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Xiao, Rong S. M. Massachusetts Institute of Technology. "Nanoengineered surfaces for advanced thermal management." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/50559.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.<br>Includes bibliographical references (leaves 53-54).<br>Thermal management is a critical challenge for a variety of applications including integrated circuits (ICs) and energy conversion devices. As the heat fluxes exceed 100 W/cm2, novel cooling solutions need to be developed. Thin film evaporation is a promising approach because the large latent heat associated with phase change can be utilized while the thermal resistance associated with the liquid film thickness can be minimized. However, traditional thin film evaporation schemes such as jet impingement and sprays suffer from several limitations, such as high power consumption, complex flow patterns, and localized cooling. In this thesis, micro- and nanostructured surfaces were investigated to enhance fluid and heat transport for thin film evaporation. This thesis includes studies of fluid interactions on surfaces with micro- and nanopillar arrays with diameters and spacings ranging from 500 nm to 10 [mu]m. First, liquid transport studies were performed where a propagating liquid on an array of pillars with scalloped features can separate into multiple layers of liquid films. The scallops were found to act as energy barriers that favored liquid separation into several layers. An analytical model based on surface energy was developed to explain the phenomenon and was validated by experiments on additional tailored pillar geometries. Subsequently, a semi-analytical model was developed to predict the propagation velocity based on Modified Washburn's Model to optimize propagation of the liquid. The results were validated by measurements of liquid propagation velocity on micropillar arrays with various geometries.<br>(cont.) Finally, the heat transfer performance was investigated on microstructure pillar arrays with integrated heaters and temperature sensors. These test devices were fabricated and the behavior of the thin liquid film under varying heat fluxes was investigated, where a two-step "dry-out" behavior was observed. The thermal resistance of the thin film including the effect of the micropillars was also analyzed. This work demonstrates the potential of micro- and nanostructures to achieve high heat fluxes via thin film evaporation.<br>by Rong Xiao.<br>S.M.
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Di, Maria Valentina. "Thermal response from different paved surfaces." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amslaurea.unibo.it/3993/.
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Robotti, Marco. "Functional surfaces obtained by thermal spray techniques." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/400558.
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The main subject of this PhD Thesis is the manufacturing of titanium dioxide multifunctional coatings by means of two spraying technologies: Cold Gas Spray (CGS) and Atmospheric Plasma Spray (APS). The characteristics of each spraying technique are a key factor to be able to understand the behaviour of the deposited material. Moreover, the process conditions strongly affect the functional response and activity of the metal oxide layers in different application sectors.
The starting scope of the PhD thesis consisted in developing nanostructured TiO2 anatase coatings by LP-CGS technique. Using this method, no melting of material feedstock is needed for being deposited and this fact is fundamental because it is possible to preserve this metastable active anatase phase at room temperature. The large specific surface of this nanometric feedstock is useful for applying it in the field of heterogeneous photocatalysis and degradation of contaminants. In order to avoid clogging phenomena of the nanometric powder and not suitable deposition of only ceramic particles, mechanical blends were prepared with ductile materials which flow properly in the pipelines. The presence of anatase phase on the top surface of the final coatings determines their photocatalytic behaviour. Samples successfully degraded NOx gases in less than half an hour (FEAM Grupo de Fotocatálisis y Espectroscopia Aplicada al Medioambiente, Universidad de Las Palmas de Gran Canaria).
A second research topic regarded different TiO2 materials with the objective to test them in photoelectrocatalysis. Three commercial powders (TiO2 rutile, TiO2 anatase and TiO2-x) onto Inconel alloy and carbon steel substrates were studied. The influence of APS thermally-activating technique is explained towards the non-stoichiometric secondary phases that are formed. The performance of the coatings as photoanodes in the solar photoelectrocatalysis (SPEC) treatment of a model azo dye was explored (Group LEMMA Laboratori d’Electroquímica de Materials i del Medi Ambient, Universitat de Barcelona). The functional role of these materials has an important added value in the environmental field because of the possibility to achieve cleaner waters in the smart cities of the future.
The third purpose of this research was to deposit metal oxides based on titanium dioxide by APS for being applied as electrodes in real batteries. Hydrogen contained in the plasma jet of APS is able to reduce TiO2 metal oxide feedstock, create oxygen
vacancies and non stoichiometric compounds such as titanium sub-oxides (TiO2-x) or Magnéli phases (TinO2n-1) during the in-flight interaction of the particles with the jet stream. This lack of oxygen in the crystal structure of TiO2 powder leads to a donor level to the conduction band; therefore a corrosion-resistance ceramic material with an enhanced conductivity was obtained. Coatings were manufactured onto stainless steel, aluminium films, carbon-polymer composite and nickel foam. Four TiO2-x plates onto aluminium substrates were applied as electrodes in a laboratory scale battery. Cyclic voltammograms curves and charge/discharge cycle of the lead acid battery were carried out and gave excellent results (Faculty of Engineering and the Environment, University of Southampton).
The fourth objective of this doctorate consisted in developing new functional gas sensors by means of APS technology. It was determined to build-up the sensing layer on a thin ceramic substrate. This fact permits to increase the working temperature respect to polymeric or metallic substrates. Spraying conditions were accurately selected to reach good deposition and not to damage the brittle substrate. The APS process offered also the advantage to increase the quantity of oxygen vacancies in titanium dioxide powder in order to enhance its conductivity and sensing function. Satisfactory performances were obtained testing the response of the device in front of various target gases and sensing efficiency was deeply studied (Group MIND Micro-nanotecnologías y nanoscopias para dispositivos electrónicos y fotónicos, Universitat de Barcelona).<br>El tema principal de esta tesis doctoral es la fabricación de recubrimientos multifuncionales de dióxido de titanio mediante técnica de proyección fría (CGS) y proyección por plasma atmosférico (APS). Cada producto en forma de recubrimiento funcional encontró su sector de aplicación: i) fotocatálisis en fase gaseosa, ii) fotoelectrocatálisis en fase liquida, iii) electrodos para baterías y iv) sensores de gas.
El primer objetivo de esta tesis doctoral consistió en el desarrollo de recubrimientos nano-estructurados de TiO2 anatasa mediante técnica de proyección fría CGS. La grande superficie específica de este material nanométrico es útil para su aplicación en el campo de la fotocatálisis heterogénea. Fueron preparadas unas mezclas mecánicas entre materiales nano-cerámicos y poliméricos con adecuada fluidez para el sistema de alimentación CGS. Las muestras obtenidas degradaron los gases NOx en breve tiempo y con elevadas eficiencias tanto con luz UV como con luz visible (FEAM Grupo de fotocatálisis y Espectroscòpia Aplicada al Medioambiente, Universidad de Las Palmas de Gran Canaria).
El segundo propósito de esta investigación consistió en proyectar tres diferentes tipos de TiO2 (100% anatasa, 100% rutilo y sub-óxidos) por tecnología APS y evaluar las actividades fotocatalíticas en fase liquida. El rendimiento de los recubrimientos aplicados como fotoánodos fue analizado con el proceso SPEC Solar Photoelectrocatalysis. El estudio llevó a la conclusión que los recubrimientos con mayor parte de fases cristalinas (anatasa y rutilo), mayor rugosidad 3D de superficie y adecuado espesor presentan mejor desempeño fotoelectrocatalítico. (Grupo LEMMA Laboratori d’Electroquímica de Materials i del Medi Ambient, Universitat de Barcelona).
La tercera finalidad de este trabajo fue depositar óxidos metálicos por APS para ser aplicados como electrodos en baterías reales. El hidrógeno contenido en el flujo de plasma de APS es capaz de reducir el óxido metálico TiO2 de partida, crear vacantes de oxígeno y compuestos no estequiométricos como sub-óxidos de titanio (TiO2-x) o fases de Magnéli (TinO2n-1). Esta falta de oxígeno aumenta la conductividad del material que además resiste bien contra la corrosión. Fueron fabricados recubrimientos sobre acero inoxidable, láminas de aluminio, material compuesto de polímero reforzado con carbono y espuma de níquel. Cuatro placas de TiO2-x sobre sustratos de aluminio se
aplicaron como electrodos en una batería de escala de laboratorio. Se realizaron las curvas de voltametría cíclica y los ciclos de carga/descarga de la batería de plomo y los resultados fueron excelentes (Facultad de Ingeniería y Medio Ambiente, Universidad de Southampton).
