Dispersion de Radiacion y Transferencia de Calor en Espumas Plasticas: Conductividades Termicas a Partir de Espectros Infrarrojos = Radiation Scattering and Heat Transfer in Cellular Plastics: Thermal Conductivities from Infrared Spectra

Abstract

The mechanism of radiative heat flow in cellular materials is analyzed in terms of their spectral properties in the infrared region. Specifically, it was found that commercial polystyrene foams having average cell diameters of 100-150 μm behave as optically dense scattering media up to about 8 μm. At longer wavelengths, i.e. in the region where black bodies display their maximum emissive power at ambient temperatures, the scattering coefficient a markedly decreases and the material becomes almost transparent above 50 μm. The behavior of σ in this critical region does not follow a simple λ^(-n) law, revealing that the process should be classified as Mie scattering. It is shown that from this information, encoded as an effective scattering coefficient, overall thermal conductivities can be actually derived by means of standard techniques dealing with energy transfer in scattering media. The physical basis for relating cellular structure and net heat flow in plastic foams is thereby established.