Prediction of gas-phase holdup in a bubble column

Hydrodynamic properties of bubble columns play a significant role in many chemical and biochemical processes. Recent theoretical and experimental work conducted by Krishna et al. (1991, 1994), and Wilkinson et al. (1992) have been examined in conjunction with a bubble column and data for the air-water system operating at ambient conditions. The bubble column is 0.108 m in internal diameter, has a 1.70 m tall test section, and is equipped with a perforated plate distributor having 91 holes of 0.8 mm diameter. The data are taken For five values of the slumped water column height in range from 0.79 to 1.15 m, and for superficial air velocities up to about 0.4 m/s. The data accord to the qualitative aspects of Krishna et al. model but lead to different values of the bubble swarm rise velocity, and superficial transition air velocity characterizing the transition from homogeneous bubbly flow regime to heterogeneous churn-turbulent Bow regime. The quantitative reproduction by the model expressions of these recent works of the experimental data is poor. This may be partly attributed the geometry of the column, diameter and distributor design. The qualitative features of Krishna et al. model for the two regimes are confirmed by the present data. For quantitative predictions of gas-phase holdup, a new model is proposed in which the large bubble Bow in the churn-turbulent regime is formulated following the drift-flux theory. The proposed theory and experimental data are in good agreement.