1 |
Effect of Interface, Density and Height of Carbon Nanotube Arrays on Their Thermal Conductivity: An Experimental StudyRaghavan, Vasudevan January 2010 (has links)
No description available.
|
2 |
Thermo-Mechanical Characterization and Interfacial Thermal Resistance Studies of Chemically Modified Carbon Nanotube Thermal Interface Material - Experimental and Mechanistic ApproachesMustapha, Lateef Abimbola, Mustapha, Lateef Abimbola January 2017 (has links)
Effective application of thermal interface materials (TIM) sandwiched between silicon and a heat spreader in a microelectronic package for improved heat dissipation is studied through thermal and mechanical characterization of high thermally conductive carbon nanotubes (CNTs) integrated into eutectic gallium indium liquid metal (LM) wetting matrix. Thermal conductivity data from Infrared microscopy tool reveals the dependence of experimental factors such as matrix types, TIM contacting interfaces, orientation of CNTs and wetting of CNTs in the matrix on the thermal behavior of TIM composite.
Observed generalized trend on LM-CNT TIM shows progressive decrease in effective thermal conductivity with increasing CNT volume fractions. Further thermal characterizations LM-CNT TIM however show over 2x increase in effective thermal conductivity over conventional polymer TIMs (i.e. TIM from silicone oil matrix) but fails to meet 10x improvement expected.
Poor wetting of CNT with LM matrix is hypothesized to hinder thermal improvement of LM-CNT TIM composite. Thus, wetting enhancement technique through electro-wetting and liquid crystal (LC) based matrix proposed to enhance CNT-CNT contact in LM-CNT TIM results in thermal conductivity improvement of 40 to 50% with introduction of voltage gradient of 2 to 24 volts on LM-CNT TIM sample with 0.1 to 1 percent CNT volume fractions over non voltage LM-CNT TIM test samples.
Key findings through this study show that voltage tests on LC- CNT TIM can cause increased CNT-CNT networks resulting in 5x increase in thermal conductivity over non voltage LC-CNT TIM and over 2x improvement over silicone-CNT TIMs. Validation of LM wetting of CNT hypothesis further shows that wetting and interface adhesion mechanisms are not the only factors required to improve thermal performance of LM-CNT TIM. Anisotropic characteristic of thermal conductivity of randomly dispersed CNTs is a major factor causing lower thermal performance of LM-CNTs TIM composite. Other factors resulting in LM-CNT TIM decreasing thermal conductivity with increasing CNT loading are (i) Lack of CNT-CNT network due to large difference in surface tension and mass density between CNTs and LM in TIM composite (ii) Structural stability of MWCNT and small MFP of phonons in ~5um MWCNTs compared to the system resulted in phonon scattering with reduced heat flow (iii) CNT percolation threshold limit not reached owing to thermal shielding due to CNT tube interfacial thermal resistance.
While mixture analytical models employed are able to predict thermal behaviors consistent with CNT-CNT network and CNT- polymer matrix contact phenomenon, these models are not equipped to predict thermo-chemical attributes of CNTs in LM-CNT TIM. Extent of LM-CNT wetting and LM-solid surface interfacial contact impacts on interfacial thermal resistance are investigated through LM contact angle, XPS/AES and SEM-EDX analyses on Au/Ni and Ni coated copper surfaces. Contact angle measurements in the range of 120o at both 55oC and 125oC show non wetting of LM on CNT, Au and Ni surfaces. Interface reactive wetting elemental composition of 21 days aged LM on Au/Ni and Ni surfaces reveals Ga dissolution in Au and Ni diffusion of ~0.32um in Au which are not present for similar analysis of 1 day LM on Au/Ni surface. Formation of Au-Ni-Ga IMC and IMC-oxide iono-covalency occurrence at the interface causes reduction in surface tension and reduction in interfacial contact resistance.
|
3 |
Characterization of the Thermal Resistance of Grain Boundaries of Cerium OxideSpackman, Jesse 01 May 2017 (has links)
Many materials are made up of small crystals, or grains. Grain boundaries are the interfaces between two grains and affect the flow of heat through the material. These interfaces serve to interfere with the energy carriers by scattering or disrupting them. Because of the negative effect these interfaces have on these energy carriers, they inhibit heat flow and act as thermal resistors. The thermal boundary resistance between two grains of the same material is sometimes referred to as the Kapitza resistance, although this term is also used to describe the thermal resistance between solid/solid interfaces of different materials or solid/liquid interfaces. A better understanding of the heat transport process on a micro-scale is especially relevant to nuclear energy applications. Nuclear fuels are polycrystalline materials that experience large heat differences over small distances. An improved understanding of these grain boundaries and the role they play in transferring heat can help better predict nuclear fuel performance and improve nuclear reactor efficiency and safety.
