Expansion and Contraction Losses

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Geometry changes in pipe create two and three-dimensional flow fields within the pipe.  Bernoulli equation based analyses of piping systems are based on one-dimensional flow.  Pressure drops associated with multi-dimensional flow phenomena are taken into account using experimental data or results from more complex 

There are other mechanisms in pipe flow that create head losses in addition to friction losses. Common sources of losses are due to expansion or contractions associated with geometry changes, valves, turns and flow splitting devices such as tees.

Head losses are computed using the equation 


where KL is a loss coefficient.  In some cases KL can be determined by analysis, while in other cases KL is determined using experiments.  Values of KL for many practical flow conditions can be found in tables or handbooks. Note that the units for the head loss are associated with distance (m or ft).  Thus they can be directly used with the “head” form of the Bernoulli equation.  Head losses are placed on the outlet side of the Bernoulli equation while head creators (pumps, fans, etc.) are placed on the inlet side.

 

Learning Objectives

How losses other than friction losses are included in Bernoulli equation analyses of piping systems.

Sudden Contractions

Sudden Contractions

A sudden contraction occurs when there is a sudden reduction of the cross sectional area along the length of the pipe.

Sudden Expansions

Sudden Expansions

A sudden expansion occurs when there is a sudden increase of the cross section area along the length of the pipe.