Internal Flow in a Centrifugal Pump of a Low Specific Speed with Semi-Open Impeller.

Abstract

The internal flow in a centrifugal pump with semi-open impeller is visualized and measured by PTV method. In this pump, the design type number is 0.244 of low specific speed. The experimental results of two impellers whose outlet angles are 30 and 90 degree are compared. At the outlet of impeller, most of the quantity of fluid flows out along the pressure side of the vane, but some climbs over the top of the vane and flows into the suction side through the tip clearance. When the total quantity is changed, the meridian velocity distribution changes only near the tongue area, and in other area the meridian velocity is almost same. When the quantity becomes small, large vortices are produced between vanes, and this vortex reduces the tangential velocity at the outlet of impeller. This causes the reduce of theoretical head and instability in the performance curve.