To see the other types of publications on this topic, follow the link: Thermal conductivities.
Dissertations / Theses on the topic 'Thermal conductivities'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Thermal conductivities.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Yao, Yulong. "THERMAL CONDUCTIVITIES OF ORGANIC SEMICONDUCTORS." UKnowledge, 2017. http://uknowledge.uky.edu/physastron_etds/48.
Full textAbstract:
Organic semiconductors have gained a lot of interest due to their ease of processing, low-cost and inherent mechanical flexibility. Although most of the research has been on their electronic and optical properties, knowledge of the thermal properties is important in the design of electronic devices as well. Our group has used ac-calorimetric techniques to measure both in-plane and transverse thermal conductivities of a variety of organic semiconductors including small-molecule crystals and polymer blends. For layered crystals composed of molecules with planar backbones and silylethynyl (or germylethynyl) sidegroups projecting between the layers, very high interplanar thermal conductivities have been observed, presumably implying that heat flows between layers mostly via interactions between librations on these sidegoups.
Since most organic semiconducting devices require materials in thin film rather than bulk crystal form, I have focused on using the “3ω- technique” to measure the thermal resistances of thin films of this class of organic semiconductors, including bis(triisopropylsilylethynyl) pentacene (TIPS-pn), bis(triethylsilylethynyl) anthradithiophene (TES-ADT), and difluoro bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT). For each material, several films of different thicknesses have been measured to separate the effects of intrinsic thermal conductivity from interface thermal resistance. For sublimed films of TIPS-pn and diF-TES-ADT, with thicknesses ranging from less than 100 nm to greater than 4 μm, the thermal conductivities are similar to those of polymers and over an order of magnitude smaller than those of single crystals, presumably reflecting the large reduction in phonon mean-free path due to disorder in the films. On the other hand, the thermal resistances of thin (≤ 205 nm) crystalline films of TES-ADT, prepared by vapor-annealing of spin-cast films, are dominated by their interface resistances, possibly due to dewetting of the film from the substrate during the annealing process.
2
Agab, Ali Faisal. "Hydraulic and thermal conductivities of soils." Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417418.
Full text
3
Tang, Xiaoli Dong Jianjun. "Theoretical study of thermal properties and thermal conductivities of crystals." Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/SUMMER/Physics/Dissertation/Tang_Xiaoli_9.pdf.
Full text
4
Rowan, Linda. "The measurement of the thermal conductivity of gaseous mixture using the transient hot wire technique." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252676.
Full text
5
Zhang, Hantao S. M. Massachusetts Institute of Technology. "Computational investigation of the thermal conductivities and phonon properties of strontium cobalt oxides." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/123356.
Full textAbstract:
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 87-91).
The thermal conductivities of electrochemically tuned strontium cobalt oxides (SCO) are significantly different among the perovskite SrCoO3 (P-SCO), the brownmillerite SrCoO2.5 (BM-SCO) and the hydrogenated HSrCoO2.5 (H-SCO)1. The underlying mechanism causing this large difference is still unclear. And phonon properties in SCO have not been investigated thoroughly or have some contradictive predictions. In this work, we have calculated the thermal conductivities in P-SCO and BM-SCO by applying molecular and lattice dynamics, and successfully reconstructed the large difference of the thermal conductivities, consistent with measurements. Furthermore, several phonon properties including heat capacities, group velocities, lifetimes and mean free paths have been calculated, and the key roles of local atomic environment and crystal symmetry in determining the thermal conductivities have been identified. We have also analyzed the impact of interfaces, isotropic strains and defects on thermal conductivities, predicted the neutron scattering intensity in P-SCO, and tested the accuracy and performance of molecular dynamics based on deep learning. Additionally, even though the calculations about the phonon properties in H-SCO are not complete, it still offers some inspirations about its thermal conductivity. The thorough investigations about the phonon properties and the mechanisms determining the thermal conductivities in SCO may benefit future research about tunable thermal conductivities in complex oxides.
by Hantao Zhang.
S.M.
S.M. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering
6
Zuo, Yanjia. "Preparation of silica aerogels with improved mechanical properties and extremely low thermal conductivities through modified sol-gel process." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/64600.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 90-96).
Reported silica aerogels have a thermal conductivity as low as 15 mW/mK. The fragility of silica aerogels, however, makes them impractical for structural applications. The purpose of the study is to improve the ductility of aerogels while retain the low thermal conductivity of silica aerogels. We have established a new synthesis route, a 3-step sol-gel processing method. The method provides better control of the formation of aerogel structures. The produced silica aerogels show much improved ductility compared to conventional methods in literatures. Furthermore, the synthesized silica aerogels have thermal conductivities as low as about 9 mW/mK, which is the lowest in all reported solids. The ultra low thermal conductivity can be explained with nano-scale structures for the silica aerogels, which have been characterized using advanced techniques including BET and SEM. We have further investigated and demonstrated the ability of enhancing mechanical properties of silica aerogels through structure modification using the proposed 3-step sol-gel processing method. The molecular-level synergism between silica particles/clusters and the doped functional materials inverts the relative host-guest roles in the produced aerogel composite, leading to new stronger and more robust low-density materials.
by Yanjia Zuo.
S.M.
7
Jäger, Tino [Verfasser]. "Thermoelectric properties of TiNiSn and Zr 0.5 Hf 0.5 NiSn thin films and superlattices with reduced thermal conductivities / Tino Jäger." Mainz : Universitätsbibliothek Mainz, 2014. http://d-nb.info/1046354167/34.
Full text
8
Gelaye, Ababu A. "UPSCALING OF A THERMAL EVOLUTION EXPERIMENT ON SHREDDED-TIRE MONOFILLS." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1512762530668535.
Full text
9
Kasali, Suraju Olawale. "Thermal diodes based on phase-change materials." Thesis, Poitiers, 2021. http://www.theses.fr/2021POIT2254.
