What is a Reaction turbine?
A reaction turbine generates torque by utilizing the pressure or weight of a moving fluid. The fundamental principle behind its operation is Newton’s third law—every action produces an equal and opposite reaction.
One distinguishing feature of reaction turbines, in contrast to impulse turbines, is that their nozzles are mounted directly on the rotor itself. When the working fluid accelerates as it exits these nozzles, a corresponding reaction force develops. This force acts on the rotor, causing it to turn in the direction opposite to the flow of the fluid.
As the fluid travels through the rotor blades, its pressure is not constant; instead, it drops noticeably. Because of this change in pressure, most reaction turbines require a pressure casing to keep the working fluid contained and to ensure efficient energy transfer. In water turbines, for example, the casing does more than just confine the fluid—it also helps maintain the necessary suction created by the draft tube.
On the other hand, if there’s no casing present, the turbine has to be fully submerged in the fluid stream, which is the case with wind turbines. The reaction turbine design is widely used in machines like Francis turbines and in the majority of steam turbines.
How Does a Reaction Turbine Work?
In a reaction turbine, the blades are immersed within a comparatively larger volume of fluid, rotating as the fluid flows past. Unlike an impulse turbine, which redirects the flow quite abruptly, a reaction turbine allows the fluid to pass through its blades with minimal change in direction.
The motion is more about the steady transfer of energy as the fluid pushes through and past, prompting the blades to spin.
Wind turbines are perhaps the most recognizable form of reaction turbines that most of us encounter.
To draw a simple comparison: if operating an impulse turbine is similar to kicking a series of soccer balls, each kick a sharp transfer of force, then working with a reaction turbine is more like swimming, but in reverse.
Picture yourself swimming freestyle: your arm stretches forward, pulls through the water, and then follows through behind you. The whole point is to maintain that pressure on the water throughout the stroke, transferring as much energy as you can with each movement.
Now, flip that image around. With a reaction turbine, imagine the water rushing by and moving your arms and legs for you, transferring its energy into motion. The key here is for the water to glide along the turbine blades for as long as possible, allowing maximum energy transfer. The interaction is smooth and sustained, not a sudden impact.
So, rather than fluid hitting and bouncing off the blades, as with an impulse turbine, a reaction turbine’s blades move in harmony with the flow, working with it, not against it.
Since turbines can only extract energy where the fluid actually touches the blades, the design of a reaction turbine, where multiple blades are constantly in contact with the fluid, means it can often draw more power than an impulse turbine of similar size. In the latter, typically only one or two blades interact with the fluid at any moment, which limits the energy captured.
Advantages of Reaction Turbine
- It has high hydraulic efficiency.
- This requires less space.
- The reaction turbines use oil-free exhaust systems.
- It has a small size.
- It has a high capacity to use high temperature and high pressure.
- This type of turbine has a high working speed.
- It is easy to construct.
- The blade has a higher efficiency than an impulse turbine.
Disadvantages of Reaction Turbine
- This type of turbine generates thrust force.
- It confronts the problem of the cavity.
- It does not have symmetrical blades.
- These turbines require higher maintenance than impulse turbines.
- Higher maintenance costs are required.
Applications of Reaction Turbine
- Apart from cross-flow turbines, this is the only turbine to achieve optimum power output at low peak water head and high velocity, which is not efficient.
- Reaction turbines are used in wind power mills to generate electricity.
- It is the most widely used turbine for generating electricity in hydroelectric plants.
FAQs
What are reaction turbines used for?
Reaction turbines are generally used for sites with lower head and higher flows and are the most common type currently used in the United States. The two most common types of reaction turbines are Propeller (including Kaplan) and Francis. Kinetic turbines are also a type of reaction turbine.
What is a turbine used for?
A turbine is a device that harnesses the kinetic energy of some fluid – such as water, steam, air, or combustion gases – and turns this into the rotational motion of the device itself. Turbines are generally used in electrical generation, engines, and propulsion systems.
What is the difference between reaction turbine and impulse turbine?
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.
What are water turbines used for?
Water turbine is used to convert energy contained in water, potential energy or kinetic energy, into mechanical or electrical energy.
What is a 50% reaction turbine?
Turbine stage in which the entire pressure drop occurs in the nozzle are called “impulse stages”. Stages in which a portion of the pressure drop occurs in the nozzle and the rest in the rotor are called reaction stages. In a 50% reaction turbine, the enthalpy drop in the rotor would be half of the total for the stage.
Why is Francis turbine a reaction turbine?
The Francis turbine is a reaction turbine, which means that the working fluid changes pressure as it moves through the turbine, giving up its energy. The turbine is located between the high-pressure water source and the low-pressure water exit, usually at the base of a dam.