Numerous alternative energy sources are being researched for sustainable energy applications, but their overall benefit is still too costly for them to be considered viable. Commonly produced temperature gradients created by the environment, or are man-made, can be converted into useful energy by using thermoelectric materials. Inorganic semiconductors are the most commonly used thermoelectric materials, but have raised concerns due to toxicity issues, rarity of heavy elements used, and high fabrication temperatures. These concerns have led research efforts into electrically conductive polymer composites prepared in ambient conditions from aqueous solutions. By combining polymer latex with carbon nanotubes (CNT), electrical conductivity can resemble metals while thermal conductivity remains similar to polymers. Using different CNT stabilizers for these fully organic composites can tailor the thermoelectric properties and harvest thermal gradients from previously inconceivable places (e.g., body heat converted into a voltage). A semiconducting CNT stabilizer, meso-tetra(4-carboxyphenyl) porphine (TCPP), was used to investigate the influence stabilizers have on composite thermoelectric properties. As TCPP was compared to a similar system containing an insulating stabilizer, sodium deoxycholate (DOC), the multi-walled carbon nanotube (MWNT)-filled composites showed a 5x increase in the Seebeck coefficient (S). TCPP did not have a distinct effect on the electrical conductivity (σ), demonstrating the tailorability of S with this molecule. An intrinsically conductive polymer, poly(3,4-ethylenedioxythiophene) :poly(styrene sulfonate) (PEDOT:PSS), was used to stabilize highly conductive double-walled carbon nanotubes (DWNT) and demonstrate the promise of fully organic composites as thermoelectric materials. This combination of CNT and stabilizer produced metallic electrical conductivity (200,000 S m-1) and power factors (S2σ) within an order of magnitude of commonly used semiconductors (~400 μW m-1 K-2). Electrical conductivity was doubled by stabilizing single-walled carbon nanotubes (SWNT) with PEDOT:PSS in a thin film without the insulating polymer latex. To further demonstrate the tailorability of polymer composites, a dual stabilizer approach using semiconducting and intrinsically conductive stabilizers was used. This approach effectively provided the high electrical conductivity from PEDOT:PSS and the enhanced Seebeck coefficients of TCPP. By using multiple stabilizers for CNTs within the same composite, power factors among the highest reported for fully organic composites are achieved (~500 μW m-1 K-2). These water-based, flexible composites are becoming real competition as their conversion efficiencies, when normalized by density, are similar to commonly used semiconductors.

Thesis (M.S.)--Ohio University, March, 2004. / Title from PDF t.p. Includes bibliographical references (leaves 129-131).

Thesis (M.S.)--Rochester Institute of Technology, 1994. / Typescript. Includes bibliographical references (leaves 234-235).

Thesis (M.S. in Mechanical Engineering)--Vanderbilt University, Aug. 2005. / Title from title screen. Includes bibliographical references.

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.

This project deals with design of universal system for temperature stabilization using a Peltier device, controlled by microcontroller. The result of this work is an autonomous equipment with automatic tuning of regulation constants, calculation of temperature stabilization limits, possibility of setting required modes and with interface for connection to PC. The regulator stabilise temperature with an accuracy of 0,1 °C within the range of temperature from 0 to 60 °C.

With improvements of thermoelectric materials leading to higher figures of merit, interest has been developed in a broad spectrum of applications. In this study, the thermal performance of a solar-driven thermoelectric (TE) generator was examined by computer simulation and analytical formulations. The hot junction of the disk-shaped TE module is heated by a conical-shaped solar concentrator reflecting rays onto a cylindrical inner electrode. Controllable cooling water flow cools the outer P ΓÇô N junctions to establish the necessary thermal potential for electric generation. Desired power output can be obtained from a number of TE modules in series and parallel. The computer program was used to examine periodic constant flow rate of the cooling water. It was found that the constant flow rate operation yielded the highest time-integrated TE thermal efficiency. Other parametrical studies performed include the height of copper rod, the ratio of outer to inner diameters of the disks, the thickness of the disks, the solar influx and the heat transfer coefficient between cooling water and the modules. The computer and analytic results on these studies show similar behaviors. It was found that the efficiency of the solar thermoelectric cogenerator ranges from 1.5 to 5.0 percent which is considerably lower than a photovoltaic system.

