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A supercritical carbon dioxide (sCO 2) Brayton cycle is an emerging high energydensity cycle undergoing extensive research due to the appealing thermo-physical properties of sCO 2 and single phase operation. Development of a solar receiver capable of delivering sCO 2 at 20 MPa and 700 o C is required for implementation of the high efficiency (~50 %) solar powered sCO 2 Brayton cycle. In this work, extensive candidate materials are review along with tube size optimization using the ASME Boiler and Pressure Vessel Code. Temperature and pressure distribution obtained from the thermal-fluid modeling (presented in a complementary publication) are used to evaluate the thermal and mechanical stresses along with detailed creep-fatigue analysis of the tubes. The resulting body stresses were used to approximate the lifetime performance of the receiver tubes. A cyclic loading analysis is performed by coupling the Strain-Life approach and the Larson-Miller creep model. The structural integrity of the receiver was examined and it was found that the stresses can be withstood by specific tubes, determined by a parametric geometric analysis. The creepfatigue analysis displayed the damage accumulation due to cycling and the permanent deformation on the tubes showed that the tubes can operate for the full lifetime of the receiver.

Direct-absorption solid particle receivers are theoretically capable of yielding temperatures in excess of 1000°C, which enables higher efficiency power cycles and lower thermal storage costs. This paper presents rigorous CFD simulations of alternative solid particle receiver designs with recirculation to help identify optimal configurations that maximize the receiver thermal efficiency. The alternative receiver designs considered are a north-facing cavity receiver and a face-down surround-field cavity receiver. The CFD simulations model incident solar radiation from a heliostat field as a boundary condition on the model domain. The CFD simulations also couple convective flow with the thermal and discrete-phase (particle) solutions, which in turn affects absorption of incident solar radiation and thermal re-radiation within the receiver. The receivers are optimized to yield comparable particle temperatures at the outlets of 750–850°C, heated from an injection temperature of 300°C, and are compared on the basis of thermal efficiency. The CFD simulations yielded thermal efficiencies of the north-facing receiver at 72.3% (losses were 6.5% radiative and 20.9% convective) and the face-down receiver at 78.9% (losses were 11.4% radiative and 9.6% convective) at solar noon on March 22. Ongoing efforts are focused on reducing convective and radiative losses from both receiver configurations.