Hydraulic Head - "Head" in Fluid Dynamics

"Head" in Fluid Dynamics

In fluid dynamics, head is a concept that relates the energy in an incompressible fluid to the height of an equivalent static column of that fluid. From Bernoulli's Principle, the total energy at a given point in a fluid is the energy associated with the movement of the fluid, plus energy from pressure in the fluid, plus energy from the height of the fluid relative to an arbitrary datum. Head is expressed in units of height such as meters or feet.

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

Head is equal to the fluid's energy per unit weight. Head is useful in specifying centrifugal pumps because their pumping characteristics tend to be independent of the fluid's density.

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

1. Velocity head is due to the bulk motion of a fluid (kinetic energy).
2. Elevation head is due to the fluid's weight, the gravitational force acting on a column of fluid.
3. Pressure head is due to the static pressure, the internal molecular motion of a fluid that exerts a force on its container.
4. Resistance head (or friction head or Head Loss) is due to the frictional forces acting against a fluid's motion by the container.