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Pressure head is a component of hydraulic head, in which it is combined with elevation head. When considering dynamic (flowing) systems, there is a third term needed: velocity head. Thus, the three terms of velocity head, elevation head, and pressure head appear in the head equation derived from the Bernoulli equation for incompressible fluids:
[1] [2] By the barometric formula, 1 bar is roughly the atmospheric pressure on Earth at an altitude of 111 metres at 15 °C. The bar and the millibar were introduced by the Norwegian meteorologist Vilhelm Bjerknes , who was a founder of the modern practice of weather forecasting , with the bar defined as one mega dyne per square centimeter .
The meter is "read" as a differential pressure head in cm or inches of water and is equivalent to the difference in velocity head. The dynamic pressure, along with the static pressure and the pressure due to elevation, is used in Bernoulli's principle as an energy balance on a closed system .
Other units of pressure, such as pounds per square inch (lbf/in 2) and bar, are also in common use. The CGS unit of pressure is the barye (Ba), equal to 1 dyn·cm −2, or 0.1 Pa. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre ("g/cm 2" or "kg/cm 2") and the like without properly identifying the force ...
The unit, named after Blaise Pascal, is an SI coherent derived unit defined as one newton per square metre (N/m 2). [1] It is also equivalent to 10 barye (10 Ba) in the CGS system. Common multiple units of the pascal are the hectopascal (1 hPa = 100 Pa), which is equal to one millibar , and the kilopascal (1 kPa = 1000 Pa), which is equal to ...
In fluid dynamics, total dynamic head (TDH) is the work to be done by a pump, per unit weight, per unit volume of fluid. TDH is the total amount of system pressure, measured in feet, where water can flow through a system before gravity takes over, and is essential for pump specification.
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Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth.The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, [1] 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. [2]