ρ = density (kg/m3)
γ = specific weight of fluid (N/m3)
v = flow velocity (m/s)
g = acceleration of gravity (9.81 m/s2)
h = elevation height (m)
Each term of this equation has the dimension force per unit area - N/m2 or psi, lb/ft2 in Imperial units.
By dividing each term with the specific weight - γ = ρ g - equation (1) can be transformed to express head as
p / γ + v2 / 2 g + h = constant along a streamline = H (2)
H = the total head (m fluid column)
Each term of this equation has the dimension length - m or ft in Imperial units.
Note! - the head unit is with reference to the density of the flowing fluid. For other units - like mm Water Column - check Velocity Pressure Head.
(2) states that the sum of
is constant along a stream line. This constant can be called the total head - H.
The total head in a flow can be determined by measuring the stagnation pressure using a pitot tube.
The sum of pressure head - p / γ - and elevation head - h - is called the piezometric head. The piezometric head in a flow can be measured through an flat opening parallel to the flow.
The Energy Line is a line that represent the total head available to the fluid and can be expressed as:
EL = H = p / γ + v2 / 2 g + h = constant along a streamline (3)
EL = Energy Line (m fluid column)
For a fluid flow without any losses due to friction (major losses) or components (minor losses) - the energy line would be at a constant level. In a practical world the energy line decreases along the flow due to losses.
A turbine in the flow reduces the energy line and a pump or fan in the line increases the energy line.
The Hydraulic Grade Line is a line representing the total head available to the fluid - minus the velocity head and can be expressed as:
HGL = p / γ + h (4)
HGL = Hydraulic Grade Line (m fluid column)
The hydraulic grade line lies one velocity head below the the energy line.
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
Conservation of energy in a non-viscous, incompressible fluid at steady flow.
Energy is the capacity to do work.
Calculate pressure loss - or head loss - in ducts, pipes or tubes.
Pitot tubes can be used to measure fluid flow velocities by measuring the difference between static and dynamic pressure in the flow.
Static pressure graphical presentation throughout a fluid flow system.
Inclined and vertical u-tube manometers used to measure differential pressure in flow meters like pitot tubes, orifices and nozzles.
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