Predicting acoustic relaxation absorption in gas mixtures for extraction of composition relaxation contributions

摘要

The existing molecular relaxation models based on both parallel relaxationtheory and series relaxation theory cannot extract the contributions of gascompositions to acoustic relaxation absorption in mixtures. In this paper, wepropose an analytical model to predict acoustic relaxation absorption andclarify composition relaxation contributions based on the rate-determiningenergy transfer processes in molecular relaxation in excitable gases. Bycombining parallel and series relaxation theory, the proposed model suggeststhat the vibration-translation process of the lowest vibrational mode in eachcomposition provides the primary deexcitation path of the relaxation energy,and the rate-determining vibration-vibration processes between the lowest modeand others dominate the coupling energy transfer between different modes. Thus,each gas composition contributes directly one single relaxation process to themolecular relaxation in mixture, which can be illustrated by the decomposedacoustic relaxation absorption spectrum of the single relaxation process. Theproposed model is validated by simulation results in good agreement withexperimental data such as $\mathrm{N_2}$, $\mathrm{O_2}$, $\mathrm{CO_2}$,$\mathrm{CH_4}$ and their mixtures.