Spectral emissivity model of steel 309S during the growth of oxide layer at 800–1100 K

Abstract

This work strived to determine the analytical relationships between the spectral emissivity and the wavelength at different temperatures during the growth of oxide layer on the specimen surface of steel 309S. In the experiment, the spectral emissivity was measured at eight wavelengths, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, and 2.1μm, at temperatures from 800 to 1100K in increments of 20K by multispectral radiation thermometry. To accurately measure the normal spectral emissivity, the detector employed in the thermometry should be perpendicular to the surface of specimens as accurately as possible. The temperature of specimen surface was measured by the two thermocouples, which were symmetrically welded onto the front surface of specimens. The average of their readings was regarded as the true temperature. With the spectral emissivity measured here, the variation in the spectral emissivity with wavelength was evaluated at different temperatures and different heating times. Ten emissivity models were evaluated. The effect of number of the parameters used in the models on the fitting accuracy was studied. Both the five-parameter LLWE and LWE models were very suitable for fitting the spectral emissivity and could farthest relieve the effect of heating time on the accuracy of temperature prediction. The uncertainties in the temperature prediction of steel 309S specimens were basically within 10K by thermometry using the two models over the present temperature and wavelength ranges.