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centrifugal pump discharge formula-Zhilong

1. Basic Discharge Formula (Volumetric Flow Rate)

The discharge (Q)of a centrifugal pump refers to the volume of fluid delivered per unit time, typically measured in m³/s, L/s, or GPM (gallons per minute). The theoretical discharge can be calculated using the following formula:

Q=A×v

where:

Q = Discharge/flow rate (m³/s)

A = Cross-sectional area of the pipe/discharge outlet (m²)

For a circular pipe: A=π d 2 4

v = Flow velocity at the discharge (m/s)

2. Using Pump Parameters (Theoretical Flow Rate)

For a centrifugal pump, the discharge depends on the impeller dimensions and speed:

Q=π D b C m 2

where:

D = Impeller diameter at the outlet (m)

b = Width of the impeller at the outlet (m)

C m 2 = Meridional (radial) component of the absolute velocity at the outlet (m/s)

3. Considering Pump Speed (RPM)

The flow rate can also be approximated using the pump's speed (N)and displacement:

Q=η v×N×V 60

where:

η v = Volumetric efficiency (typically 0.90–0.98 for centrifugal pumps)

N = Pump speed (RPM)

V = Theoretical displacement volume per revolution (m³/rev)

4. Affinity Laws (For Variable Speed)

When pump speed changes, flow rate scales proportionally:

Q 1 Q 2=N 1 N 2

where:

Q 1,Q 2 = Original and new flow rates

N 1,N 2 = Original and new speeds (RPM)

Practical Considerations

Actual flow rate may differ due to head losses, friction, and efficiency.

Pump performance curves provide accurate flow rates at different heads.