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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1251

An Experimental Study on Soil Water Characteristics and Hydraulic Conductivity of Compacted Soils

Cuceoglu, Faik 23 September 2016 (has links)
The importance of applying unsaturated soil mechanics concepts to geotechnical engineering design has been widely recognized. Soil water characteristic curve (SWCC) and hydraulic conductivity function (HCF) are vital soil properties that govern engineering behavior of unsaturated soils. In this study, a transient water release and imbibitions method (TRIM) is used to measure the SWCC and HCF under drying and wetting states, which accommodates integrated experimental and modeling techniques. The results of saturated hydraulic conductivity tests through flexible wall method are then used as input parameters for simulating experimental data. In general, the model provides a satisfactory fit to experimental data. Soil water characteristic curves (SWCCs) and hydraulic conductivity functions (HCFs) are presented for a variety of soils that were prepared at different molding water contents and compactive efforts. The influences of dry density, molding water content, and hysteresis have been investigated. Dry density affects soil-water characteristic in terms of its air-entry value (AEV), rate of drying, and size of the hysteresis loop. The test results indicate that the SWCC and HCF obtained in terms of volumetric water content is more sensitive to the changes in dry density than molding water content. Based on cohesive soil results, some statistical relations are proposed to estimate wetting-path SWCC and HCF parameters from more easily measured drying curves. Changes in the van Genuchten's fitting parameters and residual volumetric water content are investigated for both drying and wetting conditions, with changes in the kaolin clay content. / Master of Science / Traditional soil mechanics practice has experienced considerable changes during the past few decades. Within that period, the necessity of unsaturated soil mechanics has gradually emerged and become a part of geotechnical engineering practice. Soil water characteristic curve (SWCC) and hydraulic conductivity function (HCF) are very important properties in the assessment of unsaturated soil behaviors. A transient water release and imbibitions method (TRIM) is used to investigate unsaturated soil properties of a variety of test soils under laboratory conditions. TRIM integrates a testing program and a modeling technique to measure SWCC and HCF concurrently for both drying (water release upon matric suction increase) and wetting (water imbibition upon matric suction decrease) conditions. Compaction, which is a classical application involving unsaturated soil, has the preferred practice for improving the mechanical and hydraulic properties of a soil. The structure and fabric of compacted material is very dependent on the compacted conditions, including compactive effort and molding water content. This paper evaluates the influence of such mentioned factors on the SWCC and HCF. The test results indicate that the SWCC and HCF obtained in terms of volumetric water content is more sensitive to the changes in compactive effort than molding water content. Hysteresis phenomena, the difference in the relationship between the water content of the soil and the corresponding water potential under drying and wetting path, is investigated. Based on cohesive soil results, some statistical relations are proposed to estimate wetting-path SWCC and HCF parameters from more easily measured drying curves.
1252

Observation of highly decoupled conductivity in protic ionic conductors

Wojnarowska, Z., Wang, Y., Paluch, Krzysztof J., Sokolov, A.P., Paluch, M. 27 March 2014 (has links)
Yes / Ionic liquids (ILs) are key materials for the development of a wide range of emerging technologies. Protic ionic liquids, an important class of ILs, have long been envisioned as promising anhydrous electrolytes for fuel cells. It is well known that in comparison to all other cations, protons exhibit abnormally high conductivity in water. Such superprotonic dynamics was expected in protic ionic conductors as well. However, many years of extensive studies led to the disappointing conclusion that this is not the case and most protic ionic liquids display subionic behavior. Therefore, the relatively low conductivity seems to be the main obstacle for the application of protic ionic liquids in fuel cells. Using dielectric spectroscopy, herein we report the observation of highly decoupled conductivity in a newly synthesized protic ionic conductor. We show that its proton transport is strongly decoupled from the structural relaxation, in terms of both temperature dependence and characteristic rates. This finding offers a fresh look on the charge transport mechanism in PILs and also provides new ideas for design of anhydrous materials with exceptionally high proton conductivity. / National Science Centre within the framework of the Opus project (Grant No. DEC 2011/03/B/ST3/02072). Financial assistance from FNP START. The LDRD Program of ORNL, managed by UT-Battelle, LLC, for the U.S. DOE. Support from the NSF under grant CHE-1213444.
1253

