Reaction Turbine: Definition, Working & Application

What is a Reaction turbine?

A reaction turbine is a type of turbine that develops torque by reacting to the pressure or weight of a fluid. The operation of reaction turbines is described by Newton’s third law of motion (action and reaction are equal and opposite).

In a reaction turbine, unlike in an impulse turbine, the nozzles that discharge the working fluid are attached to the rotor. The acceleration of the fluid leaving the nozzles produces a reaction force on the pipes, causing the rotor to move in the opposite direction to that of the fluid.

The pressure of the fluid changes as it passes through the rotor blades. In most cases, a pressure casement is needed to contain the working fluid as it acts on the turbine; in the case of water turbines, the casing also maintains the suction imparted by the draft tube.

Alternatively, where a casing is absent, the turbine must be fully immersed in the fluid flow as in the case of wind turbines. Francis turbines and most steam turbines use the reaction turbine concept.

Reaction Turbines

How Does a Reaction Turbine Work?

In a reaction turbine, the blades sit in a much larger volume of fluid and turn around as the fluid flows past them. A reaction turbine doesn’t change the direction of the fluid flow as drastically as an impulse turbine: it simply spins as the fluid pushes through and past its blades.

Wind turbines are perhaps the most familiar examples of reaction turbines.

If an impulse turbine is a bit like kicking soccer balls, a reaction turbine is more like swimming—in reverse. Let me explain! Think of how you do freestyle (front crawl) by hauling your arms through the water, starting with each hand as far in front as you can reach and ending with a “follow-through” that throws your arm well behind you.

What you’re trying to achieve is to keep your hand and forearm pushing against the water for as long as possible, so you transfer as much energy as you can in each stroke.

A reaction turbine is using the same idea in reverse: imagine fast-flowing water moving past you so it makes your arms and legs move and supplies energy to your body! With a reaction turbine, you want the water to touch the blades smoothly, for as long as it can, so it gives up as much energy as possible.

The water isn’t hitting the blades and bouncing off, as it does in an impulse turbine: instead, the blades are moving more smoothly, “going with the flow.”

Turbines capture energy only at the point where a fluid touches them, so a reaction turbine (with multiple blades all touching the fluid at the same time) potentially extracts more power than an impulse turbine the same size (because usually only one or two of its blades are in the path of the fluid at a time).

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.