Experiment on the straw particle flow in a centrifugal pump

Centrifugal pump is extensively used in wastewater, pulp, and biomass industries for transporting of particle flows. The motion and distribution of flexible particles are critical for continuous and stable pumping. In this work, a test rig is set up for straw particle flow pumping. A stroboscopic flash is employed to capture the distribution of the straw particle. The pump performance is measured and compared to that of clear water. By increasing the particle concentration, the process from stable pumping to eventually clogging is observed. Firstly, in a wide operation range with 0.1% concentration, the particle is uniformly distributed in the flow passage and the pump is running in a hydrodynamic stable mode where the power increases gradually and is slightly over the pure water circumstance. However, the high efficiency region is shifted to lower flow rate and it becomes narrower as compared to the pure water case. Secondly, at 0.2% and 0.4% concentration, the performance resembles the 0.1% case. But with increasing concentration, the inception of small flocs is observed. In addition, small air bubble is formed near the rotating axis. This subtle change continues until clogging happens. By gradually increasing the concentration of particle, more and more particles are attached to the growing flocs. Finally, the pump runs into mechanical wear between particles and flow passage, and then it is fully clogged. In this condition, the power consumption increases rapidly and the variable frequency drive is used to bring down the shaft speed. The long-term running shows relatively light erosive wear on the surface of impeller and volute by the particles, but no damage is observed.