Visual Experiments of Bubble Growth and Departure at the Tip of Inclined Capillary Tubes in a Stagnant Liquid

Abstract

The bubble growth and departure at the tip of inclined glass capillary tubes in stagnant fluid is experimentally investigated by using a high-speed visual system. The visual experiments show that the bubble growth experiences a sphere-like growth stage and the asymmetric growth stage at the tip of an inclined capillary tube. In the asymmetric growth stage, the bubble firstly gets an upward deflection under action of buoyancy force and then the triple contact line of the bubble detaches from the downside of the tube tip and withdraws into the tube. In the period of bubble departure, the neck of the bubble shrinks towards the upside of the tube tip and finally breaks up at the far upper portion of inner surface edge. The incursion of liquid into the tube tip has been detected after the bubble departing from tube tip. It is found that the departure size and the growth cycle period of the bubble as well as the volume of liquid incursion into the tube are decreased with an increase in the inclined angle of the tube. A smaller inner diameter of the inclined capillary tube leads to a smaller bubble departure size and a shorter cycle period of the bubble growth.