Study On The Measurement Of Spectral Emissivity Of Semitransparent Solid Materials At High Temperature

Semitransparent materials have a wide application in the energy,aeronautics and astronautics,information communication and other research fields;such as thermal barrier coatings used in gas turbine blades,thermal protection material of missiles or rockets.With the development of national defense technology and material science,the demand of radiation characteristics of semitransparent materials is becoming more and more urgent.Emissivity is an important parameter that dictates the radiation properties of material and has a very broad application background in the field of engineering and scientific research.In this paper,the measurement of spectral emissivity of semitransparent solid materials at high temperature is studied.First of all,the measurement method of semitransparent materials is discussed,the electric heating method is selected to heat the sample,and moving the sample method is used to eliminate the thermal radiation effect of the electrical heater during spectral emissivity measurement.The principle and formula of the opaque material emissivity measurement is used for semitransparent solid material emissivity measurement,and the sample surface temperature is measured by a thermocouple.Secondly,based on the radiative transfer equation and the energy equation,the coupled radiation-conduction model of semitransparent solid material with high temperature is established.The solution of the model and the expression of the spectral emissivity of semitransparent solid material are given.The radiative transfer equation is solved by the discrete ordinates method.Once again,the electrical heater is designed,and emissivity measurement platform of semitransparent solid material at high temperature is built.The normal spectral emissivity of alumina,zirconia and silica semitransparent solid material at 100～400℃ is tested by high-temperature semitransparent materials emissivity measurement system,and the normal spectral emissivity at room temperature is measured indirectly by the integrating sphere.The experimental results are compared and analyzed.The analysis of the uncertainty components of the emissivity of 0.8mm thick alumina sample is performed.In particular,the influence of sample surface temperature on the emissivity uncertainty is analyzed.At last,the coupled radiation-conduction model of semitransparent solid material with high temperature is verified.Based on the coupled radiation-conduction model,using the corresponding radiation property parameters,the spectral emissivity of 1.2mm alumina sample at elevated temperature is calculated.Comparing the calculated results with the experimental results,the calculated results are in good agreement with the experimental results.According to the calculation results,the internal temperature difference between the samples is small and negligible.