Difference Between Impulse and Reaction Turbine

Difference Between Impulse and Reaction Turbine 

The hydraulic turbine is a prime mover that uses the energy of flowing water and converts  is  into  the  mechanical  energy  in  the  form  of  rotation  of  the  runner. 

Classification of Hydraulic turbines:
1) Based on type of energy at inlet to the turbine:
Impulse Turbine : The energy is in the form of kinetic form. e.g: Pelton wheel, Turbo wheel.
Reaction Turbine : The energy is in both Kinetic and Pressure form. e.g: Tubular, Bulb, Propellar, Francis turbine.

Difference Between Impulse and Reaction Turbines
Difference Between Impulse and Reaction Turbines 

Impulse Turbine

Reaction 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 essential

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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