Rushton Turbine Power Calculator
Calculate the un-aerated power draw of a Rushton turbine impeller.
Introduction
For fermentation scientists and scale-up engineers, accurately estimating the baseline motor sizing and hydrodynamic loads in sterile bioreactor tanks is critical before introducing sparge gas. This Rushton Turbine Power Calculator provides an essential tool for this preliminary assessment.
It calculates the un-aerated power draw of a Rushton turbine impeller, relying on the standard turbulent regime formula: P = Np × ρ × N³ × D⁵. This equation helps predict the mechanical energy input into the fluid, a key parameter for heat management, mixing intensity, and ultimately, bioreactor design. Note that this is for the unaerated condition, with the more complex gassed power estimation requiring additional tools.
How to Use This Tool
Input the fluid density of your broth or medium into the 'Fluid Density' field.
Enter the Rushton impeller diameter in meters into the 'Impeller Diameter' field.
Set the agitation speed in revolutions per second (rps) in the 'Impeller Speed' field.
Input the standard Power Number (Np ≈ 5–6 for Rushton turbines) into the 'Power Number' field.
View the immediate calculated Power result in Watts displayed in the output log.
FAQ
Q: What is the typical Power Number for a Rushton turbine?
A: A standard six-blade Rushton turbine typically has a Power Number (Np) between 5 and 6 in the fully turbulent regime.
Q: Can I use this tool for aerated fermentation tanks?
A: No, this calculator estimates ungassed power; introduce our Michel-Miller Gassed Power Estimator when air is sparging through the impeller.
Q: How do I convert my mixer's RPM setting to the required rps?
A: Divide the RPM value by 60 to get the revolutions per second needed for the N parameter in the formula.
Q: When does this power formula stop being accurate?
A: The formula assumes a turbulent regime (Reynolds number > 10,000); accuracy drops significantly in laminar or transition flow regimes.