g = acceleration of gravity (9.81 m/s 2 , 32.174 ft/s 2 )
In general the specific weight - γ - is constant for fluids. For gases the specific weight - γ - varies with elevation (and compression).
The pressure exerted by a static fluid depends only upon
For a incompressible fluid - as a liquid - the pressure difference between two elevations can be expressed as:
Δ p = p 2 - p 1
= - γ (h 2 - h 1 ) (3)
p 2 = pressure at level 2 (Pa, psi)
p 1 = pressure at level 1 (Pa, psi)
h 2 = level 2 (m, ft)
h 1 = level 1 (m, ft)
(3) can be transformed to:
Δ p = p 1 - p 2
= γ (h 2 - h 1 ) (4)
p 1 - p 2 = γ Δ h (5)
Δ h = h 2 - h 1 = difference in elevation - the dept down from location h 2 to h 1 (m, ft)
p 1 = γ Δ h + p 2 (6)
The absolute pressure at water depth of 10 m can be calculated as:
p 1 = γ Δ h + p 2
= (1000 kg/m 3 ) (9.81 m/s 2 ) (10 m) + (101.3 kPa)
= (98100 kg/ms 2 or Pa) + (101300 Pa)
= 199400 Pa
= 199.4 kPa
ρ = 1000 kg/m 3
g = 9.81 m/s 2
p 2 = pressure at surface level = atmospheric pressure = 101.3 kPa
The gauge pressure can be calculated by setting p 2 = 0
p 1 = γ Δ h + p 2
= (1000 kg/m 3 ) (9.81 m/s 2 ) (10 m)
= 98100 Pa
= 98.1 kPa
(6) can be transformed to:
Δ h = (p 2 - p 1 ) / γ (7)
Δ h express head - the height difference of a column of fluid of specific weight - γ - required to give a pressure difference Δp = p 2 - p 1 .
A pressure difference of 5 psi (lb f /in 2 ) is equivalent to head in water
(5 lb f /in 2 ) (12 in/ft) (12 in/ft) / (62.4 lb/ft 3 )
= 11.6 ft of water
or head in Mercury
(5 lb f /in 2 ) (12 in/ft) (12 in/ft) / (847 lb/ft 3 )
= 0.85 ft of mercury
Specific weight of water is 62.4 (lb/ft 3 ) and specific weight of mercury is 847 (lb/ft 3 ) .
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
Piping systems and pumps - centrifugal pumps, displacement pumps - cavitation, viscosity, head and pressure, power consumption and more.
The Darcy-Weisbach equation can be used to calculate the major pressure and head loss due to friction in ducts, pipes or tubes.
The overall pump and fan efficiency is the ratio power gained by the fluid to the shaft power supplied.
Power potential vs. head and flow rate.
Depth and hydrostatic pressure.
Pressure loss (bar/100 m) and velocy in PE, PEH or PVC pipes with water flow.
Elevation and potential energy in hydropower.
Static pressure graphical presentation throughout a fluid flow system.
Pressure vs. head units - like lb/in2, atm, inches mercury, bars, Pa and more.
Converting head (ft or m) to pressure (psi or bar, kg/cm2) and vice versa.
An introduction to pumps and the Net Positive Suction Head (NPSH).
Adding head and flowrate for pumps arranged in parallel vs. serial.
The suction head of a water pump is affected by its operating altitude.
The energy equation can be used to calculate the head rise in pumps and fans.
Utilize the system curve and the pump performance curve to select the proper pump for a particular application.
Centrifugal, axial and propeller fans and their capacity ranges.
Dynamic pressure or velocity head.
Pressure in pounds per square inch (psi) vs. head in feet of water (ft h2o).
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