Physical properties of fluid and fluid transport in piping system
Laminar and turbulent flow in pipe
Reynolds number
Flow in pipes and valves theory - full content
The nature of flow in pipe, by the work of Osborne Reynolds, is depending on the pipe diameter, the density and viscosity
of the flowing fluid and the velocity of the flow. Dimensionless Reynolds number is used, and is combination of these four
variables and may be considered to be ratio of dynamic forces of mass flow to the shear stress due to viscosity.
Reynolds number is:
where is:
- D - internal pipe diameter
- v - velocity
- &rho - density
- &nu - kinematic viscosity
- &mu - dynamic viscosity
Flow in pipes is considered to be laminar if Reynolds number is less than 2320, and turbulent if the Reynolds number
is greater than 4000. Between these two values is "critical" zone where the flow can be laminar or turbulent or in the
process of change and is mainly unpredictable.
When calculating Reynolds number for non-circular cross section equivalent diameter (four time hydraulic radius d=4xRh)
is used and hydraulic radius can be calculated as:
Rh = cross section flow area / wetted perimeter
It applies to square, rectangular, oval or circular conduit when not flowing with full section.
Because of great variety of fluids being handled in modern industrial processes, a single equation
which can be used for the flow of any fluid in pipe offers big advantages. That equation is Darcy formula,
but one factor - the friction factor has to be determined experimentally. This formula has a wide application
in the field of fluid mechanics and is used extensively throughout on this web site.
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