Being a special type of turbine used in hydropower plants, the reaction turbine is used all around the world for the generation of electricity. It is estimated that about 60% of turbines used in hydropower plants are reaction turbines, though still in competition with impulse turbines.
A reaction turbine is constructed of rows of fixed blades and rows of moving blades.
These fixed blades act as nozzles, and the moving blades move as a result of the impulse of steam received (caused by a change in momentum). Also, as a result of the expansion and acceleration of the steam relative to them, they still act as nozzles. This will be further explained; stick with me!
Well, in this reading, we’ll explore what a reaction turbine is, its applications, functions, components, diagram, types, and how it works. We’ll also discuss its advantages and disadvantages.
Let’s get started!
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What is a Reaction Turbine?
A reaction turbine works with Newton’s third law of motion (action and reactions are equal and opposite). The system generates torque in response to the fluid’s pressure and weight. In it working, water first strikes the fixed blades and then strikes the nozzle.
In a reaction turbine, the sum of potential energy and kinetic energy of water due to the pressure and velocity, respectively, causes the turbine blades to rotate.
The entire body of this turbine is immersed in water and changes in water pressure along with the kinetic energy of the water cause power exchange. Applications of a reaction turbine are usually at lower heads and higher flow rates than impulse type.
The turbine blades or impeller blades are designed to be able to generate a force on one side when water flows through it just like an airfoil. In an airplane, the force produced by an airfoil is responsible for its lifting. Similarly, here, the force causes the blades to rotate.
Different types of reaction turbines have their own ideal operating conditions. For examples,
- Pelton turbines are preferred where a low discharge rate can be obtained & a highd (80-1600m) is available.
- Kaplan turbines require a high discharge rate along with a low or mediumd (2-70m).
- Francis turbines work on medium flow rates & medium heads. Francis turbine is a combination of impulse & reaction turbines.
Francis turbines are the most widely used turbines because they offer the highest efficiency & could also work in a wide range of operating conditions.
Applications of Reaction Turbine
The various applications of a reaction turbine include the following:
- Wind power mills to generate electricity.
- Also, for electricity generation in hydropower plants.
- Reaction turbines are used to obtain maximum power output from a low available water head and high velocity.
Note: the primary function of a reaction turbine is for power generation.
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Components of Reaction Turbine
Below are the major components of the reaction turbine and their function.
Spiral Casing
these components of the reaction turbine have a uniformly decreasing cross-sectional area along the circumference. This decreasing cross-section area ensures a uniform velocity of water striking the runner blades.
There is an opening for water flow into the runner blades from the starting of the casing, causing pressure to decrease as it travels along with the casing. The reduction of its cross-section area along its circumference to make pressure uniform, therefore, uniform momentum or velocity striking the runner blades.
Guide Vanes
Guide vanes are mounted in the spiral casing to ensure the water striking the runner blades have direction along the length of the axis of the turbine. Otherwise, the flow would be highly swirling as it moves through a spiral casing, making it not efficient enough to rotate runner blades. In modern turbines, the angles of these guide vanes are adjustable, making the water flow rate adjustable.
Runner Blades
Runner blades are important components of a reaction turbine. In fact, it is considered the heart of the reaction turbine. The shape of the runner blades uses the pressure energy of water to run the turbine.
Their design is very essential and plays a major role in deciding the efficiency of a turbine. In the modern version, these blades can pitch about their axis; thus, the pressure force acting on them can vary according to the load and available pressure.
Draft Tube
A draft tube connects the runner exit to the tailrace, having an increased cross-section area along its length. Water coming out of runner blades is at considerably low pressure; its expanding cross-section area recovers the pressure as it flows towards the tailrace.
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Diagram
Types of Reaction Turbine
Below are the various types of reaction turbine
Propeller Turbines
Propeller types of reaction turbines usually have a 3 to 6 blade flow path, having the water in constant contact with all of the blades. Propeller turbines can only be installed at the place where load and height are constant. Its energy efficiency curve is very peaked under partial load. Which means poor performance in the system.
