Calculator Inputs
Formula Used
Main shaft power: P = Np × ρ × N³ × D⁵ × n
Motor input power: Pmotor = (P × Safety Factor) ÷ (ηmech × ηmotor)
Torque: T = P ÷ ω, where ω = 2πN
Reynolds number: Re = (ρ × N × D²) ÷ μ
Tip speed: Vtip = π × D × N
In these formulas, Np is power number, ρ is fluid density, N is rotational speed in revolutions per second, D is impeller diameter in meters, n is the number of impellers, μ is dynamic viscosity, and η represents efficiency.
The calculator first estimates shaft power from impeller geometry and fluid properties. It then applies the safety factor, mechanical losses, and motor losses to estimate actual electrical input power, energy use, and operating cost.
Power number values vary with impeller design, vessel geometry, and flow regime. Use measured or vendor values whenever available. The built-in presets are practical starting points, not strict design guarantees.
How to Use This Calculator
- Select an impeller type. Choose custom if you already know the power number.
- Enter diameter, speed, density, and viscosity using the units you prefer.
- Add the number of impellers and the efficiency assumptions for drive losses.
- Enter safety factor, operating hours, electricity cost, and working volume if needed.
- Press Calculate to show the result block above the form.
- Review shaft power, motor input power, torque, Reynolds number, energy, and cost.
- Use the chart to see how power changes with rotational speed.
- Download the result table as CSV or PDF for reporting.
Example Data Table
| Case | Impeller | D | RPM | Density | Viscosity | Np | Approx. Shaft Power |
|---|---|---|---|---|---|---|---|
| Water blend | Pitched Blade Turbine | 0.30 m | 250 | 1000 kg/m³ | 1 cP | 1.30 | 228.60 W |
| Gas dispersion | Rushton Turbine | 0.40 m | 180 | 1050 kg/m³ | 2 cP | 5.00 | 1451.52 W |
| Gentle blending | Hydrofoil | 0.50 m | 120 | 980 kg/m³ | 3 cP | 0.30 | 73.50 W |
Frequently Asked Questions
1. What does impeller power consumption mean?
It is the power needed to rotate an impeller in a fluid. The value depends on fluid density, speed, diameter, impeller geometry, and total system losses.
2. Why is power number important?
Power number links impeller geometry to power draw. Different designs transfer energy differently, so the same speed and diameter can produce very different power requirements.
3. Why does power increase so quickly with speed?
Power is proportional to rotational speed cubed in the standard correlation. A modest speed increase can therefore create a much larger rise in required shaft power.
4. Why does impeller diameter matter so much?
Power is proportional to diameter raised to the fifth power. Small diameter changes can strongly affect motor sizing, energy demand, and torque.
5. When is Reynolds number useful here?
It helps judge whether the mixing flow is laminar, transitional, or turbulent. That regime affects how reliable a chosen power number is for the process.
6. Should I use shaft power or motor input power?
Use shaft power for process mixing calculations. Use motor input power when estimating electrical demand, energy use, utility cost, and motor selection.
7. Can I use this for non-Newtonian fluids?
Only as a rough screening tool. Non-Newtonian fluids often need rheology-specific methods, because apparent viscosity changes with shear rate and mixing conditions.
8. Are the preset power numbers exact?
No. They are practical starting values. Final design should use test data, manufacturer guidance, or validated plant correlations for the exact vessel and impeller.