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1
Dougherty, Brian P. "An automated probe for thermal conductivity measurements." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/101183.
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A transient technique was validated for making thermal conductivity measurements. The technique incorporated a small, effectively spherical, heat source and temperature sensing probe. The actual thermal conductivity measurements lasted 30 seconds. After approximately 15 minutes of data reduction, a value for thermal conductivity was obtained. The probe yielded local thermal conductivity measurements. Spherical sample volumes less than 8 cm² were required for the materials tested. Thermal conductivity (and moisture) distributions can be measured for relatively dry or wetted samples.
The technique employs an encapsulated bead thermistor. A thermistor, more commonly used as a temperature transducer, has the inherent feature of being readily self-heated. A computer-based data acquisition and control system regulates the power supplied to the thermistor such that its self-heated temperature response approximates a step change. Thermal conductivity is deduced from the transient measurement of the power dissipated by the probe as a function of time.
The technique was used to measure the thermal conductivity of fifteen liquids and five insulation materials. Two different thermistor types, glass-encapsulated and Teflon-encapsulated, were evaluated. Capabilities and limitations of each probe type and the measurement technique, in general, were observed.M.S.
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Mathis, Nancy Elaine. "Measurements of thermal conductivity anisotropy in polymer materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ62173.pdf.
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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.
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Madrid, Lozano Francesc. "Thermal Conductivity and Specific Heat Measurements for Power Electronics Packaging Materials. Effective Thermal Conductivity Steady State and Transient Thermal Parameter Identification Methods." Doctoral thesis, Universitat Autònoma de Barcelona, 2005. http://hdl.handle.net/10803/5348.
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Martin, Ana Isabel. "Hydrate Bearing Sediments-Thermal Conductivity." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6844.
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The thermal properties of hydrate bearing sediments remain poorly studied, in part due to measurement difficulties inside the hydrate stability envelope. In particular, there is a dearth of experimental data on hydrate-bearing sediments, and most available measurements and models correspond to bulk gas hydrates. However, hydrates in nature largely occur in porous media, e.g. sand, silt and clay.
The purpose of this research is to determine the thermal properties of hydrate-bearing sediments under laboratory conditions, for a wide range of soils from coarse-grained sand to fine-grained silica flour and kaolinite. The thermal conductivity is measured before and after hydrate formation, at effective confining stress in the range from 0.03 MPa to 1 MPa. Results show the complex interplay between soil grain size, effective confinement and the amount of the pore space filled with hydrate on the thermal conductivity of hydrate-bearing sediments.
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Kalkundri, Kaustubh. "Development and verification of an apparatus for thermal resistance and thermal conductivity measurements." Diss., Online access via UMI:, 2006.
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Tsai, Andy 1969. "Investigation of variability in skin tissue intrinsic thermal conductivity measurements." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36036.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1995.Vita.
Includes bibliographical references (leaves 75-76).
by Andy Tsai.
M.S.
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Shaikh, Samina. "Effective thermal conductivity measurements relevant to deep borehole nuclear waste disposal." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/41301.
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Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007.Includes bibliographical references (leaves 106-107).
The objective of this work was to measure the effective thermal conductivity of a number of materials (particle beds, and fluids) proposed for use in and around canisters for disposal of high level nuclear waste in deep boreholes. This information is required to insure that waste temperatures will not exceed tolerable limits. Such experimental verification is essential because analytical models and empirical correlations can not accurately predict effective thermal conductivities for complex configurations of poorly characterized media, such as beds of irregular particles of mixed sizes. The experimental apparatus consisted of a 2.54 cm. diameter cylindrical heater (heated length = 0.5 m) , surrounded by a 5.0 cm inner diameter steel tube. Six pairs of thermocouples were located axially on the inside of the heater sheath, and in grooves on the air-fan-cooled outer tube. Test media were used to fill the annular gap, and the temperature drop across the gap measured at several power levels covering the range of heat fluxes expected on a waste canister soon after emplacement. Values of effective thermal conductivity were measured for air, water; particle beds of sand, SiC, graphite and aluminum; and an air gap subdivided by a thin metal sleeve insert. Results are compared to literature values and analytical models for conduction, convection and radiation. Agreement within a factor of 2 was common, and the results confirm the adequacy, and reduce the uncertainty of prior borehole system design calculations. All particle bed data fell between 0.3 and 0.5 W/moC, hence other attributes can determine usage.
by Samina Shaikh.
S.M.and S.B.
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Ma, Luyao. "Optimization of experimental conditions of hot wire method in thermal conductivity measurements." Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93765.
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This work studied the hot wire method in measuring thermal conductivity at room temperature. The purpose is to find the optimized experimental conditions to minimize natural convection in liquid for this method, which will be taken as reference for high temperature thermal conductivity measurement of slag. Combining room temperature experiments and simulation with COMSOL Multiphysics 4.2a, the study on different experimental parameters which may influence the accuracy of the measured thermal conductivity was conducted. The parameters studied were the diameter of crucible, the position of wire in the liquid, including z direction and x-y plane position, diameter of the hot wire, and current used in the measurement. In COMSOL simulations, the maximum natural convection velocity value was used to evaluate the natural convection in the liquid. The experiment results showed after 4~5 seconds of the measuring process, the natural convection already happened. Also when current was fixed, the thinner the hot wire, the larger convection it would cause. This is because thinner wire generates more heat per unit surface area. Using higher current in measuring, more heat generation improved accuracy of result but also had earlier and larger effect on convection. Both simulation and experiments showed that with the height of the liquid fixed, the smaller diameter of the crucible (not small to the level which is comparable with hot wire diameter), the higher the position in z direction (still covered by liquid), the less natural convection effect existed. But the difference was not significant. The radius-direction position change didn’t influence the result much as long as the wire was not too close to the wall.
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Arnold, David Feversham. "Thermal conductivity measurements of semi-crystalline silica using a modified comparative method." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ39631.pdf.
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Bogner, Manuel. "Thermal conductivity measurements of thin films using a novel 3 omega method." Thesis, Northumbria University, 2017. http://nrl.northumbria.ac.uk/36186/.
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For most micro- and nanoelectronic devices based on thin films applied for effective heat dissipation and thermoelectric devices for energy harvesting, thermal management is a critical subject for their device performance and reliability. This thesis focuses on the investigation of the cross- and in-plane thermal conductivities of both high- and low-thermal conductive thin film materials. Aluminum nitride (AlN), with its high thermal conductivity, has been studied, as it is a promising candidate for effective heat conductors in microelectronic devices. Copper iodide (CuI) has also been investigated in this thesis, because of its great interest in novel energy harvesting applications with low thermal conductivity and outstanding thermoelectric properties. Thermal conductivities of thin films tend to be substantially different from those of their bulk counterparts, which is generally caused by oxygen impurities, dislocations, and grain boundary scattering, all of which can reduce the thermal conductivity of the films. These effects also influence cross- and in-plane heat conduction differently, so that the thermal conductivities of the thin films are generally anisotropic in these two directions. Therefore, experimental work and theoretical analysis have been conducted to understand the effects of crystallinity, grain sizes, and interfacial structures of AlN and CuI films on their thermal conductivities as a function of film thickness. An improved differential multi-heater 3ω method was established and used to study the thickness-dependency of cross- and in-plane thermal conductivities of CuI and AlN thin films sputtered on p-type doped silicon substrates with film thicknesses varied between 70 - 400 nm and 100 – 1000 nm, respectively. Furthermore, our newly proposed 3ω Microscopy method, which combines the advantages of both the conventional 3ω method and atomic force microscopy (AFM) technology, was applied to quantitatively measure the local thermal conductivities of CuI and AlN thin films, with a spatial resolution in sub-micrometer range. Results revealed that both the cross- and in-plane thermal conductivities of the CuI and AlN thin films were significantly smaller than those of their bulk counterparts. The cross- and in-plane thermal conductivities were strongly dependent on the film thickness. Both the X-ray diffraction and 3ω Microscopy results indicated that the grain size of thin films significantly affected their thermal conductivity due to the scattering effects from the grain boundaries. Finally, the 3ω Microscopy has been proven to provide additional experimental findings, which cannot be identified or detected using conventional thermal characterization methods such as the standard 3ω technique. Its good spatially-resolved resolution for quantitative local thermal characterization, its nondestructive characteristic and without a need for sample preparation, make the 3ω Microscopy a promising thermal characterization method.
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Cho, Chun Hyung. "Heat transfer in nuclear fuels : measurements of gap conductance /." free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p3144408.
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deMartin, Brian J. "Laboratory measurements of the thermal conductivity and thermal diffusivity of methane hydrate at simulated in situ conditions." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/26216.
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Vieyra, Villegas Hugo Abdiel. "Resistivity and thermal conductivity measurements on heavy-fermion superconductors in rotating magnetic fields." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-107550.
