Laser Velocimetry Measurements in a Double Volute Centrifugal Pump

Laser velocimetry measurements were taken in a double volute/single discharge centrifugal pump (0.60 specific speed, 1583 US units) with symmetrical volute halves. Blade-to-blade radial and tangential velocity profiles at the impeller exit are presented and compared to data for a similar single volute pump. Flow rates ranged from 40% of design flow to the design point. The blade-to-blade profiles were more uniform than for the single volute pump. Also, the average circumferential variations for the double volute pump were more symmetric than for the single volute pump. For the double volute geometry measurements indicate that radial inward flow (recirculation) was only present for flow rates below 60% of design flow, compared to 80% of design flow for the single volute pump. Velocity data was also used to determine volute losses, slip factor, and momentum contributions to the impeller radial forces. Volute losses were quantified and shown to increase for flow rates below 80% of design flow and were approximately 10% of the developed head at 40% flow. The efficiency in the double volute compared to the single volute shows decreased performance for flows above 55% of design flow, which is attributed to increased boundary layer friction; at low flow rates increased performance is ascribed to better control over the recirculation regions. Slip factors were symmetric around the volute but were lower than for a single volute pump. Finally, momentum contributions to the total impeller radial load were shown to be maximum at the design point, contributing 40% of the force developed by the pressure distribution; the significance diminished at lower flow rates and the contribution was negligible at 40% of the design flow.