Ce mémoire de thèse porte sur l'exploitation de l'effet Seebeck pour la caractérisation thermo-physique des matériaux thermoélectriques (TE) solides et liquides. Lors de travaux récents au sein du laboratoire, la technique photothermoélectrique (PTE) a été développée pour la caractérisation thermique de matériaux TE solides de faibles conductivités électriques. Dans ce travail, l'utilisation de cette technique a été généralisée à tous les matériaux TE solides (de faibles ou de hautes conductivités électriques). Cela est rendu possible par la prise en compte de la nature gaussienne de l'excitation thermique modulée à laquelle le matériau est soumis ainsi que par la compréhension des effets de couplage des mécanismes de transport thermique et électrique dans les matériaux TE. Dans cette thèse, plusieurs matériaux thermoélectriques solides ont été étudiés : le trisulfure de titane (TiS₃), les oxydes types Bi₂Ca₂Co₁,₇Oₓ, le séléniure du tellurure de bismuth (Bi₂Te₂,₄Se₀,₆). La tension auto-induite par effet Seebeck a été aussi exploitée pour la détection des transitions de phases que présentent certains matériaux thermoélectriques, ici le cas du séléniure de cuivre a été étudié. Une nouvelle procédure qui permet de déterminer l'évolution de la diffusivité thermique d'un matériau TE en fonction de la température est présentée. En plus des matériaux TE solides, la technique PTE a été étendue à l'étude des matériaux thermoélectriques liquides (LTE). Un modèle théorique qui décrit le signal délivré par un matériau LTE soumis à une excitation thermique périodique a été développé. Ensuite, une étude de l'évolution des propriétés thermiques d'un matériau LTE en fonction de la concentration d'un soluté a été réalisée. Enfin, l'approche dite de cavité résonnante d'ondes thermiques (TWRC) a été utilisée pour investiguer thermiquement des matériaux LTE. À notre connaissance, c'est la première fois que l'approche TWRC est utilisée pour l'analyse du signal généré par un liquide thermoélectrique. L'utilisation des LTE comme capteurs thermiques a été aussi abordée dans ce travail. / The use of the self-induced Seebeck effect in thermophysical characterization of solid and liquid thermoelectric (TE) materials is described in this manuscript. In previous works, the photothermoelectric technique (PTE) has been developed in our laboratory for the thermal characterization of solid TE materials having low electrical conductivities. In this work, we first generalized the use of the PTE technique to all solid thermoelectric materials (with high or low electrical conductivities). This is achieved by taking into account the Gaussian shape of the thermal source exciting the material as well as by the understanding of the coupling effects between thermal and electrical transport mechanisms when a TE material is submitted to a modulated thermal excitation. In this thesis, several solid thermoelectric materials were studied : Titanium trisulfide (TiS₃),Bi₂Ca₂Co₁,₇Oₓ oxydes and Bismuth Selenido-telluride (Bi₂Te₂,₄Se₀,₆). Then, the self-induced Seebeck voltage was used for the detection of phase transitions exhibited by certain thermoelectric materials. The case of the copper selenide (Cu₂Se) was studied. A new procedure allowing to follow the temperature dependance of the thermal diffusivity of solid TE materials is also presented. In this work, the PTE technique was extended to liquid thermoelectric (LTE) materials. Indeed, a theoretical model describing the signal delivered by a LTE material subject to a periodic thermal excitation has been developed. Then, a study of the evolution of the thermal properties of an electrolyte as function of a solute concentration was performed. Finally, the thermal-wave resonator cavity (TWRC) approach was used to characterize thermally LTE materials. As far as we know, this is the first method proposing a TWRC approach applied directly to the sensor itself. The use of LTE such as heat sensors was also addressed here.

The introduction of this paper describes three thermoeletrical effects and their properties. It also deals with thermoelectrical cells, which are using Seebeck´s and Peltrier´s effects. The paper decribes principles how the Peltier´s cells work, their mathematical model, construction and practical use. The paper shows what kinds, shapes and output we can meet at the market and which kinds of parameters regulate their selection. The paper suggests the possibility to measure characteristic behaviour and quantity during laboratories tasks and their evaluations. At the conclusion is adduced the suggestion of laboratory task together with theoretically made pilot protocol.