Suction Cup Lysimeter Method for Extracting Pine Bark Substrate Solution

Stanley, Mary H. 01 May 2002 (has links)
The objective of this study was to determine the effectiveness of suction cup lysimeters (SCL) in extracting substrate solution from pine bark substrates. Lysimeter types tested were 4.8-cm diameter with a ½ or 1-bar air-entry value (AEV) and 2.2-cm diameter also with a ½ or 1-bar AEV. Sufficient volume could be obtained when a vacuum pressure of 30, 40 or 50 cb was applied to lysimeters with a minimum extraction time of five minutes. The 2.2-cm lysimeters were found to be suitable for extracting solution if smaller sample volumes were needed. To determine effect of vacuum pressure and extraction time on volume extracted, the 4.8-cm ½-bar lysimeters were installed in containers with pine bark substrate and Quercus phellos L. (willow oak) trees. Volumes extracted were somewhat erratic and not strongly dependent upon centibars of vacuum or extraction time. Lysimeters immersed in water demonstrated that variability was not due to individual lysimeters, but to the coarse nature of the pine bark substrate. Substrate EC levels were not affected when volume of substrate solution extracted by the SCL's varied from 10 to190 ml.â To determine the effectiveness of SCL's to monitor nutrient status of container-grown shade trees, two-year-old container-grown willow oak trees were grown in a pine bark substrate and fertilized with 0, 50, 100, 150, 200, 250 or 300 grams Osmocote Plus Northern (15N – 3.9P – 9.8K). Plant height and trunk diameter increased with up to 200 grams of Osmocote per container. There was a good relationship between solution EC and plant growth / Master of Science
1254

Development of high temperature MIEC catalytic reactors for energy conversion and storage aplications

