The Measurement Device Of Directional Spectral Emissivity Based On Optical Fiber Spectrometer

The directional spectral emissivity is one of the important thermophysical parameters to characterize the radiation ability of actual material surface,which physical meaning is the degree of radiation ability of actual material surface in different directions close to that of the reference blackbody.The directional spectral emissivity is defined as the ratio of radiant energy of material surface to that of an ideal blackbody at the same wavelength,temperature and direction.The directional spectral emissivity is a dimensionless parameter that has a certain relationship with temperature,wavelength,measurement direction,surface roughness,surface topography.The direction Spectral emissivity has a broad application background in military,surveying and mapping,solar energy,radiation temperature measurement and medicine.For example,the research of stealth technology in the military field,the delineation of landforms in surveying and mapping,and the high-temperature radiation measurement technology in the industrial field.With the increasing demand for directional spectral emissivity in various fields,scientific researchers have conducted a lot of research and developed many directional spectral emissivity measurement devices.The Fourier transform infrared spectrometer is widely used for directional spectral emissivity measurement due to the characteristics of high measurement accuracy,wide wavelength range,and high signal-to-noise ratio.However,because of the large size and high cost,it is mainly limited to laboratory research.To measure the directional spectral emissivity of material surface,it is necessary to rotate the sample,the optical system or the detection system to adjust the measurement direction.Since the sample needs to be heated to a certain temperature,the sample and the heater need to be rotated together.When the sample is in a high temperature and stable state,rotating the sample may cause fluctuations in the surface temperature of the sample and the surrounding environment,which will cause large measurement errors.The Fourier transform infrared spectrometer or monochromator is not conducive to the precise adjustment of the measurement angle due to the large size.In recent years,the fiber optic spectrometers have been widely used in rapid spectrum measurement and industrial production.The optical fiber spectrometer has no mechanical scanning system,fast measurement speed,small size and flexible and changeable to realize online or in-situ measurement.In order to realize the fast and convenient measurement of directional spectral emissivity,this paper builds a directional spectral emissivity measurement device based on fiber spectrometer and studies the directional spectral emissivity of several pure metals.The main research contents are as follows:(1)A directional spectral emissivity measurement device based on fiber optic spectrometer is established.The heating system uses a self-designed silicon carbide heater to heat the sample.The surface temperature of the sample can reach 1200 K,and the surface temperature uniformity is good.The measurement angle can be adjusted from 0° to 82° by rotating the fiber collimator lens installed on the motorized rotary stage.The collected radiation signals from the sample surface at different angles are transmitted to the miniature optical fiber spectrometer by the optical fiber.The optical fiber spectrometer detects the radiation signals of the sample and the black body in real time.(2)The measurement device is calibrated by the dual-temperature calibration method and the multi-temperature calibration method to obtain the response function and background function.The two calibration methods are compared by the sum of deviations square between the fitted data and the measured data of the blackbody radiation signal to infer a calibration method with higher accuracy.The linearity of the measurement device is verified by the fitting of the blackbody radiation signal and the radiation intensity.The uniformity of the sample surface temperature is verified by the contact measurement method.(3)The spectral emissivities of silicon wafers,silicon carbide,molybdenum and tungsten were measured using the measurement device.The reliability of the measurement device was verified by comparison with relevant domestic and foreign data.The directional spectral emissivity of high-purity titanium,chromium,cobalt and nickel in the range of 950-1600 nm and temperature range of 823-1073 K was studied.The influence of wavelength,temperature and measurement angle on the spectral emissivity is analyzed in detail.The results show that the directional spectral emissivity decreases with the increase of wavelength and temperature,and the directional spectral emissivity is basically unchanged at first and then decreases sharply with the increase of the measurement angle.In order to understand the relationship between directional spectral emissivity and temperature in detail,the spectral emissivity curve was fitted.The combined uncertainty of the directional spectral emissivity measurement was evaluated.The combined uncertainty of the built measurement system was better than 3%.