Kaplan turbines can achieve high-efficiency levels under various load conditions by properly adjusting the blades during their working. This is because the blade angle can be adjusted to the required power.
Francis Turbines
These types of reaction turbines are a modified version of the propeller turbine, as the water flows radially and axially into the runner. In its working, the flow channels are generally set in spiral housing with internally adjustable influence blades.
These types of reaction turbines have a rotor that has nine or more fixed blades. Water initiates directly above and around the runner, which then falls and turns.
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Gravity Turbines
These reaction turbine types convert gravity force into rotational force. So, in its working, the kinetic energy of the gravity force is converted into electricity.
Bulb Turbines
Bulb turbine types are variants of propeller turbines. The bulb turbine generator is enclosed and sealed in a streamlined, watertight steel housing located in the duct center. This generator is driven through a variable-pitch propeller at the downstream end of the valve. The direction of water entering and exiting the system is practically unchanged or very little. Its compactness offers more flexibility in powerhouse designing.
Straflo Turbines
These reaction turbine types are axial turbines with fixed blades. Its generator is located outside the water channel and is connected directly to the turbine runner.
Tube Turbines
In this reaction turbine, the pressure line is bent shortly after and before the flow path, enabling a straight connection to the generator.
How Does a Reaction Turbine Work?
The working of a reaction turbine is less complex and can be easily understood. In its working, a rotor contains moving nozzles that release water of high pressure. As the water leaves the nozzles, they experience a reaction force that rotates the rotor at a very high speed.
Also, a reaction force is generated by the fluid moving on the runner blades.
The reaction force produced on the runner blades causes the runner to rotate. The fluid enters the draft tube after moving over the runner blades and then finally to the tailrace.
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Advantages and Disadvantages of Reaction Turbine
Advantages:
Below are the benefits of the reaction turbine and its various applications:
- High hydraulic efficiency.
- High working speed.
- Design is less complex.
- Blades have high efficiency.
- Less space is required.
- Uses an oil-free exhaust system.
- Portable in size.
- Capable of using high temperature and pressure.
Disadvantages:
Despite the good advantages of a reaction turbine, some limitations still occur. Below are the disadvantages of a reaction turbine in its various applications.
- Require high maintenance
- Cavitation issues occur.
- The maintenance cost is high.
- Thrust force is generated.
- No symmetrical blades.
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Conclusion
A reaction turbine works with Newton’s third law of motion (action and reactions are equal and opposite). The system generates torque in response to the fluid’s pressure and weight. In it working, water first strikes the fixed blades and then strikes the nozzle.
Reaction turbines are an essential part of modern hydroelectric power systems, utilizing the pressure and velocity of water to generate mechanical energy. Unlike impulse turbines, reaction turbines work with fluid pressure changing gradually across the blades, making them ideal for low- to medium-head and high-flow applications.
Their continuous water contact design ensures efficient and reliable operation, especially in large-scale power plants. As the demand for clean and renewable energy grows, reaction turbines remain a critical component in sustainable energy production.
FAQs on Reaction Turbine
What is a reaction turbine?
A reaction turbine is a type of water turbine that generates power from the combined action of water pressure and flowing water, causing the turbine blades to rotate.
How does a reaction turbine work?
Water flows over the blades, creating pressure differences that cause the rotor to spin. Both the stator and rotor contribute to energy conversion.
What are the common types of reaction turbines?
The main types are Francis Turbine and Kaplan Turbine.
Where are reaction turbines used?
They are used in hydroelectric power stations where low to medium water heads and large volumes of water are available.
What is the difference between impulse and reaction turbines?
Impulse turbines use water’s kinetic energy and operate in air, while reaction turbines use both pressure and kinetic energy and operate fully submerged.
Are reaction turbines efficient?
Yes, they are highly efficient, especially in situations with steady, high-flow water sources.
Why do reaction turbines need to be submerged in water?
They rely on pressure differences and the reaction force of flowing water, which requires constant water contact for continuous operation.