Darcy's formula for loss of head in pipe
Key FactsGyroscopic Couple: The rate of change of angular momentum () = (In the limit).
- = Moment of Inertia.
- = Angular velocity
- = Angular velocity of precession.
Blaise Pascal (1623-1662) was a French mathematician, physicist, inventor, writer and Catholic philosopher.
Leonhard Euler (1707-1783) was a pioneering Swiss mathematician and physicist.
Henry Philibert Gaspard Darcy (1803-1858) was a French engineer who made several important contributions to hydraulics.
OverviewWhen the water is flowing in a pipe, it experiences some resistance to its motion, whose effect is to reduce the velocity and ultimately the head of water available. An empirical formula for the loss of head due to friction was derived by Henry Darcy. The loss of head due to friction according to Darcy is,
- = Loss of head due to friction
- = Length of pipe
- = Diameter of the pipe
TheoryConsider a uniform long pipe through which water is flowing at a uniform rate as shown in figure. Let,
- = Velocity of water in the pipe
- = Frictional resistance per unit area at unit velocity
- = Intensity of pressure at section (1-1)
- = Intensity of pressure at section (2-2)
Dividing both sides by -
We know that as per Froude's experiment, frictional resistance
Substituting the value of frictional resistance in the above equation,
Let us introduce another coefficient () such that,
Substituting the value of in equation (2)
Example - Determination of the loss of head
Find the loss of head due to friction in a pipe of 500mm diameter and 1.5km long. The velocity of water in the pipe is 1.0 m/s. Take coefficient of friction as 0.005.
- = 500 mm = 0.5 m
- = 1.5 km = 1500 m
- = 1 m/s
- = 0.005
Loss of head due to friction = 3.01 m