Microbubble Persistence in Fresh Water

Abstract

Preliminary research confirms that microbubbles become stabilized in a body of water and persist for long periods of time in contradiction of classical theory. The evidence was obtained by generating bubbles at the bottom of a water tank and then measuring the decay of ultrasonic attenuation as bubbles of various sizes rose to the surface. Comparison of experimental and classical decay curves disclosed persistence that appeared to be a function of the solid particle content of the water and indicated that bubbles may stabilize at sizes as large as 30 μ radius in water of high particulate content. In waters of low particulate content the decay of attenuation lasted over 100 hr. Substantial persistent abnormal attenuation was detected in all fresh tap water measured, amounting to a minimum 44% over that of distilled water (at 5.125 Mc) and is believed to be caused by stabilized bubble nuclei somewhat less than 0.8 μ in size. An interesting discovery was that attenuation rose in an uncovered test basin but fell in a covered basin, indicating that microbubbles may enter water on dust particles. A hypothesis presented to explain the persistence effect suggests that solid particles collect on the bubble surface, forming a compressed wall capable of supporting the excess pressure necessary to halt gas diffusion. Other hypotheses explore the mechanism by which dust particles may carry air globules below the water surface, and the dynamics of microbubble populations.