CENTRIFUGAL PUMP DESIGN CALCULATIONS

Centrifugal pumps are widely used in industries for fluid transport due to their efficiency and simplicity. The design involves key calculations to ensure optimal performance, including flow rate, head, power, and efficiency.

1. Flow Rate (Q)

The volumetric flow rate (Q) is determined based on system requirements, measured in m³/s or GPM. It influences impeller design and pipe sizing.

2. Total Head (H)

The total dynamic head (H) is the energy imparted to the fluid, comprising:

Static Head (vertical lift)
Friction Head (pipe losses)
Pressure Head (difference in system pressures)

The Darcy-Weisbach equation calculates friction losses:

$H_{f} = 2 g D f L v ^{2}$

where $f$ = friction factor, $L$ = pipe length, $v$ = velocity, $D$ = diameter, and $g$ = gravity.

3. Pump Power (P)

The hydraulic power ( $P_{h}$ ) required is:

$P_{h} = ρ g Q H$

where $ρ$ = fluid density. The shaft power ( $P_{s}$ ) accounts for efficiency ( $η$ ):

$P_{s} = η P ^{h}$

4. Impeller Design

The impeller diameter (D) and speed (N) affect pump performance. Specific speed ( $N_{s}$ ) helps classify pump type:

$N_{s} = H ^{3/4} N Q$

(For consistent units: $N$ in RPM, $Q$ in GPM, $H$ in ft)

5. Net Positive Suction Head (NPSH)

To avoid cavitation, the available NPSH (NPSHa) must exceed the required NPSH (NPSHr):

$NPS H_{a} = ρ g P ^{a t m} - P ^{v} + H_{s} - H_{f}$

where $P_{a t m}$ = atmospheric pressure, $P_{v}$ = vapor pressure, and $H_{s}$ = suction head.

6. Efficiency Considerations

Pump efficiency ( $η$ ) depends on hydraulic, mechanical, and volumetric losses. Proper selection of materials, seals, and bearings enhances performance.

Conclusion

Centrifugal pump design requires precise calculations to meet operational demands while ensuring energy efficiency and reliability. Parameters like flow rate, head, power, and NPSH must be optimized for effective performance in various applications.