Experimentally validated pore-scale numerical analysis for high-temperature (>700°C), high-efficiency (>90%) volumetric solar receivers

Abstract

• Proposes an innovative, high-temperature semi-transparent packed-bed solar receiver. • Hits SunShot target with one of the highest efficiencies, 92% for T outlet ≥ 700 °C. • Develops a 3-D pore-scale model which couples the optical and thermo-fluid analyses. • Minimises reflection loss via an optical baffle and the pore-scale arrangement. • Reports new experimental validation test data for heat transfer in packed bed. Concentrated solar thermal/power (CST/P) systems are evolving to operate at higher temperatures (i.e., above 700 °C) to drive advanced cycles and thermochemical processes. The development of high temperature, high efficiency solar receivers—as the highest temperature component in a CST/P system—represents a critical technical challenge in this evolution. Commercial solar receivers have been limited to operation below 600 °C due to (1) the historic trade-off between operation temperature and efficiency, and (2) the operating temperature limits of the liquid conventional heat transfer fluids. This paper investigates a gas-phase, packed-bed receiver, which is capable of addressing these limitations. To date, this novel design has shown promise for this application, but it has only been modelled on the macro-scale (i.e., a 1-D model). To obtain a more detailed understanding of this type of receiver, this paper presents the results of a novel 3-D pore-scale analysis of the proposed receiver to characterise the optical-thermo-fluid behaviour. To ensure the validity of this approach, experimental tests were conducted for a complex packed bed of spheres. The 3-D pore-scale analysis enables the development of innovative mechanisms to reduce radiosity losses. It also provides a deeper level of insight regarding the stagnation pressure loss caused by the inlet air-jet flows. The final results demonstrated that the pore-scale modifications of the design can yield an optimised packed-bed receiver with a maximum efficiency of ∼ 92 % (for a hot air outlet temperature well above 700 °C). This optimised receiver design represents a new pathway towards high-temperature solar receivers, which can operate at very high efficiency, to enable CST/P systems to utilise advanced power cycles.