Theory for a gas composition sensor based on acoustic properties

Abstract

Sound travelling through a gas propagates at different speeds and its intensity attenuates to different degrees depending upon the composition of the gas. Theoretically, a real-time gaseous composition sensor could be based on measuring the sound speed and the acoustic attenuation. To this end, the speed of sound was modelled using standard relations, and the acoustic attenuation was modelled using the theory for vibrational relaxation of gas molecules. The concept for a gas composition sensor is demonstrated theoretically for nitrogen-methane-water and hydrogen-oxygen-water mixtures. For a three-component gas mixture, the measured sound speed and acoustic attenuation each define separate lines in the composition plane of two of the gases. The intersection of the two lines defines the gas composition. It should also be possible to use the concept for mixtures of more than three components, if the nature of the gas composition is known to some extent.

Gas Composition Recognition Based on Analyzing Acoustic Relaxation Absorption Spectra: Wavelet Decomposition and Support Vector Machine Classifier

“…The acoustic-based gas sensing is a promising gas detection technology advantageous in without gas preprocessing or sampling, low cost, robustness and real-time response [1]. As a key of acoustic gas sensing, acoustic properties of different gas mixtures should be acquired comprehensively and accurately [2,3].…”

“…And these gases were treated as pseudo-binary mixtures. In Phillips' work, the acoustic attenuation as the second property, was joined into sound speed to determine the concentration of the three-component mixtures [1]. By adding effective relaxation frequency as the third property, Zhu et al developed the method to detect the concentration of gas mixtures with four components [4].…”

Relaxation Time Coupling Method for Ultrasonic Sensor Design

“…Intelligent ultrasonic sensor is applied widely to detect gas compositions [1]. Measuring acoustic relaxation absorption spectrum is a powerful method to characterize molecular relaxation process in gas mixture [1,2,3].…”

Development of Acoustic Based, Multi-tasking Sensing and Actuation Capabilities for Gas Turbines

“…The use of acoustic absorption measurements as gas phase mixture diagnostics has received limited attention to date. The majority of existing acoustic diagnostic techniques have relied on sound speed or Doppler shift measurements to infer quantities such as average temperature, gas composition of binary mixtures, or gas velocity 3,4,5,6 . Absorption measurements for diagnostic purposes have been reported in some recent studies for gas composition characterization 6 or particle sizing 7 .…”

“…The majority of existing acoustic diagnostic techniques have relied on sound speed or Doppler shift measurements to infer quantities such as average temperature, gas composition of binary mixtures, or gas velocity 3,4,5,6 . Absorption measurements for diagnostic purposes have been reported in some recent studies for gas composition characterization 6 or particle sizing 7 . The technique described here is unique in that it based upon the fact that the relaxation frequency for a particular gas is often a strong function of the other species it is in molecular contact with.…”