|Alternative Title||Analysis of Response Characteristics and Experimental Research of Coaxial Thermocouple|
|Place of Conferral||北京|
|Keyword||同轴热电偶 热乘积系数 热流传感器标定 壁面催化|
The heat flux on a surface is a significant parameter for characterizing the aerodynamic heating environment. However, it cannot be measured directly. The conventional way to obtain the heat flux is by measuring temperature with sensors, and then converting the data to heat flux by a relationship between the heat flux and the thermal product. In many heat flux sensors, coaxial thermocouples are often used. They are based on a transient heat transfer theory of semi-infinite bodies. When the measured temperature is converted into the heat flux, the thermal product is directly related to the accuracy of the measurement. Therefore, the thermal products of coaxial thermocouples often need to be calibrated. At the same time, because a coaxial thermocouple has the characteristics of rapid response, high sensitivity, and strong resistance to scour, it is often used in the study of the wall catalytic effects of high-temperature gas.
In order to calibrate the thermal products of coaxial thermocouples, a sudden immersion method is adopted. It is found that some parameters in the calibration process can affect the accuracy of the thermal product. This paper describes a standard calibration method for obtaining more accurate values for thermal products: sensors’ electronic resistance should be less than 3 Ω, the speed of the electric cylinder should be controlled in the 50-150 mm/s range, and the sensors’ depth in glycerin should be set at approximately 3 mm. It is also found that the effect of transverse heat transfer on the calibration results can be eliminated by adding a sleeve to the sensors. Experiments in a shock wave tube confirm that the thermal product calibrated by the method described above has high accuracy.
In this paper, the relationships between end surface conduction modes and the response characteristics of the sensors are studied. It is found that the thermal products of the coaxial thermocouples are affected by the thickness of the heating junction points (measured by the thickness of sandpaper), but they do not vary monotonically. Thermal products and response times of film-coating coaxial thermocouples are affected by the thicknesses, materials, and forms of the films.
At the same time, the wall catalytic effect of high-temperature gas is studied by using a film-coating coaxial thermocouple in a shock wave tunnel. In airflow with 155 kJ/mol total enthalpy, 9 kPa stagnation pressure, 23% oxygen concentration, the stagnation heat flux on the silver surface is 65% higher than that of alumina, and the stagnation heat flux on a copper surface is 57% higher than on an alumina surface. The higher the degree dissociation of the air, the larger is the heat flux generated by the wall catalytic effect.
|王兴虎. 同轴热电偶的响应特性分析与实验研究[D]. 北京. 中国科学院大学,2018.|
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