Abstract
A novel approach for fabricating selective absorbing coatings based on carbon nanotubes (CNTs) for mid-temperature solar–thermal application is presented. The developed formulations are dispersions of CNTs in water or solvents. Being coated on stainless steel (SS) by spraying, these formulations provide good characteristics of solar absorptance. The effect of CNT concentration and the type of the binder and its ratios to the CNT were investigated. Coatings based on water dispersions give higher adsorption, but solvent-based coatings enable achieving lower emittance. Interestingly, the binder was found to be responsible for the high emittance, yet, it is essential for obtaining good adhesion to the SS substrate. The best performance of the coatings requires adjusting the concentration of the CNTs and their ratio to the binder to obtain the highest absorptance with excellent adhesion; high absorptance is obtained at high CNT concentration, while good adhesion requires a minimum ratio between the binder/CNT; however, increasing the binder concentration increases the emissivity. The best coatings have an absorptance of ca. 90% with an emittance of ca. 0.3 and excellent adhesion to stainless steel.
Highlights
Solar energy conversion by concentrated solar power (CSP) systems is a leading technology in renewable energies
Raiah et al reported that imidazolium-based ionic liquids with a long hydrocarbon chain enable high concentration dispersion of double-walled carbon nanotubes (DWCNTs) in water, having a low viscosity [23]
CNT coatings were deposited on aluminum and Inconel substrates from solvent-based dispersions [27,28]
Summary
Solar energy conversion by concentrated solar power (CSP) systems is a leading technology in renewable energies. Coatings 2020, 10, 1101 good light absorption and anti-reflective performance, but its production requires unique equipment and, specific conditions are required for chemical vapor deposition (CVD), such as high temperature and pressure. This process is expensive and has several drawbacks, including limited type substrates, small collector area, and poor adhesion to the substrate. The coating showed high solar selective properties with solar absorptance and thermal emittance reaching 0.964 and 0.124, respectively. Raiah et al reported that imidazolium-based ionic liquids with a long hydrocarbon chain enable high concentration dispersion of double-walled carbon nanotubes (DWCNTs) in water, having a low viscosity [23]. We studied the effect of CNTs and the binder type and their concentrations on the absorptance, emittance, and adhesion of the thin coatings
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