Characterization of a Selective Surface Based on Chromium, Iron and Aluminum Oxides for Application in Solar-Thermal Collectors

Kaio Hemerson Dutra,Diego Caitano Pinho,Francisco Nivaldo Aguiar Freire,Felipe Alves Albuquerque Araújo

doi:10.1590/1980-5373-mr-2021-0489

Kaio Hemerson Dutra, Diego Caitano Pinho + Show 2 more

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https://doi.org/10.1590/1980-5373-mr-2021-0489

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Journal: Materials Research	Publication Date: Jan 1, 2022
Citations: 1	License type: CC BY 4.0

Affiliation: Universidade Federal do Ceará

Abstract

The depletion of conventional energy sources and the concern with the environmental impacts of the use of fossil fuels sparked interest in researching new energy sources and improving existing processes. In this context, the solar energy presents itself as one of the most promising energy sources on the planet, given its wide availability and applicability in thermal processes. However, its use still represents a great technological and economic challenge, because many systems that use this energy still have low efficiency and high cost, which makes them uncompetitive in competition with systems using other energies. With that, the search for the improvement of the processes awakens the researches in more adequate and cheaper materials, which represents a great scientific potential in the evolution of these technologies. Thus, the present work proposes to obtain and analyze a selective surface for applications in solar-thermal collectors, using CRFO (compound formed by chromium and iron oxides), varying the percentage by weight, and then mixed with aluminum oxide. For the tests, an experimental bench was built to simulate a flat plate solar-thermal collector in real operating conditions. Some characterizations were carried out, such as: techniques scanning electron microscopy (SEM), infrared analysis and UV-VIS absorptivity determination, as well as the graphs with surface temperatures and with radiation during the tests in the Sun for the composite (CRFO and aluminum oxide) and for the commercial surface (MRTiNOX). With the results obtained, it was verified in the field test that one of the produced selective surfaces obtained a result of absorptivity of 0.94 and 0.0349 of emissivity, which is close to that of the commercial surface. The results were confirmed in the characterization by UV-VIS, which showed high absorptivity values in the visible light range.

Highlights

The use of solar energy is already a reality, it is an available and abundant energy source, the systems for capturing and transforming this energy are still at an economic disadvantage compared to processes that use conventional energy, which opens up great possibilities for research into the improvement of processes and the use of materials that provide increased efficiency and reduced costs[1]
The average surface temperature 25% AL2O3 + 75% CRFO, shown in Table 2, is very close to the average of the commercial surface MRTiNOX and there is an oscination of these values in Figure 13, which is due to the proximity of the absorbance values and emittance of these two surfaces
The selective surface obtained after performing the tests described in this study, showed satisfactory visual appearance, low thickness deposited with good adhesion to the metal substrate

Summary

Introduction

The use of solar energy is already a reality, it is an available and abundant energy source, the systems for capturing and transforming this energy are still at an economic disadvantage compared to processes that use conventional energy, which opens up great possibilities for research into the improvement of processes and the use of materials that provide increased efficiency and reduced costs[1].In the specific case of solar-thermal energy, solar radiation is absorbed by solar-thermal collectors, these are composed of surfaces capable of absorbing solar radiation and converting it into thermal energy, transporting it by conduction. The absorbed radiation is conducted by the absorbers and can heat working fluids, liquids or gases. Systems using solar-thermal energy can be applied for heating water in homes, hotels and hospitals, other systems can be used for drying and dehydrating fruits in the food industry and desalination of seawater[2]. In practical applications of high efficiency, for the conversion of radiation from the sun into thermal energy, for heating working fluids, solar-theraml collectors are used with coatings on their radiation-receiving surfaces.

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