Reaction turbines are a type of water turbine, using a rotary engine to convert the energy from flowing water flow into useful mechanical energy, such as electricity. Water turbines can be divided into two main types of design; reaction turbines and impulse turbines. Each design has a different approach to converting the energy from water flow into usable energy, and although nowadays most water turbines are a hybrid of reaction and impulse designs, each design can be advantageous in certain situations.
Both impulse and reaction turbines use water hitting fan-like rotor blades to generate energy. An Impulse turbine generates mechanical energy by changing water pressure into high velocity water using nozzles. These nozzles direct water at the rotor blades, causing them to spin. Impulse turbines use Newton’s second law of motion, in which the acceleration of a body (which in this case is water) is directly proportional and in the same direction of the net force acting on the water. The blades need to be suspended in air to cause the rotor blades to spin using the directed water from the nozzles.
Reaction turbines act differently and gain torque because of the pressure of water. The rotor blades are fully immersed in a pressure casement, which maintains the pressure and causes the blades to spin. Reaction turbines use Newton’s third law of motion, that when one body (water) exerts force on a second body (the blades), the second body will exert a force equal to that of the first body in the opposite direction of that body. The pressure is maintained in reaction turbines by using directed water flow.
The rotor blades in reaction turbines spin due to being fully immersed in water, rather than spin due to directed water from a nozzle. This creates an efficiency advantage over impulse turbines, as the energy that drives the blades is harnessed from the entire flow of water, instead of the water velocity generated flow from a set of nozzles.
Input and output
Reaction turbines require less of an energy input that impulse turbines. This means that reaction turbines can be much better than impulse turbines at generating energy. The fact that less of an input is needed also results in greater energy output for reaction turbines when both types are using the same amount of input energy. Because of this, reaction turbines are often favoured over impulse turbines.
Reaction turbines are usually more costly to install than impulse turbines, as they require precisely engineered rotor blades to operate at maximum efficiency. However, after the initial installation and manufacturing expenses, reaction turbines are more cost effective in the long run than impulse turbines. The design of reaction turbines causes the rotor blades to spin at greater speeds, reducing the need for a speed increasing drive system that is often needed in impulse turbines. As a result, the maintenance cost of reaction turbines are also usually less than impulse turbines.
As both reaction and turbine designs process and produce energy in different ways, many modern turbine systems adopt both reaction and impulse turbines to create a fully effective and efficient system. Both types of turbine will be most efficient at certain power inputs, determined by the speed, head, and flow variables of the water. Because of this, it’s very rare to find a modern day turbine system that purely uses the principles of either impulse or reaction turbines. Instead, a dynamic combination turbine is often used to harness as much of the available energy as possible.
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