This work investigates detailed formation of air bobbles oil a submerged micrometer-sized nozzle. The experimental study is conducted oil a submerged nozzle of radius of 55 mu m Under low gas flow rate conditions (0.015 similar to 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 oil 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 bobble 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. (c) 2009 Elsevier Inc. All rights reserved.