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Dissertations / Theses on the topic 'Thermoelectric conversion of energy'
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Mackey, Jon A. "Thermoelectric Energy Conversion: Advanced Thermoelectric Analysis and Materials Development." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1428062038.
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Zhao, Yixin. "Developing Nanomaterials for Energy Conversion." Cleveland, Ohio : Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1270172686.
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Qiu, Xiaofeng. "NANOSTRUCTURED MATERIALS FOR ENERGY CONVERSION." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1207243913.
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Jaworski, Christopher M. "Opportunities for thermoelectric energy conversion in hybrid vehicles." Connect to resource, 2007. http://hdl.handle.net/1811/25121.
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Thesis (Honors)--Ohio State University, 2007.Title from first page of PDF file. Document formatted into pages: contains vi, 59 p.; also includes graphics. Includes bibliographical references (p. 59). Available online via Ohio State University's Knowledge Bank.
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Li, Junyue. "Perovskite thermoelectric materials for high-temperature energy conversion." Thesis, Boston University, 2014. https://hdl.handle.net/2144/21206.
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Thesis (M.Sc.Eng.)Despite of recent success in achieving the figure of merit ZT > 1 based on the nanoscale patterned thermoelectric structures, there have been few stable n-type materials with attractive thermoelectric responses for high temperature applications at T > 800K. In this thesis, we applied the first-principles density functional theory (DFT) calculations to probe the structure and thermoelectric properties relationship of a comprehensive series of perovskite materials. The density of states (DOS), Seebeck coefficient S, electric conductivity σ, and electronic contribution of the thermal conductivity Ke were obtained directly from the first-principles DFT calculations. In particular, Lanthanum (La), Gadolinium (Gd), Samarium (Sm), Yttrium (Y) doped MU+2093SrU+2081U+208BU+2093TiOU+2083 and Niobium (Nb) doped SrNbyTi1-yOU+2083 and doubly doped LaU+2093SrU+2081U+208BU+2093NbyTi1-yOU+2083 systems were studied. The change of the power factor S^2σ corresponding to the different dopant concentration had a good agreement with the experimental data. Our computed power factors S^2σ as a function of the dopant con- centration agree well with the available experimental data, and at the same time provide new insights for the optimal compositions. In the low doping region (x U+003E 12:5%), gadolinium and niobium are the best candidates of perovskite thermoelectric materials while at high doping level (x U+003E 25%), lanthanum and yttrium are the best options. In the case of doubly doped perovskites LaU+2093SrU+2081U+208BU+2093NbyTi1-yOU+2083, our calculations predict that the x= 12.5% and y= 12.5% is the best choice.
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Wirth, Luke J. "Thermoelectric Transport and Energy Conversion Using Novel 2D Materials." Wright State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=wright148433373077002.
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Jovovic, Vladimir. "Engineering of Thermoelectric Materials for Power Generation Applications." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1248125874.
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Topal, Emre Tan. "A Mems Thermoelectric Energy Harvester For Energy Generation In Mobile Systems." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613636/index.pdf.
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In this thesis design, optimization, fabrication and performance characterization of MEMS thermoelectric (TE) energy harvesters for harnessing waste heat in mobile systems are presented. As a proof of concept, chromium and nickel are used as the thermoelectric material in the proposed design. The feasibility of the state of the art thermoelectric materials is also discussed.
MEMS TE energy harvesters proposed in this study are designed to generate power at relatively lower &DeltaT values. The performance of the MEMS TE energy harvesters was optimized using analytical and 3-D finite element models. An analytical code was used for profiling the electrical power output with varying geometry. The design points with maximum generated power were selected, and the microfabricated thermoelectric energy harvesters were designed accordingly. The fabricated devices are formed on a silicon wafer and composed of Nickel and Chromium thermocouples on SiO2/Si3N4 diaphragms, and Titanium heater and monitor resistors for testing purposes. Microfabrication was followed by the performance characterization of MEMS TE energy harvesters with the conducted tests. For 10 °
C temperature difference between the hot and cold junctions (a heat source at 35 °
C), the proposed TE energy harvesters are capable of providing 1.1 µ
W/cm2 power density and 1.71 V voltage. The performance of the thermoelectric generators in general is limited by Carnot cycle efficiency. Nevertheless, the validated practical performance of MEMS TE energy harvesters proposed in this thesis is comparable to other examples in literature. It is anticipated by the calculations that this design will be able to provide the highest thermoelectric efficiency factor (4.04 µ
W/K2cm2) among the lateral TE energy harvesters if thermoelectric materials having high Seebeck coefficient values (such as p-Si, n-Si, polysilicon, Bi2Te3 etc.) are used. According to the performance results, the MEMS TE energy harvesters can be implemented in mobile systems to convert waste heat into electricity. The fabrication process can be adapted to CMOS with some modifications if needed. The lateral MEMS thermoelectric energy harvesters can also be combined with vibration energy harvesters to realize multi-mode energy scavenging. For prospective study, vertical thermoelectric generator configurations are also discussed in order to further increase the power density generated. The finite element simulations for proposed vertical configurations with air and water convection were completed. The vertical TE generators proposed can supply up to 4.2 mW/cm2 with a heat source at a temperature of 310 K.
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Minnich, Austin Jerome. "Exploring electron and phonon transport at the nanoscale for thermoelectric energy conversion." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67593.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 147-155).
Thermoelectric materials are capable of solid-state direct heat to electricity energy conversion and are ideal for waste heat recovery applications due to their simplicity, reliability, and lack of environmentally harmful working fluids. Recently, nanostructured thermoelectrics have demonstrated remarkably enhanced energy conversion efficiencies, primarily due to a reduction in lattice thermal conductivity. Despite these advances, much remains unknown about heat transport in these materials, and further efficiency improvements will require a detailed understanding of how the heat carriers, electrons and phonons, are affected by nanostructures. To elucidate these processes, in this thesis we investigate nanoscale transport using both modeling and experiment. The first portion of the thesis studies how electrons and phonons are affected by grain boundaries in nanocomposite thermoelectric materials, where the grain sizes are smaller than mean free paths (MFPs). We use the Boltzmann transport equation (BTE) and a new grain boundary scattering model to understand how thermoelectric properties are affected in nanocomposites, as well as to identify strategies which could lead to more efficient materials. The second portion of the thesis focuses on determining how to more directly measure heat carrier properties like frequency-dependent MFPs. Knowledge of phonon MFPs is crucial to understanding and engineering nanoscale transport, yet MFPs are largely unknown even for bulk materials and few experimental techniques exist to measure them. We show that performing macroscopic measurements cannot reveal the MFPs; instead, we must study transport at the scales of the MFPs, in the quasi- ballistic transport regime. To investigate transport at these small length scales, we first numerically solve the frequency-dependent phonon BTE, which is valid even in the absence of local thermal equilibrium, unlike heat diffusion theory. Next, we introduce a novel thermal conductivity spectroscopy technique which can measure MFP distributions over a wide range of length scales and materials using observations of quasi-ballistic heat transfer in a pump-probe experiment. By observing the changes in thermal resistance as a heated area size is systematically varied, the thermal conductivity contributions from different MFP phonons can be determined. We present the first experimental measurements of the MFP distribution in silicon at cryogenic temperatures. Finally, we develop a modification of this technique which permits us to study transport at scales much smaller than the diffraction limit of approximately one micron. It is important to access these length scales as many technologically relevant materials like thermoelectrics have MFPs in the deep submicron regime. To beat the diffraction limit, we use electron-beam lithography to pattern metallic nano dot arrays with diameters in the hundreds of nanometers range. Because the effective length scale for heat transfer is the dot diameter rather than the optical beam diameter, we are able to study nanoscale heat transfer while still achieving ultrafast time resolution. We demonstrate the modified technique by measuring the MFP distribution in sapphire. Considering the crucial importance of the knowledge of MFPs to understanding and engineering nanoscale transport, we expect these newly developed techniques to be useful for a variety of energy applications, particularly for thermoelectrics, as well as for gaining a fundamental understanding of nanoscale heat transport.
by Austin Jerome Minnich.
Ph.D.
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Pal, Souvik. "Control of Nanoscale Thermal Transport for Thermoelectric Energy Conversion and Thermal Rectification." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/52935.
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Materials at the nanoscale show properties uniquely different from the bulk scale which when controlled can be utilized for variety of thermal management applications. Different applications require reduction, increase or directional control of thermal conductivity. This thesis focuses on investigating thermal transport in two such application areas, viz., 1) thermoelectric energy conversion and 2) thermal rectification. Using molecular dynamics simulations, several methods for reducing of thermal conductivity in polyaniline and polyacetylene are investigated. The reduction in thermal conductivity leads to improvement in thermoelectric figure of merit. Thermal diodes allow heat transfer in one direction and prevents in the opposite direction. These materials have potential application in phononics, i.e., for performing logic calculations with phonons. Rectification obtained with existing material systems is either too small or too difficult to implement. In this thesis, a more useful scheme is presented that provides higher rectification using a single wall carbon nanotube (SWCNT) that is covalently functionalized near one end with polyacetylene (PA). Although several thermal diodes are discussed in literature, more complex phononic devices like thermal logic gates and thermal transistors have been sparingly investigated. This thesis presents a first design of a thermal AND gate using asymmetric graphene nanoribbon (GNR) and characterizes its performance.Ph. D.
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Yu, Zhang. "Solution Processed Chalcogenide Nanomaterials for Thermoelectric Application." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/670923.
