Reynold’s Number

Laminar Flow:

When all particles of the fluid are moving in a straight line in the same direction as the axis of pipe it is known as Laminar flow.

Turbulent Flow:

When all the particles of the fluid are moving in a disorderly way it is called Turbulent Flow.

The flow through pipe will be turbulent in most water supply systems.

Re = Reynolds number (dimension less).

D = diameter of pipe in m.

V = velocity of flow in m/sec.

µ = Dynamic viscosity of fluid in Pa.s.

dynamic viscosity of water = 1 mPa.s = 1 Centipoise.
Kinematic viscosity

dynamic viscosity of water = 1 cm2/s = 1 Stoke.

ρ = density of fluid in kg/m³.

The flow can be considered as fully turbulent at Re > 10,000 and fully laminar at Re < 2,300.