Acoustic Cavitation: Film Sequences and Threshold Measurements

Abstract

A novel technique for measuring the tensile strength of liquids was recently reported [R. E. Apfel, J. Acoust. Soc. Amer. 49, 145 (1971); Nature (Phys. Sci.) 233, 119 (11 Oct. 1971)]. In this technique a droplet of the sample rises slowly in a column of another liquid, the “host,” in which it is nearly insoluble. When the droplet reaches a certain position in the host, an acoustic standing-wave field at about 50 kHz is established in the column, serving two purposes: (1) to balance the buoyancy force on the droplet and thus levitate it and (2) to rend the sample apart by raising the acoustic pressure to a great enough amplitude. If the droplet is simultaneously superheated, the cavitation event takes the form of an irreversible explosion of the sample into its vapor. Taking advantage of the levitation scheme, this explosion has been filmed with both diffuse and shadow lighting at about 3500 frames/sec and shows resonant oscillations and what appears to be jet formation during the collapse of the vapor bubble. New results for the tensile strength of superheated n-pentane as a function of temperature have been measured and appear, like previous results for ether and n-hexane, to be in reasonable agreement with the theory of homogeneous nucleation. [Work supported by the U. S. Office of Naval Research, Acoustics Program.]