09 ME 93 Yasir hashmiQUEST Nawabshah

Impulse and reaction turbines

Turbines• A turbine is a rotary engine that exerts

energy from a fluid flow and converts it into useful work.

There are two basic types of turbines according to the mode of steam.

1. Impulse turbine2. Reaction turbine

Impulse turbineWorking principleIt runs by impulse of steam.Nozzle directs the steam on the curved

blades, which causes them to rotate.The blades are in the shape of buckets.

The energy to rotate an impulse turbine is derived from the kinetic energy of the steam flowing through the nozzle.

The potential energy is converted into kinetic energy when it passes through the nozzle.

The velocity of steam is reduced when it passes over the blades.

Reaction turbineWorking principle It has no nozzle.Two rows of moveable blades are separated by one row of

fixed blades.Fixed blades are attached to the casing & act as nozzles.Blades are like the wings of a plane.

Velocity of steam is increased when it passes through the fixed blades.

The enthalpy drop in moving blades is called degree of reaction.

A common arrangement can have 50% of enthalpy drop in moving blades, it is said to have 50% reaction.

If all enthalpy drops in moving blades then it is said to be 100% reaction.

Difference between impulse and reaction turbine S.NO Impulse turbine Reaction turbine

1.

The steam flows through the nozzle and impinges on the moving blades.

The steam first flows through the guide mechanism and then through the moving blades.

2.

The steam impinges on the buckets with kinetic energy.

The steam glides over the moving vanes with pressure and kinetic energy.

3.The steam may or may not be admitted over the whole circumference.

The steam pressure is reduced during its flow through the moving blades.

4. The blades are symmetrical The blades are not

symmetrical

EfficiencyTo maximize the efficiency of steam turbine

the steam is expanded, generating work in a number of stages.

Multiple stages turbines are highly efficient.Most steam turbines use a mixture of both

impulse and reaction design.Higher pressure sections are impulse type

and lower pressure sections are reaction type.

Advantages of steam turbineIt can develop higher speeds.The steam consumption is less.All the parts are enclosed in a casing so it is

safe.It requires less space and lighter foundations.There is very less friction in the turbine due

to few sliding parts.

UsesTurbines are used in force draft blowers,

pumps and main propulsion turbines.Used in the jet engines and air crafts.They are also used in power plants , ships

and submarines.

Pressure velocity graph of impulse and reaction turbines.

Thanks