Abstract
The cavity wall is an important part of a cavity receiver in determining the receiver efficiency. Using solar selective reflector (SSR) materials with low solar absorptivity and high thermal emissivity for the cavity wall design is one efficient way to improve the receiver efficiency. In this work, we present a systematic study of the optical and high-temperature stability performances of six different SSR materials: one refractory ceramic fiber based substrate material (Fiberfrax 140) and five metallic oxide coatings which are prepared by mixing metallic oxide powders of alumina, magnesium oxide and titanium dioxide with commercial inorganic adhesives. The thermal stability was studied by heating up and keeping the six candidate materials in atmospheric conditions at a temperature of 1250 °C for 200 h. The spectrum of hemispherical reflectance in the spectrum band 0.25–25 μm was measured for analyzing the optical performance of the candidate materials. The obtained results show that all the six materials studied have good solar selective reflection characteristics, i.e, low solar absorptivity and relatively high thermal emissivity. Especially, the alumina coated substrate material shows excellent performances both for thermal stability and solar selective reflection. The solar reflectivity can reach 94.6%.
Highlights
Concentrating solar power (CSP) technology, which converts the unlimited solar radiation into heat for electric power generation through different thermal power cycles, is considered to be one of the most promising pathways to the future fossil fuel free society [1,2]
We studied the performance of six different solar se lective reflector (SSR) mate rials: refractory ceramic fiber-based substrate material and five metallic oxide coatings prepared by mixing metallic oxide powders of alumina (Al2O3), magnesium oxide (MgO) and titanium dioxide (TiO2) with commercial inorganic adhesives coated on the substrate material
The colors of the 100% Al2O3 sample (Coating 1) and the Fiberfrax 140 sample (Substrate material) were not affected, while slight color changes could be observed in the other samples
Summary
Concentrating solar power (CSP) technology, which converts the unlimited solar radiation into heat for electric power generation through different thermal power cycles, is considered to be one of the most promising pathways to the future fossil fuel free society [1,2]. By using the ‘cavity effect’ (high absorptivity are achieved by multiple reflections inside the cavity), cavity receivers can achieve higher efficiencies and outlet working fluid temperatures than those receivers with flat absorbers [11]. Unlike the direct absorption receivers, the radiation energy from the concentrated solar irradiation is reflected or re-radiated by the cavity wall before arriving at the absorber in a partially indirect absorption receiver, such as tubular cavity receivers [16,17]. The main strategies for controlling the cavity wall temperature can be achieved by minimizing the ab sorption of the solar flux as well as by maximizing the thermal radiation Both phenomena’s are governed by electromagnetic energy transfer but occur at different spectral bands [22,23]. The optical performance is studied by analyzing the spectral hemispherical reflectance in the spectrum band 0.25–25 μm Al2O3 amongst the six candidate material coatings show the best solar selective reflection characteristics
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