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The bottom-up engineering of nanomaterials using solution-processing strategies is of particular interest for reducing cost and optimizing the performance of TE materials and devices. This thesis focuses on the development of scalable methods for the production of TE nanomaterials with optimized performance. The thesis is divided into 5 chapters. Chapter 1 introduces solution-based approaches for producing functional nanomaterials and the general state of the art in the field of thermoelectricity. Chapter 2 and chapter 3 present a fast and simple molecular ink-based method to produce low cost and crystallographically textured SnSe2 and SnSe nanomaterials. Molecular ink printing techniques could offer a scalable approach to fabricate TE devices on flexible substrates. In these chapters, I proved that cost-effective p-type SnSe NPLs could be produced by a molecular ink-based strategy that allowed introducing controlled amounts of Te to achieve unprecedentedly high TE figure of merit. On the other hand, n-type SnSe2 nanomaterials were also intentionally produced from the same strategy to complement an all Sn-Se based device. Both of the bulk nanomaterials displayed significant crystallographic texture after hot pressing, resulting in highly anisotropic charge and heat transport properties. Different approaches were applied to optimize their TE performance: SnSe2 NPLs were blended with metal NPs to produce a metal-semiconductor NC. The electrical conductivities of the blends were significantly improved with respect to bare SnSe2 bulk nanomaterial and a three-fold increase in the TE figure of merit was obtained, reaching unprecedented values up to ZT = 0.65 for SnSe2 material. For SnSe nanomaterials, I demonstrate that the introduction of small amounts of tellurium in the precursor ink allowed reducing the band gap, increasing both charge carrier concentration and mobility, especially cross plane, with a minimal decrease of the Seebeck coefficient. This strategy translated into record out of plane ZT values at 800 K, ZT=1.05 Chapter 4 and chapter 5 describe two different strategies to produce Bi2Te3-Cu2-xTe NCs based on the consolidation of nanostructured building blocks. I first detail a two-step solution-based process to produce the Bi2Te3-Cu2-xTe heteronanostructures, based on the growth of Cu2-xTe nanocrystals on the surface of Bi2Te3 nanowires. The transport properties of the NCs are investigated as a function of the amount of Cu introduced, which reveal that the presence of Cu decreases the material thermal conductivity through promotion of phonon scattering, modulates the charge carrier concentration through electron spillover, and increases the Seebeck coefficient through filtering of charge carriers at energy barriers. These effects result in an improvement of over 50% of the TE figure of merit of Bi2Te3. As comparison, I produced Bi2Te3-Cu2-xTe NCs by directly mixing proper ratio of individual Bi2Te3 nanowires with Cu2-xTe nanocubes and consolidating the resulting NP mixture by hot-press. A significant difference of transport properties was detected when compared with NCs fabricated by hot-pressing heterostructured Bi2Te3-Cu2-xTe nanowires. On the contrary to the composite obtained from hetero- nanostructures, the presence of Cu2-xTe nanodomains did not lead to a significant reduction of the lattice thermal conductivity of the reference Bi2Te3, which is already very low here, but it resulted in a nearly threefold increase of its power factor. Additionally, the presence of Cu2-xTe resulted in a strong increase of the Seebeck coefficient. This increase is related to the energy filtering of charge carriers at energy barriers within Bi2Te3 domains created by the accumulation of electrons in the regions nearby Cu2-xTe/Bi2Te3 junctions. Overall, a significant improvement of figure of merit, up to a 250%, was obtained with the suitable combination of Cu2-xTe NPs and Bi2Te3 nanowires. Finally, the main conclusions of this thesis and some perspectives for future work are presented.La ingeniería de nanomateriales a partir del procesado en solución es de particular interés para optimizar el rendimiento de los materiales y dispositivos termoeléctricos. . Esta tesis estáse centra en el diseño y el ensamblaje racional de nanomateriales termoeléctricos de alto rendimiento a través de procesado en solución. La tesis se divide en 5 capítulos. El Capítulo 1 aborda la introducción fundamental del enfoque sintético para producir nanomateriales funcionales. Los capítulos 2 y 3 presentan un método rápido y simple basado en soluciones para producir nanomateriales SnSe2 y SnSe con textura cristalográfica. Dado que los calcogenuros de estaño son materiales especialmente interesantes para la conversión de energía termoeléctrica, se sintetizaron nanoplacas SnSe y SnSe2 controlables por forma mediante una estrategia basada en tinta molecular para lograr una figura de mérito termoeléctrica sin precedentes por dopaje con Te/Cu. Ambos nanomateriales mostraron una textura cristalográfica significativa después del prensado en caliente, lo que dio como resultado unas propiedades de transporte de carga calor altamente anisotrópicas. Los capítulos 4 y 5 describen dos estrategias diferentes para producir nanocompuestos Bi2Te3-Cu2-xTe basados en la consolidación de nanoestructuras. La presencia de Cu2-xTe da como resultado un fuerte aumento del coeficiente de Seebeck. Este aumento está relacionado con el filtrado de los portadores de carga en función de su energía en las barreras de energía dentro de los dominios Bi2Te3 creados por la acumulación de electrones en las regiones cercanas a las uniones Cu2-xTe / Bi2Te3. En general, se obtiene una mejora significativa de la figura de mérito con nanocompuestos Bi2Te3-Cu2-xTe. Finalmente, en el último capítulo se presentan las principales conclusiones de esta tesis y algunas perspectivas para trabajos futuros.
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Büttner, Gesine [Verfasser], and Anke [Akademischer Betreuer] Weidenkaff. "Misfit-layered cobalt oxides for thermoelectric energy conversion / Gesine Büttner ; Betreuer: Anke Weidenkaff." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2017. http://d-nb.info/1159570256/34.
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Liu, Yu. "Bottom-up Engineering of Chalcogenide Thermoelectric Nanomaterials." Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/663274.
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In this thesis, it is detailed the bottom-up production and characterization of thermoelectric (TE) nanomaterials with significant enhanced performance by using colloidal nanocrystals (NCs) as building blocks. The production of TE nanomaterials with significant improved figure of merit (ZT), has to do, not only with the precise control of the NCs properties, but also with the further fine control over the crystallographic alignment of nanograins of highly anisotropic materials.
The first part of the thesis correspond to the study of synthetic routes to produce high quality chalcogenide NCs that are doped during the NC synthesis, in order to control the charge carrier concentration. The system studied was I−V−VI chalcogenide semiconductor, specifically it was produced the materials: AgSbSe2 and Cu3SbSe4. A low-cost, high-yield and scalable synthesis route to produce monodisperse of AgSbSe2 and Cu3SbSe4 NCs was obtained. After ligand displacement, the NCs were used as building blocks to produce TE nanomaterials. Additionally, by means of substitutional doping, a large increment in the power factor and relatively lower thermal conductivities were observed. The optimization of the doping concentration resulted in ZT values of 1.10 at 640 K for AgSb0.98Bi0.02Se2, and of 1.26 at 673 K for Cu3Sb0.88Sn0.10Bi0.02Se4, which represents a significant increase beyond the state of the art in Te-free multinary Ag/Cu-based chalcogenide materials.
In the second part of the thesis, the work about PbS-metal (Cu and Sn) nanocomposites produced by blending procedure is presented. The low work function metal is able to inject electrons to the intrinsic PbS matrix, which is another strategy to control the charge carrier concentration. The power factor is dramatically enhanced due to the increase of the electrical conductivity in the nanocomposites. Consequently, the ZTmax was remarkably enhanced by two times as compared with the pristine PbS. Furthermore, we also compared the TE performance of microcrystalline composites with the same composition as in nanocrystalline composites; commercial PbS host with Cu particles. The results revealed that with the same metal addition, higher electrical conductivities were obtained in the nanocomposite, but higher Seebeck coefficients were maintained in the microcomposite. Moreover, higher thermal conductivities were also obtained in the microcomposite. Finally, the figure of merit ZT were higher for the microcomposite system in the low temperature range, but much lower in the higher temperature range compared with the nanocomposites system.
In the last block, the process of production of crystallographically textured materials is presented. We face here the challenge of bottom-up approaches to control the crystallographic alignment of nanograins. The production of nanostructured Bi2Te3-based alloys is presented. This can be done with controlled stoichiometry by solution-processing, and crystallographic texture by liquid-phase sintering using multiple pressure and release steps at 480 °C, above the tellurium melting point. Additionally, we explain the possible mechanism to produce the highly textured nanomaterials. This strategy results in record TE figures of merit: ZT=1.83 at 420 K for Bi0.5Sb2.5Te3 and ZT=1.31 for Bi2Te2.7Se0.3 at 440 K when averaged over 5 materials in the c direction, respectively. These high figures of merit extended over a wide temperature range, which results in energy conversion efficiencies a 50% higher than commercial ingots in the similar temperature range.
In summary, different strategies to improve the TE performance of bulk nanostructured materials produced by bottom-up engineering of NCs, have been studied and confirmed in this thesis. Additionally, it has been proven that the solution-processed synthesis approach is low-cost, compatible with the scale-up engineering, and also versatile in tuning the size, shape, composition, and microstructure, among others parameters of different nanomaterials to optimize their TE properties.Los nanocristales (NCs) coloidales tienen excelentes propiedades para diferentes aplicaciones, como la conversión de energía, la catálisis, los dispositivos electrónicos y optoelectrónicos, entre otros. Así mismo, la síntesis coloidal de NCs tiene ventajas en el control del tamaño, forma y composición a nivel de la nanoescala; las bajas temperaturas de reacción; y la no necesidad de equipos especializados. Este proyecto se concentra en el diseño racional y la ingeniería de materiales termoeléctricos (TE) nanoestructurados de alta eficiencia, usando la estrategia del ensamblado ascendente (bottom-up) de NCs coloidales. Primero, se diseñó una ruta de síntesis de bajo costo, alto rendimiento, con la cual, se obtuvieron NCs de AgSbSe2 y Cu3SbSe4. La optimización de la concentración de dopaje resultó en valores para la figura de mérito TE, ZT, de 1.10 a 640 K para AgSb0.98Bi0.02Se2, y de 1.26 at 673 K para Cu3Sb0.88Sn0.10Bi0.02Se4. El material con mejores propiedades se usó para la producción de un generador TE en forma de anillo, para acoplarlo a los tubos de escape de gases, obteniendo una potencia eléctrica de 1mW por elemento TE con una diferencia de temperatura de 160 °C. En la segunda parte, se presenta el trabajo de la producción de nanocopuestos de PbS-metal (Cu y Sn) usando un procedimiento versátil de mezcla de NCs. La función de trabajo del metal es capaz de inyectar electrones a la matriz intrínseca de PbS. El factor de potencia TE, se ve dramáticamente incrementado debido al aumento en la conductividad eléctrica en los nanocompuestos TE. Consecuentemente, el valor máximo de ZT se vio excepcionalmente incrementado por el doble del valor comparado con el material original PbS. Finalmente, se presenta el proceso de producción de materiales texturizados cristalográficamente, produciendo materiales tipo p BixSb2-xTe3 y tipo n Bi2Te3-xSex. Se controló la estequiometria durante el procesamiento en solución y la textura cristalográfica, por medio de la sinterización en fase líquida con un procedimiento de múltiples pasos de presión y relajación a una temperatura de 480°C. Los valores de la figura de mérito TE presentan el record de: ZT=1.83 a 420 K para Bi0.5Sb2.5Te3 y ZT=1.31 para Bi2Te2.7Se0.3 a 440 K.
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Watzman, Sarah June. "Thermal Energy Conversion Utilizing Magnetization Dynamics and Two-Carrier Effects." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1523621461827864.
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McEnaney, Kenneth. "Thermoelectrics and aerogels for solar energy conversion systems." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97770.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 115-124).
Concerns about climate change, the world's growing energy needs, and energy independence are driving demand for solar energy conversion technologies. Solar thermal electricity generation has the potential to ll this demand. Solar thermal technology could also be used to displace fossil fuels in applications which require heat as an input. This thesis addresses the potential of two solar thermal technologies: solar thermoelectric generators and aerogel-based solar thermal receivers. Thermoelectrics are materials which produce a voltage when subjected to a temperature gradient. In a solar thermoelectric generator (STEG), sunlight heats one end of the thermoelectric materials, generating a voltage across the device. The voltage can be connected to a load and useful work can be extracted. By adding optical concentration and using higher-temperature materials, the power output and energy conversion eciency of STEGs can be increased. In this work, segmented thermoelectric generators (TEGs) made of bismuth telluride and skutterudite alloys are modeled, optimized, built, and tested. These TEGs achieve a heat-to-electricity conversion efficiency of 10.7% at a hot side of 550° C, the highest TEG eciency reported in this temperature range. From these TEGs, STEGs are built which achieve a sunlight-to-electricity conversion eciency of 5.7% at less than 60 suns, higher than the best reported literature values in this concentration range. With further improvements, it is projected that these STEGs will achieve 10% eciency at 100 suns. In any type of solar thermal system, heat losses from the system must be suppressed to achieve high eciency. Aerogels, which are stable ultra-low density foams, can suppress radiative and convective losses. It is shown that aerogel-based solar thermal receivers can increase the eciency of traditional solar thermal electricity and hot water generation. These results can help advance the field and expand the scope of solar thermal technologies.
by Kenneth McEnaney.
Ph. D.
