To see the other types of publications on this topic, follow the link: High thermal conductivity.
Dissertations / Theses on the topic 'High thermal conductivity'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'High thermal conductivity.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Bilek, Jaromir. "Sensors for thermal conductivity at high temperatures." Thesis, University of Southampton, 2006. https://eprints.soton.ac.uk/47126/.
Full textAbstract:
This thesis describes research undertaken to improve a technique for the measurement of the thermal conductivity of molten materials. The research follows on from the work of previous researchers who designed and tested an instrument for the measurements of the thermal conductivity of molten metals up to 750 K. The previously used transient hot-wire technique, which consisted of the experimental measurement of the voltage response of a sensor and a subsequent inverse Unite element analysis, has been significantly upgraded. The experimental part of the technique has been improved by the introduction of a new design of the sensor for the measurement of the thermal conductivity. Both the new and the original designs have been used to investigate the same material samples in order to demonstrate the robustness and repeatability of the experimental technique. Additionally, the finite element analysis employed has also undergone various major improvements and resulted in a new finite element model which not only represents the true geometry of the experimental device but also employs a more accurate solution of the transient, conductive heat transfer. The significant upgrade of the technique and the availability of two different sensor designs have helped to uncover systematic errors which could not have been previously identified and may have resulted in deviations of the measured thermal conductivity. Five original sensors and five sensors with the new design have been used to investigate the thermal conductivity of molten indium, tin and lead at various temperatures up to 750 K. The results have been compared to previously published data and the discrepancies have been discussed and explained. Each metal has been measured using at least two sensors and the consistency of the measured data has also been verified by using two different samples of pure tin. Besides the pure metals, the thermal conductivity of several metal alloys currently used in industry has been investigated within the same temperature range. The overall uncertainty of the measurements of the thermal conductivity is estimated to be ±3 %.
2
Ford, Theodore Robert. "Thermal conductivity of bonded hollow-sphere monoliths." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/20045.
Full text
3
Rees, Mary Frances. "Thermal conductivity measurements on high Tâ†c superconductors." Thesis, University of Liverpool, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317234.
Full text
4
Stolk, Jonathan Douglas. "Development of low thermal expansion, high conductivity nanocomposites /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
Full text
5
Delap, Martin Richard. "Thermal conductivity studies of YBa₂Cu₃O₇₋δ". Thesis, Durham University, 1990. http://etheses.dur.ac.uk/9301/.
Full textAbstract:
Apparatus to measure the thermal conductivity of YBa(_2)Cu(_3)O(_7-δ) at temperatures between 20K and 120K has been designed and constructed. The thermal conductivity is measured using a longitudinal steady state heat flow technique. Thermal conductivity measurements have been performed upon a sample of YBa(_2)Cu(_3)O(_7-δ) which has been subjected to a series of heat treatments in order to remove oxygen from the material. The measurements show conclusively that the thermal conductivity of YBa(_2)Cu(_3)O(_7-δ) is very strongly influenced by the oxygen content of the material. A reduction of the oxygen content of the material results in a substantial lowering of the thermal conductivity. To explain this result, a quantitative model has been constructed; the model demonstrates that consideration of the changes in phonon interactions alone cannot account for the differences in the behaviour of the thermal conductivity of YBa(_2)Cu(_3)O(_6) and YBa(_2)Cu(_3)O(_7). In addition; the model, shows that there must be a significant carrier contribution to the thermal conductivity in both the normal and superconducting states. A physical process has been proposed which provides the required large carrier contribution below T(_c). Further studies have been performed on a series of samples of YBa(_2)Cu(_3)O(_7-δ) which were sintered at slightly different temperatures. Qualitative analysis of the physical properties, of these samples has been performed.
6
Freire, Ricardo Satuf 1962. "Short fiber composites with high electrical and thermal conductivity." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278242.
Full textAbstract:
This research describes the preparation of electrically and thermally conductive polymer composites. The filler used is short carbon fibers. These were dispersed in methyl methacrylate (MMA) and settled under different vibrational and gravitational forces, resulting in well packed sediments. To improve further the dispersability of the fiber/MMA system, steric stabilization was attempted by using organic dispersants of increasing chain length. Subsequent polymerization of the dense sediments produced composites with high fiber volume fractions. The electrical and thermal conductivities of these composites were studied. Fiber size, distribution, orientation and volume fraction are shown to have a profound influence on these properties. A general effective media equation, which relates percolation and effective media theories, is shown to describe the electrical conductivity of the composites. The specific thermal conductivity of the high fiber fraction composites is greater than that of stainless steel. Applications include electronic packaging and electromagnetic interference shielding.
7
Ghai, Ramandeep Singh. "Modelling Thermal Conductivity of Porous Thermal Barrier Coatings for High-Temperature Aero Engines." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/37035.
Full textAbstract:
Thermal Barrier Coatings (TBC) are used to shield hot sections of gas turbine engines, helping to prevent the melting of metallic surfaces. TBC is a sophisticated layered system that can be divided into top coat, bond coat, and the super-alloy substrate. The highly heterogeneous microstructure of the TBC consists of defects such as pores, voids, and cracks of different sizes, which determine the coating’s final thermal and mechanical properties. The service lives of the coatings are dependent on these parameters.
These coatings act as a defensive shield to protect the substrate from oxidation and corrosion caused by elevated temperatures. Yttria Stabilized Zirconia (YSZ) is the preferred thermal barrier coating for gas turbine engine applications. There are a certain number of deposition techniques that are used to deposit the thermal coating layer on the substrate; commonly used techniques are Air Plasma Sprayed (APS) or Electron Beam Physical Vapour Deposition (EB-PVD).
The objective of this thesis is to model an optimized TBC that can be used on next-generation turbine engines. Modelling is performed to calculate the effective thermal conductivity of the YSZ coating deposited by EB-PVD by considering the effect of defects, porosities, and cracks. Bruggeman’s asymmetrical model was chosen as it can be extended for various types of porosities present in the material. The model is used as an iterative approach of a two-phase model and is extended up to a five-phase model. The results offer important information about the influence of randomly oriented defects on the overall thermal conductivity. The modelled microstructure can be fabricated with similar composition to have an enhanced thermal insulation.
The modelling results are subsequently compared with existing theories published in previous works and experiments. The modelling approach developed in this work could be used as a tool to design the porous microstructure of a coating.
8
Konôpková, Zuzana. "Thermal Conductivity of Materials under Conditions of Planetary Interiors." Doctoral thesis, Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-150396.
Full textAbstract:
The presented thesis focuses on study of transport and thermoelastic properties of materials under conditions of planetary interiors by means of high-pressure experimental tools and finite element modeling, and their role in the dynamics and states of cores of terrestrial planets. Experiments in laser-heated diamond anvil cell (LHDAC) in combination with numerical simulations of heat transfer in DAC are shown to yield information on thermal conductivity of a pressurized sample. The novel technique consists of one-sided laser heating and double-sided temperature measurements and utilizes a precise determination of several parameters in course of the experiment, including the sample geometry, laser beam power distribution, and optical properties of employed materials. The pressure-temperature conditions at the probed portion of the sample are, however, not uniform. To address this problem, thermal pressure in the laser-heated diamond anvil cell and anisotropic thermal conductivity originating from the texture development upon uniaxial compression have been studied by means of numerical simulations. The method for determination of thermal conductivity is applied to iron at pressures up to 70 GPa and temperatures of 2000 K, meeting the Earth’s lower mantle conditions and covering Mercury’s entire core. The obtained results are extrapolated to the conditions of the Earth’s core-mantle boundary using a theoretical model of the density dependence of thermal conductivity of metals and published values on Grüneisen parameter and bulk modulus. After considering the effect of minor core elements, the obtained value at these conditions supports case for the downward revision of the thermal conductivity in the core. From the point of view of core dynamics and energy budget, the lower thermal conductivity implies more favorable conditions to drive the dynamo. Similar scenario applies for Mercury where, for high values of thermal conductivity, heat flux conducted along the iron-core adiabat exceeds the actual heat flux through the core-mantle boundary. This leads to a negative rate of entropy production in the core that makes it impossible to sustain the dynamo process presumably responsible for the observed magnetic field of Mercury.
9
Park, Sang-il. "Thermal conductivity of bentonite-bonded molding sands at high temperatures." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/18386.
Full text
10
Gold, Ziv. "The thermal conductivity of the high temperature superconductor YBa2Cu3O7-delta /." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=55497.
Full textAbstract:
Previous measurements show that the thermal conductivity of $Y Ba sb2 Cu sb3 O sb{7- delta}$ in the basal plane is anisotropic with a large peak in the superconducting state. The magnitude of this anisotropy in the superconducting and normal states, and the dominant mechanism for heat conduction in the superconducting state are currently the subject of debate. We have measured the thermal conductivity of high quality $Y Ba sb2 Cu sb3 O sb{7- delta}$ for deoxygenated, twinned and detwinned samples along the a and b axes to shade light on this issue. We were able to measure the electrical and thermal conductivity using the same contacts and hence determine the Lorenz number L = $ kappa$p/T accurately.<br>Attributing the normal state anisotropy in the heat transport to electrons in the Cu-O chains, the Lorenz number takes on its full Sommerfeld value i.e. $L = L sb0.$ Under this assumption, the phonon conduction is about the same in the superconducting and deoxygenated samples.<br>Our results are discussed in connection with the two possible mechanisms for heat conduction in the superconducting state. We find that although a strong case can be made for the "electronic scenario" whereby the peak is due to rapidly increasing electron mean free path below $T sb{c},$ it is still not compelling at this stage.<br>In addition, it is found that the thermal conductivity along the a and b axes is isotropic at low temperatures, with a nonzero linear term in $ kappa,$ indicative of some uncondensed electrons as $T rightarrow$ 0. This low temperature isotropy contradicts previous explanations in terms of non-superconducting chains.
11
Wittorff, Vaughan William. "Thermal conductivity of single crystals of yttrium-based high temperature superconductors." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612054.
Full text
12
Ababneh, Mohammed. "Novel Charging Station and Computational Modeling for High Thermal Conductivity Heat Pipe Thermal Ground Planes." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1353950640.
