Centrifugal Pumps and Viscosity
When a liquid flow through a pump, hydrodynamic losses depends on fluid viscosity
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When a viscous fluid is handled by a centrifugal pump
- brake horsepower requirement increases
- the head generated is reduced
- capacity is reduced
- efficiency of pump is reduced and the Best Efficiency Point - BEP - is moved
The head, flow and capacity at other viscosities than used in the original documentation can be modifying with coefficients.
Flow
qv= cq q (1)
where
qv = flow compensated for viscosity (m3/h, gpm)
cq = viscosity flow coefficient
q = original flow according pump curve (m3/h, gpm)
Head
hv= ch h (2)
where
hv = head compensated for viscosity (m, ft)
ch = viscosity head coefficient
h = original head according pump curve (m, ft)
Efficiency
μv= cμ μ (3)
where
μv = effciency compensated for viscosity
cμ = viscosity efficiency coefficient
μ = original efficiency according pump curve
Power - SI units
Pv= qv hv ρv g / (3.6 106 μv) (4)
where
Pv = power compensated for viscosity (kW)
ρv = density of viscous fluid (kg/m3)
g = acceleration of gravity (9.81 m/s2)
Power - Imperial units
Pv= qv hv SG / (3960 μv) (5)
where
Pv = power compensated for viscosity (bhp)
SG = specific gravity of viscous fluid
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