Piping Network Losses

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[1]Piping networks can consist of turns, bends, valves, changes in pipe diameters and shape, inlets, outlets and many more components that create a head loss in the system, on top of the already existing head loss from a straight pipe. These head losses are considered to be minor, unless many of them exist over a short distance, while straight pipe head losses are considered to be major. This article discusses the calculations associated with these losses.

Contents

Textbook Readings

Cengel and Cimbala, Fluid Mechanics: Fundamentals and Applications, (2nd ed, Singapore, McGraw Hill Education, 2010), pp. 364 - 370 (Chapter 8).

Minor Losses Calculations

[2]Minor losses, like major losses, are not evaluated through a purely mathematical solution, but are rather evaluate from experimental results. The minor losses for a single bend/vale/inlet/outlet/etc. are usually given through the loss coefficient, defined as:

MinorLossCoefficient.png

Where:

hL = the added head loss in the piping system due to the component. It is given by finding the head loss due to pipe-component system and then taking away from that the head loss due to the pipe.

Note that very often, an accurate result can only be found if the head loss is evaluated between two point that are far apart (where one is far downstream) in order to incorporate the full losses from the turbulent effect the components have. In addition, when the inlet and outlet of a component have the same diameter, the loss coefficient can be determined by finding the pressure difference across the component and dividing it by the dynamic pressure, i.e.

MinoLossCoefficient2.png

and from this, the head loss can be found by:

MinorHeadLoss.png

Pipe Components and Loss Coefficient

[3]For many applications, the loss coefficient can be set to be equal to the kinetic energy correction factor, that is:

KL = α

However whenever there is a sudden expansion, the loss coefficient can be expressed as:

MinorLossesSuddenExpansion.png

while for sudden contraction, a table is used.

References

"Textbook" refers to Cengel and Cimbala, Fluid Mechanics: Fundamentals and Applications, (2nd ed, Singapore, McGraw Hill Education, 2010).

  1. Textbook p. 364
  2. Textbook p. 364
  3. Textbook p. 366
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