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# 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.

### Entrance Length

The entrance length can be expressed with the dimensionless Entrance Length Number as

El = le / d                           (1)

where

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)

where

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)

## Related Topics

• ### Fluid Mechanics

The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.

## Related Documents

• ### Darcy-Weisbach Equation - Major Pressure and Head Loss due to Friction

The Darcy-Weisbach equation can be used to calculate the major pressure and head loss due to friction in ducts, pipes or tubes.
• ### Laminar, Transitional and Turbulent Flow

Heat transfer, pressure and head loss in a fluid varies with laminar, transitional or turbulent flow.
• ### Poiseuille's Formula

Calculate the volume flow discharged through a smooth-walled circular pipe.
• ### Reynolds Number

Introduction and definition of the dimensionless Reynolds Number - online calculators.

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## Citation

• The Engineering ToolBox (2003). Fluid Flow - Entrance Length and Developed Flow. [online] Available at: https://www.engineeringtoolbox.com/entrance-length-flow-d_615.html [Accessed Day Month Year].

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7.8.15

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