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Thermal and charge conductivities of superconducting skutterudite compounds, PrRu4Sb12 and PrOs4Sb12Rahimi, Somayyeh Jay January 2007 (has links)
The measurement of thermal conductivity is a powerful probe that can be used for identifying the nature of heat and charge carriers and structure of the gap in the superconducting compounds. At low temperature when the effect of phonons in transporting heat becomes smaller, one can obtain information about the quasiparticle distribution and the superconducting gap structure.
In order to do a sensitive thermal conductivity measurement, we designed and built a thermal conductivity mount. The charge conductivity was measured through the same leads that we used for making the thermal conductivity measurements. To test the mount, we measured the heat and charge conductivity of a silver wire and determined the accuracy with which we could satisfy the Wiedemann--Franz law within 5 \%.
We will report the measurements of thermal and electrical conductivities of two filled skutterudite superconducting compounds, PrRu4Sb12 and PrOs4Sb12 at 1.1--35 K temperature range. The differences and similarities between the transport properties of these compounds in the superconducting and normal states along with the results of investigation of the Wiedemann--Franz law will be discussed in the following chapters.
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Thermal Transport Measurement of Silicon-Germanium NanowiresGwak, Yunki 2009 August 1900 (has links)
Thermal properties of one dimensional nanostructures are of interest for
thermoelectric energy conversion. Thermoelectric efficiency is related to non dimensional
thermoelectric figure of merit, ZT=S^2 o T/k, where S ,o , k and T are Seebeck
coefficient, electrical conductivity, thermal conductivity and the absolute temperature
respectively. These physical properties are interdependent. Therefore, making materials
with high ZT is a very challenging task. However, nanoscale materials can overcome some
of these limitations. When the size of nanomaterials is comparable to wavelength and mean
free path of energy carriers, especially phonons, size effect contributes to the thermal
conductivity reduction without bringing about major changes in the electrical conductivity
and the Seebeck coefficient. Therefore, the figure of merit ZT can be manipulated. For
example, the thermal conductivities of several silicon nanowires were more than two orders
of magnitude lower than that of bulk silicon values due to the enhanced boundary scattering.
Among the nanoscale semiconductor materials, Silicon-Germanium(SiGe) alloy
nanowire is a promising candidate for thermoelectric materials The thermal conductivities
of SiGe core-shell nanowires with core diameters of 96nm, 129nm and 177nm were
measured using a batch fabricated micro device in a temperature range of 40K-450K. SiGe nanowires used in the experiment were synthesized via the Vapour-Liquid-Solid (VLS)
growth method. The thermal conductivity data was compared with thermal conductivity of
Si and Ge nanowires. The data was compared with SiGe alloy thin film, bulk SiGe,
Si/SixGe1-x superlattice nanowire, Si/Si0.7Ge0.3 superlattice thin film and also with the
thermal conductivity of Si0.5Ge0.5 calculated using the Einstein model. The thermal
conductivities of these SiGe alloy nanowires observed in this work are ~20 times lower
than Si nanowires, ~10 times lower than Ge nanowires, ~3-4 times lower than Si/SixGe1-x
superlattice thin film, Si/SixGe1-x superlattice nanowire and about 3 time lower than bulk
SiGe alloy. The low values of thermal conductivity are majorly due to the effect of alloy
scattering, due to increased boundary scattering as a result of nanoscale diameters, and the
interface diffuse scattering by core-shell effect. The influence of core-shell effect, alloy
scattering and boundary scattering effect in reducing the thermal conductivity of these
nanowires opens up opportunities for tuning thermoelectric properties which can pave way
to thermoelectric materials with high figures of merit in the future.
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Thermal properties of an upper tidal flat sediment on the Texas Gulf CoastCramer, Nicholas C. 25 April 2007 (has links)
Increased land use change near fragile ecosystems can affect the ecosystem energy
balance leading to increased global warming. One component of surface energy balance
is soil storage heat flux. In past work, a complex thermal behavior was noticed in the
shrink-swell sediment of the upper Nueces Delta (upper Rincon) during summer months
as it dried. Soil storage heat flux was found to first increase, then decrease, as the soil
dried. It was suggested that the complex behavior was due to the relationship between
thermal diffusivity and soil moisture, where thermal diffusivity increases to a local
maximum before decreasing with respect to decreasing soil moisture. This study
explores the observed phenomenon in a controlled laboratory environment by relating
the sediment shrinkage curve to changing heat transfer properties.
Due to the complicated nature of the drying-shrinking sediment, it was necessary to
measure the sediment shrinkage curve and heat transfer properties in separate
experiments. The shrinkage curve was found by correlating measured sample volume
with gravimetric moisture content. Heat transfer properties were found using a single
needle heat pulse probe. A normalized gravimetric moisture content was used as a
common variable to relate the shrinkage curve and heat transfer data. Data suggests that the shrink-swell Rincon sediment portrays different behavior in
drying than that which occurs for a non-shrink-swell soil. For the shrink-swell Rincon
sediment, thermal conductivity is seen to increase with decreasing moisture, the
suggested mechanism being increased surface area contact between particles as the
shrinking sediment dries.
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The transport coefficients in (R1.5Ce0.5)RuSr2Cu2O10-5 (R=Gd,Eu) rutheno-cupratesAnatska, Maryna Petrovna 25 April 2007 (has links)
The thermal conductivity, thermopower, and electrical resistivity of
(R1.5Ce0.5)RuSr2Cu2O10-delta (R=Gd, Eu) polycrystalline samples with different oxygen
doping level are investigated in temperature range 1.8-300 K. Much attention is focused
on the dependence of the effect of the annealing in high oxygen pressures as well as the
effect of aging on transport coefficients in normal and superconducting states. It was
found that the process of deoxydation goes faster for Ru-1222(Eu) samples than for Ru-
1222(Gd) samples, which results in more pronounced granular effects in Ru-1222(Eu)
samples. The relative contribution to the thermal conductivity due to electrons and
phonons was estimated by using the Wiedemann-Franz relation and the resistivity data.
The calculation showed that the maximum electron contribution for Ru-1222(Eu) is
about 0.75% and that for Ru-1222(Gd) samples is around 4 %.
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The thermal conductivity of bismuth in transverse magnetic fields, at low temperaturesKnapp, Edwin John, January 1930 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1930. / Typescript. Title from PDF title page (viewed Nov. 6, 2008). Includes bibliographical references (p. [37]). Online version of the print original.
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Heat transfer optimization of grooved heat pipes /Riegler, Robert L., January 2004 (has links)
Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaf 59). Also available on the Internet.
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The thermal conductivity of bismuth in transverse magnetic fields, at low temperaturesKnapp, Edwin John, January 1930 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1930. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf [37]).
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Heat transfer optimization of grooved heat pipesRiegler, Robert L., January 2004 (has links)
Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaf 59). Also available on the Internet.
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Efeitos de perdas de calor na determinacao da difusividade termica pela tecnica de pulso de energiaCOSTA, GILDO J. da S. 09 October 2014 (has links)
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Efeitos de perdas de calor na determinacao da difusividade termica pela tecnica de pulso de energiaCOSTA, GILDO J. da S. 09 October 2014 (has links)
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