Full textAbstract:
Nous étudions dans cette thèse la rectification thermique de diodes thermiques radiatives ou conductive constituées de matériaux à changement de phase.Cette thèse est divisée en trois parties. Dans les premières parties, nous modélisons comparativement les performances d’une diode thermique conductive sphérique et cylindrique constitués de VO2 présentant un transition de phase et des matériaux n’en présentant pas. Des expressions analytiques aux bornes des diodes sont dérivées. Des flux thermiques, des facteurs de rectifications ainsi que les profils de température à l’intérieur de la diode sont obtenus. Nos résul-tats montrent que les différentes géométries de diodes ont un impact significatif sur les profils de température et les flux thermiques, mais moins un sur les facteurs de rectification. Dans ce travail, nous avons obtenu des facteurs de rectification maximaux allant jusqu’à 20.8% et 20.7%, qui sont supérieurs à celui prédit pour une diode plane constituée de VO2. Nous montrons également que des facteurs de rectification similaires à ceux obtenus avec le VO2 dans les géométries sphériques et cylindriques peuvent être atteints avec des matériaux à changement de phase dont le contraste de conductivité est plus important que dans le cas du VO2. Dans la deuxième partie, nous étudions la rectification de diodes thermiques constituées de deux matériaux à changement de phase. Avec, l’idée de générer un facteur de redressement plus élevé que dans le cas d’une diode thermique conductive ne comprenant qu’un matériau à changement de phase unique. Là encore, le travail a conduit à l’établissement d’expressions explicites pour les profils de température, les flux thermiques et le facteur de rectification. Nous avons obtenu un facteur de rectification optimal de 60% avec une variation de température de 250 K couvrant les transitions métal-isolant des deux matériaux. Dans la troisième partie de notre travail, nous avons modélisé et optimisé la rectification thermique de diodes thermiques planes, cylindriques et sphériques radiatives à base de deux matériaux à changement de phase. Nous savons calculer et analyser les facteurs de rectification de ces trois diodes et obtenu les facteurs de rectification optimaux respectifs pour les trois géométries 82%, 86% et 90.5%. Nos résultats montrent que la géométrie sphérique est la meilleure pour optimiser la rectification des courants thermiques radiatifs. De plus, des facteurs de rectification potentiellement supérieurs à ceux prédits ici peuvent être réalisés en utilisant deux matériaux à changement de phase avec des contrastes d’émissivités plus élevés que ceux proposés ici. Ces résultats analytiques et graphiques fournissent un guide utile pour optimiser les facteurs de rectification des diodes thermiques conductives et radiatifs basées sur des matériaux à changement de phase de géométries différentesThe thermal rectification of conductive and radiative thermal diodes based on phase-change materials, whose thermal conductivities and effective emissivities significant change within a narrow range of temperatures, is theoretically studied and optimized in different geometries. This thesis is divided into three parts. In the first part, we comparatively model the performance of a spherical and cylindrical conductive thermal diodes operating with vanadium dioxide (VO2) and non-phase-change materials, and derive analytical expressions for the heat flows, temperature profiles and optimal rectification factors for both diodes. Our results show that different diode geometries have a significant impact on the temperature profiles and heat flows, but less one on the rectification factors. We obtain maximum rectification factors of up to 20.8% and 20.7%, which are higher than the one predicted for a plane diode based on VO2. In addition, it is shown that higher rectification factors could be generated by using materials whose thermal conductivity contrast is higher than that of VO2. In the second part, on the other hand, we theoretically study the thermal rectification of a conductive thermal diode based on the combined effect of two phase-change materials. Herein, the idea is to generate rectification factors higher than that of a conductive thermal diode operating with a single phase-change material. This is achieved by deriving explicit expressions for the temperature profiles, heat fluxes and rectification factor. We obtain an optimal rectification factor of 60% with a temperature variation of 250 K spanning the metal-insulator transitions of VO2 and polyethylene. This enhancement of the rectification factor leads us to the third part of our work, where we model and optimize the thermal rectification of a plane, cylindrical and spherical radiative thermal diodes based on the utilization of two phase-change materials. We analyze the rectification factors of these three diodes and obtain the following optimal rectification factors of 82%, 86% and 90.5%, respectively. The spherical geometry is thus the best shape to optimize the rectification of radiative heat currents. In addition, potential rectification factors greater than the one predicted here can be realized by utilizing two phase-change materials with higher emissivities contrasts than the one proposed here. Our analytical and graphical results provide a useful guide for optimizing the rectification factors of conductive and radiative thermal diodes based on phase-change materials with different geometries
10
Bamford, Erik, Gustav Ek, Daniel Hedbom, Johan Nyman, Victor Petterson, Josefin Sjöberg, Ida Styffe, and Olivier Vizuete. "Quartzene – A promising thermal insulator : Studies of thermal conductivity’s dependence of density and compression of Quartzene® in the form of powder." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-228087.
Full textAbstract:
The purpose of this project was to study Svenska Aerogel AB’s product Quartzene®, and develop its capacity as a thermal insulator. Quartzene® is a silica based mesoporous material developed by Svenska Aerogel AB, with properties similar to aerogels produced by the sol-gel process. In this report, the correlation between pore structure and thermal conductivity in the material has been studied using techniques, such as scanning electron microscopy, focused ion beam, finite element simulations and transient plane source. Its properties are interesting because of the expanding market of insulated vacuum panels; in which Svenska Aerogel AB wish to expand to. It was found that the pore sizes of M21-BU increased after compression, and the pore sizes of M4-0-2 decreased. The pore sizes of M21-BU became so large that the Knudsen effect is no longer of interest, and that could explain the different behaviors in thermal conductivity.
11
Lenain, Alexis. "Conductivité thermique des alliages métalliques amorphes en conditions cryogéniques et applications." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAI100.
Full textAbstract:
Les alliages métalliques amorphes possèdent une structure désordonnée sansordre atomique local à longue distance contrairement aux alliages cristallins. Cettestructure leur confère des propriétés particulières, ouvrant la voie à de nombreusesapplications industrielles. En particulier, leur conductivité thermique est faiblecomparée aux autres matériaux métalliques du fait de l'absence de réseau cristallin.Ces alliages possèdent ainsi des propriétés isolantes permettant de minimiser lespertes thermiques par conduction. Ce travail de thèse porte d'une part sur lacompréhension des mécanismes intervenant dans la conductivité thermique desalliages métalliques amorphes, permettant d'identifier des compositions adaptées.Différentes méthodes d'optimisation des propriétés thermiques ont été étudiées etont permis de développer une composition optimisée à faible conductivité thermique.D'autre part, la capacité à être assemblé a été étudiée dans l'objectif d'intégrer ces alliages dans un dispositif industriel. Deux techniques d'assemblage ont étéconfrontées permettant de développer une solution à court et à long terme. Deuxbrevets protégeant l'utilisation de compositions avantageuses obtenus grâce auxrésultats de ce travail ont été déposés. Par ailleurs, des prototypes ont été réalisés en utilisant les procédés étudiés dans ce travail et présentent des performances augmentées par rapport à la solution actuelleBulk metallic glasses possess an amorphous structure without any atomic longrange ordering unlike their crystalline counterparts. They exhibit particularproperties due to this amorphous structure, which is very promising for futureindustrial applications. In particular, their thermal conductivity is very low compared to other metallic materials due to the absence of crystalline lattice. Thus, these alloys show some insulating properties, leading to low heat losses. This PhD work focuses on understanding the mechanisms that occur in thermal conductivity of bulk metallic glasses in order to identify suitable compositions. Several optimization methods have been carried out to minimize the thermal properties and resulted in the development of an optimized composition showing low thermal conductivity. Secondly, their joining ability has been studied with the aim to implement these alloys in an industrial device. Two different joining techniques have been faced to provide a short and a long term solution. Eventually, two patents which protect the use of beneficial compositions developed in this work have been filed. Besides, prototypes have been produced using the two processes studied in this work and show enhanced performances compared to the current solution
12
Fortin, Guy. "Détermination du coéfficient transitoire de transfert de chaleur à l'interface moule/métal lors de la solidification de l'aluminium pur commercial /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 1992. http://theses.uqac.ca.
Full textAbstract:
Mémoire (M.Sc.A.)-- Université du Québec à Chicoutimi, 1992.Résumé disponible sur Internet. CaQCU Bibliogr.: f. 158-160, 220-221. Document électronique également accessible en format PDF. CaQCU
13
Chaliche, Majed. "Contribution a l'etude de la conductivite thermique des fluides complexes en presence d'une vitesse de cisaillement : realisation d'un appareillage specifique." Nantes, 1988. http://www.theses.fr/1988NANT2013.
Full textAbstract:
On propose un appareillage de mesure avec temperature maximale 70**(o)c. La mesure de la conductivite thermique en fonction de la vitesse de cisaillement pour des fluides de viscosite differentes permet de fixer la valeur limite du parametre r=2,10**(-2) au-dela de laquelle on ne peut plus utiliser le dispositif. La dissipation visqueuse au sein du fluide qui s'ajoute au flux transmis par conduction est quantifiee par le nombre de brinkman. On a montre que l'on doit apporter une correction a la mesure de la conductivite apparente pour mettre au point une analyse theorique du champ thermique et dynamique. L'etude experimentale a permis d'etudier l'influence de la concentration, de la dissipation visqueuse et de la temperature sur la conductivite reelle de la solution cmc qui a un comportement non newtonien de type oswald
14
Beziat, Alain. "Etude experimentale de la conductivite thermique de materiaux argileux hautement compactes : contribution a l'etude du stockage de dechets radioactifs." Orléans, 1987. http://www.theses.fr/1987ORLE2026.
