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Pressure head is a term used in fluid mechanics to represent the internal energy of a fluid due to the pressure exerted on its container. It may also be called static pressure head or simply static head (but not static head pressure). It is mathematically expressed as:
Practical uses for pressure head
Fluid flow is measured with a wide variety of instruments. The venturi meter in the diagram on the right shows two columns of a measurement fluid at different heights. The height of each column of fluid is proportional to the pressure of the fluid. To demonstrate a classical measurement of pressure head, we could hypothetically replace the working fluid with another fluid having different physical properties.
For example, if the original fluid was water and we replaced it with mercury at the same pressure, we would expect to see a rather different value for pressure head. In fact, the specific weight of water is 9.8 kN/m3 and the specific weight of mercury is 133 kN/m3. So, for any particular measurement of pressure head, the height of the column of water will be about 13.6 times taller than the column of mercury would be (133/9.8 = 13.6). So if a water column meter reads "13.6 cm H2O," then a coinciding measurement is "1.00 cm Hg."
This example demonstrates why there is a bit of confusion surrounding pressure head and its relationship to pressure. Scientists frequently use columns of water (or mercury) to measure pressure, since for a given fluid, pressure head is proportional to pressure. Measuring pressure in units of "mm of mercury" or "inches of water" makes sense for instrumentation, but these raw measurements of head must frequently be converted to more convenient pressure units using the equations above to solve for pressure.
In summary, pressure head is a measurement of length, which can be converted to the units of pressure, as long as strict attention is paid to the density of the measurement fluid and the local value of g.
Implications for gravitational anomalies on
We would normally use pressure head calculations in areas in which g is constant. However, if the gravitational field fluctuates, we can prove that pressure head fluctuates with it.
See Engineering Toolbox article on Specific Weight See Engineering Toolbox article on Static Pressure Head
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Pressure_head". A list of authors is available in Wikipedia.|