Effect of local pipe bends on pump performance of a small air-lift system in transporting solid particles

The pump performance of a small air-lift system in transporting solid particles is investigated experimentally. Three types of riser pipe were used to examine the effect of local bends of riser pipes on the flow characteristics of a three-phase air–water–solid particles mixture. Two of them were locally S-shaped either below or above a gas injector. The other was vertically straight. Alumina particles of 3 or 5 mm diameter were used as solid particles. It is indicated that the pump performance is appreciably reduced when the pipe bend is above the gas injector. The critical condition under which solid particles are vertically lifted is discussed from a practical viewpoint. In addition, the particle motion in the region of a pipe bend is investigated by photographic observations.