El último objetivo de este doctorado consistió en el desarrollo de nuevos sensores de gas funcionales a través de la tecnología de APS. Se estableció hacer crecer la capa sensorica sobre un sustrato cerámico delgado para poder aumentar la temperatura de trabajo. Las condiciones de proyección fueron seleccionadas para alcanzar una buena deposición, no dañar el sustrato y aumentar la cantidad de vacantes de oxígeno. La detección fue analizada a diferentes temperaturas de trabajos y los rendimientos fueron satisfactorios (Grupo MIND Micronanotecnologies I Nanoscòpies per Dispositius electrònics i fotònics, Facultad de Física, Universitat de Barcelona).
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Hudson, Arron Daniel. "The interaction between small molecules and thermal surfaces." Thesis, University of Liverpool, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437529.
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McGivern, Richard Canice. "Light scattering studies of thermal fluctuations of liquid surfaces." Thesis, Queen's University Belfast, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356895.
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McEnaney, Kenneth. "Modeling of solar thermal selective surfaces and thermoelectric generators." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/65308.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 101-107).<br>A thermoelectric generator is a solid-state device that converts a heat flux into electrical power via the Seebeck effect. When a thermoelectric generator is inserted between a solar-absorbing surface and a heat sink, a solar thermoelectric generator is created which converts sunlight into electrical power. This thesis describes the design and optimization of solar thermoelectric generators, with a focus on systems with high optical concentration which utilize multiple material systems to maximize efficiency over a large temperature difference. Both single-stage and cascaded (multi-stage) generators are considered, over an optical concentration range of 0.1 to 1000X. It is shown that for high-concentration Bi₂Te₃/skutterudite solar thermoelectric generators, conversion efficiencies of 13% are possible with current thermoelectric materials and selective surfaces. Better selective surfaces are needed to improve the efficiency of solar thermoelectric generators. In this thesis, ideal selective surfaces for solar thermoelectric generators are characterized. Non-ideal selective surfaces are also characterized, with emphasis on how the non-idealities affect the solar thernoelectric gencrator performance. Finally. the efficiency limit for solar thermoclectric generators with non-directional absorbers is presented.<br>by Kenneth McEnaney.<br>S.M.
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Shah, Keyur. "Thermal Analysis of Water Droplets on PV Panel Surfaces." Thesis, Southern Illinois University at Edwardsville, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10844505.
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<p> Due to the increasing energy costs and concern on carbon footprint, renewable energy technologies have become more important. Especially after the COP21 Paris meeting, increase in implementation of renewable energy systems has been an important agenda item of countries globally. Among these renewable technologies, solar energy is one of the key players. Hence research on photovoltaic (PV) panels has become more important. </p><p> This study investigates the heat transfer effect of water droplets on the panel surface. As surface temperature variation plays a significant role in the efficiency of the solar panel, understanding the heat transfer phenomena between the droplet and the panel is crucial. Temperature variation around the droplet-panel interface was studied both theoretically and numerically. Different cases were studied considering droplet volume, number of droplets, and the distance between the droplets. This research concludes that droplet retention on PV panel surface after a rain, condensation or irrigation event is observed when the drag force dominates the body forces. Amount of heat transfer increases with increasing droplet volume and contact area. Hence more heat transfer is observed over hydrophilic surfaces then hydrophobic surfaces. As the number of droplets over the PV panel surface increase, cell temperature decreases which would yield panel efficiency. It was observed that as the distance between the droplets increases, cooling effect lessens. This decrease in the cooling effect would get higher as the droplets get further away from each other.</p><p>
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Olanrewaju, Babajide O. "Non-thermal processes on ice and liquid micro-jet surfaces." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39475.
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Processes at the air-water/ice interface are known to play a very important role in the release of reactive halogen species with atmospheric aerosols serving as catalysts. The ability to make different types of ice with various morphologies, hence, different adsorption and surface properties in vacuum, provide a useful way to probe the catalytic effect of ice in atmospheric reactions. Also, the use of the liquid jet technique provides the rare opportunity to probe liquid samples at the interface; hitherto impossible to investigate with traditional surface science techniques. Studies of reactions on both ice and liquid surfaces at ambient conditions are usually complicated by the rapid desorption and adsorption processes due to the high evaporation rates at the surface. To gain a better understanding and improve modeling of several atmospheric relevant reactions, it is therefore important to develop laboratory techniques that provide an opportunity to investigate non-thermal reactions on both ice and liquid surfaces. Detailed investigation of the interactions of atmospheric relevant molecules (methyl iodide and hydrogen chloride) on water ice at low temperature in UHV conditions has been carried out. These interactions were studied using different techniques such as temperature programmed desorption (TPD), electron stimulated desorption (ESD) and resonance enhanced multiphoton ionization (REMPI). Unlike probing reactions on ice surfaces, investigating air/liquid interfaces present several challenges. This is because traditional surface science techniques require an ultra high vacuum environment to prevent distortion of information due to interference from equilibrium vapor above the liquid surface during data acquisition. The liquid jet technique facilitates the direct study of continually renewed liquid surfaces in high vacuum, thereby preventing the constant changing of the properties and composition of the liquid surface due to the aging process (diffusion of impurities or liquid constituent). A linear time-of-flight mass spectrometer has been used to monitor ion ejection during laser irradiation of liquid jet containing aqueous solutions and pure water. Since these ions are ejected exclusively from the surface of the liquid and the cluster distributions observed are influenced by the local structure, these experiments provide a sensitive probe of the liquid vacuum interface of these solutions. Though the research is fundamental, the results obtained from these investigations indicate how the discontinuity of bulk properties on the surface of both ice and aqueous solutions affects interfacial reactions.
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Bailey, Jacob (Jacob S. ). "Experimental determination of the thermal properties of multi-layered surfaces." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83683.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (page 23).<br>This paper outlines a project which aims to use Certified Reduced Basis and General Empirical Interpolation Methods to conduct rapid, inexpensive, computationally simple thermal property estimation for the purpose of material identification. In this specific case, thermal conductivity and diffusivity were the parameters of interest. Towards this end, an experimental apparatus was constructed which applied a thermal load to various materials and observed their thermal responses. Bugs in the experimental apparatus were compensated for by way of a MATLAB script, until the data produced by individual tests became highly repeatable. Software was developed which simulated these thermal responses for given thermal loads and "true" parameter values. The materials were put through multiple tests (Laser Flash Test, Transient Plane Source) to independently identify possible values for these thermal properties. The "true" values were then chosen from these possible values based on how well they allowed the simulated response to fit the measured response. It was found that implementation of the CRB and GEIM allowed for an accurate estimate of these "true values," and did so without exhaustively carrying out a finite element analysis for every possible combination of parameters, creating an exponential increase in performance.<br>by Jacob Bailey.<br>S.B.
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Chapman, Bruce Douglas. "Thermal radio emission from the surfaces of Venus and Mercury." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/14886.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1986.<br>MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN.<br>Vita.<br>Bibliography: leaves 136-143.<br>by Bruce Douglas Chapman.<br>Ph.D.
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Zhu, Yangying. "Magnetic tunable microstructured surfaces for thermal management and microfluidic applications." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82355.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 46-47).<br>Micro and nanostructured surfaces have broad applications including heat transfer enhancement in phase-change systems and liquid manipulation in microfluidic devices. While significant efforts have focused on fabricating static micro/nanostructured arrays, uniform arrays that can be dynamically tuned have not yet been demonstrated. In this work, we present a novel fabrication process for magnetically tunable microstructured surfaces, where the tilt angle can be controlled upon application of an external magnetic field. We also demonstrated this platform for droplet manipulation in heat transfer applications. The tunable surfaces consist of ferromagnetic nickel (Ni) pillars on a soft PDMS substrate. The pillars have diameters of 23-35 [mu]m, pitches of 60-70 [mu]m, and heights of 70-80 [mi]m. We used vibrating sample magnetometry to obtain hysteresis loops of the Ni pillar arrays which match well the properties of bulk Ni. With a field strength of 0.5 tesla and a field angle of 600, a uniform 10.5± 1 tilt angle of the pillar arrays was observed. Furthermore, we developed a model to capture the tilt angle as a function of the magnetic field, and showed that by replacing nickel to cobalt, the tilt angle could be increased to 30' with the same field. Meanwhile, simulations show good agreement with the experiments. Future work will focus on using these surfaces to actively transport water droplets and spread the liquid film via pillar movement. This work promises tunable surface designs for important device platforms in microfluidics, biological and optical applications.<br>by Yangying Zhu.<br>S.M.