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Hasan, Atiya. "Review of solar thermoelectric energy conversion and analysis of a two cover flat-plate solar collector." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40435.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007."February 2007."
Includes bibliographical references (p. 47-48).
The process of solar thermoelectric energy conversion was explored through a review of thermoelectric energy generation and solar collectors. Existing forms of flat plate collectors and solar concentrators were surveyed. A thermal analysis of a common two-cover flat plate solar collector was then performed. The model focused specifically on radiation absorption through the cover system and radiation and convection losses from the absorption plate to determine the parameters that most significantly affect the efficiency of the collector and the overall efficiency of the solar thermoelectric generator. In this case, collector efficiency was measured by the ratio of useable energy to incident solar energy. Overall generator efficiency was measured by power generated per unit area of the collector. It was found that of several parameters, the collector area had the most significant influence on collector efficiency. For the overall efficiency of the generator, the most significant parameter was the ratio of the collector area to the cross-sectional area of the thermoelectric elements (TE). The efficiency of the generator maximized at a ratio of 250:1, with a magnitude of 5.76 W/m2. The analysis exposes some weaknesses of the flat plate collector to show where future designs should focus for improvement.
by Atiya Hasan.
S.B.
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Su, Lusheng. "Formation Mechanism and Thermoelectric Energy Conversion of Titanium Dioxide Nanotube Based Multi-Component Materials and Structures." University of Toledo / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1370793126.
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Taylor, Stephen H. "Analytical Modeling and Optimization of a Thermoelectric Heat Conversion System Operating Betweeen Fluid Streams." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2813.
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Analytical, closed-form solutions governing thermoelectric behavior are derived. An analytical model utilizing a thermal circuit is presented involving heat transfer into, through, out of, and around a thermoelectric device. A nondimensionalization of the model is presented. Linear heat transfer theory is applied to the model to obtain a series of closed form equations predicting net power output for the thermoelectric device. Fluid streams flowing through shrouded heat sinks with square pin fins are considered for the thermal pathways to and from the device. Heat transfer and pressure drop are characterized in a manner conducive to an analytical model using previously published experimental results. Experimental data is presented which validates and demonstrates the usefulness of the model in predicting power output for commercially available thermoelectric generators. A specific design for a thermoelectric power harvester is suggested consisting of a pattern of thermoelectric generators. An economic model for calculating payback time is developed. An optimization process is demonstrated that allows for the payback time of such a system to be minimized through optimization of the physical design of the system. It is shown that optimization of the thermal pathways dramatically reduces payback time. Optimized design of a system is discussed in light of theoretical cases with feasible payback times.
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McKnight, Patrick T. "Finite Element Analysis of Thermoelectric Systems with Applications in Self Assembly and Haptics." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3630.
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Micro-scale self assembly is an attractive method for manufacturing sub-millimeter sized thermoelectric device parts. Challenges controlling assembly yield rates, however, have caused research to find novel ways to implement the process while still resulting in a working device. While a typical system uses single n-type and p-type material elements in series, one method used to increase the probability of a working device involves adding redundant parallel elements in clusters. The drawback to this technique is that thermal performance is affected in clusters which have missing elements. While one-dimensional modeling sufficiently describes overall performance in terms of average junction temperatures and net heat flux, it fails when a detailed thermal profile is needed for a non-homogeneous system. For this reason, a three-dimensional model was created to describe thermal performance using Ansys v12.1. From the results, local and net performance can be described to help in designing an acceptable self-assembled device.
In addition, a haptic thermal display was designed using thermoelectric elements with the intention of testing the thermal grill illusion. The display consists of 5 electrically independent rows of thermoelectric elements which are controlled using pulse width modulating direct current motor controllers.
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Wu, Yimin. "Céramiques semiconductrices à base de séléniures pour des applications photovoltaïque et thermoélectrique." Thesis, Rennes 1, 2016. http://www.theses.fr/2016REN1S137/document.
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Ce travail porte sur les composés semi-conducteurs à base de séléniures pour la conversion d'énergie par effet photovoltaïque ou thermoélectrique. Une nouvelle famille de céramiques Cu₂GeSe₃-Sb₂Se₃ avec une microstructure unique a été synthétise par un procédé de fusion-trempe. L'influence de la composition du matériau et de l'ajout de l’iode sur la microstructure et les propriétés photoélectriques a été étudiée. Le réseau d’hétérojonctions formé par deux semi-conducteurs à bande interdite relativement étroite a un effet évident sur les propriétés photoélectriques. Le système Cu₃SbSe₄-Sb₂Se₃ a également été étudié avec l'objectif d'éliminer le germanium qui est un élément relativement rare. Et les résultats indiquent que le Cu3SbSe4 peut remplacer le Cu2GeSe3 pour former des hétérojonctions avec Sb₂Se₃, en maintenant une séparation et un transport de charges efficaces. Une approche basée sur une injection à chaud a été utilisée pour la synthèse de matériaux semi-conducteurs à base de séléniures pour des applications photovoltaïque ou thermoélectrique. Des nanoparticules et nano-feuillets monocristallins bidimensionnels de CuSe de haute qualité et ont été obtenus. La structure des nanocristaux de Cu₃Sb₁₋ₓSnxSe₄ a été étudiée et le mécanisme de formation des nano-feuillets a été proposé. Des nanoparticules de Cu₃Sb₁₋ₓSnxSe₄ avec une distribution de taille étroite ont été également synthétisées avec le procédé d’injection à chaud. Ces nanoparticules ont été utilisées comme précurseurs pour la préparation de matériaux massifs par pressage à chaud. Leur performance thermoélectrique a été étudiéeThis work was focused on selenide semiconducting compounds for energy conversion by photovoltaic or thermoelectric effect. A totally new family of Cu₂GeSe₃-Sb₂Se₃ ceramics with a unique microstructure was fabricated directly by melt-quenching method. The influence of the material composition and the iodine addition on the microstructure and photoelectrical properties was investigated. The interpenetrating heterojunction network formed by two relatively narrow bandgap semiconductors has an obvious enhancement effect on the photoelectrical properties. The Cu₃SbSe₄-Sb₂Se₃ system has also been studied with the objective to eliminate the germanium which is a relatively rare element. And the results indicated that Cu₃SbSe₄ can substitute the Cu₂GeSe₃ to form heterojunctions with Sb₂Se₃, maintaining the efficient charge separation and transport. A hot-injection based-approach has been used for the synthesis of selenide semiconducting materials for photovoltaic or thermoelectric applications. CuSe nanoparticles and CuSe nanoplates with high quality single-crystals and two dimensional nanostructure were prepared. The structure of the nanocrystals has been studied and the mechanism of the nanoplates formation has been proposed. Cu₃Sb₁₋ₓSnxSe₄ nanoparticles with a narrow size distribution had also been synthesized through the hot-injection route. They have been used as precursors for the preparation of bulk materials by hot-pressing and their thermoelectric performances have been studied
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Wodlin, Jakob. "Konceptstudie för omvandling av termisk energi till elektrisk samt mekanisk energi i en autonom undervattensfarkost." Thesis, Linköpings universitet, Fluida och mekatroniska system, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-129220.
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Rapporten avhandlar en konceptstudie för omvandling av termisk energi till elektrisk samt mekanisk energi, i den autonoma undervattensfarkosten SAPPHIRES. Inledningsvis utreds vilka förväntningar och krav som finns på konceptet för energiomvandling samt om där finns någon publicerad litteratur som redan gjort ansträngningar för att lösa det aktuella problemet. Allmän teori kring värmemotorer och en bred, systematisk litteratursökning inkluderas även i det arbetet. Energiomvandlingen antas kunna ske enligt två fall kallade ”hög-prestanda” och ”låg/medel-prestanda”, vilka innebär att mekanisk samt elektrisk effekt, respektive endast elektrisk effekt ska kunna levereras av konceptet. De mekaniska samt elektriska effekterna ska, vidare, kunna levereras om maximalt 600, respektive 6 kW, och konceptet ska åtminstone kunna uppfylla ett av energiomvandlingsfallen. Den faktiska konceptstudien utgörs av två iterationer av konceptgenereringar, -utvärderingar och -val och de visar att ett koncept kallat ”Öppet system inspirerat av nukleär värmeframdrivning” förefaller vara det bästa sättet att omvandla termisk energi i SAPPHIRES. Därtill indikerar en mer detaljerad analys, bestående av bland annat matematisk modellering och konceptuell konstruktion, att konceptet möjligen skulle kunna uppfylla så kallad ”hög-prestanda” och sedermera leverera både mekanisk och elektrisk effekt om 600, respektive 6 kW. Mer specifikt visar en matematisk analys, med hjälp av vissa antaganden rörande konceptets funktion, att ett ”Öppet system inspirerat av nukleär värmeframdrivning” skulle kunna leverera en mekanisk effekt om 1025 kW samt en elektrisk effekt om 141 kW. En grov, konceptuell konstruktion bekräftar också att konceptets vitala, ingående komponenter faktiskt kan rymmas inom de specificerade dimensionskraven (en cylinderformad volym med en längd och diameter om 1,7, respektive 0,5 m.). Det står dock klart att de möjliga koncepten för energiomvandling kraftigt begränsas av deras möjligheter att leverera tillräcklig mekanisk effekt, för att uppnå ”hög-prestanda”. Om endast ”låg/medel-prestanda” ska uppfyllas tillåts fler av de möjliga koncepten och i ett sådant fall skulle faktorer som underhåll, miljöpåverkan och SAPPHIRES signatur kunna prioriteras i högre utsträckning.The report discusses a concept study regarding the conversion of thermal energy into electrical and mechanical energy, in the autonomous underwater vehicle SAPPHIRES. First, the requirements and expectations regarding the concept of energy conversion are investigated and efforts are made to identify any published literature, which has already made attempts of solving the issue. General theory regarding heat engines and an extensive literature study are also included in this work. The energy conversion is assumed to perform according to two cases called "high-performance" and "low/medium-performance", meaning mechanical and electrical energy or electrical power should be delivered by the concept, respectively. More specifically, the mechanical and electrical powers should be delivered of a maximum of 600 and 6 kW, respectively and the concept should at least fulfill one of the performance settings. The actual concept study comprises of two iterations of concept generations, evaluations and selections and shows that a concept called "Open system inspired by nuclear thermal propulsion" seems to be the best way of converting thermal energy on-board SAPPHIRES. Moreover, a more detailed analysis, comprising of, inter alia, mathematical modelling and conceptual design, indicates that the concept possibly can meet the so-called "high-performance" and thus, deliver both mechanical and electrical powers of 600 and 6 kW, respectively. More specifically, a mathematical analysis, based on some assumptions regarding the concept's functionality, shows that an "Open system inspired by nuclear thermal propulsion" could deliver a mechanical power of 1025 kW and an electrical power of 141 kW. Rough conceptual design also shows that the vital parts of the concept could fit within the specified maximal dimensions (a cylinder-shaped volume with a length and diameter of 1.7 and 0.5 m, respectively). However, it is clear the possible concepts of energy conversion are severely limited by their capacities of delivering enough mechanical energy, to meet the "high-performance" demands. Assuming only the "low/medium-performance" has to be met, more possible concepts becomes available and in that case, factors such as maintenance, environmental impact and signature of SAPPHIRES could be considered to a greater extent.
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Apertet, Yann. "Réflexions sur l’optimisation thermodynamique des générateurs thermoélectriques." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112322/document.