Full textAbstract:
Etude de l'influence de densite, teneur en eau, temperature, et aussi des caracteristiques mineralogiques et des conditions physiques externes (accroissement de temperature, contrainte mecanique). Amelioration de la conductivite par additifs (graphite, quartz). Utilisation de modeles pour relier la conductivite a celles de chaque phase; bons resultats obtenus avec le modele geometrique (empirique) et le modele de porosite ellipsoidale
15
Tavman, Ismail H. "Contribution a l'etude de l'anisotropie thermique des polymeres en fonction de leur orientation moleculaire." Paris, ENSAM, 1987. http://www.theses.fr/1987ENAM0014.
Full textAbstract:
Modelisation de la phase de remplissage et de celle de maintien en pression dans un cycle d'injection de matieres thermoplastiques. Etude de l'influence de l'orientation moleculaire sur la diffusivite et la conductivite thermique
16
RAHELIARILALAO-RANAIVO, RABEHAJA BIENVENUE. "Etude des caracteristiques thermiques et mecaniques de betons de pouzzolane." Paris 7, 1986. http://www.theses.fr/1986PA077220.
Full textAbstract:
Etude des pouzzolanes naturelles de l'ile de la reunion, comme composants de base de beton alleges, en soulignant les avantages thermiques. Proprietes chimiques, mineralogiques et physiques des granulats de pouzzolane. Adaptation d'une modelisation thermique pour les corps poreux, avec nouvelle methode de determination de la diffusivite. Description des appareillages de mesure de la conductivite et diffusivite thermiques, et presentation des resultat
17
Troadec, Carole. "Composite à matrice métallique Al-AlN : de la poudre au matériau." Grenoble INPG, 1996. http://www.theses.fr/1996INPG4205.
Full textAbstract:
Cette etude s'inscrit dans le cadre de l'elaboration de composites a matrice metallique aluminium/nitrure d'aluminium, par metallurgie des poudres. Deux types de poudres sont utilisees: une poudre dite composite synthetisee par nitruration directe de l'aluminium par l'azote et une poudre dite melange obtenue a partir d'un melange de poudres commerciales elementaires aluminium et nitrure d'aluminium. Ces deux types de poudres subissent un broyage hautement energetique par melangeur planetaire sous argon, puis sont frittes par compression a chaud en phase solide. La microstructure de ces materiaux, etudiee en met et nanoanalyse edx, est relativement heterogene, constituee de zones denses polycristallines et de zones a forte porosite constituees de nanocristaux. La taille de ces zones microporeuses est superieure dans les materiaux melanges et varie en fonction du taux de nitrure d'aluminium et du temps de broyage. Les zones denses sont composees de grains d'aluminium entoures de nanocristaux de nitrure d'aluminium, avec des aiguilles d'alumine et quelques cristaux d'oxynitrure d'aluminium. L'ordre de grandeur des cristaux (<1 m) est confirme par diffraction des rayons x. Les proprietes physico-chimiques (coefficient de dilatation, conductivites thermique et electrique) et mecaniques (durete, module de young, limite d'elasticite, contrainte a la rupture) different en fonction du type des poudres de depart et evoluent avec la teneur en aln. Le comportement des deux types de materiaux differe egalement en usure et en corrosion. Ces nouveaux materiaux ont dans l'ensemble, a teneur en renfort similaire, des proprietes equivalentes a celles des materiaux al/sic ou al/al#2o#3
18
OUAJJI, HASSAN. "Etude de proprietes de transport d'un plasma de melange air-cuivre : modelisation de la colonne d'arc." Clermont-Ferrand 2, 1986. http://www.theses.fr/1986CLF21034.
Full textAbstract:
Calcul des coefficients de conductivite thermique, de conductivite electrique et de viscosite du melange air-cuivre a la pression atmospherique pour des temperatures comprises entre 5000 k et 14000 k et differentes valeurs de la teneur en cuivre. Dans les memes conditions de temperature et de pression, la determination de la composition d'equilibre du melange met en evidence l'evolution de la population des differentes especes chimiques en presence en fonction de la teneur en cuivre. Les caracteristiques macroscopiques de la colonne (champ electrique, profil de temperature) sont obtenues a partir du modele energetique de elenbaas-heller
19
Traoré, Jean. "Dispositif numérique de conditionnement thermique en vue de l'étude des propriétés ohmiques et thermo-électriques d'alliage binaire en couche mince." Rouen, 1992. http://www.theses.fr/1992ROUES052.
Full textAbstract:
Le traitement thermique des couches minces d'alliage binaire, l'étude de leurs propriétés résistives et thermo-électriques imposent de maîtriser avec précision la programmation des variations de température appliquée. Le dispositif électronique numérique décrit, élaboré à partir d'une première version analogique, répond à ces contraintes. Ainsi, il devient possible d'obtenir une température uniforme avec un écart ne dépassant pas 0. 5°C entre les deux extrémités de la couche mince dans un domaine allant de la température ambiante (20°C) jusqu'à 300°C, pour les mesures de résistances et un écart constant de plusieurs dizaines de degrés pour les mesures de f. é. M. Thermo-électriques. Ce système a été étudié en utilisant les techniques d'identification dynamique à base de séquences binaires pseudo-aléatoires. Sa réalisation, utilisant un correcteur PID numérique, des techniques particulières relatives aux amplificateurs à bas niveau et aux circuits électroniques de commande de puissance, a été développé autour d'un micro-ordinateur. Cette méthode de régulation peut, dans l'avenir être avantageusement remplacée par un correcteur flou
20
Adel, Norelhayate. "Influence d'un adjuvant proteique sur la texture poreuse et les proprietes mecaniques et thermiques d'un beton cellulaire autoclave." Toulouse 3, 1987. http://www.theses.fr/1987TOU30219.
Full textAbstract:
Etude en vue de la realisation de murs legers, isolants, homogenes, l'anisotropie de structure pouvant augmenter la resistance vertical et diminuer la conductivite horizontale. Etude de l'effect d'un siliceux, poudre d'aluminium et eau, autoclave a 175**(o)c. Les resultats s'expliquent par la structure dissymetrique vis-a-vis de l'eau des molecules proteiques, hydrophobes d'un cote et hydrofuges de l'autre
21
Argento, Claudio. "Modélisation du comportement thermique et mécanique des poudres métalliques : application à la compaction isostatique à chaud." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10084.
Full textAbstract:
Le but initial de cette these est de produire, a partir d'un code de calcul par elements finis existant, un outil fiable et souple pour la simulation du processus de compaction isostatique a chaud de poudres metalliques. Pour cela nous avons developpe un modele thermomecanique complet decrivant le comportement de la poudre pendant la compaction. Dans un premier temps, nous proposons une nouvelle loi constitutive elasto-viscoplastique avec ecrouissage en densite. Cette loi possede un parametre supplementaire qui permet de controler explicitement le couplage entre les parties isotrope et deviatoire des contraintes et des deformations. La deuxieme partie de ce travail est consacree au developpement d'un modele permettant de decrire la conductivite thermique des poudres metalliques tout au long de la densification. Nous proposons deux modeles: un modele utilisant la methode des elements discrets pour decrire la conduction a travers la phase solide et une methode de monte carlo associee a un programme de suivi de rayons pour decrire le rayonnement dans les pores. Nous montrons que ce dernier etait negligeable dans le cas des poudres metalliques. Dans la troisieme partie, nous decrivons le code de calcul par elements finis lagamine de l'universite de liege et la facon dont les lois constitutives mecaniques et thermiques presentees y sont integrees de facon objective. Finalement, dans la derniere partie de cette these, nous presentons une comparaison des reponses prevues par les differentes lois constitutives pour des pieces relativement simples en deux et trois dimensions. Nous mettons en evidence en particulier l'influence de la loi de comportement sur la prevision de la forme finale de la piece
22
Abada, Fella. "Transport d'humidité en matériaux poreux en présence d'un gradient de température : caractérisation expérimentale." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10135.
