It is well known that the seats in a parked vehicle become very hot and uncomfortable on warm days. A new self-powered thermoelectric car seat cooler is presented to solve this problem. This study details the design and optimization of such a device. The design relates to the high level layout of the major components and their relation to each other in typical operation. Optimization is achieved through the use of the ideal thermoelectric equations to determine the best compromise between power generation and cooling performance. This design is novel in that the same thermoelectric device is utilized for both power generation and for cooling. The first step is to construct a conceptual layout of the self-powered seat cooler. Using the ideal thermoelectric equations, an analytical model of the system is developed. The model is validated against experimental data and shows good correlation. Through a non-dimensional approach, the geometric sizing of the various components is optimized. With the optimal design found, the performance is evaluated using both the ideal equations and though use of the simulation software ANSYS. The final design consists of a flat absorber plate embedded into the car seat with a thermoelectric attached to the back. A finned heat sink is used to cool the thermoelectric. The device is shown to generate enough power to provide a reasonable temperature drop in the seat. / Master of Science

The goal of this research was to design, build and test a small burner and heat exchanger system that could be used as a source of heat for thermoelectric modules (TEMs) for the purpose of generating portable electric power for soldiers in the field. The project was conducted as a subcontract to Marlow Industries Inc. which was under contract from the U.S. Army. The scale of the burner thermal output was to be in the approximate range of 2 kW of heat production and it was to be able to operate on a liquid fuel, specifically JP8. The first burner investigated was a custom burner designed and built at UT. It was tested with various fuel and air delivery systems. Different methods to start it, with the goal of developing an electrical starting system, were also investigated. It was capable of operating at outputs over 1 kW, but was difficult to start reliably and fuel vaporization characteristics were sensitive to operating conditions. Two commercial burners were also studied, each with somewhat different designs. One of those burners, manufactured by MSR, was chosen to be further tested in conjunction with a heat exchanger and thermoelectric modules. The performance of the thermoelectric modules used in this study was determined to be very dependent on an attached resistive load, with a peak power output occurring at approximately 3 ohms. Power output was also determined to increase linearly with increasing temperature difference between the hot and cold sides of the module. Power output followed similar trends as open circuit voltage. The temperatures of the heat exchanger across its width were very uniform, but the accuracy in centering the heat exchanger over the burner could significantly affect temperatures. The time to reach steady state temperatures was relatively insensitive to the length of the heat exchanger. The presence of attached thermoelectric modules reduced the temperature of the heat exchangers and exhaust gas slightly. Reducing the heat exchanger length resulted in higher metal temperatures. Without cooling the cold side of the thermoelectric modules, performance increased while the system was heating up, but then dropped after reaching a peak. Cold side cooling improved thermoelectric performance by increasing its temperature difference. Active cooling with a blower and heat sink provided even better performance than passive cooling using just a heat sink at the expense of a larger parasitic load. The TEMs on the 5 inch long heat exchanger could generate 6.32 W with passive cooling, but active cooling would produce no net power. The 11 inch long heat exchanger could generate 12.8 W with passive cooling, and 16 W net could be generated with active cooling. A heat exchanger efficiency calculation showed that the 16, 11 and 5 inch long heat exchangers were about 94.4%, 93.4%, and 90.7% efficient respectively. This efficiency was defined as the ratio of the heat transferred to the heat exchanger to the heat released in the flame. / text

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)

In this work, a thermoelectric energy harvester system aimed at harvesting energy for locally powering sensor nodes in nuclear power plant coolant loops has been designed, fabricated and tested. Different mathematical modeling methods have been validated by comparing with experimental results. The model developed by this work has the best accuracy in low temperature range and can be adapted and used with any heat sink, heat pipe, or thermoelectric system, and have proven to provide results closely matching experimental data. Using the models, an optimization of the thermoelectric energy harvesting system has been performed which is applicable to any energy harvester of this variety. With experimental validation, the system is capable of generating sufficient energy to power all the sensors and electronical circuits designed for this application. The effect of gamma radiation on this thermoelectric harvester has also been proved to be small enough through radiation experiment. / Master of Science

