A cold fiber solid phase microextraction device was designed and constructed based on the use of a thermoelectric cooler (TEC). A three-stage thermoelectric cooler was used for cooling a copper rod coated with a polydimethylsiloxane (PDMS) hollow fiber, which served as the SPME fiber. The copper rod was mounted on a commercial SPME plunger and exposed to the cold surface of the TEC, which was enclosed in a small aluminum box. A heat sink and a fan dissipated the generated heat at the hot side of the TEC. By applying an appropriate DC voltage to the TEC, the upper part of the copper rod, which was in contact to the cold side of the TEC, was cooled and the hollow fiber reached a lower temperature through heat transfer. A thermocouple was embedded in the cold side of the TEC for indirect measurement of the fiber temperature. A portable cold fiber SPME device was made by using a car battery as the power supply. The cold fiber SPME device with thermoelectric cooling was applied in quantitative analysis of off-flavors in rice. Hexanal, nonanal, and undecanal were chosen as three test analytes in rice. These analytes were identified according to their retention times and analyzed with a GC/FID instrument. Headspace extraction conditions (i.e. extraction temperature and extraction time) were optimized. Standard addition calibration graphs were obtained at the optimized conditions and the concentrations of the three analytes were calculated. The developed method was compared to a conventional solvent extraction method. The applicability of the portable cold fiber SPME with TEC for field sampling was tested. The effect of cooling on extraction recovery and the reproducibility of extraction were examined for extractions from an n-alkane flow through system. It was found that the extraction recoveries were significantly higher when the fiber was cooled. To further investigate the effect of cooling on the sensitivity of SPME in field sampling, the portable cold fiber SPME was used for extraction of volatile components from living wisteria flowers. Both the number of identified compounds and the related peak areas increased for extractions with cold PDMS fiber relative to without cooling and commercial PDMS and PA fibers. The portable cold fiber SPME device was also used for field sampling of volatile components of living lily-of-the-valley flowers and the extracted compounds were analyzed with GC/MS. The desorption kinetics of hydrophobic organic compounds (HOCs) from environmental solid matrices was investigated using cold fiber SPME with CO2 cooling. Polycyclic aromatic hydrocarbons (PAHs) and selected volatile organic compounds (i.e. toluene, ethylbenzene, o-xylene) were used as test analytes. Sand, silica gel, and clay were used as laboratory model solid matrices and were contaminated by the test analytes. Certified sediments were used as naturally contaminated samples. In this approach, the organic compounds, released from contaminated solid samples at different elevated temperatures, were exhaustively extracted with cold fiber SPME over different extraction times. The extraction data were used to obtain desorption and Arrhenius plots. The rate constants of desorption and activation energies of desorption were measured for each contaminant using these plots. The results were comparable to those reported in the literature.

The performance of a novel micro-thermodielectric power generation device (MTDPG) was investigated in order to determine if thermodielectric power generation can compete with current portable power generation technologies. Thermodielectric power generation is a direct energy conversion technology that converts heat directly into high voltage direct current. It requires dielectric (i.e., capacitive) materials whose charge storing capabilities are a function of temperature. This property is exploited by heating these materials after they are charged; as their temperature increases, their charge storage capability decreases, forcing them to eject a portion of their surface charge to an appropriate electronic storage device. Previously, predicting the performance of a thermodielectric power generator was hindered by a poor understanding of the materials thermodynamic properties and the affect unsteady heat transfer losses have on system performance. In order to improve predictive capabilities in this study, a thermodielectric equation of state was developed that describes the relationship between the applied electric field, the surface charge stored by the thermodielectric material, and its temperature. This state equation was then used to derive expressions for the material's thermodynamic states (internal energy, entropy), which were subsequently used to determine the optimum material properties for power generation. Next, a numerical simulation code was developed to determine the heat transfer capabilities of a micro-scale parallel plate heat recuperator (MPPHR), a device designed specifically to a) provide the unsteady heating and cooling necessary for thermodielectric power generation and b) minimize the unsteady heat transfer losses of the system. The previously derived thermodynamic equations were then incorporated into the numerical simulation code, creating a tool capable of determining the thermodynamic performance of an MTDPG, in terms of the thermal efficiency, percent Carnot efficiency, and energy/power density, when the material properties and the operating regime of the MPPHR were varied. The performance of the MTDPG was optimized for an operating temperature range of 300 500 K. The optimization predicted that the MTDPG could provide a thermal efficiency of 29.7 percent. This corresponds to 74.2 percent of the Carnot efficiency. The power density of this MTDPG depends on the operating frequency and can exceed 1,000,000 W/m3.

