The roughness of the pipe wall does not influence laminar flow behavior, so the f−NRe relationship is the same for all grades of pipe. Laminar flow pressures may be predicted if desired, from Eqs. (6.51) and (6.48).
It has been found experimentally that the change from laminar to turbulent flow always occurs at approximately the same Reynolds number. With Newtonian fluids, transition to turbulent flow begins when the Reynolds number for the system is approximately 2100. Above 3000, flow is fully turbulent.
Turbulent Flow of Non-Newtonian Fluids
The Fanning friction factor and the Reynolds number may also be used to determine turbulent ...