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Fluid Flow Velocity in pipe, calculation and recommendation
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1. Introduction
2. Calculation
1. Introduction
Why is the fluid velocity in pipes important ?
The fluid velocity in a pipe is a fundamental data to calculate to be able to characterize the flow in a pipe, thanks to the Reynolds number, and size a pipe circuit calculating the pressure drop expected for a certain flow.
When designing the pipe, it is necessary to chose a fluid velocity to have good compromise in between pressure drop and economics, some recommendations are given below.
2. Calculation of fluid velocity
How to calculate the fluid velocity in pipes ?
With :
Q = Volumetric flowrate (m3/s)
D = Pipe diameter (m)
u = Fluid velocity in pipe (m/s)
Note that the velocity will be constant for a non compressible fluid but will vary with a compressible fluid such as a gas. For a gas it is therefore necessary to slice the pipe layout in several sections in order to recalculate the velocity along the pipe.
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1. Pressure drop
2. Reynolds Number
3.
Pressure drop K coefficients
4. Churchill equation
5. Moody diagram
3. Pipe velocities recommendations
What are the recommended velocities for usual process fluids ?
| Fluid | Recommended velocity |
|---|---|
| Water |
1.5-2.5 m/s [1] 1-2.5 m/s [2] |
| Air | 10-30 m/s [1] 30 m/s [2] |
| Steam |
20-40 m/s [1] HP : 45 m/s [2] LP : 30 m/s [2] |
| Gas Process flows | 15-45 m/s |
| Dry gas | 30 m/s [2] |
| Wet gas | 18 m/s [2] |
These values are given as an indication for pre-sizing. Each company should have its own guideline to be followed.
In addition to the sources given below, one may also wish to consult Applied Process Design for Chemicals and Petrochemicals plants, Ludwig, Gulf, page 85 which is giving values for specific applications like sodium hydroxide, ethylene, vinyl chloride...