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CeCu_2Si_2 was the first heavy-fermion compound showing signatures of bulk superconductivity (T_c = 0.5 K). Further observations have put in evidence the correlations between superconductivity, magnetic order, Kondo physics, and quantum critical phenomena. In spite of the interest generated, a systematic study of such correlations was hampered by strong sample dependences. Fortunately, the inherent complexity associated to the stoichiometric composition has been recently understood. The availability of single-crystals with well-defined properties has thus reignited the interest in CeCu_2Si_2 as a window to novel phenomena, such as unconventional superconductivity.
The present work summarizes the results of my doctoral research. It exemplifies the importance not only of high-quality materials, but also of suitable experimental techniques. A first step in this project involved the design of angle-dependent techniques in the milli-kelvin range, namely: electrical resistivity and thermal conductivity. It comprised the development of a rotational stage, the construction of sample holders, and the implementation of controlling and measuring components. In the second part of the project, electrical- and thermal-transport measurements on CeCu_2Si_2 were performed. Power-law behavior below T_c in the thermal conductivity suggests the presence of lines of nodes in the gap function. Also, the non-vanishing extrapolated residual terms (k_00/T ) support the presence of a residual density of states. The nodes are broadened by potential scattering, which appears to be significant in CeCu_2Si_2. The scattering hinders the determination of the symmetry of the order parameter and might be responsible for the observed isotropic angle dependence of the thermal conductivity.
In contrast, angle-dependent measurements of the upper critical field exhibit a four-folded behavior, which also points towards the presence of nodes. By comparing with a weak-coupling model including the effects of Pauli limiting and anisotropic Fermi velocity, the results point towards a d_xy-wave symmetry of the order parameter. Such results represent the first angle-dependent measurements supporting a d-wave symmetry in CeCu_2Si_2.
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Alotaibi, Moteb. "Modeling and Evaluating the Thermal Conductivity of Porous Thermal Barrier Coatings at Elevated Temperatures for Industrial Applications." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39522.
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The thermal conductivity of various porous thermal barrier coating (TBC) systems used in elevated temperature for industrial applications has been evaluated using a proposed six-phase model. These porous TBC systems rely on microstructural properties and yield different types of porosity. These microstructural properties can influence the thermal conductivity of TBC systems. The purpose of this thesis is to assess the thermal conductivity of TBC systems based on microstructural attributes, particularly the effect of different types of porosity. Thus, the first component of this thesis investigates the microstructural characterization of various TBC systems using image analysis (IA) technique. In this technique, scanning electron microscopy (SEM) and light optical microscopy (LOM) micrographs were used to measure the porosity level of different TBC materials. The volumetric fraction of porosity along with orientation, shape, and morphology have a considerable impact on the total thermal conductivity of TBCs.
The second component of this thesis evaluates the thermal conductivity of these porous TBC systems by taking into account the effect of the heat treatment process. The IA results reveal that as long as the porosity content increases, the thermal conductivity decreases for all of the TBC materials studied in this thesis. Further, while the content of microcracks and non-flat porosity play a crucial role in reducing the thermal conductivity of TBC materials, the other types of porosity (open randomly oriented, penny-shaped, and interlamellar) exert less impact on the thermal conductivity of TBCs. Comparing the results of the proposed six-phase model to experimental values and finite element analysis (FEA) values showed a relatively good agreement.
The proposed six-phase model can predict the thermal conductivity of porous microstructure of TBC systems close to real measured values; therefore, the proposed six-phase model may be utilized to fabricate the porous microstructure of TBCs.
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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.
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Stöhr, Adriana. "Thermal textile pixels : Out-of-plane and in-plane heat transfer measurements of knitted textiles." Thesis, Högskolan i Borås, Akademin för textil, teknik och ekonomi, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-22178.
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The human body possesses a highly developed range of senses that help orienting oneself in everyday life. Especially when it comes to navigating, perceiving and reacting to the world around us, people tend to rely mostly on their vision and hearing. Suffering from an impairment of either one, or both of the predominating senses means having to counterbalance this constraint. People suffering from blindness and deaf-blindness compensate their impairment mainly by relying on their haptic perception. In this case, information is usually communicated by braille or vibrotactile means. To offer another non-visual and non-audial communication concept this thesis work introduces, the thermal textile pixels. A thermal textile pixel consists of an external thermal device, able to generate hot and cold thermal impulses, and a textile interface to transmit the signal. In order to design such thermal textile pixel it was crucial to be aware of the thermal transfer occurring through and within an textile. Numerous research studies have examined the thermal properties of textiles, especially in the context of clothing comfort, thermal comfort. Nevertheless, it should be considered that as a thermal textile pixel, the textile forms part of a system, governed by many parameters. Therefore, for designing such a device it is important to be aware of the temporal and spatial resolution of the thermal transmitted signal. These characteristics are influenced by multiple textile parameters. For this purpose, a thermal study has been performed investigating in- and out-of-plane signal transmission by textiles in combination with an external thermal device. Using an external thermal device such as a Peltier element allowed to expose the specimens to heating as well as to active cooling. Different knitted structures and material combinations have been examined to gain a first impression on the behaviour of thermal pixels. It was found that thickness and density were the most influential factors for out-of-plane heat transfer. In-plane was found influenced mainly by fibre conductivity. An anisotropic behaviour was noted in-plane, as well as between in- and out-of-plane for heat transfer. Investigating active cooling signals, it was found that a significant decline of performance was noted for all specimens. Plain PA was found to be most suitable for the transmission of heat signals. But did not perform equally well during active cooling phases. Plain Shieldex was observed to perform most steady during heating and active cooling.
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Vieyra, Villegas Hugo Abdiel [Verfasser], Frank [Akademischer Betreuer] Steglich, and Joachim [Akademischer Betreuer] Wosnitza. "Resistivity and thermal conductivity measurements on heavy-fermion superconductors in rotating magnetic fields / Hugo Abdiel Vieyra Villegas. Gutachter: Frank Steglich ; Joachim Wosnitza. Betreuer: Frank Steglich." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://d-nb.info/1068151706/34.
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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.
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Cherief, Wahid. "Etude des ferrofluides et de leurs applications à l'intensification des transferts de chaleur par convection forcée." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAT102/document.
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Cette thèse a pour objectif d’étudier les performances thermiques et rhéologiques des ferrofluides sous champ magnétique pour des applications de refroidissement. L’approche adoptée dans cette thèse est de nature macroscopique, et est basée sur plusieurs études expérimentales. Cette caractérisation des performances des ferrofluides est focalisée sur trois aspects : i) étude de la rhéologie ii) étude de la convection forcée iii) étude la conductivité thermique. Différents outils de caractérisation correspondant à chaque domaine d’étude ont été développés. Dans le domaine de la rhéologie, une cellule magnétique a été construite et adaptée à un rhéomètre afin d’étudier le comportement rhéologique du ferrofluide sous un champ magnétique allant jusqu’à 0,8 T. Cette démarche met en évidence l’influence du champ magnétique et de son intensité sur les forces de cisaillement. Dans le domaine des transferts de chaleur, une boucle thermohydraulique pour l’étude de l’échange de chaleur en convection forcée avec une paroi à flux imposée sous champ magnétique a été mise au point. Ce type de dispositif permet l’étude de plusieurs paramètres liés à la configuration spatiale du champ magnétique appliqué, à l’effet de l’uniformité du champ sur l’intensification des échanges de chaleur. La compréhension et l’analyse de ces résultats sont consolidées par l’étude de la conductivité thermique du ferrofluide sous champ magnétique. Un banc a été mis en place et a permis de mettre en évidence l’influence de la température ainsi que de l’intensité du champ magnétique sur cette grandeur. Á l’issue de ces caractérisations, l’application des ferrofluides pour le refroidissement de composants électroniques de puissance est discutée par une mise en œuvre expérimentale. Ces essais ouvrent la voie pour de nouvelles recherches et permettent de mener des réflexions relatives aux domaines d’application des ferrofluidesThis thesis aims to study the thermal and rheological performances of ferrofluids under magnetic field for an application in cooling systems. The approach consists on macroscopic analysis based on experimental studies. Our approach is focused on three aspects: i) rheology ii) internal forced convection iii) thermal conductivity. We developed different characterization benches. For rheological studies, a magnetic circuit is developed and integrated into rheometer to create magnetic fields reaching 0,8 T. This approach demonstrates the influence of magnetic flux density on the shear forces. Concerning heat transfers, we carried out experimental tests based on the use of a closed loop flow system to study forced convection of ferrofluids with imposed wall flux under magnetic field. This test bench allows us to understand the impact of several parameters related to the configuration of the applied magnetic field on the enhancement of convective heat transfers. To analyze why convective heat transfers are better under magnetic field, we carried out a system for measuring the thermal conductivity. This bench tests allows us to show the effect of temperature and magnetic flux density on this physical property. All these tests are paving the way for new research activities and to the ferrofluids applications in cooling systems
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Jensen, Colby. "TRISO Fuel Thermal Conductivity Measurement Instrument Development." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/838.
