[pt] O presente trabalho, realizou-se com fim de construir aparelhos que façam a medida da condutividade térmica e a geração interna de calor em plásticos fotoelásticos durante o endurecimento dos mesmos, na obtenção de peças para análise fotoelástico. O objetivo foi fornecer um projeto para obter dados a serem usados no laboratório de fotoelasticidade da PUC. O plano de trabalho seguiu o esquema que se apresenta: a) Para a condutividade térmica a medição se baseia no resfriamento Newtoniano, isto é aquele que se pode descrever com equação exponencialmente decrescente. Mediante a simulação do sistema num programa de computador se analisou o comportamento do aparelho para valores extremos a para valores médios, não sendo erro teórico superior ao 10 por cento. Na simulação se incluiu geração interna de calor devida à reação no interior do plástico. Uma vez provado que o sistema é o apropriado, projeta-se o aparelho de tal maneira que se cumpram as hipóteses da simulação. b) Para a geração interna de calor o princípio utilizado é a medida da energia liberada, mediante a determinação da variação da temperatura com o tempo de uma massa de plástico. / [en] The present work was done with the goal of constructing devices to measure the thermal conductivity and internal heat generation in photoelastic plastics during the hardening phase in the obtainment of models for photoelastic analysis. The objective was to supply a technique to obtain data to be used in the PUC photoelasticity laboratory. The work followed the following scheme: a) For thermal conductivity, the measurement is based on Newtonian cooling which is that which can be described by na exponentially decreasing equation. By simulating the system with a computer program, the behavior of the device was analysed extreme and médium values, the theoretical error, not being greater than 10 per cent. The simulation included heat generation due to the internal reaction in the plastic. Having proved that the system is a proper one, a device was designed in such a manner that it matches the hypothetical simulation. b) For the internal heat generation, the principle employed was to measure the energy liberated by means of the temperature variation with time of plastic mass.

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.

A systematic investigation using molecular dynamics (MD) simulation involving particle volume fraction, size, wettability and system temperature is performed and the effect of these parameters on the thermal conductivity of water based nanofluids is discussed. Nanofluids are a colloidal suspension of 10 -100 nm particles in base fluid. In the last decade, significant research has been done in nanofluids, and thermal conductivity increases in double digits were reported in the literature. This anomalous increase in thermal conductivity cannot be explained by classical theories like Maxwell's model and Hamilton-Crosser model for nanoparticle suspensions. Various mechanisms responsible for thermal conductivity enhancement in nanofluids have been proposed and later refuted. MD simulation allows one to predict the static and dynamic properties of solids and liquids, and observe the interactions between solid and liquid atoms. In this work MD simulation is used to calculate the thermal conductivity of water based nanofluid and explore possible mechanisms causing the enhancement. While most recent MD simulations have considered Lennard Jones (LJ) potential to model water molecule interactions, this work uses a flexible bipolar water molecule using the Flexible 3 Center (F3C) model. This model maintains the tetrahedral structure of the water molecule and allows the bond bending and bond stretching modes, thereby tracking the motion and interactions between real water molecules. The choice of the potential for solid nanoparticle reflects the need for economic but insightful analyses and reasonable accuracy. A simple two body LJ potential is used to model the solid nanoparticle. The cross interaction between the solid and liquid atoms is also modeled by LJ potential and the Lorentz-Berthelot mixing rule is used to calculate the potential parameters. The various atomic interactions show that there exist two regimes of thermal conductivity enhancement. It is also found that increasing particle size and decreasing particle wettability cause lower thermal conductivity enhancement. In contrast to the previous studies, it is observed that increasing system temperature does not enhance thermal conductivity significantly. Such enhancement with temperature is proportional to the conductivity enhancement of base fluid with temperature. This study demonstrates that the major cause of thermal conductivity enhancement is the formation of ordered liquid layer at the solid-liquid interface. The enhanced motion of the liquid molecules in the presence of solid particles is captured by comparing the mean square displacement (MSD) of liquid molecules in the nanofluid to that of the base fluid molecules. The thermal conductivity is decomposed into three modes that make up the microscopic heat flux vector, namely kinetic, potential and collision modes. It was observed by this decomposition analyses that most of the thermal conductivity enhancement is obtained from the collision mode and not from either the kinetic or potential mode. This finding also supports the observation made by comparing the MSD of liquid molecules with the base fluid that the interaction between solid and liquid molecules is important for the enhancement in thermal transport properties in nanofluids. These findings are important for the future research in nanofluids, because they suggest that if smaller, functional nanoparticles which have higher wettability compared to the base fluid can be produced, they will provide higher thermal conductivity compared to the regular nanoparticles.

