**Reynold’s Number Definition:**

Reynold’s number is a pure number. It is equal to the ratio of the inertial force per unit area to the viscous force per unit area for a flowing fluid.

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## Reynold’s Number | Definition, Formula – Hydrodynamics

**Reynold’s Number Formula:**

Reynold number,

K = \(\frac{\text { Inertial force }}{\text { Force of viscosity }}=\frac{v_{c} \rho r}{\eta}\)

where, v_{c} = critical velocity.

For pure water flowing in a cylindrical pipe, K is about 1000.

- When 0 < K < 2000, the flow of liquid is streamlined.
- When 2000 < K < 3000, the flow of liquid is variable between streamlined and turbulent.
- When K > 3000, the flow of liquid is turbulent.

It has no unit and dimension.

**Hydrodynamics:**

In physics, hydrodynamics of fluid dynamics explains the mechanism of fluid such as flow of liquids and gases. It has a wide range of applications such as evaluating forces and momentum on aircraft, prediction of weather, etc.