Acoustic attenuation in a three-gas mixture: Results

Acoustic attenuation in a mixture of gases results from the combined effects of molecular relaxation and the classical mechanisms of viscosity and heat conduction. Consequently, the attenuation depends on the composition of the gas mixture, acoustic frequency, temperature, and pressure. A model of the relaxational attenuation that permits the calculation of acoustic attenuation is used to predict the effect of composition, frequency, temperature, and pressure on the acoustic attenuation in a three-component gas mixture of nitrogen, methane, and water vapor. The attenuation spectrum is dependent upon the composition through the appearance of peaks in the spectrum related to the relaxation frequencies of the particular components and their relaxing complexes. The relaxation peak related to methane dominates except at low methane concentrations, where the nitrogen peak, which is dependent upon the water vapor and methane concentration, is evident. Temperature and pressure significantly alter the relaxation frequency and the degree of attenuation, but water vapor plays little role in the attenuation.