Experimental studies of W-Al 2 O 3 composite thin films for solar absorptance
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ORIGINAL PAPER
Experimental studies of W-Al2O3 composite thin films for solar absorptance M K Thinakallu Ramakrishna Reddy1*
, P V Srihari1, Sahas1 and M S Krupashankara2
1
Department of Mechanical Engineering, R.V. College of Engineering, Bengaluru, India 2
Goa College of Engineering, Farmagudi, Ponda, Goa, India Received: 05 March 2020 / Accepted: 25 August 2020
Abstract: Solar energy has environmental benefits by reducing the pollution and global warming resulting in cleaner water and air. One of the key factors is the absorber surface for entrapping the solar energy that is receiving from solar spectrum under the wavelength range of 250–2500 nm. Generally, absorber surfaces are made of thin films that are mechanically resistant and are common practice in the optical industries. Motivation to carry out this research work is to develop nanocomposite thin films coatings for maximizing solar absorptance and minimizing thermal emittance. W-Al2O3 composite thin films are developed by co-sputtering process upon consideration of process parameters. Design of experiment has been adopted to study the deposition parameters and analysis. Characterization of deposited thin films was performed to determine the solar absorptance and thermal emittance using 410-Solar and ET 100 Emissometer, respectively. It was found that for deposition parameters of DC power 750 W, RF power 1050 W and argon gas flow rate 250 sccm, an absorptance of 0.709 and thermal emittance of 0.175 are observed. From the SEM analysis, the average particle size of alumina is around 0.25 lm. EDAX was performed to determine the material composition of deposited thin films. This type of coatings requires for industries manufacturing solar cooker, solar water heaters and solar driers. Keywords: Solar absorptance; Solar spectrum; Thermal emittance; 410-Solar; ET 100 Emissometer
1. Introduction The rapid depletion of ozone layer due to conventional energy resources has focused scientists toward research on non-conventional energy resources, specifically solar energy. Absorber surface is the main source of solar energy conversion based on the optical properties for efficient conversion of solar energy into heat [1]. The absorber surface contains a thin film sandwiched with base layer and antireflective layer selectively reflecting in thermal spectrum and absorbing in solar spectrum [2]. In order to achieve maximum conversion efficiency, the spectral control of emissivity of surfaces is essential. The efficient solar absorbers are vital for converting solar radiation into heat. Hence, one of the key contributions to the domain is the development of nanocomposite thin films. Nanocomposite thin films consist of composite layer with fraction of
High Metal Volume Fraction (HMVF) and Low Metal Volume Fraction (LMVF) on substrate material. Ni–Al2O3-based composite thin film coatings [3] which developed an absorptance of 0.84–0.91, emittance of 0.05– 0.07 in temperature range of 500–700 °C. NiO polycrystalline films [4] are deposited with different film thicknesse
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