The thesis deals with the problem of potential use of solar energy through the conversion into electric energy. The thesis analyses in great detail several types of conversion. My special concern included photovoltaic conversion and thermal conversion of solar energy using steam turbines for energy production. In the subsequent parts, I focus on the problem of photovoltaic, photovoltaic systems, and solar thermal power plants, their installation and use.

No description available.

Climate change is a subject of deep distress in today’s world. Over dependence on hydrocarbon has resulted in serious environmental problems. Rising sea level, global warming and ozone layer depletion are the mainstream of any discuss world over. The collective goal of cutting carbon emission by the year 2020has prompted the search for clean, alternative energy sources. This effort are already yielding good reward as other forms of energy such as solar, wind, nuclear and hydro have received huge investment and renew interest over the past decade. Thermoelectric materials over the past decades have been tipped to replace conventional means of power generations as these materials have the ability to convert heat to electrical energy and vice versa. They are simple, have no moving parts and use no greenhouse gases. But the major drawback of these materials is their low conversion efficiency. Hence there is a need to enhance the efficiency of thermoelectric material to fulfill their undeniable potentials. A parameter called the thermoelectric figure of merit, ZT defines the efficiency of a thermoelectric material. ZT relates three non-mutually exclusive transport properties namely Seebeck coefficient, electrical conductivity and thermal conductivity. Efficient thermoelectric material should possess high Seebeck coefficient, high electrical conductivity and low thermal conductivity. Hence, one of the interesting ideas in the area of thermoelectric research is the concept of designing a bulk material with high density of phonon scattering centers so has to reduce the lattice contribution to thermal conductivity but at the same time have minimum impact oncharge carriers. This is usually achieved by utilizing interphase and grain boundaries which are localized defects to scatter phonons. The volume fraction of the grain/interphase boundaries can be control through phase modification and microstructure design. This thesis is centered on Bi-Sb-Te systems which are the present room temperature state of the earth thermoelectric material. The investigation revolves around developing a new kind of microstructure in the well-studied Bi-Sb-Te system that shows tremendous potential as a means to reduce lattice contribution to thermal conductivity. The idea of having both p and n-type thermoelectric material preferably from the same material was also a motivation in our investigation. The thesis isdivided into six chapters. The first chapter introduces the concept of thermoelectricity i.e. the direct conversion of thermal energy into electricity. The physics involved and contribution of individual to the science of thermoelectricity were enumerated. Efficiency, optimization and material selection for better thermoelectric performance were briefly enumerated. Prospective materials that are currently been investigated for better thermoelectric properties were also mentioned. The structure of the Bi-Sb-Te system which is the focus of this thesis is present in this chapter including doping effect on the thermoelectric performance of the system as well as the various methods present been employed to improve the thermoelectric properties of the system. Finally the chapter enumerates the scope and object of the present thesis. The different experimental procedures adopted in the present thesis arediscussed in chapter 2. The details of different processing routes followed to synthesize flame-melted ingots, flame-melted + low temperature milled (cryo milling) + spark plasma sintering (SPS) alloy and flame-melted + melt spinning + spark plasma sintering (SPS) alloy, are discussed followed by the various structural and functional characterization techniques. The unique advantage of the spark plasma sintering techniques over the conventional sintering method was talked out in detail. The structural characterizations performed on the synthesized alloys include XRD, SEM and whilethe functional characterizations comprised of Hall measurement, Seebeck coefficient, electrical resistivity and thermal conductivity measurements. Thermoelectric properties of selected composition of Bi-Sb-Te synthesized via flame-melting are presented in chapter 3.Detail study of four analyzed compositions namelyBi24Sb20Te56, Bi20Sb12Te69, Bi16Sb5Te79 and Bi29Sb11Te60resulted in four unique microstructure and different volume fraction of primary and secondary phases. The resultant morphologies of the microstructure were observed to have influence the thermoelectric behavior corresponding to each composition. The sole influence of anti-structural defects on the conductivity type and the role of microstructure morphologies and length scale were understood in this chapter. Samples with segregated Te and a solid solution BiSbTe3(eutectic morphology) form an n-type thermoelectric material while samples with only solid solution BiSbTe3 forms a p-type thermoelectric material. Pair of n-type and p-type material was obtained without the introduction of external dopant.The pair shows good compatibility factorsuitable for thermoelectric device. In chapter 4, the thermoelectric properties of four selected composition of Bi-Sb-Te synthesized via low temperature milling plus spark plasma sintering is addressed. The analyzed compositions are as follows Bi24Sb20Te56, Bi18Sb11Te71, Bi17Sb6Te77, and Bi28Sb15Te57 respectively. The effect of low temperature milling combine with the prospect of minimum grain growth of spark plasma sintering on the thermoelectric properties of the selected compositions were determined. Samples with eutectic morphology which would otherwise scatter charge carriers were observed to have the highest carrier mobility as a result of high volume fraction of Te phase which serves as a donor injecting excess electrons into the system. The impact of small grain size was observed on the transport properties of the sample Bi28Sb15Te57 with the highest electrical resistivity, the best Seebeck coefficient and the lowest thermal conductivity. Pair of n-type and p-type material was obtained without the introduction of external doping elements. The pairshows good compatibility factor suitable for segmented thermoelectric device. Chapter 5 narrates the thermoelectric properties of four compositions namely Bi30Sb13Te58, Bi23Sb13Te65, Bi18Sb5Te77 and Bi23Sb20Te58subjected to melt spinning plus spark plasma sintering.High cooling rate obtained during melt spinning process was observed in this chapter to cause a shift of composition which resulted in a microstructure morphology with eutectic colonies that is predominantly Te rich. These Te rich colonies in the sample Bi30Sb13Te58 was observed to change the conductivity type of the sample from an otherwise p-type to n-type while also aiding bipolar conduction which was detrimental to the overall thermoelectric performance of the alloy. Segregated Te in the form of eutectic morphology helps to inject excess electron into the bulk of the sample Bi23Sb13Te65 and Bi18Sb5Te77hereby increases the observed electrical conductivity which by virtue of the microstructure morphology is expected to be low. As a result of the processing routes, all four compositions in this chapter shown-type conductivity. Chapter 6 presents the summary of the important conclusions drawn from this work.

