Date of Award
Master of Science
This thesis explored the development of isothermal selective emitters for harvesting thermal energy to be used in conjunction with photovoltaic cells. The selective emitters were Erbium doped Titania nanofibers and Erbium and Yttrium doped Titania nanofibers that may be used with a Gallium Antimonide photovoltaic cell. The ultimate aim of this research was to develop Erbium doped Yttrium Titanate nanofibers. This research is of importance in recovering heat from a number of resources including power plant boilers. The thermal energy lost in the boilers can be as high as 20% of the input fuel energy and a recovery of this energy would boost the thermal performance of the power plants. It has been observed that the temperatures of the flue gas reaching the heat recovery region may be higher than 1600K and the radiation and convective losses in the burner occurs at even higher temperatures. Thermophotovoltaics (TPV) offer a solution in terms of converting the thermal energy to electricity without any moving parts. The efficiencies of conventional TPVs are very small (10 - 20%) and thus not a solution as the primary electric generator. However, in the field of the harvesting of waste energy, TPVs have tremendous potential. In order to improve efficiencies, Erbia (which can absorb thermal energy and convert it to electromagnetic radiation with a narrow wavelength spectrum with mean wavelength of 1500nm) can be used as a selective emitter with GaSb PV cells (which have its maximum efficiency in the same wavelength range) as the collector. In order to further improve its performance, the Erbia was proposed to be supported by Titania, which is transparent to IR in this range. However, past research has shown that the Erbia doped Titania nanofibers essentially have Erbium in the form of pyrochlore Erbium Titanate. Thus the research focused on a way to synthesize ErxY2-xTi2O7 pyrochlore structure to act as the selective emitter. The self-supporting composite was designed to be nanostructured to ensure isothermal operation and a high surface to volume ratio to minimize re-adsorption and to have a compact design. The nanofiber emitters were prepared by electrospinning. This thesis demonstrated a synthesis procedure of optically selective nano-composites using electrospinning.
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