasons demand the development of cleaner diesel engines. Atomization, evaporation and mixing phenomena observed during injection of Diesel fuel affect the produced emissions. To study these phenomena, under engine-like conditions (50bar, 1000K), a chemically preheated constant volume chamber was built. A system of sensors, driven in real-time by a FPGA (Field Programmable Gate Array) and controlled by a Real Time Controller, was built to monitor and control the operations. A modern common rail fuel injection system (Bosch CP3) was driven by a purpose-modified Hartridge 1100 test stand and controlled by the FPGA (Field Programmable Gate Array). Chemical heating is a technique used widely to simulate the ambient conditions of an industrial combustor in a constant volume vessel. A flammable mixture is ignited in an optically accessible vessel, attempting to produce a post-combustion high pressure and high temperature environment. The flammable mixture usually consists of Hydrogen and a Hydrocarbon. Hydrogen is added, to assist with the ignitability of the pre-ignition mixture and to simulate the water present in industrial combustors as a result of exhaust gas recirculation. To this direction, the mole ratio of Hydrogen to Hydrocarbon and the mixture molecular weight were introduced as independent variables for the first time in the literature of constant volume combustion. An initial computer model, assuming perfect combustion, was used for calculation of adiabatic temperature and pressure. A second computer model investigated the effect of chemical dissociation by solving for the minimization of Gibbs energy and was compared to the former one. To verify the calculations, a dual pressure transducer technique and a High-Speed Schlieren technique were used to validate the combustion conditions inside the vessel To further understand the atomization, evaporation and mixing phenomena in sprays, a Diesel spray was visualized using back-illumination and Schlieren High-Speed cinematography at high pressure and room temperature. To understand the evaporation behaviour of a spray and map the vapour fuel distribution, a tracer Laser Induced Fluorescence was applied on a Dodecane/Methyl-naphthalene spray under evaporating and non-evaporating conditions. To compare the experimental findings to the theoretical models in literature, the evaporation of a single droplet in post-combustion vessel gases was simulated using a purpose-programmed FORTRAN code. A supercritical phase change was suggested to explain the sudden phase change and large differences between the theoretical model and the experimental results.

Gli stili APA, Harvard, Vancouver, ISO e altri

23

Almström, Linda, e Camilla Söderström. "Alternative materials for high-temperature and high-pressure valves". Thesis, Karlstads universitet, Fakulteten för teknik- och naturvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-7393.

Testo completo

Abstract (sommario):

