Thermal Efficiency of a New Prototype of Evacuated Tube Collector using Sn-Al2O3 as a Selective Solar Absorber

Warisa WAMAE; Tawat SURIWONG; Thotsaphon THRERUJIRAPAPONG

doi:10.48048/wjst.2018.5965

Authors

Warisa WAMAE School of Renewable Energy and Smart Grid Technology, Naresuan University, Phitsanulok 65000
Tawat SURIWONG School of Renewable Energy and Smart Grid Technology, Naresuan University, Phitsanulok 65000
Thotsaphon THRERUJIRAPAPONG Department of Materials and Production Technology Engineering, Faculty of Engineering, King Mongkut's University of Technology North Bangkok, Bangkok 10800

DOI:

https://doi.org/10.48048/wjst.2018.5965

Keywords:

Evacuated tube collector, Selective solar absorber, Anodization, Absorptance, Thermal emittance

Abstract

Three tin pigmented aluminium oxide (Sn-Al₂O₃)films were prepared with different tin content using an anodization process, which is applied as a selective solar absorber in a new prototype of evacuated tube collector (ETC). The morphology and distribution of elements on the coatings were characterized using a Scanning Electron Microscope (SEM) equipped with an Energy Dispersive X-ray (EDX) analyzer. The spectrally selective properties, defined as the ratio of solar absorptance (α_sol) to thermal emittance (ε_therm) were examined. In order to investigate the thermal performance of ETC using Sn-Al₂O₃ on an Al fin as a solar receiver, thermal efficiency (η) of the ETC was collected under steady-state conditions, as prescribed by ISO 9806-1 standard. The results, of the Sn-Al₂O₃coatings reached a darker black colour with an increase in the colouring time. The samples were composed of different contents of Sn in the Al₂O₃ layer. The solar selectivity (α_sol/ε_therm) significantly increased with the increases in Sn content. The maximum thermal efficiency (η_max) of the ETC under the nearly constant heat loss coefficient (U_L), was obviously increased with the increasing Sn content. Therefore, the Sn-Al₂O₃ with different Sn contents is a good candidate for selective solar absorbers in a new prototype of ETC.

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