Laqdiem Marín, Marwan 10 June 2024 (has links)
[ES] Esta tesis está centrada en la combinación de diferentes tecnologías para mejorar las tecnologías emergentes de captura y almacenamiento de carbono (CSS) y la revalorización del CO2 capturado. La principal tecnología estudiada en esta tesis fueron las membranas de transporte de oxigeno (OTMs), las cuales pueden producir oxigeno puro de forma más flexible que las actuales tecnologías de producción de oxigeno, como la destilación criogénica de aire. La producción de oxigeno puro es crucial para desarrollar reactores de oxicombustión que podrían ser mas eficientes para la captura de CO2 que los reactores actuales de combustión con aire. Los estudios sobre OTMs se dividieron en dos temas principales: membranas de bifásicas estables en CO2 y membranas basadas en BSCF (Ba1-xSrxCo1-yFeyO3-¿). Por otro lado, para la revalorización del CO2 capturado, se estudio' la tecnología de looping químico basada en catalizador de oxido de cerio, que aprovecha las propiedades redox del catalizador a diferentes pO2 y altas temperaturas (entre 700- 1400 ¿C). En general, las principales etapas limitantes en OTMs son la transferencia de oxigeno a trave's de la membrana y las reacciones superficiales. Por eso, una mejora en las propiedades de la capa catalítica podri'a mejorar la permeacio'n total de oxigeno. El primer estudio sobre membranas bifásicas se centro' el estudio de capas catali'ticas con distintas proporciones de ambas fases. Para este estudio, se selecciono' el NFO-CTO (NiFe2O4/Ce0.8Tb0.2O2-¿) como composite. Este material ya ha sido estudiado en nuestro laboratorio, y mostró una gran estabilidad en atmósferas de CO2, pero con baja permeación de O2 en comparación con otros composites. Este estudio mostró resultados interesantes, y se combino' con medidas de espectroscopia de impedancia electroqui'mica (EIS), utilizadas habitualmente para estudiar electrodos para pilas de combustible de o'xido so'lido (SOFC) y pilas de electro'lisis de o'xido so'lido (SOEC). El segundo estudio sobre composites para OTMs se centro' en el aumento de la permeacio'n de oxi'geno con composites basados en espinela-fluorita. En este caso, el transporte de oxigeno esta' controlado, adema's de por la temperatura y el gradiente de pO2, por la conductividad ambipolar, en la que intervienen las conductividades eléctrica e io'nica. Asi', se cambio' la fase de NFO por la fase de CMO (Co2MnO4) que tiene mayor conductividad total que el NFO. El composite resultante (CMO-CTO) ha mostrado un mayor rendimiento que el material predecesor NFO-CTO. Como se ha mencionado anteriormente, el otro estudio sobre OTM se realizo' con membranas basadas en BSCF. En este estudio, la membrana capilar BSCF fue electrificada para aumentar la temperatura de la membrana por efecto Joule y como consecuencia un aumento en la permeación de oxigeno. Además, se estudió este efecto bajo deshidrogenacio'n oxidativa de etano, obteniéndose una mejora importante para las membranas BSCF electrificadas en comparación con las membranas BSCF no electrificadas. Estos estudios abren las puertas al uso de ellas con reactores a más baja temperatura. El último estudio se centra en la revalorización del CO2 mediante el reformado de metano por ciclos químicos. Los ciclos químicos están basados en las propiedades redox del catalizador y las dos etapas de reducción y oxidación del catalizador. La reducción del catalizador es realizada mediante temperatura y en condiciones inertes o con corrientes reductoras como por ejemplo en metano. Los estudios se centran en la reducción a través de metano que trabaja a temperaturas más bajas que para corrientes inertes y, ademas, proporciona corrientes de syngas (mezcla de CO y H2) en la etapa de reducción del catalizador, que mejora la eficiencia global del proceso. La revalorización del CO2 se realizaba en la etapa de oxidación del catalizador. La oxidación de estos catalizadores podría formarse con flujos de H2O y/o / [CA] Aquesta tesi està centrada en la combinació de diferents tecnologies per millorar les tecnologies emergents de captura i emmagatzematge de carboni (CSS) i la revalorització del CO2 capturat. La principal tecnologia estudiada en aquesta tesi van ser les membranes de transport d'oxigen (OTMs), les quals poden produir oxigen pur de manera més flexible que les actuals tecnologies de producció d'oxigen, com la destil·lació criogènica de l'aire. La producció d'oxigen pur és crucial per al desenvolupament de reactors d'oxicombustió que podrien ser més eficients per a la captura de CO2 que els reactors actuals de combustió amb aire. Els estudis sobre OTMs es van dividir en dos temes principals: membranes composites de dos fases estables en CO2 i membranes basades en BSCF (Ba1- xSrxCo1-yFeyO3-). D'altra banda, per a la revalorització del CO2 capturat, es va estudiar la tecnologia de looping químic basada en catalitzador d'òxid de ceri, que aprofita les propietats redox del catalitzador a diferents pO2 i altes temperatures (entre 700-1400 ºC). En general, les principals etapes limitants en OTMs són la transferència d'oxigen a través de la membrana i les reaccions superficials. Per això, una millora en les propietats de la capa catalítica podria millorar la permeació total d'oxigen. El primer estudi sobre membranes bifàsiques es va centrar en l'estudi de capes catalítiques amb diferents proporcions de ambdues fases. Per a aquest estudi, es va seleccionar el NFO-CTO (NiFe2O4/Ce0.8Tb0.2O2-δ) com a composite. Aquest material ja ha sigut estudiat en el nostre laboratori, i va mostrar una gran estabilitat en atmosferes de CO2, però amb baixa permeació d'O2 en comparació amb altres composites. Aquest estudi va mostrar resultats interessants, i es va combinar amb mesures d'espectroscòpia d'impedància electroquímica (EIS), utilitzades habitualment per estudiar elèctrodes per a