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Engineering ToolBox > Entrance Length and Developed Flow
A fluid need some length to develop the velocity profile after entering the pipe or after passing through components as bend, valves, pumps, turbines or similar.
The entrance length can be expressed with the dimensionless Entrance Length Number:
El = le / d (1)
where
El = Entrance Length Number
le = length to fully developed velocity profile
d = tube or duct diameter
The Entrance length number correlation with the Reynolds Number for laminar flow can be expressed as:
Ellaminar = 0.06 Re (2)
where
Re = Reynolds Number
The Entrance length number correlation with the Reynolds Number for turbulent flow can be expressed as:
Elturbulent = 4.4 Re1/6 (3)