This thesis documents the design, manufacturing, and assembly of a flexible thermoelectric device. Such a device has immediate use in haptics, medical, and athletic applications. The governing theory behind the device is explained and a one dimensional heat transfer model is developed to estimate performance. This model and consideration for the manufacturing and assembly possibilities are the drivers behind the decisions made in design choices. Once the design was finalized, manufacturing methods for the various components were explored. The system was created by etching copper patterns on a copper/polyimide laminate and screen printing solder paste onto the circuits. Thermoelectric elements were manually assembled. Several proof of concept prototypes were made to validate the approach. Development of the assembly process also involved proof of concept prototyping and partial assembly analysis. A full scale device was produced and tested to assess its thermoelectric behavior. The resulting performance was an interface temperature drop of 3 °C in 10 seconds with 1.5 A supplied, and a maximum temperature drop of 9.9 °C after 2 minutes with 2.5 A supplied. While the measured behavior fell short of predictions, it appears to be adequate for the intended purpose. The differences appear to be due to larger than expected thermal resistances between the device and the heat sinks and some possible degradation of the thermoelectric elements due to excess solder coating the edges.

Two sets of experiments were performed on a simulated turbine nozzle guide vane. First, adiabatic and overall effectiveness measurements were taken in the showerhead region of the vane using adiabatic and matched Biot vane models, respectively. Measurements of overall effectiveness in the showerhead region are not found in the literature, and are a useful baseline for validating the results of computational fluid dynamics (CFD) simulations. Overall effectiveness is useful because it shows the results of combining film cooling, internal convection, and surface conduction to provide a more complete picture of vane cooling than adiabatic effectiveness. An impingement plate was utilized to generate internal jet cooling. Momentum flux ratios were matched between the models and ranged from I*SH = 0.76 to 6.70, based on showerhead upstream approach velocity. The second set of experiments used a different model to examine the effects of surface curvature on adiabatic effectiveness. Results in open literature are found by varying the radius of curvature of a fixed setup, so the current approach was novel in that it looked at adiabatic effectiveness at locations of various curvature around the same vane. Blowing ratios from M = 0.4 to M = 1.6 were tested at a density ratio of DR = 1.20 for two locations on the suction side of the vane. Results were presented in terms of laterally averaged adiabatic effectiveness and contour plots of adiabatic effectiveness, and were compared to literature. / text

Large-scale geologic CO₂ storage is a technically feasible way to reduce anthropogenic emission of green house gas to atmosphere by human beings. In large-scale geologic CO₂ sequestration, high injection rate is required to satisfy economics and operational considerations. During the injection phase, temperature and pressure of the storage aquifers may vary significantly with the introduced CO₂. These changes would re-distribute the in-situ stresses in formations and induce fracture initiation or even propagation. If fractures are not permitted by regulators, then the injection operation strategies must be supervised and designed to prevent fracture initiation, and the storage formations should be screened for risk of fracturing. In more flexible regulatory environment, if fractures are allowed, fractures would strongly influence the CO₂ migration profile and storage site usage efficiency depending on fracture length and growth rate. In this dissertation, we built analytical heat transfer models for vertical and horizontal injection wells. The models account for the dependency of overall heat transfer coefficient on injection rate to more accurately predict the borehole temperature. Based on these models, we can calculate temperature change in formation surrounding wellbores and thus evaluate thermo-elastic stress around borehole as well as its impact on fracture initiation pressure. By considering the impact of thermo-elastic effect on fracturing pressure, we predicted maximum injection rate avoiding fracture initiation and provided injection and storage strategies to increase the maximum safe injection rate. The results show that thermo-elastic stress significantly limits maximum injection rate for no-fractured injection scenario, especially for horizontal injectors. To improve injection rate, partial perforation and pre-heating CO₂ before injection have been designed, and results shows that these strategies can strongly negate thermo-elastic influence for various injection scenarios. On the other hand, the model provides parametric analysis on geological and operational conditions of CO₂ storage project for site screening work. In the case of permitting fracture occurrence, a semi-analytical model was built to quantitatively describe fracture propagation and injected fluid migration profile of a fractured vertical injector for storage systems with various boundary conditions. We examined the correlation between fracture growth and CO₂ migration in various injection scenarios. Two-phase fractional flow model of Buckley-Leverett theory has been extended to account for the CO₂-brine three-region flow system (dry CO₂, CO₂-brine, and brine) from a fractured injector. In the sensitivity study, fracture growth and fluid migration greatly depend on Young's modulus of the formation rock and storage site boundary conditions. Consequently, the results show that fast growing, long fractures may yield a flooding pattern with large aspect ratio, as well as early breakthrough at the drainage boundary; in contrast, slow growing short fractures provides high injectivity without changing flooded area shape. We studied the physics for issues related to injection induced fractures in geologic CO₂ sequestration in saline aquifers, assessed risk associated to them and developed low cost and quick analytical models. These models could easily provide predictions on maximum injection rate in no-fracture regulation CO₂ storage projects as well as estimate fracture growth and injected fluid migration under fracture allowable scenarios. "Preferred storage aquifers" have following properties: larger permeability, deep formation, no over pressure, low Young's modulus and low Poisson's ratio and open boundaries. In many practical cases, however, injection strategies have to be designed if some properties of formation are out of ideal range. Besides applications in CO₂ storage, the approach and model we developed can also be applied into any injection induced fracture topics, namely water/CO₂ flooding and wasted water re-injection. / text