piles de combustible d'òxid sòlid (SOFC) i piles d'electròlisi d'òxid sòlid (SOEC). El segon estudi sobre composites per a OTMs es va centrar en l'augment de la permeació d'oxigen amb composites basats en espinela-fluorita. En aquest cas, el transport d'oxigen està controlat, a més de per la temperatura i el gradient de pO2, per la conductivitat ambipolar, en la qual intervenen les conductivitats elèctrica i iònica. Així, es va canviar la fase de NFO per la fase de CMO (Co2MnO4) que té una major conductivitat total que el NFO. El composite resultant (CMO-CTO) ha mostrat un major rendiment que el material predecessor NFO-CTO. L'últim estudi es centra en la revalorització del CO2 mitjançant el reformat de metà per cicles químics. Els cicles químics estan basats en les propietats redox del catalitzador i les dues etapes de reducció i oxidació del catalitzador. La reducció del catalitzador és realitzada mitjançant temperatura i en condicions inertes o amb corrents reductores com per exemple en metà. Els estudis se centren en la reducció a través de metà que treballa a temperatures més baixes que per a corrents inertes i, a més, proporciona corrents de syngas (barreja de CO i H2) en l'etapa de reducció del catalitzador, que millora l'eficiència global del procés. La revalorització del CO2 es realitzava en l'etapa d'oxidació del catalitzador. L'oxidació d'aquests catalitzadors podria formar-se amb fluxos de H2O i/o CO2 a altes temperatures 700- 1000 ºC. El nostre estudi es centra en òxids de ceri dopats al 10% amb elements 19Chapter 0: Preamble trivalent, generalment lantànids. En aquest estudi es va correlacionar la velocitat de splitting del CO2 en l'etapa d'oxidació amb el volum de cel·la de l'estructura cristal·lina i la conductivitat total d'aquests materials. / [EN] This thesis is focused on the combination of different technologies to improve emerging technologies for carbon capture and storage (CSS) and the revalorization of the CO2 captured. The leading technology studied in this thesis was oxygen transport membranes (OTMs) that could produce pure oxygen more flexibly than the current oxygen production technologies like cryogenic air distillation. The production of pure oxygen is crucial for developing oxycombustion reactors that could be more efficient for carbon capture than traditional combustion reactors. The OTMs studies were divided into two main topics: dual-phase membranes with stable operation in CO2 and BSCF-based membranes (Ba1-xSrxCo1-yFeyO3-¿). For the revalorization of the captured CO2, the chemical looping technology based on a cerium oxide catalyst was studied, which takes advantage of the redox properties of the catalyst at different pO2 and high temperatures (between 700-1400 ¿C). In general, the principal limiting steps for OTMs were the bulk oxygen transfer and the surface exchange reactions. In this matter, the improvement in the behaviour of the catalytic layer could achieve better oxygen permeation. The first study for dual- phase membranes was focused on the role of the different dual-phase ratios in the behaviour as a catalytic layer in OTMs. For this study, NFO-CTO (NiFe2O4/Ce0.8Tb0.2O2-¿) was selected as dual-phase material. This material was previously studied and showed high stability under CO2 environments but with poor oxygen flux compared with other dual-phase materials. The study considered for the present Thesis showed interesting results, and it was combined with electrochemical impedance spectroscopy (EIS) measurements, commonly used to study electrodes for solid oxide fuel cells (SOFC) and solid oxide electrolysis cells (SOEC). The second study in dual-phase materials for OTMs focused on the increase in oxygen permeation for spinel-fluorite-based materials. In this matter, the bulk oxygen transports are controlled, apart from the temperature and the pO2 gradient, by the ambipolar conductivity, where the electrical and the ionic conductivities are involved. So, the NFO phase was changed for the CMO phase (Co2MnO4), which has higher total conductivity than the NFO. The resultant dual- phase material (CMO-CTO) performed better than the predecessor NFO-CTO material. As mentioned previously, the other study on OTMs focused on BSCF-based membranes. In this study, the BSCF capillary membrane was electrified in order to increase the membrane temperature via the Joule effect and, as a consequence, an increase in the oxygen permeation. In addition, this effect under oxidative dehydrogenation of ethane was studied, obtaining an essential improvement for electrified BSCF membranes compared with non-electrified BSCF membranes. These studies have opened new gates to operate these membranes at lower reactor temperatures. Finally, the last study was focused on CO2 upcycling via chemical looping methane reforming. Chemical looping is based on the redox properties of the catalyst in two principal steps, reduction and oxidation of the catalyst. The catalyst reduction is performed with temperature in inert conditions or with reducing streams like methane. We were focused on the reduction via methane that works at lower temperatures than inert streams and could provide syngas streams (a mixture of CO and H2) that improve global efficiency. The revalorization of the CO2 was performed in the other step, the oxidation part of the cycle. The oxidation of those catalysts could be formed with H2O and/or CO2 streams at high temperatures of 700-1000 ¿C. Our study was focused on 10% doped cerium oxide with trivalent elements. In this study, the CO2 splitting on the oxidation step was correlated with the crystal structure parameters and the total conductivity of these materials. / Laqdiem Marín, M. (2024). Development of high temperature MIEC catalytic reactors for energy conversion and storage aplications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/204871
1255