AB SOMAS Ventiler manufactures valves for different applications. A valve of type DN VSSL 400, PN 100, used in high-temperature and high-pressure applications was investigated in this thesis. This type of valve is coated with high cobalt alloys to achieve the tribological properties needed for this severe condition. However there is a request from AB Somas Ventiler to find another solution. This request is based on the fact that demands on higher temperatures, from customers, yields higher requirements on the material. It is also a price issue since cobalt is quite expensive. Materials investigated were high-nitrogen steel, Vanax 75, nickel-based superalloy Inconel 718 and hardened steels, EN 1.4903 and EN 1.4923 presently used as base material in the valve. Calculation of contact pressure that arises when the valve is closed was first approached by using finite element method (FEM). Several models were constructed to show the behavior of the valve during closing in terms of deformation. Hot wear tests, in which a specimen was pressed against a rotating cylinder, were performed to be able to compare the materials to the solution of today and among each other. Data extracted from the tests were compiled in the form of coefficients of friction. Profilometer examinations were used to reveal the volumes of worn and adhered material and together with scanning electron microscopy (SEM) the wear situation for each material couple could be assessed. Wear mechanisms detected in SEM were adhesive and abrasive and the results clearly showed that the steels were not a good solution because of severe adhesive wear due to the similarity of mating materials creating a more efficient bonding between the asperities. Vanax 75 showed much better performance but there was still an obvious difference between the steels and the superalloy in terms of both coefficient of friction and amount of wear. On this basis, Inconel 718 was selected as the most suitable material to replace the high cobalt alloys used in the valves today.
AB Somas ventiler är ett företag som tillverkar ventiler för ett brett spann av applikationer. I det här examensarbetet har undersökningar genomförts på en ventil av modell DN VSSL 400, PN 100, som normalt används i applikationer för höga tryck och höga temperaturer. Ventilen beläggs i dagsläget med höghaltiga koboltlegeringar för att uppnå de tribologiska egenskaper som krävs i de påfrestande arbetsförhållanden som råder. AB Somas Ventiler har dock framfört en förfrågan om att hitta en alternativ lösning, en förfrågan som grundar sig i att kundernas ständiga önskemål på att ventilerna ska klara högre arbetstemperaturer också medför högre krav på ventilmaterialen. Det är även en prisfråga, då kobolt är en dyr legering att använda sig av. De material som inkluderades i undersökningen var det kvävelegerade stålet Vanax 75, nickelbaserade superlegeringen Inconel 718 samt de två stålen EN 1.4903 och EN 1.4923 i härdat tillstånd. De två sistnämnda används idag som basmaterial i ventilen. Genom att använda den finita element metoden (FEM) kunde en första beräkning göras av det kontakttryck som uppstår då ventilen stängs. Flera modeller konstruerades för att simulera ventilens deformation vid stängning. Där efter utfördes nötningstester i hög temperatur på de alternativa materialen, genom att låta en provbit pressas mot en roterande cylinder, för att sedan kunna göra en jämförelse mellan materialen och även med den nuvarande lösningen. Från nötningstesterna erhölls data som kunde användas för att ta fram friktionskoefficienter för de olika materialparen. Med hjälp av undersökningar med profilometer och svepelektronmikroskop (SEM) kunde värden på nötta och vidhäfta volymer erhållas tillsammans med information om nötningssituationer för ytorna mellan de olika materialparen. De nötningsmekanismer som påvisades med hjälp av SEM-undersökningen var adhesiv och abrasiv nötning, och resultaten visade tydligt att nötningen av stålen var omfattande, på grund av att lika material i kontakt med varandra skapar starkare band mellan ytorna, och att de därför inte var en intressant lösning. Det kvävelegerade Vanax 75 uppförde sig visserligen bättre men en tydlig skillnad mot superlegeringarna kunde dock fortfarande konstateras, sett till både friktionskoefficient och mängden slitage. Baserat på dessa resultat valdes Inconel 718 som det bäst lämpade materialet att ersätta de höghaltiga koboltlegeringarna som idag används i ventilen.

Gli stili APA, Harvard, Vancouver, ISO e altri

24

Rowane, Aaron J. "High-Temperature, High-Pressure Viscosities and Densities of Toluene". VCU Scholars Compass, 2016. http://scholarscompass.vcu.edu/etd/4188.

Testo completo

Abstract (sommario):

High-temperature, high-pressure (HTHP) conditions are exemplified in ultra-deep petroleum reservoirs and can be exhibited within diesel engines. Accurate pure component hydrocarbon data is essential in understanding the overall behavior of petroleum and diesel fuel at these conditions. The present study focuses on the HTHP properties of toluene since this hydrocarbon is frequently used to increase the octane rating of gasoline and toluene occurs naturally in crude oil. In this thesis experimental densities and viscosity are presented to 535 K and 300 MPa extending the database of toluene viscosity data to higher temperature than previous studies. The data is correlated to a Tait-like equation and a Padѐ approximate in conjunction with a single mapping of the isotherms. Free-volume theory and a superposition of the viscosity in relation to the Leonnard-Jones repulsive force are both used to model the toluene viscosity data. It was found that the data are in good agreement with the available literature data.

Gli stili APA, Harvard, Vancouver, ISO e altri

25

Munro, Keith Alistair. "High-pressure high-temperature behaviour of the lanthanide metals". Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28881.

Testo completo

Abstract (sommario):

