IMECH-IR  > 高温气体动力学国家重点实验室
同轴热电偶的响应特性分析与实验研究
英文题名Analysis of Response Characteristics and Experimental Research of Coaxial Thermocouple
王兴虎
导师陈宏
2018-05-21
学位授予单位中国科学院大学
学位授予地点北京
学位类别硕士
学位专业流体力学
关键词同轴热电偶 热乘积系数 热流传感器标定 壁面催化
摘要

表面热流率是表征气动热环境的一项重要参数,但该物理量无法直接测量。通常先利用传感器测量温度,再根据温度和热流率之间的特定关系将温度转化为热流率。同轴热电偶热流传感器(简称:同轴热电偶)是一种基于半无限体传热理论的瞬态热流传感器,在将其测量出的温度转化为热流率时,热乘积系数直接关系到其测量精度。因此,同轴热电偶的热乘积系数一般需要标定。同时由于同轴热电偶具有响应快、灵敏度高、抗冲刷性强的特点,经常用于高温气体壁面催化效应的研究。

为了准确标定出同轴热电偶的热乘积系数,本文采用了突然浸入法。实验发现,标定过程中的一些参数的设定会影响结果的准确性。为了得到更准确的热乘积系数,本文总结出了更规范的标定方法:同轴热电偶的导通电阻尽量控制在3Ω以下,同轴热电偶浸入甘油的速度控制在50-150mm/s,其深度控制在约3mm。实验中还发现,通过给同轴热电偶加装套筒,可消除横向传热对标定结果影响。经过激波管实验验证,通过以上方法标定出的热乘积系数具有较高的准确性。

利用规范化之后的标定方法,本文研究了同轴热电偶端面结点导通方式对传感器响应特性的影响。研究发现,打磨导通的同轴热电偶的热乘积系数会受到结点的厚度(由砂纸粗细衡量)的影响,但并不随结点厚度单调变化。镀膜导通的同轴热电偶的热乘积系数和响应时间会受到镀膜的材料、形式、厚度的影响,相同的同轴热电偶在镀膜导通之后的热乘积系数比打磨导通时更大。

同时,本文利用同轴热电偶在激波风洞中研究了高温气体壁面催化效应。实验发现,总焓155kJ/mol、驻点压力9kPa、氧原子浓度23%的气流中,银表面驻点的热流比氧化铝表面高了65%,铜表面驻点的热流比氧化铝表面高了57%;空气的解离程度越高时,壁面催化效应产生的热流越大。

 

英文摘要

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.

 

语种中文
文献类型学位论文
条目标识符http://dspace.imech.ac.cn/handle/311007/73125
专题高温气体动力学国家重点实验室
推荐引用方式
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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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