工质相变对低温谐振腔声速测量的影响分析

声学气体温度计是通过精确测量球型谐振腔内的气相声速,确定热力学温度应用最为广泛的计量器具。气体工质的相变是低温区声学气体温度计高精度测量系统不确定度的主要来源。本文基于热粘性流体动力学、热力学相变和理论声学基本方程,推导了气液混合工质对声速测量的影响公式,建立了声波波数计算模型,并进行了数值计算仿真和实例验证。拟合结果显示,气液混合物对于声速测量值的相对扰动不确定度<0.03 ppm,满足声速测量的要求。随着压强的增大,偏移量呈现缓慢减小的趋势,其中扰动值变化量分别在5.4、3.3 kHz时达到最大和最小。该方法计算结果精度较高,验证了其可行性。

Influence of working medium phase transformation on acoustic gas speed measurement in cryogenic resonator

Acoustic gas thermometer(AGT) is currently the most accurate and wide method in the measurement of K. It can determine K by measuring the speed of gas sound then determine the thermodynamic temperature in the acoustic resonance cavity. The phase change of helium working medium is one of the main sources of uncertainty in the measurement system with high precision in the 4. 2 ~ 20 K cryogenic temperature. Based on the basic equations of viscous fluid dynamics,thermodynamic phase transition and theoretical acoustics,this paper deduced the influence formula of gas-liquid mixtures on gas sound speed measurement,established the calculation model of acoustic wave number,and conducted numerical calculation simulation and example verification. The fitting results show that the relative disturbance uncertainty of gas-liquid mixture to the measured sound velocity is less than 0. 03 ppm,which meets the requirements of sound velocity measurement. With the increase of pressure,the offset presented a trend of slow decrease,in which the variation of disturbance value reached the maximum and minimum at 5. 4 kHz and 3. 3 kHz respectively.