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Ugarte-Almeyda, Orlando J. "Thermal analysis of tilted roofs composed of two separated surfaces." Morgantown, W. Va. : [West Virginia University Libraries], 2008. http://hdl.handle.net/10450/5983.
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Thesis (M.S.)--West Virginia University, 2008.<br>Title from document title page. Document formatted into pages; contains xii, 58 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 54-58).
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Anderson, Tomas. "Scattering of thermal energy atoms and molecules from cold copper surfaces /." Göteborg : Göteborg university, 2001. http://catalogue.bnf.fr/ark:/12148/cb40192699j.
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Sahiti, Naser. "Thermal and fluid dynamic performance of pin fin heat transfer surfaces." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=978599829.
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Bronner, Christopher [Verfasser]. "Photoinduced and Thermal Reactions of Functional Molecules at Surfaces / Christopher Bronner." Berlin : Freie Universität Berlin, 2014. http://d-nb.info/1053653751/34.
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Fleming, Christopher. "Thermal and electron stimulated chemistry of complex adsorbates on metal surfaces." Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/529/.
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Due to intrinsic limitations of conventional silicon based devices the trend of miniaturisation cannot continue indefinitely, thus molecular devices are being used to develop smaller, faster and higher storage density memory devices. We present a thermally activated, switchable hetero-polyoxometalate (HPOM) cluster immobilised on a highly polarisable gold surface which has potential as such a device. This cluster consists of a nanometre sized Mo(IV) oxide “shell” which encapsulates two electronically active pyramidal sulfite (SIVO32-) groups, and has the ability to reversibly interconvert between two electronic states. In the passive state, at cryogenic temperatures (77 K), the two SO32- groups are non-bonding with respect to the sulfur centres, however upon thermal activation, i.e. when the temperature is increased to room (298 K), two electrons are ejected from the active sulfite anions and delocalised over the metal oxide cluster cage. This has the effect of switching it from a fully oxidised to a two-electron reduced state, along with the concomitant formation of an S-S bonding interaction between the two sulfur centres inside the cluster shell. This process does not occur in the crystalline state and to proceed requires the stabilising effects provided by an image charge, generated as a consequence of being adsorbed onto a metal surface. The prototypical enantio-selective heterogeneously catalysed reaction involves the hydrogenation of the α-ketoester, methyl pyruvate on Pt. Using TPD, XPS and UPS we have investigated this compound’s behaviour on a model Cu(111) single crystal surface. Monolayers of methyl pyruvate at 180 K consist predominately (ca. 66%) of a chemisorbed methyl pyruvate moiety, with its keto-carbonyl bonded to the surface in a η2configuration, this moiety desorbs intact at 364 K. The rest of the monolayer contains weakly adsorbed methyl pyruvate, which desorbs at 234 K, and interacts with the surface through the lone pair electrons of the oxygen atoms of the C=O groups, adopting a η1 configuration. The observation of a strongly chemisorbed moiety in the present study is attributed to the activation of the keto-carbonyl by the electron withdrawing ester group, and is consistent with the homogeneous inorganic chemistry of ketones. It is widely assumed that the α-ketoester needs to be π-bonded to the surface for the enantio-selective hydrogenation to proceed, consequently, given both the formation of a η2 bonded methyl pyruvate moiety on Cu(l11) and the known activity of Cu as a selective hydrogenation catalyst, it is suggested that it is maybe worthwhile considering the possibility of testing the effectiveness of chirally modified supported Cu as an enantio-selective catalyst. The thermal and electron induced chemistry of (S)- and (R)-methyl lactate (MLac) on Cu(111) was investigated; both enantiomers exhibited similar behaviour. MLac adopts one of two adsorption modes on the terraces of a Cu(111) crystal, which desorb molecularly at 209 K and 220 K. Concerning the molecules adsorbed at defect sites, as the temperature is increased over the range 250 – 300 K, a fraction desorb intact, while the majority lose a hydrogen atom to form the more strongly bound alkoxy species on the surface. Of these, some recombine with the hydrogen and proceed to desorb as MLac at 360 K, while a larger proportion are dehydrogenated further and methyl pyruvate and hydrogen are ejected from the surface at 380 K. When a monolayer of MLac is irradiated with a low energy electron beam, the molecules at the terrace sites are electronically excited and desorb as intact molecules, while those at the defect sites undergo electron induced hydroxyl O-H bond cleavage. Subsequent to electron bombardment there is consequently a decrease in molecularly adsorbed MLac and an increase in the number of strongly bound alkoxy species on the surface, entities which are not susceptible to ESD. We believe the ESD excitation mechanism is dissociative electron attachment. Low energy electrons of <1 eV are prevalent in the secondary electron background and can excite the hydroxyl O-H stretch, facilitating its cleavage at a threshold of 1.4 + 0.7 eV. The cross sections for the electron induced processes are high, 3.0 + 0.4 x 10-16 cm2 for 50 eV electrons, thus MLac is extremely susceptible to electron stimulated desorption. The enantio-specific adsorption of both the (S)- and (R)- enantiomers of methyl lactate on the chiral Cu(643)R surface has been investigated. The results from the (111) surface enabled us to assign the features in the TPD profiles. The peaks arising from molecular desorption at terrace and step sites occurred at the same temperature for both enantiomers, however, those attributed to desorption from the kink sites differed by 13 K, representing an enantio-specific difference in desorption energies of 0.94 kcal mol-1. This value is significantly larger than those observed in previous experimental work, although it is consistent with theoretical studies. Furthermore, we also observed enantio-specific surface reactions. It was found that there was a greater tendency for the (R)- enantiomer to undergo both the alkoxide recombination reaction and further dehydrogenation to methyl pyruvate, while the (S)-enantiomer had a greater proclivity to undergo total decomposition. We have discovered, to the best of our knowledge, the first example of enantio-specific surface chemistry initiated by a beam of non-chiral low energy electrons. When (S)- and (R)-methyl lactate molecularly adsorbed at the chiral kink sites of a Cu(643)R substrate is irradiated with 50 eV electrons, it has been found that (R)-methyl lactate is more receptive to both electron induced desorption of the parent molecule and electron induced cleavage of the hydroxyl O-H bond. This behaviour has been attributed to the (S)-enantiomer forming a more intimate bond with the kink site than the (R)-enantiomer, as evidenced by its higher desorption temperature. Consequently the substrate is more effective at providing relaxation channels to the electronically excited adsorbate, which reduces the probability of ESD occurring. Starting with a racemic mixture, we have demonstrated a 20% enantiomeric enrichment in the molecular adsorbates at the chiral kink sites, after only 30% depletion of the initial population. As a control, the initial rates of desorption from terrace and step sites were found to be unaffected by enantiomeric identity, which was to be expected because these sites are achiral, and as such both enantiomers interact to a similar degree with each. When the monolayer is considered as a whole, it was found that electron irradiation drives desorption more completely with an (R)-MLac covered surface than with (S). It has been suggested that this property of the system could be exploited in the laboratory as a method for separating racemic mixtures, and that in an astrochemical context, it could provide insight into the origins of biohomochirality.
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Emerson, Preston Todd. "Thermal Atomization Due to Boiling During Droplet Impingement on Superhydrophobic Surfaces." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/7878.