Growing concerns regarding climate change, the increase in demand for energy and the efficient utilization of energy have become of major interest in applications of heating and power generation. A large portion of the energy input to these applications is lost, due to their typical inefficiencies, in the form of waste thermal energy which, if captured and utilized, can offer an abundant source of energy for electricity generation and heating purposes. The use of thermoelectric generators (TEGs) of different designs in waste heat recovery applications has been pursued over the past few decades as the generation of electrical power using TEGs has become viable compared to other conventional systems at low temperatures. This study focuses on the implementation of an annular design for integrated TEG modules in a heat exchanger device for waste heat recovery and the investigation of the effect of different TEG design parameters on the device performance. The integration of the annular TEG design in the heat exchanger was studied using a developed numerical model to investigate the interaction between the heat transfer and the thermoelectric effects and evaluate the performance under specific operating conditions. The heat transferred from the exhaust to the water flow through the TEGs was modelled using a thermal network for the heat flow, coupled with an electrical circuit for the power output. The model was validated using experimental results of the first generation of the TEG device with good agreement (3-6 %) between the predicted and measured performance results: power output, efficiency and the exhaust and water flow temperatures. With the objectives of maximizing the power output and improving the power characteristics, a half annular TEG design was presented. It was able to generate the same power output with double the voltage and half the current, thus improved the power characteristics required for functional operation, compared to the full annular design. The effect of the annular TEG design dimensions on the device performance was studied for a multi-row heat exchanger using the numerical model. The results showed that a maximum power output can be obtained at optimum TEG diameter ratio and thickness. In addition, the TEGs performance was studied under different electrical connection configurations in series and in parallel. The series connection between TEG rows showed better power output characteristics with lower current output, minimal power loss due to temperature mismatch and higher voltage output. The effect of heat exchanger design considerations such as the axial heat conduction was also investigated using the numerical model and the results were compared with an ANSYS model for verification. Good agreement was demonstrated and the results showed a decrease in the total power output of multiple TEG rows when axial conduction of heat was allowed between the TEGs hot-side surfaces in the heat exchanger. A dimensions map was created for annular TEGs integrated in a heat exchanger combining the effects of varying the TEG diameter ratio and thickness on the power output. Further, a dimensionless design parameter (β) was introduced to locate the maximum power region on the map. Using the map as a design tool, the dimensions of the annular TEG modules in a heat exchanger were determined to maximize the power output under a typical current output constraint in order to improve the system power characteristics. Using the map, it was shown that the current output could be reduced by 46 % of its value at the maximum power available on the map and the resultant power output could be maintained at 98 % of its maximum value. This also resulted in a 48% reduction in the TEG material volume and an increased voltage output of the device. As a result, the power output was maximized, the current output was limited to reduce losses in the power management system components and material volume reduction was achieved which would increase the device power density and reduce its overall cost. / Thesis / Master of Applied Science (MASc)

A large amount of thermal energy is being wasted every day from domestic and industrial usages such as home appliance and heating system, vehicle exhaust and many industrial processes including melting, refining, annealing, and forming. However, there were a significant impact on the environment and economy if one could recover this waste energy and convert it to useful energy for the industrial or domestic consumptions. Thermoelectric (TE) generators as a direct heat conversion technology are a promising approach to scavenge waste heat and to significantly improve the overall energy efficiency of energy-intensive industries. However, the energy conversion efficiency of current thermoelectric materials is insufficient to make the technology economically viable. In this study, we investigated two potential thermoelectric materials, Co4Ge6Te6 skutterudite and SnTe, in order to enhance their TE properties. Among all the state-of-the-art thermoelectric materials, skutterudites have been found to be brilliant candidates for thermoelectric applications due to their remarkable electronic transport properties. Ternary skutterudites are isostructural to their binary analogues with the advantage of lower lattice thermal conductivity than the unfilled binary skutterudites due to the increased structural complexity. Here, in order to further understand this system and its thermoelectric properties, polycrystalline Co4Ge6Te6 (CGT) was investigated as a model ternary skutterudite material. Spark plasma sintering (SPS) was used to solidify the samples. The microstructure, phase stability, compositional homogeneity and thermoelectric behaviour of the sintered samples under SPS condition were investigated. We found that SPS can form different crystalline phases due to the migration of highly mobile species inside the sample due to the applied electrical current. There were significant inconsistencies in the physical properties of the samples. We also realized that Sb-doped CGT samples yielded to the highest power factor reported for the CGT derivatives so far. Moreover, recent environmental regulations have restricted the use of lead in many real-life applications including thermoelectric power generators. SnTe as a lead-free chalcogenide-based material can be a promising TE candidate to attain high thermoelectric performance. However, the main issue with SnTe is high intrinsic Sn vacancies leading to low Seebeck coefficient and high electrical thermal conductivity. In this regard, we aimed to introduce different metallic species into the SnTe samples (Sn1-xAxTe, A= Co, Ni, Zn, Ge, and x = 0.01, 0.03, 0.05) to enhance their TE performance. Each metallic species presented different solubility and microstructural impact on the main SnTe phase and therefore caused variations in physical properties. Ge-doped samples had more uniform microstructures with a very few Ge-rich regions, which implies higher Ge solubility in SnTe matrix. The existence of impurity phases in the Co-, Ni-, Zn-doped samples yields lower lattice thermal conductivities without deterioration in charge transport properties, leading to higher ZT values relative to the pristine SnTe sample. Microhardness of the doped samples is also improved due to the crack growth suppression and crack branching. / Thesis / Master of Science (MSc)

Advances in the field of semiconductor physics have allowed for rapid development of new, more powerful devices. The new fabrication techniques allow for reductions in device geometry, increasing the possible wafer packing density. The increased output power comes with the price of excessive heat generation, the removal of which proves problematic at such scales for conventional cooling systems. Consequently, there is a rising demand for new cooling systems, preferably those that do not add large amount of additional bulk to the system. One promising system is the thermoelectric (TE) cooler which is small enough to be integrated onto the device wafer. Unlike more traditional gas and liquid coolers, TE coolers do not require moving parts or external liquid reservoirs, relying only on the flow of electrons to transport heat energy away from the device. Although TE cooling provides a neat solution for the extraction of heat from micron scale devices, it can normally only produce small amounts of cooling of 1-2 Kelvin, limiting its application to low power devices. This research aimed to find ways to enhance the performance of the TE cooler using detailed simulation analysis. For this, a self consistent, semi-classical, ensemble Monte Carlo model was designed to investigate the operation of the TE cooler at a higher level than would be possible with experimental measurements alone. As part of its development, the model was validated on a variety of devices including a Gunn diode and two micro-cooler designs from the literature, one which had been previously simulated and another which had been experimentally analysed. When applied to the TE cooler of focus, novel operational data was obtained and signification improvements in cooling power were found with only minor alterations to the device structure and without need for an increase in volume.