Difference Between Impulse And Reaction Turbine

The turbine accounts for almost all of the power generation, all turbocharged engines, pumps, and aircraft engines. But have you thought what the turbine is; or what is the difference between an Impulse and a Reaction Turbine? Today we will learn about what they are; their working, parts, application, and types ( Impulse and Reaction ) with their differences.

An Impulse Turbine is made of a fixed set of nozzles and fixed rings of blades. High-pressure steam/gas/medium is expanded across these nozzles to produce change across the runner.

While in reaction turbines the fixed set of blades mounted on the casing acts as a nozzle. Thus steam/gas/medium is expanded across both fixed and rotating blades with a gradual decrease in pressure across the runner.

What is The Turbine and How Does it Work?

We all have heard of turbines many times in the past unaware of what it really means! A turbine is a tool or machine used to transform heat and kinetic energy of fluid ( liquid and Gas ) to obtain mechanical work.

These turbines can be used with steam, wind, and water to produce electricity, thrust, and pressure.

Hydraulic turbines are used in dams to convert the hydraulic energy of water into mechanical and electrical energy. While gas turbines are used to produce mechanical work from heat and kinetic energy of gas and steam.

In simple words it is a device with blades attached to its rotor which acts as a shaft; to transfer mechanical energy produced to other devices for electrical and thrust generation.

What is The Turbine and How Does it Work?

The rotor itself can be made of single-piece construction or made up of shaft and separate blades. In hydroelectric generation pressurized jet of water from the dam is injected on the turbine blades. This results in the rotation of turbine and so does the shaft connected to generate electricity.

The steam, water, or any other fluid is expanded along with the nozzles; converting heat and pressure energy in the medium into kinetic energy to produce high-velocity jet.

This jet is then directed to the fixed blades on the rotor wheel. The design of these blades helps change the direction and velocity of the jet.

This results into a force acted on the turbine which is the product of the mass flow rate and change in the velocity. The fluid passes from one set of blades to another called stages until it lost most of its energy.

Force on Turbine Blades ( Kg*m/S2 ) = Mass flow rate of medium ( Kg/S ) X Change in velocity ( m/s ).

Difference between Impulse & Reaction Turbine ( Turbine Parts )

Basic Parts of A Turbine

A turbine is made of stationary and moving parts such as blades, rotor, casing, bearings, etc. But we will discuss the four main parts of a turbine; Which are:

1 ) Casing

It serves as a closed structure that holds bearings, diaphragm, gland packing, nozzles, and other stationary parts. For gas turbines it’s shape and design depend upon whether it is L.P ( low pressure ) or H.P ( High pressure ) casing.

They generally came with a horizontal split arrangement for easy assembly and maintenance.

A casing is designed to withstand high pressure at inlet while sub-atmospheric pressure at the discharge/outlet side. In gas turbines high-pressure casings are made from cast steel with 3% and 0.3% of molybdenum and vanadium respectively.

On the other hand normal cast steel is used for the construction of Low-pressure casing.

In water turbines it is called scroll casing and holds guide vanes that direct the flow of water towards the blades.

2 ) Rotor

A turbine rotor acts as a shaft with fixed blades mounted onto it. The rotor assembly converts the pressure and heat energy of a medium ( Steam, gas, or water ) into mechanical work.

They are always subjected to high stress and so required at-most care during its design and manufacturing. It can be hollow, solid, or build-up design with a single piece or separate construction. Blades are fitted on to the grooves cut into rotor wheels.

3 ) Blades

The efficiency of a turbine depends largely upon its blades. All the energy converted from the pressure to kinetic and then to mechanical took place in these blades.

Its design helps change the direction and velocity of the pressure jet; which results in a force acted on to the turbine wheels. This force is the product of the change in velocity and the mass flow rate.

As the blades are rotated at high speed, they are subjected to continuous vibration.

To secure these blades under such conditions a T-slot or Fir-tree arrangement is used. It evolves placing the root of the blades into some kind of slots in the wheels. Additional practices like lacing wires are also used to dampen these vibrations.

In impulse turbines there is only one set of blades mounted on the rotor wheel while two separate sets ( Fixed and Movable ) in the reaction turbine.

4 ) Nozzle

A nozzle serves the most important purpose of converting high pressure – High energy fluid into the high-velocity jet.