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Thermal conductivity is an important thermophysical property needed for effectively predicting fuel performance. As part of the Next Generation Nuclear Plant (NGNP) program, the thermal conductivity of tri-isotropic (TRISO) fuel needs to be measured over a temperature range characteristic of its usage. The composite nature of TRISO fuel requires that measurement be performed over the entire length of the compact in a non-destructive manner. No existing measurement system is capable of performing such a measurement. A measurement system has been designed based on the steady-state, guarded-comparative-longitudinal heat flow technique. The system as currently designed is capable of measuring cylindrical samples with diameters ~12.3-mm (~0.5″) with lengths ~25-mm (~1″). The system is currently operable in a temperature range of 400 K to 1100 K for materials with thermal conductivities on the order of 10 W/m/K to 70 W/m/K. The system has been designed, built, and tested. An uncertainty analysis for the determinate errors of the system has been performed finding a result of 5.5%. Finite element modeling of the system measurement method has also been accomplished demonstrating optimal design, operating conditions, and associated bias error. Measurements have been performed on three calibration/validation materials: SS304, 99.95% pure iron, and inconel 625. In addition, NGNP graphite with ZrO2 particles and NGNP AGR-2 graphite matrix only, both in compact form, have been measured. Results from the SS304 sample show agreement of better than 3% for a 300–600°C temperature range. For iron between 100–600°C, the difference with published values is < 8% for all temperatures. The maximum difference from published data for inconel 625 is 5.8%, near 600°C. Both NGNP samples were measured from 100–800°C. All results are presented and discussed. Finally, a discussion of ongoing work is included as well as a brief discussion of implementation under other operating conditions, including higher temperatures and adaptation for use in a glovebox or hot cell.
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Hua, Zilong. "Hybrid Photothermal Technique for Microscale Thermal Conductivity Measurement." DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/1491.
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Most existing thermal conductivity measurement techniques of nuclear fuel only measure the overall effective thermal conductivity of the fuel, cladding, and gap, with low spatial-resolution. However, damage to nuclear fuel microstructure caused by neutron-irradiation can result in sharp, local changes of thermal conductivity. Additionally, extremely large temperature-gradients (~1600 K/cm) from the fuel centerline to the coolant result in similar gradients of thermal conductivity. Therefore, in pursuit of greater understanding of nuclear fuel performance, the objective of this study was to develop a non-contact thermal conductivity measurement technique to provide micron-sized spatial-resolution capability. Based on photothermal techniques and using both frequency and spatial-domain photothermal reflectance methods, an experimental measurement system was designed, built, and tested for measuring the thermal conductivity of a thin-film coated material with micron resolution. This hybrid method involves separate measurement of thermal diffusivity, D, and thermal effusivity, e, from which, thermal conductivity, k = (e2/D)1/2 is calculated. A detailed parametric analysis using analytical solutions and a numerical model has been performed to guide the experiment and optimize measurement conditions. The measurement system was validated using two calibration samples having thermal conductivities at both the upper and lower limit of the common range of nuclear fuels (~1 - 10 W/m/K). Sources of experimental errors are discussed qualitatively and the uncertainty of the measurement system for the thermal conductivity range of interest is quantified. The measured error is found to be about 10%, and up to close to 20% for the worst case (upper limit of k range). An extended application of the modulated laser excitation technique is explored to measure mechanical properties of solid materials. This technique involves obtaining the natural frequencies of different vibrational modes of a cantilever beam sample allowing for the extraction of the elasticity constants of the material. From Neumann's principle, the number of independent elasticity constants is dependent on the symmetry of the material structure. Specifically, symmetries of crystalline materials and composite materials are analyzed. Experimental results of two validation samples with cubic crystal system agreed well with the published values with experimental errors of ~10%.
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Nocentini, Kévin. "Comportement thermo-hygrique de blankets aérogels de silice et applications à l’isolation des bâtiments." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEM049/document.
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En Europe, le secteur du bâtiment est le plus énergivore et représente environ 40 % de l’énergie totale consommée. A court terme, la façon la plus efficace de baisser cette consommation est de réduire les déperditions thermiques à travers l’enveloppe du bâtiment en augmentant son isolation thermique, tout en minimisant la perte de surface habitable. Dans ce contexte, les travaux de thèse portent sur l’étude et la mise au point pour pré-industrialisation de matériaux super-isolants composites à base d'aérogel de silice. Le matériau composite étudié fait partie de la famille des blankets aérogels et est obtenu via un procédé de séchage ambiant innovant. Grâce à leur faible conductivité thermique et leurs propriétés mécaniques renforcées, les blankets aérogels sont d’un grand intérêt pour l’isolation thermique qui nécessite de fines épaisseurs d’isolants. Les travaux de thèse visent dans un premier temps à effectuer une analyse des propriétés thermophysiques des blankets aérogels étudiés à la sortie du moule de fabrication et vis-à-vis de leur mise en œuvre lorsqu’ils sont soumis à différentes sollicitations (mécaniques, hygriques ...). Des travaux de modélisation du transfert de chaleur dans le blanket aérogel sont développés afin d’étudier les relations entre le transfert thermique et les paramètres morphologiques du matériau. Dans un second temps, les travaux de thèse portent sur l’étude des performances à attendre d’un système d’isolation basé sur le blanket aérogel mis en œuvre sur un bâtiment, à la fois par l’analyse du comportement thermique d’une cellule test en climat réel, ainsi que par la conduite de simulations numériques de bâtiments prenant en compte plusieurs techniques constructives, configurations de murs, et ce, pour plusieurs climats européens. Les résultats obtenus montrent que les blankets aérogels étudiés ont une très faible conductivité thermique –0,016 W.m-1.K-1– et ont un fort potentiel d’application dans l’isolation thermique du bâtimentBuildings are the largest energy end-use sector and account for about 40 % of the total final energy consumption in the EU-28. A short-term strategy to efficiently reduce this consumption is to decrease thermal losses through the building envelope by improving its thermal insulation, while minimizing the reduction of the available indoor living space. In this context, the thesis deals with the study and development for pre-industrialization of super-insulating composite materials based on silica aerogel. The studied material is part of the aerogel blanket family and is obtained by an innovative ambient drying process. With a very low thermal conductivity and reinforced mechanical properties, aerogel blankets are of great interest for applications where they can offer a cost advantage due to a space-saving effect. Firstly, the thesis work aims at performing analyses of the thermo-physical properties of the studied aerogel blankets at the exit of the molding and drying processes, and during application, when they are subjected to different environmental stresses (mechanical, hygric …). Heat transfer modeling is developed to study the relationship between the morphological parameters of the material and thermal transfer within it. Secondly, the thesis work focuses on the study of the expected performances of an insulating system based on the aerogel blanket, by the study of the thermal behavior of an experimental building monitored under actual climate, as well as the use of whole building energy numerical simulations taking into account several constructive techniques, different wall configurations, for various European climates. The results obtained show that the aerogel blankets studied have a thermal conductivity as low as 0.016 W.m-1.K-1 and have promising applications for building thermal insulation needs
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Faghani, Farshad. "Thermal conductivity Measurement of PEDOT:PSS by 3-omega Technique." Thesis, Linköpings universitet, Fysik och elektroteknik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-63317.
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Conducting polymers (CP) have received great attention in both academic and industrial areas in recent years. They exhibit unique characteristics (electrical conductivity, solution processability, light weight and flexibility) which make them promising candidates for being used in many electronic applications. Recently, there is a renewed interest to consider those materials for thermoelectric generators that is for energy harvesting purposes. Therefore, it is of great importance to have in depth understanding of their thermal and electrical characteristics. In this diploma work, the thermal conductivity of PEDOT:PSS is investigated by applying 3-omega technique which is accounted for a transient method of measuring thermal conductivity and specific heat. To validate the measurement setup, two benchmark substrates with known properties are explored and the results for thermal conductivity are nicely in agreement with their actual values with a reasonable error percentage. All measurements are carried out inside a Cryogenic probe station with vacuum condition. Then a bulk scale of PEDOT:PSS with sufficient thickness is made and investigated. Although, it is a great challenge to make a thick layer of this polymer since it needs to be both solid state and has as smooth surface as possible for further gold deposition. The results display a thermal conductivity range between 0.20 and 0.25 (W.m-1.K-1) at room temperature which is a nice approximation of what has been reported so far. The discrepancy is mainly due to some uncertainty about the exact value of temperature coefficient of resistance (TCR) of the heater and also heat losses especially in case of heaters with larger surface area. Moreover, thermal conductivity of PEDOT:PSS is studied over a wide temperature band ranging from 223 - 373 K.
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Fox, Brandon S. "In-Pile Thermal Conductivity Measurement Methods for Nuclear Fuels." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/660.
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Measuring nuclear fuel thermal conductivity in-pile can provide much needed data for understanding fuel performance during irradiation and yield thermophysical property data needed for simulation codes and fuel databases. The objective of this research is to develop and compare two in-pile thermal conductivity methods in a laboratory setting using surrogate fuel materials.
