Relation between multiphase flow patterns and performance of an air-lift system: A visualization study

초록

The present study aims to elucidate the relationship between multiphase flow patterns and lifting performance of an air-lift system. Experiments were conducted in a vertical riser pipe of 25.4 mm in inner diameter and 1000 mm in length at a submergence ratio of 0.43. Solid particles of 2.0 mm in diameter and 1320 kg/m3 in density were used. Both gas-liquid and gas-liquid-solid flow patterns were visualized using the high-speed photography. At different superficial gas velocities, mass flow rates of liquid and solid particles, pressure drop, and lifting efficiency were measured to establish quantitative correlations between flow regime and lifting performance. The results show that the lifting efficiency reaches its maximum of 21.6 % at an intermediate superficial gas velocity corresponding to the slug-to-churn flow transition regime. Under slug flow conditions, both the Taylor bubble length and slug frequency increase with the superficial gas velocity, whereas the overall slug unit length remains nearly invariant during the transition to churn flow. The introduction of solid particles accelerates the collapse of Taylor bubbles and promotes early flow regime transition due to enhanced interfacial instability and particle-bubble interactions. At a solid volume fraction of 0.046, particles with a diameter of 2.0 mm can be effectively lifted under both slug and churn flow conditions. Although churn flow exhibits stronger oscillations and higher energy dissipation, it maintains a relatively high particle lifting rate. These findings provide new insights into the coupled hydrodynamic mechanisms governing three-phase transport in air-lift systems and offer practical guidance for the design and optimization of air-lift systems.

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