The pressure across these nozzles can be varied by using a control valve. By reducing the pressure across these nozzle one can easily control the final output of a turbine.

While the Impulse turbines have fixed nozzles; the reaction turbines has fixed blades serving the same purpose. Turbine nozzles are constructed from stainless steel or copper Monel metal with 67% nickel content.

Difference Between Impulse And Reaction Turbine
By Emoscopes [CC-BY-SA-3.0], from Wikimedia Commons

Difference Between Impulse And Reaction Turbines

Impulse Turbine
Reaction Turbine
  1. In the Impulse turbines all the pressure energy is transferred into kinetic energy through nozzles.
  1. In reaction turbines; pressure energy of the fluid is partly converted by fixed blades.
  1. Rotor blades are subjected to only kinetic energy.
  1. Rotor blades are subjected to both pressure and kinetic energy.
  1. Fluid flows through nozzles to impact on the moving blades.
  1. Fluid flows through fixed blades to impact on the moving blades.
  1. In Impulse Turbines pressure across the blades remain constant.
  1. In Reaction Turbines pressure across the blades reduce gradually.
  1. Fluid ( Gas, steam, or water ) may or may not be injected full-on rotor wheels; there can be some gap between the wheel and the vanes.
  1. The wheels must always run full; meaning fluid must be injected in such a way that no gap left in between the wheel and the vanes.
  1. Impulse turbines have a high operating speed.
  1. The reaction turbines have a low operating speed.
  1. In Impulse turbines, the relative velocity of the fluid ( Gas, Steam, or water ) remains fairly the same across the blades.
  1. In Reaction turbines, the relative velocity of the fluid ( Gas, Steam, or water ) increases gradually across the blades.
  1. A sudden drop in pressure across the nozzle results into smaller size of the turbine for the same power.
  1. A gradual drop in pressure across the turbine blades results in large or longer turbine size for the same power.
  1. The multistage turbine is possible with impulse turbines in form of pressure, velocity and mix compounding.
  1. Reaction turbines can’t produce multistage compounding.
  1. In Impulse turbines, flow-rate can be easily controlled without any loss
  1. It is not so easy to regulate flow rate in reaction turbines and impossible to do without any loss.
  1. Relatively More efficient
  1. Relatively less efficient
  1. Requires less maintenance
  1. Require more maintenance
  1. Used for steam propulsion of ship and submarines, electricity generation and for cargo operation on ship and refineries.
  1. Used mainly for electricity generation.

Application Of Various Turbines in Industries

There are mainly four types of turbine used in different industries; water turbine, steam turbine, wind turbine and gas turbine.

Kaplan and Francis turbine; which are the type of water-driven reaction turbine is used to produce electricity. An impulse turbine ( Pelton wheel ) can also be used for generating hydroelectricity.

Steam Turbines are used for propulsion of ships and submarines. They are also widely used in cargo operation on ship, cargo operation in refineries with nuclear and thermal power generation.

Almost all modern steam turbines are a combination of impulse and reaction turbines with mixed compounding. The distinct feature of these turbines are the increasing size of the blades from H.P to L.P side.

Difference Between Impulse And Reaction Turbine
Jeff Dahl [CC BY-SA 4.0], from Wikimedia Commons

Gas Turbines on other hand is more like an internal combustion engine. They can be used in power plant for generating power but is mainly used in propelling aircraft and helicopters. A gas turbine is made up of three main parts; The compressor, the combustion chamber and the exhaust turbine.

An axial compressor compress the fresh air and push it towards the combustion chamber. The air-fuel mixture is then burned in the combustion chamber and exhaust is pushed towards the turbine. The turbine runs from the exhaust gas and power the compressor.

Wind turbines are a source of renewable energy to the mankind. It is based on the working of any other turbine other than it runs very slowly. So we are required to have a gearbox installed in these turbine to increase their rpm to produce sufficient rpm to generate electricity.

Conclusion

All steam, wind, water and gas turbines are used for various purposes. As discussed above; you now know both impulse and reaction turbines can be used for almost all applications. But in practice perspective impulse turbines are used much more than compared to a reaction turbine.

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Amit Abhishek

A Marine engineer turned professional blogger who had started Shipfever.com In Jan 2018 after a brief experince at sea.

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