Some general aspects of bubble behaviour

In many chemical processes a gas containing a reactant is passed continuously through a liquid that contains another reactant. In most cases die gaseous reactant is transferred to the liquid phase and reacts there. 

The gas is introduced via a porous plate or a perforated ring, and forms bubbles, that rise to the surface under the influence of gravity. Depending on the hydrodynamic conditions, gas bubbles may coalesce and break-up. Since bubbles rise with a finite speed, there is a certain holdup of gas bubbles present in the two phase mixture, which may be constant in time. When the bubbles are smaller, they generally rise more slowly, so that the gas holdup is increased. When the gas flow rate is then increased, the gas holdup will increase also. In first approximation it will increase proportionally to the gas flow rate. 

The gas flow, moving upward as a bubble stream, will induce a certain motion in the liquid phase. The rising bubbles cause small scale circulations, on the scale of 

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