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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 FeynmanThermoelectric 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
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Verchère, Alexandre. "Génération d’architectures nanométriques intra- et inter-granulaires dans des oxydes pour la conversion thermoélectrique de l’énergie." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1196.
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Dans ce manuscrit, un travail multidisciplinaire, de la synthèse de précurseurs métalliques à la caractérisation des matériaux est présenté. La première porte sur l’élaboration de poudres d’oxyde TiO2 dopé Nb5+ et d’oxydes mixtes SnO2-TiO2 dopé Nb5+ par une approche Sol-Gel. Leur mise en forme sous forme de pastille par une méthode moderne de frittage flash (SPS) a permis d’étudier leurs propriétés physiques vibrationnelles et thermoélectriques. La deuxième partie de cette étude présente l’élaboration de nouveaux précurseurs d’étain et de tantale adaptés au procédé de dépôt de couches minces par DLI-MOCVD. Afin de répondre aux exigences de ce procédé, des dérivés moléculaires à base de ligand beta-aminoalcool fluoré ou pas ont été élaborées. Les complexes métalliques ont ensuite été entièrement caractérisés à l’état solide et en solution. Le bon comportement thermique (stabilité et volatilité) de certains de ces composés ont conduit à l’élaboration et à la caractérisation de couches minces de SnO2 et SnO2:FIn this manuscript, a multidisciplinary work, from the synthesis of metal precursors to the characterization of materials, is presented. The first concerns the development of Nb5+ doped TiO2 oxide powders and Nb5+ doped SnO2-TiO2 mixed oxides by a Sol-Gel approach. Their shaping into a pellet form by a modern flash sintering method (SPS) made it possible to study their physical, vibrational and thermoelectric properties. The second part of this study presents the development of new tin and tantalum precursors adapted to the DLI-MOCVD thin film deposition process. In order to meet the requirements of this process, molecular derivatives based on fluorinated or non-fluorinated beta-aminoalcohol ligand have been developed. The metal complexes were then fully characterized in solid state and in solution. The good thermal behaviour (stability and volatility) of some of these compounds has led to the development and characterization of thin layers of SnO2 and SnO2:F
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Siouane, Saïma. "Système thermoélectrique pour la récupération d'énergie : modélisation électrique et continuité de service de la circuiterie électronique." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0201/document.
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La récupération d'énergie thermique basée sur les générateurs thermoélectriques (TEG) est utilisée dans de nombreuses applications telles que les dispositifs médicaux auto-alimentés. La sûreté de fonctionnement et la continuité de service de ces systèmes sont aujourd'hui des préoccupations majeures. Ainsi, toute défaillance au niveau d'un des interrupteurs commandables de la circuiterie électronique d'interface peut provoquer de graves dysfonctionnements du système. Tout défaut non détecté et non compensé peut mettre en danger l'ensemble du système et interrompt l'alimentation en énergie de la charge. Par conséquent, la mise en œuvre d'une compensation de défaut efficace et rapide est impérative afin d'assurer la continuité de service. Dans ces travaux de recherche, nous étudions la continuité de service d'une interface électronique pour TEG basée sur une conversion à deux étages Buck/Buck-Boost cascadés. Une modélisation électrique générique (modèle de Thévenin) du TEG sous différentes conditions de fonctionnement et prenant en compte l'ensemble des résistances thermiques de contact est tout d'abord présentée. Ensuite, une méthode de compensation de défaut de type circuit-ouvert au niveau de l'interrupteur commandable de l'un des deux convertisseurs DC-DC est également proposée. Nous présentons une topologie originale de convertisseur DC-DC à tolérance de pannes, sans redondance matérielle classique. Cette topologie permet d'assurer la continuité de service du système de récupération d'énergie en mode nominal. Les études théoriques ont été validées par simulation et par des tests expérimentauxThermal energy harevsting based on thermoelectric generators is used in many applications such as self-powered medical devices. The reliability and continuity of service of these systems are now major concerns. Furthermore, any failure in the controllable switch of the electronic interface circuitry can cause serious system malfunctions. Any undetected and uncompensated fault can endanger the entire system and interrupt the power supply to the load. Therefore, the implementation of an efficient and rapid fault compensation is imperative in order to ensure the continuity of service. In this research, we study the continuity of service of an electronic interface for TEG, based on a two-stage conversion cascaded Buck/Buck-Boost. A generic electrical modeling of the TEG model under different operating conditions and with taking into account all the thermal contact resistances is first presented. Next, an open-circuit fault compensation method of the controllable switch of one of the two DC-DC converters is also proposed. We present an original fault-tolerant DC-DC converter topology with no conventional hardware redundancy. This topology ensures the continuity of service of the energy recovery system in nominal mode. Theoretical studies were validated by simulation and experimental tests
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Nunna, Raghavendra. "Novel chalcogenides for thermoelectric conversion." Caen, 2013. http://www.theses.fr/2013CAEN2078.
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Ce travail de thèse porte sur la synthèse et la caractérisation de nouveaux chalcogénures à propriétés thermoélectriques. Deux familles de matériaux ont été étudiées : les composés à structure pseudo-Hollandite et les composés en couches de type CdI2. Dans ces premiers, les études se sont principalement portées sur les structures à base de thallium de formulation TlxCr5Se8 and TlCr5Se8-xTex. L’influence de la non stoichiometrie en Tl ainsi que de la solution solide Sélénium-Tellure sur les propriétés électriques et thermiques a principalement été abordée. Pour les composés de structure de base CdI2, une étude systématique de substitution et intercalation chimique a été menée. Les meilleurs résultats sont rapportés dans le composé Cu0. 05TiS1. 5Se0. 5 avec une valeur de ZT de 0. 54 à 700K. D’une manière générale, ce travail de thèse démontre l’importance de la formulation chimique sur les propriétés électriques (Taux de porteurs) mais aussi sur la contribution phonique à la conductivité thermique (désordre structural). Ces résultats encourageant ont ouverts une voie dans la recherche de nouveaux matériaux thermoélectriques, notamment à base de chalcogénes, pour des utilisations futures dans des applications thermoélectriques. Ce travail démontre également que la recherche fondamentale de nouveaux composés et de nouvelles structures peut toujours permettre la découverte de matériaux aux propriétés intéressantesThe focus of this thesis work is the exploratory preparation of novel chalcogenides as potential thermoelectric materials and the analyses of their physical properties. A thermoelectric material is capable of converting heat to electricity or vice versa. Usually, narrow band gap semiconductors are good candidates for thermoelectric applications, because such materials have large Seebeck coefficient, reasonably high electrical conductivity and low thermal conductivity. In this work, two different systems were studied, intermetallic pseudo hollandite structures and layered CdI2 type structures. In the large family of pseudo hollandite systems, we mainly focused on thallium systems in which the solid solution TlxCr5Se8 and TlCr5Se8-xTex have been synthesized. In CdI2 structures, we focused our investigation on transition metal selenides for their rather semiconducting properties. Therefore we embarked on the systematic study of AgCrSe2, TiS2 and TiSe2. In addition, the effect on physical properties using different intercalated elements (Ag and Cu) in TiSe2 chalcogenides were studied. All these samples are prepared by the solid state reaction. The purity of the samples was confirmed by powder X-ray diffraction data, physical and thermal properties were measured on Spark Plasma Sintered (SPS) samples. Low thermal conductivity as well as competitive power factors was observed in these chalcogenides. The highest zT of 0. 54 is achieved in titanium dichalcogenides for the composition of Cu0. 05TiS1. 5Se0. 5 at 700K. Our results show that these structures are potential for future thermoelectric materials research
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Bosisio, Riccardo. "Thermoelectric conversion in disordered nanowires." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066212/document.
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Cette thèse porte sur la conversion thermoélectrique de nanofils semi-conducteurs désordonnés en configuration de transistor à effet de champ.On considère d’abord le régime de transport élastique à basse température. En utilisant un modèle d'Anderson 1D, on dérive des expressions analytiques pour le coefficient Seebeck typique d’un nanofil en fonction de la tension de grille, et on montre que celui-ci augmente fortement en bord de bande. Ces résultats sont confirmés par un calcul numérique du Seebeck, basé sur un algorithme de fonctions de Green récursif.On considère ensuite le régime inélastique où les électrons, assistés par les phonons, sautent entre états localisés. En résolvant numériquement le réseau de résistances aléatoires de Miller-Abrahams, on montre que le coefficient Seebeck peut atteindre des valeurs très élevées au voisinage des bords de bande du nanofil. La théorie de percolation de Zvyagin étendue au cas unidimensionnel nous permet de décrire qualitativement nos résultats. Par ailleurs, les échanges de chaleur entre électrons et phonons en bord de bande entraînent la formation de points chauds et froids à la surface du substrat, qui pourraient être utilisés pour le refroidissement de circuits électroniques. Cet effet est étudié pour un ensemble de fils en parallèle. Le facteur de puissance et la figure de mérite de ces systèmes sont aussi estimés.Enfin, on étudie un système général à trois terminaux en réponse linéaire. On calcule les coefficients de transport locaux et non-locaux, et les figures de mérite généralisées, puis l'on discute à l'aide de deux exemples la possibilité d’améliorer la performance d’une machine thermique quantique génériqueThis thesis is focused on thermoelectric conversion in disordered semiconductor nanowires in the field effect transistor configuration. We first consider a low temperature regime, when electronic transport is elastic. For a 1D Anderson model, we derive analytical expressions describing the typical thermopower of a single nanowire as a function of the applied gate voltage, and we show that it is largely enhanced at the nanowire band edges. Our results are confirmed by numerical simulations based on a Recursive Green Function calculation of the thermopower. We then consider the case of inelastic transport, achieved by phonon-assisted hopping among localized states (Variable Range Hopping). By solving numerically the Miller Abrahams random resistor network, we show that the thermopower can attain huge values when the nanowire band edges are probed. A percolation theory by Zvyagin extended to nanowires allows to qualitatively describe our results. Also, the mechanism of heat exchange between electrons and phonons at the band edges lead to the generation of hot and cold spots near the boundaries of a substrate. This effect, of interest for cooling issues in microelectronics, is showed for a set of parallel nanowires, a scalable and hence promising system for practical applications. The power factor and figure of merit of the device are also estimated.Finally, we characterize a general three-terminal system within the linear response (Onsager) formalism: we derive local and non-local transport coefficients, as well as generalized figures of merit. The possibility of improving the performance of a generic quantum machine is discussed with the help of two simple examples
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Tsangarides, Constantinos. "Thermoelectric energy harvesting in displays." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/268222.
