Research And Application On Pseudo-Brewster Angle On A Metal Surface Emissivity

The pseudo-brewster angle is the angle, at which there is the maximum emissivity value of the metal surface in the polarization direction P. At the pseudo-brewster angle, the P polarized radiation is similar to the blackbody radiation. According to this, the metal surface brightness temperature can accurately reflect the real surface temperature and the brightness temperature distortion caused by factors such as metal surface roughness and oxidation is resolved. Therefore it is important to for accurate temperature measurement of the metal surface to study the pseudo-brewster.In this thesis, the metal surface emissivity of high temperature is studied. Based on the polarization emissivity calculation model of the multi layers rough surface at the pseudo-brewster angle, the laboratory multi-angel polarized emissivity measuring device used to test the calculation model is established. The metal surface temperature measurement method based on the pseudo-brewster angle in the polarization direction P is proposed. The temperature measuring device based on the point and line measurement is designed and implemented.The main contents and innovative achievements of this dissertation are as follows:(1) The emissivity model of the one-dimensional Gaussian rough surface is established.The solution to obtain the emissivity based on the reflectivity is determined. In the case of polarization, the bistatic scattering coefficient is obtained with Kirchhoff approximation. The emissivity is calculated by the integral of the bistatic scattering coefficient. The one-dimensional Gaussian rough surface is inversely established by the statistical properties of the Gaussian. The metal polarization angle emissivity is calculated. Results indicate that the statistical parameters of the Gaussian rough surface established in this paper have no effect on the pseudo-brewster angel. But the absolute value of emissivity is affected by the mean square height and correlation length. The results are the basis for the further establishment of the rough surface layers of the metal surface emissivity model.(2) The emissivity calculation model of the metal multi layers rough surface based on the pseudo-brewster angle is proposed. Based on the establishment of the multi-layers metal plane model and one-dimensional Gaussian rough surface, the metal multi layers rough surface model is established. The emissivity calculation model of the metal multi layers rough surface is proposed. The factors that affect the pseudo-brewster angel in the calculation process of the emissivity are analyzed. Results indicate that the pseudo-brewster angel is affected by the properties of the metal itself. With the increases of the oxide thickness, the pseudo-brewster angel decreases and becomes stabilized. The rougher the surface, the greater the pseudo-brewster angel in the polarization direction P and tends to1.(3) The measurement platform of the metal slab emissivity is designedThe measurement platform of the metal slab emissivity is designed in order to validate the computational results of the emissivity based on the pseudo-brewster angle. The rough surface metal with oxide layer is studied. The radiation energy is gained from0degrees to80degrees through the Polaroid. Compared with hermocouple temperature measurement results, the polarization emissivity of different polarization angles is calculated. The relative error of the measurement device system is less than2%. The experimental results verify there is the maximum emissivity value at the pseudo-brewster angle in the polarization direction P. Compared with the experimental results of Japan scholars under the similar conditions, the conclusion that the pseudo-brewster angle decreases with the increases of the metal surface oxide layer thickness is obtained. The results are consistent with the model results, and the reliability of the computational model is verified.(4) The slab surface temperature measurement method based on the pseudo-brewster angle of the polarization direction P is proposed. The temperature measuring device based on the point and line measurement is designed and implemented.Base on the characteristic that the metal surface emissivity at pseudo-brewster angle in the polarization direction P is nearly to1and the measurement temperature characteristics equal to the metal surface temperature, the slab surface temperature measurement method based on polarization P pseudo-brewster angle is proposed. The problem that the temperature can not be measured accurately because of the emissivity inaccurate caused by the metal surface oxide layer is solved.The designed temperature measurement device consists of the point and line measurement. The point measurement part includes the high temperature radiation pyrometer and pneumatic brush, which is installed in the metal surface of the upper part. It is used to measure the vertical brightness temperature of the metal surface. The line measurement part includes linear CCD and static electric dust removal device, which is installed in the side of the metal surface and the measuring angle can be adjusted. It is used to measure the brightness temperature of the different angles. When the difference between the temperature measured by the line measurement and the temperature measured by the point measurement get to the maximum one, then the line measurement angle is the pseudo-brewster angle. The measured brightness temperature is the real surface temperature of the high temperature metal. Through a large number of data analysis, the reliability of the measurement method is verified.