Microbubble formation and entrapment from liquid-liquid impacts

Abstract

A variety of splashing phenomena from an impacting liquid drop on a deep liquid pool has been studied in the past. One of the many phenomena associated with liquid drops impacting on a liquid surface is the entrapment of small air bubbles in the bulk fluid through a variety of mechanisms. This article will describe how thousands of microbubbles « 24 µm) can be entrained in the bulk fluid. All microbubble entrapment mechanisms were found to be the result of rapidly rupturing thin air films with rupture velocities ranging from 4-17 mls. The size of the air bubbles resulting from the film rupture bore a direct relation to the velocity of the film rupture. The formation of the thin film in all cases was related to the creation of an air sheet between the impacting drop and liquid surface just prior to impact. In most cases a rapid stretching and thinning of the film lead to the rupture and formation of microbubbles. A new region of microbubble entrapment was identified from the rupture of the film that supports floating drops. A map of the different microbubble formation phenomena are described in terms of Weber and Froude numbers.