| With the rapid advancement of science and technology,the demand for accurate measurement of radiant heat flux in aerospace,aviation,metrology and other fields is constantly increasing,and the pursuit of efficient,rapid and accurate heat flux measurement methods is gradually regarded as the primary goal by researchers.At present,common radiant heat flux meters include circular foil type heat flux meter,thermal resistance type heat flux meter and calorimetric type heat flux meter.Among them,the measurement uncertainty of circular foil type heat flux meter and thermal resistance type heat flux meter is low,and the measurement accuracy is difficult to improve due to the limitations of structure and materials.The calorimetric heat flux meter based on the principle of electric substitution measurement reproduces the temperature rise of radiant heating through electric heating,so that the calorimetric radiant heat flux meter has a higher measurement accuracy.Therefore,the high precision measurement of radiant heat flux can be realized based on the calorimetric heat flux meter.However,the measurement uncertainty of calorimetric radiant heat flux meter still cannot meet the demand of accurate measurement of heat flux in various fields due to the low absorptivity of absorbent and photoelectric inequivalence.Therefore,this paper carries out research on high-precision measurement of thermal type radiant heat flux meter and photoelectric inequivalence,and achieves the goal of measuring uncertainty of radiant heat flux meter better than 1%.In this paper,the working principle and basic structure of the calorimetric radiant heat flux meter are introduced.The heat balance equation of the absorption cavity of the radiant heat flux meter based on the zero-dimensional heat conduction model is derived.The theoretical calculation formula of the time constant and responsivity is obtained,which has guiding significance for the design and optimization of the radiant heat flux meter.Secondly,the thermal structure model of radiant heat flux meter is established by finite element analysis method.The model includes heat transfer physical field and air fluid physical field.When the heat source is 0.05 W in the absorption cavity,the responsivity of the radiant heat flux meter is 1.394K/W,and the responsivity of the coupling field of heat transfer and air flow is about 32% different from that of the vacuum physical field.Subsequently,the vacuum-air responsivity comparison experiment of radiant heat flux meter was carried out.In air environment,the responsivity difference between radiant heat flux meter optical power and electric power was 0.23%;in vacuum environment,the responsivity difference between radiant heat flux meter optical power and electric power heating was 0.0801%.The difference of electric power responsiveness between vacuum environment and air environment is 30.85%,and the difference of optical power responsiveness is 30.96%.The experiment further verifies the validity of the thermal structure model of radiant heat flux meter.Then the photoelectric inequivalence characteristics of radiant heat flux meter are studied.The photoelectric inequivalence of calorimetric radiant heat flux meter is mainly absorption inequivalence and heat conduction inequivalence.The inequivalence caused by the absorption rate of the absorption cavity is studied by Monte Carlo ray tracing and experimental measurement.The heat transfer model of radiant heat flux meter was established by COMSOL software.The inequivalence existed on the detector heat conduction path was studied by finite element analysis and theoretical calculation,and the photoelectric inequivalence correction coefficient and its uncertainty were obtained.Finally,by studying the measurement method of radiant heat flux meter,the mathematical model of radiant heat flux measurement is established,and the measurement scheme of radiant heat flux meter is determined.He-Ne laser with working band of 632.8nm and power of 1m W is used as the target light source to test radiant heat flux.The measurement uncertainty of each influence quantity in the self-calibration process of radiant heat flux meter is analyzed and the standard uncertainty is synthesized.Finally,the measurement uncertainty of radiant heat flux meter is 0.74%.According to "JJF 1117-2010 Measurement Comparison",the uncertainty of the radiant heat flux meter was verified by the normalized deviation En,and the experimental En=0.67 < 1,which certified the effectiveness of the results of assessment.The results provide reference for further optimization design and development of radiant heat flux meter. |
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