Experimental Investigation of Emissivity Behaviors for Aluminum Alloys under High Vacuum

• Main Authors: Min-Chih Chu, 朱旻峙
• Other Authors: Chang-Da Wen
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/27695343394588741117

碩士 === 國立成功大學 === 機械工程學系碩博士班 === 97 === In this study, experiments were first conducted to investigate the surface emissivity for AL 1100, AL 2024, AL 5083, AL 6061, and AL 7005 at 600 K, 700 K, and 800 K under high vacuum. The data were compared with that of the same alloys at the same heating temperature under an open-air environment in order to analyze the effect of surface oxidation on emissivity. Multispectral radiation thermometry (MRT) with first-order linear emissivity model (LEM) was then applied to predict the surface temperature and examine the effect of surface oxidation on temperature determination as well. For emissivity behaviors of aluminum alloys under high vacuum: (1) emissivity decreases with increasing wavelength in the wavelength range from 2.8 μm to 4.2 μm which is chosen to exclude the atmospheric effect of water vapor and carbon dioxide; (2) overall, emissivity increases with increasing temperature; (3) emissivity dose not change with heating time; (4) the effect of alloy composition is minor at 600 K and 700 K, but much stronger at 800 K. For the effect of surface oxidation on emissivity: (1) most oxidized samples have higher emissivity than unoxidized samples, except AL 2024 and AL 7005. The exception is due to roughened surface caused by the onset of melt and the change of surface color at high heating temperature. Overall, emissivity of both oxidized and unoxidized samples increases with increasing temperature; (2) emissivity of unoxidized sample doesn’t change with time. However, emissivity of oxidized sample increases due to the growing oxide layer with time; (3) a stronger effect of alloy composition is evident for oxidized samples. For the examination of Multispectral radiation thermometry (MRT) with first-order linear emissivity model: (1) the best MRT examined wavelength range for unoxidized aluminum alloys is from 3 µm to 4 µm; (2) unoxidized samples provide better temperature prediction than oxidized samples; (3) if the emissivity model can well represent the real emissivity behaviors, the more accurate inferred temperature can be achieved.