Dissertations / Theses on the topic 'Heat generation and transport'
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Legault, Stephane. "Heat transport in quasicrystals." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0021/NQ55355.pdf.
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Legault, Stéphane. "Heat transport in quasicrystals." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36034.
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In this thesis, we performed a detailed study of the thermal conductivity in a wide range of quasicrystals. Three systems were studied: AlPdMn, AlCuFe and AlPdRe, and the samples were in both single and polycrystalline form. A further variable was added by introducing a controlled level of defects.At low temperatures (below 20K), the thermal conductivity is defect limited, being controlled by boundary scattering, two level systems, stacking faults and dislocations. At high temperatures (above 20K), we find the thermal conductivity is limited by intrinsic properties of the quasicrystalline structure and phonon-phonon scattering.
From fitting the thermal conductivity to a detailed model we are able to predict the maximum thermal conductivity of a perfect quasicrystal.
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Moe, Bjørn Kristian. "Heat Generation by Heat Pump for LNG Plants." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14671.
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Abstract The LNG production plant processing natural gas from the Snøhvit field outside Hammerfest in northern Norway utilizes heat and power produced locally with gas turbines. Building a new production train supplied with electricity from the power grid is being evaluated as a possible solution for reducing CO2 emissions from the plant. Buying electricity from the grid rather than producing it in a combined heat and power plant makes it necessary to find new ways to cover the heat loads at the production plant. A project thesis was written in the fall semester 2010 evaluating the possibility of generating the necessary heat with heat pumps. It was concluded that parts of the required heat could be delivered with reasonable efficiencies using heat pumps. Further, a heat pump delivering heat to the CO2-removal system was analyzed. Simulations showed that the required heat load, reaching approximately 62 MW at full production, could be delivered from a heat pump using butane as working fluid. The electrical power consumption for the compressors would be 23.3 MW, giving the heat pump a COP of 2.66. In this master thesis the heat pump suggested earlier is analyzed, focusing on identifying losses. Several possible changes that will enhance the heat pump’s efficiency are suggested. The use of other workings fluids and mixed refrigerants are analyzed as well, using the process simulation software Pro/II. The simulations indicates that the heat pump should be equipped with a flash tank at middle pressure, thereby reducing throttling losses and required mass flows through the evaporators. In addition, the suction gas should be overheated as much as possible. Using mixed refrigerants lowers the efficiency of the heat pump. Finally, two new systems are suggested: One with butane as workings fluid and one with pentane, both with flash tank at middle pressure and superheated suction gas. The pentane-system gives the highest system COP, but requires much bigger compressors than the butane-system. The table shows the most important results. Working fluid Electrical power consumption [MW] Volume flow suction gas [m3/h] COP Butane (C4H10) 18.6 55000 3.35 Pentane (C5H12) 17.5 150000 3.54 The power grid electricity is assumed to have been produced without any CO2 emissions. Covering the heat required by the CO2 removal system with a gas fired furnace would generate CO2 emissions of approximately 120,000 tons per year. Heat pumps are a good solution because they deliver relatively cheap heat without these CO2 emissions.
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Shukla, Nitin. "Heat Transport across Dissimilar Materials." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/27820.
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All interfaces offer resistance to heat transport. As the size of a device or structure approaches nanometer lengthscales, the contribution of the interface thermal resistance often becomes comparable to the intrinsic thermal resistance offered by the device or structure itself. In many microelectronic devices, heat has to transfer across a metal-nonmetal interface, and a better understanding about the origins of this interface thermal conductance (inverse of the interface thermal resistance) is critical in improving the performance of these devices. In this dissertation, heat transport across different metal-nonmetal interfaces are investigated with the primary goal of gaining qualitative and quantitative insight into the heat transport mechanisms across such interfaces. A time-domain thermoreflectance (TDTR) system is used to measure the thermal properties at the nanoscale. TDTR is an optical pump-probe technique, and it is capable of measuring thermal conductivity, k, and interface thermal conductance, G, simultaneously.
The first study examines k and G for amorphous and crystalline Zr47Cu31Al13Ni9 metallic alloys that are in contact with poly-crystalline Y2O3. The motivation behind this study is to determine the relative importance of energy coupling mechanisms such as electron-phonon or phonon-phonon coupling across the interface by changing the material structure (from amorphous to crystalline), but not the composition. From the TDTR measurements k=4.5 W m-1 K-1 for the amorphous metallic glass of Zr47Cu31Al13Ni9, and k=5.0 W m-1 K-1 for the crystalline Zr47Cu31Al13Ni9. TDTR also gives G=23 MW m-2 K-1 for the metallic glass/Y2O3 interface and G=26 MW m-2 K-1 for the interface between the crystalline Zr47Cu31Al13Ni9 and Y2O3. The thermal conductivity of the poly-crystalline Y2O3 layer is found to be k=5.0 W m-1 K-1. Despite the small difference between k and G for the two alloys, the results are repeatable and they indicate that the structure of the alloy plays a role in the electron-phonon coupling and interface conductance.
The second experimental study examines the effect of nickel nanoparticle size on the thermal transport in multilayer nanocomposites. These nanocomposites consist of five alternating layers of nickel nanoparticles and yttria stabilized zirconia (YSZ) spacer layers that are grown with pulsed laser deposition. Using TDTR, thermal conductivities of k=1.8, 2.4, 2.3, and 3.0 W m-1 K-1 are found for nanocomposites with nickel nanoparticle diameters of 7, 21, 24, and 38 nm, respectively, and k=2.5 W m-1 K-1 for a single 80 nm thick layer of YSZ. The results indicate that the overall thermal conductivity of these nanocomposites is strongly influenced by the Ni nanoparticle size and the interface thermal conductance between the Ni particles and the YSZ matrix. An effective medium theory is used to estimate the lower limits for the interface thermal conductance between the nickel nanoparticles and the YSZ matrix (G>170 MW m-2 K-1), and the nickel nanoparticle thermal conductivity.Ph. D.
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Sato, Ken-ichi. "Next Generation Transport Network Architecture." IEEE, 2010. http://hdl.handle.net/2237/14451.
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Rivera, Gomez Franco Wilfrido. "Heat transformer technology and steam generation." Thesis, University of Salford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360445.
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Nazari, Ashkan. "HEAT GENERATION IN LITHIUM-ION BATTERIES." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1469445487.
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Beardo, Ricol Albert. "Generalized Hydrodynamic Heat Transport in Semiconductors." Doctoral thesis, Universitat Autònoma de Barcelona, 2021. http://hdl.handle.net/10803/673590.
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La tesis presenta una descripció unificadora d'una varietat d'experiments de transport tèrmic a la micro i nano escala en semiconductors com el silici o el germani. S'utilitza un model de transport de calor hidrodinàmic per predir la resposta no difusiva de sistemes complexes en situacions de rellevància tecnològica, com el procés de refredament d'un component electrònic alliberant calor cap a un substrat semiconductor. El model no utilitza paràmetres d'ajust en funció de la geometria, sinó que utilitza paràmetres calculats des de primers principis. Els efectes de mida petita o alta freqüència es capturen a través de condicions de contorn específiques i, per tant, el model és una eina útil pel disseny de dispositiu micro electrònics. Degut a que la descripció hidrodinàmics pel silici no és el mètode convencional, en aquesta tesis es posa especial èmfasis en determinar l'aplicabilitat del model en múltiples experiments de manera unificadora. Com a resultat, s'identifiquen fenòmens no difusius com la propagació del segon so en camps tèrmics fluctuants en germani o múltiples temps de relaxació en l'evolució tèrmica d'escalfadors nano estructurats en silici. A més, la descripció hidrodinàmica es compara amb altres models moderns per descriure els mateixos experiments, i es proporciona un resum de les eines teòriques necessàries (la termodinàmica de no equilibri i la teoria cinètica). Utilitzant les evidències experimentals que s'aporten, es conclou que el model hidrodinàmic té capacitat predictiva de la resposta tèrmica de materials com el silici a la nano escala dins d'un cert rang d'aplicabilitat.Ésta tesis presenta una descripción unificadora de una variedad de experimentos de transporte térmico a la micro y nano escala en semiconductores como el silicio o el germanio. Se utilitza un modelo de transporte de calor hidrodinámico para predecir la respuesta no difusiva de sistemas complejos en situacions de relevancia tecnológica, como el proceso de enfriamento de un componente electrónico liberando calor hacia un sustrato semiconductor. El modelo no utilitza parámetros de ajuste en función de la geometría, sinó que utiliza parámetros calculados des de primeros principios. Los efectos de tamaño reducido o alta frecuencia se capturan a través de condiciones de contorno específicas y, por tanto, el modelo es una herramienta útil para el diseño de dispositivos micro electrónicos. Dado que la descripción hidrodinámica para el silicio no es el método convencional, en ésta tesis se presta especial atención a determinar la aplicabilidad del modelo en múltiples experimentos de forma unificadora. Como resultado, se identifican fenómenos no difusivos como la propagación de segundo sonido en campos térmicos fluctuantes en germanio, o múltiples tiempos de relajación en la evolución térmica de calentadores nano estructurados en silicio. Además, la descripción hidrodinámica se compara con otros modelos modernos para describir los mismos experimentos, y se proporciona un resumen de las herramientas teóricas necesarias (la termodinámica de no equilibrio y la teoria cinética). Utilizando las evidencias experimentales que se aportan, se concluye que el modelo hidrodinámico tiene capacidad predictiva de la respuesta térmica de materiales como el silicio a la nano escala dentro de un cierto rango de aplicabilidad.
