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Description
The two ways to produce electricity using solar radiation are (1) direct, by the use of photovoltaic cells or (2) indirect with an intermediate step of production of solar thermal energy. Solar thermal energy is being produced by solar power plants, which consist of a power tower with a central solar receiver on top where concentrated solar radiation coming from a heliostat field is reflected, absorbed and later transformed into electricity. The work presented in this thesis contributes to the design of a prototype for such a central solar receiver called the small particle solar receiver. It is part of a larger project and builds on an older design for the small particle heat exchange receiver first conceived 30 years ago. This thesis has the main goal of giving calculations and a feasible design for a much larger, pressurized, more efficient version of the above-mentioned solar receiver. The theoretical base comprises the previously published literature on the subject, as well as an investigation of similar products or products that share one or more features with the concept developed in this research. The methodology includes the study of theory of thin shells of revolution and follows the logical steps of a traditional design process. The techniques include finite element analysis of the model, structural optimization and other relevant studies such as failure theories and the study of the ASME Boiler and Pressure Vessel Code. Following this research, it is shown how a final, feasible and efficient design can be built on an initial simple concept of a pressure vessel that is 3 meters in diameter and 5 meters deep with windows on the end exposed to solar radiation, called the aperture structure. Each individual window mounts in its own special flange welded onto the aperture porthole and its own secondary concentrator is also mounted onto the flange. The secondary concentrators are mirrors that redirect scattered and lost sunlight into the receiver through the window. It is suggested that they are made out of highly reflective aluminum. Stainless and carbon steels were analyzed and the final product was suggested to be an austenitic stainless steel pressure vessel with custom ellipsoidal heads and with 6 same-size fused silica windows mounted on the aperture head. The presence of portholes on the aperture structure increases the maximum stress concentration by 167%. Several thermal and structural analyses were performed on the receiver model for different work conditions. The receiver walls were calculated to be a minimum of 1.7 cm for the ideal work conditions of 5 bar pressure and 100 - 400 °C wall temperature and 2.7 cm thick for 8 bar pressure and the same wall temperature. The window calculations showed that a theoretical minimum of 0.75 cm thickness is necessary for the spherical cap profile and 0.2 cm for a custom designed ellipsoidal shape for temperatures as high as 800 °C and 5 bar pressure.
