Fluid Flow - Entrance Length and Developed Flow
The entrance length is the length in a tube or duct after an obstruction - until the flow velocity profile is fully developed.
A fluid flow need some length to fully develop the velocity profile after passing through components like bends, valves, pumps, turbines or similar.
The entrance length can be expressed with the dimensionless Entrance Length Number as
El = le / d (1)
El = Entrance Length number
le = length to fully developed velocity profile (m, ft)
d = tube or duct diameter (m, ft)
Entrance Length Number for Laminar Flow
The Entrance length number correlates with the Reynolds Number and for laminar flow the relation can be expressed as:
Ellaminar = 0.06 Re (2)
Re = Reynolds Number
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)