Full text
13
Shrestha, Ramesh. "High-Precision Micropipette Thermal Sensor for Measurement of Thermal Conductivity of Carbon Nanotubes Thin Film." Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc103393/.
Full textAbstract:
The thesis describes novel glass micropipette thermal sensor fabricated in cost-effective manner and thermal conductivity measurement of carbon nanotubes (CNT) thin film using the developed sensor. Various micrometer-sized sensors, which range from 2 µm to 30 µm, were produced and tested. The capability of the sensor in measuring thermal fluctuation at micro level with an estimated resolution of ±0.002oC is demonstrated. The sensitivity of sensors was recorded from 3.34 to 8.86 µV/oC, which is independent of tip size and dependent on the coating of Nickel. The detailed experimental setup for thermal conductivity measurement of CNT film is discussed and 73.418 W/moC was determined as the thermal conductivity of the CNT film at room temperature.
14
Majerus, Laurent J. "Application of the Thermal Flash Technique for Characterizing High Thermal Diffusivity Micro and Nanostructures." Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1259794802.
Full textAbstract:
Thesis(M.S.)--Case Western Reserve University, 2009<br>Title from PDF (viewed on 2010-01-28) Department of EMC - Mechanical Engineering Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center
15
Ganvir, Ashish. "Microstructure and Thermal Conductivity of Liquid Feedstock Plasma Sprayed Thermal Barrier Coatings." Licentiate thesis, Högskolan Väst, Avd för tillverkningsprocesser, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-9061.
Full textAbstract:
Thermal barrier coating (TBC) systems are widely used on gas turbine components to provide thermal insulation and oxidation protection. TBCs, incombination with advanced cooling, can enable the gas turbine to operate at significantly higher temperatures even above the melting temperature of the metallic materials. There is a permanent need mainly of environmental reasons to increase the combustion turbine temperature, hence new TBC solutions are needed.By using a liquid feedstock in thermal spraying, new types of TBCs can be produced. Suspension plasma/flame or solution precursor plasma spraying are examples of techniques that can be utilized for liquid feedstock thermal spraying.This approach of using suspension and solution feedstock, which is an alternative to the conventional solid powder feed stock spraying, is gaining increasing research interest, since it has been shown to be capable of producing coatings with superior coating performance.The objective of this research work was to explore relationships between process parameters, coating microstructure, thermal diffusivity and thermal conductivity in liquid feedstock thermal sprayed TBCs. A further aim was to utilize this knowledge to produce a TBC with lower thermal diffusivity and lower thermal conductivity compared to state-of-the-art in industry today, i.e. solid feed stock plasma spraying. Different spraying techniques, suspension high velocity oxy fuel,solution precursor plasma and suspension plasma spraying (with axial and radialfeeding) were explored and compared with solid feedstock plasma spraying.A variety of microstructures, such as highly porous, vertically cracked and columnar, were obtained. It was shown that there are strong relationships between the microstructures and the thermal properties of the coatings.Specifically axial suspension plasma spraying was shown as a very promising technique to produce various microstructures as well as low thermal diffusivity and low thermal conductivity coatings.
16
Filip, Ethan Lee. "Evaluation and Application of Thermal Modeling for High Power Motor Improvements." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/36137.
Full textAbstract:
Electric motors for vehicle applications are required to have high efficiency and small size and weight. Accurately modeling the thermal properties of an electric motor is critical to properly sizing the motor. Improving the cooling of the motor windings allows for a more efficient and power-dense motor. There are a variety of methods for predicting motor temperatures, however this paper discusses the advantages and accuracy of using a nodal lumped thermal model. Both commercially available and proprietary motor thermal modeling software are evaluated and compared. Thermal improvements based on the model in both contact interfaces and winding encapsulant are evaluated, showing motor improvements in the ability to handle heat losses of approximately forty percent greater than the baseline, resulting in either higher power or lower motor temperatures for the same package size.<br>Master of Science
17
van, Gelder Maarten F. "A Thermistor Based Method for Measurement of Thermal Conductivity and Thermal Diffusivity of Moist Food Materials at High Temperatures." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/30286.
Full textAbstract:
The purpose of this research was to assess the suitability of the thermistor based method for measuring thermal conductivity and diffusivity of moist food materials at high temperatures. Research focused on aspects of calibration, thermal contact in solid food materials, natural convection in liquid media and the performance in moist food materials at high temperatures.
Thermistor probes were constructed in house and calibrated in three materials of known thermal conductivity and diffusivity, water, glycerol, and a heat transfer fluid, HTF 500. With few exceptions, the calibrated probe estimated thermal properties with an error of less than 5%, over the range of thermal properties spanned by the those of the calibration media. An alternate calibration using two media was also investigated. It was found to give better accuracy over a more limited range. Thermal contact in potato and lean beef was investigated through a comparative study that used a miniature line heat source probe as a reference method. The food materials were measured at 25, 50 and 100 °C. Good agreement was found between the measurements with the line heat source probe and the bead thermistor probe, indicating adequate thermal contact at the thermistor probe.
The effect of fluid viscosity and the magnitude of the temperature step on the occurrence of natural convection was studied for aqueous solutions of a thickening agent. During a sample time of 30 seconds, convection was absent in solutions with a viscosity of 25 cp or greater, when measured with a temperature step of 1.5 and 2.5 °C, and in solutions with a viscosity of 50 cp or greater, when measured with a temperature step of 5.0 °C. A Rayleigh number was defined to study the notion of a critical Rayleigh number at the onset of convection. This study found that when the Rayleigh number was below 43, convection could not be demonstrated. For a Rayleigh number of 84 and higher, convection was observed.
The performance at high temperatures in food materials was studied through tests in tomato concentrate and in a liquid food supplement. Tomato puree and tomato paste were sampled at 100, 130 and 150 °C. The thermal conductivity of tomato puree at 100, 130 and 150 °C was measured as 0.638, 0.645 and 0.647 W/m°C respectively. The thermal diffusivity was 1.63, 1.64 and 1.62 10<sup>-7</sup> m<sup>2</sup>/s respectively. For tomato paste at 100, 130 and 150 °C, a thermal conductivity was obtained of 0.590, 0.597 and 0.534 W/m°C respectively. The thermal diffusivity was 1.63, 1.84 and 2.36 10 <sup>-7</sup> m<sup>2</sup>/s respectively. With some notable exceptions the results of this study agreed well with Choi and Okos (1983). A liquid food supplement was also studied at 95 and 150 °C. The thermal conductivity of the food supplement decreased with increasing solids content from 0.62 W/m°C at a solids level of 15% to 0.41 W/m°C at a solids level of 50%.
The results of this study indicate that the thermistor based method was suitable for measuring thermal conductivity and diffusivity of moist food materials at high temperatures. However, the type of thermistor used in the research, a glass encapsulated thermistor, was too fragile for routine work. In particular the high temperature use of the glass thermistor was impacted by its susceptibility to fracture.<br>Ph. D.
18
Oddone, Valerio [Verfasser]. "Lightweight metal matrix composites with graphitic fillers showing high thermal conductivity and low thermal expansion. / Valerio Oddone." Berlin : Freie Universität Berlin, 2019. http://d-nb.info/1189139073/34.
Full text
19
Miler, Josef L. "Methods for increasing the thermal conductivity of ultra-high molecular weight polyethylene (UHMWPE)." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36291.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.<br>"June 2006."<br>Includes bibliographical references (p. 31-33).<br>A two-part study was conducted to determine methods for producing ultra-high molecular weight polyethylene with high thermal conductivity by way of polymer chain orientation. The first portion of this report surveys current research involving polyethylene chain orientation and manufacturing. This section includes analysis of shish-kebab morphology, past polymer thermal studies, self-reinforcement studies, manufacturing techniques, and experimental techniques for low thermal conductivity materials. The second portion reviews the results of an experiment conducted to test the feasibility of stretched thermoforming of UHMW-polyethylene. Sheets of UHMWPE were stretched and tested for anisotropy in thermal conductivity. For samples with draw ratios of X 10, anisotropy in thermal conductivity was observed to increase. These results show potential for future development of this proposed methodology.<br>by Josef L. Miler.<br>S.B.
20
Wang, Yanfei. "The improvement of thermal and mechanical properties of La2Zr2O7-based pyrochlores as high temperature thermal barrier coatings." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/the-improvement-of-thermal-and-mechanical-properties-of-la2zr2o7based-pyrochlores-as-high-temperature-thermal-barrier-coatings(2cb87afa-4650-4af4-a159-d1b4f2febb78).html.
Full textAbstract:
To fully exploit the strengths of La2Zr2O7 pyroclores and promote them as a next-generation thermal barrier coating (TBC), the improvements of their thermally insulating property and fracture toughness are studied in this thesis. A strong phonon scattering source, rattlers, is found in Y3+-doped La2Zr2O7 pyrochlores. Rattlers dramatically flatten k (thermal conductivity)-T curves, or even make k approach the amorphous limit. The presence of rattlers is strongly dependent on (1) oversized atomic cages that are formed in pyrochlores; and (2) the occupation of smaller guest ions in those oversized cages. To maximize the rattling effect, In3+/Sc3+ ions that are much smaller than Y3+ are introduced to the La2Zr2O7 lattice. As envisaged, the smaller ions in the oversized lattice voids make k glass-like at a much lower doping content. Nevertheless, they are still not effective in reducing the high temperature plateau kmin. Instead, oxygen vacancies are very effective in reducing kmin, because they generate an electrostatic repulsion force among cations surrounding them, resulting in stronger lattice anharmonicity and weaker bonds. The plateau kmin is reduced dramatically by the filling of the B-sites in La2Zr2O7 with a 21% larger (and 50% heavier) Ce4+ guest ion rather than a 96% heavier (but similar-sized) Hf4+ ion, suggesting that a large absolute size of substitutional atoms is more effective in reducing kmin than a heavy absolute mass. This is because: (1) kmin is proportional to (E/M)0.5 (where E is the elastic modulus and M is the average atomic mass); (2) a larger size of guest ions tends to produce a weaker ionic bond and consequently, a lower E; and (3) the changing extent of E by introducing larger guest ions is much greater than that of M induced by adding heavier ones. Lastly, the fracture toughness (KIc) has been increased by dispersing the tetragonal 3 mol% Y2O3-stabilized zirconia (t-3YSZ) particulates in the La2Zr2O7 (LZ) matrix. The tendency of the dispersive t-3YSZ second phases transforming to monoclinic (m) phases strongly depends on the volume fraction introduced. For samples made from equilibrium route, they are toughened by phase transformations within the dispersive t-3YSZ second phases and a crack shielding effect arising from the residual compressive stress within the LZ matrix. An anticipated increase of KIc from ferroelastic toughening together with the residual compressive stress toughening highlights a potential to improve coating durability by depositing t’-3YSZ/LZ composite TBCs by the non-equilibrium route.
