Effects of thermal diffusion on sound attenuation in evaporating and condensing gas-vapor mixtures in tubes

An investigation of sound propagation in an air-water vapor mixture contained in a cylindrical tube with wet walls was recently presented [Raspet et al., J. Acoust. Soc. Am. 105, 65-73 (1999)]. The formulation of the problem paralleled the "low reduced frequency method'' of Tijdeman [J. Sound Vib. 39, 1-33 (1975)]. It was pointed out that a term of reduced frequency order had been neglected in the radial component of the diffusion equation [G. Swift, personal communication (1999)]. This term represents the additional mass diffusion driven by the temperature gradient, or Soret effect, and is proportional to the thermal diffusion ratio. The solution for the complex wave number of the acoustic mode with this additional term is presented here. Numerically calculated predictions for the air-water vapor mixture show little change in acoustic attenuation due to the coupling. Therefore, a description of the acoustic attenuation where the viscous, thermal, and diffusion processes are decoupled is adequate for the specific case previously discussed by Raspet et al. [J. Acoust. Soc. Am. 105, 65-73 (1999)]. (C) 2000 Acoustical Society of America. [S0001-4966(00)01402-8].