This study focused on experimentally measuring the performance of a fully cooled, scaled up C3X turbine vane. Experimental measurements focused on investigating row-to-row interactions of coolant jets and the contributions of external film cooling and internal impingement cooling to overall cooling effectiveness. Overall effectiveness was experimentally measured using a thermally scaled, matched Biot number vane model featuring a realistic internal impingement scheme and had normalized surface temperatures that were representative of those found on engine components. A geometrically identical vane was also constructed out of low conductivity polystyrene foam to measure the normalized adiabatic wall temperature, or adiabatic effectiveness of the film cooling configuration. The vanes featured a full coverage film-cooling scheme with a five-row showerhead and 13 total rows of holes containing 149 total coolant holes. This study was the first study to make highly detailed measurements of overall effectiveness on a fully-cooled vane model and expands on previous studies of adiabatic and overall effectiveness on the showerhead and single rows of holes on a matched Biot vane by considering a fully cooled configuration to determine if the results from these previous studies also hold for a fully cooled configuration. Additionally, velocity and thermal fields were measured just upstream of two different suction side rows of holes in order to study the effect of introducing upstream coolant injection. The effects of mainstream turbulence and span-wise location were examined and at the downstream row of holes, the contributions of different rows of holes to the approach flow were compared. This study was the first to measure mean and fluctuating velocity data on the suction side of a turbine vane with upstream coolant injection. Understanding the effects of how upstream injection affects the performance of downstream rows of holes is critical to understanding the film cooling performance on a fully cooled turbine airfoil. / text

Two separate heat transfer problems that involve jet flows impinging on a reacting target are studied through modeling and experimentation. The first system is an ablating carbon-carbon specimen exposed to high heat fluxes from an oxy-acetylene torch which has applications in atmospheric re-entry vehicles. The second system involves the penetration of hot gases into the void space in a compartment. The fire protection stands to benefit from knowledge of this system, both in building component design and informing firefighting personnel. Both problems can be modeled as a jet flow impinging on a flat surface where hot gases from the jet lead to primarily convective heat transfer. Ablation experiments are outlined and a theoretical framework is developed. A serial inversion technique is tested for predicting the recession rate observed in the experiments. A novel inversion technique that takes advantage of parallel computing is developed to circumvent the shortcomings of the serial technique. These techniques are then compared to synthetically generated and experimental data for different data streams and error signals. Compartment-scale experiments were conducted to test hot gas penetration into void spaces. Anecdotal evidence was observed outside of the intended test section prompting further investigation into the mechanics of ignition in void spaces. A theoretical framework is established to predict possibility of ignition under varied environmental factors. A leakage-scale experiment is constructed to gain insight into conditions that result in ignition of materials in void spaces. / text

Film cooling is used in gas turbine engines to cool turbine components. Cooler air is bled from the compressor, routed internally through turbine vanes and blades, and exits through discrete holes, creating a film of coolant on the parts’ surfaces. Cooling the turbine components protects them from thermal damage and allows the engine to operate at higher combustion temperatures, which increases the engine efficiency. Shaped film cooling holes with diffuser exits have the advantage that they decelerate the coolant flow, enabling the coolant jets to remain attached to the surface at higher coolant flow rates. Furthermore, the expanded exits of the coolant holes provide a wider coolant distribution over the surface. The first part of this dissertation provides data for a new laidback, fan-shaped hole geometry designed at Pennsylvania State University’s Experimental and Computational Convection Laboratory. The shaped hole geometry was tested on flat plate facilities at the University of Texas at Austin and Pennsylvania State University. The objective of testing at two laboratories was to verify the adiabatic effectiveness performance of the shaped hole, with the intent of the data being a standard of comparison for future experimental and computational shaped hole studies. At first, measurements of adiabatic effectiveness did not match between the labs, and it was later found that shaped holes are extremely sensitive to machining, the material they are machined into, and coolant entrance effects. In addition, the adiabatic effectiveness was found to scale with velocity ratio for multiple density ratios and mainstream turbulence intensities. The second part of this dissertation measures heat transfer coefficient augmentation (hf/h0) at density ratios (DR) of 1.0, 1.2, and 1.5 using a uniform heat flux plate and the same shaped hole geometry. In the past, heat transfer coefficient augmentation was generally measured at DR = 1.0 under the assumption that hf/h0 was independent of density ratio. This dissertation is the first study to directly measure the wall and adiabatic wall temperature to calculate heat transfer coefficient augmentation at DR > 1.0. The results showed that the heat transfer coefficient augmentation was low while the jets were attached to the surface and increased when the jets started to separate. At DR = 1.0, hf/h0 was higher for a given blowing ratio than at DR = 1.2 and DR = 1.5. However, when velocity ratios are matched, better correspondence was found at the different density ratios. Surface contours of hf/h0 showed that the heat transfer was initially increased along the centerline of the jet, but was reduced along the centerline at distances farther downstream. The decrease along the centerline may be due to counter-rotating vortices sweeping warm air next to the heat flux plate toward the center of the jet, where they sweep upward and thicken the thermal boundary layer. This warming of the core of the coolant jet over the heated surface was confirmed with thermal field measurements. / text

The hydrogen (H2) gas sensing mechanism driving 3C-SiC resistive gas sensors is investigated in this work in which two hypotheses are proposed. One hypothesis involves the surface adsorption of H2 on the sensor surface with the adsorbed molecules influencing the flow of current in a resistive gas sensor, termed the surface adsorption detection mechanism. The second hypothesis includes the transfer of heat from the sensor to the gas, producing a change in the temperature of the device when the heat transfer characteristics of the gas change, termed the thermal detection mechanism. The heat transfer characteristics of the gas are dependent on the thermal conductivity of the gas, a property which is a strong function of gas composition. Thus, the thermal detection mechanism mainly detects changes in the thermal conductivity of a gas or gas mixture.Initial experiments suggested the surface adsorption mechanism as the detection mechanism of resistive 3C-SiC gas sensors. However, these experiments were performed in the absence of device temperature measurements. Recent experiments in which the device temperature was measured with a resistance temperature detector (RTD) in thermal contact with the device strongly support the thermal detection mechanism as being responsible for hydrogen gas detection. Experimental observations show the temperature of the resistive 3C-SiC hydrogen gas sensors changes greatly with changing hydrogen gas composition. For example, a 3C-SiC/SOI resistive sensor biased at 10 Vdc displayed a change in temperature from ~400°C to ~216°C, correlating to a change in current from ~41 mA to ~6mA, upon the introduction of 100% H2. The this 3C-SiC/SOI resistive sensor, this large decrease in temperature caused a large increase in resistance which is detected as a decrease in current. Several different experiments have also been performed to confirm the thermal detection mechanism hypothesis.

A new receiver concept utilizing impinging jet cooling technology has been developed for a small scale solar dish-Brayton system. In a typical impinging receiver design, the jet nozzles are distributed evenly around the cylindrical absorber wall above the solar peak flux region for managing the temperature at an acceptable level. The absorbed solar irradiation is partially lost to the ambient by radiation and natural convection heat transfer, the major part is conducted through the wall and taken away by the impingement jets to drive a gas turbine. Since the thermal power requirement of a 5 kWe Compower® micro gas turbine (MGT) perfectly matches with the power collected by the EuroDish when the design Direct Normal Irradiance (DNI) input is 800 W/m2, the boundary conditions for the impinging receiver design in this work are based on the combination of the Compower®MGT and the EuroDish system. In order to quickly find feasible receiver geometries and impinging jet nozzle arrangements for achieving acceptable temperature level and temperature distributions on the absorber cavity wall, a novel inverse design method (IDM) has been developed based on a combination of a ray-tracing model and a heat transfer analytical model. In this design method, a heat transfer model of the absorber wall is used for analyzing the main heat transfer process between the cavity wall outer surface, the inner surface and the working fluid. A ray-tracing model is utilized for obtaining the solar radiative boundary conditions for the heat transfer model. Furthermore, the minimum stagnation heat transfer coefficient, the jet pitch and the maximum pressure drop governing equations are used for narrowing down the possible nozzle arrangements. Finally, the curves for the required total heat transfer coefficient distribution are obtained and compared with different selected impinging arrangements on the working fluid side, and candidate design configurations are obtained. Furthermore, a numerical conjugate heat transfer model combined with a ray-tracing model was developed validating the inverse design method and for studying the thermal performance of an impinging receiver in detail. With the help of the modified inverse design method and the numerical conjugate heat transfer model, two impinging receivers based on sintered α-SiC (SSiC) and stainless steel 253 MA material have been successfully designed. The detailed analyses show that for the 253 MA impinging receiver, the average air temperature at the outlet and the thermal efficiency can reach 1071.5 K and 82.7% at a DNI level of 800 W/m2 matching the system requirements well. Furthermore, the local temperature differences on the absorber can be reduced to 130 K and 149 K for two different DNI levels, which is a significant reduction and improvement compared with earlier published cavity receiver designs. The inverse design method has also been verified to be an efficient way in reducing the calculation costs during the design procedure. For the validation and demonstration of the receiver designs, a unique experimental facility was designed and constructed. The facility is a novel high flux solar simulator utilizing for the first time Fresnel lenses to concentrate the light of 12 commercial high power Xenon-arc lamps. Finally, a prototype of a 253 MA based impinging was experimentally studied with the help of the 84 kWe Fresnel lens based high flux solar simulator in KTH. / <p>QC 20151123</p> / Optimised Microturbine Solar Power System , OMSOP

