In fluid dynamics, head refers to the constant right hand side in the incompressible steady version of Bernoulli's equation. It is possible to express head in either units of height (e.g. meters) or in units of pressure such as pascals (the SI unit).

This is best understood by considering a waterwheel: the head is the vertical distance from the top of the waterwheel to the free surface of the millpond.

More generally, when considering a flow, one says that head is lost if energy is dissipated, usually through turbulence; equations such as the Prony equation and the Darcy-Weisbach equation have been used to calculate the head loss due to friction. In the context of steam trains, one talks of a good head of steam, referring to the pressure in the boiler.

The static head of a pump is the maximum height (pressure) it can deliver. The capacity of the pump can be read from its Q-H curve (flow vs. height).

Head is used to exemplify the influence in incompressible fluids. Head has units of aloofness and equals the fluid's energy per unit weight. Head is useful in specifying centrifugal pumps because their pumping distinctiveness tend near be self-regulating of the fluid's density.

There are four types of head used to calculate the total head in and out of a pump:

• Static head is due to gravitational force on a column of fluid.
• Velocity head is due to the motion of a fluid.
• resistance head is due to the frictional forces against a fluid's motion.
• Pressure head is due to other mechanical forces acting on a fluid.

Fluid dynamics

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