Characteristics and Flow Patterns of a Small Screw-Type Centrifugal Pump Operating in Air-Water Two-Phase Flow.

A screw type centrifugal pump was manufactured to carry solids primarily and its impeller has a wide flow passage. However, the effect of flow passage shape on delay of the choke due to entrained air has not been clarified yet. For that reason, we carried out the pump performance experiment under air-water two-phase flow condition with different impeller tip clearances and void fractions. And we obtained the result that Δψ (loss of pump head from single-phase flow to the choke due to air entrainment) became less at a wide tip clearance than that at a narrow tip clearance. Moreover, at a narrow tip clearance, the pump head became partially higher in two-phase flow than that in single-phase flow near the best efficiency point in low void fraction region. Therefore, we have observed the internal flow pattern by using a stroboscope and measured mean size of bubbles from the images obtained by using a high speed camera. Then, we have investigated the influences of mean size of bubbles, tip clearances as well as flow patterns on pump performance.