RESUMEN
Blackbody cavity reflectivity is normally measured using an integrating sphere to collect hemispherical reflected radiation from a blackbody opening when illuminated by a directional light source. The challenge of taking this method without an integrating sphere arises for blackbody cavity emissivity measurement in satellites due to space constraints. The ratio of hemispherical-given solid angle reflections is proposed to calculate the total reflected power from a blackbody cavity by multiplying a measurable reflected power in a given solid angle. The ratio is obtained by simulating the distribution relationship between the total hemispherical reflected light power and the reflected light power in the given solid angle under different coating emissivity. The emissivity measurement results are consistent with radiometric method measurements and simulation results, with an uncertainty of 0.0005.
RESUMEN
Zirconium oxide (ZrO2) is widely used as the thermal barrier coating in turbines and engines. Accurate emissivity measurement of ZrO2 coating at high temperatures, especially above 1000 °C, plays a vital role in thermal modelling and radiation thermometry. However, it is an extremely challenging enterprise, and very few high temperature emissivity results with rigorously estimated uncertainties have been published to date. The key issue for accurately measuring the high temperature emissivity is maintaining a hot surface without reflection from the hot environment, and avoiding passive or active oxidation of material, which will modify the emissivity. In this paper, a novel modified integrated blackbody method is reported to measure the high temperature normal spectral emissivity of ZrO2 coating in the temperature range 1000 °C to 1200 °C and spectral range 8 µm to 14 µm. The results and the associated uncertainty of the measurement were estimated and a relative standard uncertainty better than 7% (k = 2) is achieved.