## 29 August 2020

### Difference between impulse and reaction turbine

The main difference between impulse and reaction turbines is that all hydraulic is converted into kinetic energy by a nozzle in the impulse turbine and while in reaction turbine only some amount of the available energy is converted into in the form of kinetic energy. So here this article gives the main difference between impulse and reaction turbines to better understand this topic.

What is the impulse turbine?

In the impulse, the turbine changes the velocity of the water jet. The jet impinges on the turbine curved blade which changes the direction of the flow. The resulting change in the momentum causes a force on the turbine blades basis.

What is the reaction turbine?

The reaction turbines are acted on by water which changes pressure as it moved through the turbine and gives up its energy. They must be encased to contain the water pressure, there must be fully submerged in the water flow.

## Difference between impulse turbine and reaction turbine:

• The impulse turbine only the kinetic energy is used to rotate the turbine, while in reaction turbine both the kinetic and pressure energy are used to rotate the turbine.
• The impulse turbine all hydraulic energy is converted into kinetic energy by a nozzle and it is the jet so produced which strikes the runner blades, while in the reaction turbine only some amount of the available energy is converted into the form of kinetic energy before the fluid enters the runner.
• In an impulse turbine, the watertight casing is not necessary. The casing has no hydraulic function to perform. It only serves to prevent splashing and guide water to the tailrace. But in the reaction turbine, the runner must be enclosed within a watertight casing.
• The impulse turbine doesn't run full and air has free access to a bucket, while in reaction turbine water completely fills at the passes between the blades and while flowing between the inlet and outlet section does work on the blades.
• In Impulse, turbine water is admitted only in the form of jets. There may be one or more jet striking the equal number of buckets simultaneously but in reaction turbines, the water is admitted over the entire circumference of the runner.
• Impulse turbine has a high operating speed, while in reaction turbine has a low operating speed.
• In an impulse, the turbine is always installed above the tailrace and there is no draft tube used, while in reaction turbine is generally connected to the grade to the tailrace through a draft tube which is a gradually expanding passage. It may be installed below or above the tailrace.
• In an impulse turbine, the pressure of the water remains unchanged and is equal to the atmospheric pressure during the process, while in reaction turbine the pressure of the water is reducing after passing through vanes.
• For the same power development, the number of stages required in an impulse turbine is way less when compared to the number of stages required in the reaction turbine.
• Impulse turbine has less maintenance work where the reaction turbine has high maintenance work.
• Impulse turbine is used for steam propulsion of ship and submarines, electricity generation and for cargo operation on ship and refineries. While in reaction turbine is mainly used for electricity generation.
• Example of the Impulse turbine is a Pelton wheel, Banki turbine, on the other hand, the reaction turbine is Francis turbine, Kaplan and propeller turbine, Deriaz turbine, Fourneyron, tubular turbine, etc.
• In an impulse turbine, relative velocity of fluids remains fairly same across the blades, while in reaction turbine relative velocity of a fluid increases gradually across the blades.
• The degree of reaction is 0 in impulse turbine, while in reaction turbine the degree of reaction between 0 and 1.