New experimental facility for measurement of total and spectra! emissivities of various thermal protection materials and coatings at high temperatures

摘要

A second generation of drop furnace facility based on a novel transient technique has been developed for measurement of wavelength and temperature dependences of normal spectral emissivity in the temperature range 1000-1800 K and the wavelength region 1.5-5.5 urn, and the temperature dependence of total emissivity in the same temperature range. The new apparatus is most suitable for the investigation of various thermal protection materials and coatings with fine or rough structure. The measurement of the emissivities is achieved by comparing radiation from a test sample and the blackbody model. The experimental apparatus, its optical measurement and computerised data acquisition and control systems are described. These allow measurement of the emissivity in a broad range of its value, from low (~0.01), up to high (~ 1). The volumetric optical properties (the absorption coefficient and the radiation diffusion coefficient) of scattering semitransparent thermal protection materials such as glass or ceramic fibre thermal insulation can be determined on the basis of the measurement of spectral emissivity as a function of the thickness of test samples.