A steady-state radial heat flow method was investigated to understand its viability as an in-pile steady-state thermal conductivity technique. By using Joule heating to simulate volumetric heat generation within a surrogate fuel rod, thermal conductivity was measured with two thermocouples at different radial positions within the rod. Examinations were completed on two batches of surrogate materials over the temperature range of 500 to 700 °C. The selected surrogate rod was fabricated from the only material identified to possess the required thermal conductivity and electrical resistivity required for the selected laboratory approach. Evaluations estimated a measurement uncertainty of 12% and values were within 33% of values obtained using laboratory material property measurement systems for this surrogate material. Results indicate that the selected surrogate rod material limited the ability to assess this approach at higher temperatures in a laboratory setting.
A transient needle probe method adapted from American Standard Test Method standards was also used to measure temperature-dependent thermal conductivity of surrogate fuel rod materials for temperatures ranging from room temperature to 400 °C. The needle probe has a heating element and a temperature sensor contained in a metal sheath, and it is inserted into the surrogate fuel rod whose thermal conductivity is to be measured. The thermal conductivity is calculated from the power applied to the heating element, and the temperature rise detected in the sample. Needle probes were designed and fabricated using materials recommended for in-pile application. Scoping room-temperature values obtained using the needle probe method were within acceptable accuracies defined by the ASTM needle probe reference standard. Temperature-dependent values were within 2% of values for the well-characterized ASTM recommended reference material, fused silica. A measurement uncertainty under 6% was calculated for the needle probe method.
As a result of this study, the needle probe method was selected for additional testing at the Idaho National Laboratory for anticipated testing in Materials Test Reactors. This would result in the first-ever transient in-pile thermal conductivity sensor.
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Radhakrishnan, Arjun. "Thermal conductivity measurement of gas diffusion layer used in PEMFC /." Online version of thesis, 2009. http://hdl.handle.net/1850/10839.
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Kwiecinski, Przemyslaw Mark. "Non contact all optical thermal conductivity measurement utilizing Raman spectroscopy." Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/27260.
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Original experimental data for the temperature dependence of the Raman shift in silicon and gallium sulfide is presented. An all optical thermal conductivity method, using an equation presented by Perichon et a1.2 and Nonnenmacher et al. 23, is applied to silicon and gallium sulfide. Theoretical calculations by Moody et al.20 and Nissam et al. 22 are compared to the experimental results of Perichon et al. for the first time. The thermal conductivity of silicon is measured at 23°C, 200°C, and 300°C, and of gallium sulfide at 23°C. We investigate the possibility of measuring thermal conductivity at high pressures.
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Folsom, Charles P. "Effective Thermal Conductivity of Tri-Isotropic (TRISO) Fuel Compacts." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1448.
Full textAbstract:
Thermal conductivity is an important thermophysical property needed for effectively predicting nuclear fuel performance. As part of the Next Generation Nuclear Plant (NGNP) program, the thermal conductivity of tri-isotropic (TRISO) fuel needs to be measured over a temperature range characteristic of its usage. The composite nature of TRISO fuel requires that measurement be performed over the entire length of the compact in a non-destructive manner. No existing measurement system is capable of performing such a measurement.
A measurement system has been designed based on the steady-state, guarded comparative-longitudinal heat flow technique. The system is capable of measuring cylindrical samples with diameters ∼12.3 mm (∼0.5 in.) with lengths ∼25 mm (∼1 in.). The system is currently operable in a temperature range of 100-700°C for materials with thermal conductivities on the order of 10-70 W*m-1*K-1. The system has been designed, built, and tested. An uncertainty analysis for the determinate errors of the system has been performed finding a result of 6%.
Measurements have been performed on three calibration/validation materials: a certified glass ceramic reference material, 99.95% pure iron, and Inconel 625. The deviation of the validation samples is < 6-8% from the literature values. In addition, surrogate NGNP compacts and NGNP graphite matrix-only compacts have been measured. The results give an estimation of the thermal conductivity values that can be expected. All the results are presented and discussed.
A Finite Element Analysis was done to compare the accuracy of multiple effective conductivity models. The study investigated the effects of packing structure, packing fraction, matrix thermal conductivity, and particle heat generation. The results show that the Maxwell and the Chiew & Glandt models provide the most accurate prediction of the effective thermal conductivity of the TRISO fuel compacts.
Finally, a discussion of ongoing work is included as well as the possibility of correlating effective thermal properties of fuel compacts to their constituents with measurements of well-defined samples.
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Chemminian, Rakhith. "Thermal Conductivity Measurement of Dry and Intermediate Moisture Porous Food Materials." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1394718856.
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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/.
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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.
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Rowan, Linda. "The measurement of the thermal conductivity of gaseous mixture using the transient hot wire technique." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252676.
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de, Koninck David Andrew. "Thermal conductivity measurement using the 3-omega technique: applications to power harvesting microsystems." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=22039.
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The optimal design of power generating microsystems requires accurate knowledge of the thermal properties of their constituent materials at the appropriate length scale. The goal of this thesis was to build an apparatus for measuring the thermal conductivity of thermally-insulating dielectric materials using the so-called 3-omega technique. This technique utilizes a microfabricated metal line deposited on the specimen to act as a resistive heater. When an alternating current (AC) voltage signal is used to excite the heater at a frequency ω, the periodic heating generates oscillations in the electrical resistance of the metal line at a frequency of 2ω. In turn, this leads to a third harmonic (3ω) in the voltage signal, which is used to infer the magnitude of the temperature oscillations. The frequency dependence of these oscillations can be analyzed to obtain the thermal properties of the specimen. The device consisted of a voltage source, a custom-built analog circuit and sample mount, a lock-in amplifier. The sample was placed within a vacuum chamber and evacuated using a made-to-order vacuum system. Personalised LabVIEW and MATLAB programs were created for autonomous data acquisition and analysis. The 3ω technique is simple, quick and accurate; tests using a standard fused quartz specimen (k = 1.38+/-0.04 W/m•K) yielded a measured thermal conductivity of 1.47+/-0.16 W/m•K. Subsequently, the technique was used to measure the thermal conductivity of Lead Zirconate Titanate (PZT-5A4E), which is a piezoelectric ceramic of interest for integration with microfabricated vibration energy harvesters. This material was found to exhibit a low thermal conductivity of 1.38+/-0.10 W/m•K.Le design optimal de microsystèmes pour la génération d'énergie demande une connaissance précise des propriétés thermiques des matériaux utilisés, à la bonne échelle. Le but de ce projet fut de créer un instrument pour mesurer la conductivité thermique des matériaux fonctionnels pour ces microsystèmes en utilisant la méthode 3-oméga. Cette méthode se sert d'une ligne métallique déposée en surface qui agit comme élément chauffant. Quand le filament métallique est alimenté par un courant alternatif (CA) à une fréquence ω, la puissance dissipée par effet Joule génère une oscillation sinusoïdale dans la résistance électrique à une fréquence 2ω. Cette résistance électrique sinusoïdale à son tour crée une harmonique de rang 3 (3ω) dans la tension électrique de l'élément chauffant. Cette harmonique est utilisée pour déduire l'amplitude des oscillations de température dans le spécimen. La variation de ces oscillations thermiques en fonction de la fréquence d'excitation nous permet d'obtenir la conductivité thermique de l'échantillon. L'instrument consiste d'une source de tension, un « lock-in amplifier », un circuit analogique et une monture à échantillon personnalisés. L'échantillon fut placé dans une chambre à vide et évacué à l'aide d'un système à vide fait sur mesure. Des programmes LabVIEW et MATLAB fut écrits pour réaliser l'acquisition et l'analyse de donnés automatisées. La méthode 3ω est facile à réaliser et donne des résultats précis : des tests avec des échantillons de quartz amorphe (k = 1.38+/-0.04 W/m•K) ont donné une conductivité thermique de 1.47+/-0.16 W/m•K. Le quartz amorphe fut utilisé comme référence pour valider l'instrument. Par la suite, l'appareil fut utilisé pour caractériser une céramique PZT (Titano-Zirconate de Plomb), un matériau piézoélectrique souvent utilisé dans la fabrication de microgénérateurs pour la récupération d'énergie vibratoire. Un
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Karami, Peyman. "Robust and Durable Vacuum Insulation Technology for Buildings." Doctoral thesis, KTH, Byggnadsteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176494.