The high-pressure behaviour of the lanthanide series of metals has been the subject of study since the work of Percy Bridgman in the 1940s. Differences in said behaviour between the different lanthanide metals are attributed to the increasing occupation of the 4f electron shell as Z increases. Upon compression, or as Z decreases, the trivalent lanthanides (La to Lu, excluding Eu and Yb) undergo a common phase transformation sequence through various close packed structures: hcp → Sm-type (the structure adopted by samarium at ambient conditions) → dhcp → fcc → distorted fcc (d-fcc). Upon further compression, the lanthanide metals experience a first order transition to a "volume collapsed" phase. Many studies have focused on the low-Z members of the series, since the various phase transitions occur at much lower pressure where it is comparatively easy to collect high quality data. By contrast, the other members of the series have received comparability little attention, and there are even fewer reports of the structural behaviour of the lanthanide metals at high pressure and high temperature. This thesis contains the results of angle-dispersive x-ray powder diffraction experiments at high pressure and high temperature of the various members of the lanthanide metals. Ce has been the subject of many previous studies, but a systematic x-ray diffraction study of the fcc/d-fcc phase boundary has never been attempted. Furthermore, the location in P-T space of the high temperature fcc/bct/d-fcc triple point has only been inferred, due to the lack of data on the fcc/bct phase boundary at high temperature. The high-pressure high-temperature phase diagram of Ce is presented and discussed. La is unique amongst the lanthanide metals due to its empty 4f shell at ambient conditions. Despite this, La undergoes the common lanthanide transformation sequence up to the d-fcc phase, after which it undergoes a re-entrant transition back to the fcc phase at 60 GPa. The diffraction peaks of d-fcc La are shown in this thesis to undergo changes in intensity upon compression, indicating a transformation to the oI 16 structure found in Pr. La is one of the few elements whose behaviour has been unknown above 100 GPa, and results of La's structural behaviour upon compression to 280 GPa are presented and discussed. At 76 GPa, La begins a transition from the fcc phase to a new phase with the bct structure. Finally, the d-fcc→fcc re-entrant phase transition has been determined at various temperatures, and the d-fcc stability region has been mapped out. Finally, x-ray diffraction experiments were performed on Gd up to 100 GPa and ~700 K, to determine the structure of the d-fcc phase and the "volume collapsed" phase. While d-fcc Gd does not undergo pressure-induced changes similar to its low Z brethren, the d-fcc Gd remains stable up to 41 GPa at 700 K, putting a constraint on the d-fcc stability region. The data collected on Gd's "volume collapsed" phase cannot be fitted to the currently accepted mC4 structure. This has implications for our understanding of the lanthanide series as a whole, since most of of the heavier members, and some of the lighter lanthanides, are reported to adopt the mC4 structure.

Gli stili APA, Harvard, Vancouver, ISO e altri

26

Fang, Xiaojun. "Sapphire fiber based high temperature extensometer". Master's thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-01262010-020150/.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

27

Alépée, Christine. "Technologies for high-temperature silicon microreactors /". Lausanne, 2000. http://library.epfl.ch/theses/?nr=2298.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

28

Ersson, Anders. "Materials for High-Temperature Catalytic Combustion". Doctoral thesis, KTH, Chemical Engineering and Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3501.

Testo completo

Abstract (sommario):

Catalytic combustion is an environmentally friendlytechnique to combust fuels in e.g. gas turbines. Introducing acatalyst into the combustion chamber of a gas turbine allowscombustion outside the normal flammability limits. Hence, theadiabatic flame temperature may be lowered below the thresholdtemperature for thermal NO_Xformation while maintaining a stable combustion.However, several challenges are connected to the application ofcatalytic combustion in gas turbines. The first part of thisthesis reviews the use of catalytic combustion in gas turbines.The influence of the fuel has been studied and compared overdifferent catalyst materials.

The material section is divided into two parts. The firstconcerns bimetallic palladium catalysts. These catalysts showeda more stable activity compared to their pure palladiumcounterparts for methane combustion. This was verified both byusing an annular reactor at ambient pressure and a pilot-scalereactor at elevated pressures and flows closely resembling theones found in a gas turbine combustor.

The second part concerns high-temperature materials, whichmay be used either as active or washcoat materials. A novelgroup of materials for catalysis, i.e. garnets, has beensynthesised and tested in combustion of methane, a low-heatingvalue gas and diesel fuel. The garnets showed some interestingabilities especially for combustion of low-heating value, LHV,gas. Two other materials were also studied, i.e. spinels andhexaaluminates, both showed very promising thermal stabilityand the substituted hexaaluminates also showed a good catalyticactivity.

Finally, deactivation of the catalyst materials was studied.In this part the sulphur poisoning of palladium, platinum andthe above-mentioned complex metal oxides has been studied forcombustion of a LHV gas. Platinum and surprisingly the garnetwere least deactivated. Palladium was severely affected formethane combustion while the other washcoat materials were mostaffected for carbon monoxide and hydrogen.

Keywords:catalytic combustion, catalyst materials,palladium, platinum, bimetallic, garnet, spinel, hexaaluminate,deactivation, sulphur, poisoning, diesel, methane,hydrocarbons

Gli stili APA, Harvard, Vancouver, ISO e altri

29

Martin, Marianne. "High-Temperature Superconductivity in Doped BaFe2As2". Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-126344.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

30

Everett, John. "Dissipation in high temperature superconducting tapes". Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/8576.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

31

Ekström, Mattias. "High Temperature Memories in SiC Technology". Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-177192.

