Validation of the Infrared Emissivity Characterization of Materials Through Intercomparison of Direct and Indirect Methods
Leonard M. Hanssen, Sergey Mekhontsev, V B. Khromchenko
A comparison of the spectral directional emissivity of samples as a function of wavelength was performed at the Fourier Transform Infrared Spectrophotometry (FTIS) Facility and the Advanced Infrared Radiometry and Imaging (AIRI) Laboratory at NIST. At the FTIS, the emissivity is obtained indirectly through the measurement of directional-hemispherical reflectance (DHR) using an infrared integrating sphere. The integrating sphere is used for near-normal, temperature dependent DHR. At AIRI, the near-normal directional emissivity is obtained directly through the measurement of sample spectral radiance referenced to that from blackbody sources, while the sample is located behind a black plate of known temperature and emissivity. On the same setup at AIRI, the normal emissivity at near ambient temperatures is also measured indirectly by a two-temperature method in which the sample spectral radiance is measured while the background temperature is controlled and varied, while the sample temperature is held constant. Results of the spectral directional emissivity measurements on the comparison samples are presented over a wavelength range of 3.4 to 13.5 microns at several near-ambient temperatures and for near-normal incidence. The results obtained validate the two independent capabilities and demonstrate the potential of the controlled background methods for measurements of the radiative properties of IR materials.
Proceedings of the Asian Thermophysical Properties on Conference | 2007 |