Title: Gas equilibrium heat capacity synthesis under the influence of acoustic relaxation process and its application in gas detection

Author(s): ZHANG Kesheng; ZHANG Xiangqun; SHAO Fang

Affiliation(s): School of Electrical and Information Engineering, Guizhou Institute of Technology; School of Electronic Information and Communications, Huazhong University of Science and Technology; School of Mechanical Engineering, Guizhou Institute of Technology

Abstract: In an excitable gas, the molecular vibration relaxation process caused by an acoustic disturbance leads the equilibrium heat capacity to the effective one that depends on the acoustic frequency, resulting in acoustic dispersion and acoustic 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 acoustic speed and absorption measurements. The two measurement frequencies are selected in the range where the acoustic relaxational absorption is obvious. The method can obtain the heat capacities of internal and external degrees of freedom of gas molecules respectively, and effectively eliminate the influence of the acoustic relaxation process on the measurement results of excitable gas heat capacity. For various gases, consisting of CO_2, CH_4, Cl_2, N_2 and O_2 at room temperature, the gas heat capacities obtained in this paper agree with the thermodynamic theoretical calculations based on the Planck-Einstein formula, and the maximum relative error is 3.51% in comparison to the experimental result. 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.