Energy line and hydraulic
grade line (EL AND HGL)
The Energy Line
EL = H = p / γ + v2 / 2 g + h =
constant along a streamline
where
EL = Energy Line
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
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
where
HGL = Hydraulic Grade Line
The hydraulic grade line lies one
velocity head below the the energy line.
EXAMPLE OF EL AND HGL
Example 1
Example 2
CONCLUSION FOR EL AND HGL
• EL
always higher or same level w ith HGL.
• The
difference between 2 lines is the value of kinetic energy head,V2/2g.
• Major
losses - cause EL and HGL to decrease gradually.
• Minor
losses - cause EL and HGL to decrease rapidly.
• Use
of pump - Lines increased immediately
• Use
of turbine - Lines decrease immediately
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