Experiments were conducted to investigate the flow characteristics in the riser pipe and the suction pipe of airlift pump at a series of air flow rates and submergence ratios by using a high speed camcorder and a Laser Doppler Velocimetry system (LDV). A modified model was developed to predict the performance of airlift pump operating in gas-liquid two-phase flow. The results show that an unstable flow structure composed by a water falling film

a bubbly mixture

a water ascending film appearing alternately in riser pipe dominates the performance of airlift pump at large air flow rates. The bubbly mixture with a strongest capacity for pumping water first increases to its maximum and then slightly decreases. In suction pipe

the average velocity shows a flat profile and increases with increasing submergence ratio. Moreover

the predicted results of modified model are in good agreement with the experimental data in a margin of ±12%.