This thesis presents a unifying description of a variety of experiments on micro- and nano-scale heat transport in semiconductors like silicon or germanium. A hydrodynamic-like heat transport model is used to predict the non-diffusive thermal response of complex systems in technologically relevant situations, like the process of energy release from nanostructured heat sources towards a semiconductor substrate. The model does not use geometry-dependent or fitted parameters, but use intrinsic material properties that can be calculated from first principles. Small-size and high-frequency effects are captured through the use of specific boundary conditions, thus resulting in a practical tool for complex microelectronic device design. Since hydrodynamic modeling is not the state-of-the-art approach to describe standard semiconductors like silicon, special care is devoted to quantitatively determine the applicability of the model, and multiple experiments using different techniques are considered and studied in a unifying way. As a result, previously unreported non-Fourier phenomena in materials like silicon or germanium is identified and demonstrated (e.g. second sound in rapidly varying thermal fields or multiple decay times characterizing the evolution of nano-structured heaters). Furthermore, the hydrodynamic description is compared with alternative modern frameworks describing size and frequency effects in semiconductor heat transport, and a summarized overview of the theoretical background, namely non-equilibrium thermodynamics and kinetic theory, is presented. In light of the extensive experimental evidence provided, this thesis demonstrate the predictive capability of hydrodynamic-like thermal transport modeling in semiconductors within a certain range of applicability that is well beyond the diffusive regime.
Universitat Autònoma de Barcelona. Programa de Doctorat en Física
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Niemi, Daniel, and Joel Hambraeus. "Heat Transport in Inhomogeneous Harmonic Chains." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-275699.
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It is still to this day a challenge for theoretical physicists to derive Fourier’s law from microscopic models. Motivated by this, we study in this thesis the thermal conduction properties of harmonic chains. A semi-analytical method and simulation are used to find that on average the conduction through harmonic chains resembles Fourier like conduction when impurities of the form k_i=kw_i and 1/m_i=1/m*w_i are introduced, where k_i and m_i are the spring constants and masses of the chain and w_i are weights drawn from a random distribution. A few of these distributions are studied in detail, with similar results.Also the classical field theory limit of this model is studied. It is shown by analytical means that heat is transported diffusively in this model when impurities are introduced, whereas the transport is completely ballistic in the absence of impurities.
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Visarraga, Darrin Bernardo. "Heat transport models with distributed microstructure." Access restricted to users with UT Austin EID, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3036605.
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Sharma, Mukta. "Parallel Heat Transport in Magnetized Plasma." DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/1470.
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A code that solves the coupled electron drift kinetic and temperature equations has been written to study the effects of collisionality and particle trapping on temperature equilibration along magnetic field lines. A Chapman-Enskog-like approach is adopted with the time-dependent distribution function written as the sum of a dynamic Maxwellian and a kinetic distortion expanded in Legendre polynomials. The drift kinetic equation is solved on a discrete grid in normalized speed, and an FFT algorithm is used to treat the onedimensional spatial domain along the magnetic field. The dependence of the steady-state temperature on collisionality and magnetic well depths is discussed in detail. As collisionality decreases (increasing background temperature), temperature variations decrease. As magnetic well depth increases (at fixed collisionality), temperature variations along the field line increase.
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Cartaxo, Justino Carvalho. "Heat release analysis for second generation biodiesels." Universidade Federal do CearÃ, 2016. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=16984.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorSecond generation biodiesel fuels extracted from sources such as beef tallow and castor bean oil have gone through an increase in production, as they are being gradually added to soybean biodiesel which constitutes the primary biofuel in the country. These alternative materials have potential do increase the fuelâs oxidation stability and, specifically in the case of beef tallow, reduce the cost of producing biodiesel. However, these sources also contribute to making the properties of the biodiesel/diesel blend more distant from those of conventional diesel fuel. Beef tallow biodiesel, for example, has a cetane number of 64.70, compared to 46.44 the soybean and 48 for mineral diesel fuel. In the case of castor bean biodiesel, its viscosity is 14.5 cSt, while soybeanâs is 4.2 cSt and mineral dieselâs is 2.5. It is expected that these unique characteristics should have noteworthy consequences in the injection, tomization and combustion processes of the fuel. This work intends to determine the extent of these consequences by characterizing each second generation biodiesel fuelâs impact on the apparent heat release rate. To this end, experimental data on cylinder pressure and a heat release â or energy - analysis model on a combustion zone were utilized. The data were obtained from a medium sized turbo diesel engine operating at steady state for three different load levels. Biodiesel and diesel blends were prepared at concentration levels B10, representative of current commercial use, and B20, corresponding to a greater biofuel adoption in a future scenario. Second generation sources were also compared to data from soybean biodiesel, which forms around 75% of Brazilâs biodiesel production. At B20 concentrations, it was found that beef tallow biodiesel, due to its higher cetane number, hastened combustion by about 1◦ compared to soybean and 3◦ compared to mineral diesel. This anticipation in ignition also caused a reduction in the amount of fuel consumed as a premixed flame. Combustion of castor bean biodiesel was mostly unchanged for high and medium loads compared to mineral diesel fuel. However, on the low load configuration (BMEP = 250kPa) and at B20 concentration, it caused a significant delay in combustion, likely from the collision of the fuel jet against the cylinder wall.
Os biodieseis de segunda geraÃÃo oriundos de fontes, tais como o sebo bovino e a mamona, vÃm experimentando uma expansÃo em sua produÃÃo, sendo adicionados gradualmente ao biodiesel de soja, que constitui a matÃria-prima predominante no paÃs. Essas matÃrias-primas alternativas podem aumentar a estabilidade à oxidaÃÃo do combustÃvel e, no caso do sebo, diminuir o custo de produÃÃo do biodiesel. Contudo, elas tambÃm contribuem para um maior distanciamento entre as propriedades das misturas diesel/biodiesel e o Ãleo diesel convencional. O biodiesel proveniente do sebo bovino, por exemplo, possui um nÃmero de cetano de 68,77 frente aos 52,10 do de soja e 48 do Ãleo diesel mineral. Jà o biodiesel de mamona possui viscosidade de 14,5 cSt, frente aos 4,16 do de soja e 2,5 do Ãleo diesel mineral. Espera-se que essas caracterÃsticas singulares tenham consequÃncias importantes nos processos de injeÃÃo, atomizaÃÃo e queima do combustÃvel. O objetivo deste trabalho à determinar a extensÃo dessas consequÃncias, caracterizando-se o impacto de cada um desses biodieseis de segunda geraÃÃo sobre a taxa aparente de liberaÃÃo de energia. Empregou-se, para tanto, dados experimentais de pressÃo no cilindro e um modelo de anÃlise de liberaÃÃo de calor, ou de energia, com uma zona de combustÃo. Os dados foram obtidos com um motor diesel turbo de mÃdio porte operando em condiÃÃes de regime permanente e a trÃs nÃveis de carga. Preparou-se misturas entre diesel e biodiesel nas concentraÃÃes B10, representativas do patamar atual de adiÃÃo de biodiesel ao diesel mineral, e B20, que corresponderiam à maior adoÃÃo de biocombustÃveis em um cenÃrio futuro. As matÃrias-primas de segunda geraÃÃo, sebo bovino e mamona, tambÃm foram comparadas a dados obtidos com o biodiesel de Ãleo de soja, que corresponde a cerca de 75% a atual produÃÃo brasileira de biodiesel. Para as misturas B20, constatou-se que o biodiesel de sebo bovino, por ter maior nÃmero de cetano, adianta a combustÃo em cerca de 1◦ com relaÃÃo ao de soja e 3◦ com relaÃÃo ao diesel mineral. Devido a este adiantamento da igniÃÃo, o biodiesel de sebo bovino tambÃm reduziu a quantidade de combustÃvel consumido pelo modo prÃ-misturado. A combustÃo das misturas contendo biodiesel de mamona ficou praticamente inalterada para as condiÃÃes de alta e mÃdia carga com relaÃÃo ao Ãleo diesel mineral. Contudo, em baixa carga (bmep=250 kPa) e na concentraÃÃo correspondente a B10 e B20, o biodiesel de mamona provocou um atraso expressivo na combustÃo, provavelmente devido à colisÃo do jato combustÃvel com as paredes do pistÃo.
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Hu, Shih-Yung. "Heat transfer enhancement in thermoelectric power generation." [Ames, Iowa : Iowa State University], 2009.
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Splith, Tobias, Christian Chmelik, Frank Stallmach, Stefan K. Henninger, Gerrit Füldner, Panagiotis D. Kolokathis, Evangelia Pantatosaki, and George K. Papadopoulos. "Adsorptive heat transformation with SAPO-34." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198701.
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Fan, Jing, and 范菁. "Heat transport in nanofluids and biological tissues." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B47752853.
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The present work contains two parts: nanofluids and bioheat transport, both involving
multiscales and sharing some common features. The former centers on addressing the
three key issues of nanofluids research: (i) what is the macroscale manifestation of
microscale physics, (ii) how to optimize microscale physics for the optimal system
performance, and (iii) how to effectively manipulate at microscale. The latter
develops an analytical theory of bioheat transport that includes: (i) identification and
contrast of the two approaches for developing macroscale bioheat models: the
mixture-theory (scaling-down) and porous-media (scaling-up) approaches, (ii)
rigorous development of first-principle bioheat model with the porous-media
approach, (iii) solution-structure theorems of dual-phase-lagging (DPL) bioheat
equations, (iv) practical case studies of bioheat transport in skin tissues and during
magnetic hyperthermia, and (v) rich effects of interfacial convective heat transfer,
blood velocity, blood perfusion and metabolic reaction on blood and tissue macroscale
temperature fields.