Molten salts are high-temperature heat transfer fluids intended for cooling and/or storage purposes in a variety of energy applications. The current work seeks to ultimately study the thermophysical properties of fluoride and chloride salts, which are commonly considered for use in advanced nuclear reactors. Thermophysical properties like thermal conductivity are fundamental to ensuring safe, efficient, and competitive designs for advanced commercial nuclear reactors. Measurement challenges with liquid salts such as electrical conduction, corrosion, convection, and thermal radiation have hindered traditional approaches in their attempts to accurately quantify these properties at high temperatures. Here, a needle probe is developed, which modifies principles from existing instrumental techniques in order to experimentally measure the thermal conductivity of molten salts with reduced error. An analytical heat transfer model is developed to characterize 1D radial heat flow in a multilayered cylindrical system. This includes a thin layer of salt located between the needle probe and a crucible to limit natural convection. After being validated with finite-element methods, the needle probe is used to measure the thermal conductivity of several reference liquids, whose thermophysical properties are well-established at low temperatures. These seven samples are water, sodium nitrate (molten salt), potassium nitrate (molten salt), toluene, ethanol, propylene glycol, and galinstan. The needle probe was able to accurately measure thermal conductivity between 0.40-0.66W/mK for these samples with 3.5-10% uncertainty. Three eutectic halide molten salts (presented by molar composition) were selected for high-temperature testing. These include the ternary fluorides LiF(46.5%)-NaF(11.5%)-KF(42%) and NaF(34.5%)-KF(59%)-MgF2(6.5%), as well as the binary chloride NaCl(58.2%)-KCl(41.8%). Because testing temperatures range between 500-750C, the governing model is adapted to account for radiative heat transfer through the salt sample in parallel with conductive heat transfer. Improvements to the experimental apparatus are also made. For all three salts, the needle probe accurately measured thermal conductivity between 0.490-0.849W/mK with total uncertainty generally being less than 20%. A linear fit to the data demonstrates a clear negative relationship between thermal conductivity and an increase in temperature, which agrees with theoretical and computational predictions. These results indicate that the needle probe successfully handles the assortment of measurement challenges associated with high-temperature molten salts and provides reliable data to create correlations for thermophysical property databases.

This thesis documents research done for a transient hot wire system that will be used in future thermal conductivity measurements of molten salts. Research done with molten salts have been limited because of erroneous measurement capabilities, but the current research strives to introduce a new technique to accurately record thermal conductivity over a wide range of temperatures. This work follows up on past transient hot wire researchers whose designs and tests produced an instrument that can measure the thermal conductivity of molten metals up to 750 K. The transient hot wire (THW) technique has been selected to be used in molten salt to derive thermal conductivity values. While running a THW test in molten salts is outside the scope of this thesis, a modular system has been created for the use of running transient hot wire test that allows for a robust and repeatable testing. A PEGDA/galinstan sensor is used for the validation of the system. A robust GUI has been created to automate the experimental procedure in a glovebox environment. The inverse finite element method has been paired with a non linear fit script to optimize calculations and reduce run times. Test have been done to determine the thermal conductivity of PEGDA. The overall uncertainty of the thermal conductivity measured with the PEGDA sensor is estimated to be ±5% at a 95% confidence level. With a THW system implemented and validated a sensor has been designed to work in molten salts. A model has been created in two separate FEA programs to validate design changes and material properties. The sensor is made up of a chemical vapor deposition (CVD) diamond substrate and tungsten wires to overcome corrosion and heat challenges introduced when measuring molten salts. New manufacturing processes have been designed to allow the technique to use these materials in the THW sensor design. The selected material properties of the sensor and extensive finite element work have laid down the ground work for future experimentation and understanding of the thermal properties of molten salts. It is predicted that the CVD diamond (carbide) apparatus design will use the THW techniques to operate with an estimated accuracy of ±3% over a wide range of temperatures, from ambient up to 1200 K. Manufacturing of the diamond-tungsten sensor have proven the viability of depositing tungsten wire onto CVD diamond and growing a secondary layer of CVD diamond over the tungsten wire.

