Influence of bubble size on the transition from low-Re bubbly flow to slug flow in a vertical pipe

Abstract

An upward air–water bubbly flow in a pipe was studied experimentally, special attention being paid to the transition from bubbly flow to slug flow. The pipe diameter was 72 mm and the height 18 m. The Reynolds number based on liquid flow was low-to-moderate ( U sl<0.2 m s−1), so that bubble break-up due to turbulence was nearly absent. Three different inlet devices were used, which had a significant influence on the initial bubble size and initial bubble concentration distribution. The transition from bubbly flow to slug flow was shown to be strongly dependent on the inlet configuration, particularly on the bubble size. A number of theoretical models for the transition from bubbly flow to slug flow were reviewed. The Taitel et al. [2] approach was combined with a bubble-size-dependent critical void-fraction expression of Song et al. [7]. This new formulation for the transition from bubbly flow to slug flow was in good agreement with the measurements.