Theory for a gas composition sensor based on acoustic properties

Abstract

Sound travelling through a gas propagates at different speeds and its intensityattenuates to different degrees depending upon the composition of the gas.Theoretically, a real-time gaseous composition sensor could be based on measuringthe sound speed and the acoustic attenuation. To this end, the speed of soundwas modelled using standard relations, and the acoustic attenuation wasmodelled using the theory for vibrational relaxation of gas molecules. Theconcept for a gas composition sensor is demonstrated theoretically fornitrogen–methane–water and hydrogen–oxygen–water mixtures. For athree-component gas mixture, the measured sound speed and acousticattenuation each define separate lines in the composition plane of two of thegases. The intersection of the two lines defines the gas composition. Itshould also be possible to use the concept for mixtures of more than threecomponents, if the nature of the gas composition is known to some extent.