Acoustic attenuation in gas mixtures with nitrogen: experimental data and calculations.

Attenuation in a gas results from a combination of classical attenuation, attenuation from diffusion, and attenuation due to molecular relaxation. In previous papers [J. Acoust. Soc. Am. 109, 1955 (2001); 110, 2974 (2001)] a model is described that predicts the attenuation from vibrational relaxation in gas mixtures. In order to validate this model, the attenuation was measured using a pulse technique with four transducer pairs, each with a different resonant frequency. The attenuation calculated using the model was compared to the measured values for a variety of gases including: air, oxygen, methane, hydrogen, and mixtures of oxygen/nitrogen, methane/nitrogen, carbon dioxide/nitrogen, and hydrogen/nitrogen. After the measured data is corrected for diffraction, the model matches the trends in the measured attenuation spectrum for this extensive set of gas mixtures.