Techreport,
Vapor Cavity Formation in Liquids
Acoustics Research Lab, Harvard U., Cambridge, Mass., (February 1970)
Abstract
The work is devoted to the experimental and theoretical study of vapor cavity formation in pure and impure liquids. A novel experimental technique was developed for studying the properties of liquids under conditions that are not ordinarily accessible. This technique involves the use of an acoustic standing wave field established in a column of one liquid in order to trap an immiscible droplet of another liquid. In this experiment an either droplet suspended in glycerine was superheated and acoustically stressed until the combination produced an explosive liquid-to-vapor phase transition. The measured trade-off between tensile stress and superheat as causes of this vapor cavity formation is in gratifying agreement with the theory of homogeneous nucleation in liquids. The theoretical efforts go beyond this study of nucleation in pure liquids to consider the nucleation of vapor cavities from imperfectly wetted solid impurities (motes) in liquids. The qualitative conclusions of this theory bring some semblance of order to a wide variety of observations of statically-induced cavitation and low-frequency acoustic cavitation reported in the literature. A theory for the frequency dependence of the acoustic cavitation threshold, based on numerical solutions for the motion of a vapor cavity in a viscous, incompressible liquid subjected to an acoustic field, also yields results consistent with the available experimental data.
