Agitator Impeller Power Number & Reynolds Calculator
Determine impeller Reynolds number Re, flow regime (laminar, transition, turbulent), power number Np, and shaft motor power draw per Dickey & Hemrajani.
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Frequently Asked Questions
What is the impeller Reynolds number and why does it matter?
The impeller Reynolds number Re = (ρ·N·D²)/μ characterizes the ratio of inertial to viscous forces in an agitated vessel. At Re > 10,000, flow is fully turbulent and the power number Np becomes constant, independent of fluid viscosity.
Why does shaft power scale with the 5th power of impeller diameter (D⁵)?
Power draw is proportional to N³·D⁵ in the turbulent regime. Increasing impeller diameter by just 15% increases power draw by over 100%, making geometric scaling critical to avoid tripping electric motors or damaging gearboxes.
What is the difference between radial and axial flow impellers?
Radial flow impellers like the Rushton turbine discharge fluid outward toward vessel walls, generating high shear ideal for gas-liquid dispersion. Axial flow hydrofoils (A310) pump fluid downward along the shaft axis, producing high bulk liquid turnover with minimal power draw.