Full textAbstract:
Ce travail de these porte sur des etudes experimentales relatives aux transferts monodimensionnels d'humidite sous differents gradients thermiques dans des materiaux poreux qui sont: le beton autoclave non expanse, la vermiculite, deux roches extraites de carrieres (rouffach et rorschach) servant a la restauration de monuments historiques. Un dispositif experimental est utilise pour le suivi continu des evolutions de teneurs en eau (methode gammametrique) et de temperatures (sondes thermiques) durant des essais de condensation et de sechage. L'objectif principal de ce travail est la determination des coefficients de transfert pour chaque materiau, determination basee sur la theorie classique du transfert de masse et de chaleur de de vries. Les coefficients de transfert sont calcules par un procede de regression entre les variables mesurees: flux de masse, gradient de temperature et gradient de teneur en eau, on donne leurs evolutions avec la teneur en eau et pour differentes temperatures. D'autres experiences sont aussi realisees donnant les conductivites thermiques et les isothermes d'adsorption permettant, ainsi, d'acquerir des informations sur le comportement des materiaux vis a vis du transfert de chaleur et de vapeur d'eau
23
Zemirli, Saliha. "Etude sous haute pression de quelques fermions lourds : effets de cohérence et ordre magnétique." Grenoble 1, 1986. http://www.theses.fr/1986GRE10148.
Full textAbstract:
Mesures de conductivite sous haute pression a differentes temperatures pour ceal::(2), cecu::(2) et cecu::(6). Etudes par diffraction de neutrons, resistivite thermique et electrique, pouvoir thermoelectrique interpretees a l'aide de differents modeles
24
Peysson, Yves. "Propriétés thermiques de quelques composés du Cérium, en particulier CeB6." Grenoble 1, 1986. http://www.theses.fr/1986GRE10108.
Full textAbstract:
Mesures detaillees de chaleur massique entre 2 et 250 k sous champ magnetique jusqu'a 8 t. Mise en evidence du niveau fondamental du cerium. Une bande interdite a ete identifiee dans le spectre d'excitation des ondes de spin. Renforcement tres important de l'anomalie de chaleur massique a la temperature d'ordre quadripolaire. Etude de la conductivite thermique de ceb::(6) en relation avec un effet jahn teller entre 60 mk et 200 k
25
AKA, BOKO. "Photodecomposition sensibilisee au mercure du monosilane (hg-photo-cvd) : application au depot en couches minces de silicium amorphe hydrogene (a-si : h)." Université Louis Pasteur (Strasbourg) (1971-2008), 1989. http://www.theses.fr/1989STR13026.
Full textAbstract:
L'etude fondamentale des parametres mis en jeu montre que la limitation de la quantite de cilane decompose et la formation importante d'hydrogene doivent etre associees a un mecanisme chimique en phase gazeuse et a la surface plutot qu'a la diminution de la transparence de la fenetre d'entree consecutive au depot du film si. Il est ainsi mis en evidence que la quantite relative de si depose est tres importante aux basses pressions et que la vitesse de depot peut etre accrue en operant a forte intensite lumineuse. La qualite des couches depend fortement des conditions de preparation, en particulier de la temperature du support. Les couches obtenues ont des proprietes essentielles pour la fabrication de dispositifs photovoltaiques et microelectroniques de dimensions reduites et a bon marche
26
Pastol, Yvon. "Etude de la cristallisation en phase solide de couches minces de silicium implantees." Paris 7, 1987. http://www.theses.fr/1987PA077142.
Full textAbstract:
Etude des effets de dopage par implantation de bore et de phosphore. Etude du role des defauts d'irradiation dans des couches implantees au silicium. Les couches implantees et non implantees sont cristallisees en phase solide par recuit thermique a basse temperature. Etude de la taille des grains, de la texture, de la morphologie de surface et de la conductivite electriques des couches en fonction de la concentration d'ions implantes
27
SUDERON, HERMANN. "Conduction thermique des phases supraconductrices de UPt3." Université Joseph Fourier (Grenoble), 1997. http://www.theses.fr/1997GRE10266.
Full textAbstract:
Cette these decrit le transport de chaleur dans le supraconducteur upt#3. La particularite de ce compose a fermions lourds est de presenter differentes phases supraconductrices dans le diagramme de phase champ magnetique-temperature et un gap supraconducteur qui s'annule sur des lignes et/ou des points a la surface de fermi (supraconductivite non-conventionnelle). Apres une introduction a ce type de supraconductivite, nous decrivons notre montage experimental en detail. L'experience que nous avons mise au point permet de mesurer la conductivite thermique a tres basse temperature (15mk - 1k), et sous champ magnetique (4 t). Nous discutons ensuite en detail nos mesures a champ nul, notamment l'anisotropie de la conduction thermique et les lois de puissance trouvees a basse temperature, qui demontrent que le gap supraconducteur est hybride avec une ligne de zero et des points de zero. Nos mesures a tres basse temperature (15mk < t < 30mk) montrent l'effet de brisure de paires predit dans le cas des supraconducteurs non conventionnels, meme dans des echantillons tres purs. Nous avons mesure la conductivite thermique dans les phases supraconductrices sous champ magnetique de ce compose. Nous discutons en detail nos resultats qui montrent le changement du parametre d'ordre a la transition entre deux des trois phases supraconductrices de upt#3. Nous observons aussi la diffusion des excitations thermiques par les vortex. La partie basse temperature bas champ magnetique, que nous avons etudiee avec un soin special, constitue une mise en evidence experimentale de la prediction theorique recente de lois d'echelle dans la phase mixte des supraconducteurs avec des zeros dans le gap. Nous avons aussi realise les premieres mesures de conduction thermique sur le compose sr#2 ruo#4. La supraconductivite dans ce compose a ete decouverte recemment. A l'heure actuelle, c'est le seul compose perovskite lamellaire sans plans cuivre-oxygene qui devienne supraconducteur (t#c 1k). Nous discutons nos mesures de conduction thermique (jusqu'a 20mk) sur ce compose.
28
Boumaraf, Latra. "Etude des réactions chimiques dans les ammoniacates solides : application du système BaCl2/NH3 à la réfrigération solaire." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0026.
Full textAbstract:
Conception d'un dispositif experimental dans le but d'etudier les proprietes physiques et cinetiques des systemes bacl::(2)/nh::(3) et cacl::(2)/nh::(3). Mesures de vitesses de desorption et d'absorption. Modele d'optimisation des processus et experimentation d'un prototype de refrigeration a capteur solaire plan
29
Alquier-Villepelet, Cécile. "Syntheses et proprietes des gels d'oxyde de niobium." Paris 6, 1988. http://www.theses.fr/1988PA066019.
Full textAbstract:
On etudie le procede sol-gel applique au niobium v sous divers aspects. On ameliore les synthese et proprietes physiques des gels. On etudie les gels et oxydes amorphes obtenus par analyse chimique et thermique, diffraction rx, spectrocopies ir, raman et exafs. On etudie les proprietes et applications potentielles: fabrication de ceramiques linbo::(3) et pb(nb2/3 mg1/3)o::(3), avec abaissement de la temperature de frittage et obtention de grains homogenes monodisperses, mesure de la conductivite ionique dans les xerogels hydrates, proprietes optiques(photochromie)
30
Lahiouel, Rachid. "Evolution du réseau Kondo en fonction de l'hybridation : les systèmes CeIn(Ag,Cu)2 et Ce(Ge,Si)2." Grenoble 1, 1987. http://www.theses.fr/1987GRE10054.
