Measured and predicted acoustic attenuation in binary gas mixtures

Acoustic attenuation in a gas mixture results from the combined effects of molecular relaxation and the classical mechanisms of viscosity and heat conduction. Acoustic attenuation was measured in methane–nitrogen mixtures for a wide range of concentrations in a large vessel using a pulsed technique. The signals from four pairs of transducers, each operating at a different frequency, were measured as a function of the distance between the transducers. The pressure in the vessel was varied to cover a wide range of f/p. A correction for diffraction for each transducer pair was applied to the data resulting in overlap between the data from different transducers at the same f/p. The pure methane measurements are in good agreement with published results. Measurements for mixtures of methane and nitrogen agree well with calculations that include both relaxational and classical attenuation [J. Acoust. Soc. Am. 109, 1955 (2001)]. Similar measurements were completed for mixtures of carbon dioxide and nitrogen. Calculations to predict the attenuation for these mixtures are ongoing. [This work was funded in part by the State of Oklahoma.]