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The development of a complete thermoelectric generator and its application on a display polarizer film was successfully accomplished in this thesis. A systematic study of the prospective thermoelectric materials, PEDOT:PSS-based and ${ZnON}$, used for the present application is presented. To the best of our knowledge, this is the first exploration of the thermoelectric parameters of ${ZnON}$ reported here. Thin-film deposition of these materials was performed via both solution- and vacuum-based techniques. In addition, certain doping mechanisms were tested in an attempt to further understand the correlation between electrical conductivity and Seebeck coefficient. A maximum power factor of $42{\mu}Wm^{-1}K^{-2}$ was achieved for the PEDOT:PSS-based thin film at room temperature. It was initially doped via 5vol% of DMSO and sequentially treated with ethylene glycol. Specifically, its electrical conductivity displayed a 2-fold increase after EG treatment, reaching a value of about 1632 Scm$^{-1}$. Systematic studies performed on the association between thin-film thickness and its Seebeck coefficient shows a decrease in the latter as the number of multilayers printed increases. Among the different $O_{2}/N_{2}$ ratios that were tested for ${ZnON}$ thin films, a maximum power factor value of 163${\mu}Wm^{-1}K{-2}$ was achieved with the lowest $O_{2}$ flow rate configuration. In contrast to PEDOT:PSS-based thin films, the ${ZnON}$ displayed the opposite effect on the relation of the Seebeck coefficient with respect to thin-film thickness. Furthermore, a heterostructure was also developed by implementing ${ZnO}$ nanowires into the ${ZnON}$ thin film. ${ZnO}$ nanowires have been fabricated through the hydrothermal method on inkjet-printed patterns of zinc acetate dihydrate. It has been demonstrated that with the right inkjet-printing parameters and substrate temperature, ${ZnO}$ nanowires can be effortlessly fabricated in accordance with the desired pattern variations under low temperature and mild conditions. Finally, a complete device of the thermoelectric generator was fabricated using the above materials and a special set-up developed in order to test the device on the polarizer. The power output achieved from a 1-thermoelectric couple under normal backlight illumination and ambient conditions was 23pW. Overall, it is thought that the particular design and proof of concept presented here can be the basis of a prospective energy harvesting scheme via thermoelectrics in future display-based handheld devices.
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James, Ashley. "Oxide thermoelectric energy harvesting materials." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9277.
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Conventional thermoelectric materials found in many thermoelectric devices have unfavourable properties; they often suffer instability at high temperatures and contain toxic metals which pose a hazard to the environment. Oxide thermoelectric materials are stable, less toxic and could eventually replace conventional materials. The thermoelectric performance of oxide materials currently do not match conventional materials however, there is potential for improvement through doping and altering the microstructure and chemistry through modification of the processing conditions. This project aims to examine the doping and processing conditions and the effect this has upon the thermoelectric behaviour of oxide based thermoelectric materials. Zinc oxide (ZnO) has been investigated as an oxide thermoelectric material and doping of ZnO with aluminium (Al) and antimony (Sb) by mixed oxide synthesis was investigated. Al2O3 and Sb2O3 were used as aluminium (Al) and antimony (Sb) dopant sources for ZnO, which were reacted with ZnO at temperatures of 1000°C-1300°C. Al was found to incorporate effectively into the ZnO system and was shown to produce n-type behaviour. The Sb doped ZnO material was also found to display n-type behaviour which is intriguing as Sb is considered a p-type dopant in the ZnO system; at low levels <1.0at.%, Sb incorporates onto the Zn site rather than the O site as expected, which leads to n-type behaviour. The addition of Sb dopant leads to the formation of secondary phase of Zn7Sb2O12, which appears to increase the Seebeck coefficient by an energy filtering effect with higher levels of dopant leading to higher levels of secondary phase. Grain size and porosity also play a significant role in both the Al and Sb doped systems with small grains and higher levels of porosity leading to higher values of Seebeck coefficient up to -100µV.K-1 for Al (0.5at.%) and - 115µV.K-1 for Sb (0.8at.%). The ZT figure of merits were found to be highest for materials sintered at 1300°C with values of 6×10-5 and 2×10-10 for Al and Sb doped ZnO respectively, these values are low compared to literature values, which are in the region of 0.01. This is due to high electrical resistivities of the synthesised samples, which is linked to porosity. A better understanding of the effects that microstructure plays on thermoelectric behaviour has been developed and procedures to isolate the contributions from grain size, and degree of dopant incorporation to the thermoelectric properties have been conducted.
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Kraemer, Daniel Ph D. Massachusetts Institute of Technology. "Solar thermoelectric power conversion : materials characterization to device demonstration." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103490.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 268-289).
Meeting the ever growing global energy demand with mostly fossil fuel based energy technologies is not sustainable, pollutes the environment and is the main cause of climate change threatening our planet as we know it. Solar energy technologies are a promising, sustainable and clean alternative due to the vast abundance of sunlight. Thus far, photovoltaic solar cells and concentrated solar power are considered to be the most promising approaches. Solar cells directly convert sunlight into electricity by photon induced electron-hole pair generation. Concentrated solar power captures the sunlight in form of heat which is then converted to electricity by means of a traditional mechanical power block. In this thesis, we explore solar thermoelectric generators (STEGs) as an alternative way to convert sunlight to electricity. Similar to concentrated solar power STEGs capture the sunlight in form of heat. However, the captured heat is directly converted to electricity by means of a thermoelectric generator. This solid-state direct heat-to-electricity conversion significantly simplifies the system, reduces cost and maintenance and enables transient operation and system scalability without affecting the performance. Therefore, STEGs have the potential to be deployed as small scale solar power converters in remote areas and on rooftops and as large scale concentrated solar power plants. While the concept of solar thermoelectric power conversion has been proposed over a century ago, most successful experimental efforts reported in, the literature have been limited to below 1 % for STEGs without optical concentration and to approximately 3 - 5 % with optical concentration. Theoretical STEG performances as modeled and discussed in this thesis predict significantly higher efficiencies. A detailed STEG model is introduced to theoretically investigate various parasitic losses and how to minimize their effect to obtain highest and most realistic performance predictions. Additionally, a methodology to optimize a photovoltaic-thermoelectric hybrid system based on spectral splitting is introduced. The optimization and performance prediction of a STEG is only accurate if the relevant material properties are known with high accuracy. However, typical spectroscopy techniques to determine the optical properties, namely the solar absorptance and infrared emittance, of a solar absorber have shortcomings which can lead to significant errors. Similarly, typical commercial equipment to measure the properties of thermoelectric materials including the Seebeck coefficient, the electrical resistivity and the thermal conductivity are prone to large errors. Therefore, we introduce in this thesis novel experimental techniques to measure all relevant properties with improved accuracies in particular the techniques to measure the total hemispherical emittance of a surface and a material's thermal conductivity. A record-low total hemispherical emittance of 0.13 at 500 °C is demonstrated for an Yttria-stabilized-Zirconia-based cermet solar absorber with solar absorptance of 0.91 and thermal stability up to 600 °C. Furthermore, a method was developed to directly measure the efficiency of a thermoelectric leg. Using this method a record-high thermoelectric efficiency of 8.5 % is demonstrated at a relatively small temperature difference of 225 °C for a novel MgAgSb-based compound with hot-pressed silver contact pads. By increasing the temperature difference to a material's compatible 275 °C a thermoelectric efficiency of 10 % is achievable which, thus far, has only been achieve at almost twice the temperature difference. The third main contribution of this thesis is the experimental demonstration of solar thermoelectric power conversion. A record-high STEG efficiency of 4.6 % is demonstrated at AM1.5G (1 kW/m 2) conditions which is 7 times higher than previously reported best values. The performance improvement is achieved by using a STEG with nano-structured bulk thermoelectric materials, a spectrally-selective solar absorber and taking advantage of large thermal concentrations under a vacuum. Despite the vacuum environment and the use of a low-temperature spectrally-selective solar absorber the optimal hot-junction operating temperature is limited to approximately 200 °C due to increasing thermal radiation heat loss. In order to substantially increase the operating temperature difference and STEG efficiency, larger incident solar power densities are required. Furthermore, the STEG requires segmented thermoelectric legs and a high-temperature stable solar absorber. The optimized STEGs are fabricated and tested at moderate and high optical solar concentration. Efficiencies of close to 8 % at 38 suns and close to 10 % at 211 suns, measured based on the solar flux at the absorber, are demonstrated for a STEG with a spectrally-selective solar absorber. The maximum demonstrated solar-to-electricity CSTEG efficiency is 7.5 %. Furthermore, the performance of a STEG at moderate optical concentration with a high-temperature stable black paint solar absorber and a directionally-selective solar receiver cavity is demonstrated to be comparable to a STEG with a spectrally-selective surface at similar insolation.
by Daniel Kraemer.
Ph. D.
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Cao, Zhuo. "Printable thermoelectric devices for energy harvesting." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/381196/.
Full textAbstract:
This thesis describes the approaches of fabricating and testing thermoelectric generators (TEG) using screen printing. It includes the formation of the pastes, optimizing of the manufacture processes and the measurement of the thermoelectric properties. A nickel/copper based high temperature TEG was made to demonstrating the screen printing can be applied to fabricate thermoelectric materials. A bismuth/antimony based low temperature TEG was fabricated to identify the proper polymer binder for low temperature TEG application. A flexible bismuth tellurium/antimony tellurium low temperature TEG with 4 thermocouples was presented with a generated voltage of 23 mV and an output power of 194 nW when ΔT=20°C. Moreover, a dispenser printed structured TEG was also demonstrated for its ability to achieve 3D structured thermocouples with a thickness of 500 μm. The objective of this work involves developing screen printable thermoelectric material pastes and suitable processes; a proper approach to transfer the printed TEGs from rigid substrate onto flexible substrate (Kapton). The flexibility allows the printed TEGs to be applied on heat sources with curved surface, such as, human body. An additional research on the interface material of textile is also presented.
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Wu, Yongjia. "Thermoelectric Energy Harvesting for Sensor Powering." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/90891.
Full textAbstract:
The dissertation solved some critical issues in thermoelectric energy harvesting and tried to broaden the thermoelectric application for energy recovery and sensor powering. The scientific innovations of this dissertation were based on the new advance on thermoelectric material, device optimization, fabrication methods, and system integration to increase energy conversion efficiency and reliability of the thermoelectric energy harvester.
The dissertation reviewed the most promising materials that owned a high figure of merit (ZT) value or had the potential to increase ZT through compositional manipulation or nano-structuring. Some of the state-of-art methods to enhance the ZT value as well as the principles underneath were also reviewed. The nanostructured bulk thermoelectric materials were identified as the most promising candidate for future thermoelectric applications as they provided enormous opportunities for material manipulation.
The optimizations of the thermoelectric generator (TEG) depended on the accuracy of the mathematical model. In this dissertation, a general and comprehensive thermodynamic model for a commercial thermoelectric generator was established. Some of the unnecessary assumptions in the conventional models were removed to improve the accuracy of the model. This model can quantize the effects of the Thomson effect, contact thermal and electrical resistance, and heat leakage, on the performance of a thermoelectric generator. The heat sink can be another issue for the design of high-performance TEG. An innovative heat sink design integrated with self-oscillating impinging jet generated by the fluidic oscillator arrays were adopted to enhance the heat convection. The performance of the heat sink was characterized by large eddy simulation.
The compatibility mismatch had been a practical problem that hindered the further improvement of energy conversion efficiency of thermoelectrics. In this dissertation, a novel method to optimize the geometry of the thermo-elements was developed. By varying the thickness and cross-sectional area of each thermoelectric segment along the length of the thermo-element, the compatibility mismatch problem in the segmented TEG construction was eliminated. The optimized segmented TEG can make the best of the existing thermoelectric materials and achieve the maximum energy conversion efficiency in a wide temperature range. A segmented TEG with an unprecedented efficiency of 23.72% was established using this method. The complex geometry structure of the established thermo-elements would introduce extra difficulty in fabrication. Thus selective laser melting, a high-temperature additive manufacture method, was proposed for the fabrication. A model was built based on the continuous equations to guide the selective-laser-melting manufacturing of thermoelectric material with other nanoparticles mixed for high thermoelectric performance.