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Superhydrophobic (SH) surfaces are characterized by their extraordinary water repellent qualities. When water comes in contact with these surfaces, it beads up and rolls around. This phenomenon is due partially to surface chemistry which promotes weak adhesive forces between liquid and solid. However, micro- and nanoscale surface roughness also plays a crucial role by trapping air beneath the liquid, reducing liquid-solid contact. Many advantages of these surfaces have been identified, including drag reduction and self-cleaning properties, and the body of research regarding them has grown rapidly over the past few decades.This thesis is concerned with water droplets impinging superheated, superhydrophobic surfaces. In these scenarios, boiling is common in the droplet, producing vapor bubbles which burst through the droplet lamella and cause a spray of miniscule water particles known as thermal atomization. The work contained in this thesis uses an image processing technique to quantify trends in thermal atomization intensity during droplet impingement scenarios for a range of surface microstructure configurations, superheat temperatures, and Weber numbers.In one study, droplet impingement on a smooth hydrophobic and three post-patterned SH surfaces of similar solid fraction is considered. In general, as pitch (center-to-center distance between posts) increases, atomization intensity decreases. This is attributed to the enhanced ability for vapor escape beneath the droplet that is present for wider pitch surfaces. Atomization intensity increases with increasing Weber number for each of the surfaces considered. Additionally, the Leidenfrost point is found to increase with increasing Weber number and decreasing pitch.Next, thermal atomization on SH surfaces with two distinct microstructure configurations is considered: square posts (which allow vapor escape between structures) and square holes (which block vapor escape). Tests are done for each configuration with varying microstructure height, and structure spacing and solid fraction are held constant. Comparing the two configurations at each structure height and Weber number, the post-patterned surfaces suppress atomization for a large number of scenarios compared to the hole surfaces, supporting the theory that vapor escape through microstructures suppresses atomization. Microstructure height significantly affects trends in atomization intensity with surface temperature and Weber number. The LFP is seen to decrease with increasing height.
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Mahfoudhi, Marouen. "Numerical optimisation of electron beam physical vapor deposition coatings for arbitrarily shaped surfaces." Thesis, Cape Peninsula University of Technology, 2015. http://hdl.handle.net/20.500.11838/2225.
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Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology.<br>For the last few decades, methods to improve the engine efficiency and reduce the fuel consumption of jet engines have received increased attention. One of the solutions is to increase the operating temperature in order to increase the exhaust gas temperature, resulting in an increased engine power.
However, this approach can be degrading for some engine parts such as turbine blades, which are required to operate in a very hostile environment (at ≈ 90% of their melting point temperature).
Thus, an additional treatment must be carried out to protect these parts from corrosion, oxidation and erosion, as well as to maintain the substrate’s mechanical properties which can be modified by the high temperatures to which these parts are exposed.
Coating, as the most known protection method, has been used for the last few decades to protect aircraft engine parts. According to Wolfe and Co-workers [1], 75% of all engine components are now coated. The most promising studies show that the thermal barrier coating (TBC) is the best adapted coating system for these high temperature applications.
TBC is defined as a fine layer of material (generally ceramic or metallic material or both) directly deposited on the surface of the part In order to create a separation between the substrate and the environment to reduce the effect of the temperature aggression.
However, the application of TBCs on surfaces of components presents a challenge in terms of the consistency of the thickness of the layer. This is due to the nature of the processes used to apply these coatings. It has been found that variations in the coating thickness can affect the thermodynamic performance of turbine blades as well as lead to premature damage due to higher thermal gradients in certain sections of the blade. Thus, it is necessary to optimise the thickness distribution of the coating.
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Tait, Steven L. "Desorption kinetics of small n-alkanes from MgO(100), Pt(111), and C(0001)/Pt(111) and studies of Pd nanoparticles : growth and sintering on Al₂O₃(0001) and methane dissociation on MgO(100) /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9630.
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Kunkee, David Bryan. "Polarimetric millimeter-wave thermal emission from anisotropic water surfaces : application to remote sensing of ocean surface wind direction." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/14689.
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Bostanci, Huseyin. "HIGH HEAT FLUX SPRAY COOLING WITH AMMONIA ON ENHANCED SURFACES." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3209.
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Many critical applications today, in electronics, optics and aerospace fields, among others, demand advanced thermal management solutions for the acquisition of high heat loads they generate in order to operate reliably and efficiently. Current competing technologies for this challenging task include several single and two phase cooling options. When these cooling schemes are compared based on the high heat flux removal (100-1000 W/cm2) and isothermal operation (within several oC across the cooled device) aspects, as well as system mass, volume and power consumption, spray cooling appears to be the best choice. The current study focused on high heat flux spray cooling with ammonia on enhanced surfaces. Compared to some other commonly used coolants, ammonia possesses important advantages such as low saturation temperature, and high heat absorbing capability. Moreover, enhanced surfaces offer potential to greatly improve heat transfer performance. The main objectives of the study were to investigate the effect of surface enhancement on spray cooling performance, and contribute to the current understanding of spray cooling heat transfer mechanisms. These objectives were pursued through a two stage experimental study. While the first stage investigated enhanced surfaces for the highest heat transfer coefficient at heat fluxes of up to 500 W/cm2, the second stage investigated the optimized enhanced surfaces for critical heat flux (CHF). Surface modification techniques were utilized to obtain micro scale indentations and protrusions, and macro (mm) scale pyramidal, triangular, rectangular, and square pin fins. A third group, multi-scale structured surfaces, combined macro and micro scale structures. Experimental results indicated that micro- and macrostructured surfaces can provide heat transfer coefficients of up to 534,000 and 426,000 W/m2oC at 500 W/cm2, respectively. Multi-scale structured surfaces offered even a better performance, with heat transfer coefficients of up to 772,000 W/m2oC at 500 W/cm2, corresponding to a 161% increase over the reference smooth surface. In CHF tests, the optimized multi-scale structured surface helped increase maximum heat flux limit by 18%, to 910 W/cm2 at nominal liquid flow rate. During the additional CHF testing at higher flow rates, most heaters experienced failures before reaching CHF at heat fluxes above 950 W/cm2. However, the effect of flow rate was still characterized, suggesting that enhanced surfaces can achieve CHF values of up to 1,100 W/cm2 with 67% spray cooling efficiency. The results also helped shed some light on the current understanding of the spray cooling heat transfer mechanisms. Data clearly proved that in addition to fairly well established mechanisms of forced convection in the single phase regime, and free surface evaporation and boiling through secondary nucleation in the two phase regime, enhanced surfaces can substantially improve boiling through surface nucleation, which can also be supported by the concept of three phase contact lines, the regions where solid, liquid and vapor phases meet. Furthermore, enhanced surfaces are capable of retaining more liquid compared to a smooth surface, and efficiently spread the liquid film via capillary force within the structures. This unique advantage delays the occurrence of dry patches at high heat fluxes, and leads to higher CHF.<br>Ph.D.<br>Department of Mechanical, Materials and Aerospace Engineering<br>Engineering and Computer Science<br>Mechanical Engineering PhD
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Lammers, Zachary A. "Thermal Management of Electromechanical Actuation System for Aircraft Primary Flight Control Surfaces." University of Dayton / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1399021324.
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Fagan, Danny T. "Electrochemical and thermal desorption analysis of glassy carbon and carbon fiber surfaces /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487584612164174.
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Lazzeri, Michele. "A first principles study of the thermal expansion in some metallic surfaces." Doctoral thesis, SISSA, 1999. http://hdl.handle.net/20.500.11767/3944.
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York, David Christopher. "Studies of thermal transpiration." Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323501.
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Davies, Jason W. "Analysis of Viscous Drag Reduction and Thermal Transport Effects for Microengineered Ultrahydrophobic Surfaces." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1205.pdf.
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Crabtree, Helen M. "Thermal and photon-induced decomposition reactions of small molecules on single crystal surfaces." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308687.
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DeSimone, Alice Johnson. "Thermal desorption, photodesorption, and photodissociation of water on amorphous ice and lunar surfaces." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50322.
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The temperature-programmed desorption profiles of water from three lunar analogs were measured. These experiments showed that glassy materials were hydrophobic, that water on multiphase materials occupied a continuum of adsorption sites, and that feldspar exhibited significant chemisorption of water. The competition between photodissociation and photodesorption of amorphous solid water (ASW) was investigated on three substrates: copper with a thin oxide coating, an impact melt breccia from Apollo 16, and a mare basalt from Apollo 17. The rotational temperature of desorbing H₂O did not vary significantly with substrate, but the H₂O time-of-flight spectra were broader on the lunar slabs than on copper. Additionally, the cross sections for water removal at low coverages were higher on the lunar slabs than on copper. O(³PJ) produced by 157-nm irradiation of ASW on the same three substrates was measured as a function of spin-orbit state, H₂O exposure, and irradiation time. The same Maxwell-Boltzmann components were present in each case, with translational temperatures of 10,000 K, 1800 K, 400 K, and the surface temperature, but the relative intensities of these components differed widely between substrates. Evidence for diffusion out of pores in the ASW and in the lunar slabs was observed for H2O exposures of at least 1 Langmuir. Cross sections for H2O and O(3PJ) depletion due to 157-nm irradiation of ASW were applied to icy grains in the rings of Saturn, and corresponding cross sections on the lunar substrates were used to estimate the flux of water desorbing from the Moon and the density of oxygen atoms in the lunar atmosphere.
