Mechanical Energy Balance

MECHANICAL ENERGY BALANCE
THE BERNOULLI EQUATION
The Bernoulli equation is an approximate relation between pressure, velocity, and elevation, and is valid in regions of steady, incompressible flow where net frictional forces are negligible.
Limitations on the Use of the Bernoulli Equation
1. Steady flow
2. Frictionless flow :( frictional effects are negligible for short flow sections with large cross sections, especially at low flow velocities)
not negligable:
– in region downstream of an object
-in diverging flow sections
-near solid surfaces
3. No shaft work (Bernoulli equation is not applicable in a flow section that involves a pump, turbine, fan, or any other machine or impeller since such devices destroy the streamlines and carry out energy interactions with the fluid particles. )
4. Incompressible flow
5. No heat transfer ( density changes)
Hydraulic Grade Line (HGL)
and Energy Grade Line (EGL)
HGL= ( measured by piezometer)

EGL= (measured by pitot tube)

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