Sound attenuation in a condensing vapor

Abstract

The process of acoustic attenuation in a condensing medium is investigated using a continuumlike formulation that allows for the phase-exchange process. The liquid phase is assumed sufficiently disperse so that the field may be treated as a continuum. The elementary relaxation processes associated with droplet velocity, temperature, and vapor pressure equilibration are equally important in determining the attenuation when vapor, liquid, and inert gas mass fractions are of the same order. When the liquid mass fraction is small, however, a strong attenuation band appears at low frequencies. This attenuation process involves a coupled relaxation process in which heat transfer and vaporization processes combine to change the temperature of the relatively large gas mass. This attenuation band (i) centers on a frequency that is proportional to the concentration of liquid, and (ii) has a maximum value that varies directly as the concentration of condensible vapor and roughly as the square of the latent heat of vaporization. When the concentrations of liquid and condensible vapor are both small, the low-frequency attenuation band is nearly isolated and may be described in a convenient analytical manner.