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# Laminar, Transitional and Turbulent Flow

## Heat transfer, pressure and head loss in a fluid varies with laminar, transitional or turbulent flow.

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There are in general three types of fluid flow in pipes

• laminar
• turbulent
• transient

### Laminar flow

Laminar flow generally happens when dealing with small pipes and low flow velocities. Laminar flow can be regarded as a series of liquid cylinders in the pipe, where the innermost parts flow the fastest, and the cylinder touching the pipe isn't moving at all.

Shear stress in a laminar flow depends almost only on viscosity - μ - and is independent of density - ρ.

### Turbulent flow

In turbulent flow vortices, eddies and wakes make the flow unpredictable. Turbulent flow happens in general at high flow rates and with larger pipes.

Shear stress in a turbulent flow is a function of density - ρ.

### Transitional flow

Transitional flow is a mixture of laminar and turbulent flow, with turbulence in the center of the pipe, and laminar flow near the edges. Each of these flows behave in different manners in terms of their frictional energy loss while flowing and have different equations that predict their behavior.

Turbulent or laminar flow is determined by the dimensionless Reynolds Number.

### Reynolds Number

The  Reynolds number is important in analyzing any type of flow when there is substantial velocity gradient (i.e. shear.) It indicates the relative significance of the viscous effect compared to the inertia effect. The Reynolds number is proportional to inertial force divided by viscous force.

The flow is

• laminar when Re < 2300
• transient when 2300 < Re < 4000
• turbulent when 4000 < Re
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## 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.
• ### 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.
• ### Liquids - Kinematic Viscosities

Kinematic viscosities of some common liquids like motor oil, diesel fuel, peanut oil and many more.
• ### Pipe Line Velocities vs. Fluid

Typical fluid flow velocities for common liquids, gases and vapors.
• ### Pressure Gradient Diagrams

Static pressure graphical presentation throughout a fluid flow system.
• ### Reynolds Number

Introduction and definition of the dimensionless Reynolds Number - online calculators.
• ### Viscous Liquids - Friction Loss vs. Viscosity and Flow

Friction loss in steel pipes for fluids with viscosities ranging 32 - 80000 SSU.
• ### Water - Absolute (Dynamic) Viscosity vs. Temperature and Pressure

Absolute viscosity for water in centipoises for temperatures between 32 - 200oF.
• ### Water Flow in Tubes - Reynolds Number

Reynolds number for clean cold water flow.
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## Citation

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• The Engineering ToolBox (2004). Laminar, Transitional and Turbulent Flow. [online] Available at: https://www.engineeringtoolbox.com/laminar-transitional-turbulent-flow-d_577.html [Accessed Day Month Year].

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9.19.12

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