Thermally-driven slope winds are mesoscale atmospheric circulations, known as breezes, that take place because of the heating (cooling) of the air layer close to the ground during daytime (nighttime). Mostly known to occur on days with weak synoptic forcing and under clear sky conditions, the wind blows up valleys and slopes during the daytime, and in the opposite direction during nighttime. A better comprehension of slope winds can improve the understanding of the soil-atmosphere turbulent exchange processes and of the energy budget over complex terrain, in addition to the evaluation of the along-slope transport of dangerous species (pollutants, pesticides), as well as water vapor (relevant for the development of convection). This research project aims to improve the knowledge of thermally-driven slope winds, with particular attention to the differences between the diurnal and nocturnal regimes. This is done through a multiple-way approach. Field data analysis, analytical solutions with realistic forcing, and numerical models are all employed to fulfill the objective. At first, data from two stations located on slopes were analyzed. Measurements were taken in the surroundings of the Alpine city of Innsbruck, as part of the i-Box field campaign, covering a period of 7 years (2013 to 2020). Observation indicates a marked seasonality of the phenomena, with warm season months being more prone to the occurrence of slope winds. Moreover, the results highlighted the key role played by the local topographical characteristics in the development of pure slope wind days, with both slope angle and orientation playing a major role in the interplay between valley and slope winds. Previous results suggested the development of an improved analytical model which uses the available net radiation at the surface as the forcing for slope circulations, in the form of a truncated Fourier series expansion. The net radiation model accounts for both the seasonality (day of the year) and the local topographic characteristics (latitude, slope angle, orientation, elevation). Therefore, differences in the properties of slope winds occurring in different seasons and on slopes with different slope angles and orientations are highlighted and studied. The last chapter of the thesis investigates the structure of the eddy viscosity and diffusivity employing numerical models. These parameters govern the mass, momentum, and heat turbulent exchanges from slope winds. A simple one-dimensional model was developed to test different turbulence closures. In particular, the attention focused on the so-called K-l closure, meaning that the eddy viscosity and diffusivity parameters are bounded to the turbulence length scale l, representing the distance a turbulent eddy can travel “carrying” heat, momentum, and mass. In the current work, different parameterizations of the turbulence length scale l are tested and compared. Results show how simple K-l closures are compared with other non-constant K profiles proposed in the literature for the case of katabatic winds. Nevertheless, such simple parameterizations for the turbulence length scale l still fail to properly discriminate between the daytime and nighttime regimes of slope winds.

Lignin-derived precursors were used in the synthesis of bio-based high-performance polymers. The project consisted of synthesizing a series of poly(ester amide)s (PEAs) from lignin building blocks and natural amino acids. In particular, the amino acid moieties were incorporated into the PEAs’ architecture to explore the effect of the side-chain size on the thermal properties and the crystallinity of the resulting materials. The polymers, which were prepared by melt polycondensation, all possessed high thermal stability in nitrogen and air with onsets of thermal degradation (Td onset) exceeding 330 °C and glass transition temperatures (Tg) ranging from 136 °C – 238 °C. It is worth noting that the Tg greatly depended on the size of the pendant R-group on the amino acid. Remarkably, the thermal stability was mostly maintained even after subjecting the polymers to various pH media (pH 1, 4 and 8) for 1 week at 50 °C. Furthermore, wide-angle X-ray scattering experiments revealed semi-crystalline polymers with identical diffraction patterns and percent crystallinity ranging from 21 – 37%. To probe the impact of chirality on the thermal properties, a meso polymer of DL-alanine was prepared and compared to the chiral version. A slight drop in the Td onset and Tg of the DL-alanine-containing polymer relative to the L-alanine counterpart occurred, signifying moderate thermal stability resulting from the chiral group. Overall, these characteristics make these bio-based PEAs potential candidates for further investigation as alternatives to petrochemical-derived thermoplastics for high-performance materials.

Cooling, Heating, and Power (CHP) is an emerging category of energy systems consisting of power generation equipment coupled with thermally activated components. The application of CHP systems to residential and small commercial buildings is known as micro-CHP (m-CHP). This instructional module has been developed to introduce engineering students to m-CHP. In the typical engineering curriculum, a number of courses could contain topics related to m-CHP. Thermodynamics, heat transfer, HVAC, heat and power, thermal systems design, and alternate energy systems courses are appropriate m-CHP topics. The types of material and level of analysis for this range of courses vary. In thermodynamics or heat transfer, basic problems involving a m-CHP flavor are needed, but in an alternate energy systems course much more detail and content would be required. This instructional module contains both lecture material and a compilation of problems/exercises for both m-CHP systems and components.

