Sound absorption in N2−H2O gas mixtures at elevated temperatures

Abstract

Sound absorption measurements were conducted in N2−H2O gas mixtures at 297°, 343°, and 387°K to determine the location of the vibrational relaxation peak of N2 on the frequency/pressure (f/P) axis as a function of humidity and temperature. At low humidities, the best fit of the reported data to a linear relationship between (f/P)max and humidity h yields, within experimental error, the same slope (2.00 × 104 Hz/atm mole fraction) at all three temperatures. The slope is lower than the value of 2.6 × 104 reported by Chang, Shields, and Bass at higher humidities [J. Acoust. Soc. Am. 63, 577–581 (1977)], but the two sets of data are shown to be mutually consistent by means of a model in which V-V transfer is assumed to provide the dominant relaxation path. The relationship between (f/P)max and h written into ANSI Standard S1.26/ASA23-1978 contains an excessively large slope, does not account for the observed transition between the low-humidity and high-humidity slopes, and specifies an erroneous temperature dependence. [Work supported by NASA Grant NSG 1324.]