Thermoelectric energy harvesting played a critical role in the self-powered wireless sensors, as it was compact and quiet. In this dissertation, various thermoelectric energy harvesters were established for self-powered sensors to in-situ monitor the working condition in the gas turbine and the interior conditions in nuclear canisters. The sensors, taking advantage of the thermal energy existing in the local environment, can work continuously and provide tremendous data for system monitor and diagnosis without external energy supply.Doctor of Philosophy
The dissertation addressed some critical issues in thermoelectric energy harvesting and broadened its application for energy recovery and sensor powering. Some of the most advanced technologies were developed to improve the energy conversion efficiency and reliability of the thermoelectric energy harvesters. In this dissertation, a general and comprehensive thermodynamic model for a commercial thermoelectric generator (TEG) was established. The model can be used to optimize the design of the existing commercial TEG modules. High performance heat sink design was critical to maximize the temperature drop in the TEG module, thus increase the power output and energy conversion efficiency of the TEG. An innovative heat sink design integrated with self-oscillating impinging jet generated by the fluidic oscillator arrays were designed to cool the cold end of the TEG, thus enhance the performance of the TEG. The performance of the heat sink was characterized by large eddy simulation. A single thermoelectric material only had high thermoelectric performance in a narrow temperature range. A segmented TEG could achieve a high energy conversion efficiency over a wide temperature range by adopting different materials which had high thermoelectric performance at low, moderate, and hight temperature ranges. However, the material compatibility mismatch had been a practical problem that hindered the further improvement of energy conversion efficiency of the segmented TEG. In this dissertation, a novel method was developed to eliminate the compatibility mismatch problem via optimizing the geometry of the thermo-elements. A segmented TEG with an unprecedented efficiency of 23.72% was constructed using the method proposed in this dissertation. The complex geometry structure of the established thermo-elements would introduce extra difficulty in fabrication. Thus selective laser melting, a high-temperature additive manufacture method, was proposed for the fabrication. A physical model based on the v conservation equations was built to guide the selective-laser-melting manufacturing of the optimized segmented TEG mentioned above. In this dissertation, two thermoelectric energy harvesters were built for self-powered sensors to in-situ monitor the interior conditions in nuclear canisters. The sensors, taking advantage of the thermal energy existing in the local environment, can work continuously and provide tremendous data for system monitor and diagnosis without external energy supply. Also, a compact thermoelectric energy harvester was developed to power the gas sensor for combustion monitoring and control.
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Lundin, Staffan. "Marine Current Energy Conversion." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-280763.
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Marine currents, i.e. water currents in oceans and rivers, constitute a large renewable energy resource. This thesis presents research done on the subject of marine current energy conversion in a broad sense. A review of the tidal energy resource in Norway is presented, with the conclusion that tidal currents ought to be an interesting option for Norway in terms of renewable energy. The design of marine current energy conversion devices is studied. It is argued that turbine and generator cannot be seen as separate entities but must be designed and optimised as a unit for a given conversion site. The influence of support structure for the turbine blades on the efficiency of the turbine is studied, leading to the conclusion that it may be better to optimise a turbine for a lower flow speed than the maximum speed at the site. The construction and development of a marine current energy experimental station in the River Dalälven at Söderfors is reported. Measurements of the turbine's power coefficient indicate that it is possible to build efficient turbines for low flow speeds. Experiments at the site are used for investigations into different load control methods and for validation of a numerical model of the energy conversion system and the model's ability to predict system behaviour in response to step changes in operational tip speed ratio. A method for wake measurements is evaluated and found to be useful within certain limits. Simple models for turbine runaway behaviour are derived, of which one is shown by comparison with experimental results to predict the behaviour well.
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Li, Molan. "Thermoelectric-Generator-Based DC-DC Conversion Network for Automotive Applications." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-42358.
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As waste heat recovering techniques, especially thermoelectric generator (TEG technologies, develop during recent years，its utilization in automotive industry is attempted from many aspects. Previous research shows that TEG as a waste heat harvesting method is feasible. Even though efficiencies for TEGs are as low as 3-5% with existing technology, useful electricity generation is possible due to the great amount of waste heat emitted from the internal combustion engine operation. This thesis proposes the innovative concept of thermoelectric-generator-based DC-DC conversion network. The proposed structure is a distributed multi-section multi-stage network. The target is to tackle problems facing the traditional single-stage system and to advance TEG application in automotive settings. The objectives of the project consists of providing optimal solution for the DC-DC converter utilized in the network, as well as developing a systematic and bottom-up design approach for the proposed network. The main problems of the DC-DC converters utilized in the TEG system are presented and analyzed, with solution to dynamic impedance matching suggested. First, theoretically-possible approaches to balance the large TEG internal resistance and small converter input resistance are discussed, and their limitations are presented. Then, a maximum power point tracking (MPPT) regulation model is developed to address the temperature-sensitive issue of converters. The model is integrated into a TEG-converter system and simulated under Simulink/Simscape environment, verifying the merits of MPPT regulation mechanism. With the developed model, MPPT matching efficiency over 99% is achieved within the hot side temperature range of 200°C ~300°C. A design flow is suggested for the proposed network. Analysis is conducted regarding aspects of the design flow. Several state-of-the-art thermoelectric materials are analyzed for the purpose of power generation at each waste heat harvesting location on a vehicle. Optimal materials and TE couple configurations are suggested. Besides, a comparison of prevailing DC-DC conversion techniques was made with respect to applications at each conversion level within the network. Furthermore, higher level design considerations are discussed according to system specifications. Finally, a case study is performed comparing the performances of the proposed network and traditional single-stage system. The results show that the proposed network enhances the system conversion efficiency by up to 400% in the context of the studied case.
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Thiel, Philipp [Verfasser]. "Calcium Manganese(IV) Oxides for Thermoelectric Power Conversion / Philipp Thiel." München : Verlag Dr. Hut, 2015. http://d-nb.info/1080754431/34.
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Thorburn, Karin. "Electric Energy Conversion Systems : Wave Energy and Hydropower." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7081.
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Balouchi, Farouk. "Footfall energy harvesting : footfall energy harvesting conversion mechanisms." Thesis, University of Hull, 2013. http://hydra.hull.ac.uk/resources/hull:8433.
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Ubiquitous computing and pervasive networks are prevailing to impact almost every part of our daily lives. Convergence of technologies has allowed electronic devices to become untethered. Cutting of the power-cord and communications link has provided many benefits, mobility and convenience being the most advantageous, however, an important but lagging technology in this vision is the power source. The trend in power density of batteries has not tracked the advancements in electronic systems development. This has provided opportunity for a bridging technology which uses a more integrated approach with the power source to emerge, where a device has an onboard self sustaining energy supply. This approach promises to close the gap between the increased miniaturisation of electronics systems and the physically constrained battery technology by tapping into the ambient energy available in the surrounding location of an application. Energy harvesting allows some of the costly maintenance and environmentally damaging issues of battery powered systems to be reduced. This work considers the characteristics and energy requirements of wireless sensor and actuator networks. It outlines a range of sources from which the energy can be extracted and then considers the conversion methods which could be employed in such schemes. This research looks at the methods and techniques for harvesting/scavenging energy from ambient sources, in particular from the motion of human traffic on raised flooring and stairwells for the purpose of powering wireless sensor and actuator networks. Mechanisms for the conversion of mechanical energy to electrical energy are evaluated for their benefits in footfall harvesting, from which, two conversion mechanisms are chosen for prototyping. The thesis presents two stair-mounted generator designs. Conversion that extends the intermittent pulses of energy in footfall is shown to be the beneficial. A flyback generator is designed which converts the linear motion of footfall to rotational torque is presented. Secondly, a cantilever design which converts the linear motion to vibration is shown. Both designs are mathematically modelled and the behaviour validated with experimental results & analysis. Power, energy and efficiency characteristics for both mechanisms are compared. Cost of manufacture and reliability are also discussed.
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Lee, Dongwook Ph D. Massachusetts Institute of Technology. "Low-grade heat conversion into electricity by thermoelectric and electrochemical systems." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120186.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Developing cost effective technologies that convert low-grade heat into electricity is essential to meet the increasing demand for renewable energy systems. Thermoelectric and recently emergent electrochemical heat conversion devices are promising candidates for this purpose. However, current performance and cost of these devices limit their widespread application. In this thesis, we investigate design guidelines for heterostructured thermoelectric systems and electrochemical heat energy harvesters to address these challenges. Material cost and scarcity of elements in state-of-the-art thermoelectric materials are current limitations. Conductive polymers has become an attractive alternative to those materials, however they suffer from low Seebeck coefficient. Nanoscale composites of inorganic semiconductors with conductive polymers could improve low Seebeck coefficients and power factors of conductive polymers, however quantitative understandings on the mechanisms lying behind the enhancements were often missing. In our research, thin film heterostructures of a conductive polymer, PEDOT:PSS / undoped Si or undoped Ge were selected as templates for mechanistic investigations on thermoelectric performance enhancements. With the combination of experiments and simulation, it was determined that p-type PEDOT:PSS transferred holes to the interfaces of adjacent Si and Ge, and these holes could take advantage of higher hole mobility of Si and Ge. This phenomenon called modulation doping, was responsible for thermoelectric power factor enhancements in Si / PEDOT:PSS and Ge / PEDOT:PSS heterostructures. Another technology to transform low-grade heat into electricity is electrochemical heat conversion. Traditionally, the electrochemical heat conversion into electricity suffered from low conversion efficiency originating from low ionic conductivity of electrolytes, even though high thermopowers often reaching several mV/K has been an alluring advantage. Recently developed breakthrough on operating such devices under thermodynamic cycles bypassed low ionic conductivity issue, thereby improving the conversion efficiency by multiple orders of magnitude. In this study, we focused on improving efficiency by increasing thermopowers and suppressing heat capacity of the system, while maintaining the autonomy of thermodynamic cycles without need for recharging by external sources of electricity. These detailed interpretations on nanoscale composite thermoelectric systems and electrochemical heat harvester provide insights for the design of next-generation thermoelectric and electrochemical heat energy harnessing solutions.
by Dongwook Lee.
Ph. D.
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Laestander, Joakim, and Simon Laestander. "OTEC - Ocean Thermal Energy Conversion." Thesis, KTH, Energiteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-98974.
