Study On The Factors Affecting The Emissivity And The Emissivity Model

Emissivity is one of basic thermal parameters of an object which is important to describe the object’s thermal radiation character.With important application value and research significance in aviation,aerospace,scientific research,national defense,industrial and agricultural production filed.its measuring level of accuracy,the dimension control,the variation of characteristics control that is an important technical indication for measure of related product quality,occupies an important position in the infrared measurement technology.However,spectral emissivity sometimes depends drastically on the wavelength and temperature,and it may be sensitive to emission angle,surface roughness,surface oxidization state,presence of pollutants,and composition of the object.As it is difficult to accurately measure the spectral emissivity of a target,it becomes even more difficult to accurately measure the variation in the spectral emissivity with respect to wavelength and temperature under various surface conditions.In particular,gaining knowledge about the spectral emissivity,wavelength,and temperature possibly becomes more complicated when the surface of a target is oxidized in air for a long time.In this article,we explored the variation in the normal spectral emissivity with heating time and temperature and discussed the effect of surface oxidization and nitridation on the normal spectral emissivity of titanium TA2 and Ti–6Al–4V alloys at a temperature range of 800–1100K and a wavelength of 1.5μm,nine emissivity models were examined for accuracy in the temperature prediction of Steel 304 over a temperature range from 800 to 1100 K and a wavelength range from 1.4 to 2.1μm.Titanium and titanium alloys have extensive applications in every field of industry,particularly those such as aerospace,automobile,defense,medical and chemical industries,because of advantages such as high tensile strength and high strength–weight ratio,good heat and corrosion resistance properties and low density.Of all the applications,spectral emissivity of titanium and titanium alloys is almost a key parameter.It is no exaggeration to say that determination and estimation of spectral emissivity of titanium and titanium alloys have become major challenges for some applications.For example,spectral emissivity data are required in heat-transfer calculations in aerospace and aircraft components;fabricating aerospace and aircraft components of titanium and titanium alloys is usually involving in a high temperature process,even in a melting state.At this time,the spectral emissivity is an essential parameter for accurate measuring of the temperature in the manufacturing process by the noncontact temperature measurement;the spectral emissivity is also necessary for the calibration and validation of the laser metal deposition process models.However,the spectral emissivity of titanium and titanium alloys are rather scarce,only few spectral emissivity were reported in the literature.In the first part of the article,we mainly supplement the emissivity of titanium and titanium alloy.Radiation thermometry subject may be sub-divided into single-wavelength thermometry and multispectral radiation thermometry.To determine the temperature accurately using single-wavelength thermometry,we must know the accurate spectral emissivity of an object.In multispectral radiation thermometry,we must have prior knowledge of the spectral emissivity,wavelength and temperature.A lot of experiments have been conducted to study the spectral emissivity variation due to the growth of an oxide layer on the steel surface.As reported in our earlier papers,oxidization on a steel surface can significantly affect normal spectral emissivity and bring about obvious temperature measurement uncertainty.As we know,the accuracy of temperature measurement is greatly dependent on the spectral emissivity model employed in multispectral radiation thermometry.Does surface oxidization affect the normal spectral emissivity model? We would answer the question in this article.Finally,the emissivity values of titanium,titanium alloy and steel 304 were supplemented by comparing the experimental data,obtained many important conclusions,which are of great significance to industrial production and application.