Testo completo

Abstract (sommario):

This thesis is part of the Working On Venus (WOV) project. The aim of the project is to design electronics in silicon carbide (SiC) that can withstand the extreme surface environmen of Venus. This thesis investigates some possible computer memory technologies that could survive on the surface of Venus. A memory must be able to function at 460 °C and after a total radiation dose of at least 200 Gy (SiC). This thesis is a literature survey. The thesis covers several Random-Access Memory (RAM) technologies: Static RAM (SRAM), Dynamic RAM (DRAM), Ferroelectric RAM (FeRAM), Magnetic RAM (MRAM), Resistive RAM (RRAM) and Phase Change Memory (PCM). The Electrical Erasable Programmable Read-Only Memory, Flash memory and SONOS are also covered. Focus lies on device- and material-physics of the memory cells, and their extreme environment behaviour. This thesis concludes with a discussion on technology options. The technologies are compared for their suitability for extreme environment. The thesis gives a recommendation for which memory technologies should be investigated. The final recommendation is to investigate SRAM, SONOS, FeRAM and RRAM technologies for high temperature applications.
Denna uppsats är en del av projektet Working On Venus (WOV). Projektets mål är att designa elektronik i kiselkarbid (SiC) som tål Venus extrema ytmiljö. Denna uppsats undersöker några möjliga datorminnestekniker som kan överleva på Venus yta. Ett minne måste kunna fungera vid 460 °C och efter en total strålningsdos på minst 200 Gy (SiC). Denna uppsats är en litteraturstudie. Uppsatsen täcker flera olika typer av RAM-minnes teknologier (eng. Random-Access Memory): Statiskt RAM-minne (SRAM), Dynamiskt RAM-minne (DRAM), Ferroelektriskt RAM-minne (FeRAM), Magnetiskt RAM-minne (MRAM), Resistivt RAM-minne (RRAM) och fasändringsminnen (PCM). EEPROM (eng. Electrical Erasable Programmable Read-Only Memory), Flash-minnen och SONOS täcks också. Fokus ligger på minnescellernas komponent- och materialfysik, samt deras extremmiljösbeteende. Denna uppsats avslutas med en diskussion om teknikmöjligheter. Teknikerna jämfors för hur passande de är för extrema miljöer. Uppsatsen ger en rekommendation för vilka minnestekniker som bör undersokas. Den slutliga rekommendationen är att undersöka SRAM, SONOS, FeRAM och RRAM teknologier for högtemperatursanvändning.

Gli stili APA, Harvard, Vancouver, ISO e altri

32

Gay, Pierre. "Ultrafast processes in high temperature superconductors". Thesis, University of Oxford, 2000. https://ora.ox.ac.uk/objects/uuid:140cc366-58a1-41ad-919b-2cb5f65c3fe9.

Testo completo

Abstract (sommario):

Using time-resolved photo-induced reflectivity, we reported for the first time a systematic work on the ultrafast response of Bi₂Sr₂CaCu₂O_8+Î´ (BSCCO-2212) and Tl₂Ba₂CuO_6+Î´ (TBCO-2201), measurements of detwinned YBa₂Cu₃O_7-Î´ (YBCO-123) single crystal with the electric field Ì²E parallel to the a and b-axis and high-resolution measurements of the rising edge dynamics of YBCO-123 thin films. We identified similar photo-induced responses for BSCCO, TBCO and for YBCO with Ì²E â¥ Ì²b, which indicates that we observed a universal response of HTSC coming from the CuO2 superconducting planes. This latter dynamics is composed of three different components corresponding to the superconducting, pseudogap and normal state. A bi-molecular model has been put forward to explain the linear temperature dependence of the decay rate; the model implies that the re-formation of the condensate is limited by the rate at which quasiparticle interact. Moreover, we observed superconducting fluctuations up to 13K above T_c and a divergence of the long-lived component magnitude at very low temperature, which is explained by a cw heating model. In the pseudogap state, we have several indications that the negative peak observed between T_c and T* has a different origin from that of the superconducting signal below T_c. We argued that the probe mechanism of the pseudogap signal is electronic excitations of the pseudogap correlations. In the normal state, the observed dynamics is similar to that of simple metals. In the second part of this thesis, the rising edge dynamics of YBCO has been resolved in time. The model developed to interpret the results implies that the hot quasiparticles relaxation time down to the Fermi energy is 55fs. In this context, we proved that the Mazin model cannot explain both the oscillatory and the non-oscillatory part of the dynamics in YBCO. Finally, in YBCO-123, a new response has been observed with Ì²E â¥ Ì²b. We argued that the origin of this component is intraband transitions. This dynamics is solely responsive to the pseudogap, coming from the difference in scattering rate between pre-formed pairs and quasiparticles in the Drude reflectivity. The response with Ì²E â¥ Ì²b exhibits a strong a-b plane anisotropy in its long-lived component, which can be interpreted as a d-wave gap symmetry using the thermally-activated model.