21
Cooper, John H. "Process-dependence of properties in high thermal conductivity aluminum nitride substrates for electronic packaging." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28470.
Full text
22
Ramaswamy, Raghupathy. "Thermal behavior of food materials during high pressure processing." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1190122901.
Full text
23
Sarfraz, Sohab. "A high temperature gas flow invariant thermal conductivity sensor developed in SOI CMOS MEMS technology." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708412.
Full text
24
Barzegar, Farshad. "Synthesis and characterization of Polymer/Graphene electrospun nanofibers." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/41188.
Full textAbstract:
Polymer nanofibers have attracted a lot of industrial interest in the past decade. In general, these
fibers need to be thermally stable for many applications, such as in the aerospace industry.
However, most of these polymer nanofibers suffer from low temperature degradation, limiting
their use in many potential applications. Graphene, which is one sheet of graphite, has unique
properties such as high conductivity, and high thermal stability. This exceptional material can be
incorporated into the polymer nanofibers as nanofillers in order to enhance their thermal
properties.
The aim of this dissertation is to investigate the effect of adding graphene nanofillers into the
polymer fiber on the resulting fibers’ thermal properties. For that purpose, polyvinyl alcohol
(PVA), a non-conductive polymer and a different source of graphene, namely graphene foam,
expendable graphite and graphite powder were used. The growth technique was the
electrospinning technique which offers a variety of parameters that need to be optimized. For this
includes, the amount of PVA in the water solvent, the flow rate, the applied voltage, the growth
time, and the tip/collector distance. In summary, it has been optimized that the best conditions
for growth of fibers will be as follows: PVA concentration will be fixed at 10 wt%, flow rate will
be 3 ml/h, applied voltage will be 30 kV, growth time of 60 s and tip/collector distance will be
fixed at 12 cm. The resulted PVA fibers from these conditions were smooth continuous and
hollow with diameter ranging between 190-340 nm, while PVA/graphene nano-fibers are much
thinner with diameter ranging between 132 - 235 nm when the same parameters were used with
only graphene concentration varied.
The fiber obtained with PVA showed a hollow structure which is desirable for incorporation of
graphene nanofillers. The dispersion of the different source of graphene sheets in the starting
PVA solution showed enhanced thermal stability compared to the PVA fibers alone.
Furthermore, an increase in the thermal stability is observed with increasing concentration of
graphene nanofillers. This work shows the promising use of graphene as nanofillers for PVA fibers. This can be
expended to other non-conductive and conductive polymers in order to broaden the application
of these fibers in the industries, where thermal stability is a prerequisite.<br>Dissertation (MSc)--University of Pretoria, 2013.<br>gm2014<br>Physics<br>unrestricted
25
Fox-Neff, Kristen. "Inverse Methods in Parameter Estimation for High Intensity Focused Ultrasound (HIFU)." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1459155373.
Full text
26
Kosuga, Atsuko, Yuri Isse, Yifeng Wang, Kunihito Koumoto, and Ryoji Funahashi. "High-temperature thermoelectric properties of Ca0.9−xSrxYb0.1MnO3−delta (0<=x<=0.2)." American Institite of Physics, 2009. http://hdl.handle.net/2237/12623.
Full text
27
Lei, Man I. "Silicon Carbide High Temperature Thermoelectric Flow Sensor." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1283278445.
Full text
28
Hrubiak, Rostislav. "Exploring Thermal and Mechanical Properties of Selected Transition Elements under Extreme Conditions: Experiments at High Pressures and High Temperatures." FIU Digital Commons, 2012. http://digitalcommons.fiu.edu/etd/696.
Full textAbstract:
Transition metals (Ti, Zr, Hf, Mo, W, V, Nb, Ta, Pd, Pt, Cu, Ag, and Au) are essential building units of many materials and have important industrial applications. Therefore, it is important to understand their thermal and physical behavior when they are subjected to extreme conditions of pressure and temperature. This dissertation presents: An improved experimental technique to use lasers for the measurement of thermal conductivity of materials under conditions of very high pressure (P, up to 50 GPa) and temperature (T up to 2500 K). An experimental study of the phase relationship and physical properties of selected transition metals, which revealed new and unexpected physical effects of thermal conductivity in Zr, and Hf under high P-T. New phase diagrams created for Hf, Ti and Zr from experimental data. P-T dependence of the lattice parameters in α-hafnium. Contrary to prior reports, the α-ω phase transition in hafnium has a negative dT/dP slope. New data on thermodynamic and physical properties of several transition metals and their respective high P-T phase diagrams. First complete thermodynamic database for solid phases of 13 common transition metals was created. This database has: All the thermochemical data on these elements in their standard state (mostly available and compiled). All the equations of state (EoS) formulated from pressure-volume-temperature data (measured as a part of this study and from literature). Complete thermodynamic data for selected elements from standard to extreme conditions.
The thermodynamic database provided by this study can be used with available thermodynamic software to calculate all thermophysical properties and phase diagrams at high P-T conditions. For readers who do not have access to this software, tabulated values of all thermodynamic and volume data for the 13 metals at high P-T are included in the APPENDIX. In the APPENDIX, a description of several other high-pressure studies of selected oxide systems is also included.
Thermophysical properties (Cp, H, S, G) of the high P-T ω-phase of Ti, Zr and Hf were determined during the optimization of the EoS parameters and are presented in this study for the first time. These results should have important implications in understanding hexagonal-close-packed to simple-hexagonal phase transitions in transition metals and other materials.
29
Ram, Gokul, and Vishnu Harikrishnan. "INFLUENCE OF CARBON CONTENT AND COOLING CONDITIONS ON THE THERMAL CONDUCTIVITY AND TENSILE STRENGTH OF HIGH SILICON LAMELLAR GRAPHITE IRON." Thesis, Tekniska Högskolan, JTH, Material och tillverkning, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-51152.
Full textAbstract:
Much study has been carried out to determine the properties of Lamellar Graphite Iron (LGI) or grey iron and their relations to factors such as the cooling rate, the dendrite morphology, the pouring temperature, and so on. However, there hasn’t been much comprehensive study on the properties of LGI outside the generally used and accepted composition, with 1 to 3% Silicon. The scope of this study is to measure and evaluate the thermal conductivity and tensile strength of LGI, for a higher concentration of Si and different carbon contents. The concentration of Si aimed for was 4% but the concentration obtained after spectroscopy was between 4.1% to 4.15%. There are two hypereutectic, one near-eutectic and three hypoeutectic samples considered and these six chemical compositions were cast under different cooling conditions . The cooling time has been varied by providing different molds of 30mm, 55mm, and 80mm diameter cylinders respectively, for all the six sample compositions. The microstructure analysis carried out studies the segregation of Si, the graphite morphology, primary austenite morphology. These factors are then compared to the thermal and tensile behavior measured in this study. It can be observed that the thermal conductivity studied in the present work has a direct correlation for a higher Si content and tends to be greater than the thermal conductivity values observed from other studies with lower content Of Si. However, the conductivity shows an inverse relation with the cooling rate and is maximum for the samples with the lowest cooling rate. The tensile strength, on the other hand, seems to have a lower value than that observed in previous studies for LGI with 1 to 3% Si, but shows a direct correlation with the cooling rate. The mean area fraction of dendrites obtained and the mean interdendritic hydraulic diameter is also measured and their influence on the properties are also studied. The addition of more Si has greatly favored the thermal behavior positively but has also reduced the tensile strength.
30
Albert, Rene [Verfasser], and Hartmut [Akademischer Betreuer] Wiggers. "Thermal Conductivity Measurements of Metal Hydrides as High Temperature Heat Storage Materials under Operating Conditions / Rene Albert ; Betreuer: Wiggers Hartmut." Duisburg, 2020. http://d-nb.info/1204826714/34.