The study of the thermal resistance across crystal interfaces and their potential influence on nuclear fuels is a topic that has received relatively little attention. While the thermal resistance across a single grain boundary is rather small, the total resistance generated from many grain boundaries can have a big impact on the material. Smaller grains mean there are more interfaces, which will result in a lower overall thermal conductivity.
For this study, Kapitza resistance across individual grain boundaries was measured using a laser-based measurement technique. The sample material was Cerium Oxide. It was used because of its similar properties to Uranium Oxide, which is a popular material used in nuclear fuel. The average interfacial thermal resistance measured at room temperature in this thesis study was 9.88∙10-9 �2�/�. The average measured value fit in an accepted range from other results found in similar studies.
|
4 |
[en] PULL-OUT STRENGTH OF NAILS IN GNAISSIC RESIDUAL SOIL / [pt] RESISTÊNCIA AO ARRANCAMENTO DE GRAMPOS EM SOLO RESIDUAL DE GNAISSE15 March 2006 (has links)
[pt] A presente pesquisa trata da avaliação da resistência ao
arrancamento de grampos em solo residual de gnaisse. Foram
realizados ensaios de arrancamento em uma obra de solo
grampeado executada em um maciço de solo residual de
gnaisse. A resistência ao arrancamento foi avaliada em 4
cotas diferentes ao longo do perfil de escavação. Foram
realizados 8 ensaios de arrancamento em grampos de 4m de
comprimento. Quatro ensaios foram executados em grampos
instrumentados com strain-gages, para avaliar a
distribuição das cargas de tração durante os estágios de
carregamento. Foram também realizados ensaios de
cisalhamento direto no solo e na interface solo/cimento
para avaliação das propriedades mecânicas destes
materiais. Amostras indeformadas foram coletadas
imediatamente à frente dos furos de instalação dos grampos
ensaiados garantindo uma maior representatividade dos
materiais. Uma relação semi-empírica é proposta para se
avaliar a resistência do solo e da interface solo/nata de
cimento, obtidos em ensaios de cisalhamento direto no
laboratório. Os resultados obtidos nesta pesquisa são
comparados com ensaios realizados por outros autores, em
encostas de solos residuais de gnaisse e empregados para
validação da relação desenvolvida. / [en] The present research presents an evaluation of the pullout
resistance of nails in residual gneissic soil. Pullout
tests were carried out in 4 different levels of the nailed
wall with nails 4m long. Four tests were carried out in
strain-gauged nails for evaluating the tension
distribuition along the nail. A series of direct shear
tests in soil specimens and in the soil/grout interface
were also performed for obtaining the mechanical
properties of these materials. Undisturbed samples had
been collected very close to the pull-out test locations.
A semi-empirical relation is proposed for evaluating the
pullout resistance of nails, based on the shear strenghth
parameters of the soil and of the soil/grout interface
from laboratory direct shear tests.
|
5 |
[en] STUDY OF SOIL-GEOSYNTHETIC INTERFACE RESISTANCE USING AN RAMP APPARATUS / [pt] ESTUDO DA RESISTÊNCIA DE INTERFACE SOLO-GEOSSINTÉTICO UTILIZANDO O EQUIPAMENTO DE RAMPAEMILIANA DE SOUZA REZENDE 22 September 2005 (has links)
[pt] Em obras ambientais, onde geossintéticos são utilizados
como sistema de
proteção e de cobertura de taludes, é de extrema
importância o conhecimento do
mecanismo de interação solo-geossintético, através da
obtenção dos parâmetros de
resistência da interface (adesão e ângulo de atrito da
interface). O ensaio de
laboratório mais adequado para a obtenção desses
parâmetros, nestas condições, é
o de cisalhamento em plano inclinado ou ensaio de rampa,
pois permite simular a
condição de campo onde o cisalhamento ocorre em um plano
inclinado sob baixas
tensões. Assim, este trabalho apresenta um estudo sobre a
interação sologeossintético
através de ensaios de rampa, executados em um equipamento
de
grandes dimensões, visando analisar a influência de alguns
fatores, tais como, tipo
de geossintético, tipo de solo, densidade relativa do solo
e tensão confinante.
Foram utilizados dois tipos de geossintéticos, uma
geomembrana de PVC e uma
geogrelha uniaxial e dois tipos de solo, areia e
pedregulho (brita). A análise da
influência da densidade relativa do solo foi realizada
através de ensaios na
interface areia-geossintético em duas densidades relativas
diferentes (35 e 100%).
