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.