The flow pattern of a fluid can be defined by the dimensionless quantity called Reynoldszahl.
It is the ratio of inertial forces to viscous forces.
Calculating the Reynolds number of a fluid we need to multiply the velocity with a characteristic linear dimension and divide it by the kinematic viscosity.
The critical Reynolds number where the flow behaviour changes from laminar to turbulent flow is approximately for tubes 2300.
In the plastic industry the Reynolds number is important for the subject of the cooling system.