Shape of long bubbles in horizontal slug flow

This paper presents a theoretical and experimental study of the shape of lo ng isolated bubbles similar to those observed in horizontal slug flows. Bub bles of different volumes were studied, their lengths varying from 30 to 10 0 times the pipe diameter. Two different shapes were observed corresponding to plug and slug flow regimes. The transition between plug and slug flow w as shown to depend on both Froude number and bubble length. A model based o n the mass and momentum conservation equations of each phase is proposed. I t is able to predict the transition between plug and slug flow regimes as w ell as the volume and the shape of long bubbles. It is shown that usual slu g flow codes that aim to predict the void fraction tend to overestimate the gas fraction in the bubble region. The model may be easily implemented int o slug tracking codes. (C) 1999 Elsevier Science Ltd. All rights reserved.