Experimental investigation of emissivity of aluminum alloys and application of multispectral radiation thermometry

Experiments were first conducted to measure the emissivity values of a variety of aluminum alloys at 600, 700, and 800 K. The effects of wavelength, temperature, alloy composition, and heating time on emissivity were investigated. Multispectral radiation thermometry (MRT) with linear emissivity models (LEM) and log-linear emissivity models (LLE) were then applied to predict surface temperature. Parametric influences of wavelength number, heating time and order of emissivity models were examined. Results show that the spectral emissivity decreases with increasing wavelength and increases with increasing temperature. A stronger alloy effect is evident at higher temperature. The spectral emissivity reaches steady state after the first hour heating due to the surface oxidation becoming fully-developed. Half of the temperature predictions by MRT emissivity models provide the absolute temperature error under 10% and quarter of the results are under 5%. Increasing the order of emissivity model and increasing the number of wavelengths cannot improve temperature measurement accuracy. Overall, LLE models show higher accuracy than LEM models. The first-order and second-order LLE models and the first-order LEM model give good results most frequently and provide the best compensation for different alloys, the number of wavelengths, and temperatures.