Full textAbstract:
Observation du passage d'un regime kondo mixte a un regime kondo pur ou a un regime de valence intermediaire sous l'effet de la pression chimique. Etude du diagramme de phases magnetiques. Determination du coefficient de couplage entre electrons 4 f et la bande de conduction jn(e::(f)). Coefficient de la chaleur specifique, temperature de kondo et coefficient de grueneisen electronique de ceincu::(2)
31
Goy, Laurent. "Mesure et modélisation des températures dans les massifs rocheux : application au projet de tunnel profond Maurienne-Ambin." Phd thesis, Université Joseph Fourier (Grenoble), 1996. http://tel.archives-ouvertes.fr/tel-00642650.
Full textAbstract:
Pour les projets de tunnels profonds; la prévision des températures naturelles au rocher est essentielle pour le choix des méthodes de perforation, de ventilation et de refroidissement. Une méthode numérique de prévision des températures a été développée à cet effet, à partir d'un logiciel 2D d'éléments finis. Les températures sont calculées dans un plan vertical du massif, à partir de l'équation fondamentale de la chaleur en conduction pure. La modélisation nécessite la connaissance de cinq paramètres de base que sont: le profil topographique, les températures de surface, la structure géologique, la conductivité anisotrope des roches et le flux géothermique profond. Une méthode de correction du profil topographique permet de prendre en compte la troisième dimension. Différents tests sont effectués sur un profil de montagne idéalisé, pour évaluer le poids des différents paramètres dans la modélisation. Le modèle est appliqué ensuite au massif comprenant le tunnel Maurienne-Ambin, dans le cadre du projet de ligne à grande vitesse entre Lyon et Turin. Une sonde de mesure des températures a été mise au point et utilisée dans les sondages de reconnaissance pour ce projet de tunnel profond (55km sous un recouvrement maximal de 2500m). Les forages nous permettent de déterminer la structure géologique, les valeurs de conductivité des roches et le flux géothermique de la région en appliquant la "méthode des intervalles". La température maximale calculée le long du tunnel est de 48,5°C. La confrontation entre les mesures de température dans les forages et la modélisation permet de valider les résultats, sauf dans les premières centaines de mètres du massif, où les circulations d'eau, qui ne sont pas prises en compte par notre modèle, modifient la distribution des températures.
32
Po-Wei, Tang. "Thermal Conductivities of MWCNT-Reinforced Epoxy Composites." 2007. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0009-2501200717475900.
Full text
33
Jean, Chung-Tzong, and 簡城宗. "Research on Thermal Conductivities of Composite Soil." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/66401125774746623766.
Full textAbstract:
碩士國立中央大學
土木工程學系
84
The thermal problem civil engineering always faces is how to control the situation of heat dissipating or insulation between structures and surroundingenvironment. The thermal properties like coefficient of thermal conductivity design or determination of buffer materials around some special underground structures would be the important key. To obtain a desired thermal conductivi-ty, mixing two kinds of soil material possessing different thermal properties at various volumetric fractions was usually economical and probable. A heat-flow-meter method was used to measure the thermal conductivities of mixtures of two dry porous materials. Also we observed the relationship between thermal conductivities and volumetric fractions of composites. Mix- tures that owned two kinds of particles and porous could be regarded as a three- phases system coming from two kinds of two-phases materials that owned only one kind particle and porous. A constituent volumetric fraction model was conducted to distinguish the very respective fractions and thermal con- ductivities of the two composites. Both they''re two-phases materials. Results indicated that the high-thermal-conductivity materials had a pronounced influ-ence on the heat-conduction process in the composite mixtures. Evaluations andcomparisons with some theories also indicated that prediction value all well agreed with experiment value.
34
Tang, Po-Wei, and 唐伯偉. "Thermal Conductivities of MWCNT-Reinforced Epoxy Composites." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/03230303573395807098.
Full textAbstract:
碩士元智大學
機械工程學系
95
Due to its excellent thermal conductivity, carbon nanotubes (CNTs) are considered as candidates for heat management materials. In the present works, the epoxy resin is used as the matrix, and the multi-walled carbon nanotubes (MWCNTs) with different diameters are as the reinforcement. The objectives of this study are to understand the effects of MWCNT weight percent (0.1 – 5 wt. %), MWCNT diameter (20 – 40 or 40 – 60 nm), and the thickness of the specimens (1 or 3 mm) on the effective thermal conductivities of the composite. The results show that under 50 and the specimen with thickness = 1 mm, the thermal conductivity of the pure epoxy is 0.204 W/m K. The thermal conductivity of the composite increases with the increase in the MWCNTs weight percent. By adding of the MWCNTs under 0.9 wt. %, the thermal conductivity of the MWCNT/epoxy composite increases linearly, but the increasing rate decreases once the MWCNTs weight percent is over 0.9 wt. %. The thermal conductivities of 0.9 wt. % MWCNT/epoxy composites with a MWCNT diameter D = 20 - 40 nm or D = 40 - 60 nm are 0.289 or 0.281 W/m K, respectively. Compare with the pure epoxy, the thermal conductivities increase 42 or 38 %, respectively. The thermal conductivities of 5 wt. % MWCNT/epoxy composites with a MWCNT diameter D = 20 - 40 nm or D = 40 - 60 nm are 0.404 or 0.423 W/m K, respectively, with the increments of 98 or 107 %. The experimental results of the composite specimens with thickness = 3 mm is lower than that with thickness = 1 mm. This is attributed to the fact that there is a larger lateral area exposing to the external environment in the specimens with thickness = 3 mm, which results in a large heat loss. The micromechanics model, Eshelby, is developed to predict the thermal conductivity of MWCNT-reinforced composites. Compared with the experimental data, the predictions are fitted well with the experimental data of the composite specimens with thickness = 1 mm by adding MWCNTs under 0.9 wt. %, no matter the diameters of the MWCNTs are between 20 - 40 nm or 40 - 60 nm. However, at high wt. % of MWCNTs (> 0.9 wt. %), there are large discrepancies between the predictions and the experimental data because the trend of the increase by adding high wt. % MWCNTs are nonlinear.
35
Kao, Song-Shun, and 高頌舜. "Analysis of the Effective Thermal Conductivities and Thermal Stresses of Composites." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/82674522534880862786.
Full textAbstract:
碩士逢甲大學
航空工程所
93
ABSTRACT The aim of this study is to analyze the effective thermal conductivities of composites containing randomly distributed spherical inclusions or cylindrical fibers. Theoretical studies have shown that the effective thermal conductivity of composites is strongly dependent on the volume fraction, the distribution, inclusion size and the thermal conductivities of constituents. Interfacial thermal contact resistance between matrix and inclusion is known to have a significant influence on the effective thermal conductivity of the composite. A generalized self-consistent model (GSCM) is developed to predict the effective thermal conductivity of composites reinforced with multi-layered spherical inclusion and multi-layered cylindrical orthotropic fibers. The interfacial thermal contact resistances between different constituent phases are considered in the formulation. This approach provides explicit expressions of the effective thermal conductivity of composites in terms of components of thermal conductivity, interfacial contact resistance and volume fraction of each layer of the inhomogeneous inclusion and orthotropic fibers. The proposed approach recovers the existing theoretical results for some simple special cases. The predicted results are compared with finite element analysis in published reference. The results show that the present model gives good prediction of the effective thermal conductivities for composites with multilayered interphases and interfacial thermal resistance. The local temperature and thermal stress fields of such composites subjected to uniform heat flux are estimated using present micromechanics model.