Energy harvesting is a technology for generating electrical power from ambient or wasted energy. It has been investigated extensively as a means of powering small electronic devices. The recent proliferation of devices with ultra-low power consumption - devices such as RF transmitters, sensors, and integrated chipsets - has created new opportunities for energy harvesters. There is a variety of ambient energies such as vibration, thermal, solar, stray current, etc. Depending on energy sources, different kinds of energy conversion mechanism should be employed. For energy harvesters to become practical, their energy conversion efficiency must improve. This efficiency depends upon advances in two areas: the system or structural design of the energy harvester, and the properties of the materials employed in energy conversion. This dissertation explores developments in both areas. In the first area, the role of nano-, micro-, and bulk structure of the energy conversion materials were investigated. In the second area, piezoelectric energy harvesters and a magneto-thermoelectric generator are treated from the perspective of system design. In the area of materials development, PbTiO3 (PTO) nanostructures consisting of nanofibers and three-dimensional (3-D) nanostructure arrays were hydrothermally synthesized. The growth mechanism of the PTO nanofibers and 3-D nanostructures were investigated experimentally and theoretically. The PTO nanostructures were composed of oriented PTO crystals with high tetragonality; these arrays could be promising candidates for nanogenerators. Different designs for energy harvesters were explored as a means of improving energy conversion efficiency. Piezoelectric energy harvesters were designed and constructed for applications with a low frequency vibrational energy and for applications with a broadband energy spectrum. A spiral MEMS piezoelectric energy harvester design was fabricated using a silicon MEMS process and demonstrated to extract high power density at ultra-low resonance frequencies and low acceleration conditions. For a broadband energy harvester, a magnetically-coupled array of oscillators was designed and built that broadened the harvester's effective resonance frequency with considerably improved output power. A new design concept for thermal energy harvesting that employs a magneto-thermoelectric generator (MTG) design was proposed. The MTG exploits a thermally-induced second order phase transition in a soft magnetic material near the Curie temperature. The MTG harvested electric power from oscillations of the soft magnet between hot and cold sources. For the MTG design, suitable soft magnetic materials were selected and developed using La0.85Sr0.15MnO3-Ni0.6Cu0.2Zn0.2Fe2O4 magnetic composites. The MTG was fabricated from a PVDF cantilever and a gadolinium (Gd) soft magnetic material. The feasibility of the design for harvesting energy from the waste heat was demonstrated by attaching an MTG array to a computer CPU. / PHD

Les phénomènes thermoélectriques sont un moyen de convertir directement l’énergie thermique en énergie électrique ; ils sont à ce titre au cœur de nombreuses recherches dans le domaine de l’énergétique. Au-delà de l’optimisation des matériaux constituants les générateurs thermoélectriques, il est également nécessaire de mener une réflexion sur la manière dont ces générateurs sont utilisés. La contribution des contacts thermiques entre le générateur et les réservoirs thermiques est un facteur qui va modifier les conditions de fonctionnement optimales du générateur. En utilisant la notion de courant thermique convectif, développée par Thomson il y a plus de 150 ans, nous généralisons les expressions classiques du fonctionnement à puissance maximum pour le générateur pour ce cas de figure. Nous constatons toutefois que ces conditions se réduisent à une adaptation d’impédance, à la fois thermique et électrique Outre son intérêt pratique, le générateur thermoélectrique est également un système modèle de choix pour étudier la théorie du transport couplé et des phénomènes irréversibles. En utilisant la description donnée par Ioffe de ce système, nous montrons que l’efficacité à maximum de puissance, un coefficient de performance au cœur de la thermodynamique à temps fini, s’exprime comme une fonction relativement simple des paramètres du système. La nouveauté de ce travail repose sur une prise en compte appropriée des dissipations internes associées au processus de conversion d’énergie. Les résultats sont généralisés enfin aux cas d’autres machines thermiques telle que la roue à rochet de Feynman. / Thermoelectric phenomena are a way to directly convert thermal energy into electrical energy; they thus are at the heart of several researches in the field of energy conversion. The optimization of the thermoelectric generators includes materials improvement but a reflection on their working conditions is also mandatory. The contribution of the thermal contacts between the generator and the heat reservoirs is a factor that will change the optimum operating conditions of the generator. Using the concept of convective heat flow, developed by Thomson more than 150 years ago, we generalize the classical expression of maximum power conditions. Moreover, we note that these conditions may be reduced to impedance matching conditions, both thermal and electrical. In addition to its practical interest, the thermoelectric generator is also an ideal model system to study the theory of coupled transport and of irreversible phenomena. Using the description of this system given by Ioffe, we show that the maximum power efficiency, a coefficient of performance at the heart of finite time thermodynamics, expressed as a simple function of the system parameters. The novelty of this work is based on a proper consideration of internal dissipation associated with the energy conversion process. The results are then generalized to other thermal engines such as the Feynman ratchet.

In the face of the internationally tightened requirements and regulations for CO2 emissions from the transportation sector, waste heat recovery using a thermoelectric generator (TEG) has become the most significant research interest. A vehicular TEG, converting otherwise wasted thermal energy from engines to electricity directly for use in the vehicle systems, is a promising approach for vehicle original equipment manufacturers (OEMs) to reduce fuel consumption and lower CO2 emissions. This thesis aims to explore the main challenges to be faced in the commercialization of TEGs. Based on a review of the literature, four research gaps have been identified, which are respectively: * Translating the material improvements into TEG Performance, * Transient behaviors of vehicular TEGs under driving cycles, * Fuel saving percentage and cost-benefit estimation of TEG, * Bidirectional characteristic of TEM and bifunctional vehicular TEG. To directly address these research gaps, a quasi-static TEM model, a dynamic TEG model, a semi-empirical vehicular TEG model, and a dual-model TEM model have been respectively developed and validated through experiments on both TEM test rigs and TEG engine test benches. These developed models are used as tools to investigate the performance of TEG, parameters sensitivity, and integration effects. Model-based TEG control, TEG cost benefit ratio and feasibility of a bifunctional TEG are also explored based on the developed models. The simulation results show that TEG power generation is highly sensitive to the heat transfer coefficient of hot side heat exchanger and thermal contact resistance. The TEG installation position is identified as the most important integration effect. It has been found by the simulation result that the fuel saving with TEG installed upstream of the three-way catalyst (TWC) is 50% higher than the fuel saving with TEG installed downstream of the TWC. The fuel saving percentage for a skutterudite vehicular TEG, which can generate around 400-600W in constant speed 120km/h, is 0.5-3.6% depending on the integration position in the exhaust line. A 3-minute faster warm-up effect of engine oil can be obtained when the bifunctional TEG works in engine warm-up mode with electrical current applied.

