The Bubble Motion Charactristics In Stagnant Highly Viscous Liquids

The viscosity of the liquid has significant affect on the bubble terminal velocity. The motion characteristics of single and conjunct bubbles rising freely in stagnant water and glycerol aqueous solution were experimentally measured by a high speed charge coupled device (CCD) camera. The results for single bubble show that, in low-viscosity liquids, the bubble shows large distortion and oscillation, the bubble shape changes from the spherical shape to the irregular ellipsoid and the bubble rising trajectory changes from a rectilinear path to a zigzag or spiral path as the bubble equivalent diameter increases. In the high viscosity liquid, the bubble shape changes gradually from spherical shape to spherical cap as the increase of bubble diameter, the periodical oscillation and the bubble terminal velocity decreases while the aspect ratio increase. The results for conjunct bubbles show that, the drag coefficient of single bubble is twice as that of conjunct bubbles, and the existence of trailing bubble size or size ratio affects rising velocity a little. The experimental correction equations of single and conjunct bubbles terminal velocity are proposed respectively, the predicted values are in good agreement with the experimental data and have a better prediction than the previous reports.The surrounding liquid flow fields of the single and conjunct bubbles were measured by high speed particle image velocimetry(PIV). In water system, the bubble tail consists of a pair of unsteady vortexes which are twisted along a helical path. The pair of vortexes are firstly attached to the bubble tail at two asymmetrical positions and then detached along the bubble rising path. In pure glycerin, there are three relative high velocity regions for the single bubble: the top, tail and posterior lateral the bubble. There are only two relative high velocity regions for the conjunct bubbles: the top of heading bubble and side of bubbles juncture.