Laser powder bed fusion (LPBF), one of the most promising additive manufacturing (AM) techniques, has enabled the production of previously impossible structures. This breakthrough in AM has not only facilitated the creation of new designs, but also the redesign of existing industrial and engineering components to produce lightweight and highly efficient dies and molds, biomaterial scaffolds, aircraft brackets, heat sink and heat exchangers. In many of the mentioned applications in industries such as automotive, aerospace, heat exchanger, and electronics, aluminum (Al), Al alloys, and Al matrix composites (AMCs) are considered potential candidates. In the first phase of this study, the optimum powder particle size and size distribution of an Al alloy powder (i.e., AlSi10Mg) was determined with the aim being to achieve highest densification levels and dimensional accuracies. In the second phase, three materials with high thermal conductivities were selected, namely, pure Al, AlSi12 and AlSi10Mg alloys. Since Al/Al alloys are prone to oxidation, the LPBF process parameters were optimized not only in terms of the densification level but also oxygen content of the fabricated parts. It was found out that the rate of oxide diminishment for Al/Al alloys during the LPBF process is more than in-situ oxidation. Despite the efforts, the optimized LPBF fabricated samples showed lower thermal conductivity than their conventionally manufactured counterparts. To tackle the issue, two different potential solutions were put into test. In the third phase, the influence of preheating on thermal properties of pure Al, AlSi12, and AlSi10Mg was investigated and a huge improvement in the thermal conductivity of the optimized as-built parts was obtained. In the fourth phase, the possibility of enhancing thermal conductivity of the LPBF fabricated Al/Al alloys in as-built condition through the incorporation of a second constituent with a higher thermal conductivity (i.e., graphene) was investigated. / Thesis / Doctor of Philosophy (PhD)

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.

The study demonstrates the systematic investigation of thermophysical properties of synthetic slags and commercial mold fluxes in a wide temperature range. Focal points of the work are (i) the development and the construction of the transient hot-wire method for the thermal conductivity measurement of solid and molten slags and (ii) the investigation of the thermal conductivity of all layers of casting powders being in the mold. The work includes viscosity, density and surface tension measurements as well as the investigation of characteristic temperatures. The crystallization behavior of mold fluxes was characterized using a SHTT/DHTT (single hot and double hot thermocouple technique). The study discusses the temperature dependence, the influence of the basicity and the non-bridging oxygen per tetrahedra (NBO/T) on the slag properties. The novelty of the work is the systematic characterization of properties of two commercial mold fluxes and the thermal conductivity measurement in the glass transition temperature range.

No description available.

This thesis investigates the validity of the standard thermal response test (TRT) results when performed on a series of boreholes (string). The typical TRT consists of subjecting a single borehole to a constant heat injection rate to obtain the temperature response in the ground which can then be used to determine the ground thermal conductivity. When completed on a single borehole, the results may be analyzed with the line source theory, since the assumption of a single line heat source is valid. For multiple boreholes, the assumption of a single line source becomes invalid if the spacing between the boreholes is small enough for borehole thermal interaction to occur. Moreover, for boreholes that are charged in series, heat transfer from the horizontal pipes that connect the vertical boreholes may also influence the ground thermal response. This thesis takes an in-depth look at the different factors that affect the results of TRTs performed on borehole strings. Different analysis methods are implemented to determine areas of improvement for determining the thermal conductivity of the soil surrounding the borehole string. For the analysis, the infinite line source (ILS) model and a model developed using TRNSYS 18 were used to determine the effective thermal conductivity. The results show that TRNSYS is unable to accurately model a TRT performed on a borehole string. The horizontal pipe model within TRNSYS proved to have significant fundamental issues, as the effective thermal conductivity is greatly underestimated with values of 1.2±0.1W/mK and the results of increasing the horizontal length both increased and decreased the effective thermal conductivities. The results from the ILS demonstrate that an effective thermal conductivity of 1.7±0.2W/mK is an appropriate estimate of the soil at the BTES field tested, as the borehole string with the furthest spacing between boreholes gave an effective thermal conductivity of 1.7W/mK. Performing multiple thermal response tests within the same BTES field also provided evidence of the need to implement multiple TRTs as common practise. The testing presented shows that the effective thermal conductivity can vary within ±0.2W/mK within the same relative location. With better knowledge of the thermal properties within the BTES field location comes the opportunity for improved planning of operation and control of thermal distribution within the field. This would be especially beneficial when dealing with seasonal BTES fields / Thesis / Master of Applied Science (MASc)