Gli stili APA, Harvard, Vancouver, ISO e altri

33

Barrie, Scott Bernard. "Magnetic properties of high temperature superconductors". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0006/MQ32467.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

34

Huang, Jiachang. "A helium high-temperature drift chamber". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0013/NQ38900.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

35

Davis, Caitlin. "Sigma delta modulation at high temperature". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq64995.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

36

Elm, Svensson Erik. "Nanomaterials for high-temperature catalytic combustion". Licentiate thesis, Stockholm : School of Chemical Science, KTH, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4360.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

37

Lidmar, Jack. "Phase transitions in high-temperature superconductors". Doctoral thesis, Stockholm : Tekniska högsk, 1998. http://www.lib.kth.se/abs99/lidm0111.pdf.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

38

Li, Su. "Phase transitions of high temperature superconductors". College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/7276.

Testo completo

Abstract (sommario):

Thesis (Ph. D.) -- University of Maryland, College Park, 2007.
Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Gli stili APA, Harvard, Vancouver, ISO e altri

39

Koob, Christopher E. "High temperature fiber optic strain sensing". Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-02132009-171339/.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

40

Crumley, Winfred H. Jr. "Supersonic expansion from high-temperature sources". Diss., Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/27447.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

41

Wade, James Matthew. "Calorimetry studies of high temperature superconductors". Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363078.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

42

Nicolson, David Macnab. "Scuffing at high speed and temperature". Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243521.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

43

Bianchi, Giovanni. "Ultrafast phenomena in high-temperature superconductors". Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410319.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

44

Jenkins, A. P. "Microwave applications of high temperature superconductors". Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259904.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

45

Richens, P. E. "High temperature superconductors in electromagnetic applications". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365792.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

46

Potter, Darren James. "The Joining of High Temperature Alloys". Thesis, University of Liverpool, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507706.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

47

Mills-Brown, Joseph. "High temperature composite materials and structures". Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.617589.

Testo completo

Abstract (sommario):

The recent resurgence and growing interest in high temperature structures to maximise design space and performance in motorsport applications, led to the need for greater understanding of high temperature composite materials. This study aimed to investigate suitable materials for high temperature structures with application to the motorsport environment. Composite materials were quickly identified as the most appropriate materials given the needs of motorsport, with polysialate composites championed after a thorough review of available materials. A commercially available composite reinforced with silicon carbide fibres was selected to meet the study requirements. This led to the need for thermal and mechanical characterisation in order to provide temperature dependant data suitable for accurate design of high temperature structures. The result of .this was a full engineering dataset for the most widely used polysialate composites, filling In significant gaps in the literature, whilst simultaneously producing a novel and unique high temperature tensile testing rig for this composite laminates. In turn, this new data was exploited with application to a polysialate composite case study structure; an exhaust liner used on current Formula One vehicles. This required full understanding of the thermal and mechanical load cases experienced by the liner, in order to accurately simulate the liner and environment using finite element analysis. Not only did this provide an application of the newly acquired temperature dependant material properties, but it also highlighted the need for temperature dependant properties in the design of high temperature structures. The study, its aims and approach, were validated through comparison of simulation failure predictions against component failed in service.

Gli stili APA, Harvard, Vancouver, ISO e altri

48

Lapthorn, Andrew Craig. "High Temperature Superconducting Partial Core Transformers". Thesis, University of Canterbury. Electrical and Computer Engineering, 2012. http://hdl.handle.net/10092/7130.

