Effects of coating layer with pigment on the reflectance of external radiation

Abstract

A coating layer with pigment is known to reflect radiation. This knowledge cart be used to reduce the hazard of combustible materials exposed to fire. In order to obtain high reflectivities in the infrared range (0.4-10 mu m), several dielectric pigments, such as titanium dioxide, iron oxide, and silicon, can be synthesized to polymer coatings. In this numerical analysis of radiation, the effects of the dependent scattering, the absorption in a polymeric binder, and the internal interface reflection on the reflectance are elucidated. The finite volume method is used to solve the nongray radiative transfer equation for the absorbing, emitting and highly anisotropic scattering medium. The results show that a coating layer with pigment size in the range 1.5-2.5 mu m and volume fraction in the range 0.1-0.2 is found to be very effective in retarding the surface temperature increase of the substrate. A detailed temperature variation in the semitransparent coating layer and an opaque substrate (polymethyl metacrylate, or PMMA) is also obtained to examine the thermal effects of the coating with a view toward fire safety.