CHAPTER 6
VELOCIS SOLUTIONS @2018
10
Figure 7.8: System and performance curve
Example 6.1
A process liquid is pumped from a storage tank to a distillation column, using a centrifugal pump.
The pipeline is 80 mm internal diameter commercial steel pipe, 100 m long. Miscellaneous losses
are equivalent to 600 pipe diameters. The storage tank operates at atmospheric pressure and the
column at 1.7 bara. The lowest liquid level in the tank will be 1.5 m above the pump inlet, and the
feed point to the column is 3 m above the pump inlet. Plot the system curve on the pump
characteristic given in Figure A and determine the operating point and pump efficiency.
Properties of the fluid: density 900 kg/m
3
, viscosity 1.36 mNs/m
2
.
Solution
o Difference in elevation, ∆z = 3.0 − 1.5 = 1.5 m
o Difference in pressure, ∆P = (1.7 − 1.013)10
5
= 0.7 × 10
5
N/m
2
o as head of liquid = (0.7 × 10
5
)/(900 × 9.8) = 7.9 m
o Total static head = 1.5 + 7.9 = 9.4 m
As an initial value, take the fluid velocity as 1 m/s, a reasonable value.
Cross-sectional area of pipe =
π
4
(80 × 10
−3
)
2
= 5.03 × 10
−3
m
2
Volumetric flow-rate = 1×5.03×10
-3
×3600 = 18.1 m
3
/h
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