Vibrating Liquid Surfaces as Generators of Bubbles and Drops

Abstract

Capillary vibrations of a flat liquid surface were studied in 1830 by Faraday, later became known as Faraday crispations, and still later were further analyzed by Lord Rayleigh (well described in his Theory of Sound, Chap. XX). It was known (as a nuisance) that a too vigorous vibration caused drops of liquid to be thrown into the air. It is now discovered that crispations of a flat liquid surface in air may generate a copious supply of minute bubbles of air below the liquid surface, as well as drops of liquid above the surface. The bubble and drop diameters and the half-wavelength of the sonic ripple on the liquid surface are of the same order of magnitude. Further, it is found that a vibrating drop of liquid may throw off smaller droplets into the air and that a vibrating gas bubble in a liquid may throw off smaller bubbles into the liquid. This mechanism of bubble generation is of great significance in the study of sonically induced cavitation in liquids and clarifies some past enigmas. It has been observed at audio-frequencies, at 18 kc, and probably at 2.5 mc. Known frequency formulas have been checked by observing the resonant frequency of bubbles of a range of sizes. Certain combinations of bubble diameter and frequency are especially effective in bubble formation.