What is a Reaction Turbine – Main Components and Working Principle

Nowadays, electricity is producing with the help of different turbines. There are multiple types of turbines, and reaction turbine is one of them.  According to the position of nozzle and runner blades, turbines are divided into two following types:

  1. Impulse turbine
  2. Reaction turbine

In the previous article, we discussed impulse turbines. Therefore, in this article, we will deeply examine the reaction turbine. 

What Is A Reaction Turbine?

A reaction turbine generates torque in response to the fluid’s pressure and weight. 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 on the fixed blades. 

reaction turbine

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

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.  

Read also: How does an Impulse Turbine work?

Reaction Turbine Working Principle

The reaction turbine has a very simple working principle that is given below with an example.

reaction turbine

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 impeller blades. The reaction force generated by the impeller blade causes the impeller to rotate. After water driving over the impeller blades, the water ends up in the drain and finally in the trail race.

How does a Reaction turbine work?

A reaction turbine works on the Newton’s third law. 

reaction turbine working

As the reaction turbine starts to work, a high velocity with low-pressure water jet enters into the casing. As long as water remains in the casing, it begins to flow through the guide vanes to the impeller blades (as shown in the above diagram).

The guide blade guides the water jet toward the impeller or runner and also hits the water on the impeller blade at the right angle for maximum performance. 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. The reaction turbine’s guide blades can vary their position according to the water flow rate (decrease or increase) inside the turbine.

reaction turbine working

After hitting the impeller blade, the water discharges by the impeller at very low pressure but its speed increases. After passing through the impeller, the water enters into the draft tube, where it is passed through a uniformly increased cross-sectional area so that water can regain its dropped pressure until it enters into the tailrace. But 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. 

As the water passing through the impeller, the impeller transforms the water kinetic energy into speed. When this high-speed water strikes the turbine, it rotates the generator coil and produces electricity.

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

Reaction Turbine Efficiency

Two main features that determine the reaction turbine efficiency are the profile of the impeller on which the water slides and the angle of attack when the water hits the impeller blades. Thanks to the adjustability of the impeller and guide blades, the turbine can now be used with different load requirements and water potentials.

The impeller 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. Conversely, when the turbine load is high, and the water flow rate will be low then these blades will be adjusted at a larger angle to the turbine axis. 

The velocity diagram of the reaction turbine is given below:

velocity diagram

Types of Reaction Turbine

There are different types of reaction turbine that are given below:

Types of reaction turbine

1) Propeller Turbines

Main Article: Propeller Turbine

The propeller turbine includes in the 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 only install at the place where the load and height are constant. Under partial load, this turbine’s energy efficiency curve is very peaked, which means poor performance.

propeller turbine

2) Francis Turbines

Main Article: Francis Turbine

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

Francis turbine, reaction turbine

Francis turbine rotor typically has nine or more fixed blades. Water enters directly above and around the runner, then the waterfalls and turns the turbine. The other main components are the draft tube, gate, and spiral in addition to the corridor.

Today, cross-flow turbines are an inexpensive (albeit less efficient) alternative to Francis’s spiral casing machines.

3) Gravity Turbines

Main Article: Types of Turbines

These reaction turbine types convert gravity force into rotational force. So, the gravity turbine converts the kinetic energy of the gravity force into electricity.

gravity turbines

4) Bulb Turbine

This turbine is a variant of a propeller turbine. In these reaction turbines assembly, 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.

bulb reaction turbine

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 designing.

5) Straflo Turbine

The straflo turbine is an axial turbine. It has fixed blades. These types of reaction turbines have generators outside the water channel. The generator is connected directly to the turbine runner.

straflo turbines

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.

6) Tube Turbine

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

Tube Turbine

7) Kaplan Turbine

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

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.

Components of Reaction Turbine 

The reaction turbine components are given below in detail.

reaction turbine components

1) Guide vanes

This component of the reaction turbine attaches to the spiral casing. The most important function of the guide vanes is to ensure that the water hitting the impeller blade must be in the direction of the turbine axis. Otherwise, the water will create a strong vortex as it passes through the volute casing. Due to this reason, the impeller blades will be inefficient to rotate. With the latest turbines, the angles of these vanes are flexible.

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

A volute housing is a component that has a uniform reduction in cross-sectional area along the circumference. Its reducing cross-section area 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 a uniform velocity water strikes the impeller blade.  

3) Draft tube

The draft tube makes a link between the impeller’s exit and the tail run. It has a cross-sectional area that increases according to its length. When the water exits the blades of the impeller 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.

4) Runner or Impeller blades 

It includes in the major components of the reaction turbine. The purpose of the impeller 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. 

Advantages of Reaction Turbines

  • 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 compare 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.

Disadvantages of Reaction Turbines

  • These turbines require high maintenance as compare to an impulse turbine.
  • It requires high maintenance costs.
  • Thrust force generates in this type of turbine.
  • It has cavitation problems.
  • It has not symmetrical blades.

Applications of Reaction Turbine

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

This article deeply discusses reaction turbine components, reaction turbine working, and some 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 your confusion.

Do you Know?

  1. What are the different types of Turbines?
  2. What is the difference between an Impulse Turbine and Reaction Turbine?

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