Nanofluids, fluid suspensions of nanostructures, find applications in various
fields due to their unique thermal, electronic, magnetic, wetting and optical properties
that can be obtained via engineering nanostructures. The present numerical simulation
of structure-property correlation for fourteen types of two/three-dimensional
nanofluids signifies the importance of nanostructure’s morphology in determining
nanofluids’ thermal conductivity. The success of developing high-conductive
nanofluids thus depends very much on our understanding and manipulation of the
morphology. Nanofluids with conductivity of upper Hashin-Shtrikman bounds can be
obtained by manipulating structures into an interconnected configuration that
disperses the base fluid and thus significantly enhancing the particle-fluid interfacial
energy transport. The numerical simulation also identifies the particle’s radius of
gyration and non-dimensional particle-fluid interfacial area as two characteristic
parameters for the effect of particles’ geometrical structures on the effective thermal
conductivity. Predictive models are developed as well for the thermal conductivity of
typical nanofluids.
A constructal approach is developed to find the constructal microscopic physics
of nanofluids for the optimal system performance. The approach is applied to design
nanofluids with any branching level of tree-shaped microstructures for cooling a
circular disc with uniform heat generation and central heat sink. The constructal
configuration and system thermal resistance have some elegant universal features for
both cases of specified aspect ratio of the periphery sectors and given the total number
of slabs in the periphery sectors.
The numerical simulation on the bubble formation in T-junction microchannels
shows: (i) the mixing enhancement inside liquid slugs between microfluidic bubbles,
(ii) the preference of T-junctions with small channel width ratio for either producing
smaller microfluidic bubbles at a faster speed or enhancing mixing within the liquid
phase, and (iii) the existence of a critical value of nondimensional gas pressure for
bubble generation. Such a precise understanding of two-phase flow in microchannels
is necessary and useful for delivering the promise of microfluidic technology in
producing high-quality and microstructure-controllable nanofluids.
Both blood and tissue macroscale temperatures satisfy the DPL bioheat equation
with an elegant solution structure. Effectiveness and features of the developed
solution structure theorems are demonstrated via examining bioheat transport in skin
tissues and during magnetic hyperthermia.published_or_final_version
Mechanical Engineering
Doctoral
Doctor of Philosophy
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Jayne, Steven Robert. "Dynamics of global ocean heat transport variability." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/69203.
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Thesis (Sc. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and Woods Hole Oceanographic Institution), 1999.Includes bibliographical references (p. 161-169).
A state-of-the-art, high-resolution ocean general circulation model is used to estimate the time-dependent global ocean heat transport and investigate its dynamics. The north-south heat transport is the prime manifestation of the ocean's role in global climate, but understanding of its variability has been fragmentary owing to uncertainties in observational analyses, limitations in models, and the lack of a convincing mechanism. These issues are addressed in this thesis. Technical problems associated with the forcing and sampling of the model, and the impact of high-frequency motions are discussed. Numerical schemes are suggested to remove the inertial energy to prevent aliasing when the model fields are stored for later analysis. Globally, the cross-equatorial, seasonal heat transport fluctuations are close to +4.5 x 1015 watts, the same amplitude as the seasonal, cross-equatorial atmospheric energy transport. The variability is concentrated within 200 of the equator and dominated by the annual cycle. The majority of it is due to wind-induced current fluctuations in which the time-varying wind drives Ekman layer mass transports that are compensated by depth-independent return flows. The temperature difference between the mass transports gives rise to the time-dependent heat transport. The rectified eddy heat transport is calculated from the model. It is weak in the central gyres, and strong in the western boundary currents, the Antarctic Circumpolar Current, and the equatorial region. It is largely confined to the upper 1000 meters of the ocean. The rotational component of the eddy heat transport is strong in the oceanic jets, while the divergent component is strongest in the equatorial region and Antarctic Circumpolar Current. The method of estimating the eddy heat transport from an eddy diffusivity derived from mixing length arguments and altimetry data, and the climatological temperature field, is tested and shown not to reproduce the model's directly evaluated eddy heat transport. Possible reasons for the discrepancy are explored.
by Steven Robert Jayne.
Sc.D.
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Witharana, S. "Thermal transport in nanofluids : boiling heat transfer." Thesis, University of Leeds, 2011. http://etheses.whiterose.ac.uk/1648/.
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This thesis is constructed around the topic of thermal transport in nanofluids, with special emphasis of boiling heat transfer. Nanofluids boiling, as it is popularly known, have been researched nearly for two decades. While some controversies surrounding the boiling mechanisms had been sorted out, others still remained. The aim of this thesis is to address the remaining concerns. For the best treatment of the research problem, the experimental work was divided into three segments. Time-resolved small angle x-ray scattering studies of nanofluids were focused to examine the nanoparticle aggregation in liquid media. These were conducted at two national synchrotron facilities located at Daresbury Laboratory and Diamond Light source in Oxford, UK. In-situ experiments were conducted with static and convective nanofluidic samples. Types of nanofluids and the experimental conditions were chosen to cover a broad range of practical applications. Water based nanofluids of spherical particles of aluminium oxide (Al2O3) and titanium dioxide (TiO2) and acicular particles of aluminium oxide (Al2O3) were exposed to 1Ă wavelength x-ray beam for varying duration of times at a frame rate of 10miliseconds. Data analysis was conducted using the Dream and SAXS Utilities software. Signs of change in particle size were discovered with the near-IEP nanofluids. For further clarification of these SAXS observations, microscopic and photography studies were conducted in the laboratory. SEM studies were supported by optical microscopy. It helped to estimate the aggregate sizes and porosity within aggregates. The settling rates were determined by still photography, which were subsequently compared with the prediction of Stoke’s settling theory. At the end of data and image analysis, it was discovered that the x-ray beam had successfully predicted the settling rates of nanoparticle aggregates. Although SAXS has long been used to analyse particulate systems, for the best of the knowledge of this author, this is the first time its capability as a tool to estimate particle settling rates in nanofluids has been showcased. Furthermore, by fine tuning the present methodology, it seems possible to determine the nanoparticle aggregation rates in a nanofluid. Saturated pool boiling of nanofluids was experimentally investigated under the atmospheric pressure. A boiling test rig was designed and constructed for this purpose in the Leeds University. Water based and water-ethylene glycol (WEG) based nanofluids were examined for boiling heat transfer on flat copper substrates. The substrates were resistively heated from the bottom, providing surface heat fluxes up to 189kW/m2. Boiling heat transfer coefficients were calculated using the measured temperature differences between substrate and the boiling liquid at each surface heat flux. All nanofluids in general displayed deterioration in boiling heat transfer. Moreover all substrates were found fouled with nanoparticles after boiling. SEM observation on fouled substrates revealed the presence of structures consisting of sub-micron size cavities and pores, which are possibly interconnected by sub-surface network of channels. By measuring their surface roughness, it was further understood that the degree of change of roughness due to boiling depended upon its initial roughness, the particle concentration in the nanofluid, as well as the shape of nanoparticles. This study also points to an interval of roughnesses that gives optimum boiling heat transfer performance. Further experiments are recommended to focus on this aspect. Also to avoid in future is the bubble nucleation in the periphery of the copper substrates that became a major obstacle to visualise bubbles in the middle. The need to explore the bubble nucleation phenomena on at sub-micron size cavities was inspired by the presence of such cavities on nanofouled substrates. Moreover in literature sometimes the inconsistencies on the degree of enhancement or deterioration were attributed to hitherto-unknown boiling phenomena at these length scales. Two key challenges were to create very small cavities on a smooth substrate and to conduct phenomenally clean boiling experiments on them. In principle there should not be a foreign particle inside the boiler which is larger than the cavity mouth. The biggest challenge however was to find a technique to measure the temperature of the liquid layer on top of the cavities. The infrared thermometry facility at the Nuclear Science and Engineering Department of the Massachusetts Institute of Technology (MIT) was used as a part of research collaboration. Tiny cavities were machined on ultra smooth silicon substrate using the focus ion beam (FIB) technology at the University of Leeds and at Harvard Centre for Nanoscale Systems. The mouth diameters of conical cavities were ranging from 0.6µm to 4.5µm. A boiling test rig was simultaneously developed at MIT. Heating to the liquid was provided by a halogen spot heater. The cleanliness of the test rig was successfully proved by reaching the heterogeneous nucleation superheat of liquid methanol on a silicon wafer. Water and a water based dilute SiO2 nanofluid were boiled in this novel test rig. Temperature profiles of bubble evolution were captured using the IR thermometry. Also the superheated liquid layer temperatures were measured. It was found that the measured values were in good agreement with Young-Laplace theory. Moreover the SiO2 0.01wt%-water nanofluid in most cases demonstrated boiling heat transfer enhancement up to 40% above water. With this work, for the first time the classical Young-Laplace theory was proved for sub-micron cavities. It further removed the suspicion that there might be a different phenomenon governing the bubble nucleation on nanofouled substrates.
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Ronetti, Flavio. "Charge and heat transport in topological systems." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0541/document.
