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=:::~ .................... ...... - Fluid properties

13.3 Viscous liquids

When handling viscous liquids with a centrifugal pump, some marked
differences are noticed from the values that are identified on the
characteristic performance curves. There is a marked increase in the
horsepower draw, a reduction in total head and some reduction in
capacity.
The charts under Figures 13.3 and 13.4 have been designed to assist
with the calculation of the viscous performance of a standard
centrifugal pump when the regular water performance is known.
As an example, consider the conditions where the pump is required to
deliver 750 gpm at a total head of 100 feet, when the liquid has a
viscosity of 1,000 SSU and a specific gravity of 0.9 at the pumping
temperature.
Enter Figure 13.4 at the bottom at the flow of 750 gpm, go up to a
Head of 100 feet. From that point, move horizontally on the chart to
the viscosity of 1,000 SSU, and then vertical upwards to intersect the
curves for the correction factors.
The lowest curve Ch provides the correction for the Efficiency at 0.635
The next curve CQ identifies the correction for Capacity at 0.95
The next series of curves CH identifies the correction for the Total
Head at various percentages of the B.E.P., and at the 1.0 x Q~v (or
B.E.P) the correction is 0.92

750
Qw = 0.95 = 790gpm

lOO
Hw = = 109ft. of Head
0.92

With this data, we can now select a pump with a water capacity of 790
gpm at a head of 109 feet. The selection should be made as close as
possible to the maximum efficiency point (B.E.P.) for water
performance. At that condition on the sample performance Figure 13.6
the efficiency is identified as 81%. Consequently the efficiency for the
viscous liquid will be as shown in the formula below.

Evis. = 0.635 x 81% = 51.5%

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