Bubble formation on a submerged micronozzle.

This work investigates detailed formation of air bubbles on a submerged micrometer-sized nozzle. The experimental study is conducted on a submerged nozzle of radius of 55 microm under low gas flow rate conditions (0.015-0.83 ml/min). The bubble formation is recorded by a high-speed optical camera and detailed characteristics of bubble formation such as the variations of instantaneous contact angles, bubble heights and the radii of contact lines are obtained, which shows a weak dependence on the flow rate under the conditions of current work. Using experimentally captured values of the height of bubble and the radius of contact line, the Young-Laplace equation is solved, which is found to be able to predict the bubble evolution quite well until the last milliseconds before the detachment. A force analysis of bubble formation reveals that the observed variations of contact angles and other characteristics during the bubble growth period are associated with the relative contribution of surface tension, buoyancy force and gravitational force.