Full text
31
Salazar, Alex III. "The thermal conductivity of filler materials and permeability of a cement sealant for deep borehole repositories for high level nuclear waste." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82868.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2013.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 129-134).<br>The Department of Energy is contractually obligated to begin the removal of spent nuclear fuel from reactor sites by the year 2020 at the risk of increased liabilities. The Blue Ribbon Commission on America's Nuclear Future proposed in 2012 that further development is necessary for geological repositories for spent nuclear fuel (SNF) and high level waste (HLW). They also noted that deep boreholes drilled into granite bedrock may be a viable option. Among the major concerns regarding this type of repository are the retention of radionuclides and the tolerance of heat from the canisters in situ. As a barrier against buoyancy-induced flows of groundwater through the borehole, a special cement formulation has been proposed as a sealant for the waste emplacement zone. Such a sealant must be expansive to prohibit flow through lateral gaps and should have a permeability that is less than or equal to that of the surrounding bedrock. Tests of the cement cured under pressure were conducted using a pressure decay method and water as a pore fluid. Data indicate that bulk permeability of this ideal sample is on the order of 0.1[mu[D, which is sufficient to inhibit flow through the bulk material for the immense expanse of time needed for long-lived radioactive species (e.g. 1-129) to decay. However, a less homogenous variation cured under atmospheric conditions indicated a two order-of-magnitude increase in permeability when subjected to increasing temperature and pressure. Furthermore, the harsh aquatic environment is likely to induce chemical changes that may impact longevity and durability. The decay heat of the waste canisters is conceptually able to induce water flows through air gaps, cracks and voids in the borehole and can lead to enhanced degradation of the canisters themselves. Therefore, thermal conductivity tests have been performed in an apparatus simulating the annular gap between waste canisters and the borehole wall liner on materials that can function as fillers for the gap and canisters themselves. These include mixtures of bentonite and crushed granite, bentonite mud, salt, and dehydrated borax. The effects of air and helium as fillers for the void space of porous materials was also analyzed, along with convection effects in vertical and horizontal orientations. The procedure involved controlling the linear power (13, 50, and 190 W/m) of a rod-shaped electrical heat source surrounded by an annulus of material in an insulated steel pipe and measuring the average temperature change across the gap at steady-state. These data have promoted a 3:7 mixture of bentonite and granite as an optimal gap filler with a value of thermal conductivity at 0.30 W/m-K and adequate absorptive characteristics when in contact with water. Furthermore, helium enhances the thermal conductivity of anhydrous borax, a candidate for a canister filler, by a factor of 1.9, and water increases that for bentonite (in the form of clay) by a lesser degree. Data overall indicate that the horizontal orientation of a canister is optimal at increasing the thermal conductivity of the filler due to enhanced convective heat transfer, which favors slanted borehole designs. The findings of this thesis can be used in future studies involving computational fluid dynamics of the system as a whole, and future work is suggested in the analysis of compacted materials, corrosion inhibitors, and variations on the cement formulation that optimize swelling/voiding at high pressures and temperatures. The latter would involve varying curing temperatures and pressures and employing X-ray crystallography to analyze the phases that are present.<br>by Alex Salazar III.<br>S.B.
32
Huber, Tanja [Verfasser], Winfried [Akademischer Betreuer] Petry, Olivier [Akademischer Betreuer] Tougait, and Katharina [Akademischer Betreuer] Krischer. "Thermal Conductivity of High-Density Uranium-Molybdenum Fuels for Research Reactors / Tanja Huber. Betreuer: Winfried Petry. Gutachter: Winfried Petry ; Olivier Tougait ; Katharina Krischer." München : Universitätsbibliothek der TU München, 2016. http://d-nb.info/1082973505/34.
Full text
33
Nguyen, Loc Thai. "Quality and Thermophysical Properties of Pressure Treated Foods." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1259093512.
Full text
34
Naldi, Matteo. "The effect of the temperature dependency of building insulation conductivity in continental and humid temperate climate." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
Find full textAbstract:
Constant conductivity values of insulating materials are typically used in building design and assessment. However, the thermal conductivity of insulating materials changes with temperature. Linear temperature-dependent law exist for many inorganic fibrous materials such as fiberglass or rockwool, that exhibit a decreased thermal conductivity (better performance) at low temperatures, and a higher thermal conductivity (weaker performance) at high temperatures. However some insulating materials, especially the petrochemical-foamed insulation such as the polyisocyanurate (PIR), exhibit less regular behavior with poorer performance at cold temperatures.
In this scenario, using constant thermal resistance values results in actual building are different from the design predictions, with increasing building energy consumptions, greater risks of condensation issues, and decreased occupant comfort.
This thesis aims to understand the impact of the thermal conductivity change due to temperature when the insulation is used for exterior walls and flat roofs. Experimental results were used in detailed building energy simulations in the continental and humid temperate climates of Toronto and Milan respectively.
Common rigid insulating materials boards were taken into account, such as fiberglass, rock- wool, polyisocyanurate, extruded polystyrene, and a hybrid insulation system, that is constituted by two different materials, polyisocyanurate and rockwool.
35
Hicks, David Cyprian. "Aligned Continuous Cylindrical Pores Derived from Electrospun Polymer Fibers in Titanium Diboride." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/99423.
Full textAbstract:
The use of electrospun polystyrene (PS) fibers to create continuous long range ordered multi-scale porous structures in titanium diboride (TiB2) is investigated in this work. The introduction of electrospun PS fibers as a sacrificial filler into a colloidal suspension of TiB2 allows for easy control over the pore size, porosity, and long range ordering of the porous structures of the sintered ceramic. Green bodies were formed by vacuum infiltrating an electrospun-fiber-filled mold with the colloidal TiB2 suspension. The size, volume, distribution, and dispersion of the pores were optimized by carefully selecting the sacrificial polymer, the fiber diameter, the solvent, and the solid content of TiB2. The green bodies were partially sintered at 2000 C in argon to form a multiscale porous structure via the removal of the PS fibers. Aligned continuous cylindrical pores were derived from the PS fibers in a range of ~5 - 20 μm and random porosity was revealed between the ceramic particles with the size of ~0.3 - 1 μm. TiB2 near-net-shaped parts with the multi-scale porosities (~50 to 70%) were successfully cast and sintered. The multi-scale porous structure produced from electrospun fibers was characterized both thermally and mechanically, at room temperature. The conductivity ranged from 12-31 W m^(-1) K^(-1) at room temperature and the compressive strength ranged from 2-30 MPa at room temperature. Analytical thermal and mechanical models were employed to understand and verify he processing-structure-properties relationship. Finally, a method was devised for estimating the effective thermal conductivity of candidate materials for UHTC applications at relevant temperatures using a finite difference model and a controlled sample environment. This low-cost processing technique facilitates the production of thermally and mechanically anisotropic structures into near-net shape parts, for extreme environment applications, such as ultra high temperature insulation and active cooling components.<br>MS
36
Zeaiter, Amal. "Thermal Modeling and Cooling of Electric Motors : Application to the Propulsion of Hybrid Aircraft Thermal Sensitivity Analysis of a High Power Density Electric Motor for Aeronautical Application Numerical Approach to Determining Windings’ Thermal Conductivity Electro-thermal Models and Design Approach for High Specific Power Electric Motor for Hybrid Aircraft Determination of electric motor losses and critical temperatures through an inverse approach." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0015.
Full textAbstract:
Le travail présenté dans ce mémoire concerne la modélisation thermique de moteurs électriques de forte densité de puissance. Le but est de trouver les techniques de refroidissement efficaces et adaptées aux moteurs conçus pour application à la propulsion de l’avion hybride du futur. Deux cibles de densité de puissance, 5 kW/kg pour le court terme (année 2025) et 10 kW/kg pour le long terme (année 2035), sont abordées avec leurs propres exigences. Les moteurs électriques étudiés sont de type synchrone à aimants permanents montés en surface du rotor. Ce type de moteur est caractérisé par un rendement élevé et contraint par les températures maximales admissibles relativement faibles de son bobinage et de ses aimants. Une fois atteintes, ces valeurs de température entraînent le dysfonctionnement du moteur ou la limitation de sa durée de vie. En outre, avec un design fermé imposé et des densités élevées de flux de chaleur dissipées dans la machine, une optimisation du refroidissement est incontournable.Pour se familiariser avec le problème, un état de l’art détaillé sur le refroidissement des machines électriques est réalisé. En conséquence, les différentes techniques utilisées et les avancements technologiques récents sont analysés vis-à-vis de notre cas d’application. Ensuite, afin de prédire le comportement thermique du moteur et d’assurer le suivi des températures critiques (surtout au bobinage et aux aimants), un modèle nodal transitoire est mis en place et résolu sous Matlab. Ce dernier est construit en considérant l’intégralité du système moteur avec son circuit de refroidissement. Les conditions externes liées à l’environnement sont prises en compte, en particulier la variation de la température d’air extérieur en fonction de l’altitude et le profil de mission de vol de l’avion. En effet, les pertes dans le moteur, qui constituent les sources de chaleur, varient en fonction de la puissance pendant le vol. Afin d’identifier précisément les paramètres intrinsèques du modèle, une étude par éléments finis a été menée et des corrélations permettant l’estimation de la conductivité thermique du bobinage en sont déduites par interpolation polynomiale. Plusieurs études ont ensuite été menées concernant l’influence des propriétés thermophysiques, de la température extérieure, de la nature du liquide de refroidissement, de son débit ainsi que la surface extérieure de l’échangeur sur les réponses en température du modèle. Plusieurs designs du moteur sont étudiés grâce à ce modèle afin de proposer des solutions de refroidissement adaptées. Pour chacune des cibles, une configuration optimale du moteur avec son système de refroidissement a été adoptée.Par ailleurs, les pertes électromagnétiques et mécaniques étant difficiles à estimer dans ces machines, un chapitre est consacré à leur identification par résolution d’un problème inverse. La technique est séquentielle et utilise la spécification de fonction de Beck comme méthode de régularisation. Trois cas, de complexité croissante, sont étudiés et montrent la fiabilité de la méthode qui permet également d’estimer les températures inaccessibles dans le moteur. C’est finalement ce modèle nodal à faible nombre de degré de liberté qui nous permet d’assurer, en temps réel, le suivi des points chauds<br>The concern of this thesis is the thermal modeling of high-specific power electric motors. The aim is to allow finding the efficient and adequate cooling solutions of the motors designed for hybrid aircraft propulsion application. Two specific power values, 5 kW/kg for the short-term (year 2025) and 10 kW/kg for the long-term (year 2035), are targeted, each with specific requirements. The investigated type of electric motors is the synchronous machine with surface-mounted permanent magnets. This motor type is constrained by relatively low values of maximum allowed temperatures in windings and magnets. Once reached, these temperature values lead to a failure in motor operation or at least to shortening its lifetime. Moreover, with a closed motor design and high heat fluxes generated, the optimization of the cooling is essential.To become acquainted with the issue, a detailed state of the art on electric machine cooling is elaborated. Then, the commonly used techniques and the recent technological advancements are analyzed with respect to our case study. Afterward, in order to predict motor thermal behavior and ensure the monitoring of critical temperatures (windings and magnets), a nodal transient model is implemented and solved on Matlab software. This latter is built for the whole system of the motor and cooling circuit. Specific conditions of the flight are taken into account, particularly the outside air temperature variation in terms of altitude and the flight mission profile. Actually, the motor losses, generating the heat in the machine, vary depending on the motor power during the mission. For the identification of crucial parameters, a Finite-Element study was conducted and corresponding correlations were elaborated to estimate the windings thermal conductivity through polynomial interpolation.Several studies were carried out involving the influence of the thermo-physical properties, the outside temperature, the coolant nature, its flow rate as well as the exchanger surface, on the temperature response of the model. This model has allowed studying several motor designs and proposing adequate cooling solutions. For each target, a final optimal configuration of the motor with its cooling system was adopted.Besides, since the electromagnetic and mechanical losses are hardly estimated in this machine type, a chapter was dedicated to identifying them through an inverse approach. A sequential technique, that uses Beck’s function specification for regularization, was developed. Three cases of unknown losses, with increasing complexity, were studied, proving the method's reliability. Finally, using the same developed low-order model, the real-time procedure also allows monitoring low-accessibility motor temperatures (specifically hot spots)
37
Balog, Paul S. "High pressure and temperature electrical resistivity measurements of HCP transition metals Ti, Zr and Gd and the potential anisotropy of thermal conductivity of the inner core of the Earth." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0006/MQ30777.pdf.