Thermoelectric generators (TEG) directly convert heat energy into electrical energy. The impediments as to why this technology has not yet found extensive application are the low conversion efficiency and high costs per watt. On the one hand, the manufacturing process is a cost factor. On the other, the high-­‐priced thermoelectric (TE) materials have an enormous impact on the costs per watt. In this thesis both factors will be examined: the production process and the selection of TE materials. Technical screen printing is a possible way of production, because this method is very versatile with respect to the usable materials, substrates as well as printing inks. The organic conductor PEDOT:PSS offers reasonable thermoelectric properties and can be processed very well in screen printing. It was demonstrated by prototypes of fully printed TEGs that so-­‐called vertical printed TEGs are feasible using standard graphic arts industry processes. In addition, the problems that occur with print production of TEGs are identified. Finally, approaches to solve these problems are discussed.

Atualmente um dos grandes responsáveis pela emissão de CO2 (Dióxido de Carbono) são os veículos movidos a motor de combustão interna, em sua maioria os automóveis. Pesquisas recentes têm mostrado maneiras de aumentar a eficiência dos automóveis por meio do aproveitamento do calor de exaustão para geração de energia elétrica, com consequente redução no consumo de combustível. Esta dissertação tem por objetivo apresentar um estudo de viabilidade técnica de um gerador termoelétrico aproveitando o calor residual dos gases de exaustão de um motor de combustão interna para geração de energia elétrica. O trabalho apresenta o modelamento matemático e a implementação de um protótipo para realização dos ensaios para a obtenção de resultados experimentais. O protótipo foi montado utilizando módulos termolétricos cujo princípio de funcionamento é baseado nos efeitos Seebeck e Peltier, que devido ao conceito de reversibilidade podem funcionar como geradores elétricos, aquecedores ou refrigeradores. Por meio das equações teóricas e dos resultados dos ensaios experimentais foi possível avaliar o desempenho do sistema de geração de energia elétrica, determinar o comportamento dos principais parâmetros envolvidos e finalmente concluir sobre a exequibilidade e viabilidade do projeto. / Currently one of the most responsible for CO2 (Carbon Dioxide) emissions are vehicles powered by internal combustion engine, in their majority the automobiles. Recent research has shown ways to improve the efficiency of automobiles through the use of exhaust heat to generate electric power, with consequent reduction in fuel consumption. This paper aims to present a technical feasibility study of a thermoelectric generator using the residual heat from exhaust gases of an internal combustion engine to generate electric power. The paper presents the mathematical modeling and implementation of a prototype for tests to obtaining experimental results. The prototype was assembled using thermoelectric modules whose operating principle is based on the phenomena called Seebeck and Peltier Effects, which due to the concept of reversibility can act as electric generators, heaters or coolers. Through the theoretical equations and experimental results it was possible to evaluate the performance of electric power generation system, determine the behavior of the main parameters and finally conclude on the feasibility and viability of the project.

Today many processes generate a lot of waste heat, for example industries or cars. One way to make this thermal energy useful is to transform it into electrical energy with a thermoelectric generator (TEG) or thermoelectric cooler (TEC). This technology is not used in any large scale today, but a lot of research is being done on the subject. The technology is based on the Seebeck effect and uses a temperature difference between two sides of an element to generate an electrical current. The reason that the research has gained more attention in recent years is because of the increasing electricity prices and the diminishing natural resources. Other benefits are that they run quietly and do not demand much maintenance.Another area where this technology could be useful is in off-grid cabins where it is easy to generate a lot of thermal energy by burning wood, but electrical energy is in high demand.In this thesis two different types of TEGs and one type of TEC are tested to investigate how much power they generate at different temperature differences, how well they meet the specified values in their respective data sheet and what their power per euro value is. For this, an experimental setup was made with:- An induction plate to increase the temperature on the hot side.- A CPU-fan, to reduce the temperature on the cold side.- Two temperature sensors (one for measuring the hot temperature and one for the cold one).- An electric circuit featuring a voltmeter, an amperemeter and an adjustable resistor (rheostat).The results show that, for this experiment the highest received power (6,38 W) comes from the medium-priced element but the highest power per euro comes from the lowest priced element (1,16 W/€). A quality problem for the lowest priced element was that parts of the solder melted when the temperature exceeded 225 °C. Another problem was that the induction plate was unable to provide enough heat for the most expensive of the elements to reach the temperature for which the retailer supplies their measured data.