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Reynolds Number
Reynolds Number is a core engineering term. Definition, usage notes, and a practical example.
Definition
Reynolds number is a dimensionless ratio of inertial to viscous forces.
Why it matters
It is a practical first check for flow regime.
How it is used
In a design check, first define the relevant load, dimension, material, or flow condition. Then interpret this term by its role in the formula and compare it with limits.
Re = density x velocity x diameter / dynamic viscosity
Example
In pipe flow, low Reynolds suggests laminar behavior and high Reynolds suggests turbulent behavior.
Related calculators and resources
Formulas
Re = density x velocity x diameter / dynamic viscosity