Testo completo

Abstract (sommario):

The thesis begins by providing an introduction to transformer theory. An ideal transformer is examined first, followed by full core transformer theory. The partial core transformer is then introduced and compared to the full core design. An introduction to superconductors is then presented where a simplified theory of superconductivity is given. High temperature superconductors are then examined including their physical structure, superconducting properties and the design of the superconducting wire. The early development of high temperature superconducting partial core transformers at the University of Canterbury is then examined. Early partial core development is discussed followed by some material testing at cryogenic temperatures. This work lead into the development of the first high temperature superconducting partial core transformer. This transformer failed during testing and an examination of the failure mechanisms is presented. The results of the failure investigation prompted an alternative winding insulation design which was implemented in a full core superconducting transformer. The modelling used to design a high temperature superconducting partial core transformer is then presented. Based upon the reverse design method, the modelling is used to determine the components of the Steinmetz equivalent transformer circuit. The modelling includes a combination of circuit theory and finite element analysis. An ac loss model for high temperature superconductors is also presented. A new 15 kVA, 230-230V high temperature superconducting partial core transformer was designed, built and tested. The windings are layer wound with first generation Bi2223 high temperature superconductor. The modelling was used to predict the performance of the transformer as well as the ac losses of the high temperature superconductor. A series of electrical tests were performed on the transformer including open circuit, short circuit, resistive load, overload, ac withstand voltage and fault ride through tests. The test results are compared with the model. The transformer was found to be 98.2% efficient at rated power with 2.86% voltage regulation.

Gli stili APA, Harvard, Vancouver, ISO e altri

49

Lekholm, Ville. "High-Temperature Microfluidics for Space Propulsion". Doctoral thesis, Uppsala universitet, Mikrosystemteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-246057.

Testo completo

Abstract (sommario):

In this thesis, microfabrication methods and tools for analysis of heated cold-gas microthrusters are presented, with the aim of improving their reliability and performance. Cold-gas thrusters operate by accelerating pressurized gas through a nozzle. These thruster systems are very straightforward in both design and operation, relying on little more than a pressurized tank, a valve, and a nozzle. This makes them suitable for miniaturization, enabling their use on very small spacecraft. However, an inherent drawback with cold-gas thrusters is their low propellant efficiency – in thrusters known as specific impulse, or Isp. This is compounded by the fact that when reducing length, the volume, e.g., that of the propellant tank, reduces with the cube of the length, meaning that the maximum amount of storable fuel reduces quickly. Hence, maximizing fuel efficiency is even more important in miniaturized systems. Still, because of their other advantages, they remain suitable for many missions. Schlieren imaging – a method of visualizing differences in refractive index – was used thrughout this thesis to visualize exhaust jets from microthrusters, and to find leaks in the components. It was found that effects of the processing of conventionally fabricated silicon nozzles, resulted in a misalignment of up to 3° from the intended thrust vector, increasing propellant consumption by up to 5%, and potentially causing unintended off-axis acceleration of the spacecraft. Schlieren imaging was also used to verify that the exhaust from thrusters fabricated with close to circular cross-sections was well behaved. These nozzles did not suffer from the previous misalignment issue, and the shape of the cross-section decreased viscous losses. For applications requiring higher temperatures, a microthruster nozzle with an integrated flow sensor was fabricated from tape cast yttria stabilized zirconia. The ceramic substrate enabled heater temperatures of the nozzle exceeding 1000 °C, resulting in an increase in Isp of 7.5%. Integration of a flow sensor allowed the elimination of couplings and reduced the number of interfaces, thereby reducing the overall risk of failure. Close integration of the sensor allowed moving the point of measurement closer to the nozzle, enabling improved reliability of the measurements of the propellant consumption. The temperature of the heater, in combination with the ion conductive properties of the substrate proved to be a limiting factor in this design. Two routes were explored to overcome these problems. One was to use the temperature dependence of the ion conductivity as a sensing principle, thereby demonstrating a completely new flow sensor principle, which results in better calibration, tighter integration, and 9 orders of magnitude stronger signal. The other was using hafnium oxide, or hafnia, as a structural material for high-temperature micro-electromechanical systems. This involved developing a recipe for casting hafnia ceramic powder, and determining the Young's modulus and thermal shock resistance of the cast samples, as well as studying the minimum feature size and maximum aspect ratio of cast microstructures.

Gli stili APA, Harvard, Vancouver, ISO e altri

50

Greer, Caroline J. "Spectral emission from high temperature plasmas". Thesis, Queen's University Belfast, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337035.

Testo completo

Gli stili APA, Harvard, Vancouver, ISO e altri

Tesi sul tema "High temperature"

Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili