Thermoelectric generator (TEG) is a solid state technology based on the Seebeck effect that can generate electrical power from waste heat. For continuous electrical power generation heat exchangers are integrated into the “cold side” and the “hot side” of the TEG such that a temperature difference across the TEG can be established and maintained. This thesis will focus on characterizing two different flat-plate cold side heat exchanger prototypes specifically designed for dissipating the thermal loads from TEG modules. The majority of TEGs modules available have a flat geometry design and a square shape with typical dimension of 40 mm × 40 mm or 56 mm × 56 mm. To maximize the net electrical power generated by the TEGs the cold side heat exchanger is required to have uniform surface temperature distribution, and excellent heat transfer performance with minimum pressure drop. To achieve the previously mentioned requirements, two flat-plate heat exchanger prototypes having two distinct heat transfer techniques were investigated. Each heat exchanger is designed to accommodate an array of 14 TEG modules arranged in two parallel rows with 7 TEGs per row a typical arrangement for large waste energy harvesting applications. The first heat exchanger prototype utilized single-phase forced convection through 140 minichannels (1 mm × 1 mm × 90 mm long) as a heat transfer technique. The second prototype utilized 14 liquid jets, 3 mm in diameter and 40.3 mm apart, impinging on a flat surface located 5 mm above. Each impinging jets was positioned at the centre of the TEG cooling area. An experimental facility was constructed in order to test the minichannels heat exchanger and the impinging jets thermally and hydrodynamically. The heat transfer, pressure drop and temperature distribution results were compared to determine the most appropriate cold side heat exchanger prototype for the TEG POWER system. The TEG POWER system is a waste heat recovery system designed to recoup waste heat from the exhaust gases of commercial pizza ovens. The TEG POWER system is capable of harvesting waste thermal energy produced by an establishment and utilize it for electrical power generation and thermal storage purposes. Heat transfer results indicated that for a given mass flow rate the minichannels heat exchanger has better heat transfer performance compared to the impinging jets heat exchanger. The minichannels heat exchanger design had a thermal conductance of 238 W/C at 0.19 kg/s coolant flow rate compared to 111 W/C for the impinging jets heat exchanger. The total pressure drop and the minor losses for each heat exchanger prototype were measured experimentally. For the minichannels heat exchanger, the total pressure drop is 23.3 kPa at flow rate of 0.235 kg/s. Comparatively, the total pressure drop for the impinging jets heat exchanger was 27.4 kPa at the same flow rate. Fittings losses for the minichannels heat and impinging jets heat exchanger were found to be 50% and 80% respectively. The maximum total measured drop corresponded to pumping power requirements of 5.7 W and 6.8 W for the minichannels and impinging jets heat exchanger respectively. Local and average temperature distributions and their influence on the electrical power generated were studied for both heat exchanger prototypes. It was found that the minichannels heat exchanger offers more uniform surface temperature distribution per row of TEGs compared to the impinging jets heat exchanger. Therefore the minichannels heat exchanger is well suited for cooling two rows of TEGs simultaneously. Based on the thermal and hydrodynamics comparison results the minichannels heat exchanger prototype is recommended for implementation in the TEG POWER system. / Thesis / Master of Applied Science (MASc)

<p>In the United States, buildings are responsible for almost 40% of the country’s total energy consumption and 38% of the total greenhouse gas emissions. Researchers are constantly seeking sustainable and efficient energy generation solutions for buildings as society continues to cope with the intensifying energy crisis and environmental deterioration. Thermoelectric technology is one such solution that potentially can lead to significant energy recovery and conversion between waste or excess thermal energy and electrical energy. One promising application is integrating thermoelectric materials into the building envelope (TBE) for power generation and building heating and cooling without transporting energy among subsystems and refrigerant use. TBE can combine structural support and thermal storage with power generation and thermal-activated cooling and heating, thereby contributing to sustainable living and energy. </p> <p>TBE technology is still in its early development stages. This dissertation aimed to develop a fundamental understanding of the characteristics, behaviors, operation, and control of TBE systems as energy-efficient measures for thermal energy harvesting and thermal comfort regulation and to address the significant research gaps concerning high-conversion efficiency materials and optimal module configuration as well as system deployment related to real-world applications. Accordingly, this dissertation focused on the following three key objectives: (1) development and characterization of new thermoelectric composite materials; (2) identification of optimal designs and controls of TBE and established mathematical models for performance simulation; and (3) quantification of the energy-saving benefits of TBE. </p> <p>The following five aspects specifically were investigated:</p> <p>(1)<em> Material development and characterization</em>. New thermoelectric cement composites were developed with cement and various additives, material concentrations, and fabrication methods in the laboratory. Their thermoelectric properties (e.g., Seebeck coefficient, thermal conductivity, electrical conductivity, power factor, and the figure of merit) were measured simultaneously and characterized at 300–350 K.</p> <p>(2)<em> Module evaluation.</em> Commercially available thermoelectric modules (TEMs) were assessed using well-designed test apparatus in both the heat pumping and power generation modes. The test results validated the numerical model, which assisted with performance comparison and material selection between cement-based and commercial TEMs for the TBE prototype.</p> <p>(3)<em> Prototype assessment. </em>A convective TBE prototype and a radiant TBE prototype were designed, assembled, and evaluated in a pair of controlled testing chambers. The TBE’s surface temperature, thermal capacity, and COP were assessed under summer and winter conditions. </p> <p>(4)<em> Prototype modeling. </em>The first-principle-based numerical models of both the convective and radiant TBE prototypes were developed in Modelica. The modeling results indicated good agreement with the experimental data. The verified models were used to study the impacts of the design parameters and operating conditions on the heat pumping performance of TBE.</p> <p>(5)<em> System simulation. </em>A TBE building system model was established by integrating the TBE prototype model within a building’s heat balance model, considering the building construction, climate condition, power control, etc. Its seasonal performance under various climate conditions was studied to identify the potential optimal operation and energy savings. </p> <p>This dissertation confirmed several key findings in the areas of material development, system design and operation, and energy savings. The TBE achieved higher efficiency with a heat pump for heating than for cooling generally. The TBE heating system performed better than a conventional electric heater (efficiency assumed at 0.9). The measures that improved TBE heating efficiency were enhancing the material’s thermoelectric properties, optimizing the geometry and number of TEMs, and improving the boundary heat transfer of TEMs. </p> <p>This dissertation concluded that the TBE system is a promising alternative to conventional heating systems in buildings. Furthermore, the knowledge gained will strengthen the understanding of thermoelectrics in the building domain and guide further development in TBE, as well as facilitate the operation of net-zero energy and carbon-neutral buildings. </p>

This dissertation covers the study of the thermoelectric properties of GeTe and SnTe. The goal of this research is to develop high-performance lead-free thermoelectric materials that can replace PbTe-based systems so that thermoelectric technology could be bring into real application. During the study, extensive investigations on the electrical and thermal transport behaviors were conducted both experimentally and theoretically. In Chapter 1 ~ 3, the origin of thermoelectricity, modelling and characterization methods are discussed in detail. In Chapter 4, study on the thermoelectric properties of Bi, Zn and In co-doped GeTe was presented. Initial doping with Bi enhanced the performance by tuning the electronic properties and bringing down the thermal conductivity. Subsequent Zn doping permitted to maintain the high power factor by increasing carrier mobility and reducing carrier concentration. Subsequent In doping boosted the density of state effective mass. A peak zT value of 2.06 and an average zT value of 1.30 have been achieved in (Ge0.97Zn0.02In0.01Te)0.97(Bi2Te3)0.03. In Chapter 5, we thoroughly investigated the transport properties of SnTe-Sb2Te3 alloying system, provided useful insight of the mechanism of the enhanced Seebeck coefficient. To also overcome the poor carrier mobility, Pb compensation was performed which effectively optimized the carrier mobility. Meanwhile, Pb compensation broke the charge balance, allowing Sb to precipitate out of the structure. These second-phase particles provided additional source of phonon scattering, effectively suppressing the lattice thermal conductivity. As a result, a peak zT of 1.1 at 778K and an average zT of 0.56 from 300K to 778K was achieved in (Sn0.98Ge0.05Te)0.91 (Sb2Pb0.5Te)0.09, which is one of the best SnTe-based thermoelectric systems. / Thesis / Master of Science (MSc) / Thermoelectric materials can generate energy from temperature gradient, making them potential solutions for the escalating energy crisis. The state-of-the-art thermoelectric material is PbTe which shows outstanding performance and high stability. However, the toxicity of Pb element limits its practical application. It is the purpose of this work to develop high-performance GeTe and SnTe-based thermoelectrics to reduce the usage of PbTe. Combining theoretical calculations and experimental characterizations, detailed investigation on the transport properties, crystal structure and microstructure were performed on both GeTe and SnTe. Relations between their thermoelectric properties and their composition, synthesis method and microstructure were revealed. This work paves the path for the development of environmentally friendly and high-performance thermoelectric systems.

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We develop a simplified one-dimensional numerical model that simulates the performance of thermoelectric generators (TEG). The model is based on the energy and electrical potential field equations. The Seebeck coefficient, thermal conductivity, electrical resistivity and Thomson coefficient of the TEG material are used to predict the harvested power. Bismuth-telluride is used as semiconductors materials of the TEG, which is the most commonly used material by industry. Experiments on three TEG modules were performed to validate the numerical model. A comparison with predicted levels of harvested energy based on the TEG specifications is also performed. The results show differences between the experimental and numerical values on one hand and the predicted ones on the other hand. The reason for these differences are discussed. A procedure to estimate the sensitivity of the harvested power to different inputs and TEG parameters is detailed. In the second part of the dissertation, we integrate a thermoelectric generator with an organic storage device. The performance of the integrated system for different values of load resistances and temperature gradients is determined. Finally, we demonstrate that power generated from a TEG is related to the flow rate in a pipe and can, thus, be used as a flow meter. Particularly, a dimensionless relation between the TEG's peak power and Reynolds number is determined. / Ph. D.

Conventional understanding of quality of energy suggests that heat is a low grade form of energy. Hence converting this energy into useful form of work was assumed difficult. However, this understanding was challenged by researchers over the last few decades. With advances in solar, thermal and geothermal energy harvesting, they believed that these sources of energy had great potential to operate as dependable avenues for electrical power. In recent times, waste heat from automobiles, oil and gas and manufacturing industries were employed to harness power. Statistics show that US alone has a potential of generating 120,000 GWh/year of electricity from oil , gas and manufacturing industries, while automobiles can contribute upto 15,900 GWh/year. Thermoelectric generators (TEGs) can be employed to capture some of this otherwise wasted heat and to convert this heat into useful electrical energy. This field of research as compared to gas turbine industry has emerged recently over past 30 decades. Researchers have shown that efficiency of these TEGs modules can be improved by integrating heat transfer augmentation features on the hot side of these modules. Gas turbines employ advanced technologies for internal and external cooling. These technologies have applications over wide range of applications, one of which is thermoelectricity. Hence, making use of gas turbine technologies in thermoelectrics would surely improve the efficiency of existing TEGs. This study makes an effort to develop innovative technologies for gas turbine as well as thermoelectric applications. The first part of the study analyzes heat transfer augmentation from four different configurations for low aspect ratio channels and the second part deal with characterizing improvement in efficiency of TEGs due to the heat transfer augmentation techniques. / Master of Science

As wearable technology and wireless sensor nodes become more and more ubiquitous, the batteries required to power them have become more and more unappealing as they limit lifetime and scalability. Energy harvesting from body heat provides a solution to these limitations. Energy can be harvested from body heat using thermoelectric generators, or TEGs. TEGs provide a continuous, scalable, solid-state energy source ideal for wearable and wireless electronics and sensors. Unfortunately, current TEG technology produces low power (< 1 mW) at a very low voltage (20-90 mV) and require the load to be matched to the TEG internal resistance for maximum power transfer to occur. This thesis research proposes a power management integrated circuit (PMIC) that steps up ultralow voltages generated by TEGs to a regulated 3 V, while matching the internal resistance. The proposed boost converter aims to harvest energy from body heat as efficiently and flexibly as possible by providing a regulated 3 V output that can be used by a variable load. A comparator-based burst mode operation affords the converter a high conversion ratio at high efficiency, while fractional open circuit voltage maximum power point tracking ensures that the controller can be used with a variety of TEGs and TEG setups. This control allows the converter to boost input voltages as low as 50 mV, while matching a range of TEG internal source resistances in one stage. The controller was implemented in 0.25 µm CMOS and taped out in February 2016. Since these fabricated chips will not be completed and delivered until May 2016, functionality has only been verified through simulation. Simulation results are promising and indicate that the peak overall efficiency is 81% and peak low voltage, low power efficiency is 73%. These results demonstrate the the proposed converter can achieve overall efficiencies comparable to current literature and low power efficiencies better than similar wide range converters in literature. / Master of Science

no abstract provided by author / Master of Science