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Today’s buildings are responsible for 40% of the world’s energy use and also a substantial share of the Global Warming Potential (GWP). In Sweden, about 21% of the energy use can be related to the heat losses through the climatic envelope. The “Million Program” (Swedish: Miljonprogrammet) is a common name for about one million housing units, erected between 1965 and 1974 and many of these buildings suffer from poor energy performance. An important aim of this study was to access the possibilities of using Vacuum Insulation Panels (VIPs) in buildings with emphasis on the use of VIPs for improving the thermal efficiency of the “Million Program” buildings. The VIPs have a thermal resistance of about 8-10 times better than conventional insulations and offer unique opportunities to reduce the thickness of the thermal insulation. This thesis is divided into three main subjects. The first subject aims to investigate new alternative VIP cores that may reduce the market price of VIPs. Three newly developed nanoporous silica were tested using different steady-state and transient methods. A new self-designed device, connected to a Transient Plane Source (TPS) instrument was used to determine the thermal conductivity of granular powders at different gaseous pressure combined with different mechanical loads. The conclusion was that the TPS technique is less suitable for conducting thermal conductivity measurements on low-density nanoporous silica powders. However, deviations in the results are minimal for densities above a limit at which the pure conduction becomes dominant compared to heat transfer by radiation. The second subject of this work was to propose a new and robust VIP mounting system, with minimized thermal bridges, for improving the thermal efficiency of the “Million Program” buildings. On the basis of the parametric analysis and dynamic simulations, a new VIP mounting system was proposed and evaluated through full scale measurements in a climatic chamber. The in situ measurements showed that the suggested new VIP technical solution, consisting of 20mm thick VIPs, can improve the thermal transmittance of the wall, up to a level of 56%. An improved thermal transmittance of the wall at centre-of-panel coordinate of 0.118 to 0.132 W m-2K-1 and a measured centre-of-panel thermal conductivity (λcentre-of-panel) of 7 mW m-1K-1 were reached. Furthermore, this thesis includes a new approach to measure the thermal bridge impacts due to the VIP joints and laminates, through conducting infrared thermography investigations. An effective thermal conductivity of 10.9 mW m-1K-1 was measured. The higher measured centre-of-panel and effective thermal conductivities than the published centre-of-panel thermal conductivity of 4.2 mW m-1K-1 from the VIP manufacturer, suggest that the real thermal performance of VIPs, when are mounted in construction, is comparatively worse than of the measured performance in the laboratory. An effective thermal conductivity of 10.9 mW m-1K-1 will, however, provide an excellent thermal performance to the construction. The third subject of this thesis aims to assess the environmental impacts of production and operation of VIP-insulated buildings, since there is a lack of life cycle analysis of whole buildings with vacuum panels. It was concluded that VIPs have a greater environmental impact than conventional insulation, in all categories except Ozone Depilation Potential. The VIPs have a measurable influence on the total Global Warming Potential and Primary Energy use of the buildings when both production and operation are taken into account. However, the environmental effect of using VIPs is positive when compared to the GWP of a standard building (a reduction of 6%) while the PE is increased by 20%. It was concluded that further promotion of VIPs will benefit from reduced energy use or alternative energy sources in the production of VIP cores while the use of alternative cores and recycling of VIP cores may also help reduce the environmental impact. Also, a sensitivity analysis of this study showed that the choice of VIPs has a significant effect on the environmental impacts, allowing for a reduction of the total PE of a building by 12% and the GWP can be reduced as much as 11% when considering both production and operation of 50 yes. Finally, it’s possible to conclude that the VIPs are very competitive alternative for insulating buildings from the Swedish “Million Program”. Nevertheless, further investigations require for minimizing the measurable environmental impacts that acquired in this LCA study for the VIP-insulated buildings.Dagens byggnader ansvarar för omkring 40% av världens energianvändning och står också för en väsentlig del av utsläppen av växthusgaser. I Sverige kan ca 21 % av energianvändningen relateras till förluster genom klimatskalet. Miljonprogrammet är ett namn för omkring en miljon bostäder som byggdes mellan 1965 och 1974, och många av dessa byggnader har en dålig energiprestanda efter dagens mått. Huvudsyftet med denna studie har varit att utforska möjligheterna att använda vakuumisoleringspaneler (VIP:ar) i byggnader med viss fokus på tillämpning i Miljonprogrammets byggnader. Med en värmeledningsförmåga som är ca 8 - 10 gånger bättre än för traditionell isolering erbjuder VIP:arna unika möjligheter till förbättrad termisk prestanda med minimal isolerings tjocklek. Denna avhandling hade tre huvudsyften. Det första var att undersöka nya alternativ för kärnmaterial som bland annat kan reducera kostnaden vid produktion av VIP:ar. Tre nyutvecklade nanoporösa kiselpulver har testats med olika stationära och transienta metoder. En inom projektet utvecklad testbädd som kan anslutas till TPS instrument (Transient Plane Source sensor), har använts för att mäta värmeledningsförmågan hos kärnmaterial för VIP:ar, vid varierande gastryck och olika mekaniska laster. Slutsatsen blev att transienta metoder är mindre lämpliga för utföra mätningar av värmeledningsförmåga för nanoporösa kiselpulver låg densitet. Avvikelsen i resultaten är dock minimal för densiteter ovan en gräns då värmeledningen genom fasta material blir dominerande jämfört med värmeöverföring genom strålning. Det andra syftet har varit att föreslå ett nytt monteringssystem för VIP:ar som kan användas för att förbättra energieffektiviteten i byggnader som är typiska för Miljonprogrammet. Genom parametrisk analys och dynamiska simuleringar har vi kommit fram till ett förslag på ett nytt monteringssystem för VIP:ar som har utvärderats genom fullskaleförsök i klimatkammare. Resultaten från fullskaleförsöken visar att den nya tekniska lösningen förbättrar väggens U-värde med upp till 56 %. En förbättrad värmegenomgångskoefficienten för väggen i mitten av en VIP blev mellan 0.118 till 0,132 W m-2K-1 och värmeledningstalet centre-av-panel 7 mW m-1K-1 uppnåddes. Detta arbete innehåller dessutom en ny metod för att mäta köldbryggor i anslutningar med hjälp av infraröd termografi. En effektiv värmeledningsförmåga för 10.9 mW m-1K-1 uppnåddes. Resultaten tyder även på att den verkliga termiska prestandan av VIP:ar i konstruktioner är något sämre än mätvärden för paneler i laboratorium. En effektiv värmeledningsförmåga av 10.9 mW m-1K-1 ger dock väggkonstruktionen en utmärkt termisk prestanda. Det tredje syftet har varit att bedöma miljöpåverkan av en VIP-isolerad byggnad, från produktion till drift, eftersom en livscykelanalys av hela byggnader som är isolerade med vakuumisoleringspaneler inte har gjorts tidigare. Slutsatsen var att VIP:ar har en större miljöpåverkan än traditionell isolering, i alla kategorier förutom ozonnedbrytande potential. VIP:ar har en mätbar påverkan på de totala utsläppen av växthusgaser och primärenergianvändningen i byggnader när både produktion och drift beaktas. Miljöpåverkan av de använda VIP:arna är dock positiv jämfört med GWP av en standardbyggnad (en minskning med 6 %) medan primärenergianvändningen ökade med 20 %. Slutsatsen var att ytterligare användning av VIP:ar gynnas av reducerad energiförbrukning och alternativa energikällor i produktionen av nanoporösa kiselpulver medan användningen av alternativa kärnmaterial och återvinning av VIP kärnor kan hjälpa till att minska miljöpåverkan. En känslighetsanalys visade att valet av VIP:ar har en betydande inverkan på miljöpåverkan, vilket ger möjlighet att reducera den totala användningen av primärenergi i en byggnad med 12 % och utsläppen av växthusgaser kan vara minska, så mycket som 11 % när det gäller både produktion och drift under 50 år. Avslutningsvis är det möjligt att dra slutsatsen att VIP:ar är ett mycket konkurrenskraftigt alternativ för att isolera byggnader som är typiska för Miljonprogrammet. Dock krävs ytterligare undersökningar för att minimera de mätbara miljöeffekter som förvärvats i denna LCA-studie för VIP-isolerade byggnader.
QC 20151109
Simulations of heat and moisture conditions in a retrofit wall construction with Vacuum Insulation Panels
Textural and thermal conductivity properties of a low density mesoporous silica material
A study of the thermal conductivity of granular silica materials for VIPs at different levels of gaseous pressure and external loads
Evaluation of the thermal conductivity of a new nanoporous silica material for VIPs – trends of thermal conductivity versus density
A comparative study of the environmental impact of Swedish residential buildings with vacuum insulation panels
ETICS with VIPs for improving buildings from the Swedish million unit program “Miljonprogrammet”
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Hartvigsen, Peter Ward. "Thermal Conductivity and Diffusivity Measurement Assessment for Nuclear Materials Raman Thermometry for Uranium Dioxide and Needle Probe for Molten Salts." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8622.
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In the near future, Gen II, III, and IV nuclear reactors will be in operation. UO2 is a common fuel for reactors in each of these generations and molten salts are used as coolant/fuel in Gen IV molten salt reactors. This thesis investigates potential ways to measure thermal conductivity for these materials: Raman thermometry for UO2 and a needle probe for molten salts. Four Raman thermometry techniques are investigated in this thesis: The Two Laser Raman (TLR), Time Differential Domain Raman (TDDR), Frequency Resolved Raman (FRR), and Frequency Domain Raman (FDR). The TLR is a steady state method used with a thin film. The TDDR and FRR are both time domain methods used with thin cantilever samples. The FDR is a frequency domain method used with a thermally thick sample. Monte Carlo like simulations are performed for each technique. In the simulations, the affect introduced uncertainty has on the measurement of thermal conductivity and thermal diffusivity is measured. From the results, it is recommended that the TLR should be used for measuring thermal conductivity and the FRR used for measuring thermal diffusivity. The TDDR and FDR were heavily affected by the uncertainty which resulted in inconsistent measured thermal properties. For measuring the thermal conductivity of molten salt, a needle probe was designed and manufactured to withstand the corrosive environment found in using molten salts. The probe uses modulated joule heating and measures the temperature rise in a thermocouple. The phase delay and temperature amplitude of the thermocouple are used in determining the thermal conductivity. A new thermal quadrupole based analytical solution, which takes into consideration convection and radiation, to the temperature rise of the probe is presented. The analytical solution is verified using a numerical solution found using COMSOL. Preliminary data was obtained with the probe in water.
