| Summary: | 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 over that of 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 fibre alone. With both 2 percent consistency pulp fibres and 100 ppm of PAM
polymers present, we measure an 8 percent increase in efficiency over that of pulp
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.
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