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Difference between Impulse Turbine and Reaction Turbine
A turbine is a device which converts the energy of some fluid into rotational mechanical energy. There are a number of turbines available based on the type of input fluid used such as steam turbine, water turbine, gas turbines, etc.
Also, based on the action of fluid (water) the hydro-turbines are classified into two types, viz.
Impulse Turbine
Reaction Turbine
In this article, we will discuss all the major differences between an impulse turbine and a reaction turbine. But, before discussing the difference, let's get a basic overview of these two types of turbines.
What is an Impulse Turbine?
The type of hydro-turbine, where the turbine is rotated by the impulse force of the water jet is known as impulse turbine. In the impulse turbine, the pressure of water is converted into kinetic energy in a nozzle and then the velocity of the water jet drives the turbine.
The main components of an impulse are: set of runner blades and nozzle. The nozzle converts the pressure of water jet into kinetic energy, after discharging from the nozzle, the water jet strikes the runner blades and turns the runner through its axis. In this way, the impulse force of water jet drives the turbine.
The most common examples of impulse turbines are − Pelton wheel turbine, Turgo turbine, and Cross flow turbine.
What is a Reaction Turbine?
The type of hydro turbine, which uses the pressure as well as velocity of the moving water to spin the runner is called a reaction turbine. The reaction turbines are placed in the water stream where the water enters the turbine casing and after rotating the blades, the water leaves the turbine casing.
The Francis turbine and the Kaplan turbine are the two most popular reaction type water turbines. A typical reaction turbine consists of rows of fixed blades and rows of moving blades. In the reaction turbine, the moving water can produce a reaction force on the runner blades, which can rotate the runner on its axis. After moving the runner blades, the water leaves the turbine cashing.
Difference between Impulse Turbine and Reaction Turbine
The key differences between an impulse turbine and a reaction turbine are highlighted in the following table −
| Basis of Difference | Impulse Turbine | Reaction Turbine |
|---|---|---|
| Definition | The type of turbine in which only kinetic energy of water (impulse force) is used to rotate the turbine is known as impulse turbine. | The type of water turbine in which both kinetic energy as well as pressure energy of water is used turn the turbine is called the reaction turbine. |
| Water flow | In an impulse turbine, the water flows through a nozzle and strikes to the blades of the turbine. | In reaction turbine, the water is guided by the guide blades (fixed blades) to flow over the turbine. |
| Force on blades | In impulse turbine, an impulsive force rotates the turbine. | In reaction turbine, a reaction force on the blades is rotation the turbine. |
| Pressure of water while flowing over moving blades | In impulse turbine, the pressure of water remains unchanged and is equal to atmospheric pressure when it flows over the moving blades. | In the reaction turbine, the pressure of water continuously decreases when it flows over the blades. |
| Decrease in pressure of water | In impulse turbine, the pressure of water is reduced in the nozzle before entering the turbine. | In reaction turbine, the pressure of water is decreasing while flowing over the blades. |
| Change in pressure of water | In impulse turbine, all the pressure of water is converted into kinetic energy before striking the turbine blades. | In reaction turbine, there is no change in the pressure of water before striking the turbine blades. |
| Water head | The impulse turbines are most suitable for large water heads. | The reaction turbines are suitable for relatively low water heads. |
| Water flow rate | The impulse turbines are suitable for comparatively low water flow rates. | Reaction turbines are suitable in cases where water flow rates are higher. |
| Necessity of turbine casing | In impulse turbine, there is no necessity of turbine casing as it has no hydraulic function. It is just provided to prevent splashing of water. | In reaction turbine, the turbine casing is required because the pressure at inlet is very high as compared to pressure at outlet. Therefore, the casing seals it from the atmospheric pressure. |
| Blades profile | The blades of an impulse turbine are of symmetrical profile. | The blades of a reaction turbine are asymmetrical, having aerofoil profile. |
| Water discharge | In impulse turbine, the water discharges directly from the turbine wheel to tail race. | In a reaction turbine, the water discharges into a draft tube first and then into the tail race. |
| Turbine size | For the same power output, the size of impulse turbine is smaller. | The reaction turbine have relatively large size for the same power output. |
| Examples | Popular examples of impulse turbine are: Pelton wheel turbine, Turgo turbine and cross-flow turbine. | Popular examples of reaction turbines are: Francis turbine and Kaplan turbine. |
Conclusion
The most significant difference between an impulse turbine and a reaction turbine is that the impulse turbine uses only kinetic energy of water to rotate its runner, while the reaction turbine uses both pressure and kinetic energy of water to spin the turbine.
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