# What is a Reaction Turbine? | How does Reaction Turbine work?

Turbines are most commonly used all over the world. They are mainly used in hydroelectric power plants to produce electricity. According to the runner blades and water flowing through the runner, the turbines are divided into two major types; i.e., reaction turbine and impulse turbine. In the previous article, we discussed impulse turbines. This article mainly explains the working, types, and applications of the reaction turbine.

## What is a Reaction Turbine?

A reaction turbine generates torque by reacting to the fluid’s mass or pressure. A reaction turbine has fixed rotor blades and a rotating nozzle.

Newton’s third law of motion (actions and reactions are equal but opposite in direction) describes the working of the reaction turbine (RT). It produces force due to the water movement over the fixed blades of the rotor.

In the case of a reaction turbine, the water first strikes the rotor and then strikes the nozzle. These turbines are best suitable for low and medium head flow rates.

While impulse turbines use for high head flow rates. And also, in the case of an impulse turbine (IT), the water first hits the fixed nozzle and then hits the rotor blades.

Reaction turbines have many types that we will discuss in the next section, but wind turbine is the most common type.

## Reaction Turbine Working Principle

The reaction turbine works according to Newton’s third law. It has a simple working principle that is given below with an example.

Using a rotor with a moving nozzle and high-pressure water coming out of the nozzle will help us to understand the reaction turbine working principle in a good way. The nozzle receives a reaction force when the water departs the nozzle. This reaction force causes the rotor to spin at high speed.

Similarly, in a reaction turbine, the reaction force is produced by the moving fluid over the runner blades. The reaction force generated by the runner blade causes the runner to rotate. As the water passes through the impeller blades, it ends up in the drain and finally in the tail race.

Read also: Working of Gas Turbine?

## Working of Reaction Turbine

A reaction turbine works on Newton’s third law

As the reaction turbine starts to work, a high-velocity water jet with low pressure enters the casing. The water flowing through the spiral casing has a uniform reduction in cross-sectional area, which means that the volute casing’s pressure remains constant.
As long as water remains in the casing, it flows through the guide vanes to the runner blades (as shown in the diagram above).
The guide vane guides the water jet toward the runner where it hits the runner blade at the right angle for maximum performance.
The turbine’s guide vanes have the ability to adjust their position according to the water flow rate (decrease or increase).
As the water hits the runner blades, these blades transform the water’s kinetic energy into speed. In this way, the runner reduces the water pressure and increases its speed.

As the high-speed water jet is discharged from the runner, it enters the draft tube, where it flows through a uniformly increased cross-sectional area (i.e., draft tube) so that it can regain its dropped pressure until it enters into the tail race.
The pressure variance is too much that it is very hard to recover from the draft tube. Due to this reason, the problems like corrosion and cavitation start appearing in the turbine.
The resulting high-speed water rotates the turbine shaft. This shaft further rotates the generator coil and produces electricity.

For betting understanding the reaction turbine working, watch the below-given video:

Read also: Working of Impulse Turbine

## Reaction Turbine Efficiency

The overall efficiency of the reaction turbine is the ratio of the produced power by the turbine to the supplied energy by the turbine. The maximum efficiency of the reaction turbine can be determined by the below-given formula:

η = 2cos2α/1+ cos2α

In the above equation

α = 90o for the maximum efficiency where ‘α’ is the absolute velocity vector’s angle at the opening.

Two main features that determine the reaction turbine efficiency are the profile of the runner on which the water slides and the angle of attack when the water hits the runner blades.

Thanks to the adjustability of the runner and guide blades, the turbine can now be used with different load requirements and water potentials.

The runner blades also have a flexible angle, such as if you have low energy requirements while the turbine’s water has a high flow rate; in this case, the impeller blades will adjust themselves at a smaller incline angle according to the turbine axis.

When the energy requirements are high, but the water flow rate passing through the turbine is low then these blades will be adjusted at a larger angle to the turbine axis.

## Types of Reaction Turbine

The reaction turbines have the following major types:

1. Francis turbine
2. Propeller turbine
3. Gravity turbine
4. Bulb turbine
5. Kaplan turbine
6. Kinetic turbine
7. Straflo turbine
8. Tube turbine

### 1) Propeller Turbines

The propeller turbine is one the most famous types of reaction turbine. These turbines usually have 3 to 6 impeller blades, and the water is in constant contact with all of these blades.

Propeller turbines are usually installed at a place where the load and height are constant. Under partial load, this turbine’s energy efficiency curve is very peaked, which means poor performance.

Read Also: Working of Propeller Turbine

### 2) Francis Turbines

This type of reaction turbine is basically an improved version of the propeller turbine, with the water flowing radially and axially into the runner. In the middle section of the Francis turbine, the flow channels are generally set in spiral housing with internally adjustable influence blades.

The runner of this turbine typically has nine or more fixed blades. In this turbine, the water enters directly above and around the runner, then it falls on the turbine and turns the shaft. The other main components of the Francis turbine are the draft tube, gate, and spiral in addition to the corridor.

The latest cross-flow turbine is a cheap alternative to Francis turbines.

Read More: Working of Francis Turbine

### 3) Gravity Turbines

This type of reaction turbine converts gravity force into rotational force. It transforms the kinetic energy of the gravity force into electricity.

