Thermal Radiation in Silica Aerogel and its Composite Insulation Materials

This paper engages in experimental measurements on thermal radiative transfer in silica aerogel and its composite insulation materials (xonotlite-aerogel composite and ceramic fibre-aerogel composite). The samples of silica aerogel, xonotlite-type calcium silicate, and ceramic fibre insulation materials are all considered as a semi-transparent medium capable of absorbing, emitting and scattering thermal radiation. The spectral transmittances are then measured at different infrared wavelengths ranging from 2.5 to 25μm with a Fourier transform infrared spectrometer (FTIR), and subsequently used to determine the specific spectral extinction coefficient and the specific Rossland mean extinction coefficient of the sample. The radiative conductivities deduced from the overall thermal conductivities measured with the transient hot-strip (THS) method are compared with the predictions from the diffusion approximation by using the measured spectral extinction coefficient. The results show that the spectral extinction coefficients of the samples are strongly dependent on the wavelength, particularly in the short wavelength regime (<10μm). The total Rossland mean extinction coefficients of the samples are all decreasing with the temperature increasing. The radiative conductivities are found almost proportional to the cubic temperature, and decreases as the sample density increases.

Light Extinction by Fire Smokes

Visibility of escape routes is most important to guarantee the safety of people indoors during fires. In the case of a fire, visibility is strongly in fluenced by the smoke present in the room. In the present work, the extinction co efficient of the visible light has been experimentally measured in the presence of the smoke produced by four different test fires, named TF2, TF3, TF4, and TF5. Tests have been carried out in a specially suited test room in the Italian Fire De partment Research Center, provided with instruments to measure the optical density of smoke and the spectral extinction coefficient.

Horizon line scanning telephotometry

The horizon line softening method of determining the atmospheric spectral extinction coefficient σ(λ) is analyzed in detail indicating an inherent lower limit σ0(λ) on the range of σ(λ) which can be measured by this technique. As the observation height h above the earth surface increases, σ0(λ) decreases. A comparative experimental study of horizon line scanning telephotometry and contrast telephotometry is described, the results of which show the former technique to be useful under certain observing conditions.