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Yes / This study aims to evaluate the impacts of using thermally enhanced concrete on the thermal performance of geoenergy structures and interaction between the thermo-active-structures and adjacent dry and partly saturated soils. Experiments using a fully instrumented testing rig were carried out on prototypes of energy pile and diaphragm wall made from normal concrete and thermally enhanced concrete by the addition of graphTHERM powder. Results illustrated that adding 36% of graphTHERM powder to the concrete by weight of cement was found to double the thermal conductivity of concrete and improve the stiffness by 15% without detrimental effects on the compressive strength. The heat transfer efficiency of energy pile and energy diaphragm wall made from thermally enhanced concrete was significantly improved by 50% and 66% respectively, in comparison with the efficiency of the same type of energy structure that was made from a typical normal concrete.

The presented work is intended to develop a geometrically reduced order (homogenized) model for a large antenna space structure with flexible joints. An energy equivalence concept is employed to find the continuum model for the system. The kinetic and strain energy expressions of the fundamental elements are found based on the assumptions of the micropolar elasticity theory. Necessary assumptions are made to reduce the order of the strain variables while retaining the effects of the micro-rotations that are coupled to the primary strain terms. As a result, a micropolar-based continuum model is found for the structure with torsional joints. The vibrations equations of motion for various coordinates of the one dimensional equivalent model are presented. Subsequently, the relations between the physical parameters of the distributed parameter model and the radar structure are introduced. The effect of the asymmetric mass distribution as a result of the addition of the radar panel to the truss system is studied. For the purpose of the experimental validation of the suggested model a planar truss structure with Pratt Girder configuration was built and tested in the laboratory. The results for the experimental frequency response functions are shown to be in good agreement with the theory. Finally, the continuum model is used to quantify the effects of the thermally induced disturbances on the satellite system during the eclipse transition. / Ph. D.

The scope of this research entailed the synthesis of novel polyorganosiloxanes with pendent phosphine, phosphine oxide, nitrile and carboxylic acid moieties. Such polysiloxanes were prepared with controlled concentrations of both the polar moieties and hydrido or vinyl pendent crosslinkable sites to afford precursor materials for well-defined networks. The intention was to generate stable microcomposite dispersions with very high concentrations of polar thermally conductive fillers. Lightly crosslinked elastomeric networks with controlled amounts of polar moieties were prepared via a hydrosilation curing mechanism. High concentrations of thermally conductive micro-fillers were dispersed throughout the resins and the microcomposites were investigated as thermally conductive adhesives. Random polysiloxane copolymers containing controlled number average molecular weights (Mns) and compositions with systematically varied concentrations of hydridomethylsiloxy- or vinylmethylsiloxy- units were prepared via ring-opening equilibrations of cyclosiloxane tetramers. These precursors were functionalized with precise concentrations of polar pendent moieties via hydrosilation (nitrile) or free radical addition reactions (phosphine and carboxylic acids). Valuable additions to the family of polysiloxanes were prepared by oxidizing the phosphine moieties to form phosphine oxide containing polysiloxanes. Defined concentrations of residual hydrido- or vinyl- reactive sites were crosslinked via hydrosilation to yield elastomeric adhesives. Specific interactions between the nitrile and phosphine oxide substituted polysiloxanes and the acidic proton of chloroform were shown using 1H NMR. The magnitude of the shift for the deshielded chloroform proton increased with the degree of hydrogen bonding, and was larger for the phosphine oxide species. The polar polysiloxane resins were filled with high concentrations of thermally conductive fillers including silica-coated AlN, Al spheres, BN and Ag flake, then hydrosilated to form microcomposite networks. Microcomposite adhesive strengths, thermal properties (glass transition temperature (Tg) and high temperature stability), and thermal conductivities were studied. An unfilled polysiloxane network containing only 15 mole percent phosphine oxide exhibited a dramatic improvement (46 N/m) in adhesive strength to Al adherends relative to a control polydimethylsiloxane network (2.5 N/m). Importantly, stable polysiloxane micro-dispersions were obtained with up to 67 volume percent (86 weight percent) silica-coated AlN. TEM data confirmed the dispersion homogeneity and XPS demonstrated that the particle surfaces were well-coated with the functionalized polysiloxanes. A microcomposite comprised of 67 volume percent silica-coated AlN and a polysiloxane containing only 9 molar percent nitrile groups had a thermal conductivity of 1.42 W/mK. The glass transition temperatures of the microcomposites were controlled by the amounts of polar functional moieties on the resins and the network crosslink densities. All of the microcomposites exhibited Tgs lower than -44°C and the materials remained stable in dynamic TGA measurements to approximately 400°C in both air and nitrogen. / Ph. D.

