Interaction of Acoustic Waves with Solid-Gas and Liquid-Vapor Interfaces

Abstract

Adsorption and condensation are presented as mechanisms for the interaction of acoustic waves with solid-gas and liquid-vapor interfaces, respectively. Interface boundary conditions are derived and are used, in turn, to derive equations that describe normal reflection of one-dimensional acoustic waves at infinitely rigid solid-gas and liquid-vapor interfaces. Results show that, as the frequency of the incident wave goes from zero to infinity, the velocity amplitude reflection ratio decreases monotonically from unity to a limiting value that may be as small as 0.42, and the phase shift of the reflected velocity wave goes from zero through a maximum and back to zero. Calculations indicate that significant absorption of the incident wave may begin at frequencies as low as about 1.0 cps (for solid-gas interfaces exhibiting chemisorption and for liquid-vapor interfaces) or as high as about 10 Mcps (for solid-gas interfaces exhibiting monomolecular physical adsorption). The interaction mechanism presented in this paper should prove useful in investigating the effects of acoustic disturbances on (1) heterogeneous chemical reactions between gaseous species adsorbed on a solid or liquid surface and (2) water-vapor condensation small solid or liquid nuclei.