Entrance Length and Developed Flow
The entrance length is the length in a tube or duct until the flow velocity profile is fully developed after obstructions.
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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
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 for Laminar Flow
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 for Turbulent Flow
The Entrance length number correlation with the Reynolds Number for turbulent flow can be expressed as:
Elturbulent = 4.4 Re1/6 (3)
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