Centrifugal pumps viscosity effect

Characteristic curves for a typical centrifugal pump showing effect of viscosity. 

There are several similar relationships for centrifugal pumps that can be used if the effects of viscosity of the pumped fluid can be neglected. These relate the operating performance of any centrifugal pump for one set of operating conditions to those of another set of operating conditions, say conditions, and conditions 2. 

Figure 32.23 Effect of viscosity on centrifugal pump performance...

Figure 7.15. Effects of viscosity on performance of centrifugal pumps (a) Hydraulic Institute correction chart for pumping liquids, (b) Typical performances of pumps when handling viscous liquids. The dashed lines on the chart on the left refer to a water pump that has a peak efficiency at 750 gpm and 100 ft head on a liquid with viscosity 1000 SSU (220 CS) the factors relative to water are efficiency 64%, capacity 95% and head 89% that of water at 120% normal capacity (1.2QH).

Meyerhofer (4) examines the problem of spinning a two component system which is composed of solids" and a volatile "solvent". He includes the effect of solvent evaporation and a viscosity which depends on solvent concentration. In this model, the film height decreases with time not only because of the centrifugal pumping, but also because of the evaporation from the surface. As the film is depleted in solvent, the viscosity increases and less fluid is lost because of pumping. Eventually a finite film thickness can be reached because all of the solvent evaporates, and the film consists of only an immobile solid phase. The present analysis is similar to Meyerhofer s. His treatment of the evaporation is corrected, as is his conclusion on the effect of spin speed (which apparently is due to numerical error on his part), and some of his assumptions in developing the equations are relaxed. 

In general, the effective flow rate of reciprocating pumps decreases as the viscosity of the fluid being pumped increases, because the speed of the pump must be reduced. In contrast to centrifugal pumps, the differential pressure generated by reciprocating pumps is independent of fluid density. It is dependent entirely on the amount of force exerted on the piston. 

FIGURE 8-43 Effect of viscosity on the performance of centrifugal pumps. 

SeUgrem et al. (2000) conducted tests on sand as well as sand-clay mixtures pumped by centrifuged pumps. The phosphate clays had a diameter d Q between 1 p-m and 50 p,m. The sands were much coarser with of 0.64 mm (0.025 in), 1.27 mm (0.05 in), and 2.2 mm (0.09 in). The presence of clay and other particles finer than 75 p,m and a concentration smaller than 20% had a beneficial effect by reducing the head loss and efficiency derating factor. The data recorded by SeUgrem et al. (2000) should not be applied to a higher concentration of clays because the viscosity effect introduces a new component to the equation. 

Two effects on pump performance must be discussed viscosity and gas content. Figures 32.23 and 32.24 illustrate the effects of viscosity change on centrifugal and... 

ANSI/HI standard 9.6.7-2010 [B131], Effects of Liquid Viscosity on Rotodynamic (Centrifugal and Vertical) Pump Performance, published by Hydraulic Institute, Dec. 2010. 

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