A influência da tensão confinante foi estudada através de
ensaios com três tensões
confinantes distintas (2,1; 3,2 e 5,1 kPa). Os resultados
mostram que a influência
de fatores como densidade relativa do solo, tensão
confinante e tipo de solo,
dependem do tipo do geossintético. O aumento da densidade
relativa do solo
promove um acréscimo de resistência na interface para a
geogrelha e uma redução
para a geomembrana. O aumento da tensão confinante reduz o
ângulo de rampa na
ruptura, sendo este efeito mais pronunciado na interface
areia-geogrelha. Em
relação ao tipo de material, a interface brita-geogrelha é
a que apresenta maior
resistência. / [en] In environmental works, where geosynthetics are used as
protection system
and of slope covering, it is of extreme importance the
knowledge of the
interaction mechanism soil-geosynthetic, through the
obtaining of the parameters
of resistance of the interface (adhesion and interface
friction angle). The
laboratory test more appropriate for the obtaining of
those parameters, in these
conditions, is it the inclined plane test or ramp test,
because it allows to simulate
the field condition where the shearing happens in inclined
plane under low
tensions. Like this, this work presents a study about the
interaction soilgeosynthetic
through ramp tests, executed in an equipment of great
dimensions
seeking to analyze the influence of some factors, such as,
geosynthetic type, soil
type, relative density of the soil and confinement
pressure. Two geosynthetics
types, a PVC geomembrane and a uniaxial geogrid, two soil
types, it sand and
gravel (break). The analysis of the influence of the
relative density of the soil was
accomplished through tests in the interface sand-
geosynthetic in two different
relative densities (35 and 100%). The influence of the
confinement pressure was
studied through tests with three different confinement
pressures (2,1; 3,2 and 5,1
kPa). The results show that the influence of factors as
relative density of the soil,
pressure confinement and soil type, they depend on the
type of the geosynthetic.
The increase of the relative density of the soil promotes
an increment in the
interface resistance for the geogrid and a reduction for
the geomembrana. The
increase of the confinement pressure reduces the ramp
angle in the rupture, being
this more pronounced effect in the interface sand-geogrid.
In relation to the
material type, the interface gravel-geogrid presents
larger resistance.
|
6 |
Neuartige Charakterisierungsmethoden für moderne Thermische Interface-Materialien einschließlich deren Struktur-Eigenschafts-KorrelationAbo Ras, Mohamad 11 June 2020 (has links)
Die fortschreitende Miniaturisierung von elektronischen Systemen begleitet von steigender Leistung und Funktionalität führt zur Erhöhung der Leistungsdichte. Um diesem Trend zu entsprechen, werden neue Entwärmungskonzepte benötigt, die wiederum neuartige Materialien und Materialverbünde fordern. Ein wichtiger Aspekt dieser Arbeit ist deshalb die Konzentration auf die für den Wärmetransport entscheidenden Materialien. Diese Arbeit befasst sich mit der Entwicklung von Methoden für die umfassende thermische Charakterisierung von den verschiedenen Materialien und Materialklassen, die in der Elektronikindustrie verwendet werden. Die Messsysteme wurden so entworfen und entwickelt, dass spezifische Anwendungsbedingungen berücksichtigt werden können, keine aufwändige Probenherstellung notwendig ist und gleichzeitig eine hohe Messgenauigkeit gewährleistet ist. Es wurden vier verschiedene Messsysteme innerhalb dieser Arbeit entwickelt und realisiert, die in ihrer Gesamtheit die Charakterisierung von fast allen Package-Materialien unter gewünschten Randbedingungen ermöglichen. Zahlreiche Materialien und Effekte wurden daraufhin im Rahmen dieser Arbeit mit den entwickelten Messsystemen untersucht und diskutiert. / The continuous miniaturization of electronic systems accompanied by increasing performance and functionality leads to an increase in power density. In order to comply this trend, new heat dissipation concepts are needed which demand new materials and material composites. An important aspect of this work is therefore the concentration on the materials that are decisive for the heat flow. This thesis deals with the development of Methods for comprehensive thermal characterization of the different materials and material classes used in the electronics industry. The measuring systems have been designed and developed in such a way that they enable to take into account specific application conditions, no costly sample preparation is necessary and at the same time high measuring accuracy is ensured. Four different measuring systems were developed and realized within this work, which, in their entirety, enable the characterization of almost all package materials under desired boundary conditions. Based on this, numerous materials and effects were investigated and discussed in the context of this work with the developed measurement systems.
|
Page generated in 0.1284 seconds