Opto-thermo-hydraulic and exergy performance of a serpentine-baffled receiver with radiation shields in a hybrid Fresnel-dish concentrator

This study presents a serpentine-baffled receiver with two conical radiation shields for a hybrid parabolic dish concentrator (PDC) and Fresnel lens (FRL) system. It is heated on both outer faces by the FRL above and the PDC below. A coupled Monte Carlo ray tracing and computational fluid dynamics (MCRT-CFD) framework, benchmarked against experimental data with mean absolute percentage errors (MAPE) below 1.12%, resolves the nonuniform flux on both faces and couples it to the conjugate heat transfer, laminar flow, and exergy calculations. At the exact focal point, the maximum wall temperature reaches 1374.5 °C, while at R PDC = 0.9, the receiver-to-dish distance over the focal distance, with a shield inclination angle θ shield = 60°, the same power spreads over a broad annulus and the peak drops to a safe 277.4 °C, giving average daily thermal and exergy efficiencies of 73.4% and 2.74%. The shields return part of the spilled radiation to the absorbing faces, raising the intercepted power from 71.7% to 81.1% on the PDC side and from 68.0% to 82.5% on the FRL side, and improving the efficiencies from 69.9% and 2.47% without shields. The baffles impose a negligible hydraulic penalty, with Reynolds numbers ranging from 468 to 937. The exergy efficiency stays low because internal destruction takes 94.0–97.9% of the incident solar exergy at peak irradiation. Under the same geometry, flow rate, and daily conditions, the thermal and exergy efficiencies for solar air heating fall to 17.7% and 0.66%, showing far better performance with water than with air.