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Archer, Robert Joseph 1957. "Effects of spacial variation of the thermal coefficient of expansion on optical surfaces." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276887.
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The deformation of a mirror's optical surface due to a spacial variation of the coefficient of thermal expansion is examined. Four types of variations of the coefficient of thermal expansion are studied. These represent variations which result after typical manufacturing and/or fabrication processes. Equations describing the deformations resulting from the variations in the coefficient of thermal expansion are derived for some of the cases. Deformations due to more complex variations in the coefficient of thermal expansion are developed empirically using data generated by the finite-element method.
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Cowley, Adam M. "Hydrodynamic and Thermal Effects of Sub-critical Heating on Superhydrophobic Surfaces and Microchannels." BYU ScholarsArchive, 2017. https://scholarsarchive.byu.edu/etd/6572.
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This dissertation focuses on the effects of heating on superhydrophobic (SHPo) surfaces. The work is divided into two main categories: heat transfer without mass transfer and heat transfer in conjunction with mass transfer. Numerical methods are used to explore the prior while experimental methods are utilized for the latter. The numerical work explores convective heat transfer in SHPo parallel plate microchannels and is separated into two stand-alone chapters that have been published archivally. The first considers surfaces with a rib/cavity structure and the second considers surfaces patterned with a square lattice of square posts. Laminar, fully developed, steady flow with constant fluid properties is considered where the tops of the ribs and posts are maintained at a constant heat flux boundary condition and the gas/liquid interfaces are assumed to be adiabatic. For both surface configurations the overall convective heat transfer is reduced. Results are presented in the form of average Nusselt number as well as apparent temperature jump length (thermal slip length). The heat transfer reduction is magnified by increasing cavity fraction, decreasing Peclet number, and decreasing channel size relative to the micro-structure spacing. Axial fluid conduction is found to be substantial at high Peclet numbers where it is classically neglected. The parameter regimes where prior analytical works found in the literature are valid are delineated. The experimental work is divided into two stand-alone chapters with one considering channel flow and the other a pool scenario. The channel work considers high aspect ratio microchannels with one heated SHPo wall. If water saturated with dissolved air is used, the air-filled cavities of SHPo surfaces act as nucleation sites for mass transfer. As the water heats it becomes supersaturated and air can effervesce onto the SHPo surface forming bubbles that align to the underlying micro-structure if the cavities are comprised of closed cells. The large bubbles increase drag in the channel and reduce heat transfer. Once the bubbles grow large enough, they are expelled from the channel and the nucleation and growth cycle begins again. The pool work considers submerged, heated SHPo surfaces such that the nucleation behavior can be explored in the absence of forced fluid flow. The surface is maintained at a constant temperature and a range of temperatures (40 - 90 °C) are explored. Similar nucleation behavior to that of the microchannels is observed, however, the bubbles are not expelled. Natural convection coefficients are computed. The surfaces with the greatest amount of nucleation show a significant reduction in convection coefficient, relative to a smooth hydrophilic surface, due to the insulating bubble layer.
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Morfeldt, Johannes. "Optically Selective Surfaces in low concentrating PV/T systems." Thesis, Örebro University, School of Science and Technology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-7396.
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<p>One of the traditional approaches to reduce costs of solar energy is to use inexpensive reflectors to focus the light onto highly efficient solar cells. Several research projects have resulted in designs, where the excess heat is used as solar thermal energy.</p><p>Unlike a solar thermal system, which has a selective surface to reduce the radiant heat loss, a CPV/T (Concentrating PhotoVoltaic/Thermal) system uses a receiver covered with solar cells with high thermal emittance.</p><p>This project analyzes whether the heat loss from the receiver can be reduced by covering parts of the receiver surface, not already covered with solar cells, with an optically selective coating. Comparing different methods of applying such a coating and the long-term stability of low cost alternatives are also part of the objectives of this project.</p><p>To calculate the heat loss reductions of the optically selective surface coating a mathematical model was developed, which takes the thermal emittances and the solar absorptances of the different surfaces into account. Furthermore, a full-size experiment was constructed to verify the theoretical predictions.</p><p>The coating results in a heat loss reduction of approximately 20 % in such a CPV/T system and one of the companies involved in the study is already changing their design to make use of the results.</p>
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Campbell, Michael Ma Hongbin. "Analysis and optimization of electroformed dendritic structures as enhanced heat transfer surfaces." Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/6549.
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The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on October 21, 2009). Thesis advisor: Dr. Hongbin Ma. Includes bibliographical references.
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Hausgen, Paul E. "A thermal analysis of an alkali metal thermal to electric converter with geometrically designed interior surfaces exhibiting directionally dependent radiative properties." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/16701.
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Jurgens-Kowal, Teresa Ann. "Preparation and characterization of synthetic mineral surfaces : adsorption and thermal decomposition of tetraethoxysilane on magnesium oxide, molybdenum, and titanium dioxide surfaces /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/9865.
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Accardo, Mario G. "Effects of high pressure water jet on aluminum surfaces prior to thermal spray coating." Master's thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-10222009-124845/.
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Searle, Matthew Clark. "Thermal Transport at Superhydrophobic Surfaces in Impinging Liquid Jets, Natural Convection, and Pool Boiling." BYU ScholarsArchive, 2018. https://scholarsarchive.byu.edu/etd/7065.
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This dissertation focuses on the effects of superhydrophobic (SHPo) surfaces on thermal transport. The work is divided into two main categories: thermal transport without phase change and thermal transport with phase change. Thermal transport without phase change is the topic of four stand-alone chapters. Three address jet impingement at SHPo surfaces and the fourth considers natural convection at a vertical, SHPo wall. Thermal transport with phase change is the topic of a single stand-alone chapter exploring pool boiling at SHPo surfaces. Two chapters examining jet impingement present analytical models for thermal transport; one considered an isothermal wall and the other considered an isoflux wall. The chapter considering the isothermal scenario has been archivally published. Conclusions are presented for both models. The models indicated that the Nusselt number decreased dramatically as the temperature jump length increased. Further, the influence of radial position, jet Reynolds number, Prandtl number and isoflux versus isothermal heating become negligible as temperature jump length increased. The final chapter concerning jet impingement reports an experimental exploration of jet impingement at post patterned SHPo surfaces with varying microfeature pitch and cavity fraction. The empirical results show a decrease in Nusselt number relative to smooth hydrophobic surfaces for small pitch and cavity fraction and the isoflux model agrees well with this data when the ratio of temperature jump length to slip length is 3.1. At larger pitch and cavity fractions, the empirical results have higher Nusselt numbers than the SHPo surfaces with small pitch and cavity fraction but remain smaller than the smooth hydrophobic surface. We attribute this to the influence of small wetting regions. The chapter addressing natural convection presents an analytical model for buoyant flow at a vertical SHPo surface. The Nusselt number decreased dramatically as temperature jump length increased, with greater decrease occurring near the lower edge and at higher Rayleigh number. Thermal transport with phase change is the topic of the final stand-alone chapter concerning pool boiling, which has been archivally published. Surface heat flux as a function of surface superheat was reported for SHPo surfaces with rib and post patterning at varying microfeature pitch, cavity fraction, and microfeature height. Nucleate boiling is more suppressed on post patterned surfaces than rib patterned surfaces. At rib patterned surfaces, transition superheat decreases as cavity fraction increases. Increasing microfeature height modestly increases the transition superheat. Once stable film boiling is achieved, changes in surface microstructure negligibly influence thermal transport.
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Sarde, Deepti R. "Thermal/fluid characteristics of elliptic cross-section filament box-lattices as heat exchanger surfaces." abstract and full text PDF (free order & download UNR users only), 2006. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1436470.
