ChemCalc's pump module sizes centrifugal pumps from first principles: hydraulic power from flow and differential pressure, shaft power corrected for efficiency, and NPSHa check to prevent cavitation. All per Perry's Chemical Engineers' Handbook Chapter 10.
Inputs
| Parameter | Notes |
|---|---|
| Flow rate Q (m³/h) | Volumetric flow at pump inlet conditions |
| Suction pressure P1 (kPa, abs) | Pressure at pump suction flange |
| Discharge pressure P2 (kPa, abs) | Pressure at pump discharge flange |
| Pump efficiency η | Overall hydraulic efficiency, typically 0.6–0.85 |
| Fluid density ρ (kg/m³) | At pumping temperature |
Outputs
| Output | Formula |
|---|---|
| Hydraulic power P_h (kW) | P_h = Q · ΔP (SI units: m³/s × Pa) |
| Shaft power P_s (kW) | P_s = P_h / η |
| Differential head H (m) | H = ΔP / (ρ · g) |
| Specific speed N_s | N_s = N·√Q / H¾ (dimensionless) |
NPSHa Calculator
A separate NPSHa module prevents cavitation by checking available suction head:
NPSHa = (P_s − P_v) / (ρ·g) + h_s − h_f
| Symbol | Meaning |
|---|---|
| P_s | Absolute surface pressure in suction vessel (kPa) |
| P_v | Liquid vapor pressure at pumping temperature (kPa) |
| h_s | Static suction head — liquid level above pump centerline (m) |
| h_f | Friction losses in suction piping (m) |
Rule of thumb: NPSHa ≥ NPSHr + 0.5 m safety margin. ChemCalc flags NPSHa < 2 m with a cavitation warning.
Affinity Laws
For variable-speed or impeller-trim sizing:
- Flow: Q₂ / Q₁ = N₂ / N₁
- Head: H₂ / H₁ = (N₂ / N₁)²
- Power: P₂ / P₁ = (N₂ / N₁)³
Typical Efficiency Ranges
| Pump Type | Typical η |
|---|---|
| Large centrifugal (>100 kW) | 0.75–0.87 |
| Medium centrifugal (10–100 kW) | 0.65–0.80 |
| Small centrifugal (<10 kW) | 0.50–0.70 |
| Gear pump | 0.70–0.90 |
| Diaphragm pump | 0.40–0.60 |