Behavior of single rising bubbles in superpurified water

Abstract

We experimentally studied the motion and shape of single rising bubbles in superpurified water. We developed an apparatus, which was equipped with a measurement system of both resistance and TOC value of water, in order to maintain water purity by monitoring it during the experiment. We investigated the critical Reynolds number over which the rising bubble motion changed from rectilinear motion to zigzag or spiral motion. In the case of Re=650, the bubble reached the terminal velocity at the height of 40 mm and the onset of transition to zigzag or spiral motion was observed at the height of 140 mm. On the other hand, in the case of Re=700, both the terminal velocity and onset of transition were observed at the approximately same height; hence the critical Reynolds number was unable to be uniquely determined. The height of the onset of transition increased with the decrease in Reynolds number. We also compared experimental results of both the terminal rise velocities and drag coefficients with those obtained theoretically for ellipsoidal bubble in the limit of potential flow theory. For smaller bubbles, experimental values of the terminal velocities and drag coefficients showed good agreement with those obtained theoretically. For larger bubbles, however, the deferences between experimental and theoretical values in the terminal velocities and drag coefficients became prominent. Finally we quantitatively evaluated the bubble shapes by expanding them in terms of Legendre's polynomials and proposed the new correlations of the aspect ratio with either Weber number or Eotvos number. Copyright © 2007 The Society of Chemical Engineers.