Research About Radiation Characteristic Of Translucent Blackbody

The blackbody cavity sensor has broad development prospects in liquid temperature measurement due to its good temperature measurement accuracy and stability.However,its application is limited by the poor dynamic characteristic.The fundamental reason is that the traditional blackbody cavity is made of opaque material,which brings the thermal hysteresis when radiation transport from the outer to the inner wall of the cavity.Hence,we put forward the idea of making blackbody cavity with transparent material.By this way,the liquid forms a blackbody cavity through the translucent wall directly and the temperature could be measured rapidly.For the translucent blackbody cavity,the following research was carried out:(1)The establishment of a geometric model of a translucent blackbody cavity.Compared with the single-layer geometric model of opaque cavity,the model of translucent blackbody cavity is a complex multi-layer structure as its transmission property,so does the geometric model.Besides,the shape of the blackbody cavity is mostly the spatial axisymmetric structure.Therefore,in this thesis,we used the circular vector method in differential geometry to establish the three-dimensional vector mathematical model of the cavity,and the vector expressions of each surface.It laid a foundation for the calculation of effective emissivity.(2)The effective emissivity calculation and modeling method of translucent blackbody cavity.The model of effective emissivity must be accurately express the characteristics of the diffuse reflection,transmission,and scattering of the translucent blackbody cavity.Based on vector method,this thesis established the algorithms of ray tracing for specular reflection,diffuse reflection,refraction,scattering and absorption.Then we established the effective emissivity calculation method of the cavity by Monte Carlo method.It laid the foundation for the study of the radiation characteristics of the new cavity.(3)The radiation characteristic study of the cavity with uniform mirror diffuse surface.As the new cavity is translucent,its characteristics contain a large number of mirror reflection components and the cylindrical flat bottom or circular bottom cavity is no longer applicable.In this thesis used the cavity with incline bottom that suitable for non-diffusion condition.We studied the influence of the optical property of the new cavity on its radiation characteristics.Such as diffuse-rate,the angle of inclined bottom,airtightness of the cavity and so on.As a result,the reasonable structure of the cavity was preliminarily determined.(4)The radiation characteristic study of the transparent cavity.Based on the preliminary cavity structure and the effective emissivity calculation method,the influence of the refractivity,cavity thickness and angle of inclined bottom on the effective emissivity of the cavity was studied.As a result,the temperature measurement accuracy of the black body cavity sensor was evaluated.(5)The radiation characteristic study of the translucent cavity.Under the above conditions of initial cavity structure parameters,this thesis studied the influence of the translucent and pure absorbent material on the sensor's temperature measurement accuracy.It mainly includes some parameters such as attenuation coefficient,transmittance,refractivity,and angle of inclined bottom of the cavity.Through the above research,this thesis established a research method for the radiation characteristics of the transparent blackbody cavity,which laid a theoretical foundation for the rapid,accurate and stable continuous measurement of the liquid internal temperature.The existing research results are in good agreement with the results of the computational model in this thesis,and the deviations are less than 5×10-5.Therefore,the calculation results of effective emissivity of opaque blackbody cavity on Monte Carlo method in this thesis are correct.What's more the results have the same accuracy as those in reference documentation.It demonstrate that the geometric model of the cavity and the mathematical model and calculation method of the effective emissivity of cavity established in this thesis are correct.Through the study of the radiation characteristics of the transparent cavity,the theory of blackbody cavity radiation was further improved.