Full text
38
Dalpiaz, Felipe Lewgoy. "Estudo numérico da influência da geometria sobre resfriamento de corpos aletados geradores de calor utilizando Design Construtal." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/156491.
Full textAbstract:
A presente dissertação desenvolve um estudo numérico em duas direções espaciais com o objetivo de encontrar a configuração de geometrias acopladas a aletas de alta condutividade térmica em forma de “T” que resultam na menor resistência ao fluxo de calor utilizando o método Design Construtal. Como restrição as áreas de ambos os componentes, o corpo sólido onde há geração de calor e a aleta, são mantidas constantes. A equação diferencial da difusão do calor bidimensional, em regime permanente e propriedades constantes, com as condições de contorno, foram solucionadas pelo método dos elementos finitos utilizando o programa MATLAB ®, mais precisamente a ferramenta PDETOOL, Partial Differential Equations Tool. Em outras palavras, minimizar a resistência térmica ao fluxo de calor gerado para uma melhora na refrigeração, variando somente os comprimentos e larguras que formam o sólido de baixa condutividade térmica e a aleta composta por material de alta condutividade térmica. Para cada geometria proposta foram avaliadas todas as possibilidades geométricas dentro do domínio estabelecido Três geometrias foram propostas para os sólidos geradores de calor: retangular, trapezoidal e semicircular, todas acopladas com a aleta na forma de T. Além dos graus de liberdade, também foram avaliados o efeito dos seguintes parâmetros adimensionais: (condutividade térmica da aleta), (fração de área), (fração de área auxiliar) e ℎ . O melhor design encontrado é aquele que distribui melhor as imperfeições, ou seja, a geometria que distribui melhor os pontos de temperatura máxima. Os resultados reforçam, ainda, o entendimento de que sistemas multicomponentes devem ser estudados globalmente e não cada componente individualmente. Para a geometria retangular houve uma melhora de 66% no desempenho quando comparados os desempenhos da primeira para a última otimização. O melhor desempenho obtido para a geometria trapezoidal superou em aproximadamente 3,5% o desempenho da geometria retangular. Por fim a geometria semicircular atingiu o melhor desempenho entre as geometrias estudadas, superando em 40% o resultado atingido pela geometria trapezoidal.<br>This work used the method Construtal Design to develop a numerical study trying to find out the best configuration of geometries coupled to T-shaped materials of high thermal conductivity to improve the heat transfer between the heat generating body, which is a low heat conductor, and the environment. As a restriction, both areas are kept constant. The differential equations of heat diffusion, steady state and constant properties, and their boundary conditions were solved numerically using the MATLAB ® software, specifically the PDETOOL tool. The objective of this work is to improve the flux of heat through the Tshaped materials of high thermal conductivity, in other words, minimize the thermal resistance to improve the refrigeration, changing only the values of the lengths and widths that setup the solid of low thermal conductivity and the T-shaped materials of high thermal conductivity. All geometric possibilities were evaluated, respecting the domain. The optimal geometry was that which resulted in lower thermal resistance. Three geometries have been proposed for solid heat generators: rectangular, trapezoidal and semicircular. All coupled with the T-shaped materials of high thermal conductivity Besides the degrees of freedom were also evaluated the effect of the following dimensionless parameters: (thermal conductivity), (area fraction), (auxiliary area fraction) and ℎ . The best design found is that better distributes the imperfections, in other words, it is the geometry that better distributes the points of maximum temperature. The results reinforce also the understanding that multicomponent systems should be studied globally rather than each component individually. For the rectangular geometry there was an improvement of 66% in performance when comparing the performances of the first to the last optimization. The best performance obtained for the trapezoidal geometry exceeded by approximately 3.5% performance of the rectangular geometry. Finally the semicircular geometry achieved the best performance among the studied geometry, exceeding by 40% the result achieved by the trapezoidal geometry.
39
Rahmanian, Ima. "Thermal and mechanical properties of gypsum boards and their influences on fire resistance of gypsum board based systems." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/thermal-and-mechanical-properties-of-gypsum-boards-and-their-influences-on-fire-resistance-of-gypsum-board-based-systems(d8eb4bf5-706a-4264-911f-9584ebfbbc83).html.
Full textAbstract:
Gypsum board assemblies are now widely used in buildings, as fire resistant walls or ceilings, to provide passive fire protection. The fire resistance of such systems is fundamentally due to the desirable thermal properties of gypsum. Yet there is wide variability in reported values of thermal properties of gypsum at high temperatures and a lack of understanding of its integrity in fire. To evaluate the fire protection performance of gypsum board assemblies, it is essential to quantify its thermal properties and obtain information on its mechanical properties at high temperatures. Gypsum boards shrink and crack at high temperatures, and this leads to collapse of parts of the gypsum boards in fire. Fall-off of gypsum in fire affects the fire resistance of the assembly considerably, and cannot be overlooked when evaluating the fire resistance of gypsum board assemblies. The current research proposes a model to define the temperature-dependent thermal properties of gypsum boards at high temperatures. Thermal conductivity of gypsum is considered as the most influential parameter in conduction of heat through gypsum, and a hybrid numerical-experimental method is presented for extracting thermal conductivity of various gypsum board products at elevated temperatures. This method incorporates a validated one-dimensional Finite Difference heat conduction program and high temperature test results on small samples of gypsum boards. Moreover, high temperature mechanical tests have been performed on different gypsum board products; thermal shrinkage, strength and stress-strain relationships of gypsum products at elevated temperatures are extracted for use in numerical mechanical analysis. To simulate the structural performance of gypsum boards in fire, a two-dimensional Finite Element model has been developed in ABAQUS. This model successfully predicts the complete opening of a through-thickness crack in gypsum, and is validated against medium-scale fire tests designed and conducted as part of this research. Gypsum fall-off in fire is a complex phenomenon; however, it is believed that delaying the formation of through-thickness cracking will delay falling off of gypsum in fire, and hence improve the fire resistance of gypsum board assemblies. Finally, a study has been performed on the effects of various detailing parameters in gypsum board wall assemblies, and recommendations are offered for improving the fire resistance of such systems.
40
Samvin, Daniel, and Stefan Markovic. "InsuFlex : Framtagning och analys av högpresterande isoleringskoncept i sandwichelement." Thesis, Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-25546.
Full textAbstract:
Rapportens huvudsyfte är att ta fram en isoleringskombination av högpresterande material, som ska bidra till ett förbättrat U-värde och reducerad väggtjocklek. Konstruktionen är baserad på en befintlig sandwichvägg från Strängbetong, där författarna ersatt den ursprungliga isoleringen med det utvecklade isolerskiktet för att slutligen studera väggarna med lika villkor. Den framtagna väggens isolerings- förmåga presenteras genom handberäkningar, där det erhålls U-värde och temperaturfördelningar mellan elementens olika skikt vid stationära förhållanden. Det har även utförts värmesimuleringar för att analysera samma fysikaliska faktorer dock baserat på 3D förhållanden. I samarbete med företag har flera högpresterande isoleringsmaterial valts ut att ingå i väggkonstruktionen. Genom fördjupade studier av materialens fysikaliska egenskaper kunde en komplett isoleringskombination utvecklas och fick namnet InsuFlex. InsuFlex applicerades sedan i en sandwichkonstruktion för vidare analyser och värmesimuleringar. De nya väggresultaten visade mycket goda förbättringar av den ursprungliga sandwichväggen, tack vare det utvecklade skiktet av InsuFlex. Genom utförda beräkningar kunde författarna konstatera att isoleringsförmågan förbättrats med 46,5- samt 29 %, samtidigt som tjockleken reducerats med 5,5- samt 16,5 %, i jämförelse med Strängbetongs befintliga produkt. Den nya väggen erbjuder goda förutsättningar att reducera energiförlusterna och komma närmare framtida energikrav. Isoleringsmetoden förväntas även kunna appliceras i flera olika konstruktionselement.<br>The main objective of this report is development of an insulation-layer of high performance materials for a sandwich structure, which will contribute to an improved U-value and reduced wall thickness. The design is based on an existing sandwich wall, where the authors replaced the original insulation with the developed insulation-layer, to study the walls with equal conditions. The insulating ability is presented through calculations and thermal simulation to analyze the thermal aspects of the stationary conditions and 3D conditions. A complete insulation combination was developed through extensive studies of material’s physical properties, and named “InsuFlex”. The insulation-layer was then applied in a sandwich construction for further analysis and thermal simulations. The new design showed improvements in several areas.
41
Le, Foll Sébastien. "Modélisation du couplage conduction/rayonnement dans les systèmes de protection thermique soumis à de très hauts niveaux de températures." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0079/document.
