Manual for the Design of Pipe Systems and Pumps - GEA ...

4.4 Friction
losses
4.5 Reynolds
number
The occurance of friction losses in a pipe system is very complex and of essential importance
when selecting the pump. Friction losses in components caused by the flow in the pipe
system (laminar flow and turbulent flow) are specified by the pump manufacturer.
There are two different types of flow
Laminar flow is characterized by concentric layers moving in parallel down the length of the
pipe, whereby highest velocity is found in the centre of the pipe, decreasing along the pipe
wall (see Fig. 9). Directly at the wall the velocity decreases down to zero. There is virtually no
mixing between the layers. The friction loss is proportional to the length of the pipe, flow
rate, pipe diameter and viscosity.
Fig. 9 - Laminar flow
In case of turbulent flow strong mixing takes place between the layers whereby the
the velocity of the turbulences is extremely high.
Turbulent flow occurs mainly in low viscous fluids and is characterised by higher friction
losses. The friction losses behave proportional to the length of the pipe, square flow rate,
pipe diameter and viscosity.
Fig. 10 - Turbulent flow
In transition between laminar flow and turbulent flow there is a multitude of so called
„mixed flows“. They are characterised by a combination of properties of the turbulent flow
and the laminar flow. For determination and simple computing of the specific characteristics
the Reynolds number was introduced. This dimensionless number is the ratio of fluid
velocity multiplied by pipe diameter, divided by kinematic fluid viscosity.
Re = v x DN / ν Re = Reynolds number
v = Fluid velocity (m/s)
DN = Pipe diameter
ν = Kinematic fluid viscosity
General: Laminar flow - if Re < 2320
Turbulent flow - if Re ≥ 2320
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GEA Tuchenhagen