High-Efficiency Selective Solar Absorber from Nanostructured Carbonized Plant Raw Material
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 4, July, 2020
HIGH-EFFICIENCY SELECTIVE SOLAR ABSORBER FROM NANOSTRUCTURED CARBONIZED PLANT RAW MATERIAL N. G. Prikhod′ko,a,b G. T. Smagulova,a,c M. Nazhipkyzy,a,c N. B. Rakhymzhan,a T. S. Temirgalieva,a,c B. T. Lesbaev,a,c A. A. Zakhidov,d and Z. A. Mansurova,c
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The results of investigation into the absorptivity of carbonized rice-husk plant material with regard to solar radiation have been given. It has been shown that an absorber based on leached carbonized rice husk has higher solar absorptivity than an absorber based on carbonized apricot pits with an Apricus coating and an absorber based on a commercial Chinese-made coating. The results of investigation into the physical and chemical properties of carbonized rice husk have been presented. It has been shown that the carbon content in the initial unleached rice husk powder is 82.3%, and after leaching, the percentage of carbon rises up to 93.3%. Based on the results of a BET (Brunauer–Emmet–Teller) analysis, it has been established that leached rice husk has a more developed specific surface (447–641 m2/g) and a higher specific volume of pores (0.27–0.392 cm2/g) than unleached rice husk (127–160 m2/g and 0.054–0.127 cm2/g respectively). The advantage of the considered plant-based carbon materials compared to the exiting coatings lies in their porous structure. Cavities are known to be a model of a blackbody, which is a decisive factor in using a material as an absorber, and, simultaneously, a porous structure has a heatinsulating property. Keywords: carbonized rice husk, solar absorber, carbon maternal, solar collector, efficiency of absorption of solar energy. Introduction. The main element of a solar collector determining its cost and operating efficiency is the material of the absorber, which must have a selective property: to absorb in a broad wavelength range and, in practice, not radiate in the infrared range [1, 2]. In this case, the absorber material must have a low reflection coefficient in the visible region and a high reflection coefficient in the infrared region, and also minimum heat losses at a corresponding temperature [2–4]. At present, the efficiency of vacuum solar collectors is in the range 70–80%. If we are to use an absorber with increased efficiency of absorption of solar energy compared to the existing absorbers, it is possible to obtain higher heat removal from an absorber surface unit, which will allow a rise in the solar collector efficiency to a value higher than 80%. Selective coatings for solar collectors used at present have a good absorptivity but are quite difficult to manufacture and to apply as a compound on the collector tubes. Therefore, the problem of search for and production of absorbers that would have higher absorptivities in combination with low costs for their manufacture and application on a glass surface is still relevant today. Various methods and components capable of raising the efficiency of absorption of solar energy have
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