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Dans cette thèse, j'adresse le sujet fascinant et attirant du transport de charge électrique et de chaleur dans les systèmes Hall quantiques, qui sont parmi l'exemple le plus célèbre des phases topologiques de la matière, en présence de potentiels électriques dépendantes du temps. L'effet Hall se produit dans des systèmes électroniques bidimensionnels dans la limite de forts champs magnétiques perpendiculaires. Le cachet de systèmes de Hall quantiques est l'apparition d'états de bord métalliques unidimensionnels sur les frontières du système.La longueur de cohérence assurée par la protection topologique garantit d’avoir accès à la nature ondulatoire des électrons. Ces propriétés ont inspiré un nouveau domaine de la recherche, connu comme la l'optique quantique électronique. Une source d’électrons individuels peut être réalisée en s'appliquant à un système de Hall quantique impulsions Lorentzian. En considérant l'application d'un train périodique d'impulsions Lorentzian à un système Hall quantique, j'examine la densité de charge d'un état composé par beaucoup de levitons dans le régime de Hall quantique fractionnaire, constatant ainsi qu'il est réarrangé dans une configuration réguliere de sommets et des vallées. Alors, j'analyse les propriétés de transport de chaleur des levitons dans les systèmes Hall quantiques, qui représente un nouveau point de vue sur l'optique quantique électronique, étendant et généralisant les résultats obtenus dans le transport de chargeIn this thesis, I address the intriguing and appealing topic of charge and heat transport in quantum Hall systems, which are among the most famous example of topological phases of matter, in presence of external time-dependent voltages. Quantum Hall effect occurs in two-dimensional electron systems in the limit of strong perpendicular magnetic fields. The hallmark of quantum Hall systems is the emergence of one-dimensional metallic edge states on the boundary. Along these edge states particles propagate with a definite direction. The coherence length ensured by topological protection guarantees to access wave-like nature of electrons. This properties inspired a new field of research, known as electron quantum optic. Single-electron source can be realized by applying to a quantum Hall system a periodic train of Lorentzian-shaped pulses.Plateaus of the Hall resistance appear also at fractional values of the resistance quantum. The physical explanation of fractional quantum Hall effect cannot neglect the correlation between electrons and this phase of matter is inherently strongly-correlated. By considering the application of a periodic train of Lorentzian pulses to a quantum Hall system, I investigate the charge density of a state composed by many levitons in the fractional quantum Hall regime, thus finding that it is re-arranged into a regular pattern of peaks and valleys, reminiscent of Wigner crystallization in strongly-interacting electronic systems. Then, I analyze heat transport properties of levitons in quantum Hall systems, which represent a new point of view on electron quantum optics, extending and generalizing the results obtained in the charge domain
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RONETTI, FLAVIO. "Charge and heat transport in topological systems." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/933059.
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In this thesis, I address the intriguing and appealing topic of charge and heat transport in quantum Hall systems, which are among the most famous example of topological phases of matter, in presence of external time-dependent voltages. The interest of condensed matter community towards topological systems has been considerably raised in recent years. For instance, it is worth to recall the Nobel prize for physics 2016 awarded to Professors Thouless, Kosterlitz and Haldane for their contribution to the study of topological states of matter.
These states are exotic phases of matter, whose properties are described in terms of quantities that do not depend on the details of a system, are very robust against defects and perturbations. The research field of topological systems takes place due to the interplay between condensed matter physics and mathematics. As a matter of fact, many concepts have been borrowed from the mathematical branch of topology in order to classify these novel states of matter.
Quantum Hall effect was discovered almost forty years ago and still attracts a lot of attention from the theoretical and experimental point of view. This remarkable physical phenomenon occurs in two-dimensional electron systems in the limit of strong perpendicular magnetic fields. In quantum Hall systems, the transverse resistance, which is commonly defined Hall resistance, is very precisely quantized in terms of the resistance quantum. When this quantization occurs for integer values, this phenomenology is termed integer quantum Hall effect. It can be understood in a satysfying way by resorting to a non-interacting quantum mechanical description. The hallmark of quantum Hall systems is the emergence of one-dimensional metallic edge states on the boundaries of the system. Along these edge states particles propagate with a definite direction. As a result, they are topologically protected against backscattering.
The coherence length ensured by topological protection guarantees to access the wave-like nature of electrons. Intriguingly, this investigation can be pushed to its fundamental limit by exploring quantum transport at the single-electron level. This idea embodies the core of a new field of research, known as electron quantum optics Single-electron source can be realized by applying to a quantum Hall system a periodic train of Lorentzian-shaped pulses, carrying an integer number of particles per period, thus emitting into the edge states minimal single-electron excitations, then termed levitons.
Plateaus of the Hall resistance appear also at fractional values of the resistance quantum. Contrarily to the integer case, the physical explanation of fractional quantum Hall effect cannot neglect the correlation between electrons and this phase of matter is inherently strongly-correlated. Intriguingly, elementary excitations of fractional quantum Hall systems are quasi-particle with fractional charge and statistics. Remarkably, one-dimensional conducting edge states arise also in the fractional quantum Hall effect and their excitations inherit the charge and statistical properties of the one in the bulk.
By considering the application of a periodic train of Lorentzian pulses to a quantum Hall system, I focus on the transport properties of levitons propagating along integer and fractional edge states. I investigate the charge density of a state composed by many levitons in the fractional quantum Hall regime, thus finding that it is re-arranged into a regular pattern of peaks and valleys, reminiscent of Wigner crystallization in strongly-interacting electronic systems. Then, I analyze heat transport properties of levitons in quantum Hall systems, which represent a new point of view on electron quantum optics, extending and generalizing the results obtained in the charge domain.
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Stark, Andrew Joseph. "16QAM for next-generation optical transport networks." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47732.
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Fiber-optic networks are continually evolving to accommodate ever-increasing data transport rates demanded by modern applications, devices, and services. Network operators are now beginning to deploy systems with 100 Gb/s per-wavelength data rates while maintaining the 50 GHz dense wavelength division multiplexing grid that is (generally) standard for 10 Gb/s systems. Advanced modulation formats incorporating both amplitude- and phase-based data symbols are necessary to meet the spectral efficiency requirements of fiber-optic data transport. These modulation formats require coherent detection, enabling future networks to take advantage of advances in silicon CMOS via digital signal processing algorithms and techniques.
The primary challenge for future networks is the fiber nonlinear response; changes in the intensity of the propagating optical signal induce changes in the optical fiber refractive index. Limiting the allowed propagation intensity will reduce these nonlinear effects and correspondingly limit the total available signal-to-noise ratio (SNR) within the channel. Predicting the nonlinear SNR limits of fiber-optic transport for data rates 100 Gb/s and beyond is a primary purpose of this research.
This dissertation expressly matches several novel expressions for nonlinear interference accumulation to experimental data and demonstrates robust theoretical prediction of nonlinear transmission penalties. The experiments were performed to isolate the transmission performance of the fiber medium in the highly dispersive regime -- no dispersion compensation or Raman amplification was employed and all other hardware was kept static. These results are the first experimental validation of the nonlinear interference expressions on a fiber-type basis.
Second, this dissertation moves to data transport beyond per-wavelength rates of 100 Gb/s by employing 16QAM at baud rates as high as 32 GHz. It examines signal processing strategies for 16QAM transport and extends the nonlinear interference prediction techniques to 16QAM. The results reveal that the SNR requirements of 16QAM as limited by nonlinear interference will likely limit deployments to high-density regional and metro networks.
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Podpaly, Yuri Anatoly. "Rotation generation and transport in tokamak plasmas." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/77061.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 187-201).
Plasma toroidal rotation is a factor important for plasma stability and transport, but it is still a fairly poorly understood area of physics. This thesis focuses on three aspects of rotation: momentum transport, Ohmic rotation reversals, and LHCD induced rotation. Momentum transport is approached in a semi-empirical method through the development of the "Toy Model." The "Toy Model" assumes that the toroidal momentum is transported via diffusive and convective profiles, and, using assumptions about the diffusive and convective terms, it can generate the profiles of the residual stress or source as a function of space and time. Several resultant source profile calculations are shown for SSEP sweeps, rotation reversals, H-modes, and I-modes. Generally, it is observed that the convective profiles do not greatly improve the fits to the data, and that source profiles have peaks around the steep core rotation gradient region of the plasma. Rotation reversals, spontaneous reversals of the rotation direction during the Ohmic phase, are also described in this work. It is seen that they are related to the Linear Ohmic Confinement (LOC) to Saturated Ohmic Confinement (SOC) regime changeover. This relation is supported through linear gyrokinetic simulations that show that the co- to counter- reversal coincides with a change from marginally electron to ion diamagnetic direction most unstable modes which is believed to play a role in the LOC to SOC explanation as well. Lower Hybrid Current Drive (LHCD) induced rotation is also described, including the first experimental observations of bi-directional rotation on a single tokamak. These observations help to explain differences in rotation seen among the various devices running lower hybrid. The LHCD rotation reverses direction as a function of plasma current, and this occurs in a similar parameter space as the Ohmic rotation reversal; it also has turbulence changes that are reminiscent of the Ohmic reversal as well. This suggests that LHCD is, in fact, causing the plasma to transition from the ITG dominated regime to the TEM dominated regime, which explains the rotation differences. These experiments and models provide new tools to understand rotation transport and generation in tokamaks.
by Yuri Anatoly Podpaly.
Ph.D.
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Blanquart, Fanny. "Perspectives for Power Generation fromIndustrial Waste Heat Recovery." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-215985.
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Schnauß, Jörg, Martin Glaser, Carsten Schuldt, Tom Golde, Tina Händler, Sebastian Schmidt, Stefan Diez, and Josef Käs. "Motor-free force generation in biological systems." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198921.