Full textAbstract:
Les travaux présentés dans cette thèse CIFRE financée par AIRBUS Defence & Space s’intègrent dans une problématique de développement de nouveaux Systèmes de Protection Thermique (TPS) pour l’entrée atmosphérique. Ils se focalisent sur l’étude du transfert radiatif dans la zone d’ablation du TPS et son couplage avec le transfert conductif au travers de la matrice fibreuse de faible densité. Pour réaliser cette étude, il a été nécessaire d’évaluer les propriétés thermiques de ces matériaux, notamment les propriétés radiatives qui, contrairement aux conductivités thermiques, demeurent mal connues. La première étape de cette étude a donc visé à caractériser les propriétés optiques et radiatives de certains matériaux fournis par AIRBUS Defence & Space et par le CREE Saint-Gobain. Pour réaliser ces caractérisations, nous avons développé une méthode originale d’identification des propriétés radiatives basée sur des mesures de l’émission propre. Les spectres d’émission à haute température, réalisés sur des échantillons en fibre de silice ou en feutre de carbone nécessaires à l’identification, sont obtenus sur un banc de spectrométrie FTIR développé lors de ces travaux. Les échantillons sont chauffés à haute température à l’aide d’un laser CO2 et un montage optique permet de choisir entre la mesure du flux émis par l’échantillon ou un corps noir servant à l’étalonnage du banc. L’identification des propriétés repose sur la modélisation des facteurs de distribution du rayonnement calculés à l’aide d’une méthode de lancé de rayons Monte Carlo utilisant la théorie de Mie pour un cylindre infini pour le calcul des propriétés radiatives. Les températures identifiées sont comparées aux températures mesurées par pyrométrie au point de Christiansen dans le cas de la silice et montrent un bon accord avec ces dernières. Enfin la dernière partie de ce document est consacrée au couplage conduction-rayonnement dans ce type de milieu. Les échantillons ayant une très forte extinction, le modèle utilisé repose sur la définition d’une conductivité équivalente de Rosseland pour traiter les transferts radiatifs volumiques et ainsi simuler les champs de température au sein des échantillons dans les conditions de chauffage utilisées lors de l’identification. Dans le cas de la silice, cependant, les températures prédites par le modèle utilisant la conductivité équivalente de Rosseland, sont nettement supérieures à celles obtenues par identification ou par pyrométrie au point de Christiansen. Le fait que la conductivité équivalente de Rosseland ne fasse pas la distinction entre une forte extinction due à la diffusion ou à l’absorption est probablement la cause de cette différence<br>The work presented in this thesis has been financed by AIRBUS Defence and Space. It is part of the development strategy of new Thermal Protection Systems (TPS) for atmospheric reentry purposes. The aim is to study the radiative transfer in the ablation zone of the TPS as well as the coupling of the radiative and conductive heat transfer in the low density fibrous matrix. To this end, radiative properties of the materials have to be evaluated since they are not well known. The first step of this study is therefore to characterize the optical and radiative properties of sample provided by AIRBUS Defence and Space and the CREE Stain-Gobain laboratory. Thus, an original identification method based on radiative emission measurement was developed to obtain the radiative properties. The needed emission spectra are measured on silica or carbon samples at high temperature with an experimental setup based on Fourrier Transformed InfraRed spectrometry. The samples are heated using a CO2 laser. An optical setup allows us to measure emission spectra on the sample or a black body used to calibrate the experiment. The identification process is based on the modeling of the radiative distribution factor computed by a Monte Carlo ray-tracing method. It uses Mie theory for infinite cylinder to compute the radiative properties. Temperature are also identified and, for silica, compared to the one measured by a Christiansen pyrometry technique. The last part of this study focuses on the coupled radiative/conductive heat transfer modeling in low density fibrous media. Samples being greatly absorbing, we used the Rosseland equivalent conductivity to model the radiative transfer in volume and obtain the thermal response of the samples in the conditions of the experimental setup used for the identification. For silica, predicted temperatures are superior to the identified ones or those measured with the Christiansen pyrometry technique. This is probably because the Rosseland equivalent conductivity makes no difference between extinction due to absorption and extinction due to scattering
42
Cunsolo, Salvatore. "Radiative properties computational modeling of porous cellular materials." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI005/document.
Full textAbstract:
Les transferts thermiques par rayonnement dans des mousses sont modélisés à partir de la morphologie du matériau et des propriétés de sa phase solide. Dans ce travail de thèse, une attention particulière est portée sur les modèles radiatifs de Monte Carlo. Les différentes approches d’homogénéisation telles que « Homogeneous Phase » (HPA) and « Multi Phase » (MPA) sont discutées et comparées. Des développements novateurs sont proposés pour améliorer la précision des résultats. Nos avancées permettent de générer numériquement trois types de mousses périodiques couvrant un large domaine de matériaux cellulaires: mousse à pores fermés à haute porosité, mousse à cellules ouvertes à basse et haute porosité. Pour ces dernières, des comparaisons morphologiques avec des données expérimentales tomographiques, montrent des résultats satisfaisants et tendent à valider nos modèles de génération. Des mousses dont la phase solide est opaque ont tout d’abord été étudiées. Nos simulations ont permis de trouver de nouvelles lois analytiques précises permettant d’estimer les propriétés radiatives de ces matériaux à partir de données morphologiques. Ensuite, nous avons considéré des mousses, dont la phase solide est semi transparente. La modélisation du transfert radiatif au sein de ces milieux cellulaires est plus complexe. Les méthodes de modélisation des propriétés radiatives de la littérature, HPA et MPA, sont testées. Des simulations de Monte carlo directes dans les matériaux ont permis de mettre en exergue les limites de ces modèles. Des modèles novateurs ont été proposés afin d’ améliorer la précision des simulations. Ils sont basés sur une méthode hybride directe-inverse et une modification de l’équation de transfert radiatif classique. Ces nouveaux modèles (HPA+ et MPA+) ont été testés sur un ensemble varié de morphologies générées numériquement. Les modèles améliorés sont systématiquement plus précis que les modèles existants<br>Cellular media such as plastic, ceramic and metal foams present specific characteristics that make them interesting for a number of applications related to thermal engineering. Their ability to minimize natural convection makes them ideal candidates for insulation applications, while the high specific surface and permeability to fluid of open cell foams makes them interesting heat transfer enhancers. In addition, their permeability to light makes them an ideal candidate for thermal radiation based applications, such as porous burners or solar energy collectors. In many of these application, thermal radiation heat transfer can have a significant influence on the heat transfer process. Both accurate radiation models and accurate morphological models of the structure of the foam are required. This work provides an original contribution on both these accounts. A discussion of the literature on numerical methods for radiation heat transfer in cellular media is presented, with focus on Monte Carlo methods. Homogeneous Phase (HPA) and Multi Phase (MPA) methods are discussed. Further efforts are required to accurately model and digitally replicate of foam morphologies. Our goal is to digitally generate three commonly occurring types of foam structures, covering a large range of real materials: high-porosity open cell foams, high-porosity closed cell foams, low-porosity open-cell structures. For high-porosity open cell foams, the automated parametric digital generation technique was validated against a dataset consisting of raw morphological data obtained by tomographic analysis. The generation capabilities were then applied to parametrically investigate the influence of morphological parameters on the radiative properties (namely, the extinction coefficient) of an opaque open-cell foam. Highly accurate analytical relationships were subsequently deduced and validated by comparison with results obtained from tomography samples. Modeling radiation in foams with a semi-transparent solid phase is substantially more complex. A Direct Monte-Carlo Homogenization reference technique is proposed, that allows to simulate radiation within arbitrary cavities and calculate macroscopic radiative quantities based on a Representative Elementary Volume (REV) of cellular material. The technique is validated against full scale Monte Carlo simulations. Improvements of the existing Homogeneous Phase and Multi Phase approach are proposed, through extensive use of inverse methods and the addition of one equation to take into account specific phenomena taking place in the semi-transparent solid phase. The resulting Improved Homogenized Approaches are extensively tested by comparing them with Direct Monte Carlo Homogenization simulations and existing homogenized models, on a varied set of morphologies making full use of the previously developed digital generation techniques. The improved models consistently outperform existing homogenized models
43
Evans, Llion Marc. "Thermal finite element analysis of ceramic/metal joining for fusion using X-ray tomography data." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/thermal-finite-element-analysis-of-ceramicmetal-joining-for-fusion-using-xray-tomography-data(5f06bb67-1c6c-4723-ae14-f03b84628610).html.
Full textAbstract:
A key challenge facing the nuclear fusion community is how to design a reactor that will operate in environmental conditions not easily reproducible in the laboratory for materials testing. Finite element analysis (FEA), commonly used to predict components’ performance, typically uses idealised geometries. An emerging technique shown to have improved accuracy is image based finite element modelling (IBFEM). This involves converting a three dimensional image (such as from X ray tomography) into an FEA mesh. A main advantage of IBFEM is that models include micro structural and non idealised manufacturing features. The aim of this work was to investigate the thermal performance of a CFC Cu divertor monoblock, a carbon fibre composite (CFC) tile joined through its centre to a CuCrZr pipe with a Cu interlayer. As a plasma facing component located where thermal flux in the reactor is at its highest, one of its primary functions is to extract heat by active cooling. Therefore, characterisation of its thermal performance is vital. Investigation of the thermal performance of CFC Cu joining methods by laser flash analysis and X ray tomography showed a strong correlation between micro structures at the material interface and a reduction in thermal conductivity. Therefore, this problem leant itself well to be investigated further by IBFEM. However, because these high resolution models require such large numbers of elements, commercial FEA software could not be used. This served as motivation to develop parallel software capable of performing the necessary transient thermal simulations. The resultant code was shown to scale well with increasing problem sizes and a simulation with 137 million elements was successfully completed using 4096 cores. In comparison with a low resolution IBFEM and traditional FEA simulations it was demonstrated to provide additional accuracy. IBFEM was used to simulate a divertor monoblock mock up, where it was found that a region of delamination existed on the CFC Cu interface. Predictions showed that if this was aligned unfavourably it would increase thermal gradients across the component thus reducing lifespan. As this was a feature introduced in manufacturing it would not have been accounted for without IBFEM.The technique developed in this work has broad engineering applications. It could be used similarly to accurately model components in conditions unfeasible to produce in the laboratory, to assist in research and development of component manufacturing or to verify commercial components against manufacturers’ claims.
44
Low, Zi Kang. "Matériaux cellulaires isolants haute température : Relation microstructure-propriétés." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI122.