Micro-Pipette Thermal Sensor: A Unique Technique for Thermal Characterization of Microfluids, Microsphere, and Biological Cell

Shrestha, Ramesh 05 1900 (has links)
In this research work, an innovative method for measurement of thermal conductivity of a small volume of liquids, microsphere, and the single cancer cell is demonstrated using a micro-pipette thermal sensor (MPTS). The method is based on laser point heating thermometry (LPHT) and transient heat transfer. When a single pulse of a laser beam heats the sensor tip which is in contact with the surrounding liquids or microsphere/cells, the temperature change in the sensor is reliant on the thermal properties of the surrounding sample. We developed a model for numerical analysis of the temperature change using the finite element method (FEM) in COMSOL. Then we used MATLAB to fit the simulation result with experiment data by multi-parameter fitting technique to determine the thermal conductivity. To verify the accuracy in the measurement of the thermal conductivity by the MPTS method, a 10µl sample of de-ionized (DI) water, 50%, and 70% propylene glycol solution were measured with deviation less than 2% from reported data. Also, to demonstrate that the method can be employed to measure microparticles and a single spherical cell, we measured the thermal conductivity of poly-ethylene microspheres with a deviation of less than 1% from published data. We estimated the thermal conductivity of two types of cell culture growth media for the first time and determined the thermal conductivity of cancerous Jurkat Clone E6-1 to be 0.538 W/m.K ± 2%. Using the sensor of 1-2μm tip size, we demonstrated the MPTS technique as a highly accurate technique for determining the thermal conductivity of microfluidic samples, microparticles, biological fluids, and a non-invasive method for measuring the thermal conductivity of single cancer cell. This MPTS technique can be beneficial in developing a diagnosis method for the detection of cancer at an early stage. We also compared three effective thermal conductivity models for determining the weight percentage of Jurkat cell, considering water and protein as the major constituents. We discovered that a combination of Maxwell-Euken and effective medium theory model provides the closest approximation to published data and, therefore, recommend for the prediction of the cell composition.
1256

Artificial Neural Network Based Thermal Conductivity Prediction of Propylene Glycol Solutions with Real Time Heat Propagation Approach

Jarrett, Andrew Caleb 08 1900 (has links)
Machine learning is fast growing field as it can be applied to solve a large amount of problems. One large subsection of machine learning are artificial neural networks (ANN), these work on pattern recognition and can be trained with data sets of known solutions. The objective of this thesis is to discuss the creation of an ANN capable of classifying differences in propylene glycol concentrations, up to 10%. Utilizing a micro pipette thermal sensor (MTS) it is possible to measure the heat propagation of a liquid from a laser pulse. The ANN can then be trained beforehand with simulated data and be tested in real time with temperature data from the MTS. This method could be applied to find the thermal conductivity of unknown fluids and biological samples, such as cells and tissues.
1257