The thermal evolution of pyroclastic density currents (PDCs) is the result of entrainment of ambient air, particle concentration, and initial eruptive temperature, which all impact PDC dynamics and their hazards, such as runout distance. The associated hazards and opaqueness of PDCs make it impossible for in-situ entrainment efficiencies or concentration measurements that would provide critical information on the thermal evolution and physical processes of PDCs. The thermal evolution of explosive eruptive events such as volcanic plumes and pyroclastic density currents (PDCs) is reflected in the textures of the material they deposit. A multiscale model is developed to evaluate how the rinds of breadcrust bombs can be used as a unique thermometer to examine the thermal evolution of PDCs. The multiscale, integrated model examines how bubble growth, pyroclast cooling, and dynamics of PDC and projectile pyroclasts form unique pyroclast morphology. Rind development is examined as a function of transport regime (PDC and projectile), transport properties (initial current temperature and current density), and pyroclast properties (initial water content and radius). The model reveals that: 1) rinds of projectile pyroclasts are in general thicker and less vesicular than those of PDC pyroclasts; 2) as the initial current temperature decreases due to initial air entrainment, the rinds on PDC pyroclasts progressively increase in thickness; and 3) rind thickness increases with decreasing water concentration and decreasing clast radius. Therefore, the modeled pyroclast’s morphology is dependent not only on initial water concentration but also on the cooling rate, which is determined by the transport regime. The developed secondary thermal proxy is then applied to the 2006 PDCs from the Tungurahua eruption to constrain the entrainment efficiency and thermal evolution of PDCs. A three-dimensional multiphase Eulerian-Eulerian-Lagrangian (EEL) model is coupled to topography and field data such as paleomagnetic data and rind thicknesses of collected pyroclasts to study the entrainment efficiency and thus the thermal history of PDCs at Tungurahua volcano, Ecuador. The modeled results that are constrained with observations and thermal proxies demonstrate that 1) efficient entrainment of air to the upper portion of the current allows for rapid cooling, 2) the channelized pyroclastic density currents may have developed a stable bed load region that was inefficient at cooling and 3) the PDCs had temperatures of 600-800K in the bed load region but the upper portion of the currents cooled down to ambient temperatures. The results have shown that PDCs can be heterogeneous in particle concentration, temperature, and dynamics and match observations of PDCs down a volcano and the thermal proxies. Lastly, the entrainment efficiencies of PDCs increases with increasing PDC temperature and entrainment varies spatially and temporally. Therefore, the assumption of a well-mixed current with a single entrainment coefficient cannot fully solve the thermal evolution and dynamics of the PDC.

A study of the condensation of hydrocarbons and zeotropic hydrocarbon mixtures in smooth horizontal tubes was conducted. Measurements of condensation heat transfer coefficients and frictional pressure drop were taken over a range of mass fluxes (G = 150 – 450 kg m-2 s-1), a range of reduced pressures (Pr = 0.25 - 0.95), for two tube diameters (D = 7.75 and 14.45 mm), several working fluid-to-coolant temperature differences (ΔTLM = 3 – 14°C) and temperature glides (ΔTGlide) between 7 - 14°C. The wide range of conditions investigated in this study provides considerable insight on the transport phenomena influencing condensation in pure fluids and their mixtures. The trends in heat transfer coefficient and frictional pressure gradient are discussed and compared with the predictions of correlations from the literature. The results of the experiments, combined with previous flow visualization studies on hydrocarbons, were used to develop physically consistent heat transfer and frictional pressure gradient models that are applicable to pure fluids and zeotropic mixtures. A framework was developed for zeotropic mixture condensation that recommends a specific modeling approach based on the observed trends in the heat transfer coefficient and the points of deviations from pure fluid trends. The documentation of the condensation heat transfer and pressure drop behavior of environmentally friendly refrigerants, and the development of accurate correlations, will facilitate their widespread introduction as a working fluid for refrigeration cycles. Furthermore, the accurate pure fluid models, which serve as a baseline case for zeotropic mixture modeling, yield more effective predictions of zeotropic mixture condensation, which will lead to increased efficiencies of chemical processing plants.