Yi Mao
James M. Sabatier
Natl. Ctr. for Phys. Acoust., Univ. of Mississippi, University, MS 38677
The influence of evaporation--condensation processes on the sound propagation in a cylindrical tube were studied in an attempt to understand the sound attenuation in porous materials. In the theoretical model, the tube wall was rigid and kept a constant temperature. A very thin layer of water on the wall was allowed to evaporate into or condense from 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. The sound attenuation was obtained by applying the boundary conditions on the tube wall to these four modes. Analytic expressions for the asymptotic behaviors of 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 would increase to a substantially large level when the percentage of vapor in the tube was high, but it still underestimated the experimental results in porous materials. [Work supported by ONR.]