Effect of Superficial Gas Velocity on Bubble Size, Terminal Bubble Rise Velocity and Gas Hold‐up in Bubble Columns

It is important to have a reliable estimate of bubble size, terminal bubble rise velocity and gas hold‐up in bubble columns, since these parameters are directly related to the transfer coefficients and the transfer area. Mean bubble diameters have been measured as a function of the superficial gas velocity in air‐water systems. In the bubbly flow regime, the bubble size is a strong function of the orifice diameter and the wettability of the gas distributor and a weak function of superficial gas velocity. In the turbulent churn flow regime this functionality is reversed and the bubble diameter becomes a strong function of the superficial gas velocity. A correlation is presented which covers both regimes. The terminal bubble rise velocity was measured as a function of the bubble size and the results were compared with correlations recommended in the literature. Finally, the gas hold‐up was measured over a wide range of superficial gas velocities. The results were compared with a variety of empirical and theoretical correlations. New equations are presented which predict gas hold‐up of the air‐water system with good accuracy.