System Curves for Viscous Applications

Will a system curve look the same for pulp or viscous applications as it does for water?

Pump and system curves are often represented based on water-like liquids. The curves have different shapes for viscous and non-Newtonian liquids, as illustrated in Image 4. In these images, the pump head decreases as a function of increased flow and the system curve increases as a function of flow. Their intersection point is the operating flow and head.  

The laminar flow regime is maintained at higher flow velocities for the viscous liquid and a more typical shape occurs, but at lower flow velocities, there is a turbulent flow regime and the shape of the system curve changes. The performance curve for the rotodynamic pump falls off more quickly with increased viscosity, which reduces the flow through the piping. The efficiency curve will also be reduced.

The pumping of a pulp suspension is shown in Image 5 as an example of system curves for non-Newtonian liquids. The liquid characteristics of a pulp suspension are reflected in the shape of the system curve. The pump curve also changes to some extent in comparison to water. Much of this change is caused by the higher air content in the pulp.

 For more information on pump system efficiency, refer to HI’s “Pump Life Cycle Cost: A Guide to LCC Analysis for Pumping Systems” at pumps.org. 

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