The Impeller Reynolds Number: The first among the dimensionless numbers

What is the Reynolds Number? In simple terms, it is an equation that compares the input forces to the viscous forces. This is our most important dimensionless number. It provides the most insight into the mixing environment we have.


What is the Reynolds Number? In simple terms, it is an equation that compares the input forces to the viscous forces.   This is our most important dimensionless number. It provides the most insight into the mixing environment we have.

What does the Reynolds Number tell us? It helps define the regime within the agitated/stirred vessel. For ratios that are above 10,000 we know that the mixing regime is fully turbulent. For numbers between 1000 and 10,000 we know that the mixing environment is transitional. For numbers or ratios below 1000, the mixing regime is partially laminar or fully laminar.

Why is it important to know the Reynolds Number? The Reynolds Number tells us the type of impeller, the correction factors for impeller horsepower and impeller flow rates. It also determines the relative size of the impeller compared to the mixing vessel diameter.

How is the Reynolds Number calculated?

Nre = [(N) (D)2(Density)]÷[Viscosity]

What are important questions that  should I ask the mixer manufacturer about the Reynolds Number?

  •  What is it? Turbulent, Transitional or Laminar?

  • Which impeller type was selected and how does it perform in the particular fluid regime I am mixing in?

  • What were the correction factors if any, that were used in determining the horsepower draw or the impeller flow rate?