Geometric optimization of a solar tower receiver operating with supercritical CO2 as working fluid

Concentrated solar power (CSP) plants represent a viable technology already operational in several locations worldwide. Among the numerous challenges associated with this technology, the proper design of the receiver is arguably one of the most critical. In that sense, the present study proposes using supercritical carbon dioxide (sCO2) as the working fluid for a cylindrical solar tower receiver. The receiver is modeled at steady state and considers a hybrid formulation that combines a 1-D model for the fluid flow and a 2-D CFD-based model for the conduction heat transfer process within the receiver walls. The analysis parametrically considers the number of plates composing the receiver and the number of channels in each plate, the s-CO2 mass flow rate, and the receiver aspect ratio as independent variables while focusing on the receiver's efficiency as the figure of merit. The analysis also considers two radiation boundary conditions over the receiver surface: (i) an idealized uniformly distributed heat flux and (ii) a real TMY-based spatially distributed radiation heat flux. As expected, the results indicate that the number of plates and the mass flow rate of the cooling fluid highly influence the receiver's efficiency. More interesting, however, is that by assuming a fixed external area for the receiver and parametrically varying the number of plates composing that receiver, it is possible to identify the design that maximizes the receiver's efficiency. The optimal number of plates changes with the receiver height, while the maximized efficiency is lightly sensitive to it. Furthermore, the analysis reveals that the appearance of a maximal value for the receiver's efficiency is associated with a competition between the radiation heat losses and the pumping expenditure needed to move the s-CO2 through the receiver.