In a reaction turbine, the blades are placed in a large amount of liquid and rotate as the fluid flows through the blades. A reaction turbine does not change the orientation of the liquid flow as much as impulse turbines. It only spins when the liquid flows through the blades. Wind turbines are probably the best-known example of reaction turbines.
Reaction turbines are called “reaction” due to the design of the blades. As liquid flows through the blades, the liquid flowing below and above the surface of the blade have different velocities and creates a pressure difference (as explained in Bernoulli’s equation, the energy is the same throughout the process, so the decrease in velocity change generates the pressure difference to keep the constant amount.
This pressure differential causes the blade to move towards the low-pressure area. And this makes the blades to be moveable.
In the reaction turbine, the speed of the blades is caused because of the pressure energy loss of the liquid (While in the impulse turbine, this is due to the impact of the fluid on the blades, which move the blades, and pressure remains constant. In this process, the momentum decreases by the liquid that is collected by the blades.
Working Principle of Reaction Turbine
During the working of a reaction turbine, the liquid is provided with the help of a penstock from the reservoir to the turbine when water enters in the housing. The impeller fully surrounds the housing. This housing delivers the liquid in the circumferential direction to the turbine impellers. The housing of the turbine always fills with the liquid. The fixed blades inside the turbine housing transform the available water head section into a dynamic head. The cross-sectional housing area gradually reduces to keep the water speed constant in the flow path of the turbine impeller. These several parts and blades help the water to flow into the impeller with minimal loss of energy.
As water introduces over the rotor in the impeller, it has pressure and kinetic energy. When the water hits the rotating blades, it exerts an impact force through the action of kinetic energy, similar to the Pelton turbine. Due to the aerodynamic shape of the blades, as the water flows over a rotating/curved blade, it creates a pressure differential in the blade, and the water applies a buoyancy force on the moving blades. This buoyancy is also known as the reaction force. This generated reaction and impulse force helps to rotate the impeller.
After the impeller, the water flows through a discharge pipe that connects to the impeller bottom. The discharge pipe makes available a suction head at the outlet of the impeller. The drained water enters the tailstock and is used for different purposes.
This is a complete working principle of the reaction turbine. All reaction turbines work according to this same principle.
Components of a Reaction Turbine
A reaction turbine has the following major components.
It is a great area for storing water. The reservoir is a steady water source with a lot of hydropower. It may be natural as a lake, or it may be artificially called a dam. A large number of water stores here for regular water supply.
A penstock is also known as a pressure pipe. It is a pipe that has a large diameter that uses to transport water from a reservoir to a turbine.
3) Surge tank
A surge tank is another type of reservoir situated near a turbine to prevent water hammers from entering the water.
The housing is made of concrete, plate steel, or cast steel, varying on the operating conditions of the reaction turbine. It is spiral-shaped, and its area gradually decreases. The objective of housing is to supply constant velocity water at the impeller entrance and sustain a constant water velocity. The tapered area helps to sustain a constant flow of water through the impeller.
5) Fixed Blades
The fixed blades have two roles. It directs the liquid from the housing to the guide vane, and it also helps to distribute the load due to the internal water pressure. These fixed blades are usually made of fabricated steel, cast steel, or cast iron.
6) Guide Vanes
The guide vane serves to guide the water in the impeller along the directional angle of the guide vanes. These vanes have a fixed position but can turn on their own axis. The shape of these vanes is aerodynamic and generally consists of plate steel, stainless steel, or cast steel. These guide vanes can control discharge by controlling the flow area with the help of a regulator. Alternatively, it can be operated with the wheels during a small unit.
7) Draft Pipe or Tube
The main part of the reaction turbine is the draft pipe. It doesn’t require for impulse turbines. A draft tube is a pipe that slowly rises its cross-section area. It will be installed at the exit of the impeller. It uses to change kinetic energy into pressure energy to improve the turbine’s effectiveness. This component of the turbine is made of plate steel, cast steel, or can also be made of concrete. The drain pipe must be airtight under all circumstances, and the bottom of the drain pipe must be submerged to a certain degree in the water on the back wall. You can change the shape and size of the drain pipe used according to your needs.