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Turbines

Used to generate electricity. Direction of energy transfer is fluid to machine.

Rotating element is called as the runner.

Types of turbines

Reaction turbines

Aka. pressure turbines. Similar to pumps. Operating in reverse direction (direction of fluid flow and energy transfer). Guide vanes are placed to guide fluid flow onto the runner.

3 types of reaction turbines based on the direction of fluid flow.

Radial flow

Aka. Francis turbine. Commonly used to get a head output of 30 to 500m.

Axial flow

Aka. Kaplan turbine. Commonly used to get a head output of 3 to 70m.

Mixed flow

A combination of radial flow and axial flow.

Impulse turbines

Aka. velocity turbines. Used for high heads. Highly efficient. Includes a runner (a wheel with buckets attached) mounted on a shaft. High velocity jet is focused on the buckets.

Efficiency of an impulse turbine is given by:

Here:

  • - velocity of the jet of fluid
  • - velocity of the bucket
  • - loss coefficient (a little less than 1)
  • - angle of deflection of fluid inside the bucket

can be considered as a function of . And from that, the turbine works at maximum efficiency when .