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Verma, Navni. "Development and Demonstration of Thermal Contact Conductance (TCC) Models for Contact Between Metallic Surfaces." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555452213472626.
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Hays, Robb C. "Thermal Transport to Sessile Water Droplets on Heated Superhydrophobic Surfaces of Varying Cavity Fraction." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4241.
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The hydrophobicity of a surface is defined as the degree to which it repels water molecules, and the internal contact angle that the droplet makes with the surface is a measure of the hydrophobicity. Contact angles less than 90° occur on hydrophilic surfaces, while contact angles greater than 90° occur on hydrophobic surfaces. If a surface's contact angle is greater than 120° the surface is commonly defined as superhydrophobic (SH). Superhydrophobicity is accomplished through a combination of microscale surface roughness and water repellant surface chemistry. The roughness creates cavities, or pockets, of vapor underneath the droplet which act to increase the effects of surface tension and lead to increased contact angles. The cavity fraction, F_c, of a surface is a measure of the surface roughness and is defined as the ratio of the projected cavity area to the projected total area of the surface. This thesis investigates the effects of varying cavity fraction, F_c, and substrate temperature, T_s, on heat transfer to evaporating water droplets. Distilled water droplets of nominally 3 mm in diameter were placed on heated SH substrates of varying F_c (0.5, 0.8, and 0.95). A smooth hydrophobic surface was included in the experiments for comparative purposes. The temperature of the surface was held constant at temperatures ranging from 60 to 230°C while the droplet evaporated. Measurements of droplet temperature and size were taken throughout the evaporation process using CCD and infrared camera images. These images were analyzed to yield heat transfer rates for the various surface types and surface temperatures studied. At temperatures below the saturation point of water, average droplet temperatures and heat transfer rates decrease with increasing cavity fraction. Differences in heat transfer rate between substrates increase with substrate temperature. Nusselt number decreases as cavity fraction is increased. Cavity fractions less than about 0.5 show only modest differences in Nusselt number between surfaces. As cavity fraction approaches unity, differences in Nusselt number become amplified between surfaces. At temperatures above the saturation point of water, boiling behavior on SH surfaces deviates dramatically from that of smooth untextured surfaces. Average heat transfer rates decrease with increasing cavity fraction. Nucleate boiling is delayed to highter superheats than normal or is not observed. The Liedenfrost point is advanced to lower superheats as cavity fraction is increased. Similar heat transfer rates are observed beyond the Leidenfrost point.
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Mason, Daniel Riordean. "Theoretical investigation of thermal tweezers for parallel manipulation of atoms and nanoparticles on surfaces." Thesis, Queensland University of Technology, 2009. https://eprints.qut.edu.au/30359/1/Daniel_Mason_Thesis.pdf.
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A major focus of research in nanotechnology is the development of novel, high throughput techniques for fabrication of arbitrarily shaped surface nanostructures of sub 100 nm to atomic scale. A related pursuit is the development of simple and efficient means for parallel manipulation and redistribution of adsorbed atoms, molecules and nanoparticles on surfaces – adparticle manipulation. These techniques will be used for the manufacture of nanoscale surface supported functional devices in nanotechnologies such as quantum computing, molecular electronics and lab-on-achip, as well as for modifying surfaces to obtain novel optical, electronic, chemical, or mechanical properties. A favourable approach to formation of surface nanostructures is self-assembly. In self-assembly, nanostructures are grown by aggregation of individual adparticles that diffuse by thermally activated processes on the surface. The passive nature of this process means it is generally not suited to formation of arbitrarily shaped structures. The self-assembly of nanostructures at arbitrary positions has been demonstrated, though these have typically required a pre-patterning treatment of the surface using sophisticated techniques such as electron beam lithography. On the other hand, a parallel adparticle manipulation technique would be suited for directing the selfassembly process to occur at arbitrary positions, without the need for pre-patterning the surface. There is at present a lack of techniques for parallel manipulation and redistribution of adparticles to arbitrary positions on the surface. This is an issue that needs to be addressed since these techniques can play an important role in nanotechnology. In this thesis, we propose such a technique – thermal tweezers. In thermal tweezers, adparticles are redistributed by localised heating of the surface. This locally enhances surface diffusion of adparticles so that they rapidly diffuse away from the heated regions. Using this technique, the redistribution of adparticles to form a desired pattern is achieved by heating the surface at specific regions. In this project, we have focussed on the holographic implementation of this approach, where the surface is heated by holographic patterns of interfering pulsed laser beams. This implementation is suitable for the formation of arbitrarily shaped structures; the only condition is that the shape can be produced by holographic means. In the simplest case, the laser pulses are linearly polarised and intersect to form an interference pattern that is a modulation of intensity along a single direction. Strong optical absorption at the intensity maxima of the interference pattern results in approximately a sinusoidal variation of the surface temperature along one direction. The main aim of this research project is to investigate the feasibility of the holographic implementation of thermal tweezers as an adparticle manipulation technique. Firstly, we investigate theoretically the surface diffusion of adparticles in the presence of sinusoidal modulation of the surface temperature. Very strong redistribution of adparticles is predicted when there is strong interaction between the adparticle and the surface, and the amplitude of the temperature modulation is ~100 K. We have proposed a thin metallic film deposited on a glass substrate heated by interfering laser beams (optical wavelengths) as a means of generating very large amplitude of surface temperature modulation. Indeed, we predict theoretically by numerical solution of the thermal conduction equation that amplitude of the temperature modulation on the metallic film can be much greater than 100 K when heated by nanosecond pulses with an energy ~1 mJ. The formation of surface nanostructures of less than 100 nm in width is predicted at optical wavelengths in this implementation of thermal tweezers. Furthermore, we propose a simple extension to this technique where spatial phase shift of the temperature modulation effectively doubles or triples the resolution. At the same time, increased resolution is predicted by reducing the wavelength of the laser pulses. In addition, we present two distinctly different, computationally efficient numerical approaches for theoretical investigation of surface diffusion of interacting adparticles – the Monte Carlo Interaction Method (MCIM) and the random potential well method (RPWM). Using each of these approaches we have investigated thermal tweezers for redistribution of both strongly and weakly interacting adparticles. We have predicted that strong interactions between adparticles can increase the effectiveness of thermal tweezers, by demonstrating practically complete adparticle redistribution into the low temperature regions of the surface. This is promising from the point of view of thermal tweezers applied to directed self-assembly of nanostructures. Finally, we present a new and more efficient numerical approach to theoretical investigation of thermal tweezers of non-interacting adparticles. In this approach, the local diffusion coefficient is determined from solution of the Fokker-Planck equation. The diffusion equation is then solved numerically using the finite volume method (FVM) to directly obtain the probability density of adparticle position. We compare predictions of this approach to those of the Ermak algorithm solution of the Langevin equation, and relatively good agreement is shown at intermediate and high friction. In the low friction regime, we predict and investigate the phenomenon of ‘optimal’ friction and describe its occurrence due to very long jumps of adparticles as they diffuse from the hot regions of the surface. Future research directions, both theoretical and experimental are also discussed.
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Mason, Daniel Riordean. "Theoretical investigation of thermal tweezers for parallel manipulation of atoms and nanoparticles on surfaces." Queensland University of Technology, 2009. http://eprints.qut.edu.au/30359/.
