A novel high-temperature (>700 °C), volumetric receiver with a packed bed of transparent and absorbing spheres

Abstract

The concentrated solar power industry requires high-temperature receivers to push towards advanced power cycles. However, as the outlet temperature of a receiver increases, radiation losses (which are ∝T4) become dominant. In addition, at high temperatures, not many liquid working fluids are suitable. To address these issues, this research proposes an innovative, robust design of a gas-phase cavity receiver which utilises semi-transparent spheres as a volumetric absorption medium. The motivation behind this design is to break the long-standing outlet temperature versus efficiency trade-off by maximising the “volumetric effect” (i.e. obtaining a higher outlet fluid temperature than the receiver's surface temperature). A range of designs were compared (i.e. packed beds of semi-transparent and high-transparency quartz spheres against an opaque bed of ceramic spheres). This study is important because it determines how the volumetric effect modifies the overall receiver efficiency via a holistic metric (proposed herein) which accounts for the optical, thermal, and pumping power efficiencies. Through a detailed ray-tracing analysis and a comprehensive thermal circuit model, this study reveals that a semi-transparent quartz packed bed receiver can have an overall receiver efficiency of around 80% at outlet temperatures above 700 °C. Most significantly, the best proposed design achieved a high value for the elusive volumetric effect (e.g. a maximum index value of 1.45). Based upon these results, the authors can conclude that these packed bed designs represent a promising new pathway towards reliable and cost-effective high-temperature and high-efficiency receivers which can be implemented into advanced, high-temperature power cycles.