Calculator
Example Data Table
| Case | Diameter (m) | Speed (rpm) | Density (kg/m³) | Dynamic Viscosity (Pa·s) | Reynolds Number | Regime |
|---|---|---|---|---|---|---|
| A | 0.20 | 150 | 1000 | 0.25 | 400 | Laminar |
| B | 0.25 | 300 | 1000 | 0.05 | 6250 | Transitional |
| C | 0.30 | 600 | 997 | 0.001 | 897300 | Turbulent |
| D | 0.15 | 480 | 1200 | 0.02 | 10800 | Turbulent |
| E | 0.50 | 120 | 900 | 0.50 | 900 | Transitional |
Formula Used
The impeller Reynolds number compares inertial effects with viscous effects during agitation.
Using dynamic viscosity: Re = (ρ × N × D²) / μ
Using kinematic viscosity: Re = (N × D²) / ν
Where:
- Re = impeller Reynolds number
- ρ = fluid density in kg/m³
- N = rotational speed in rev/s
- D = impeller diameter in m
- μ = dynamic viscosity in Pa·s
- ν = kinematic viscosity in m²/s
Common mixing guidance uses these flow zones: laminar below 10, transitional from 10 to 10000, and turbulent above 10000.
How to Use This Calculator
- Enter the impeller diameter and choose its unit.
- Enter the rotational speed and choose rpm, rps, or rad/s.
- Enter the fluid density and pick the matching density unit.
- Select dynamic or kinematic viscosity, then enter the value and unit.
- Click the calculate button to view Reynolds number, regime, graph, and export options.
Frequently Asked Questions
1. What does impeller Reynolds number show?
It indicates whether mixing around the impeller is dominated by viscosity or inertia. That helps you judge flow regime, scaling behavior, and whether circulation is likely to be smooth or strongly turbulent.
2. Why is impeller diameter squared in the equation?
Diameter strongly affects local flow conditions. Because diameter appears as D², a larger impeller can raise Reynolds number quickly, even if speed and fluid properties stay unchanged.
3. Should I use rpm or rps?
You can enter either one here. The calculator converts the speed internally to revolutions per second before applying the Reynolds number equation.
4. When should I use dynamic viscosity?
Use dynamic viscosity when your fluid data sheet lists values in Pa·s, mPa·s, or cP. The calculator then derives kinematic viscosity using the entered density.
5. When should I use kinematic viscosity?
Use kinematic viscosity when your data is reported in m²/s or cSt. This is common for oils and some process liquid references.
6. Are the regime limits exact?
No. They are practical guidelines used for mixing analysis. Actual flow also depends on impeller geometry, baffling, tank shape, and non-Newtonian fluid behavior.
7. Why does the graph only change speed?
The graph isolates one variable for clarity. It keeps diameter and viscosity constant so you can see how rotational speed alone shifts Reynolds number.
8. Can I use this for scale-up checks?
Yes. It is useful for quick comparisons between pilot and production conditions. Match or compare Reynolds numbers to understand whether the flow regime stays similar.