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)

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.

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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)

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