Characteristic of bubble rise in quiescent liquids

Abstract

The shapes and trajectories of a rising bubble in a column of water are studied experimentally, using videography and image processing algorithms to obtain its position and dimensions. The experiments were conducted by varying the bubble diameters ranging from 3.6mm to 10.5mm, corresponding to a Reynolds number between 1700 to 5000. Familiar bubble trajectories such as the zigzag and helical motion were observed, and an inverse relationship could be seen between bubble diameter and aspect ratio. Further data analysis showed that a rising bubble possesses terminal velocity, with minor fluctuations about a mean value. The plot of drag coefficient against Reynolds number also described a slight upward trend for Reynolds number between 1700 and 17000, where the drag coefficient of the bubble is generally higher than that of a solid smooth sphere, due to the increased form drag brought about by its ellipsoidal shape. This empirical model forms a basis for the derivation of a logarithmic regression equation to describe the relationship between a bubble’s shape and terminal velocity.