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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.
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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 10-7 m2/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 -7 m2/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.Ph. D.
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Cruz, Carolina Abs da. "Termo-refletância transiente: implementação, modelamento e aplicação a filmes." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2008. http://hdl.handle.net/10183/16771.
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Este trabalho apresenta uma revisão de técnicas para medir propriedades térmicas de lmes, seguida de enfoque na termo-re etância transiente (TTR). Dentre as tecnologias existentes para medir propriedades térmicas, métodos ópticos são preferidos devido à sua natureza não-destrutiva, potencial de alta resolução temporal e espacial e calibração independente de contato físico. A implementação experimental deste método é apresentada, assim como a teoria da linha de transmissão utilizada para tratamento por Transformada de Laplace da equação de Fourier unidimensional do calor. Para facilitar o cálculo de invers ão desta Transformada, uma aproximação numérica, empregando o método Stehfest, foi usada. Experimentalmente, a evolução temporal da temperatura normalizada é mostrada para um lme de Au sobre Si e para lmes de Cu sobre substratos de vidro e Si, assim como foram utilizadas técnicas complementares de caracterização dos lmes (per lometria, elipsometria, microscopia de força atômica, eletrônica de varredura e de transmissão). Para o filme de ouro com espessura de 4:6µm, a teoria apresenta boa concordância com os resultados experimentais, já que o valor encontrado para a condutividade térmica do ouro está entre 230W/m.K e 280W/m.K, próximo e abaixo do valor da condutividade térmica do Au em volume (318W/m.K), indicando a validade do método implementado. Para lmes de cobre, porém, os resultados iniciais não apresentam a mesma concordância, e possíveis causas são discutidas. Futuramente, a TTR implementada poderá ser utilizada para determinação da condutividade térmica de lmes nos dielétricos ou semicondutores, e possivelmente na caracterização da componente transversal em filmes anisotrópicos.This work presents a review of techniques to measure thermal properties off films, followed by a focused attention to the transient termo-re ectance (TTR). Amongst the existing technologies to measure thermal properties, optical methods are preferred due their nondestructive nature, high potential of spacial and temporal resolution, and independence from physical contact. The experimental implementation of this method is presented, as well as the theory of the transmission line theory used in the Laplace Transform treatment of the Fourier one-dimensional heat conduction equation. To facilitate the calculation of the Transform inversion, a numerical method, using the Stehfest method, was used. Experimentally, evolution of the normalized temperature is shown for a lm of Au on Si and for films of Cu on glass and Si substrates, whereas complementary techniques were used for film characterization (pro lometry, ellipsometry, atomic force microscopy, scanning and transmission eletron microscopy). For the Au film 4:6µm thick, the theory presents good agreement with the experimental results, and the value found for the thermal conductivity of the gold film is between 230W/m.K and 280W/m.K, near and below the bulk Au thermal conductivity (318W/m.K), indicating the validity of the method implementation. For Cu films, however, the initial results do not present the same agreement, and possible causes are discussed. In the future, the implemented TTR could be used for determination of the thermal conductivity of dielectric or semicondutors thin films, and possibly in the characterization of the transversal component in anisotropic films.
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Munro, Troy Robert. "Thermal Property Measurement of Thin Fibers by Complementary Methods." DigitalCommons@USU, 2016. https://digitalcommons.usu.edu/etd/4702.
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To improve measurement reliability and repeatability and resolve the orders of magnitude discrepancy between the two different measurements (via reduced model transient electrothermal and lock-in IR thermography), this dissertation details the development of three complementary methods to accurately measure the thermal properties of the natural and synthetic Nephila (N.) clavipes spider dragline fibers. The thermal conductivity and diffusivity of the dragline silk of the N. clavipes spider has been characterized by one research group to be 151-416 W m−1 K −1 and 6.4-12.3 ×10−5 m2 s −1 , respectively, for samples with low to high strains (zero to 19.7%). Thermal diffusivity of the dragline silk of a different spider species, Araneus diadematus, has been determined by another research group as 2 ×10−7 m2 s −1 for un-stretched silk. This dissertation seeks to resolve this discrepancy by three complementary methods. The methods detailed are the transient electrothermal technique (in both reduced and full model versions), the 3ω method (for both current and voltage sources), and the non-contact, photothermal, quantum-dot spectral shape-based fluorescence thermometry method. These methods were also validated with electrically conductive and non-conductive fibers. The resulting thermal conductivity of the dragline silk is 1.2 W m−1 K −1 , the thermal diffusivity is 6 ×10−7 m2 s −1 , and the volumetric heat capacity is 2000 kJ m−3 K −1 , with an uncertainty of about 12% for each property
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Gurrum, Siva P. "Thermal Modeling and Characterization of Nanoscale Metallic Interconnects." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10435.
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Temperature rise due to Joule heating of on-chip interconnects can severely affect performance and reliability of next generation microprocessors. Thermal predictions become difficult due to large number of features, and the impact of electron size effects on electrical and thermal transport. It is thus necessary to develop efficient numerical approaches, and accurate metal and dielectric thermal characterization techniques. In this research, analytical, numerical, and experimental techniques were developed to enable accurate and efficient predictions of interconnect temperature rise.
A finite element based compact thermal model was developed to obtain temperature rise with fewer elements and acceptable accuracy. Temperature drop across the interconnect cross-section was ignored. The compact model performed better than standard finite element model in two and three-dimensional case studies, and the predictions for a real world structure agreed closely with experimentally measured temperature rise.
A numerical solution was developed for electron transport based on the Boltzmann Transport Equation (BTE). This deterministic technique, based on the path integral solution of BTE within the relaxation time approximation, free electron model, and linear response, was applied to a constriction in a finite size thin metallic film. A correlation for effective conductance was obtained for different constriction sizes.
The Atomic Force Microscope (AFM) based Scanning Joule Expansion Microscopy (SJEM) was used to develop a new technique to measure thermal conductivity of thin metallic films in the size effect regime. This technique does not require suspended metal structures, and thus preserves the original electron interface scattering characteristics. The thermal conductivities of 43 nm and 131 nm gold films were extracted to be 82 W/mK and 162 W/mK respectively. These measurements were close to Wiedemann-Franz Law predictions and are significantly smaller than the bulk value of 318 W/mK due to electron size effects. The technique can potentially be applied to interconnects in the sub-100 nm regime.
A semi-analytical solution for the 3-omega method was derived to account for thermal conduction within the metallic heater. It is shown that significant errors can result when the previous solution is applied for anisotropic thermal conductivity measurements.
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Smith, Andrew Paul. "Application of flash methods to measurement of the thermal conductivity of heterogeneous and non-planar materials." Thesis, University of Salford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261989.
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Harris, Kurt E. "Characterization of Carbon Nanostructured Composite Film Using Photothermal Measurement Technique." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/6931.
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Graphene is a form of carbon with unique thermal and structural properties, giving it high potential in many applications, from electronics to driveway heating. Advanced fabrication techniques putting small, graphene-like structures in a polymer matrix could allow for incorporation of some of the benefits of graphene into very lightweight materials, and allow for broader commercialization. Measuring the thermal properties of these thin-film samples is a technical capability in need of development for use with the specific specimens used in this study. Relating those thermal properties to the microstructural composition was the focus of this work.
Several conclusions could be drawn from this study which will help guide future development efforts. Among these findings, it was found that increasing carbon content only improves thermal and electrical conductivity if the samples were of low porosity. Samples of approximately identical overall carbon content and void content had higher thermal conductivity if some carbon nanotubes were added in place of graphite. Nanotubes also appeared to reduce variability in thermal conductivity between pressed and unpressed samples, allowing for more predictable properties in fabrication.
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Choo, Hyunwook. "Engineering behavior and characterization of physical-chemical particulate mixtures using geophysical measurement techniques." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52178.
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Natural geomaterials exhibit a wide range in size, physical properties, chemical properties, and mechanical behaviors. Soils that are composed of mixtures of particles with different physical and chemical properties pose a challenge to characterization and quantification of the engineering properties. This study examined the behavior of particulate mixtures composed of differently sized silica particles, mixtures composed of aluminosilicate and organic carbon particles, and mixtures composed of particles with approximately three orders of magnitude difference in particle size. This experimental investigation used elastic, electromagnetic, and thermal waves to characterize and to quantify the small to intermediate strain behavior of the mixtures.