Att minska energianvändningen är något det pratats mer och mer om de senaste åren. Det finns olika sätt att minska energianvändningen på och ett av dessa är att återvinna värmeenergi. Det kan gälla både spillvärme och nyttig värme. Detta går att tillämpa i industrin, transportsektorn, hushåll och till vardags. Gemensamt för dessa processer är att det används stora mängder energi vilket till stor grad består av förluster till omgivningen eller att processerna inte optimeras. På senare tid har det forskats kring teknologi som kan ta vara på denna värmeenergi och på så vis minska förlusterna. En teknologi för detta är termoelektriska generatorer (TEG) som bygger på Seebeckeffekten för att generera elektricitet från temperaturskillnader. När ett TEG-element utsätts för värme på en sida och kyla på den andra sidan så genereras en elektrisk spänning. En elektrisk ström och effekt kan tas ur kretsen om elementet kopplas till en elektrisk last. Materialet i elementet består av halvledarmaterial med låg värmeledningsförmåga och en hög elektrisk ledningsförmåga. Teknologin har funnits länge men aldrig tillämpats i någon större grad. Nu på senare år har intresset ökat och kommersiella produkter med TEG-element har tagits fram. I detta arbete har en sådan produkt testats för att se hur lämpligt det skulle vara att använda dessa vid hushåll som inte är anslutna till elnätet och har en vedkamin för uppvärmning. TEG-enheten testas på en värmeplatta där ställbara temperaturer är möjliga för att testa prestandan vid temperaturerna 150° C, 200° C och 230° C. En krets sätts ihop för att kunna mäta av värden på spänning och ström vid olika laster som sätts med resistorer. Mätningarna görs med en ökning på 0,1 A vid varje mätning. Resultatet från dessa tester visar att maximal effekt på 14 W uppnås hos produkten vid 230° C. När modifiering av produkten görs för att öka temperaturskillnaden uppnås 17,8 W vilket tyder på att effekten ökar när delta T ökar. Den spänning som uppnås vid öppen krets var som högst 31 V och vid maximal effekt var den 17,8 V. Strömmen var då 1 A. De resultat som testerna gav levde inte upp till de 25 W som produkten sägs kunna ge. Produkten saknar även viktiga komponenter så som spänningsreglerare.Det går av både teori och tester avgöra att det är ett lämpligt sätt att använda sig av TEG-enheter för att generera små mängder elektricitet vid hushåll utan koppling till elnätet. / In recent years the topic of reducing the energy usage has been on the agenda. There are several ways of reducing the energy usage and one of these is to recycle heat energy. It could be both waste heat and useful heat. This can be implied to the industry, transport sector, households and on daily activities. The common factor between these is that large quantities of energy is used and to a large extent consists of losses to the surrounding or from processes that are not optimized. In recent time there has been done research around technology that can recycle and use this heat energy and in return reduce the energy usage. One technology to do this is thermoelectric generators (TEG) that are implementing the Seebeck effect to generate electricity from temperature differences. When a TEG-element have one side that is exposed to a heat source and one side being cooled down an electric voltage is being generated. An electric current and power can then be used from the circuit if the element is connected to an electric load. The material in the element exists of semiconductive materials with low heat conductivity and high electric conductivity. The technology has existed for a long time but has never been implemented to a larger extent. It is only in recent years that the interest has grown and some commercial products with TEG-elements has been developed. In this thesis one of these products has been tested to see how viable it would be to use these within a household that is not connected to the electrical grid and where the house is heated with a wood-burning stove. The TEG-product is tested on a heat plate where it is possible to set a desired temperature. The temperatures of 150° C, 200° C and 230° C are chosen for testing the performance of the product. A circuit is put together to be able to read the values of the voltage and current at different loads that are set with resistors. The measurements are done with an increase of 0,1 A for every measurement. The result from these tests shows that the maximum power of 14 W is achieved at 230° C on the hot side. But when modification of the product is made to increase the temperature difference a value of 17,8 W is attained. This indicate that the power is increasing when the temperature difference is increasing. The attained voltage at open circuit was as highest 31 V and at maximum power it was 17,8 V. The current was then 1 A. The results that the testing gave did not match the value of 25 W that the datasheet says the product can deliver. Also, the product is missing important components such as voltage regulator.It is possible from both the theory and the testing to see that it is suitable to use a TEG-product to generate small amount of electricity to households that are not connected to the electrical grid.

