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Gas holdups and the rising velocity of large and small bubbles are measured using the dynamic gas disengagement approach in a pressured bubble column of 0.3 m in diameter and 6.6 m in height. The effects of superficial gas velocity, liquid surface tension, liquid viscosity, and system pressure on the gas holdups and the rising velocity of small and large bubbles are investigated. The holdup of large bubbles and the rising velocity of small bubbles increase with increasing liquid viscosity and liquid surface tension. Meanwhile, the holdup of small bubbles and the rising velocity of a swarm of large bubbles decrease. Moreover, the holdup of large bubbles and the rising velocity of a swarm of small bubbles decrease with increasing system pressure. A correlation for the holdup of small bubbles is obtained from experimental data.

Detailed local three-phase hydrodynamic parameters, namely, the liquid velocity, bubble rise velocity, and gas holdup, were obtained for an external-loop airlift reactor using a fiber-optic probe and laser Doppler anemometry techniques. The radial and axial evolutions of these parameters and the effect of the solid fraction on the flow hydrodynamics were studied. The experiments showed that the bubble size has a large influence on the evolutions of these parameters because of radial forces acting on the bubbles. Bubble coalescence prevails near the distributor, while bubble breakup is more important in the fully developed flow. The liquid velocity and gas holdup decrease and the bubble rise velocity increases as the solid fraction increases.