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A central part of soft matter physics is the investigation of effects in an active environment. These systems are driven out of equilibrium by a constant energy consumption. In biological systems, for instance, energy is consumed in the dynamic polymerization process of cytoskeletal filaments or by motor-filament interactions. These active processes convert chemical energy into mechanical work and impede a trapping of cellular structures in thermodynamically frozen states. Thus, active soft matter is crucial for biological systems to fulfill a broad range of tasks. Inherent physical principles relying on entropy maximizing arguments, however, cannot be easily switched off even in active systems. Cells might even employ these principles to accomplish certain tasks without the need to arrange elaborate, energy dissipating structures. Within the presented studies we demonstrate possibilities how biological relevant forces can be generated in the absence of any active accessory proteins. The presented studies are based on the cytoskeletal key components actin and microtubules. We demonstrate different approaches ranging from light induced softening to cross-linker expansion, which realize entropy driven contractions of the according system.
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Hlubek, Nikolai. "Magnetic heat transport in one-dimensional quantum antiferromagnets." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-70187.
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Fundamental conservation laws predict a dissipationless transport behavior in one-dimensional S=1/2 spin chains. This truly ballistic heat transport suggests anomalously large life times and mean free paths of the elementary excitations of the spin chain, spinons. Despite this rigorous prediction, in any real system, the transport is dissipative, due to the interaction of spinons with defects and phonons. Nevertheless, a promising large magnetic thermal conductivity \\kappa_{mag} has been observed in a few copper-oxide systems. Characteristic for these cuprate systems is a large exchange interaction J along the spin chain. However, due to the limited number and knowledge of the systems showing a large \\kappa_{mag}, it has been difficult, to identify overarching trends. The goal of this thesis therefore is twofold. First, to test new compounds for the appearance of magnetic heat transport and second, to broaden the understanding of the known compounds by studying the influence of various kinds of impurities.
In particular, three families of materials are studied. First, the thermal conductivity \\kappa(T) of the compounds TiOBr and TiOCl is investigated. Below room temperature the compounds undergo two phase transitions T_{c2} and T_{c1}. Above T_{c2} the compounds contain S=1/2 spin chains with J_{Cl}=676 K and J_{Br}=375 K respectively, formed by direct orbital overlap of the Ti-atoms. Below T_{c1} the chains dimerize to form a non-magnetic ground state. The thermal conductivity exhibits pronounced anomalies at T_{c2} and T_{c1} confirming the transitions being of second and first order respectively. Surprisingly, \\kappa(T) appears to be dominated by phonon heat conduction, since no indications of a significant magnetic contribution is found. This is in contrast to the expectation of a spin chain system. In this context possible scenarios to understand the unusual behavior of the thermal conductivity are discussed.
Second, two related materials, the single chain Sr_{2}CuO_{3} and the double chain SrCuO_{2} are investigated. In high purity samples huge magnetic heat conductivities and concomitantly, extremely large spinon mean free paths of >0.5 µm for Sr_{2}CuO_{3} and >1 µm for SrCuO_{2} are observed. This demonstrates that \\kappa_{mag} is only limited by extrinsic scattering processes, which is a clear signature of ballistic transport in the underlying spin model. Additionally, various subtle modifications of the spin chain are studied. Due to the large mean free path a pristine picture of the intrinsic incidents is expected. In particular, a chemical pressure is applied to the spin chain by doping SrCuO_{2} with Ca. This has a surprisingly strong effect on \\kappa_{mag}. Furthermore, the influence of magnetic Ni and non-magnetic Mg doping is studied for SrCuO_{2}. While Ni-doping has a large impact on the magnetic thermal conductivity, Mg-doping shows no influence. In order to clarify this surprising behavior, \\kappa_{mag} is compared to measurements of the single chain compound Sr_{2}CuO_{3}.
Third, the magnetic thermal conductivity of the spin chain material CaCu_{2}O_{3} doped with non-magnetic Zn impurities is studied. \\kappa_{mag} of the pure compound is linear up to room temperature, which is indicative of a T-independent scattering rate of the magnetic excitations. Both, magnitude and T-dependence of \\kappa_{mag} exhibit a very unusual doping dependence. At moderate Zn-doping the linear temperature dependence of \\kappa_{mag} is preserved and the absolute value of \\kappa_{mag} increases. A slight suppression of \\kappa_{mag} occurs only at high Zn doping, where, surprisingly, the T-dependence of \\kappa_{mag} changes from linearity to one with a higher power of T . In order to clarify this surprising behavior, the results are compared to a detailed study of the g-tensor of the impurities in the material by means of ESR experiments, which reveal a change of the impurity type with increasing Zn-content.
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Jeong, Taehee. "Spin-dependent heat transport and thermal boundary resistance." Research Showcase @ CMU, 2011. http://repository.cmu.edu/dissertations/66.
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Spin-dependent heat transport is a new research area and can create many future applications. The Giant Magnetoresistance (GMR) effect, which was discovered in 1988, is significant change in electric resistance due to spin-dependent electron scattering. The GMR effect has greatly impacted on techniques of data storage and magnetic sensors. For example, the areal density of hard disk drive was increased 100 times using the GMR effect. Likewise, spin-dependent heat transport, which is also called the Giant Magnetothermal Resistance (GMTR) effect, is expected to create a wealth of new applications, for example nanoscale heat or temperature detectors and spin thermoelectrics. In addition, the technique developed for this study will help with heat management in micro/nano electronics including data storage devices and heat/energy assisted magnetic recording.
In this thesis, thermal conductivity change depending on the magnetic configurations has been studied. In order to make different magnetic configurations, we developed a spin valve structure, which has high MR ratio and low saturation field. The high MR ratio was achieved using Co/Cu multilayer and 21Å or 34Å thick Cu layer. The low saturation field was obtained by implementing different coercivities of the successive ferromagnetic layers. For this purpose, Co/Cu/Cu tri-layered structure was used with the thicknesses of the Co layers; 15 Å and 30 Å. For the thermal conductivity measurement, a three-omega method was employed with a thermally isolated microscale rod. We fabricated the microscale rod using optical lithography and MEMS process. Then the rod was wire-bonded to a chip-carrier for further electrical measurement. For the thermal conductivity measurement, we built the three-omega measurement system using two lock-in amplifiers and two differential amplifiers. A custom-made electromagnet was added to the system to investigate the impact of magnetic field.
We observed titanic thermal conductivity change depending on the magnetic configurations of the Co/Cu/Co multilayer. The thermal conductivity change was closely correlated with that of the electric conductivity in terms of the spin orientation, but the thermal conductivity was much more sensitive than that of the electric conductivity. The relative thermal conductivity change was 50% meanwhile that of electric resistivity change was 8.0%. The difference between the two ratios suggests that the scattering mechanism for charge and heat transport in the Co/Cu/Co multilayer is different. The Lorentz number in Weidemann-Franz law is also spin-dependent. The application of this significant thermal conductivity change is remained for future work.
Thermal boundary resistance between metal and dielectrics was also studied in this thesis. The thermal boundary resistance becomes critical for heat transport in a nanoscale because the thermal boundary resistance can potentially determine overall heat transport in thin film structures. A transient thermoreflectance (TTR) technique can be used for measuring the thermal conductivity of thin films in cross-sectional direction. In this study, a pump-probe scheme was employed for the TTR technique. We built an optical pump-probe system by using a nanosecond pulse laser for pumping and a continuous-wave laser for probing. A short-time heating event occured at the surface of a sample by shining a laser pulse on the surface. Then the time-resolved thermoreflectance signals were detected using a photodetector and an oscilloscope. The increased temperature decreases slowly and its thermal decay depends on the thermal properties of a sample. Since the reflectivity is linearly proportional to the temperature, the time-resolved thermoreflectance signals have the information of the thermal properties of a sample. In order to extract the thermal properties of a sample, a thermal analysis was performed by fitting the experimental data with thermal models. We developed 2-layered and 3-layered thermal models using the analogies between thermal conduction and electric conduction and a transmission-line concept.
We used two sets of sample structures: Au/SiNx/Si substrate and Au/CoFe/SiNx/Si substrate with various thickness of SiNx layer. Using the pump-probe system, we measured the time-resolved thermoreflectance signals for each sample. Then, the thermal conductivity and thermal boundary resistance were obtained by fitting the experimental data with the thermal models. The thermal conductivity of SiNx films was measured to be 2.0 W/mK for both structures. In the case of the thermal boundary resistance, it was 0.81´10-8 m2K/W at the Au/SiNx interface and 0.54´10-8 m2K/W at the CoFe/SiNx interface, respectively. The difference of the thermal boundary resistance between Au/SiNx and CoFe/SiNx might be came from the different phonon dispersion of Au and CoFe. The thermal conductivity did not depend on the thickness of SiNx films in the thickness range of 50-200nm. However, the thermal boundary resistance at metal/SiNx interfaces will impact overall thermal conduction when the thickness of SiNx thin films is in a nanometer order. For example, apparent thermal conductivity of SiNx film becomes half of the intrinsic thermal conductivity when the thickness decreases to 16nm. Therefore, it is advised that the thermal boundary resistance between metal and dielectrics should be counted in nano-scale electronic devices.
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Sulistyo, Hary. "Axial and radial heat transport in packed beds." Thesis, University of Salford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293824.
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Raju, Mandhapati P. "HEAT AND MASS TRANSPORT INSIDE A CANDLE WICK." Case Western Reserve University School of Graduate Studies / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1157564736.
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Hamed, Myriam. "Electron heat transport in tokamak H-mode pedestals." Electronic Thesis or Diss., Aix-Marseille, 2019. http://theses.univ-amu.fr.lama.univ-amu.fr/191128_HAMED_534gjvrc761ijwn176jbu525de_TH.pdf.