36
WU, SHI-YI, and 吳昌賢. "Studies on effective thermal conductivities of powder beds." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/02856557868991536448.
Full text
37
Chen, Fu-Ren, and 陳附任. "Thermal and Electrical Conductivities of a Single Copper Nanowire." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/zth25w.
Full textAbstract:
碩士國立交通大學
機械工程系所
107
This study aims to investigate the thermal and electrical conductivities of a single copper nanowire. With the advance in semiconductor technology, the integrated circuits become smaller while the power densities of the circuits increase. This results in the severe adverse effect of Joule heating on the integrated circuits. Therefore, dissipating the heat efficiently is one of the main goals in the electrical industry. Thermal and electrical conductivities of the nanoscale copper thin film were investigated before. Based on the Wiedemann-Franz law, the Lorenz number of the copper thin film was also obtained. Nevertheless, although a lot of researchers had studied the electrical resistivity of copper nanowires, there is no complete investigation of the thermal conductivity on a single copper nanowire. Therefore, this work attends to measure the thermal and electrical conductivities of a single copper nanowire. In this study, the electrical resistivity and thermal conductivity of single copper nanowires with different diameters were measured. The measured temperature ranged from 20 K to 300 K. And the diameters of the measured copper nanowires are 119.4 nm (Sample A), 172.6 nm (Sample B), 201.7 nm (Sample C), respectively. At room temperature, the experimental result showed that the electrical resistivity of the sample A was about 6 times that of bulk copper. The phonon-electron coupling parameter of sample A was larger than that of bulk copper. This indicates that the phonon-electron scattering in the copper nanowire is more severe than that in the bulk copper, resulting in the larger electrical resistivity of the nanowire. This is presumably due to the size reduction and polycrystalline structure of the nanowire. In addition, at room temperature, the thermal conductivity was reduced by 71% from that of bulk copper. The thermal conductivity of sample A decreased with decreasing temperature, whereas the bulk copper thermal conductivity increased with temperature. To explain the opposite trends of thermal conductivity of the copper nanowire and the bulk copper, a unified thermal resistivity was introduced. A large residual unified thermal resistivity was observed for the copper nanowire while that of bulk copper was almost zero. Besides, a more significant temperature dependence of unified thermal resistivity was observed for the nanowire. This also proposed that the copper nanowire had a larger phonon-electron scattering than that in the bulk copper. Moreover, the Lorenz number of sample A was larger than the theoretical value. The difference was larger at a lower temperature. The electrons in the nanowire can transfer both the thermal energy and electrical current. The grain boundaries in the polycrystalline nanowire might exert different scattering mechanism on the thermal electrons which are responsible for carrying thermal energy and on the elections which are responsible for carrying electrical current. This can be evidenced from the smaller mean free path of the thermal electron than that of the electron at a low temperature. The grain boundary scattered thermal electrons more severely than the electrons and resulted in the deviation of the obtained Lorenz number for the nanowire. Besides, literature showed that the reduction of nanowire size increased the chance of electron scattering, resulting in the smaller electrical and thermal conductivity of the thinner nanowires. However, the copper nanowire with three different diameters in our study did not meet the description in the literature. As the diameter increased, the copper nanowire showed a lower electrical and thermal conductivity. According to the Transmission Electron Microscope images, sample C which had the lowest electrical and thermal conductivities possessed the largest numbers of the irregular grains in the nanowire. The number of grains in sample B was less than that sample C but more than that in the sample A. Thus, sample A had the highest electrical and thermal conductivities. The polycrystalline structure in the nanowires dominated the electron scattering, resulting in the lower electrical and thermal conductivities for the thicker wires. In the future, the electrical resistivity and thermal conductivity of copper nanowire with single crystalline structure and different diameters will be measured to study the diameter effect on the transport properties of the nanowires. In addition, the nanowire size effect on the Lorenz number will be evaluated.
38
GUO, BO-WEN, and 郭博文. "Studies on the thermal conductivities of wood-based materials." Thesis, 1989. http://ndltd.ncl.edu.tw/handle/37307082419251971245.
Full text
39
Peng, Mingfeng, and 彭明烽. "Application of Modified Plasma-melted Slags in Thermal Conductivities of Thermal Interface Materials." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/23052325545457338774.
Full textAbstract:
碩士國立聯合大學
環境與安全衛生工程學系碩士班
100
The present work includes the studies of modulation of plasma-melted slags by single/bi-metal nanoparticle fillers and application of the novel thermal interface materials (TIMs) on electric devices. Thus, TIMs with high thermal conductivity is developed when plasma-melted slags are modified by single/bi-metal nanoparticle fillers, e.g. Ag, Cu, and ZnO because their high thermal conductivities. The main objective of this work is to study the speciation of copper and zinc nano particles on plasma-melted slags dispersed grease (Y-500) by X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectoscopies, Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), and dummy heater. Due to low leach of toxic materials from plasma-melted slags, stable slags are safe to be reused. Combining XRD and XANES data, grain size of Cu nanoparticles coated on the plasma-melted slags with 0.210 and 0.088 mm are 24-60 nm with electroless coating. By EXAFS, the structural perturbation of Cu is observed. Bond distances of Cu-Cu are 2.53 and 2.52 Å on the plasma-melted slags. Due to the decreased the Cu/Ag mole ratio, bond distance of Cu-Cu is confined. Thermal conductivity of Cu-Ag coated on the plasma-melted slags with 0.088 mm dispersed Y-500 is 1.354 W/m-K. Because of small size of fillers, a lot of amount of particles should be added into Y-500, which can increase the pathways of heat conduction by Cu-Ag coated plasma-melted slags. About 0.1 and 3.5% of silver and copper were coated on surfaces of plasma-melted slags by electroless coating. By XRD, copper nanoparticles with ~30 nm are observed. Even the plasma-melted slags are not het conductors. The thermal conductivity of Cu-Ag coated slags dispersed Y-500 is also enhanced to 1.432 W/m-K. Moreover, about 1 and 5% of Cu with 0.1% of Ag are coated on plasma-melted slags for TIMs by electroless coating, respectively. Thermal conductivities of 1 and 5% of Cu with 0.1% of Ag coated plasma-melted slags dispersed Y-500 are 1.295 and 1.356 W/m-K. However, metal concentration and thermal conductivity are linear but not in direct ratio. The least-square fitted XANES spectra show that main zinc and copper species on the plasma-melted slags in Y-500 is ZnO, Cu (74%), and Cu(EDTA)2 (26%). Because zinc coated plasma-melted slags immersed in an acidic solution of PdCl2 before coating Cu processes, the pores on ZnO thin film was formed. Cu(EDTA)2 should migrate into the pores. It is also observed that enhanced thermal conductivity of Cu-ZnO coated on the plasma-melted slags dispersed Y-500 is increased by 15.3%.
40
Wang, Tai-Yuan, and 王泰元. "Characterizing Mechanical Properties and Thermal Conductivities of Graphene/Epoxy Nanocomposites." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/65086099886363224843.
