Study On Spectral Emissivity Characteristic Of Target In Infrared Temperature Measurement

Titanium alloy(Ti-6Al-4V)is widely used in the aviation field because of its high specific strength,small specific gravity,and corrosion resistance.Its infrared temperature measurement plays a vital role in early warning of key components.The spectral emissivity is a key parameter that determines the accuracy of infrared radiation temperature measurement.In addition,the emissivity has important applications in the fields of thermal protection,infrared stealth,infrared heating,medical physiotherapy,and solar energy utilization.But the emissivity is not constant,it will show different rules with temperature,wavelength,measurement angle,surface composition and state,which makes its measurement difficult.According to the needs of the spectral emissivity characteristics of Ti-6Al-4V,an emissivity measurement device is built in this paper,and the influence of different parameters on the emissivity characteristics is studied.The specific research content is as follows:(1)Based on the principle of emissivity measurement by the energy method,an emissivity measurement device based on a near-infrared optical fiber spectrometer is built.Its main modules include a near-infrared fiber spectrometer(NIRQUEST 512-2.5of Ocean Optics),a reference black body(Land 1500T,?>0.99),a self-made heating device(the environmental radiation effect is fully considered,heated by electric iron core),and an optical focusing system(receive radiation by transmissive lens,focusing range:0~300mm,zoom ratio:4:1),also includes data acquisition and analysis software required by the measurement system.Temperature measurement range of the entire device:550~oC~1000~oC,spectral range:900~2500 nm,the spot diameter:4.16mm.(2)The accuracy and repeatability of the emissivity measurement device is tested,and the temperature of the indicated value of the blackbody and thermocouple is calibrated to ensure the accuracy of the measurement data.Before the experiment,the two-point calibration method is used to solve the linear conversion relationship between the output value of the spectrometer and the absolute radiation.(3)Finally,high temperature oxidation experiments of titanium alloys in air are carried out.The result shows that the emissivity increase with the increase of temperature and the trend of overall decline with the increase of wavelength.However,the oscillation occurs,and the cause of the oscillation phenomenon is analyzed by interference.Besides,oxidation at different temperatures will also cause different degrees of changes in surface morphology,composition content,roughness,and oxide layer thickness,and changes in emissivity are also directly related to these factors.In order to describe the variation law of emissivity with time,a Gaussian approximation mathematical model is established by curve fitting,and the maximum error of the fitting result do not exceed 6%.Finally,the uncertainty analysis of the measurement system and data is performed,and the maximum uncertainty of the emissivity measurement of this experiment is calculated to be 3.88%,by integrating the various influencing factors.