Tez (Yüksek Lisans) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, Elektronik-Bilgisayar Eğitimi Anabilim Dalı, 2008. / Kaynakça var.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Includes abstract. Title from first page of PDF file (viewed March 12, 2010). Available via ProQuest Digital Dissertations. Includes bibliographical references (p. 117-136). Also issued in print.

Nanoparticle and nanoparticulate films have been grown by a unique approach combining a microwave and nebulized droplets where the concentration and thus the resulting particle size can be controlled. The goal of such a scalable approach was to achieve it with the least number of steps, and without using expensive high purity chemicals or the precautions necessary to work with such chemicals. This approach was developed as a result of first using a laser unsuccessfully to achieve the desired films and particles. Some problems with the laser approach for growing desired films were solved by substituting the higher energy microwave for the laser. Additionally, several materials were first attempted to be grown with the laser and the microwave, and what was learned as result of failures was implemented to successfully demonstrate the technique. The microwave system was characterized by using direct temperature measurements and models. Where possible, the temperature of deposition was determined using thermocouples. In the region of the waveguide, the elemental spectral lines were measured, and the temperature was calculated from measured spectral peaks. From the determined temperature, a diffusion calculation modeled the rate of heat transfer to the nebulized droplets. The result of the diffusion calculations explained the reason for the failure of the laser technique, and success for the microwave technique for simple chemistries. The microwave assisted spray pyrolysis (MPAS) technique was used to grow ZnO nanoparticles of varying size. The properties of the different size particles was measured by optical spectroscopy and magnetic measurements and was correlated to the defects created. The MPAS technique was used to grow films of Ca3Co4O9 containing varying sizes of nanoparticulates. The resistivity, Seebeck coefficient, and the power factor (PF) measured in the temperature range of 300-700 K for films grown by MPAS process with varying concentrations of calcium and cobalt chlorides are presented. Films with larger nanoparticles showed a trend toward higher PFs than those with smaller nanoparticles. Films with PFs as high as 220 μW/mK 2 were observed in films containing larger nanoparticles.

The energy-water nexus represents a complex system of correlated resources, with particular relevance to thermoelectric power plants. Since thermoelectric power plants typically depend on water for cooling, these facilities are prone to water-related challenges. At the same time, large water withdrawals for power plants can adversely impact other water users in a watershed. This work aims to evaluate water impacts on Texas power plant operations and the associated effects these power plants have on water availability. An evaluation of the water impacts on power generation in Texas was completed through four analyses: 1) water availability effects of changing cooling technologies, 2) economic value of drought resiliency through use of alternative cooling technologies, 3) dynamic impacts of reservoir storage on power generation operations, and 4) potential for reclaimed water as a cooling source. Based on the results of these analyses, the following general conclusions were drawn [bulleted list]: [bullet] Use of alternative cooling technologies decreases water withdrawals at the expense of additional energy and water consumption. However, the reduced withdrawals for power plants leaves more water in the stream for other water users, including instream flows. [bullet] Alternative cooling technologies incur additional capital costs, but gain value from reduced water withdrawals. The lower withdrawal requirements make such facilities more resilient to drought, which can have economic value from additional generation during possible drought-related curtailment or suspension. [bullet] Changing surface water reservoir storage at power plants has dynamic impacts on power generation operations, as well as other users in a river basin. Generally, decreasing power plant reservoir storage benefits other users in the basin. Instances arise where both beneficial and detrimental impacts are also observed. [bullet] Reclaimed water can be a technologically and economically feasible cooling source for many existing power plants. The future suitability of using reclaimed water for power plant cooling depends on water pipeline construction costs, reclaimed water flow, and water stress [end of bulleted list]. These general conclusions, along with further details, provide insight into the relationship between water resources and thermoelectric power plants. As resources become increasingly strained, understanding and responding to tradeoffs within the energy-water nexus, through such analyses, might become imperative for sustainable resource management. / text

