Centrifugal Pumps and Viscosity

When a liquid flow through a pump, hydrodynamic losses depends on fluid viscosity

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

q_v= c_q q  (1)

where

q_v = flow compensated for viscosity (m³/h, gpm)

c_q = viscosity flow coefficient

q = original flow according pump curve (m³/h, gpm)

Head

h_v= c_h h  (1)

where

h_v = head compensated for viscosity (m, ft)

c_h = viscosity head coefficient

h = original head according pump curve (m, ft)

Efficiency

μ_v= c_μ μ  (1)

where

μ_v = effciency compensated for viscosity

c_μ = viscosity efficiency coefficient

μ = original efficiency according pump curve

Power - SI units

P_v= q_v h_v ρ_v g / (3.6 10⁶  μ_v) (1)

where

P_v = power compensated for viscosity (kW)

ρ_v = density of viscous fluid (kg/m³)

g = acceleration of gravity (9.81 m/s²)

Power - Imperial units

P_v= q_v h_v SG / (3960 μ_v) (1)

where

P_v = power compensated for viscosity (bhp)

SG = specific gravity of viscous fluid

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