Full textAbstract:
Cette thèse CIFRE réalisée en collaboration avec Saint-Gobain Research Provence porte sur la modélisation des propriétés thermiques d’une mousse d’alumine NorFoam XPure®, conçue pour l’isolation thermique haute température (1200°C–1700°C). L’objectif est de développer et valider des modèles numériques multiéchelles pour calculer le transfert de chaleur par conduction et rayonnement dans cette mousse, à partir des microstructures 3D tomographiées et des propriétés intrinsèques des composants. La mousse étant composée des cellules ouvertes et d’un squelette solide lui-même poreux, la prise en compte de l’influence de cette double porosité est particulièrement novatrice. Dans un premier temps, le transfert thermique par conduction à travers la mousse est modélisé avec des techniques d’homogénéisation par éléments finis. Il est démontré que des conditions aux limites périodiques couramment utilisées ne sont pas adaptées aux mousses tomographiées, et qu’un jeu de conditions aux limites mixtes permet d’obtenir des résultats plus précis sur ces dernières. Quant au transfert radiatif à travers le squelette poreux, qui présente une forte diffusion volumique avec des phénomènes ondulatoires, le développement d’une nouvelle approche de modélisation basée sur l’approximation dipolaire discrète permet de prendre en compte l’influence desdits phénomènes. Les propriétés radiatives de la mousse sont ensuite calculées par méthode de lancer de rayons en tenant compte du comportement radiatif complexe du squelette poreux. L’influence des phénomènes de réflexion et réfraction non-spéculaires aux interfaces entre le squelette et les cellules a été étudiée. Enfin, une modélisation numérique basée sur les techniques d’homogénéisation permet de calculer le transfert thermique à travers la mousse, avec couplage de la conduction et du rayonnement. Le bon accord entre les résultats issus de chaque modèle et les mesures thermiques et optiques réalisées sur la mousse et le squelette poreux confirme le caractère prédictif des modèles développés<br>This CIFRE doctoral study, performed in collaboration with Saint-Gobain Research Provence, aims to model the thermal properties of NorFoam XPure®, an alumina foam designed for high temperature thermal insulation (1200°C–1700°C). The goal is to develop and validate multiscale numerical models to compute the conductive and radiative heat transfer through the foam from 3D tomography-reconstructed microstructures and the intrinsic properties of each constituent phase. Specific attention is given to the complex porosity in the studied foam: in addition to the open-cell network, smaller pores are also found within the foam skeleton. Novel approaches are proposed in the present work to take into account the influence of this dual-scale porosity. Firstly, effective heat conduction through the foam is modeled with finite element homogenization techniques. It is demonstrated that the commonly used periodic boundary conditions are unsuitable for tomography-reconstructed foams, and that a set of mixed boundary conditions gives more accurate and precise results for such foams. As radiative transfer through the porous foam skeleton is characterized by high volume scattering and significant wave effects, a novel physical optics approach based on the discrete dipole approximation is next developed to model the influence of these phenomena. The radiative properties of the foam are then determined through a ray tracing method that takes into account the complex radiative behavior of the porous foam skeleton. The influence of non-specular reflection and refraction at the interfaces between the foam cells and skeleton is studied. Finally, the homogenized properties are applied to simulate the coupled conductive and radiative heat transfer through the foam. The model predictions are systematically compared to thermal and spectroscopic measurements performed on samples of the foam and the foam skeleton material. The good agreement between numerical and experimental results confirms the predictive capabilities of the models developed in this study
45
Desmars, Loriane. "Etude des propriétés électriques et thermiques de matériaux composites à matrice époxy-anhydride pour l'isolation haute tension." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI021.
Full textAbstract:
L’avènement des énergies renouvelables, notamment offshore, et la nécessité de transporter l’électricité sur des distances toujours plus grandes tout en réduisant les pertes en ligne requièrent la mise en place d’un nouveau réseau électrique plus performant, le supergrid. L’amélioration des sous-stations ultra haute tension en courant alternatif (UHVAC) de type poste sous enveloppe métallique (PSEM), i.e. la réduction de leur empreinte au sol ou leur montée en tension, s’inscrit parmi les défis engendrés par le développement du supergrid. L’amélioration de la tenue aux contraintes électrothermiques des isolants solides employés dans les PSEM a été identifiée comme le principal verrou technologique pour le perfectionnement de ces appareillages, déjà pleinement maîtrisés en HVAC. Les travaux présentés dans ce manuscrit ont été motivés par la nécessité de développer un matériau isolant électrique plus performant que les matériaux existant actuellement sur le marché. L’un des matériaux couramment employés pour la fabrication d’isolants solides pour PSEM, une matrice époxy-anhydride chargée d’alumine micrométrique, a servi de référence commerciale à notre étude. Suite à une étude bibliographique, nous avons choisi de conserver la matrice époxy du système commercial de référence et de jouer sur les charges inorganiques employées pour optimiser les propriétés du matériau isolant. Les travaux présentés mettent en évidence l’influence de la nature des charges inorganiques (alumine ou nitrure de bore hexagonal), de leur facteur de forme (quasi sphérique ou lamellaire) et de leur fraction volumique sur la conductivité thermique, le coefficient d’expansion thermique, les propriétés mécaniques dynamiques, les propriétés diélectriques, la conductivité électrique à haute tension (DC) et la rigidité diélectrique (AC) des matériaux composites. L’étude expérimentale des relations structure-propriétés est complétée par un travail de modélisation des propriétés diélectriques et de la conductivité thermique des matériaux composites<br>The integration of renewable energies to the power grid requires its modification in order to ensure its stability, security and efficiency. Improving ultra-high voltage alternative current (UHVAC) gas insulated substations (GIS), e.g. reducing their size or increasing their voltage, is one of the challenges induced by the development of the future power grid, the supergrid. Increasing the ability of solid insulators used in such equipment to withstand electro-thermal stress has been identified as the main obstacle to overcome. The work presented in this manuscript has been motivated by the necessity to develop more efficient electrical insulating materials compared to commercially available ones. An epoxy-anhydride matrix filled with micron sized alumina, often used to produce GIS solid insulators, has been used as a reference for this study. We decided to keep the matrix of the reference material throughout our work and to concentrate on the filler influence in order to optimize the properties of the composites. The impact of the nature of the filler (alumina or hexagonal boron nitride), its shape factor (platelets or almost spherical particles) and its volume fraction upon thermal conductivity, coefficient of thermal expansion, dynamic mechanical properties, dielectric properties, high voltage direct current (DC) conductivity and AC breakdown strength have been highlighted. The experimental study of structure-property relationships is completed by dielectric properties and thermal conductivity modelling using the effective medium theory
46
Viggiano, Rocco P. III. "Investigations into High Surface Area and Hierarchical Phase Segregated Network Structures." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1440572438.
Full text
47
Moradi, Sasan. "A study of epoxy composites for high thermal conductivty applications." Doctoral thesis, Universitat Politècnica de Catalunya, 2021. http://hdl.handle.net/10803/672326.
Full textAbstract:
Nowadays. both electronic and microelectronic circuits have great relevance and wide application in our daily lives and are increasingly being used with higher powers and frequencies. One of the main problems faced by their manufacturers is the
dissipation of heat generated during their operation. since it reduces the useful life of these devices. One of the useful options that can help dissipate the generated heat is the lnsulated Metal Substrate (IMS). The IMS consists of three layers: copper foil, a dielectric layer, and a metallic substrate. The thermal conductivity of the material that constitutes the dielectric layer will be of vital importance when it comes to dissipating the heat generated. The most widely used system as a dielectric layer for IMS is an epoxy resin matrix with a crosslinking agent and a filler. As the thermal conductivity of the epoxy resin is low, it is essential to use a filler with high thermal conductivity that allows efficient dissipation of the generated heat. Therefore, in this thesis, the preparation of samples based on epoxy resins with boron nitride (BN) charges is studied. The effect of the BN particle size, the effect of the crosslinking agent used, the curing kinetics, the shape of the BN particles, the application of pressure on the material during the curing process, and the role of densification are analyzed. lt is found that the thenmal conductivity of epoxy-BN composites increases with increasing BN particle size for a given content of filler, and that BN agglomerates provide a higher thermal conductivity in comparison with the same size platelets, which is attributed to there being fewer interfaces with the epoxy matrix for the agglomerates. The epoxy-thiol system provides a higher thermal conductivity than the epoxy-Jeffamine system, which is attributed to a Lewis acid-base interaction. In the cure kinetics experiments, it was observed that the cure reaction of the epoxy-thiol composites was retarded with increasing the BN content for all particles (platelets or agglomerates). For the epoxy-Jeffamine system, it was observed that the cure reaction is independent of BN particle content, which is also correlated with the thermal conductivity measurements. The heat of reaction (L':.Hee) and the glass transition temperature of the fully cured system, Tgm, are independent of BN particle content, size and shape for both epoxy-thiol and epoxy-Jeffamine. On the other hand, the thermal conductivity increases by applying pressure for both epoxy-thiol and epoxy-Jeffamine systems in comparison with the composites cured at ambient pressure; the enhancement for the epoxy-Jeffamine system is greater. lt is revealed that the mechanisms of the enhancement of the thermal conductivity by application of pressure for each system are different. And finally, densification is shown to be a way of increasing the thermal conductivity; it is also shown to be a reversible effect.<br>En la actualidad, tanto los circuitos electrónicos como los microelectrónicos tienen una gran
relevancia y una amplia aplicación en nuestra vida diaria y cada vez se utilizan mayores
potencias y frecuencias. Uno de los principales retos que encaran sus fabricantes es la
disipación del calor generado durante su funcionamiento, ya que reduce la vida útil de estos
dispositivos. Una de las opciones útiles que pueden ayudar a disipar el calor generado es
el denominado sustrato metálico aislado (IMS). El IMS consta de tres capas: una lámina de
cobre, una capa dieléctrica y un sustrato metálico. La conductividad térmica del material
que constituye la capa dieléctrica será de vital importancia a la hora de disipar el calor
generado. El sistema más utilizado como capa dieléctrica para IMS es una matriz de resina
epoxi con un agente reticulante y un relleno (filler). Dado que la conductividad térmica de la
resina epoxi es baja, es fundamental utilizar un relleno con alta conductividad térmica que
permita una eficiente disipación del calor generado. Por tanto, en esta tesis se estudia la
preparación de muestras a base de resinas epoxi con cargas de nitruro de boro (BN). Se
analiza el efecto del tamaño de partícula de BN, el efecto del reticulante utilizado, la cinética
de curado, la forma de las partículas de BN, la aplicación de presión sobre el material
durante el proceso de curado y el papel de la densificación. Se encuentra que la
conductividad térmica de los compuestos epoxi-BN aumenta con el aumento del tamaño de
partícula de BN para un contenido dado de relleno, y que los aglomerados de BN
proporcionan una conductividad térmica más alta en comparación con los platillos (platelets)
del mismo tamaño, lo que se atribuye a que hay menos interfaces con la matriz epoxi para
los aglomerados. El sistema epoxi-tiol proporciona una conductividad térmica más alta que
el sistema epoxi-Jeffamine, que se atribuye a una interacción ácido-base de Lewis. En los
experimentos de cinética de curado, se observó que la reacción de curado de los
compuestos de epoxi-tiol se retrasó al aumentar el contenido de BN para todas las
partículas (platillos o aglomerados). Para el sistema epoxi-Jeffamine, se observó que la
reacción de curado es independiente del contenido de partículas BN, que también se
correlaciona con las medidas de conductividad térmica. El calor de reacción (ΔHee) y la
temperatura de transición vítrea del sistema completamente curado, Tgꝏ, son
independientes del contenido, tamaño y forma de partículas de BN tanto para el epoxi-tiol
como para la epoxi-Jeffamina. Por otro lado, la conductividad térmica aumenta aplicando
presión para los sistemas epoxi-tiol y epoxi-Jeffamine en comparación con los compuestos
curados a presión atmosférica; remarcar que la mejora del sistema epoxi-Jeffamine resulta
mayor. Se hace evidente que los mecanismos de mejora de la conductividad térmica mediante la aplicación de presión para cada sistema son diferentes. Y finalmente, se
demuestra que la densificación es una forma de incrementar la conductividad térmica; que
también se muestra como un efecto reversible.<br>Polímers i biopolímers
48
Zhang, Xinxin. "Métrologie thermique par méthode quasi-stationnaire : modélisation, identification et application a la caractérisation de solides." Vandoeuvre-les-Nancy, INPL, 1993. http://www.theses.fr/1993INPL037N.
