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FLUID MECHANICS
5.2.3 Friction Loss
A
Figure 5.5 : Friction Loss
When there is a loss of head due to friction in a pipeline in terms of the velocity
head; we assume that the frictional resistance per unit area of the pipe wall is
proportional to the square of the mean velocity of flow. Consider a cylinder of fluid of
length L completely filling the pipe with cross sectional area, A and moving with a mean
velocity v ( Figure 5.5).
The force acting on the cylinder is the force due to pressure difference and the force due
to frictional resistance. Since the velocity is constant and there is no acceleration, the
resultant of these two forces in the direction of motion must be zero.
4 fL v 2
Loss of head due to friction, hf =
d 2 g
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