Thermoelectric (TE) materials, which can convert temperature gradients directly into electricity and vice versa, have received renewed interest for waste heat recovery and refrigeration applications. Higher manganese silicides (HMS) are promising p-type TE materials due to the abundance of the constituent elements, environmental friendliness, and good chemical stability. The objective of this dissertation is to establish a better understanding of the structure-TE properties relationship of HMS with a complex Nowotny chimney ladder structure. The focus of this work is on the investigations of the phonon dispersion of HMS crystals and the effects of chemical doping and nanostructuring on the TE properties of polycrystalline HMS. HMS crystals have been synthesized by the Bridgeman method for inelastic neutron scattering measurements of the phonon dispersion. In conjunction with density functional theory calculations, the results clearly show the presence of numerous low-lying optical phonon branches, especially an unusually low-energy optical phonon polarization associated with the twisting motions of the Si helical ladders in the Mn chimneys. The obtained phonon dispersion can be used to explain the low and anisotropic thermal conductivity of HMS crystals. (Al,Ge) double doping was found to be effective in modifying the electrical properties of HMS polycrystals. The peak thermoelectric power factor occurs at an optimized hole concentration of 1.8~2.2×10²¹ cm⁻³ at room temperature. On the other hand, Re substitution can suppress the lattice thermal conductivity to approach the calculated minimum value corresponding to the amorphous limit. Meanwhile, the thermoelectric power factor does not markedly change at low Re content of x ≤ 0.04 although it drops considerably with increasing Re content. Hence, the peak ZT has been improved to ~0.6 in both systems. The effects of nanostructuring on the TE properties have been studied in the cold-pressed samples and ball-milled samples. The thermal conductivity was reduced remarkably by decreasing the grain size. It is found that the grain size effects are more significant at low temperature. However, it is difficult to reduce the grain size to less than 50 nm without the formation of impurity phases by ball milling. These facts limit the ZT enhancement of the nanostructured HMS at high temperatures in this study. / text

The state of the art in artificial micro self assembly concepts are reviewed. The history of assembly is presented with a comparison to macro assembly, which has been widely studied, and micro self assembly. Criteria were developed and tested to show that macro assembly is more complex in ways that micro self assembly is not. Self assembly requirements for successful and complex self assembly, which evolved from the macro and micro comparison, are also established and tested. A method to assemble complex structures in the micro scale is proposed and demonstrated at the meso scale. The basic concepts of self assembly and a novel approach to complex multi layer self assembly is analyzed.

Transport through nanostructures is studied at the many-body level using exact diagonalization and nonequilibrium Green's functions. Organic molecular junctions are a particular focus because of their technological promise. Work is presented regarding: (1) A π-electron model of organic molecular junctions developed using effective field theory; (2) series transmission and transmission node structure in interacting systems; (3) the effect of interactions on quantum interference and thermoelectricity in polycyclic junctions; and (4) nanoscale transport calculations using self-consistent statistical ensembles.

Computers and their constituent electronics continue to shrink. The same amount of work can be done with increasingly smaller and cheaper components that need less power to function than before. In wireless sensor networks, the energy needed by one sensor node borders the amount that is already present in its immediate surroundings. Equipping the electronics with a micro generator or energy harvester gives the possibility that it can become self-sufficient in energy. In this thesis two kinds of energy harvesters are investigated. One absorbs vibrations and converts them into electricity by means of piezo-electricity. The other converts heat flow through a semiconductor to electricity, utilizing a thermoelectric effect. Principles governing the performance, actual performance of off-the-shelf components and design considerations of the energy harvester have been treated. The thermoelectric micro generator has been measured to output power at 2.7 mW and 20°C with a load of 10 W. The piezoelectric micro generator has been measured to output power at 2.3 mW at 56.1 Hz, with a mechanical trim weight and a load of 565 W. In these conditions the power density of the generators lies between 2-3 W/m2.