The Effects of Using Some Common White Pigments on Thermal and Aesthetic Performances of Pigmented Coatings

Abstract

A coated surface with high reflectance in the near infrared (NIR) region and low reflectance in the visible (VIS) region can both stay cool in the sun and retain its appearance by reducing the glare of reflected sunlight. To design such coatings, an optimization method that embraces both thermal and aesthetic effects is introduced. White pigments are widely used in designing cool coatings due to their relatively high reflectance of sunlight. However, using white pigments may produce glare, which can cause visual discomfort. It is possible to control these effects by controlling the size of pigment particles, volume concentration of pigments and coating thickness. Among the various white pigments that are available, we chose titanium dioxide, zinc oxide and alumina for this study. Radiative heat transfer in an anisotropic scattering, monodisperse pigmented layer was analyzed using the radiation element method by ray emission model (REM²). Both collimated and diffuse solar irradiations were considered. The CIE (International Commission on Illumination) colorimetric system was used for color analysis. Finally, the optimum values of particle size, volume fraction of pigment, and coating thickness were obtained and compared for the three mentioned pigments.