Use the Pipe Flow Reynolds Number for Turbulent Flow to find the Entrance Length for Fully Developed Flow

The entrance length to reach fully developed flow can be calculated for turbulent flow and for laminar flow in pipes or ducts. It may be of interest in order to determine whether the entire pipe flow can be treated as fully developed flow. The Reynolds Number is used to determine whether there is turbulent flow or laminar flow. Then equations are available for estimation of the entrance length, which is the length of the entrance region, in which the velocity profile changes. At the end of the entrance region, the pipe flow becomes fully developed flow and the velocity profile becomes constant. The Reynolds Number is used in the equations for calculating the entrance length.