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    Off-design performance of micro-scale solar Brayton cycle
    Akba, Tufan; Mengüç, Mustafa Pınar; Mengüç, Mustafa Pınar; Önal, Mehmet; Güler, M. G.; Department of Mechanical Engineering
    A novel methodology to design a micro-scale, solar-only Brayton cycle and assess its on- and off-design performance is presented. The method is applied to generate and assess six thermodynamic layouts over a range of solar irradiation levels. All plants have the same on-design requirements to create a baseline to compare their off-design performance. PyCycle, a thermodynamic cycle modeling library to model jet engine performance, is revised to transform the jet engine performance modeling to solar thermal plant performance modeling and used to create a volumetric receiver component. Initially, a gradient-based receiver design methodology is proposed. Even, gradient calculation is the longest step in this methodology and compared to the design of experiment study, 77% fewer designs are iterated in gradient-based optimization. The final result is 6% more efficient receiver design compared to 62% efficient, the best design of experiment result. For an efficient receiver design process, surrogate model algorithms are tested, and using the design of experiment results as training data and surrogate-based design optimizations are performed. Then a response surface surrogate model of the receiver is selected for design optimization to maximize the component-level efficiency. Because of the surrogate simplicity, the optimization process was completed with fewer designs in a shorter time and reached a better objective than the gradient-based optimization of the base model. For the plant design phase, the compressor and turbine maps are scaled for the balance of the plant. Off-design efficiency, mass flow rate, operation range, turbomachinery maps, and maximum power output are presented. Since the methodology can be adapted to all plant sizes, the results are normalized to on-design condition. The outcome of this study demonstrates the impact of the thermodynamic configuration on off-design performance and provides a methodology to design plants that are more robust across a range of solar irradiation levels and can be operated in a more flexible manner. For given design conditions in thesis, the solar radiation operation envelope can be extended 5%, with 6% less mass flow, and operates more efficiently than the benchmark case over 85% of the operating regime.