Droplet generation via oscillation of a transient bubble inside a funnel-like chamber

摘要

A new microdroplet generation technique based on the bubble oscillation in a funnel-like chamber is developed and investigated numerically using combined BEM-finite difference method. In this technique, the droplet is generated and ejected from the top opening of the chamber due to the oscillation of a transient bubble inside. The water in the chamber is exposed to the atmospheric air from the top side and is connected to a liquid reservoir from the bottom side. The bubble may be generated by an electrical spark, a laser beam or a high-intensity focused ultrasound (HIFU). The effects of the bubble-free surface distance (standoff distance) on the bubble and the ensuing droplet characteristics are evaluated. It was found that the when the bubble is initiated at the narrow part of the chamber it will be affected by the chamber's lateral wall so that parts of its surface that are closer to the wall takes the wall shape. As the bubble gets closer to the free surface, the wall effects are attenuated. In addition, the droplet size and pinch off time depend on the standoff distance so that as the standoff distance increases the droplet size decreases but its pinch off time increases.