Thermal performance enhancement of a closed porous solar receiver using a morning-glory-inspired cavity and an ellipsoidal window

A morning-glory-inspired porous solar receiver with an ellipsoidal window is proposed to reduce peak temperatures of the porous absorber and the optical window while enhancing optical-thermal conversion efficiency. Coupled radiative-convective heat transfer within the receiver is investigated numerically using the Monte Carlo ray-tracing method with a local thermal non-equilibrium model. The numerical model's reliability is further validated through indoor experiments. An orthogonal experimental design evaluates how key geometric parameters of the biomimetic cavity affect receiver performance. Results show that the opening radius of the biomimetic cavity is the primary factor affecting thermal efficiency, whereas cavity depth primarily determines the porous absorber's peak temperature. At a mass flow rate of 5 g/s, the combined effects of the biomimetic cavity and the ellipsoidal window reduce the peak temperatures of the porous absorber and the glass window by 32.33% and 33.22%, respectively. Meanwhile, optical, thermal, and optical-thermal efficiencies increase by 1.78, 11.87, and 11.83 percentage points, respectively, compared with the flat-window receiver. In addition, within the tested range, optical losses consistently dominated in the EW-BCPSR, whereas for the other three absorbers, energy losses were alternately dominated by optical and infrared radiation losses. These findings demonstrate that integrating a morning-glory-inspired cavity with an ellipsoidal window is an effective strategy for improving the efficiency and thermal safety of closed receivers.