Full textAbstract:
Nous développons une méthode en régime quasi stationnaire pour déterminer les propriétés thermiques de matériaux solides en utilisant une technique d'estimation de paramètres. La démarche systématique utilisée consiste à modéliser l'expérience par la méthode des quadripôles thermiques. On choisit le modèle d'estimation par comparaison entre divers modèles obtenus. Les bons paramètres à identifier ainsi que le bon intervalle sur lequel ces paramètres seront estimés sont mis en évidence par une analyse de sensibilité et une analyse asymptotique. La sonde plane fait intervenir un seul paramètre caractéristique du milieu, (c)#1#/#2, qui est sensible et donc facile à estimer. La sonde cylindrique fait intervenir deux paramètres: et a/r#2. Dans ce cas, l'étude de sensibilité montre que seul λ est identifiable. La sonde sphérique fait apparaitre deux grandeurs indépendantes (λ, α) dans trois groupements: a, a/r#2 et 1/4 r. Le paramètre caractéristique du milieu a apparait au deuxième ordre du développement asymptotic. C'est une difficulté pour l'identification. Une étude expérimentale portant sur les matériaux céramiques pour les sondes plane et cylindrique et sur un lit de billes de verre pour la sonde sphérique, a validé notre méthode et a confirmé les prédictions théoriques
49
Festin, Örjan. "On the Zero and Low Field Vortex Dynamics : An Experimental Study of Type-II Superconductors." Doctoral thesis, Uppsala University, Department of Engineering Sciences, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3907.
Full textAbstract:
<p>Dynamic properties of type-II superconductors have been experimentally studied in zero and low magnetic fields using SQUID magnetometry and <i>I–V</i> measurements.</p><p>In zero magnetic field close to the critical temperature, the physical properties of type-II superconductors are dominated by spontaneously created vortices. In three dimensions (3D) such vortices take the form of vortex loops and in two dimensions (2D) as vortex-antivortex pairs.</p><p>The 2D vortex dynamics has been probed using mutual inductance and flux noise measurements on YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub> (YBCO) and MgB<sub>2</sub> thin films in zero and low magnetic fields. In such measurements, information about vortex correlations is obtained through a temperature dependent characteristic frequency, below (above) which the vortex movements are uncorrelated (correlated). The results obtained in zero magnetic field indicate that sample heterogeneities influence the vortex physics and hinder the divergence of the vortex-antivortex correlation length.</p><p>In low magnetic fields the vortex dynamics is strongly dependent on the applied magnetic field and a power law dependence of the characteristic frequency with respect to the magnetic field is observed. The results indicate that there is a co-existence of thermally and field generated vortices.</p><p>The <i>I–V</i> characteristics of untwinned YBCO single crystals show that only a small broadening of the transition region influences the length scale over which the vortex movements are correlated. The dynamic and static critical exponents therefore exhibit values being larger in magnitude as compared to values predicted by relevant theoretical models. The results also suggest that the copper oxide planes in YBCO decouple slightly below the mean field critical temperature and hence, the system has a crossover from 3D to 2D behaviour as the temperature is increased. </p><p>From temperature dependent DC-magnetisation measurements performed on untwinned YBCO single crystals in weak applied fields, detailed information about the critical current density and the irreversibility line is obtained.</p>
50
Newby, Pascal. "Fabrication de semiconducteurs poreux pour améliorer l'isolation thermique des MEMS." Thesis, Lyon, INSA, 2013. http://www.theses.fr/2013ISAL0154/document.
Full textAbstract:
L'isolation thermique est essentielle dans de nombreux types de MEMS (micro-systèmes électro-mécaniques). Selon le type de dispositif, l'isolation permet de réduire la consommation d'énergie, diminuer le temps de réponse, ou augmenter sa sensibilité. Les matériaux d'isolation thermique actuellement disponibles sont difficiles à intégrer en couche épaisse dans des dispositifs en silicium. À cause de cela, l'approche la plus utilisée pour l'isolation est d'intégrer les zones à isoler sur des membranes minces (~ 1 µm). Cela assure une bonne isolation, mais est restrictif pour la conception du dispositif et la fragilité des membranes complique la fabrication et l'utilisation de celui-ci. Le silicium poreux est facile à intégrer puisqu'il est fabriqué par gravure électrochimique de substrats de Si cristallin. On peut aisément fabriquer des couches épaisses (100 µm) et sa conductivité thermique est 2-3 ordres de grandeur plus faible que celle du Si massif. Par contre sa porosité cause des problèmes : mauvaise résistance chimique, structure instable au-delà de 400°C, et tenue mécanique réduite. La facilité d'intégration des semiconducteurs poreux est un atout majeur, et nous visons donc de réduire les désavantages de ces matériaux afin de favoriser leur intégration dans des dispositifs en silicium. La première approche qui a été développée consiste à amorphiser le Si poreux en l'irradiant avec des ions à haute énergie (uranium, 110 MeV). Nous avons montré que l'amorphisation, même partielle, du Si poreux entraîne une diminution de sa conductivité thermique, sans endommager sa structure poreuse. On peut atteindre ainsi une réduction de conductivité thermique jusqu’à un facteur de trois. La seconde approche est de développer un nouveau matériau. Le SiC poreux a été choisi, puisque le SiC massif a des propriétés physiques exceptionnelles et supérieures à celles du silicium. Nous avons mené une étude systématique de la porosification du SiC en fonction de la concentration en HF et le courant, ce qui nous a permis de fabriquer des couches poreuses uniformes d’une épaisseur d’environ 100 µm. Nous avons implémenté un banc de mesure de la conductivité thermique par la méthode « 3 oméga » et l'avons utilisé pour mesurer la conductivité thermique du SiC poreux. Nos résultats montrent que la conductivité thermique du SiC poreux est environ deux ordres de grandeur plus faible que celle du SiC massif. Nous avons aussi montré que le SiC poreux est résistant à tous les produits chimiques typiquement utilisés en microfabrication et est stable jusqu'à au moins 1000°C<br>Thermal insulation is essential in several types of MEMS (Micro electro mechanical systems). Depending on the device, insulation can reduce the device’s power consumption, decrease its response time, or increase its sensitivity. Existing thermal insulation materials are difficult to integrate as thick layers in silicon-based devices. Because of this, the most commonly used approach is to integrate the areas requiring insulation on thin membranes. This provides effective insulation, but restricts the design of the device and the membrane’s fragility makes the device’s fabrication and use more complicated. Poreux silicon is easy to integrate as it is made by electrochemical etching of crystalline silicon substrates. 100 µm thick layers can easily be fabricated and its thermal conductivity is 2-3 orders of magnitude lower than that of bulk silicon. However, its porosity causes other problems : low chemical resistance, its structure is unstable above 400°C, and reduced mechanical stability. The ease of integration of porous semiconductors remains a major advantage, so we aim to reduce the disadvantages of these materials in order to help their integration in microfabricated devices. The first approach we developed was to amorphise porous Si by irradiating it with heavy ions. We have shown that amorphisation of porous Si, even partial, causes a reduction of its thermal conductivity without damaging its porous structure. In this way a reduction in thermal conductivity by up to a factor of three can be achieved. The second approach was to develop a new material. Porous SiC was chosen, as bulk SiC has exceptional physical properties which are superior to those of silicon. We carried out a systematic study of the porosification process of SiC versus HF concentration and current, which enabled us to make thick (100 µm) and uniform layers. We have implemented a system for measuring thermal conductivity using the “3 omega” technique and used it to measure the thermal conductivity of porous SiC. Our results show that the thermal conductivity of porous SiC is about two orders of magnitude lower than that of bulk SiC. We have also shown that porous SiC is resistant to all chemical commonly used in microfabrication, and is stable up to at least 1000°C