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Dans les plasmas en mode H, la modélisation de la dynamique du piédestal est une question importante pour prédire les profils de température et de densité dans le bord et le cœur des tokamaks. Le modèle EPED , basé sur la stabilité de modes Magnetohydrodynamiques, est le plus souvent utilisé pour caractériser la région du piédestal. Ce modèle EPED ne prend pas en compte les microinstabilités pouvant se développer dans la région du piédestal. Ainsi, la prédiction des caractéristiques du piédestal est toujours une question ouverte. De plus, certaines analyses récentes des plasmas JET suggèrent qu’une autre classe d’instabilités, appelée modes de microdéchirement, peut être responsable du transport de chaleur des électrons et jouer ainsi un certain rôle dans la détermination des caractéristiques du piédestal. Les modes de microdéchirement appartiennent à une classe d’instabilités où une modification de la topologie des lignes de champ magnétique. Cela conduit à la formation d’îlots magnétiques qui peuvent augmenter le transport de chaleur électronique. La stabilité des MTMs a été théoriquement étudiée dans le passé, montrant qu’une couche de courant est stable en l’absence de collisions. En revanche, des simulations gyrocinétiques récentes ont révélé que les MTMs étaient instables, même à faible collisionalité. Le but de cette thèse est d'améliorer la compréhension de la stabilité des modes de microdéchirement en comparant une théorie analytique avec des simulations gyrocinétique. Plus précisément, différents mécanismes physiques (dérive magnétique..) ont été ajouté progressivement au modèle dans le but de réconcilier les résultats numériques avec la théorie analytiqueIn H-mode plasmas, the modeling of the pedestal dynamics is an important issue to predict temperature and density profiles in the tokamak edge and therefore in the core. The EPED model, based on the stability of large scales MagnetoHydroDynamic (MHD) modes, is most commonly used to characterize the pedestal region. The EPED model has been successful until now. However, EPED model does not take into account small scales instabilities linked the the sharp pressure gradient and the pedestal characteristics prediction in terms of width and height is still open. Moreover, some recent analysis of JET plasmas suggest that another class of instabilities, called microtearing modes, may be responsible for electron heat transport in the pedestal, and thereby play some role in determining the pedestal characteristics. Microtearing modes belong to a class of instabilities where a modification of the magnetic field line topology is induced at the ion Larmor radius scale. This leads to the formation of magnetic islands, which can enhance the electron heat transport. The stability of MTMs has been theoretically studied in the past showing that a slab current sheet is stable in the absence of collisions. In contrast, recent gyrokinetic simulations in toroidal geometry found unstable MTMs, even at low collisionality. The purpose of our work is to improve the MTM stability understanding by comparing new analytical theory to linear gyrokinetic simulations. More precisely, physical mechanisms (magnetic drift, electric potential) are progressively included in the analytical description to recover the numerical simulations results and to "reconcile" numerical MTM investigations with theory
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Fleming, Laura Elizabeth. "The Influence of heat transport on Arctic amplification." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122324.
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Thesis: S.M., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 53-58).
The Arctic surface air temperature has warmed nearly twice as much as the global mean since the mid-20th century. Arctic sea ice has also been declining rapidly in recent decades. There is still discussion about how much of this Arctic amplification is caused by local factors, such as changes in surface albedo, versus remote factors, such as changes in heat transport from the midlatitudes. This thesis focuses mainly on the role of poleward heat transport on Arctic amplification. Most of the previous studies on this topic have defined ocean heat transport as the zonally averaged ocean heat transport at 65°N or 70°N, which ignores the physical pathways of heat into the Arctic and may include recirculation of heat in the North Atlantic. In this thesis, we define the ocean heat transport as the heat transport across five sections surrounding the Arctic, to create a closed domain in the Arctic.
Previous studies on Arctic amplification have used either a single model run or have compared results from a multi-model ensemble. While the multi-model ensemble approach may potentially average out biases in individual models, the ensemble spread confounds the model differences and the internal climate variability. In this thesis, we investigate the Arctic amplification in the Community Earth System Model version 1 (CESMi) Large Ensemble. The CESMI Large Ensemble includes 40 members that use the same model and external forcing, but different initializations. This simulates different climate trajectories that can occur in a given atmosphere-ocean-land-cryosphere system. We find that CESMI Large Ensemble projects a large increase towards the end of the 21st century in ocean heat transport into the Arctic, and that the increase in ocean heat transport is significantly correlated with Arctic amplification.
The main contributor to the increase in ocean heat transport is the increase across the Barents Sea Opening. The increase in Barents Sea Opening ocean heat transport is highly correlated with the decrease in sea ice in the Barents-Kara Sea region. We propose that this is because the increase in ocean heat transport melts the ice at the sea ice margin, which results in increased surface heat flux from the ocean and further local feedback through decreased surface albedo and increased cloud coverage. We also find that while the changes in atmosphere heat transport into the Arctic circle at 66.5 N are on the same order as the changes in ocean heat transport, they are not correlated with Arctic amplification.
by Laura Elizabeth Fleming.
S.M.
S.M. Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)
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BAIOCCHI, BENEDETTA. "UNDERSTANDING AND PREDICTING ION HEAT TRANSPORT IN TOKAMAKS." Doctoral thesis, Università degli Studi di Milano, 2012. http://hdl.handle.net/2434/170629.
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One of the most attractive options to satisfy the continuously growing world energy demand is controlled thermonuclear fusion. The scientific and technological work for achieving it has been significantly boosted after the recent decision to build the international tokamak ITER (International Thermonuclear Experimental Reactor). Amongst the physical problems still open, understanding and controlling heat transport is of primary importance for the optimization of the operational scenarios of ITER. Given the complexity of plasma transport processes, a full theoretical understanding of the experimental observations and validated numerical models for the simulation of a complete tokamak discharge are not yet available. Work in this field is therefore actively ongoing, with a view to increasing integration between theoretical developments, experimental results and numerical predictions. This is the context in which the present thesis work takes place. It has long been known that the high measured levels of heat transport in tokamaks are due to turbulent phenomena, in particular the so-called drift waves. The ion heat transport, on which is focused this thesis, is carried by ion temperature gradient (ITG) modes, that are destabilized when a threshold value of the inverse ion temperature gradient length (1/LTi=|∇Ti/Ti|) is exceeded. Above threshold, the ion heat flux is a strongly increasing function of 1/LTi, which prevents the Ti profiles from departing significantly from threshold, a property known as profile stiffness. The main target of ion heat transport studies is to find ways to suppress or mitigate ITG modes, namely by increasing the threshold or reducing the stiffness level, in order to be able to achieve high core Ti values without having to rely on too high edge Ti values, which would raise plasma-wall interaction issues. Sophisticated ion heat transport experiments carried out at the JET tokamak have recently indicated that a strong reduction of ion stiffness takes place in presence of low magnetic shear and high toroidal rotation. This mechanism has been proposed as the key ingredient to explain the improved core ion confinement observed in Hybrid scenarios or Advanced Tokamak (AT) scenarios with Internal Transport Barriers, two regimes that are considered for ITER operations beyond the standard inductive H-mode regime.
This thesis work starts from the above mentioned JET results and from the already developed theoretical models and existing numerical codes, and includes four main items of work, with the purpose of integrating experimental analysis and theory-based numerical modelling of JET experiments, in order to reach predictive capabilities for the future tokamak FAST, a device proposed by the Italian Fusion Association as a possible ITER satellite. First, new experiments have been carried out in JET and analyzed in detail, in order to assess if the cause for ion stiffness reduction is the rotation value or the rotational shear. The data analysis has given as result that it is the absolute value of the rotational shear the key factor for ion stiffness mitigation. This gives the indication for ITER that the necessary condition for reducing the ion stiffness and access improved core confinement regimes is to induce some rotational shear, which may be easier than achieving high absolute values of rotation.
Second, a numerical study has been carried out in JET and ITER plasmas to quantify the impact of ion threshold and stiffness on global confinement and fusion power compared to the effect of edge Ti value. This work has the aim of evaluating if threshold and particularly stiffness are indeed two useful control tools for scenario performance optimization. The variation of global confinement has been found quantitatively significant for changes of the ion stiffness, and comparable with the ones due to changes of ion threshold and Ti pedestal height, when they are varied in an experimentally realistic range. In ITER, the calculated fusion power, which is what really matters for a fusion device, is as much affected by variations of ion stiffness as by changes of ion threshold and Ti pedestal height. This work gives the indication that all the three investigated parameters influence comparably the core performances in present and future machines. In particular the quantitative level of ion stiffness, which is a parameter not much considered until now, and assumed or predicted very high in most existing models, can be a useful knob to act upon in order to optimize the scenario performance and must be taken into account for an accurate predictive modelling of future machines.
Third, a prediction work for the foreseen scenarios of FAST has been carried out, using a mixture of first-principle models and experiment driven considerations. The results obtained in the two previous steps have led to the conviction that predictive modelling of future devices cannot neglect including toroidal rotation profiles and their effects on transport, which is not common practice in tokamak simulation work. Both H-modes and fully non-inductive AT scenarios have been simulated, predicting profiles of current, ion and electron temperature, density and toroidal rotation. Various heating options have been explored. The simulations have provided a set of FAST scenarios in which fast particle and burning plasma studies can be performed, reaching values of thermal and fast particle energy contents well in line with the needs for exciting meso-scale fluctuations with the same characteristics of those expected in reactor relevant conditions.
Fourth, linear gyro-kinetic simulations have been carried out to check the validity of simplified threshold formulae used in simulations in the high toroidal field and high density FAST plasmas. Very good agreement was found between the analytical threshold approximation and the GKW simulations with adiabatic electrons, whilst the threshold with kinetic electrons is slightly lower. The discrepancy is anyway small enough to justify the use of the threshold analytic approximation for FAST simulations, taking into account the other sources of uncertainty linked to various other modelling approximations and to empirical extrapolations from experimental data of existing machines.