Read Also: Different Types of Turbines

### 4) Bulb Turbine

This turbine is a variant of a propeller turbine. In these reaction turbines, the generator is enclosed and sealed in a streamlined watertight steel housing located in the duct center. The generator drives with the help of a variable pitch propeller at the downstream end of the valve.

In the bulb turbine, the direction of the water entering and exiting the device is practically unchanged or very little. The compactness of this design gives more flexibility in powerhouse design.

### 5) Straflo Turbine

The Straflo turbine is an axial flow turbine. It has fixed blades. These types of reaction turbines have generators outside the water channel. The generator is coupled directly with the turbine runner.

A tubular Straflo turbine with variable speed uses in the Tidetec turbine design. It is a very famous type of reaction turbine with almost a hundred existing installations.

Read Also: Different types of Compressors

### 6) Tube Turbine

In this type of reaction turbine, the pressure line is bent shortly before or after the flow path which enables a straight connection to the generator.

### 7) Kaplan Turbine

Kaplan turbines can achieve high-efficiency levels under various load conditions by properly adjusting the blades during their work.

Kaplan turbines allow you to adjust the blade angle or the impeller according to the required power. This allows the Kaplan turbine to work according to the load changes. This is the only reason why Kaplan turbines have full load efficiency and high part load. However, this is impossible with propeller turbines.

Read More: Working of Kaplan Turbine

## Components of Reaction Turbine

The reaction turbine has the following major components:

1. Runner
2. Guide Vanes
3. Spiral Casing

#### 1) Guide Vanes

This component of the reaction turbine is attached to the spiral casing. The main function of the guide vanes is to ensure that the water hitting the runner blades must be in the direction of the turbine shaft.

Otherwise, the water will create a strong vortex as it passes through the volute casing. Due to this reason, the runner blades will be inefficient to rotate. With the latest turbines, the angles of these vanes are flexible.

The guide vanes are properly designed in order to:

1. To ensure the water entry in the runner without shock.
2. Permit the water to flow over the runner blades without forming eddies.
3. Permit the desired quantity of water to enter the turbine.

According to the turbine load, the flow of the water can adjust by changing the angle of these guide vanes.

#### 2) Spiral Casing or Volute Housing

The spiral casing is a component that has a uniform reduction in cross-sectional area along the circumference.

The reducing cross-section area of the volute casing ensures that we have a constant velocity of the water flow that is hitting the impeller blades. Because of the small cross-sectional area, there is an opening through which water can flow from the casing entrance into the impeller blade.

The water pressure drops when it flows inside the casing. Therefore, the cross-sectional area in the circumferential direction decreases to produce a uniform pressure, so that uniform velocity water strikes the runner blades.

Read Also: Working of the Rankine Cycle

#### 3) Draft Tube

The draft tube makes a link between the runner’s exit and the tailrace. It has a cross-sectional area that increases according to its length.

When the water exits the runner blades at relatively low pressure, the draft tube’s cross-sectional area continues to expand, which helps to recover the water pressure as it moves towards the tailrace.

The runner is a major part of the reaction turbine. The main function of the runner blade is to drive the turbine by using the water’s pressure energy. Its design plays an important role in determining turbine efficiency.

Most reaction turbines have adjustable runner blades. The latest turbines allow these blades to tilt around the turbine axis, which allows the blades to change the pressure force acting on them depending on the available pressure and turbine load.

Read Also: Different Types of Pumps

• It has high hydraulic efficiency.
• This type of turbine has a high working speed.
• It is easy to construct.
• The blades have high efficiency as compared to the impulse turbine.
• It requires less space.
• The reaction turbine uses an oil-free exhaust system.
• It has a small size.
• It has a high capability to use high temperature and high pressure.

• These turbines require high maintenance as compared to an impulse turbine.
• It requires high maintenance costs.
• Thrust force generates in this type of turbine.
• It has cavitation problems.
• It doesn’t have symmetrical blades.

## Applications of Reaction Turbine

• It uses in hydroelectric power plants.
• These turbines use in wind power mills for electricity generation.

## FAQ Section

### What is a Reaction Turbine?

A reaction turbine generates torque by reacting to the fluid’s mass or pressure. A reaction turbine has fixed rotor blades and a rotating nozzle.

### What are the examples of Reaction Turbine?

The reaction turbine has the following examples:

1. Tube turbine
2. Francis turbine
3. Straflo turbine
4. Kinetic turbine
5. Propeller turbine
6. Kaplan turbine
7. Gravity turbine
8. Bulb turbine

### Where are reaction turbines used for?

The reaction turbines are used for low and medium head flow rates. The reaction turbines are used to generate electricity in hydroelectric power plants.

### What are the parts of the reaction turbine?

1. Runner
2. Guide vanes
3. Nozzle
4. Distributor
5. Spiral casing

### Which turbine has highest speed?

The Kaplan turbine has the highest speed (600 rpm to 1000 rpm) than other types of turbines.

### What are the types of the Reaction Turbines?

The reaction turbines have the following types:

1. Kaplan turbine
2. Tube turbine
3. Gravity turbine
4. Francis turbine
5. Straflo turbine
6. Kinetic turbine
7. Propeller turbine
8. Bulb turbine

This article deeply discusses reaction turbine components, working, types, and other aspects. I hope that this article will be too much helpful for you. So, feel free and contact me if you have any confusion related to this topic. I will try my best to clear up your confusion.