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OTEC is a technology where power is produced by utilizing the temperature difference in the oceans between surface water and water from the deep. It is considered that a temperature difference of 20K is required – a temperature difference found close to the equator.This report investigates if OTEC can produce enough electricity to provide 100 000 people, living on a generic island of 10 km2 somewhere alongside the equator in the pacific ocean, with their electricity needs. In this project a literature review has been made to establish a basic knowledge of OTEC and later a mathematical model has been programmed and simulated. Finally the results of the simulation has been examined and discussed.Two different cycles has been simulated alongside each other with the goal to establish which one of these two cycles that were best suited the island. To facilitate computing some assumptions and simplifications were made.The closed cycle (CC) was the most effective but the open cycle (OC) had several positive synergies that the closed cycle didn’t have. The costs of a facility of both cycles were based on older studies in the field and the conclusion was that the open cycle was the cheaper one. Facilities of both cycles can effectively meet the islands energy needs but if OC is chosen before CC more facilities has to be built due to the OC has lower energy output.Further work and development is necessary before OTEC seriously can challenge todays fossil fuel based energy systems, or until the oil starts to get too expensive. Today OTEC technology demands large investments but if the positive environmental effects and the fact that the island releases itself from import of energy are taken into account there are incentives to invest in OTEC already.OTEC är en teknik där kraft utvinns från havsvatten genom att utnyttja temperaturdifferensen mellan ytvatten och vatten från djupet. Denna teknik kräver dock generellt en temperaturdifferens på minst 20K. En sådan temperaturskillnad är geografiskt begränsad till den tropiska zonen runt ekvatorn.I rapporten undersöks om OTEC kan användas till att förse 100 000 människor, boende på en 10 stor generisk ö i just den tropiska zonen, med dess elbehov. I detta projekt har det gjorts en litteraturstudie för att etablera en kunskapsbas och sedan gjorts en matematisk modell i programmet EES och slutligen har resultaten från modellen granskats och diskuterats. I modellen jämfördes två olika cykler och målet var att bestämma vilken av dessa som var det bästa alternativet för ön. För att underlätta beräkningarna gjordes vissa antaganden och förenklingar.Den slutna cykeln var mest effektiv men den öppna cykeln (OC) hade positiva synergieffekter som den sluta cykeln (CC) saknade. Kostnaden för en anläggning baserades på äldre studier och enligt dessa var den öppna cykeln billigare än den slutna. Anläggningar av de båda cyklerna kan tillgodose den fiktiva öns energibehov, det behöver dock byggas fler anläggningar om OC väljs framför CC.Det kommer krävas ytterligare arbete med att utveckla tekniken innan OTEC på allvar kan utmana dagens fossilbränslebaserade energisystem – eller att oljan helt enkelt blir för dyr. Idag är OTEC för dyrt för att kunna motiveras rent ekonomiskt, men om även miljövinsterna beaktas, samt att ön befriar sig från importer och därigenom får större kontroll över sitt eget energisystem, finns goda incitament att investera i OTEC redan idag.
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Chin, Timothy Edward. "Electrochemical to mechanical energy conversion." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/63015.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references.
Electrode materials for rechargeable lithium ion batteries are well-known to undergo significant dimensional changes during lithium-ion insertion and extraction. In the battery community, this has often been looked upon negatively as a degradation mechanism. However, the crystallographic strains are large enough to warrant investigation for use as actuators. Lithium battery electrode materials lend themselves to two separate types of actuators. On one hand, intercalation oxides and graphite provide moderate strains, on the order of a few percent, with moderate bandwidth (frequency). Lithium intercalation of graphite can achieve actuation energy densities of 6700 kJ m-3 with strains up to 6.7%. Intercalation oxides provide strains on the order of a couple percent, but allow for increased bandwidth. Using a conventional stacked electrode design, a cell consisting of lithium iron phosphate (LiFePO4) and carbon achieved 1.2% strain with a mechanical power output of 1000 W m 3 . Metals, on the other hand, provide colossal strains (hundreds of percent) upon lithium alloying, but do not cycle well. Instead, a self-amplifying device was designed to provide continuous, prolonged, one-way actuation over longer time scales. This was still able to achieve an energy density of 1700 kJ n 3, significantly greater than other actuation technologies such as shape-memory alloys and conducting polymers, with displacements approaching 10 mm from a 1 mm thick disc. Further, by using lithium metal as the counterelectrode in an electrochemical couple, these actuation devices can be selfpowered: mechanical energy and electrical energy can be extracted simultaneously.
by Timothy Edward Chin.
Ph.D.
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Clark, Joanna Helen. "Inorganic materials for energy conversion." Thesis, University of Liverpool, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.569768.
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In an effort to design systems that harvest solar light and convert this into chemical energy, the primary aim of the work presented in this thesis was to develop complex metal oxide materials that were active photocatalysts under visible light. The existing methods for visible light incorporation into photocatalytically active materials are reviewed. Of these, metal to metal charge transfer (MMCT) between bimetallic surface- grafted assemblies was taken as particular inspiration. It was hypothesised that MMCT between metal centres within a bulk complex metal oxide could be similarly applied to yield photocatalytic ally active charge carriers. This approach takes advantage of the stability of bulk systems and the ability to tune the compositions of complex oxide materials. Moreover, it was proposed that MMCT between metal centres located on crystallographically distinct sites of a bulk material would aid charge separation and migration throughout the extended lattice. The optical properties of the RE2 Ti207 (RE = Y, La, Ce, Pr) and Ba2XTizM3015 (X = La, Ce, Pr, Nd, Bi; M = Nb, Ta) series, which include some novel cerium(III) titanates, revealed systematic changes in the electronic structures of these materials. These were rationalised with respect to the energy of Ln 4f states. The proposed electronic structures present the partial achievement of the bulk MMCT hypothesis, with optical transitions from occupied Ce 4f midgap states to the unoccupied primarily Ti 3d conduction band. These Ce3+ /rr" charge transfer materials were inactive photocatalysts, attributed to the presence the Ce 4f-based midgap states that facilitate charge recombination. The double perovskite CaCu3T40IZ, with A-site Cu2+ and B-site Ti4+ cations and whose dielectric properties have been studied extensively in the past, is an ideal candidate for the two site MMCT strategy. Here, the optical and photocatalytic properties, rationalised with the aid of DFT calculations, present the partial achievement of the bulk MMCT hypothesis. Sol-gel derived Pt-CaCu3 Ti4012 is an active photocatalyst toward the visible light photo-oxidation of model pollutants methyl orange (MO) and 4-chlorophenol (4CP). Optical spectra and product analysis show that these reactions proceed via more selective routes than the typical reaction over TiOz P25 under DV light. Interestingly, the products of 4CP photo-oxidation were shown to be dependent on the wavelength of incident light. Cu-doping of BizTiz07 was found to stabilise the pyrochlore structure with respect to the Aurivillius phase Bi4 Ti3012 and to impart significant visible light absorption. Sol-gel derived Pt-BiI.6Cuo.4 Tiz07 photo-oxidised MO under visible light via conventional band gap excitation, as determined by quantum efficiency measurements. In contrast, sol-gel derived Pt-B4 Ti3012 photo-oxidised MO via the excitation of adsorbed MO, and was also active toward 4CP photo-oxidation under visible light. The excitation method, mechanisms and product distributions have been investigated for each of the photo-oxidation reactions presented in this thesis. In particular, the photo- oxidation of MO over some Pt-modified metal oxides has been shown to proceed via excitation of adsorbed MO and not of the semiconductor. Additionally, the mechanism and products of these processes are far more selective than the related DV reactions over TiOz P25, and have been shown to depend to some extent on the semiconductor support.
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Pedrosa, Steven Michael. "Study of high efficiency micro thermoelectric energy harvesters." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4820.
Full textAbstract:
Thermal energy sources, including waste heat and thermal radiation from the sun, are important renewable energy resources. Thermal energy can be converted into electricity by thermoelectric phenomena; the thermoelectric phenomena can also be operated in reverse when provided an electric current, producing a temperature gradient across the device. Thermoelectric devices are scalable, renewable, and cost effective products that offer capabilities to harness waste heat or environmental heat sources, and convert the captured heat into usable electricity. The operating principle of a thermoelectric device requires that a temperature gradient be present across the device, which induces the flow of electrons from the hot side of the device to the cold side. Thermoelectric devices are currently hampered by the low conversion efficiencies and strict operating temperatures for certain materials. This study investigates the main factors affecting efficiencies of thermoelectric devices as energy harvesters and aims to optimize the devices for maximum efficiency and lower costs by using microfabrication processes and self-assembled materials for complete thermoelectric modules (TEMs). By first establishing operating conditions and a desired mode of operation, optimization equations have been established to determine device dimensions and performance parameters. Compact integration realized by microfabrication technologies that allow for multiple output voltages from a single chip was also investigated. Additionally, cost savings were found by reducing the number of fabrication processing steps and eliminating the need for precious metals during fabrication. The optimized design proposed in this study utilizes copper electrodes and requires fewer applications of photoresist than previous proposed designs. In fabrication of thin film based micro devices, the film quality and the composition of the film are essential elements for producing TEMs with desired efficiencies. Although Bi2Te3 has been investigated as thermoelectric material, this study determined that there was a possibility that both N-type and P-Type Bi2Te3 could be created from a single electrolyte solution by controlling the amount of Te present in the film. Films were produced with both AC and DC signals and varied composition of Te at.% of Bi2Te3 was achieved by controlling the average current density during electrochemical deposition. A linear relationship was established between the average current density and the resultant Te content. SEM and EDS were used to characterize the morphology and the composition of the thin films created. With the fabricated thermoelectric materials, analytical models could be developed using known material properties of thermoelectric films with a given Te content. The analytical results obtained by the developed optimization equations were comparable with the FEA models produced by using COMSOL, a multiphysics program with powerful solving algorithms that was used to evaluate designs. Further improvements to device performance can be achieved by designing a segmented thermoelectric device with multiple layers of thermoelectric material to allow the device to operate across a larger temperature gradient.ID: 031001306; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Title from PDF title page (viewed March 18, 2013).; Thesis (M.S.M.E.)--University of Central Florida, 2011.; Includes bibliographical references (p. 88-89).
M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Miniature Engineering Systems Track
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Jackson, Samuel. "Thermoelectric n-type oxide materials for energy generation." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/thermoelectric-ntype-oxide-materials-for-energy-generation(1fa87b0b-b734-485e-a1a3-6e08d929a109).html.
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The thermoelectric properties of lanthanum-doped strontium titanate (LSTO) were investigated for high temperature applications. Ceramics with the formulation La(2x/3)Sr(1-x)TiO(3-delta) (x = 0.1, 0.3, 0.5, 0.7, 0.9) were produced using the conventional mixed oxide route. After 18 hours of milling the powders were calcined at 1373 K for 4 hours and sintered at 1733 K (± 180 K/hour) for 4 hours in air. SEM, XRD, and TEM techniques were employed to characterise the microstructure of the ceramics as well as density measurements. Subsequently the electrical conductivity, Seebeck coefficient, and thermal conductivity in order to determine the thermoelectric figure of merit of the ceramics. Key thermal conductivity results were further investigated using a computational approach. This production method resulted in high quality, high density (> 97 %) ceramics that were mostly single phase determined by XRD with a Pm3m space group, with the exception of the x = 0.9 ceramic that had a Cmmm space group. SEM imaging confirmed this finding and revealed a core-shell structure in x = 0.1 and x = 0.3 ceramics whereby the core was La-rich/Sr-deficient. Thermal conductivity of the ceramics decreased with increasing La content. This was investigated further computationally employing the Green-Kubo method. It was established that the decrease in thermal conductivity was due to phonon-scattering from A-site vacancies, and not from the stabilisation of oxygen vacancies as suggested elsewhere. The electrical properties were dramatically improved through sintering the LSTO ceramics in a 5 % H2 95 % Ar atmosphere. This led to a reduction of Ti4+ to Ti3+. The maximum electrical conductivity increased to 789 S.cm-1 resulting in a power factor of 0.0013 W.m-1 K-2 at 477 K for x = 0.3. A zT of 0.27 at 870 K for x = 0.5 was obtained due to a lower thermal conductivity. The ceramic LSTO x50H was subsequently doped with excess lanthanum; A maximum of 3 % excess was able to be fully incorporated into the lattice. This resulted in a further increase of the electrical conductivity to 875 S.cm-1 at 377 K. A decrease in the lattice thermal conductivity of ∼ 1 W.m-1 K-1 was also achieved due to the oxygen vacancies that were introduced as a result of the reducing sintering conditions. Overall a zT 0.27 at 1016 K was obtained for 3 % excess lanthanum. The ceramic LSTO x50H was also doped with niobium and vanadium. Reduction in the lattice parameter from the La substitution inhibited the niobium from fullyincorporating into the matrix. This was not the case for vanadium that resulted in an electrical conductivity of 144 S.cm-1 , Seebeck coefficient of -106 µV.K-1 , and thermal conductivity of 2.08 W.m-1 K-1 at 308 K, resulting in an overall maximum zT of 0.08 at 1070 K.