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Souccar, Adham. "Heat transfer and mass transfer with heat generation in drops at high peclet number /." Connect to Online Resource-OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1177603981.
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Dissertation (Ph.D.)--University of Toledo, 2007.Typescript. "Submitted as partial fulfillment of the requirements for The Doctor of Philosophy degree in Engineering." Bibliography: leaves 65-74.
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Souccar, Adham W. "Heat Transfer and Mass Transfer with Heat Generation in Drops at High Peclet Number." University of Toledo / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1177603981.
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Memon, Rizwan Ahmed. "Statistical analysis of urban heat island and modeling of heat generation within street canyon." Thesis, Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42664445.
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Velayutham, Aravind Murugesan. "Transport Protocols for Next Generation Wireless Data Networks." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6957.
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Emerging wireless networks are characterized by increased heterogeneity in wireless access technologies as well as increased peer-to-peer communication among wireless hosts.
The heterogeneity among wireless access interfaces mainly exists because of the fact that different wireless technologies deliver different performance trade-offs.
Further, more and more infrastructure-less wireless networks such as ad-hoc networks are
emerging to address several application scenarios including military and disaster recovery. These infrastructure-less wireless networks are characterized by the peer-to-peer communication
model. In this thesis, we propose transport protocols that tackle the challenges that arise
due to the above-mentioned properties of state-of-the-art wireless data networks.
The main contributions of this work are as follows:
1. We determine the ideal nature and granularity of transport adaptation for efficient operation in heterogeneous wireless data networks by performing comprehensive experimental analysis. We then design and implement a runtime adaptive transport framework, *TP, which accommodates the capabilities of the ideal transport adaptation solution.
2. We prove that conversational transport protocols are not efficient under peer-to-peer wireless data networks. We then design and implement NCTP which is a non-conversational transport protocol.
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Işık, Emre. "Magnetic flux generation and transport in cool stars." [Katlenburg-Lindau] Copernicus Publ, 2008. http://d-nb.info/988508087/04.
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Hu, Xiaoqin. "Modelling and simulation of soot generation and transport." Thesis, University of Greenwich, 2016. http://gala.gre.ac.uk/18094/.
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Soot released from fires not only causes danger to lives and property damage, but also effects fire spread by altering the radiation characteristics of fire effluents. In many situations, it is the soot concentration that controls the fire development. Therefore, soot modelling is of great importance in fire safety science. This necessitates the development of a global and general soot model within fire field models that can simulate the amount of soot generated and transported in large-scale fires in order to obtain an accurate soot concentration distribution within the building. A soot transport model, called Multi-Particle-Size (MPS) model, has been developed in this study to improve the prediction of soot particle behaviour during transportation by considering the uneven soot mass size distributions and gravitational settling force on soot particles. The efficiency of the MPS model was investigated by simulating soot movements in three real experiments. The first two validation experiments were cable fires in a large-scale enclosed corridor and the third experiment analysed the soot produced from a soot generator in a warehouse with a high ceiling. The soot layers predicted by the MPS model matched the measurements/observation better than that from the Conventional Model in which the soot generation is modelled with a constant soot yield (CY) value and soot particles are treated as a gaseous combustion product. A global soot generation model, called Beta soot generation (BSG) model has also been developed for non-premixed laminar flames. By making use of the characteristics of the beta function, the model has been extended to turbulent flames in the pre-scribed probability density function (PDF) approach with low cost in terms of computational resources. The model was validated by two turbulent methane and ethylene pool fires. The simulation results demonstrated that the soot volume fractions produced by the BSG model were in good agreement with the experimental data. Further, the two new models have been integrated into a single soot model called BSG+MPS model. The performance of the model was examined by predicting the soot generation and transport in a large-scale enclosed corridor. The BSG+MPS model improved the prediction of soot concentration distribution in the corridor compared with the CY +MPS model. Finally, the entire work is summarised and future work is suggested.
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Wieczorek, Christopher John. "Carbon Monoxide Generation and Transport from Compartment Fires." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/28006.
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The aim of the present research was to gain a better understanding of the species generation and transport from enclosure fires. The species generation experiments were conducted with a half-scale ISO 9705 enclosure with three different ventilation conditions and heat release rates ranging from 50 kW to 500 kW. The transport study was conducted with a 6.1 m long hallway connected to the compartment in a head-on configuration. All measurements were performed at the compartment or hallway exit plane during the steady-state period of the fire. Measurements included species mole fractions of oxygen, carbon dioxide, carbon monoxide, and unburned hydrocarbons, along with gas pressure (used to determine gas velocities) and gas temperatures.
Species mappings performed at the exit plane of the compartment indicated that the exiting species are not spatially uniform. Horizontal and vertical gradients in the species mole fractions were observed for all ventilation conditions and heat release rates examined.
Predictive techniques developed previously were applied to the data obtained in the present study and were determined to be inappropriate for situations were the plume equivalence ratio was not equal to the global equivalence ratio. A new methodology for predicting species levels at the exit plane of an enclosure was developed. The proposed methodology correlates the species yields based on the combustion within the compartment as a function of a non-dimensional heat release rate. The non-dimensional heat release rate is based on the fuel load and geometrical parameters of the enclosure. The present methodology in applicable to situations where a well-mixed uniform layer is not present and the overall global conditions are of interest.
Species transport to remote locations was also examined. Experiments were conducted with the baseline ventilation at x = 0 m (the compartment/hallway interface) and three different ventilation conditions at x = 6.1 m (end of hallway). The three ventilation conditions consisted of the narrow, baseline, and wide doorways. Experiments were conducted for heat release rates of 85 kW, 127 kW, and 150 kW. The results from the tests indicated that, for over-ventilated compartment fires, the hallway and hallway ventilation had no impact on the species generation within the compartment. This allows the correlations developed from the compartment study to be applied to more complex scenarios.
Differences in species mole fractions between x = 0 m and x = 6.1 m were shown to be a result of air entrainment into the upper layer within the hallway, which acted as a dilutent or as a source of oxygen for further oxidation reactions. For non-dimensional heat release rates less than 1.0, the reduction in carbon monoxide levels along the hallway was a result of dilution, while for non-dimensional heat release rates greater than or equal to 1.0 the reduction in carbon monoxide levels along the hallway was a combination of dilution and further oxidation reactions.Ph. D.
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Wüthrich, Stefan. "Generation and transport of 2,9 [my]m radiation /." Bern, 1991. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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Gao, Yufei. "Model of Heat Generation Effects During Uniaxial Tensile Test." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1391590277.
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Davison, Thomas M. "Numerical modelling of heat generation in porous planetesimal collisions." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6333.
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An important unanswered question in planetary science is how planetesimals, the ~1–100 km solid precursors to asteroids and planets, were heated in the early Solar System. This thesis quantifies one possible heat source: planetesimal collisions. Recent work has predicted that collision velocities and planetesimal porosities were likely to have been higher than previously thought; this is likely to have significant implications on collision heating. The approach adopted in this research was to numerically model shock heating during planetesimal collisions. Simulations showed that an increase in porosity can significantly increase heating: in a 5 km s-1 collision between equal sized, non-porous planetesimals, no material was heated to the solidus, compared to two thirds of the mass of 50% porous planetesimals. Velocity also strongly influences heating: at 4 km s-1, an eighth of the mass of 50% porous planetesimals was heated to the solidus, compared to the entire mass at 6 km s-1. Further simulations quantified the influence on heating of the impactor-to-target mass ratio, the initial planetesimal temperature and the impact angle. A Monte Carlo model was developed to examine the cumulative heating caused by a population of impactors striking a parent body. In the majority of collisions the impactor was much smaller than the parent body, and only minor heating was possible. However, some larger or faster impactors were capable of causing significant heating without disrupting the parent body; these collisions could have heated up to 10% of the parent body to the solidus. To cause global heating, the collision must have catastrophically disrupted the parent body. The increase in specific internal energy from collisions was compared with the decay of short-lived radionuclides. In the first ~6 Ma, radioactive decay was the most important heat source. After ~10 Ma, the energy caused by collisions was likely to have overtaken radioactive decay as the dominant source.
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Benjamin, Daniel. "Thermal transport and photo-induced charge transport in graphene." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42746.
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The electronic material graphene has attracted much attention for its unique physical properties such as, linear band structure, high electron mobility, and room temperature ballistic conduction. The possibilities for device applications utilizing graphene show great variety, from transistors for computing to chemical sensors. Yet, there are still several basic physical properties such as thermal conductivity that need to be determined accurately.
This work examines the thermal properties of graphene grown by the chemical vapor deposition technique. The thermoelectric power of graphene is studied in ambient and vacuum environments and is shown to be highly sensitive to surface charge doping. Exploiting this effect, we study the change in thermoelectric power due to introduction of gaseous species. The temperature dependent thermal conductivity of graphene is measured using a comparison method. We show that the major contribution to the thermal conductivity is the scattering of in-plane phonons.
Graphene also shows promise as an optoelectronic material. We probe the Landau level structure of graphene in high magnetic fields using a differential photoconductivity technique. Using this method we observed the lifting of spin and valley degeneracies of the lowest Landau level in graphene.
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Hofmann, Michael. "Anomalous heat transport in low dimensional quantum spin systems." [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=964915626.
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Lambert, Patrik. "Heat transport in bismuth and electron-doped cuprate superconductors." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0027/MQ50810.pdf.
