Reynolds number and its significance

Reynolds number 

• The Reynolds number is the basic tool to predict the flow pattern in a conduit.
• It is the ratio of the inertial force to the viscous force.

        where

        D = diameter of the pipe, ( m)

        u = average velocity, ( m/s )

        ρ = density of the fluid, ( kg/m³ )

        μ = viscosity of the fluid, ( kg/m.s )

        N_Re = Reynolds number

        Significance of Reynolds number

• It is a dimensionless number.
• It is a useful tool to determine the nature of the flow, whether laminar or turbulent flow.

         When

                  N_Re  < 2100, the flow is always laminar

                  N_Re  > 4000, the flow is turbulent laminar

         When 

                 2100<NRe < 4000  Flow is transition flow where the flow is changed                           from laminar to turbulent