The mechanical property of stiffness of mixed materials (e.g. binary mixtures of silica particles and fly ashes with various carbon and biomass contents) was evaluated through the stiffness of active grain contacts, and the stiffness of particles which carry applied load, using the physical concepts of intergranular void ratio and interfine void ratio. Additionally, the change in both contact mode/stiffness and electrical property due to the presence of nano-sized particles (i.e., iron oxides) on the surface of soil grains was evaluated according to applied stress, packing density, iron coating density, and substrate sand particle size. Finally, the biomass fraction and total organic carbon content of mixtures was used to quantify the electrical and thermal conductivities when particulate organic was mixed with aluminosilicate particles.
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Park, Jungkyu. "THERMAL TRANSPORT IN NOVEL THREE DIMENSIONAL CARBON NANOSTRUCTURES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1455101197.
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Al-Khudary, Nadine. "Material thermal conductivity measurement by the 3-omega method : application to polymers characterization using inkjet printing technology." Thesis, Lille 1, 2014. http://www.theses.fr/2014LIL10135/document.
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Dans le domaine de l'électronique souple, les substrats flexibles à base de polymères sont de plus en plus utilisés. Si dans les prochaines années, les structures de propagation mises en œuvre sur ce type de substrat véhiculent une puissance, alors la connaissance de la conductivité thermique de ces matériaux est essentielle. Dans ce travail, nous mesurons la conductivité thermique de matériaux de type polymère en utilisant la méthode 3 omégas. Des mesures ont été effectuées sur du polydiméthylsiloxane (PDMS). Un procédé technologique particulier est utilisé pour la fabrication des échantillons de PDMS. De ce fait, les conducteurs métalliques sont encapsulés dans le polymère et non en surface de ce dernier. Mais cela est sans conséquence sur les valeurs de conductivité thermique mesurées. Les procédés photolithographiques utilisés traditionnellement pour réaliser les lignes métalliques sont coûteux et longs. Par conséquent, nous proposons pour ce type de matériaux une méthode alternative pour la réalisation des lignes conductrices grâce à la technologie d'impression par jet d'encre. Les conductivités thermiques du polyimide et polyétheréthercétone ont été mesurées en utilisant la méthode 3omega combinée à la technologie d'impression par jet d'encre.Des simulations numériques basées sur la méthode des éléments finis ont été développées au cours de la thèse. Les mesures expérimentales obtenues sont comparées aux résultats obtenus par une solution analytique et par notre modélisation numérique.Ainsi durant cette thèse nous montrons avec succès la possibilité d'utiliser la technologie d'impression jet d'encre pour mesurer la conductivité thermique d'un substrat soupleThe characterization of polymers is gaining a great attention as they are one of the main constituents of future flexible or organic electronics. Given the fact that thermal management is an important issue in the frame work of flexible electronics, the knowledge of the thermal conductivity of polymer materials is needed. In this work, we propose the measurement of polymer material thermal conductivity using the three omega method. This method requires heating a metallic line conductor placed on the surface of the material under test by an alternating current source. The first measurements were done on polydimethyl siloxane (PDMS) polymer material for which a special procedure that consists in embedding the metallic line conductors near the surface has been applied.In addition to the well-known limitations of photolithography process which are the cost and the process duration, a particular concern lies in the fabrication of the metallic conductors by such process which might be destructive in case of polymer materials. Consequently, we propose an alternative method for this kind of materials based on inkjet printing technology. The thermal conductivities of polyimide and polyetherether ketone have been successfully measured using the three omega method combined with inkjet printing technology for sample preparation. Numerical simulations using finite element method (FEM) are also performed. Finally, experimental measurements are compared to Cahill’s analytical solution and FEM modelling. The overall results demonstrate that the inkjet printing technology is a good candidate for the characterization of flexible materials in terms of thermal conductivity
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Khatun, Ayesha. "Assessment of the impact of the measurement precision of thermal properties of materials on the prediction of their thermal behaviour." Mémoire, Université de Sherbrooke, 2010. http://hdl.handle.net/11143/5950.
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Résumé : Les propriétés thermiques des matériaux utilisées pour la construction des murs latéraux d’une cuve d’électrolyse de l’aluminium captent l’attention depuis les deux dernières décennies. Une bonne prédiction du comportement thermique dynamique des cellues Hall-Heroult, y compris une estimation précise des pertes d'énergie et de l'emplacement du gel sur le coté, est rendue possible lorsque les matériaux de coté sont bien caractérisés en fonction de la température. L'objectif de ce travail consiste à mesurer la diffusivité thermique, la capacité calorifique et la conductivité thermique du carbure de silicium, des matériaux carbones du coté (graphitique et graphitise) et de la cryolite à l’aide de techniques de caractérisation transitoires. La diffusivité thermique et la capacité de calorifique sont mesurées en utilisant respectivement un diffusivimètre thermique et un calorimètre à balayage différentiel. La conductivité thermique est calculée en supposant une masse volumique constante. La marge d'erreur sur la precision de chaque propriété thermique a également été calculée pour un nombre fini d'ensembles de données. Une conflation empirique a été élaborée pour chacune des propriétés pour décrire la relation avec la température en termes mathématiques. La caractérisation thermique de la chaleur latente dégagée lors de la fonte de la gelée de coté est également effectuée. Enfin, sur la base des calculs effectués avec un modele 2-D numérique, l'effet des erreurs de mesure entachant les différentes propriétés thermiques des matériaux du coté sur le comportement dynamique d'un réacteur à changement de phase de type laboratoire est également présenté. Les résultats obtenus montrent l’intérêt de nouvelles études sur les propriétés thermiques des matériaux utilisés dans les cellules d’électrolyse de l'aluminium pour découvrir l’influence de l'environnement thermique intérieur de la cellule, pour estimer les pertes de chaleur et l'effet des additifs sur l’emplacement du front de solidification. // Abstract : The thermal properties of the sidewall lining materials are capturing attention since the last two decades. Good prediction of the dynamic thermal behaviour of Hall Heroult cells, including precise estimation of energy losses and location of the side ledge formed by the solidification of electrolytic bath, is made possible when the sidelining materials are well characterized in function of temperature. The present work aim at measuring the thermal diffusivity, heat capacity and thermal conductivity of silicon carbide (SiC), graphitic and graphitized carbon materials and cryolite (NasAlFe) based on transient characterization techniques. The thermal diffusivity and the heat capacity are measured by using state-of-the-art transient laser flash analyzer and differential scanning calorimeter respectively. The thermal conductivity is calculated by assuming a constant density. The range of precision error for each thermal property is also calculated for a finite number of data sets. Empirical correlation has been drawn for each of the properties to describe the relation with temperature in mathematical terms. Thermal characterization of the latent heat evolved during the melting of ledge is also carried out. Finally, based on the calculations conducted with a 2-D numerical model, the effect of the precision errors of temperature varying thermal properties of the sidewall materials and ledge on the dynamic behaviour of a laboratory scale phase change reactor is also presented. The results, so obtained, encourage further studies on the thermal properties of materials used in the aluminium reduction cell to find out the thermal environment inside the cell, heat loss estimation and effect of the additives on the location of ledge.
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Koppanooru, Sampat Kumar Reddy. "Estimating Thermal Conductivity and Volumetric Specific Heat of a Functionally Graded Material using Photothermal Radiometry." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1062896/.
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Functionally graded materials (FGMs) are inhomogeneous materials in which the material properties vary with respect to space. Research has been done by scientific community in developing techniques like photothermal radiometry (PTR) to measure the thermal conductivity and volumetric heat capacity of FGMs. One of the problems involved in the technique is to solve the inverse problem, i.e., estimating the thermal properties after the frequency scan has been obtained. The present work involves finding the unknown thermal conductivity and volumetric heat capacity of the FGMs by using finite volume method. By taking the flux entering the sample as periodic and solving the discretized 1-D thermal wave field equation at a frequency domain, one can obtain the complex temperatures at the surface of the sample for each frequency. These complex temperatures when solved for a range of frequencies gives the phase vs frequency scan which can then be compared to original frequency scan obtained from the PTR experiment by using a residual function. Brute force and gradient descent optimization methods have been implemented to estimate the unknown thermal conductivity and volumetric specific heat of the FGMs through minimization of the residual function. In general, the spatial composition profile of the FGMs can be approximated by using a smooth curve. Three functional forms namely Arctangent curve, Hermite curve, and Bezier curve are used in approximating the thermal conductivity and volumetric heat capacity distributions in the FGMs. The use of Hermite and Bezier curves gives the flexibility to control the slope of the curve i.e. the thermal property distribution along the thickness of the sample. Two-layered samples with constant thermal properties and three layered samples in which one of the layer has varying thermal properties with respect to thickness are considered. The program is written in Fortran and several test runs are performed. Results obtained are close to the original thermal property values with some deviation based on the stopping criteria used in the gradient descent algorithm. Calculating the gradients at each iteration takes considerable amount of time and if these gradient values are already available, the problem can be solved at a faster rate. One of the methods is extending automatic differentiation to complex numbers and calculating the gradient values ahead; this is left for future work.