Full textAbstract:
A major focus of research in nanotechnology is the development of novel, high throughput techniques for fabrication of arbitrarily shaped surface nanostructures of sub 100 nm to atomic scale. A related pursuit is the development of simple and efficient means for parallel manipulation and redistribution of adsorbed atoms, molecules and nanoparticles on surfaces – adparticle manipulation. These techniques will be used for the manufacture of nanoscale surface supported functional devices in nanotechnologies such as quantum computing, molecular electronics and lab-on-achip, as well as for modifying surfaces to obtain novel optical, electronic, chemical, or mechanical properties. A favourable approach to formation of surface nanostructures is self-assembly. In self-assembly, nanostructures are grown by aggregation of individual adparticles that diffuse by thermally activated processes on the surface. The passive nature of this process means it is generally not suited to formation of arbitrarily shaped structures. The self-assembly of nanostructures at arbitrary positions has been demonstrated, though these have typically required a pre-patterning treatment of the surface using sophisticated techniques such as electron beam lithography. On the other hand, a parallel adparticle manipulation technique would be suited for directing the selfassembly process to occur at arbitrary positions, without the need for pre-patterning the surface. There is at present a lack of techniques for parallel manipulation and redistribution of adparticles to arbitrary positions on the surface. This is an issue that needs to be addressed since these techniques can play an important role in nanotechnology. In this thesis, we propose such a technique – thermal tweezers. In thermal tweezers, adparticles are redistributed by localised heating of the surface. This locally enhances surface diffusion of adparticles so that they rapidly diffuse away from the heated regions. Using this technique, the redistribution of adparticles to form a desired pattern is achieved by heating the surface at specific regions. In this project, we have focussed on the holographic implementation of this approach, where the surface is heated by holographic patterns of interfering pulsed laser beams. This implementation is suitable for the formation of arbitrarily shaped structures; the only condition is that the shape can be produced by holographic means. In the simplest case, the laser pulses are linearly polarised and intersect to form an interference pattern that is a modulation of intensity along a single direction. Strong optical absorption at the intensity maxima of the interference pattern results in approximately a sinusoidal variation of the surface temperature along one direction. The main aim of this research project is to investigate the feasibility of the holographic implementation of thermal tweezers as an adparticle manipulation technique. Firstly, we investigate theoretically the surface diffusion of adparticles in the presence of sinusoidal modulation of the surface temperature. Very strong redistribution of adparticles is predicted when there is strong interaction between the adparticle and the surface, and the amplitude of the temperature modulation is ~100 K. We have proposed a thin metallic film deposited on a glass substrate heated by interfering laser beams (optical wavelengths) as a means of generating very large amplitude of surface temperature modulation. Indeed, we predict theoretically by numerical solution of the thermal conduction equation that amplitude of the temperature modulation on the metallic film can be much greater than 100 K when heated by nanosecond pulses with an energy ~1 mJ. The formation of surface nanostructures of less than 100 nm in width is predicted at optical wavelengths in this implementation of thermal tweezers. Furthermore, we propose a simple extension to this technique where spatial phase shift of the temperature modulation effectively doubles or triples the resolution. At the same time, increased resolution is predicted by reducing the wavelength of the laser pulses. In addition, we present two distinctly different, computationally efficient numerical approaches for theoretical investigation of surface diffusion of interacting adparticles – the Monte Carlo Interaction Method (MCIM) and the random potential well method (RPWM). Using each of these approaches we have investigated thermal tweezers for redistribution of both strongly and weakly interacting adparticles. We have predicted that strong interactions between adparticles can increase the effectiveness of thermal tweezers, by demonstrating practically complete adparticle redistribution into the low temperature regions of the surface. This is promising from the point of view of thermal tweezers applied to directed self-assembly of nanostructures. Finally, we present a new and more efficient numerical approach to theoretical investigation of thermal tweezers of non-interacting adparticles. In this approach, the local diffusion coefficient is determined from solution of the Fokker-Planck equation. The diffusion equation is then solved numerically using the finite volume method (FVM) to directly obtain the probability density of adparticle position. We compare predictions of this approach to those of the Ermak algorithm solution of the Langevin equation, and relatively good agreement is shown at intermediate and high friction. In the low friction regime, we predict and investigate the phenomenon of ‘optimal’ friction and describe its occurrence due to very long jumps of adparticles as they diffuse from the hot regions of the surface. Future research directions, both theoretical and experimental are also discussed.
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Lhermerout, Romain. "Mouillage de surfaces désordonnées à l'échelle nanométrique." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEE041/document.
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Durant cette thèse, nous avons d'abord développé un dispositif expérimental permettant de mesurer la dynamique de l'angle de contact avec une précision record de 0,01° sur 7 décades de vitesses de la ligne triple, gamme jamais atteinte auparavant. Pour la première fois, la résolution numérique des équations de lubrification a permis de déduire l'angle de contact à l'échelle microscopique de ces mesures macroscopiques, découplant donc le problème hydrodynamique multi-échelles de la physique de la ligne de contact à petite échelle. Avec ces outils, nous avons montré qu'une pseudo-brosse - une couche nanométrique de polymères - peut complètement piloter la dynamique, en produisant des hystérésis les plus faibles jamais mesurées (<0,07° !) et des surdissipations massives provenant de la nature visco-élastique de la couche. Cette étude ouvre la voie à la nano-rhéologie, permettant de sonder la dynamique extrêmement rapide (~100 ns) de polymères confinés à l'échelle nanométrique. Grâce à un travail collaboratif fructueux, nous avons ensuite développé un modèle permettant de décrire quantitativement et de façon unifiée la dissipation hydrodynamique, l'hystérésis et l'activation thermique. Enfin, beaucoup d'efforts ont été fournis pour la fabrication de surfaces aux défauts nanométriques contrôlés en taille, forme et concentration. La dynamique s'est révélée insensible à cette échelle de désordre, la présence des défauts n'affectant que l'hystérésis. Ces résultats ont été interprétés semi-quantitativement avec des lois d'échelle, et la caractérisation complète des défauts devrait permettre à terme de développer des modèles plus quantitatifs<br>During this thesis, we first developed an experimental set-up to measure contact angle dynamics with a record precision of 0.01° over 7 decades of velocity of the triple line, a range never before attained. For the first time, numerically solving the lubrication equations has allowed us to deduce the contact angle at the microscopic scale from these macroscopic measurements, and thus enabled the multi-scale hydrodynamic problem to be disentangled from the physics of the contact line at small scales. With these tools we have shown that the dynamics can be completely piloted by a pseudo-brush -a nanometric layer of polymers-, producing the lowest ever reported hysteresis (<0.07°!) and giving rise to a huge source of dissipation originating from the viscoelasticity of the coating. This study points the way towards nano-rheology, to probe extremely fast dynamics (~100 ns) of polymers confined at the nano-scale. Thanks to a fruitful collaborative work, we then developed a model that provides a single quantitative framework to account for hydrodynamic dissipation, hysteresis and thermal activation. Finally, a great deal of effort has been made to produce nano-defects whose size, shape and density are controlled. The dynamics appears to be insensitive to this scale of disorder, and the presence of defects is observed to only modify the hysteresis. These results have been interpreted semi-quantitatively with scaling laws, and we expect that the complete characterization of the defects should eventually allow the development of more quantitative models
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Ginn, James. "PHASE SHAPING IN THE INFRARED BY PLANAR QUASI-PERIODIC SURFACES COMPRISED OF SUB-WAVELENGTH ELEMENTS." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4179.
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Reflectarrays are passive quasi-periodic sub-wavelength antenna arrays designed for discrete reflected phase manipulation at each individual antenna element making up the array. By spatially varying the phase response of the antenna array, reflectarrays allow a planar surface to impress a non-planar phasefront upon re-radiation. Such devices have become commonplace at radio frequencies. In this dissertation, they are demonstrated in the infrared for the first time--at frequencies as high as 194 THz. Relevant aspects of computational electromagnetic modeling are explored, to yield design procedures optimized for these high frequencies. Modeling is also utilized to demonstrate the phase response of a generalized metallic patch resonator in terms of its dependence on element dimensions, surrounding materials, angle of incidence, and frequency. The impact of realistic dispersion of the real and imaginary parts of the metallic permittivity on the magnitude and bandwidth of the resonance behavior is thoroughly investigated. Several single-phase reflectarrays are fabricated and measurement techniques are developed for evaluating these surfaces. In all of these cases, there is excellent agreement between the computational model results and the measured device characteristics. With accurate modeling and measurement, it is possible to proceed to explore some specific device architectures appropriate for focusing reflectarrays, including binary-phase and phase-incremental approaches. Image quality aspects of these focusing reflectarrays are considered from geometrical and chromatic-aberration perspectives. The dissertation concludes by briefly considering two additional analogous devices--the transmitarray for tailoring transmissive phase response, and the emitarray for angular control of thermally emitted radiation.<br>Ph.D.<br>School of Electrical Engineering and Computer Science<br>Engineering and Computer Science<br>Electrical Engineering PhD
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Li, Qiang. "Surface Chemistry of Hexacyclic Aromatic Hydrocarbons on (2x1) and Modified Surfaces of Si(100)." Thesis, University of Waterloo, 2004. http://hdl.handle.net/10012/1263.