Full textAbstract:
博士國立交通大學
機械工程系所
105
The aim of this study is to characterize the mechanical properties and thermal conductivities of graphene/epoxy nanocomposites. The elastic constants and thermal conductivity were investigated for the pristine graphene and functionalized graphene through molecular dynamics (MD) simulations. The results indicated that implanting functional groups would reduce the in-plane Young’s modulus and thermal conductivity. Subsequently, the influences of functional groups grafted on the graphene surface on the properties of nanocomposites were explored by examining the interfacial thermal conductance (ITC), phonon mismatch, and normalized interaction energy. It was shown that functional groups could increase the interactions and decrease the phonon mismatch at the interface so that the ITC and thermal transport in the interfacial epoxy could be enhanced significantly. Afterward, the atomistic simulation together with micromechanical analysis was employed to characterize the Young’s modulus and thermal conductivity of graphene/epoxy nanocomposites. The atomistic interaction between graphene and the surrounding epoxy was considered in the molecular dynamic simulation and then used to derive the effective properties of graphene. Subsequently, the Young’s moduli and thermal conductivities of nanocomposites with randomly oriented graphene were modeled from the Mori–Tanaka micromechanical model. The nanocomposites containing pristine graphene, carboxyl (COOH)-functionalized graphene, and COOH- and amine (NH2)-functionalized graphene were considered in the simulation. The results indicated that the COOH- and NH2-functionalized graphene nanocomposite exhibited superior mechanical and thermal properties to those of the other two material systems. Moreover, the model predictions were in good agreement with the experimental data.
41
Chao, Wen-Hsun, and 趙文汛. "Effects of Microstructure on the Thermal Conductivities of Carbon Nanotubes." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/26908199508514869147.
Full textAbstract:
碩士元智大學
機械工程學系
95
The thermal conductivities of carbon nanotubes (CNTs) are estimated by using the double-inclusion model (Nemat-Nasser and Hori, 1999), where one inclusion (the inner void) is embedded in the other (the outer single-crystal graphite shell). The concept of homogenization is utilized and vital microstructural variables such as CNT diameter, length and aspect ratio are included in the present model. The interaction between the microstructure and the thermal conductivities of CNTs are quantitatively characterized. To check the validity of the developed analytic model, the thermal conductivity experiments are performed and benchmarked with the present model. Our results show that the thermal conductivities of CNT are 1241~1974 W/m-K. The thermal conductivity is found to be strongly dependent of the diameter of CNT with little dependence on the length of CNT. The thermal conductivities of CNTs increase with an increase in CNT aspect ratio. In addition, the experimental results obtained agree well with theoretical predictions.
42
Rahimi, Somayyeh Jay. "Thermal and charge conductivities of superconducting skutterudite compounds, PrRu4Sb12 and PrOs4Sb12." Thesis, 2007. http://hdl.handle.net/10012/2733.
Full textAbstract:
The measurement of thermal conductivity is a powerful probe that can be used for identifying the nature of heat and charge carriers and structure of the gap in the superconducting compounds. At low temperature when the effect of phonons in transporting heat becomes smaller, one can obtain information about the quasiparticle distribution and the superconducting gap structure.
In order to do a sensitive thermal conductivity measurement, we designed and built a thermal conductivity mount. The charge conductivity was measured through the same leads that we used for making the thermal conductivity measurements. To test the mount, we measured the heat and charge conductivity of a silver wire and determined the accuracy with which we could satisfy the Wiedemann--Franz law within 5 \%.
We will report the measurements of thermal and electrical conductivities of two filled skutterudite superconducting compounds, PrRu4Sb12 and PrOs4Sb12 at 1.1--35 K temperature range. The differences and similarities between the transport properties of these compounds in the superconducting and normal states along with the results of investigation of the Wiedemann--Franz law will be discussed in the following chapters.
43
Rostro, Betty Catalina. "Novel fibrillar carbon nanotube heat transfer gels with enhanced thermal conductivities." Thesis, 2007. http://hdl.handle.net/1911/20534.
Full textAbstract:
Lubricants and cooling agents such as oil, ethylene glycol, and water are often used as traditional heat transfer fluids (HTFs) in engines, radiators, heat pumps, and other equipment which require cooling and/or energy maintenance. The United States of America (USA) spends over $80 billion on energy maintenance and increasing the thermal efficiency of HTFs by 25% could annually save over $20 billion. This study was aimed at improving the thermal conductivity (TC) of synthetic and vegetable oil heat transfer fluids (HTFs) by using Single-Walled Carbon Nanotubes (SWNTs) additives that resulted in a semi-solid lubricant that was a nanotube-HTF (n-HTF). The n-HTFs were processed with nitrogen containing additives that coupled with toluene and acetone solvent processing promoted the gelation of the carbon nanotube fibers in the oil. Such processing improved the nanotube dispersion due to hydrogen bonding (H bonding) and micelle formation of the amine groups around the carbon nanotube rod-like fibers and the additive-oil matrix. This allowed for high weight percent (Wt %) loadings of carbon nanotubes in the oil.
Characterization via thermal graviometric analysis (TGA) and Fourier Infrared Transform (FTIR) showed that high temperature radical mechanisms breakdown both the oil and nanotubes, and optical microscopy showed that sonication-homogenizing-mixing affects the coagulation-flocculation-aggregation-agglomeration of the nanotubes. Additionally we used two new TC instruments, the Mathis-Hot Disk and KD2 systems, to provide accurate and reproducible data with a 10% and 4% error margin for the Mathis and KD2, respectively. Raman and FTIR spectroscopies suggest that the TC enhancements result from SWNT phonon mechanisms, these being phonon-phonon, phonon-defect, and phonon-interface, all of which are present at room temperature with the absence of ballistic and superconductivity phenomena. Additional vibrations in the oil that occur due to Brownian motion and electron-phonon and H bonding from the additives would have also contributed to the TC mechanism and were evidenced via Raman spectroscopy and FTIR.
The optical microscopy, Raman, FTIR, and TC values indicated that the n-HTFs had a three-dimensional (3D) SWNT networked structure due to the inclusion of the oleylamine additive and the toluene-acetone processing. This would have resulted in the formation of oleylamine-nanotube micelles that were suspended in the oil-additive mixture. Raman spectroscopy evidenced a percolation effect that was coupled with fluid vibrations and Brownian motion, which led to the absence of the one- or two-dimensional (1D, 2D) ballistic or superconductivity phenomena that is often associated with aligned and single SWNTs and other 1D or 2D media, and this was reflected in the TC values. Nevertheless, the TC of the resulting n-HTFs was improved by over 80-96% when compared to other HTFs and the dispersion of the nanotubes in the oil-additive mixture was greatly enhanced. Applications of the n-HTFs include: mechanical-frictional damping, semiconductor packaging, thin-films, hydraulic oil lubricant use, thermoelectric power, thermo-sensing, fuel cells, additive-antioxidant-viscosity modifiers, and filtration.
44
Huang, Chieh, and 黃杰. "Effects of CNT Diameter on the Thermal Conductivities of MWCNT/Epoxy Composites." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/89443360833870804336.
Full textAbstract:
碩士元智大學
機械工程學系
96
Carbon nanotubes (CNTs) exhibit excellent thermal as well as mechanical properties. In the present work, multi-walled carbon nanotubes (MWCNTs) are used as reinforcements to increase the thermal conductivity of epoxy resin. Two groups of MWCNTs are used – one with diameters being less then 10 nm and the other with diameters ranging between 40 to 60 nm. Epoxy and MWCNTs are well mixed and MWCNT/epoxy composites are cured at room temperatures. The thermal conductivities of MWCNT/epoxy specimens are experimentally determined using a thermal conductivity apparatus, LW-9021 developed by Longwin Company. The average thermal conductivity of pure epoxy is 0.23 W/mK and the percentage in increase in average thermal conductivities of 1 wt.%-, 3 wt.%- and 5 wt.%-MWCNT/epoxy composites where the diameter of MWCNT is 40 – 60 nm is 4.3 %, 11.7 % and 27.8%, respectively, higher than that of pure epoxy. For the case of MWCNTs with smaller diameters D < 10 nm, the percentage increase in the average thermal conductivities of 1 wt.%-, 3 wt.%-, and 5 wt.%- MWCNT/epoxy composites is 16.1%, 37.8% and 62.3%, respectively, in comparison with that of pure epoxy. The micromechanics model developed by Eshelby is employed to estimate the thermal conductivities of MWCNT/epoxy. The predicted results agree well with the experimental data of MWCNT/epoxy where the diameters of MWCNT range between 40 and 60 nm. The discrepancy between the experimental data and the predicted results for MWCNT/epoxy where the diameters of MWCNT are less than 10 nm, however, is significant using the microstructural parameters provided by the vendor.