PAOFLOW-Aided Computational Materials Design

Wang, Haihang 12 1900 (has links)
Functional materials are essential to human welfare and to provide foundations for emerging industries. As an alternative route to experimental materials discovery, computational materials designs are playing an increasingly significant role in the whole discovery process. In this work, we use an in-house developed python utility: PAOFLOW, which generates finite basis Hamiltonians from the projection of first principles plane-wave pseudopotential wavefunctions on pseudo atomic orbitals(PAO) for post-process calculation on various properties such as the band structures, density of states, complex dielectric constants, diffusive and anomalous spin and charge transport coefficients. In particular, we calculated the dielectric function of Sr-, Pb-, and Bi-substituted BaSnO3 over wide concentration ranges. Together with some high-throughput experimental study, our result indicates the importance of considering the mixed-valence nature and clustering effects upon substitution of BaSnO3 with Pb and Bi. We also studied two prototype ferroelectric rashba semiconductors, GeTe and SnTe, and found the spin Hall conductivity(SHC) can be large either in ferroelectric or paraelectric structure phase. Upon doping, the polar displacements in GeTe can be sustained up to a critical hole concentration while the tiny distortions in SnTe vanish at a minimal level of doping. Moreover, we investigated the sensitivity of two dimensional group-IV monochalcogenides to external strain and doping, which reveal for the first time giant intrinsic SHC in these materials, providing a new route for the design of highly tunable spintronics devices based on two-dimensional materials.
1258

Many-body theory for the lattice thermal conductivity of crystalline thermoelectrics

Hübner, Axel Felix 16 June 2023 (has links)
Thermoelektrika (TE) sind Materialien die Elektrizität aus Abwärme gewinnen können. Eine wichtige Kenngröße für die Effizienz, und damit die Anwendbarkeit, von TE ist ihre Gitterwärmeleitfähigkeit. In meiner Doktorarbeit habe ich die Invarianz dieser Größe im Kontext der Linear-Response Theorie (LR) bewiesen. Dies ermöglichte es, eine Korrektur der Boltzmann-Transport Gleichung (BTE) für die Gitterwärmeleitfähigkeit in kristallinen Materialien mittels LR herzuleiten. Diese Korrektur ist wichtig um zu beurteilen, wie genau die BTE die Wärmeleitfähigkeit eines Kristalls vorhersagen kann. Um die dafür notwendigen symbolischen Umformungen durchzuführen, habe ich ein Computer-Algebra System (CAS) entwickelt. Die Anzahl an Beiträgen zum finalen Resultat stellte sich als zu groß heraus um Grenzfälle zu analysieren oder prüfbare Approximationen herzuleiten. Aus diesem Grund habe ich alle Beiträge mit so wenigen Approximationen wie möglich ausgewertet. Dafür habe ich eine Software entwickelt, um diese Terme numerisch auszuwerten. Damit habe ich meine Korrektur für altbekannte wie auch vielversprechende TE ausgewertet, nämlich PbTe, Bi2Te3 , SnSe und B4 C. Zusätzlich habe ich MgO und KF untersucht. Das Resultat lässt sich wie folgt zusammenfassen: Die Korrektur zur BTE für die Gitterwärmeleitfähigkeit hat in keinem der untersuchten Materialien und bei keiner der simulierten Temperaturen einen nennenswerten Einfluss. Meine Untersuchung legt nahe, dass die BTE für eine große Bandbreite an Materialien sicher angewandt werden kann, auch besonders stark Anharmonische. Folglich ist diese Arbeit in Übereinstimmung mit der Literatur, dass die am stärksten anharmonischen Materialien genau die mit der niedrigsten Wärmeleitfähigkeit sind. Es scheint daher sinnvoll, dass sich zukünftige Forschung weniger auf die Herleitung solcher Korrekturen zur BTE als vielmehr auf die korrekte Berechnung des Phononpropagators in stark anharmonischen Materialien konzentrieren sollte. / Thermoelectrics (TE) are materials that can be used to generate electricity from waste heat. A key quantity to the efficiency, and therefore the applicability, of TE is the lattice thermal conductivity. In this work, I prove the invariance of the lattice thermal conductivity in the context of linear-response theory (LR). This invariance enables me to derive novel formulas for a correction to the widely used Boltzmann-transport equation (BTE) for lattice thermal transport in crystalline solids using LR. It turned out that these derivations cannot be performed by a human by hand, using the formalism I chose. To perform the necessary symbolic manipulations, I programmed a computer algebra system (CAS), that implements LR, starting from expectation values, over Feynman diagrams to mathematical formulas. The number of resulting terms turned out to be too large for an analysis of all limiting cases. Consequently, I aimed at evaluating all terms, with as few approximations as possible, to generate a simple, numerical result. To do so, I developed a software package to evaluate the formulas numerically without further approximation and applied it to long-serving as well as promising new TE, namely PbTe, Bi2 Te3 , SnSe, and B4C. Additionally I investigated MgO and KF. The result can be summed up as follows: The correction to the BTE for the lattice thermal conductivity has almost no influence in the investigated materials at any simulated temperature. My investigation suggests that the BTE can be used for a wide range of materials, including the most anharmonic ones. Consequently, this work is in agreement with the literature, that the most anharmonic materials are exactly those with the lowest lattice thermal conductivity. It suggests that future theoretic work on lattice thermal conductivity should focus to find the correct phonon-propagator of strongly anharmonic systems.
1259