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Christopher, Michael Donald. "Application of the Transient Hot-Wire Technique for Measurement of Effective Thermal Conductivity of Catalyzed Sodium Alanate for Hydrogen Storage." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/32955.
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Sodium alanate, or the Na-Al-H system, has been the focus of intense research over the past decade due to its ability to hold almost 5 wt% of hydrogen. In this research, the effective thermal conductivity, k, of a sample of titanium-doped sodium alanate is studied over a range of operating conditions pertinent to practical on-board hydrogen storage. A transient technique employing a platinum hot-wire is used to make the measurements. A cylindrical experimental apparatus was designed with the aide of a finite element model that was used to quantify the cylinder boundary effects. The apparatus dimensions were optimized based on the finite element results with the goal of minimizing measurement uncertainty and temperature rise during testing. Finite element results were also used to predict test times and current requirements. A sample of sodium alanate was obtained and loaded into the experimental apparatus which was enclosed in a pressure vessel with a controlled atmosphere. Effective thermal conductivity was measured as a function of pressure at the fully-hydrided and fully-dehydrided states. The results from the pressure-dependence investigation were compared to an existing study that utilized an alternate measurement technique. The results matched well qualitatively â the effective thermal conductivity was highly dependent on pressure, and was found to be significantly higher in the fully-dehydrided state. However, the results of this study were 20 to 30% lower than the existing available data. Additionally, an exploratory investigation used the PCI technique to study the effect of varying composition between the fully-hydrided state and the intermediate decomposition step at a relatively constant pressure. Effective thermal conductivity did not vary significantly over this range of compositions.Master of Science
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Gaspar, Jonathan. "Fluxmétrie et caractérisation thermiques instationnaires des dépôts des composants face au plasma du Tokamak JET par techniques inverses." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4739/document.
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Ces travaux portent sur la résolution successive de deux problèmes inverses en transferts thermiques : l'estimation de la densité de flux en surface d'un matériau puis de la conductivité thermique équivalente d'une couche déposée en surface de ce matériau. Le modèle direct est bidimensionnel orthotrope (géométrie réelle d'un matériau composite), instationnaire, non-linéaire et ses équations sont résolues par éléments finis. Les matériaux étudiés sont les composants face au plasma (tuiles composite carbone-carbone) dans le Tokamak JET. La densité de flux recherchée varie avec une dimension spatiale et avec le temps. La conductivité du dépôt de surface varie spatialement et peut également varier au cours du temps pendant l'expérience (toutes les autres propriétés thermophysiques dépendent de la température). Les deux problèmes inverses sont résolus à l'aide de l'algorithme des gradients conjugués associé à la méthode de l'état adjoint pour le calcul exact du gradient. La donnée expérimentale utilisée pour la résolution du premier problème inverse (estimation de flux surfacique) est le thermogramme fourni par un thermocouple enfoui. Le second problème inverse utilise, lui, les variations spatio-temporelles de la température de surface du dépôt inconnu (thermographie infrarouge) pour identifier sa conductivité. Des calculs de confiance associée aux grandeurs identifiées sont réalisés avec la démarche Monte Carlo. Les méthodes mises au point pendant ces travaux aident à comprendre la dynamique de l'interaction plasma-paroi ainsi que la cinétique de formation des dépôts de carbone sur les composants et aideront au design des composants des machines futures (WEST, ITER)This work deals with the successive resolution of two inverse heat transfer problems: the estimation of surface heat flux on a material and equivalent thermal conductivity of a surface layer on that material. The direct formulation is bidimensional, orthotropic (real geometry of a composite material), unsteady, non-linear and solved by finite elements. The studied materials are plasma facing components (carbon-carbon composite tiles) from Tokamak JET. The searched heat flux density varies with time and one dimension in space. The surface layers conductivity varies spatially and can vary with time during the experiment (the other thermophysical properties are temperature dependent). The two inverse problems are solved by the conjugate gradient method with the adjoint state method for the exact gradient calculation. The experimental data used for the first inverse problem resolution (surface heat flux estimation) is the thermogram provided by an embedded thermocouple. The second inverse problem uses the space and time variations of the surface temperature of the unknown surface layer (infrared thermography) for the conductivity identification. The confidence calculations associated to the estimated values are done by the Monte Carlo approach. The method developed during this thesis helps to the understanding of the plasma-wall interaction dynamic, as well as the kinetic of the surface carbon layer formation on the plasma facing components, and will be helpful to the design of the components of the future machines (WEST, ITER)
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Beltrán, Pitarch Braulio. "Advanced characterization of thermoelectric materials and devices by impedance spectroscopy." Doctoral thesis, Universitat Jaume I, 2020. http://hdl.handle.net/10803/670007.
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Els dispositius termoelèctrics (TEs) poden convertir directament calor en electricitat o usar electricitat per crear una diferència de temperatura, no obstant això, actualment no estan molt estesos a causa de la seua baixa eficiència. El desenvolupament de nous materials més eficients es basa típicament en l'optimització de la figura de mèrit adimensional, que està determinada per tres propietats del material: el coeficient Seebeck (S), la conductivitat elèctrica (σ) i la conductivitat tèrmica (λ), i també la temperatura (T). Per tant, la determinació d'aquestes propietats en funció de la temperatura és un pas necessari en el desenvolupament de qualsevol material nou. Lamentablement, la caracterització de tots aquests paràmetres requereix temps i és tediosa. Per aquesta raó, l'objectiu principal d'aquest treball és avançar en l'aplicació de l’espectroscòpia d’impedància (IS) en el camp de la termoelectricitat per a establir-la potencialment com un mètode estàndard en aquest camp.Thermoelectric (TE) devices can directly convert heat into electricity or use electricity to create a temperature difference, however, they are not widely spread currently due to their low efficiency. The development of new, more efficient materials is typically based on the optimization of the dimensionless figure of merit, which is determined by three material properties: the Seebeck coefficient (S), the electrical conductivity (σ) and the thermal conductivity (λ), and also the temperature (T). Hence, the determination of these properties as a function of temperature is a necessary step in the development of any new material. Regrettably, the characterization of all these parameters is quite lengthy and tedious. For this reason, the main objective of this work is to advance the application of impedance spectroscopy (IS) in the TE field to potentially establish it as a standard method in thermoelectricity.
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Thuau, Damien. "Fabrication and characterisation of carbon-based devices." Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/5879.
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Thin film material properties and measurement characterisation techniques are crucial for the development of micro-electromechanical systems (MEMS) devices. Furthermore, as the technology scales down from microtechnology towards nanotechnology, nanoscale materials such as carbon nanotubes (CNTs) are required in electronic devices to overcome the limitations encountered by conventional materials at the nanoscale. The integration of CNTs into micro-electronics and material applications is expected to provide a wide range of new applications. The work presented in this thesis has contributed to the development of thin film material characterisation through research on the thermal conductivity measurement and the control of the residual stress of thin film materials used commonly in MEMS devices. In addition, the use of CNTs in micro-electronics and as filler reinforcement in composite materials applications have been investigated, leading to low resistivity CNTs interconnects and CNTs-Polyimide (PI) composites based resistive humidity sensors. In the first part of this thesis, the thermal conductivity of conductive thin films as well as the control of the residual stress arising from fabrication process in PI micro-cantilevers have been studied. A MEMS device has been developed for the thermal conductivity characterisation of conductive thin films showing good agreement with thermal conductivity of bulk material. Low energy Ar+ ion bombardment in a plasma has been used to control the residual stress present in PI cantilevers. Appropriate ion energy and exposure time have led to stress relaxation of the beams resulting in a straight PI cantilever beam. In the second part of this thesis, low resistivity CNTs interconnects have been developed using both dielectrophoresis (DEP) and Focused Ion Beam (FIB) techniques. An investigation of the effects of CNT concentration, applied voltage and frequency on the CNTs alignment between Al and Ti electrodes has resulted in the lowering of the CNTs’ resistance. The deposition of Pt contact using FIB at the CNTs-metal electrodes interface has been found to decrease the high contact resistances of the devices by four and two orders of magnitude for Al and Ti electrodes respectively. The last part of this thesis focuses on the preparation of CNTs-PI composite materials, its characterisation and its application as resistive humidity sensor. The integration of CNTs inside the PI matrix has resulted in enhancing significantly the electrical and mechanical properties of the composites. In particular, a DEP technique employed to induce CNTs alignment inside the PI matrix during curing has been attributed to play an important role in improving the composite properties and lowering the percolation threshold. In addition, the fabrication and testing of CNTs-PI resistive humidity sensors have been carried out. The sensing performance of the devices have shown to be dependent highly on the CNT concentration. Finally, the alignment of CNTs by DEP has improved the sensing properties of CNTs-PI humidity sensors and confirmed that the change of resistance in response to humidity is governed by the change of the CNTs’ resistances due to charge transfer from the water molecules to the CNTs.
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Islam, Arnob. "BLACK PHOSPHORUS NANOSCALE DEVICES AND EMERGING APPLICATIONS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1568124549519621.
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