Calculate shaft power from fluid properties. Test speed, diameter, viscosity, and power number before scale-up. Export results, inspect trends, and improve agitation decisions confidently.
This calculator estimates impeller shaft power and motor demand for stirred vessels. It combines fluid properties, impeller geometry, rotational speed, and either a manual or estimated power number. It also reports Reynolds number, flow regime, torque, tip speed, tank volume, and power per unit volume.
It is useful for quick screening during mixer selection, scale-up checks, fermentation studies, blending analysis, and preliminary motor sizing. For final equipment design, compare these results with vendor curves, pilot data, and process-specific constraints such as gas dispersion, solids loading, or non-Newtonian behavior.
The main agitation power equation is:
P = Np × ρ × N³ × D⁵
Where P is shaft power in watts, Np is the power number, ρ is fluid density in kg/m3, N is rotational speed in revolutions per second, and D is impeller diameter in meters.
The Reynolds number is calculated as:
Re = (ρ × N × D²) / μ
Where μ is dynamic viscosity in Pa·s. Reynolds number helps identify whether the flow is laminar, transition, or turbulent.
When you choose estimated power number mode, the calculator applies an impeller-based approximation. In laminar flow it uses a K/Re style estimate. In turbulent flow it uses a typical constant power number for the selected impeller. Between those limits it interpolates smoothly.
Additional outputs use these relationships:
Motor Power = Shaft Power × Service Factor / Efficiency
Tip Speed = π × D × N
Torque = P / (2πN)
Tank Volume = π × T² × H / 4
Power per Volume = P / V
| Case | Speed | Impeller Diameter (m) | Reynolds Number | Power Number | Shaft Power (kW) | Motor Power (kW) |
|---|---|---|---|---|---|---|
| Small blending tank | 300 rpm | 0.10 | 5,000.00 | 1.3000 | 0.0016 | 0.0022 |
| Fermenter mixing duty | 180 rpm | 0.35 | 126,175.00 | 5.2000 | 0.7595 | 0.9705 |
| Viscous liquid agitation | 60 rpm | 0.50 | 197.92 | 27.7270 | 0.8231 | 1.1225 |
These sample rows show how power changes with speed, viscosity, and impeller style. Use them as a reference point when validating your own entries.
Agitation power input is the shaft energy transferred by an impeller into a fluid. It shows how strongly the mixer circulates, disperses, suspends, or blends the process liquid.
Reynolds number indicates whether mixing flow is laminar, transitional, or turbulent. That regime changes the power number and strongly affects the predicted shaft power.
Use manual mode when you already know the impeller power number from vendor data, pilot trials, literature correlations, or previous plant measurements. It is usually more reliable than a generic estimate.
Yes. Enter the value and choose cP. The calculator converts centipoise to pascal-seconds automatically before calculating Reynolds number and power.
Total shaft power is calculated as power per impeller multiplied by the number of impellers. Real systems may still need a design review for spacing and interaction effects.
No. This is a fast engineering estimate. Final selection should also consider geometry ratios, gas handling, solids concentration, non-Newtonian flow, heat transfer, and manufacturer performance data.
Motor power includes service factor and efficiency losses. Shaft power is what the fluid requires, while motor sizing must cover actual operating losses and margin.
Power per volume compares mixing intensity across different vessel sizes. It is helpful for scale-up, fermentation studies, blending work, and process benchmarking.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.