声弛豫过程影响下的气体平衡态热容合成方法及其在气体检测中的应用

声扰动形成的分子振动弛豫过程使得气体热容成为依赖于声频率的有效热容,导致随频率变化的声速频散和声弛豫吸收。本文基于单弛豫过程合成算法,提出一种基于两频点声速和声吸收测量值的气体平衡态热容合成方法。该方法两个测量声频点只需在声弛豫吸收显著的频率范围即可分别合成可激发气体分子内外自由度热容,并有效消除声弛豫过程对气体平衡态热容测量结果的影响。对于室温下由CO₂、CH₄、Cl₂、N₂和O₂组成的多种气体,合成的气体热容值与基于Planck-Einstein公式的热力学理论计算结果相符,相比实验数据最大相对误差为3.51%。合成的转动和振动热容还可应用于气体分子几何结构、振动频率大小和混合气体摩尔分数的检测。 

Acoustic method of synthesizing equilibrium heat capacities of excitable gases under influence of acoustic relaxation process and its application in gas detection

The molecular vibration relaxation process caused by the acoustic disturbance leads the heat capacity of excitable gas to the effective heat capacity that depends on the sound frequency,resulting in sound dispersion and sound relaxational absorption.Based on the algorithm of synthesizing a single-relaxation process,we develop a synthesizing method to get the equilibrium heat capacities of excitable gases from the two-frequency sound velocity and sound absorption measurements.The two measurement frequencies can be selected in the range where the sound relaxational absorption is obvious.The method can respectively obtain the heat capacities of internal and external degrees of freedom of gas molecules,and effectively eliminate the influence of the acoustic relaxation process on the measurement results of excitable gas heat capacity.For various gases,consisting of CO₂, CH₄, Cl₂, N₂ and O₂ at room temperature,the gas heat capacities acquired by this paper are consistent with the thermodynamic theoretical calculations based on the Planck-Einstein formula,and the maximum relative error is 3.51% in comparison to the experimental data.The synthesized heat capacities of rotation and vibration can be applied to the detection of gas molecular geometry,vibration frequency and mole fractions of gas mixtures.