FLOW CHARACTERISTICS OF DRAG-REDUCING FIBER SUSPENSIONS IN A CENTRIFUGAL PUMP¹⁾

The drag reducing feature is observed in the performance measurement of the suspension pumping with fibers by an open-impeller centrifugal pump (with the rated rotating speed n = 1450 r/min, the flow rate Q = 26.8 m^3/h). The flow characteristics are investigated by the particle image velocity to examine the effect of the fiber particle on the flow field. It is found that, for the mass concentration of 0.1%\sim0.2% at the flow rate of 0.4Q\sim1.4Q, the flow loss caused by the fiber suspension decreases with the increasing concentration. The particle distribution is investigated by the high-speed photography. At a lower flow rate, the fiber is mainly orientated toward the circumferential direction. At the rated flow rate and a larger flow rate, the fiber orientation becomes randomly distributed. The flow passage is occupied by the fabricate fiber structure as the fiber-fiber interaction increases with the concentration, which may be beneficial for reducing the flow loss. The effect of the drag-reducing in a random distribution case is more significant than that in the circumferential distribution, which may be due to the greater rise of the relative velocity level in the random case. But no sediment of fiber flocs and clogs occur during the full operational range.