Pumping Performance Increase Through the Addition of Turbulent Drag-Reducing Polymers to Pulp Fibre Suspensions

Abstract

The addition of a small amount of long chain polymers to a turbulent fluid is known to reduce the wall shear stress and drag. Similarly, the addition of pulp fibres to a turbulent suspension is also turbulent-drag reducing despite pulp fibres having a length scale that is 1000 times larger than polymer molecules. The mechanism of drag reduction and its impact on centrifugal pump performance is poorly understood, especially when there is a combination of polymer and fibres in suspension. Centrifugal (slurry) pump performance was measured as a function of pulp fibre and PAM polymer concentration. Both the pump best efficiency and maximum head rise were greater when pumping modest concentrations of polymer solutions and low consistency pulp fibre than pure water. We measured an efficiency increase of 22 percent and a maximum head increase of 4.3 percent with the addition of 150 ppm PAM polymer relative to pure water. We measured an increase of 8 percent and 2.3 percent in pump efficiency and maximum head coefficient, respectively, with 2 percent pulp fibres over that of water alone. With both 1 percent consistency pulp fibres and 100 ppm of PAM polymers, we measured a 12 percent increase in efficiency over that of pulp suspension alone. With both 2 percent consistency pulp fibres and 100 ppm of PAM polymers, we measured an 8 percent increase in efficiency over that of pulp fibre suspension alone. The reasons for the increased pump efficiency with addition of additives is not known but are thought to be due to the turbulent-drag-reducing properties associated with flow of these suspensions.

Experimental analysis of the influence of polymer solutions on performances and cavitation of small size pumps for professional appliances

“…13 In AbuYousef et al. 3 a study with a 20 ppm solution reports 12% increase of the maximum efficiency even though the head coefficient remains approximately equal compared to pure water. In our case, the increments of head and efficiency are lower, probably because of the polymer degradation which occurs in re-circulatory systems.…”

“…The most significant effect of polymers could be the reduction of some internal losses of the pump, as clearance viscous dissipation and, in particular, disk and casing friction, 2–4 leading to more or less significant efficiency increments, depending on the mechanical structure of the pump.…”

“…Indeed, a cleaning product is a mixture of builders, surfactants, acids, alkalis, and other substances that influence in various manners the properties of the solution. 1 Polymers, in particular, could have an influence on pump performances 2–5 mainly due to the drag reduction caused by their presence, especially at high Reynolds numbers. As reported in Bird et al., 6 this effect was declared by Toms in 1948, observing that a small concentration of poly methyl methacrylate, approximately 10 ppm, diminished the friction factor, also if density and viscosity of the solution had a minor variation compared to the pure solvent.…”