Sound attenuation in a cylindrical tube due to evaporation-condensation

The influence of evaporation-condensation processes on sound propagation in a cylindrical tube was studied in an attempt to understand sound attenuation in porous materials. In this theoretical model, the tube wall is assumed to be rigid and kept at constant temperature. Water in a very thin layer on the wall is allowed to evaporate into or condense from the gas/vapor mixture due to the sound field propagating in the tube. In addition to the acoustical, thermal, and vorticity modes in Kirchhoff's theory, there exists a mass-diffusion mode. Sound attenuation was obtained after applying the boundary conditions at the tube wall for these four modes. Analytical expressions for the asymptotic behavior in both high- and low-frequency limits were derived. While the sound attenuation due to viscosity could be identified, those due to thermal conduction and evaporation-condensation were coupled. The sound attenuation due to the evaporation-condensation process was significant when the concentration of vapor in the tube was high, but it still underestimated the experimental results in porous materials. (C) 1997 Acoustical Society of America. [S0001-4966(97)04912-6]