Experimental testing of a solar air cavity-receiver with reticulated porous ceramic absorbers for thermal processing at above 1000 °C

Abstract

Concentrated solar energy can be used as the source of high-temperature heat for industrial processes, but the challenge is to design a solar receiver that can effect such a thermal conversion efficiently. This study reports on the engineering design and experimental testing of a 5 kW solar cavity-receiver containing a reticulated porous ceramic (RPC) structure that can absorb high-flux radiation volumetrically and heat up, by convection, an air flow serving as the heat transfer fluid. The thermal performance, characterized by the thermal efficiency and the air outlet temperature, was determined experimentally for four parameters, namely: RPC material (silicon-infused silicon carbide or SiSiC, alumina, and ceria), mean pore size (range 0.8–2.5 mm, corresponding to 10–30 pores per inch or PPI, at 0.90 porosity), solar concentration ratio (range 1965–3900 suns over a 4 cm-diameter cavity aperture, supplied by a high-flux solar simulator), and air mass flow rate (range 2–10 kg/h). Thermal efficiencies between 0.22 and 0.69 were obtained at steady-state air outlet temperatures ranging from 1160 to 450 °C. Larger pores enhance heat transfer while variable porosity across the RPC can reduce temperature gradients and potentially contribute to the design optimization. The highest efficiency of 0.69 was achieved by the SiSiC 10 PPI cavity at an air outlet temperature of 1133 °C and air mass flow rate of 9.9 kg/h. The solar receiver design proved to deliver a high-temperature air flow (>1000 °C) with a reasonably high thermal efficiency (>0.65).