Acoustic attenuation in a three-gas mixture: Results

Abstract

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.

Safety-related conclusions for the application of ultrasound in explosive atmospheres

“…Ignition due to direct absorption of the sound wave is not possible (Simon et al, 2014) because of the limited sound pressure levels and the low acoustic absorption coefficients in gases, vapors or dusts (Bhatia, 1996;Dain and Lueptow, 2001;Ejakov, 2003;Bass et al, 1990;Lyman, 1977;Dukhin and Goetz, 2002). The situation changes, however, if (solid) materials with high acoustic absorption coefficients (above 5 kHz) are placed in the standing wave field and transform the acoustic energy into heat.…”

Silence on Shangri-La: Attenuation of Huygens acoustic signals suggests surface volatiles

“…Note the very strong absorption by CO 2 , although this peaks at a frequency an order of magnitude lower than that for ethylene (C 2 H 4 ). Curves extracted from Petculescu et al (2006) and Dain and Lueptow (2001): see also Ejakov et al (2003). Fig.…”

“…Thus the localized atmosphere in the SSP cavity has an attenuation coefficient α of 8.7/0.12 $ 70 dB/m or $ 8 np/m: it is probable that this aggregate attenuation is the result of the absorption by several different gas species together, each at a modest concentration. Dain and Lueptow (2001) examine the attenuation in methane-air mixtures, showing that the attenuation (αλ) at 600 kHz/bar is substantially influenced by molecular relaxation of methane, having αλ $0.01 for high methane concentrations at 297 K. For the wavelength of the Titan experiment with c $ 200 m/s, λ $ 0.2 mm and thus α $50 np/m for pure methane. The methane concentration was measured (Niemann et al, 2005) to be $ 5% in the free atmosphere (where of course the pulses were transmitted successfully), but it could have risen slightly in the SSP cavity.…”

Relaxation Time Coupling Method for Ultrasonic Sensor Design

“…Over the years, some relaxation time theories have been proposed [7][8][9][10]. However, these theories did not provide an appropriate physical model to demonstrate the theoretical derivation.…”