45
YU, XIAN-GUAN, and 余鑑泉. "Numerical determination of effective thermal conductivities of composite material with spherical inclusions." Thesis, 1987. http://ndltd.ncl.edu.tw/handle/45899343856375764168.
Full text
46
Hsiao, Wei-Che, and 蕭偉哲. "Enhancements of Thermal Conductivities in Polymeric Nano-Composites by Doping Boron Nitride." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/81741399417558051600.
Full textAbstract:
碩士國立交通大學
平面顯示技術碩士學位學程
104
The rapid development of semiconductor technology, electronic components towards the light、thin、short、small and high-density evolution of the product in recent years. The waste heat generated in the electronic components during operation ,if we can’t remove these waste heat . These waste heat will effect electronic signals and cause distortion lower reliability, or worse still will lead to component damage. So everyone actively involved in various research institutions to reduce power or heating elements to enhance heat dissipation mechanism. Boron nitride material for electronic applications very popular material, which comes from its potential to be applied with good electrical insulation properties, low dielectric constant and dielectric loss. This paper is for thermal mechanism of BN and Al2O3 .We would like to modify on the surface of BN to improve dispersibility in Silicon, and sprate this composite on electronic component to improve better thermal conductivity.
47
Chu, Chao-Hung, and 朱昭宏. "The Effect of Zr &; Ti Addition on Thermal Conductivities and Thermal Fatigues of Diamond/Silver Composites." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/5dumxd.
Full text
48
Chen, Ting-Gang, and 陳亭綱. "Theoretical and Experimental Study of Reduced Thermal Conductivities for Vertically-Aligned Silicon Nanowires." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/09363777577726458910.
Full textAbstract:
碩士國立交通大學
顯示科技研究所
97
Since silicon is widely used in the integrated circuit (IC) industry, the ability to tailor the thermoelectric properties of bulk silicon using its nanostructures can enable a variety of exciting applications, such as efficient thermo-photovoltaic devices, and monolithically- integrated electronic and optoelectronic device cooling. In late 2007, scientists have reported that a single silicon nanowire (Si NW) with a diameter less than 52nm exhibits a low thermal conductivity ~1.6 Wm-1k-1 and ZT ~1 at room temperature, suggesting the potential of using Si NWs for efficient thermoelectric energy conversion. In order to realize a practical thermoelectric device based on Si NWs, it is essential to fabricate large-area and highly-oriented Si NW arrays on silicon substrates. In this paper, we demonstrate the preparation of vertically-aligned Si NWs with diameters of tens of nanometers, heights ranging from tens of micrometers to over 100 μm, and most importantly, an area over 5x5 cm2. Characterizations using a hot-disk slab-module system show the thermal conductivity reduced for the fabricated Si NW samples, compared to that of bulk silicon. Two-dimensional microscale heat-transfer analyses of Si NWs based on the equation of phonon radiative transfer are presented. The high-aspect-ratio and vertically-aligned Si NW arrays were fabricated using a silver-induced wet deposition and wet chemical etching method. The surface morphology and the etching length depend on the concentration of both AgNO3 and HF solution, the etching temperature, and etching time. The concentration of AgNO3 affects the structure of the nanowire arrays because the porosity is determined by the density of deposited Ag particles. A Hot Disk 2500 slab-module system was then employed to measure the thermal conductivity of the fabricated NWs. During the measurement, the sensor was sandwiched between two samples, while the other side of samples was insulated by a material with a low thermal conductivity in order to reduce the heat losses to the surroundings. The thermal conductivities obtained from Si NW samples were lower than bare Si substrates for all six individual experiments. Then we use equation of phonon radiative transfer to simulate our structure. Compare to thermal resistance model, the equation of phonon radiative transfer consider size effect when the boundary is comparable to phonon mean free path. In summary, we have successfully fabricated large-area, high-aspect-ratio Si NW arrays, and measured their thermal properties using a Hot Disk system. The Si NW samples exhibit a reduced thermal conductivity, compared to that of bulk Si, showing great potential for next-generation thermoelectric devices.
49
Chang, Wei-Ting, and 張偉庭. "Thermal Conductivities of Si and Ge at Different Index Planes by Molecular Dynamics Simulation." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/21559590516816301527.
Full textAbstract:
碩士國立臺灣大學
應用力學研究所
96
In recent years, many researches on nanotube, nanowire, and superlattices have been carried out. In this thesis, we study the thermal conductivities of silicon and germanium at different index planes in the nanoscale. The simulation method used molecular dynamics simulation, and the governing equation is Hamiltonian equations of motion in classical Newtonian mechanics. The molecular initial position of a diamond unit cell structure is used for periodic boundary condition and expresses the infinite boundary crystal lattice arrangement by the limited bulk material. The molecular initial velocity is determined by Maxwell-Boltzmann distribution. Because silicon and germanium mainly belongs to three body potential for the covalent bonding and also the needs to consider the intermolecular bonding angle, we choose Tersoff potential to calculate covalent bonding intermolecular force and molecular acceleration. We obtain each molecular new position and the new velocity by the Velocity-Verlet integration method, and obtain the heat flux under the state of equilibrium. Through the different time evolution, we calculate the autocorrelation function from heat flux. Finally, we calculate the thermal conductivity by Green-Kubo formalism. We compare the thermal conductivities of silicon and germanium at different index planes.
50
Chiu, Jui-Ting, and 邱瑞霆. "Enhancements of Thermal Conductivities in Polymeric Composites by Blending Boron Nitride(BN) and Aluminum Nitride (AlN)." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/40757901158237724735.
Full textAbstract:
碩士國立交通大學
平面顯示技術碩士學位學程
104
Boron nitride (BN) has good thermal conductive capacities and cheap price, so BN becomes common filler inorganic materials for heat dissipation in the industrial applications. We got some good results from our present project in the past half an year, i.e., “Enhancements of Thermal Conductivities in Polymeric Nano-Composites by Doping Boron Nitride (BN)”. The thermal conductivities of the polymeric composites were enhanced gradually (up to 0.8 W / mK) as BN was added gradually in the polymers (RTV). In addition, the crystallinity of BN in the polymers was increased as the additive (1,8-diiodooctane) was introduced in the polymeric composites, and the XRD patterns prove the crystallinity of BN is proportional to the amounts of 1,8-diiodooctane. Thus, the thermal conductivities of the polymeric composites were improved due to the higher crystallinity of BN induced by the additive (1,8-diiodooctane). In this proposal, we focus on two different inorganic materials (boron nitride BN and aluminum nitride AlN with excellent thermal conductivities) blended with three different kinds of monomers containing various functional groups (including acrylic group, and C=C combined with Si-H groups). Different types and ratios of inoganic materials (boron nitride and aluminum nitride with various sizes) and polymers (containing acrylic group, and C=C, Si-H) were blended to produce various polymeric composites. Therefore, according to the adjustment of previous parameters, polymeric composites can be optimized to possess many different requested merits, such as packaging, thermal conductivity, thermal stress, and transparency, via the following characterization techniques: Thermal conductive equipments. Finally, we expect to obtain polymeric composites with the optimized thermal conductivities, thermal stress, transparency, and mechanical properties. Key Words: Polymer Composites, Hexagonal Boron Nitride, Aluminum Nitride, Heat Dissipation.