<p dir="ltr">Increasing power density and power consumption in electronic devices require heat dissipating components with high thermal conductivity to prevent overheating and improve performance and reliability. Polymers offer the advantages of low cost and weight over conventional metallic components, but their intrinsic thermal conductivity is low. Previous studies have shown that the thermal conductivity of polymers can be enhanced by aligning the polymer chains or by adding high thermal conductivity fillers to create percolation paths within the polymeric matrix. To further enhance the in-plane thermal conductivity, the conductive fillers can be aligned preferentially, but this leads to a lower increase in performance in the cross-plane direction. Yet, the cross-plane thermal conductivity plays a vital role in dissipating heat from active devices and transmitting it to the surrounding environment. Alternatively, when the fillers are aligned to enhance cross-plane thermal transport, the enhancement in the in-plane direction is limited. There is a need to develop polymer composites with an approximately isotropic increase in thermal performance compared to their neat counterparts.</p><p dir="ltr">To achieve this goal, in this study, I combine conductive fibers and fillers to enhance thermal conductivity of polymers without significantly inducing thermal anisotropy while preserving the mechanical performance of the matrix. I employ three approaches to enhance the thermal conductivity () of thermoset polymeric matrices. In the first approach, I fabricate thermally conductive polymer composites by creating an emulsion consisting of eutectic gallium indium alloy (EGaIn) liquid metal in the uncured polydimethylsiloxane (PDMS) matrix. In the second approach, I infiltrate mats formed from chopped fibers of Ultra High Molecular Weight Polyethylene (UHMWPE) with an uncured epoxy resin. Finally, the third approach combines the two previous methods by infiltrating the UHMWPE fiber mat with an emulsion of the liquid metal and uncured epoxy matrix.</p><p dir="ltr">To evaluate the thermal performance of the composites, I use infrared thermal microscopy with two different experimental setups, enabling independent measurement of in-plane and cross-plane thermal conductivity. The results demonstrate that incorporating thermally conductive fillers enhances the overall conductivity of the polymer composite. Moreover, I demonstrate that the network structure achieved by the fiber mat, in combination with the presence of liquid metal, promotes a more uniform increase in the thermal conductivity of the composite in all directions. Additionally, I assess the impact of filler incorporation and filler concentration on matrix performance through tension, indentation, and bending tests for mechanical characterization of my materials.</p><p dir="ltr">This work demonstrates the potential of strategic composite design to achieve polymeric materials with isotropically high thermal conductivity. These new materials offer a solution to the challenges posed by higher power density and consumption in electronics and providing improved heat dissipation capabilities for more reliable devices.</p>

Thermally rearranged (TR) polymers have outstanding gas separation properties, but are limited in their industrial application due to being mechanically brittle. A series of low volume fraction of a poly(arylene ether sulfone) (PAES) block was introduced into the TR precursor polyhydroxyimide (PI) chain to improve mechanical properties without compromising gas transport properties. The multiblock copolyhydroxyimide incorporated the PAES in systematically varied amounts and copolymerized it with 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 3,3’-dihydroxy-4,4’-diaminobiphenyl. Before thermal rearrangement, the PI-co-PAES precursors exhibited much more improved mechanical properties (tensile stress and strain at break) than those of homo polyimide precursor. After thermal rearrangement, tensile stress and strain at break of all TR copolymers decreased comparing to their corresponding precursors, but improved comparing to the homo TR polymer. Poly(phenylene oxide) (PPO) based copolymers (Chapter 4) and polymer blends (Chapter 5) were also studied for use as gas separation membranes. The polymer materials were cast into films, then crosslinked in the solid state with UV light. The ketone and benzylic methyl groups crosslinked upon exposure to UV light. For the study of PPO copolymers, copolymers were prepared by polycondensation of a difunctional PPO oligomer with 4,4’-difluorobenzophenone or 1,3-bis(4-fluorobenzoyl)benzene respectively. This study offers a means for fabrication of membrane films, fibers or composites, as well as tuning of gas transport properties through crosslinking in the solid state. While for the study of PPO polymer blends, PPO polymers with Mn’s from 2000-22,000 g/mole were synthesized and blended with a poly(arylene ether ketone) derived from bisphenol A and difluorobenzophenone (BPA-PAEK). The crosslinked blends had improved gas selectivities over their linear counterparts. The 90/10 wt/wt 22k PPO/BPA PAEK crosslinked blends gained the most O2/N2 selectivity and maintained a high permeability. / Ph. D.