Optical analysis of a semi-transparent packed bed of spheres for next-generation volumetric solar receivers

Mohammadreza Sedighi, Ricardo Vasquez Padilla, Andrew Rose and Robert A. Taylor

Energy, 2022, vol. 252, issue C

Abstract: Volumetric solar absorbers are attractive for high-temperature concentrating solar applications because they—theoretically—have lower re-radiation losses than surface absorbers since concentrated radiation penetrates their volume. In practice, however, the incident radiation is predominantly absorbed in the top/frontal surfaces of porous and distributed absorber materials. Another challenge with high-temperature absorbers, generally, is the risk of creating hot spots resulting from a non-uniform temperature distribution. To overcome these limitations, this study reports on a semi-transparent absorber design, enabling the peak temperature to occur within the internal volume. Eight different ‘constant-transmittance’ and ‘variable-transmittance’ combinations of transparent/semi-transparent/opaque spheres were packed into a cylindrical cavity and exposed to a solar simulator for a layer-by-layer transmission test. A 3-D ray-tracing model was also developed to further elucidate the relative optical absorption of the cavity walls and spheres. An optimal variable-transmittance design enabled ∼40% of the rays to penetrate to >70% of the absorber's depth, and ∼56% of the total rays were absorbed within the inner volume. Therefore, the optimal design yields uniform absorption, potentially leading to a uniform temperature distribution and a minimisation of thermal emission losses. This study provides the first experimental proof that a semi-transparent packed bed can significantly outperform an opaque design.

Keywords: Volumetric receivers; Semi-transparent absorber; Ray-tracing analysis; Solar simulator; Optical analysis (search for similar items in EconPapers)
Date: 2022
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Citations: View citations in EconPapers (2)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:252:y:2022:i:c:s036054422200888x

DOI: 10.1016/j.energy.2022.123985

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