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Lambert, Patrik 1973. "Heat transport in bismuth and electron-doped cuprate superconductors." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21584.
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Thermal conductivity is a powerful probe of electronic quasiparticles, especially at low temperatures. At higher temperatures it gives very useful information on the behavior of quasiparticles and phonons, however both contributions are more difficult to identify precisely.We carried out a comparative study of the thermal conductivity in the hole and electron-doped cuprates, focussed on Bi2Sr2CaCu 2O8 (hole-doped) and Pr1.85Ce0.15CuO 4 (electron-doped). After a brief review of the literature it was clear that these families show very different physical properties, although they present similar features in their structure and phase diagram.
We detected the presence of a residual normal fluid in Bi2Sr 2CaCu2O8, in rather good agreement with the theory for d-wave superconductors, and showed its absence in Pr 1.85Ce0.15CuO4, firm indication of a nodeless gap. At higher temperatures we observed for the first time a peak below Tc in the thermal conductivity of Pr1.85Ce 0.15CuO4.
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Chughtai, Zahoor. "Nuclear transport of heat shock proteins in stressed cells." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37616.
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Nuclear import of proteins that are too large to passively enter the nucleus requires soluble factors, energy, and a nuclear localization signal (NLS). Nuclear protein transport can be regulated, and different forms of stress affect nucleocytoplasmic trafficking. As such, import of proteins containing a classical NLS is inhibited in starving yeast cells. In contrast, the heat shock protein hsp70 Ssa4p concentrates in nuclei upon starvation. Nuclear concentration of Ssa4p in starving cells is reversible, and transfer of nutrient-depleted cells to fresh medium induces Ssa4p nuclear export. This export reaction represents an active process that is sensitive to oxidative stress. Upon starvation, the N-terminal domain of Ssa4p mediates Ssa4p nuclear accumulation, and a short hydrophobic sequence, termed Star (for starvation), is sufficient to localize the reporter proteins green fluorescent protein or beta-galactosidase to nuclei. To determine whether nuclear accumulation of Star-beta-galactosidase depends on a specific nuclear carrier, I have analyzed its distribution in mutant yeast strains that carry a deletion of a single beta-importin gene. With this assay I have identified Nmd5p as a beta-importin required to concentrate Star-beta-galactosidase in nuclei of stationary phase cells.
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Mead, C. T. "Asymmetries of oceanic thermohaline circulation and meridional heat transport." Thesis, University of Southampton, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234444.
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PACHECO, HUGO GUILLERMO JIMENEZ. "TRANSPORT COEFFICIENTS OF ICE SLURRY IN PLATE HEAT EXCHANGER." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2003. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=4382@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOO uso da pasta de gelo começou recentemente a ser aplicado em sistemas de refrigeração e condicionamento de ar. Como principais vantagens deste fluido, podem ser citados: a possibilidade de armazenar calor latente do gelo e a possibilidade de ser bombeado como a água fria. Assim, o pasta de gelo pode ser usado para o armazenamento térmico no lugar da água fria ou do gelo, desde que, até determinadas concentrações, possa ser bombeado através dos trocadores de calor. Para que esta tecnologia seja aceita extensamente, informações de engenharia são requeridas nas características de transporte nos equipamentos de troca de calor. Um dispositivo experimental foi desenvolvido para estudar os coeficientes de transporte do pasta de gelo em um trocador de calor de placas, utilizando água como carga térmica a resfriar. Foram investigadas várias situações para diferentes frações iniciais e vazões do pasta de gelo. As condições de entrada da carga térmica, foram mantidas constantes. São monitoradas a temperatura, a queda de pressão, a fração do gelo sólido e a vazão do pasta de gelo no trocador de calor, assim como a vazão e a de temperatura na parte da carga térmica. Os resultados mostram que o coeficiente global de troca de calor aumenta com aumento da fração inicial do gelo. A capacidade do resfriamento do trocador de calor aumenta consideravelmente, em relação da água, quando a pasta de gelo, é utilizada como fluido secundário. Finalmente, a queda de pressão aumenta com o aumento da fração inicial de gelo.
The use of the ice slurry is recently applied in the refrigeration and air conditioning systems. Advantages such as the possibility to store latent heat on ice and the possibility of being pumped as cold water can be considered. Ice slurries can be used both for cold storage in place of chilled water or ice and as a secondary refrigerant since, up to certain concentrations, they can be pumped directly through distribution pipeworks and heat exchangers. For ice slurries to become more widely accepted, however, more engineering information is required on fluid flow and heat transfer characteristics. An experimental device was developed to study the transport properties of the ice slurry in plate heat exchangers. Several situations were investigated for different initial fractions and flows of ice slurry. The conditions of the thermal load (pure water), had been kept constant. The temperature field, the pressure loss, the initial fraction and the flow of ice slurry are monitored in the heat exchanger, beyond the flow and the temperature field is monitored in the part of the thermal load. The overall heat transfer coefficient, increases in function of the initial ice fraction. The capacity cooling of the heat exchanger increases with the use of ice slurry when compared to pure water. Finally can be showed that the loss of pressure increases for higher initial ice fraction.
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Iskandar, Abdo. "Phonon Heat Transport and Photon-phonon Interaction in Nanostructures." Thesis, Troyes, 2018. http://www.theses.fr/2018TROY0010.
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Cette thèse avait pour cadre, le contrôle du transport thermique via les phonons et leur interaction avec des photons dans des nanostructures. Le manuscrit comprend cinq chapitres. Dans le premier, nous introduisons la physique des phonons et excitations élémentaires optiques de la matière. Le deuxième chapitre fournit une description des procédés de croissance, techniques de structuration et techniques de caractérisation utilisées. Dans le troisième chapitre, nous démontrons qu’à la fois, phonons et photons peuvent être confinés et interagir dans une même nanostructure. Dans le quatrième chapitre, nous montrons expérimentalement que le spectre de phonons d'un matériau peut être modifié par des mécanismes d'hybridation entre des modes de surface introduits par une nanostructuration et les modes normaux du matériau massif. Nous montrons que la forme et la taille des nanostructures sur la surface du matériau ont des effets sur le spectre de phonons du substrat. Dans le cinquième chapitre, nous montrons qu'à basse température (inférieure à 4 K), la chaleur spécifique des nanofils est équivalente à celle d'un cristal essentiellement bidimensionnel. Encore plus étonnant à l'interface entre les nanofils et le substrat, nous avons mis en évidence une transition entre une transmission élastique spéculaire et une transmission élastique diffuse. Lorsque la température augmente on observe alors une transition entre une diffusion élastique et une diffusion inélastique. L’ensemble de ces résultats laisse entrevoir des perspectives intéressantes pour le contrôle des propriétés thermiques de matériaux massifs par nanostructuration de surfaceIn this dissertation, we investigate phonon heat transport and phonon interaction with optical elementary excitations in nanostructures. In the first chapter, we present an introduction to the physics of phonons and optical elementary excitations in nanostructured materials. The second chapter provides a detailed description of the samples growth and fabrication procedures and the various characterization techniques used. In the third chapter, we demonstrate that phonons and photons of different momenta can be confined and interact with each other within the same nanostructure. In the fourth chapter, we present experimental evidence on the change of the phonon spectrum and vibrational properties of a bulk material through phonon hybridization mechanisms. We demonstrate that the phonon spectrum of a bulk material can be altered by hybridization between confined phonon modes in nanostructures introduced on the surface of the material and the underlying bulk phonon modes. Shape and size of the nanostructures made on the surface of the substrate have strong effects on the phonon spectrum of the bulk material itself. In the fifth chapter, we demonstrate that at low temperatures (below 4 K) the nanowire specific heat exhibits a clear contribution from an essentially two-dimensional crystal. We also demonstrate that transitions from specular to diffusive elastic transmission and then from diffusive elastic to diffusive inelastic transmission occur at the interface between nanowires and a bulk substrate as temperature increases. Perspectives include the control of bulk material thermal properties via surface nanostructuring
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Mai, Trieu Thanh. "Anomalous heat transport and numerical studies of magnetic hysteresis /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2007. http://uclibs.org/PID/11984.
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Tozer, Robert Michael. "Cold generation systems with absorption cycles." Thesis, London South Bank University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336379.
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A review is presented on the technology, thermodynamics, applications and economics of absorption cycles such as refrigeration, heat pumps and temperature amplifiers; single and multistage cycles, and systems into which they are integrated such asCHP. From this present situation the fundamental thermodynamics of ideal absorption refrigeration is established for single, double and multistage cycles. An exergy analysis is used to prove this theory. The ideal absorption cycle theory is developed to cover absorption heat pumps, cooling with heat recovery, temperature amplifiers and hybrid systems incorporating vapour compression and absorption machines. Having proved absorption cycles to be comprised of Carnot cycles (direct and reverse), this theory was then merged with Carnot driving and cooling cycles' theory to establish a universal law of cold generation cycles. These are combinations of driving and cooling cycles for which the main pmpose is to produce cooling from a combustion driven cycle. The applications and economic evaluations of real direct fired absorption chillers, cold generation systems and the application of absorption chillers to combined heat and power (CHP) systems are analysed. Direct fired chillers have been proved to be economically feasible. The analysis of cold generation cycles indicated the feasibility of certain plant configurations. For the CHP analysis, the exergy costing method was seen to be the most appropriate one for determining the most cost effective application. A review of thermoeconomics applied to an air conditioning system with absorption and CHP is presented. Thermoeconomics was shown to be an appropriate method for optimising systems where absorption cycles are applied. Finally theoretical, practical and economic conclusions are presented regarding the equivalence of vapour compression and absorption cycles.