Theoretical and experimental evaluation of the radiative properties of a dispersed particulate medium

Recent research on construction materials has shown that depending on the pigment system used to impart color, a significant temperature rise may occur due to absorption of solar radiation. Heat buildup of polymeric materials used in these applications often leads to dimensional stability failures of the parts while in service. Recent studies have suggested that the heat buildup of these materials may be significantly reduced by the incorporation of scattering particles.; Scattering particles of two material compositions, and three particle size and volume percent ranges were added to a pigmented polymeric material. The change in diffuse reflectance due to the addition of these particles was experimentally determined using an Integrating Sphere Spectrophotometer. In addition, the resulting change in temperature rise due to the incorporation of the particles was determined using ASTM D4803. The radiative heat transfer was then modeled using a Mie Scattering Fortran program for the particles of smallest size (1–20 um) and Large Sphere Scattering theory was applied for particles of largest size (88–106 um). The theoretical diffuse reflectance and temperature rise changes were calculated and compared to the experimental results.; The scattering particles were found to alter the diffuse reflectance of the material, depending on the refractive index, volume percent, and particle size combination. For the Mie Scattering case, greater values of relative refractive index and smaller particle sizes provided higher values of diffuse reflectance and lower temperatures. Similarly, for Large Specularly reflecting spheres, higher values of diffuse reflectance and lower temperatures were found for spheres with a higher refractive index. However, Large Diffusely reflecting spheres provide lower diffuse reflectance values and higher temperatures. In addition, it was found that the theoretical model correlated well with the experimentally measured values and accurately predicted increases in diffuse reflectance and drops in temperature. Thus, the model may be effectively used to design dark colored polymeric materials with reduced heat buildup properties.