Research On Radiation Characteristics Of Non-Isothermal Translucent Blackbody Cavity

Blackbody cavity temperature sensor,combining the advantages of contact and noncontact thermometry,has good temperature measurement accuracy and stability.However,the conventional cavity is composed of the opaque wall,thermal conduction lag from outer to inner wall leads to the relatively slow response speed of the sensor.Making the cavity smaller and thinner can improve the response speed.It is impossible to reduced and thin without limitation,and still cannot fundamentally solve the problem.A novel blackbody cavity temperature sensor is proposed by replacing blackbody cavity’s opaque wall with transparent wall,with the measured medium outside the cavity directly forming the blackbody cavity,achieving the rapid temperature measurement.Without the presence of complete transparency in reality,translucent materials are used instead in the study.For the novel translucent blackbody cavity,the following research was carried out:(1)The geometric model of a translucent blackbody cavity was established.When the light was incident on the surface or inside of the translucent material,reflection,transmission,refraction,scattering,and absorption may occur.According to its optical characteristics,the influence of the bottom shape of the cylindrical cavity on the effective emissivity was analyzed.A cylindrical inclined bottom cavity was selected.It is difficult to describe the inclined surface using Cartesian coordinates.The three-dimensional vector mathematical model of inclined bottom cavity structure and the vector expression of each structural plane were established.(2)Radiation Characteristics of isothermal translucent blackbody cavity was studied.The trace model of the beam in thetranslucent cavity was established based on MCM.The correctness of the model was proved by calculating the effective emissivity of the isothermal opaque cavity,which deviation from the result in the literature[53]is less than 5×10-5.According to the calculation results,the radiation characteristics of opaque,fully transparent and translucent blackbody cavities under isothermal conditions were studied,the cavity calculation parameters were initially determined.(3)Radiation characteristics of non-isothermal translucent blackbody cavity was studied.With the closed and isothermal temperature measurement conditions,temperature distribution affects blackbody cavity radiation characteristics.A temperature simulation model of the translucent cavity was established using Fluent,and the influence of the coupled radiationthermal conduction heat transfer on the temperature distribution of the translucent cavity was studied.The effects of temperature distribution,transmittance,angle,cavity aspect ratio and cavity length transmittance on the effective emissivity were studied.(4)Experiment on temperature measurement accuracy of translucent blackbody cavity was studied.The real translucent cavities with four bottom shapes and three wall thicknesses were made of quartz glass.The effects of the shape of the cavity bottom and the thickness of the cavity wall on the temperature measurement accuracy were studied through experiments.The experimental results are consistent with the theoretical calculations.(5)Experiment on rapid temperature measurement of translucent blackbody cavity was studied.With the ensuring accuracy,the response speed of translucent cavity,opaque cavity,metal protection tube thermocouple and ceramic protection tube thermocouple in liquid temperature measurement is studied experimentally.Comparing the temperature changes,the speed order was obtained,which proves the rapidity of the translucent black body cavity.Based on the above work,the radiation characteristics of a translucent blackbody cavity under unequal temperature had been studied.The experimental results had proved the correctness of the theoretical calculation results.The translucent cavity has good temperature measurement accuracy and response speed.The temperature measurement accuracy of the inclined bottom cavity is obviously higher than that of the flat bottom,and the influence of thickness is small.The four types of temperature sensors are fast to slow in response speed:translucent black body cavity,metal protective tube thermocouple,opaque black body cavity,ceramic protective tube thermocouple.