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 contain ed in a cylindrical tube with wet walls was recently presented [Raspet et a l., J. Acoust. Soc. Am. 105, 65-73 (1999)]. The formulation of the problem paralleled the "low reduced frequency method'' of Tijdeman [J. Sound Vib. 3 9, 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. Sw ift, personal communication (1999)]. This term represents the additional ma ss diffusion driven by the temperature gradient, or Soret effect, and is pr oportional to the thermal diffusion ratio. The solution for the complex wav e number of the acoustic mode with this additional term is presented here. Numerically calculated predictions for the air-water vapor mixture show lit tle change in acoustic attenuation due to the coupling. Therefore, a descri ption of the acoustic attenuation where the viscous, thermal, and diffusion processes are decoupled is adequate for the specific case previously discu ssed by Raspet et al. [J. Acoust. Soc. Am. 105, 65-73 (1999)]. (C) 2000 Aco ustical Society of America. [S0001-4966(00)01402-8].