Waste heat recovery is a multi-billion-dollar industry with a compound annual growth rate of 8.8% assessed between 2016 to 2024 and low-grade waste heat (< 230^oC ± 20^oC) makes up 66% of this ubiquitous resource. Thermoelectric generators are preferred for the recovery process because they are cheap and are well suited for this temperature range. They generate power by converting thermal potential to electric potential, known as the Seebeck effect. Since they have no moving parts, they are inherently immune to mechanical failure or an intermittent need for maintenance. However, the challenge has been to effectively harvest waste heat with these modules to generate power, using passive processes. This work is focused on designing a device for optimized harvesting of waste energy from the ambient with a custom, evaporatively-cooled heat sink. This heat sink is designed to passively handle the cooling of the other side of the thermoelectric module so as to enable the attainment of a minimum of 5V, which is the minimum voltage required to power small mobile devices. The heat sink model is similar to a loop heat pipe but engineered for compactness. To ensure this level of efficacy is attained, several studies are made to optimize the wick. Non-metal wicks were considered as they do not contribute to an increase in temperature of the compensation chamber in loop heat pipes. A non-metal wick integrated with nanoparticles is tested and results show a clear thermal management enhancement over similar but virgin non-metal wicks, at over 16%. The heat source section of the device is optimized for energy-harvesting in low grade temperature regimes by incorporating a near-black body coating on the metal heat source section. Experimental results show that both the heat source and sink sections were able to induce sufficient thermal potential for the thermoelectric modules to passively generate up to 5V using eight 40mm by 40mm Bismuth Telluride modules in 3.5 minutes. The prototype is relatively cheap, inherently reliable and presents the possibility of passively harvesting low-grade waste heat for later use, including powering small electronic devices.

No description available.

