Introduction
In an Impulse turbine, all hydraulic energy is converted into kinetic energy by a nozzle. While In a reaction turbine, only some of the available energy is converted into kinetic energy. Before further detailed explanation let’s have some overview of Impulse and Reaction Turbine.
Impulse Turbine
The impulse turbine changes the velocity of the water jet. The jet impinges on the turbine’s curved blade which changes the direction of the flow. The resulting change in momentum (impulse) causes an impact force on the turbine blades. Since the turbine is spinning, the force acts through a distance, and the diverted water flow is left with diminished energy.
Before hitting the turbine blades, the water pressure (potential energy) is converted to kinetic energy by a nozzle and focused on the turbine. No pressure change occurs at the turbine blades The turbine doesn’t require housing for operation. Newton’s second law describes the transfer of energy for an impulse turbine. Impulse turbines are most often used in very high head application. This turbine works at atmospheric pressure.
The following are the types of Impulse turbines:
- Turgo Turbine
- Banki (cross-flow) turbine
- Girard Turbine
- Pelton Turbine.
Reaction Turbine
Reaction turbines are acted on by water which changes pressure as it moves through the turbine and gives up its energy. They must be encased to maintain the water pressure (or suction), and they must be fully submerged in the water flow.
Newton’s third law describes the transfer of energy for the reaction turbine. Most water turbines use a reaction turbine. They are used in low and medium-head applications. This turbine works above atmospheric pressure. The following are the types of Reaction turbines:
- Thompson Turbine
- Francis Turbine
- Kaplan Turbine
- Fourneyron Turbine
- Propeller Turbine.
Difference between Impulse and Reaction Turbine
| Sr. No | IMPULSE TURBINE | REACTION TURBINE |
| 1 | All hydraulic energy is converted into kinetic energy by a nozzle. | Only some amount of the available energy is converted into kinetic energy. |
| 2 | Requires less maintenance. | Reaction turbines require more maintenance. |
| 3 | The degree of reaction is zero. | The degree of reaction is between ‘0’ and ‘1’ |
| 4 | It needs low discharge of water. | It needs medium and high discharge of water. |
| 5 | Water flow is tangential to the turbine wheel. | Water flow is radial and axial to the turbine wheel. |
| 6 | Impulse Turbine has more hydraulic efficiency. | Reaction Turbine has relatively less efficiency. |
| 7 | Impulse turbine operates at high water heads. | It operates at medium and low heads. |
| 8 | An example of an impulse turbine is the Pelton wheel. | An example of a Reaction turbine is Francis & Kaplan turbine. |
| 9 | Flow regulation is done using a needle valve fitted into the nozzle. | Flow regulation is carried out using guide vane assembly. |
| 10 | The turbine is always installed above the tailrace and there is no draft tube used. | The reaction turbine is generally connected to the tailrace through a draft tube which is a gradually expanding passage. |
| 11 | The turbine doesn’t get completely full and air has free access to the bucket. | Water completely fills at the passage between the blades and while flowing between the inlet and outlet sections. |
| 12 | Water is admitted only in the form of jets. There may be one or more jets striking an equal number of buckets simultaneously. | Water is admitted over the entire circumference of the runner. |
FAQ:
What is Impulse Turbine?
What is the Reaction Turbine?
Newton’s third law describes the transfer of energy for the reaction turbine. Most water turbines uses a reaction turbine.
What is the difference between the Impulse and Reaction Turbine?
References:
https://www.sciencedirect.com/topics/engineering/impulse-turbine
