Difference Between Impulse and Reaction Turbine
Classification of Hydraulic turbines:
1) Based on type of energy at inlet to the turbine:
All the available energy of the fluid is converted into kinetic energy by an
efficient nozzle that forms a free jet
Only a portion of the fluid energy is transformed into kinetic energy before the
fluid enters the turbine runner.
The jet is unconfined and at atmospheric pressure throughout the action of water
on the runner, and during its subsequent flow to the tail race.
Water enters the runner with an excess pressure, and then both the velocity and
pressure change as water passes through the runner
Blades are only in action when they are in front of the nozzle.
Blades are in action all the time.
Water may be allowed to enter a part or whole of the wheel circumference
Water is admitted over the circumference of the wheel.
The wheel does not run full and air has free access to the buckets.
Water completely fills the vane passages throughout the operation of the turbine.
Casing has no hydraulic function to perform; it only serves to prevent splashing and
to guide the water to the tail race.
Pressure at inlet to the turbine is much higher than the pressure at outlet ; unit has
to be sealed from atmospheric conditions and, therefore, casing is absolutely
Unit is installed above the tail race.
Unit is kept entirely submerged in water below the tail race.
Flow regulation is possible without loss.
Flow regulation is always accompanied by loss.
When water glides over the moving blades, its relative velocity either remains
constant or reduces slightly due to friction.
Since there is continuous drop in pressure during flow through the blade passages,
the relative velocity does increase.
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