Reaction Turbine: Construction, Working, Efficiency, Advantages, Applications
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We are aware that there are various types of turbines that can be used to produce electricity, but they can be categorized primarily based on the nozzle position and runner blades, such as a reaction turbine and an impulse turbine. However, a large majority (60–70%) of the turbines used globally to produce electricity use reaction turbines. A reaction turbine, as opposed to an impulse turbine, is submerged in water to harness the pressure energy of water to generate power. When the turbine is submerged in water, the weight of the water is used to efficiently rotate the turbine’s blades as opposed to striking the wheel’s base. The overview of a reaction turbine and its uses are covered in this article.
What is Reaction Turbine
A reaction turbine is one that generates torque in response to changes in liquid, mass, or gas pressure. Newton’s third law of motion, which states that actions and reactions are equal but reverse in direction, can be used to operate a reaction turbine. Water flowing over the fixed blades causes the turbine to produce force. The diagram of a reaction turbine is displayed below.
The turbine’s wheel in this type of turbine moves completely and may either be submerged under the tailrace or may discharge into the atmosphere when water enters the turbine with some pressure and supplies above the vanes.
Reaction Turbine Construction and Working
Different parts, including guide vanes, spiral casing, draft tubes, and runner blades, can be used to build a reaction turbine.
A guide vane is directly coupled to the spiral casing in a reaction turbine. This component’s primary job is to check to see if the impeller blade is being hit by water coming from the turbine axis or not. If not, a powerful vortex will form as the water passes through the volute casing. Therefore, this is the primary cause of the impeller blades’ ineffective turning. The vane’s angles can be adjusted in modern turbines. Therefore, the water supply can be adjusted by changing the guide vanes’ angle depending on the load on the turbine.
Spiral Casing or Volute Housing
Volute housing, which has an identical reduction in the cross-sectional area along the boundary, is another name for spiral casing. As a result, this area makes sure that a steady velocity supply is reaching the impeller blades. Due to the small cross-sectional area in this instance, the impeller blade has an opening through which water can be supplied. The pressure of the water will decrease as it flows through the area. Thus, in the circumferential direction, the cross-sectional area decreases to produce a constant force, causing uniform water velocity to strike the impeller blade.
A draft tube’s primary purpose is to create a connection between the impeller’s exit and tail run. The cross-sectional area of this tube grows as it gets longer. The cross-sectional area of the draft tube will increase as the pressure of the water decreases as it exits the impeller blades, which aids in recovering the pressure of the water because it moves in the direction of the tailrace.
Impeller Blade or Runner
The reaction turbine is driven by the impeller blade or runner using the force of the water pressure. As a result, since these turbines have adaptable runner blades, turbine efficiency can be determined by looking at their design. So These impeller blades can adjust the pressure on them based on the current pressure and load of the turbine thanks to the ability of the current turbines to tilt them near the axis of the turbine.
Reaction Turbine Working
The operation of the reaction turbine is simple, making it simple to comprehend. A rotor in a reaction turbine has moving nozzles that forcefully release water. A reaction force that rotates around the rotor at its fastest speed will be felt by the water as it exits the nozzles. Additionally, the moving water above the runner blades can generate a reaction force. As a result, the runner may spin due to the reaction force exerted on its blades. After moving along the runner’s blades, the water enters the draft tube and then travels to the trail race.
Reaction Turbine Efficiency
The ratio of power generated by the turbine to energy supplied by the turbine can be used to define the reaction turbine’s overall efficiency. Consequently, the turbine’s maximum efficiency can be expressed as
η = 2cos2α/1+ cos2α
So α = 90o for the maximum efficiency where ‘α’ is the absolute velocity vector’s angle at the opening.
Reaction Turbine Types
There are different types of reaction turbines which include the following.
- Francis Turbine
- Propeller Turbine
- Gravity Turbine
- Kinetic Turbine
Axial and radial water supplies enter the runner in the Francis turbine, an improved version of the propeller turbine. The gate, draft tube, and spiral are this turbine’s three main parts. So The flow channels are typically arranged in spiral housing through internally adjustable influence blades in the center of this Francis turbine. This turbine typically has a rotor with a minimum of nine fixed blades or more. The turbine only turns once water is directly supplied above and around the runner.
The propeller turbine features a runner with a propeller shape that is common in ships and submarines. Where the water flow comes into contact with these impeller blades, this turbine is equipped with 3 to 6 of them. This turbine has adjustable wicket gates or guide vanes that allow the water flow to be altered. The guide vanes aid in directing the water’s energy toward the blades by forcing it into the runner. So Propeller turbines come in a variety of designs, including the Tyson, Kalpan, Starflo, Tube, and Bulb. Propeller turbines are typically used in hydraulic sites with high flow rates. These turbines are merely placed in locations with stable height and load. The energy efficiency curve of this turbine performs very poorly at partial load.
The main function of a gravity turbine is to change the force from gravity to rotational. And also converts the kinetic energy (K.E) of the gravity force into electricity.
The primary purpose of these turbines, also referred to as free-flow turbines, is to produce electricity using the kinetic energy (K.E.) present in the water flow rather than the potential energy (P.E.) from the head. These systems may work in tidal waters, rivers, ocean currents, or Human made channels. These turbines make use of water’s steam in a natural way. They don’t require the water to be diverted through pipes, riverbeds, or artificial channels. Large civil works are not necessary for kinetic systems; instead, they can make use of already-existing structures like tailraces, channels, and bridges.
The advantages of a reaction turbine include the following.
- High efficiency.
- The speed of rotation is high.
- High pressure and temperature used.
- The exhaust system is oil-free.
- Blade efficiency is high.
- Stage spacing is low.
- Elevated capacity & weight ratio.
- Both kinetic energy & pressure at the inlet.
- Less complex design.
- These are portable.
- Simple to design.
The disadvantages of a reaction turbine include the following.
- The blade is not symmetric.
- Blade tip wear problem.
- Airtight casing.
- Cavitation problem.
- Generates thrust force.
- Small steam turbine effectiveness is poor.
- High maintenance cost.
- It cannot be arranged reversible.
- It needs high maintenance.
The applications of a reaction turbine include the following.
- This type of turbine benefits from high velocity and low accessible water head to produce the most power.
- By responding to the weight or pressure of a liquid, this turbine produces torque.
- These turbines are used for generating electricity in wind power mills and hydropower plants.