Research On The Radiative Transfer In One-dimensional Medium Under Collimated Light/pulse Irradiation

Building energy efficiency is considered as a very promising field in 21 st century and arouses people’s research interests, especially in the spectral selective coating areas. The influence of surface conditions on the transient radiative heat transfer in the pigmented coating also needs to be investigated.The spectral selective coating is widely used in building areas due to its nice appearance. The performance of double-layer coating with TiO2 and ZnO particles shows less VIS reflectance and more NIR reflectance than that with single particles. The DRESOR method which is based on the ray tracing technology is developed to design the double-layer coating with submicron particles. The results show that an optimized double-layer coating with particles should be the one with an appropriate particle diameter,volume fraction and the black substrate.Since the white pigment coating is prone to produce optical pollution in higher building, a new approach of using double-layer pigmented coating with different volume fractions of CuO submicron particles is proposed. Comparison of the calculated spectral reflectance of the double-layer coating with the uniformly pigmented coating(single layer)shows that the double-layer coating can significantly reflect the solar irradiation especially in the near-infrared region and thus, decreases the heat absorbed by the building to save energy. Furthermore, coatings with different volume fraction distributions, thicknesses,particle diameters, as well as substrate conditions are investigated.At last, the influence of surface conditions on the transient radiative heat transfer in the pigmented coating is investigated. The accuracy of DRESOR method is carried out first.The comparison between BRDF surface and diffuse surface is also studied. With the increase of optical thickness, the time-resolved reflectance and transmittance profiles change from a single peak, to a double-peak, and finally to a single peak with a relativelylarge scattering albedo. With the increase of parameter k of Minnaert model, the difference between BRDF surface and diffuse surface enlarges significantly.