What is Reynolds number?

(N/A) Reynolds number is a dimensionless quantity used in fluid mechanics to predict flow patterns in different fluid flow situations.
It is defined as the ratio of inertial forces to viscous forces within a fluid which is subjected to relative internal movement due to different fluid velocities.
It depends on the density of the fluid $(\rho)$,the velocity of the fluid $(v)$,the characteristic length or diameter of the tube $(D)$,and the coefficient of viscosity $(\eta)$.
The formula for Reynolds number $(N_R)$ is:
$N_R = \frac{\rho v D}{\eta}$
Reynolds number is used to determine whether the flow of a liquid is laminar (streamline) or turbulent.