一种裸线热电偶时间常数新公式的仿真和试验验证

Simulation and Experimental Verification of a New Time Constant Formula for Bare-wire Thermocouple

为准确获取热电偶测量动态来流温度的响应时间即时间常数,根据能量守恒,考虑热电偶结点的对流、辐射和导热,推导了热电偶时间常数的新公式。时间常数公式中涉及2个参数α和e,其中与表面辐射相关的参数α通过计算流体力学(CFD)仿真小球在来流参数变化时的球温动态响应时间拟合获得,而与导热相关的参数e通过CFD仿真S型热电偶在来流参数变化时的热电偶结点温度动态响应时拟合获得。通过仿真和试验2种方式对时间常数公式进行验证。结果表明:在不同工况下,公式计算和CFD仿真得到的时间常数误差在20%以内,且仿真结果下的特定工况辐射和导热综合影响,能够使时间常数最低降为仅考虑对流的33%;采用S型热电偶测量了标准高温燃气,通过对热电偶加载然后撤销电流获得热电偶测温的动态响应曲线和时间常数,试验与公式获得的时间常数之间的最大误差为-12%,证实了公式的准确性较高。

In order to accurately determine the response time(time constant)of the thermocouple to measure the dynamic temperature changes,a new time constant formula for thermocouple was derived based on energy conservation and considering convection,radiation,and heat conduction at the thermocouple junction.Two parameters,αand e are involved in the time constant formula.The parameterαrelated to the surface radiation was obtained by fitting the CFD(Computational Fluid Dynamics)simulated time constant of a sphere under varying flow parameters;while the parameter e related to conduction was obtained by fitting the CFD simulated time constant of an S-type thermocouple.The time constant formula was verified by simulation and experiment.The results show that under different working conditions,compared with CFD simulation results,the errors of the formula are less than 20%.For a specific CFD simulation case considering the combined effect of radiation and heat conduction,the time constant can be reduced to 33%of the case considering only convection.Using an S-type thermocouple to measure the temperature of the standard high-temperature gas,the dynamic response curves and the time constants of the thermocouple were obtained by loading the thermocouple and then removing the current.Compared with the experimental data,the maximum error of the formula is-12%,demonstrating the high accuracy of the formula.