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Room-temperature chemisorption of hexacyclic aromatic hydrocarbons on the 2x1, sputtered, oxidized and H-terminated Si(100) surfaces, as well as those upon post treatments of hydrogenation, oxidization and electron irradiation have been investigated by using thermal desorption spectrometry (TDS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). This work focuses on the effects of the functional groups (phenyl, methyl, vinyl, heteroatom, and H atom) in the chemisorbed aromatic hydrocarbons (benzene, toluene, xylene isomers, styrene and pyridine) on organic functionalization of the Si(100) surface, particularly on such surface processes as cycloaddition, dative adsorption, hydrogen abstraction, desorption, dissociation, diffusion, and condensation polymerization. Unlike the earlier notion that hydrogen evolution in the hydrocarbon/Si(100) systems is the result of hydrocarbon dissociation (into smaller hydrocarbon fragments and H atoms) on the surface, condensation polymerization of the adsorbed aromatic hydrocarbons is proposed in the present work, in order to explain the higher-temperature hydrogen evolution feature in the toluene/Si(100) system. This hypothesis is supported by our TDS results for other hydrocarbon adsorbates, especially in the pyridine/Si(100) system where electron-induced condensation polymerization has been observed at room temperature. The improved techniques in the TDS experiments developed in the present work have enabled us to observe condensation polymerization and the effect of H on the surface processes (via surface reconstruction) on Si(100) for the first time. New analysis methods have also been developed to determine the adsorption coverage from the AES data, and this work has not only improved the accuracy of the elemental-coverage evaluation, but also provided a means to estimate the rate and the order of chemisorption. By using the density functional theory with the Gaussian 98 program, the adsorption geometries and the corresponding adsorption energies of various adsorption phases have been calculated. These computational results have provided useful insights into the chemisorption structures on the Si(100) surface. The present work also presents the development of three kinetics models for hydrogen evolution in the aforementioned aromatic-hydrocarbon systems on Si(100). Based on a modified collision theory with consideration of diffusion, these theoretical models have proven to be quite successful in simulating the observed TDS profiles and in estimating the kinetic parameters for the analysis of condensation polymerization in 2-dimensional diffusion systems. The present work illustrates that TDS experiments can be used effectively with quantum computation and theoretical kinetics modelling to elucidate the intricate nature of organosilicon surface chemistry.
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Balantrapu, Kiran. "Thermal/fluid characteristics of cylindrical-filament open-cell box-lattice structures as heat exchanger surfaces." abstract and full text PDF (free order & download UNR users only), 2006. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1433298.
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Malekzadeh, Fatemeh. "Integration of Phase Change Materials in Commercial Buildings for Thermal Regulation and Energy Efficiency." Thesis, The University of Arizona, 2015. http://hdl.handle.net/10150/603534.
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One of prospective procedures of absorbing thermal energy and releasing it during the required time is the application of phase change materials known as PCMs in building envelopes. High thermal energy storage (TES) materials has been a technology that effects the energy efficiency of a building by contributing in using onsite resources and reducing cooling or heating loads. Currently, many TES systems are emerging and contributing in building assemblies, however using an appropriate type of TES in a specific building and climate requires an in-depth knowledge of their properties. This research aims to provide a thorough review of a broad range of thermal energy storage technologies including their potential application in buildings. Subsequently, a comparative study and simulation between a basecase and an optimized model by PCM is thoroughly considered to understand the effect of high thermal storage building's shell on energy efficiency and indoor thermal comfort. Specifically this study proposes that the incorporation of PCM into glazing system as a high thermal capacity system will improve windows thermal performance and thermal capacity to varying climatic conditions. The generated results by eQUEST energy modeling software demonstrates approximately 25% reduction in cooling loads during the summer and 10% reduction in heating loads during the winter for optimized office building by PCM in hot arid climate of Arizona. Besides, using PCM in glazing system will reduce heat gain through the windows by conduction phenomenon. The hourly results indicates the effect of PCM as a thermal energy storage system in building envelopes for building's energy efficiency and thermal regulation. However, several problems need to be tackled before LHTES can reliably and practically be applied. We conclude with some suggestions for future work.
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Roland, Jason Howard. "Forced Convection Over Flat and Curved Isothermal Surfaces with Unheated Starting Length." University of Dayton / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1418343439.
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Bharadwaja, Saketh. "Molecular Dynamics Simulations of Si binding and diffusion on the native and thermal Silicon Oxide surfaces." University of Toledo / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1333738718.
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SPENCER, JOHN ROBERT. "THE SURFACES OF EUROPA, GANYMEDE, AND CALLISTO: AN INVESTIGATION USING VOYAGER IRIS THERMAL INFRARED SPECTRA (JUPITER)." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184098.
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In 1979, the IRIS infrared spectrometers on the two Voyager spacecraft obtained over 1000 disk-resolved thermal emission spectra of Europa, Ganymede, and Callisto, Jupiter's three large icy satellites. This dissertation describes the first detailed analysis of this data set. Ganymede and Callisto subsolar temperatures are 10°K and 5°K respectively below equilibrium values. Equatorial nighttime temperatures are between 100°K and 75°K, Callisto and Europa being colder than Ganymede. The diurnal temperature profiles can be matched by 2-layer surfaces that are also consistent with the eclipse cooling observed from earth, though previous eclipse models underestimated thermal inertias by about 50%. Substrate thermal inertias in the 2-layer models are a factor of several lower than for solid ice. These are 'cold spots' on Ganymede and Callisto that are not high-albedo regions, which may indicate large thermal inertia anomalies. All spectra show a slope of increasing brightness temperature with decreasing wavelength, indicating local temperature contrasts of 10-50°K. Callisto spectra steepen dramatically towards the terminator, a trend largely matched with a laterally-homogeneous model surface having lunar-like roughness, though some lateral variation in albedo and/or thermal inertia may also be required. Subsolar Ganymede spectra are steeper than those on Callisto, but there is no steepening towards the terminator, indicating a much smoother surface than Callisto's. The spectrum slopes on Ganymede may indicate large lateral variations in albedo and thermal inertia. A surface with similar areal coverage of dark, very low thermal inertia material, and bright material with thermal inertia a factor of 2-3 below solid ice, fits the diurnal and eclipse curves, and (less accurately) the IRIS spectrum slopes. Europa spectra have very small slopes, indicating a smooth and homogeneous surface. Modelling of surface water ice migration gives a possible explanation for the inferred lateral inhomogeneities on Ganymede. Dirty ice surfaces at Jupiter are subject to segregation into high-albedo ice-rich cold spots and ice-free regions covered in lag deposits, on decade timescales. Ion sputtering and micrometeorite bombardment are generally insufficient to prevent the segregation. The reflectance spectra of Ganymede and Callisto may be consistent with this type of segregated surface.
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Schneck, William Carl III. "Estimation of the Real Area of Contact in Sliding Systems Using Thermal Measurements." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/35244.
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This thesis seeks two objectives. One objective is to develop a means to estimate time invariant real contact areas and surface temperatures through thermal measurements in 1D/2D systems. This allows computationally easier models, resulting in faster simulations within acceptable convergence. The second objective is to provide experimental design guidance.
The methods used are a modified cellular automata technique for the direct model and a Levenberg-Marquardt parameter estimation technique to stabilize inverse solutions. The modified cellular automata technique enables each piece of physics to be solved independently over a short time step, thus frequently allowing analytical solutions to those pieces.
Overall, the method was successful. The major results indicate that appropriately selected measurement locations can determine the contact distribution accurately, and that the preferred measurement location of the sensor is not very sensitive to the contact distribution specifics. This is useful because it allows selection of measurement locations regardless of the specifics of the generally unknown contact distribution. Further results show the combined effects of the normalized length and the Stanton number have a significant impact on the estimation quality, and can change the acceptable sensor domain, if the loss is high. The effect of placing the sensor in the static body can, for low loss, provide a coarse image of the contact distribution. This is useful because the static body is easier to instrument than a moving body. Finally, the estimation method worked well for the most complex model utilized, even in a sub-optimal measurement location.<br>Master of Science