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Ismael, Ali. "Towards molecular-scale sensing and thermoelectric energy harvesting." Thesis, Lancaster University, 2017. http://eprints.lancs.ac.uk/87396/.
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Zhou, Yu. "Energy Harvesting Using a Thermoelectric Generator and Generic Rule-based Energy Management." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1196802707.
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Chandrasekaran, Rajeswari. "Modeling of electrochemical energy storage and energy conversion devices." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37292.
Full textAbstract:
With increasing interest in energy storage and conversion devices for automobile applications, the necessity to understand and predict life behavior of rechargeable batteries, PEM fuel cells and super capacitors is paramount. These electrochemical devices are most beneficial when used in hybrid configurations rather than as individual components because no single device can meet both range and power requirements to effectively replace internal combustion engines for automobile applications. A system model helps us to understand the interactions between components and enables us to determine the response of the system as a whole. However, system models that are available predict just the performance and neglect degradation. In the first part of the thesis, a framework is provided to account for the durability phenomena that are prevalent in fuel cells and batteries in a hybrid system. Toward this end, the methodology for development of surrogate models is provided, and Pt catalyst dissolution in PEMFCs is used as an example to demonstrate the approach. Surrogate models are more easily integrated into higher level system models than the detailed physics-based models. As an illustration, the effects of changes in control strategies and power management approaches in mitigating platinum instability in fuel cells are reported. A system model that includes a fuel cell stack, a storage battery, power-sharing algorithm, and dc/dc converter has been developed; and preliminary results have been presented. These results show that platinum stability can be improved with only a small impact on system efficiency. Thus, this research will elucidate the importance of degradation issues in system design and optimization as opposed to just initial performance metrics.
In the second part of the thesis, modeling of silicon negative electrodes for lithium ion batteries is done at both particle level and cell level. The dependence of the open-circuit potential curve on the state of charge in lithium insertion electrodes is usually measured at equilibrium conditions. Firstly, for modeling of lithium-silicon electrodes at room temperature, the use of a pseudo-thermodynamic potential vs. composition curve based on metastable amorphous phase transitions with path dependence is proposed. Volume changes during lithium insertion/de-insertion in single silicon electrode particle under potentiodynamic control are modeled and compared with experimental data to provide justification for the same. This work stresses the need for experiments for accurate determination of transfer coefficients and the exchange current density before reasoning kinetic hysteresis for the potential gap in Li-Si system. The silicon electrode particle model enables one to analyze the influence of diffusion in the solid phase, particle size, and kinetic parameters without interference from other components in a practical porous electrode. Concentration profiles within the silicon electrode particle under galvanostatic control are investigated. Sluggish kinetics is established from cyclic voltammograms at different scan rates. Need for accurate determination of exchange current density for lithium insertion in silicon nanoparticles is discussed. This model and knowledge thereof can be used in cell-sandwich model for the design of practical lithium ion cells with composite silicon negative electrodes. Secondly, galvanostatic charge and discharge of a silicon composite electrode/separator/ lithium foil is modeled using porous electrode theory and concentrated solution theory. Porosity changes arising due to large volume changes in the silicon electrode with lithium insertion and de-insertion are included and analyzed. The concept of reservoir is introduced for lithium ion cells to accommodate the displaced electrolyte. Influence of initial porosity and thickness of the electrode on utilization at different rates is quantitatively discussed. Knowledge from these studies will guide design of better silicon negative electrodes to be used in dual lithium insertion cells for practical applications.
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Boström, Cecilia. "Electrical Systems for Wave Energy Conversion." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-140116.
Full textAbstract:
Wave energy is a renewable energy source with a large potential to contribute to the world's electricity production. There exist several technologies on how to convert the energy in the ocean waves into electric energy. The wave energy converter (WEC) presented in this thesis is based on a linear synchronous generator. The generator is placed on the seabed and driven by a point absorbing buoy on the ocean surface. Instead of having one large unit, several smaller units are interconnected to increase the total installed power. To convert and interconnect the power from the generators, marine substations are used. The marine substations are placed on the seabed and convert the fluctuating AC from the generators into an AC suitable for grid connection. The work presented in the thesis focuses on the first steps in the electric energy conversion, converting the voltage out from the generators into DC, which have an impact on the WEC's ability to absorb and produce power. The purpose has been to investigate how the generator will operate when it is subjected to different load cases and to obtain guidelines on how future systems could be improved. Offshore experiments and simulations have been done on full scale generators connected to four different loads, i.e. one linear resistive load and three different non-linear loads representing different cases for grid connected WECs. The results show that the power can be controlled and optimized by choosing a suitable system for the WEC. It is not obvious which kind of system is the most preferable, since there are many different parameters that have an impact on the system performance, such as the size of the buoy, how the generator is designed, the number of WECs, the highest allowed complexity of the system, costs and so on. Therefore, the design of the electrical system should preferably be carried out in parallel with the design of the WEC in order to achieve an efficient system.Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 727
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Giddings, S. L. "Heterogeneous reactions in solar energy conversion." Thesis, Swansea University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637056.
Full textAbstract:
Photochemical systems for the splitting of water into hydrogen and oxygen represent an attractive route for the conversion of solar energy into a chemical fuel. However, the success of such systems depends on the identification of suitable redox catalysts for the oxidation and reduction processes. While colloidal platinum has proved to be an efficient catalyst for the reduction of water, the development of stable and effective catalysts for water oxidation has been less successful. The work described in this thesis involves the study of ruthenium dioxide hydrate (RuO2.xH2)O as a heterogeneous catalyst for the oxidation of water to oxygen. Although this material has already been widely used as an oxygen catalyst, there have been many doubts as to its ability to act in this capacity. In Chapter Three an attempt is made to resolve this controversy via an investigation of the stability and catalytic activity of RuO2.xH2O when exposed to various oxidising agents. The results indicate that the catalytic activity and corrosion stability of an RuO2.xH2O sample is related to its degree of hydration. In Chapter Four an investigation is described into the effect of heat-treatment of RuO2.xH2O at different temperatures on its physical and chemical properties. From these results it appears that any sample of RuO2xH2O may be transformed into a stable, reproducible oxygen catalyst by simply heat-treating it at 140-150oC in air for ca. 5 hours. The latter conditions represent an optimum for catalytic activity where anodic corrosion is absent. This 'thermally-activated' RuO2.xH2O is shown to compare favourably with alternative oxygen catalysts. Chapters Five and Six involve a kinetic study of the RuO2.xH2O-catalysed oxidation of water by Ce(IV) ions in an attempt to elucidate the mechanism of catalysis of the oxide powder. The study is based on an electrochemical model in which the RuO2.xH2O particles are considered as microelectrodes. The initial charging of the RuO2.xH2O prior to water oxidation is discussed in Chapter Five and in Chapter Six the effect of an increase in the redox potential of the Ce4+/Ce3+ couple by changing the acid medium is investigated.
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Hassan, Ibrahim. "Solar energy conversion by photoelectrochemical processes." Thesis, University of Bath, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542078.
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Muralidharan, Shylesh. "Assessment of ocean thermal energy conversion." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/76927.
Full textAbstract:
Thesis (S.M. in Engineering and Management)--Massachusetts Institute of Technology, Engineering Systems Division, System Design and Management Program, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 103-109).
Ocean thermal energy conversion (OTEC) is a promising renewable energy technology to generate electricity and has other applications such as production of freshwater, seawater air-conditioning, marine culture and chilled-soil agriculture. Previous studies on the technology have focused on promoting it to generate electricity and produce energy-intensive products such as ammonia and hydrogen. Though the technology has been understood in the past couple of decades through academic studies and limited demonstration projects, the uncertainty around the financial viability of a large-scale plant and the lack of an operational demonstration project have delayed large investments in the technology. This study brings together a broad overview of the technology, market locations, technical and economic assessment of the technology, environmental impact of the technology and a comparison of the levelized costs of energy of this technology with competing ones. It also provides an analysis and discussion on application of this technology in water scarce regions of the world, emphasized with a case study of the economic feasibility of this technology for the Bahamas. It was found that current technology exists to build OTEC plants except for some components such as the cold water pipe which presents an engineering challenge when scaled for large-scale power output. The technology is capital intensive and unviable at small scale of power output but can become viable when approached as a sustainable integrated solution to co-generate electricity and freshwater, especially for island nations in the OTEC resource zones with supply constraints on both these commodities. To succeed, this technology requires the support of appropriate government regulation and innovative financing models to mitigate risks associated with the huge upfront investment costs. If the viability of this technology can be improved by integrating the production of by-products, OTEC can be an important means of producing more electricity, freshwater and food for the planet's increasing population.
by Shylesh Muralidharan.
S.M.in Engineering and Management
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Mur, Miranda José Oscar 1972. "Electrostatic vibration-to-electric energy conversion." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/16609.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 193-197).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Ultra-Low-Power electronics can perform useful functions with power levels as low as 170 nW. This makes them amenable to powering from ambient sources such as vibration. In this case, they can become autonomous. Motivated by this application, this thesis provides the necessary tools to analyze, design and fabricate MEMS devices capable of electrostatic vibration-to-electric energy conversion at the microwatt level. The fundamental means of en- ergy conversion is a variable capacitor that is excited through a generating energy conversion cycle with every vibration cycle of the converter. This thesis presents a road map on how to design MEMS electrostatic vibration-to- electric energy converters. A proposed converter is designed to illustrate the design process, and is based on vibration levels typical of rotating machinery, which are around 2% of the acceleration of gravity from 1-5 kHz. The converter consists of a square centimeter with a 195 mg proof mass which travels ±200 pm. This mass and travel can couple to a sinusoidal acceleration source of 0.02g at 2.5 kHz, typical of rotating machinery, so as to capture 24 nJ per cycle. This moving proof mass is designed to provide a variable capacitor ranging from 1 pF to 80 pF. Adding a capacitor of 88 pF in parallel with this device will result in a capacitance change from 168 pF to 89 pF that is required to extract 24 nJ using a charge-constrained cycle.
(cont.) This device can be attached to power electronics that implement a charge-constrained cycle and deliver 0.5 nJ back to the reservoir for a total power output of 1.3 [mu]/W at 2.5 kHz. The efficiency of the electrical conversion is 2%. Including packaging, the power per volume would be 0.87 [mu]W/cm3 and the power per mass would be 1.3 [mu]W/g. System improvements are also identified such as those that address the principal sources of loss. For example, decreasing the output capacitance of the MOSFET switches from 10 pF to 1 pF, while keeping the energy conversion cycle the same, results in an energy output of 13 nJ out of 24 nJ, for an efficiency of 54% and a power output of 33 [mu]W. This argues strongly for the use of integrated circuits in which the output capacitance of the MOSFET switches can be reduced for this application.
José Oscar Mur Miranda.
Ph.D.