Der thermische Widerstand ist eine wichtige Kenngröße von Silicium-Germanium-Hetero-Bipolartransistoren (SiGe-HBTs). Bisher kam es bei der quantitativen Bestimmung der thermischen Widerstände von SiGe-HBTs zu deutlichen Abweichungen zwischen Simulation und Messung. Der Unterschied zwischen Simulation und Messung betrug bei den untersuchten HBTs mehr als 30 Prozent. Diese Arbeit widmet sich der Aufklärung und Beseitigung der möglichen Ursachen hierfür. Zu diesem Zweck werden als erstes die Messmethoden analysiert. Es zeigt sich, dass die bisher verwendete Extraktionsmethode sensitiv auf den Early-Effekt (Basisweitenmodulation) reagiert. Im Rahmen der Untersuchungen wurde ein neues Extraktionsverfahren entwickelt. Die neue Extraktions­methode ist unempfindlich gegenüber dem Early-Effekt. Mit Bauelemente­simulationen wird erstmalig die Wirkung des Seebeck-Effektes (Thermospannungen) auf die elektrisch extrahierten thermischen Widerstände demonstriert. Der Seebeck-Effekt bewirkt, dass die elektrisch extrahierten thermischen Widerstände der untersuchten HBTs nahezu 10 Prozent kleiner als die erwarteten Werte sind. Dieser Effekt wurde bisher nicht beachtet und wird hier erstmals nachgewiesen. Weiterhin wird die Abhängigkeit des thermischen Widerstandes vom Arbeitspunkt untersucht. Dabei hat sich gezeigt, dass bis zu einer Basis-Emitter-Spannung von 0,91 Volt die geometrische Form des Wärme abgebenden Gebietes unabhängig vom Arbeitspunkt ist. Anhand von Messungen wird gezeigt, dass die Dotierung die spezifische Wärmeleitfähigkeit von Silicium reduziert. Die Abnahme wird für Dotierungen größer als 1*1019 cm‑3 deutlich sichtbar. Ist die Dotierung größer als 1*1020 cm‑3, beträgt die Abnahme der spezifischen Wärmeleitfähigkeit mehr als 75 Prozent. Mithilfe einer Simulatorkalibrierung wird die spezifische Wärmeleitfähigkeit als Funktion der Dotierung bestimmt. Die erhaltene Funktion kann künftig beim thermischen Entwurf von HBTs verwendet werden. Somit können zukünftig genauere Vorhersagen zum thermischen Widerstand der HBTs gemacht werden. Dies ermöglicht zuverlässigere Aussagen darüber, wie Änderungen des Transistordesigns zur Minimierung des thermischen Widerstandes beitragen. / The thermal resistance is an important parameter of silicon-germanium heterojunction bipolar transistors (SiGe HBTs). Until now, the quantitative determination of the thermal resistance showed significant differences between measurements and simulations. The difference between simulation and measurement of the investigated HBTs was more than 30 percent. This thesis devotes the clarification and elimination of potential sources for it. For this purpose, the measurement methods are analyzed at first. It is shown, that the currently used extraction method is sensitive to the Early effect (basewidth modulation). A now extraction method was developed, which is not sensitive to the Early effect. For the first time, the influence of the Seebeck effect (thermoelectric voltages) on the electrically extracted thermal resistance is shown by device simulations. The Seebeck effect leads to a 10 percent lower extracted thermal resistances compared to the expected values of the investigated HBTs. This effect was not taken into account up to now and is demonstrated here for the first time. Furthermore, the dependence of the thermal resistance on the operating point was investigated. The results show that the shape of the heat source is independent of the operating point if the base emitter voltage is smaller than 0.91 volt. The thermal conductivity of silicon is decreased by increasing doping concentrations. This is shown by measurements. The reduction of the thermal conductivity is well observable for doping concentrations higher than 1*1019 cm‑3. For doping concentration higher than 1*1020 cm‑3 the reduction amounts to more than 75 percent. The thermal conductivity was determined as a function of the doping concentration with the aid of a simulator calibration. This function can be used in the future thermal design of HBTs. It facilitates the optimization of the HBTs with respect to a minimal thermal resistance.

This master´s thesis is directed to an research of thermoelectric cells as power sources. It is discoursing about general properities of thermoelectric cells and their using at practical aplications in the first part. Then a heating and cooling system is designed and made for a selected type of thermoelectric cell which represents the emergency back-up power source. In the next part a DC/DC step-up converter is designed for a selected type of thermoelectric cell. This converter generates the DC load voltage 12V. The converter is controlled by PWM with a carrier frequency 50kHz.