Compostable Soy-Based Polyurethane Foam with Kenaf Core Modifiers

Hoyt, Zachary 08 1900 (has links)
Building waste and disposable packaging are a major component in today's landfills. Most of these are structural or thermally insulative polymer foams that do not degrade over a long period of time. Currently, there is a push to replace these foams with thermoplastic or biodegradable foams that can either be recycled or composted. We propose the use of compostable soy-based polyurethane foams (PU) with kenaf core modifiers that will offer the desired properties with the ability to choose responsible end-of-life decisions. The effect of fillers is a critical parameter in investigating the thermal and mechanical properties along with its effect on biodegradability. In this work, foams with 5%, 10%, and 15% kenaf core content were created. Two manufacturing approaches were used: the free foaming used by spray techniques and the constrained expansion complementary to a mold cavity. Structure-property relations were examined using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermal conductivity, compression values, scanning electron microscopy (SEM), x-ray micro-computed tomography (micro-CT), and automated multiunit composting system (AMCS). The results show that mechanical properties are reduced with the introduction of kenaf core reinforcement while thermal conductivity and biodegradability display a noticeable improvement. This shows that in application properties can be improved while establishing a responsible end-of-life choice.
1260

Modeling of Hexagonal Boron Nitride Filled Bismalemide Polymer Composites for Thermal and Electrical Properties for Electronic Packaging

Uddin, Md Salah 12 1900 (has links)
Due to the multi-tasking and miniaturization of electronic devices, faster heat transfer is required from the device to avoid the thermal failure. Die-attached polymer adhesives are used to bond the chips in electronic packaging. These adhesives have to hold strong mechanical, thermal, dielectric, and moisture resistant properties. As polymers are insulators, heat conductive particles are inserted in it to enhance the thermal flow with an attention that there would be no electrical conductivity as well as no reduction in dielectric strength. This thesis focuses on the characterization of polymer nanocomposites for thermal and electrical properties with experimental and computational tools. Platelet geometry of hexagonal boron nitride offers highly anisotropic properties. Therefore, their alignment and degree of orientation offers tunable properties in polymer nanocomposites for thermal, electrical, and mechanical properties. This thesis intends to model the anisotropic behavior of thermal and dielectric properties using finite element and molecular dynamics simulations as well as experimental validation.

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