Research On Effective Emissivity Of Blackbody Cavity Based On The Finite Element Method

As the blackbody radiation source, blackbody cavity is applied to the calibration of the infrared radiation thermometer, the measurement of the spectrum and the high temperature radiation thermometer. The emissivity, standing for the radiation characteristic of the blackbody cavity, is difficulty to measurement. The calculating method is usually used to obtain the emissivity, but all of the traditional methods have their defects.A new method based on the finite element analysis (FEA) is proposed in this thesis, which is especially suitable for calculating the effective emissivity of the cavity with a complicated structure. The research contents of this thesis are as follows:(1)The finite element method (FEM) for calculating the effective emissivity and integral emissivity is investigated. According to the definition of the integral emissivity, the respond heat flow rate is translated into the energy of the probe received based on the law of conservation of energy. Furthermore, the effective emissivity is studied according to the analysis of the energy balance of payments. The energy exchange of a certain area of each node and its blackbody radiation energy are calculated, and then the effective emissivity is calculated.(2) The calculating accuracy of the blackbody cavity’s effective emissivity, based on the ANSYS FEM, is studied. And this calculating result is compared to the reference’s result. Under the isothermal condition, the calculating error of every point is less than1×10-4on the target surface and side wall (0-400mm) of the cavity. Under the non-isothermal condition, the calculating error of the effective emissivity for the total and spectrum radiation of the cavity is less than5x10compared with the Monte Carlo method. Therefore, the ANSYS FEM for calculating the effective emissivity of the blackbody cavity is valid and exact.(3) The ANSYS FEM is applied to calculate the effective emissivity of the composite cavity. The calculation error of this result and the Monte Carlo method is less than1×10-4under isothermal condition, and which is less than5×10-4under non-isothermal condition. All of these verify the exact of this method used for the composite cavity. Meanwhile, the effect of the composite cavity’s structure parameters on the effective emissivity of the target surface is analyzed. And then, the optimum parameters of the structure for the blackbody cavity pyrometer are suggested.