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MEN -Lecture 12 for fundamental of ME.pptx

Turbines
• A turbine is a rotary engine that extracts 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 turbine
2. Reaction turbine

Impulse turbine
Working principle
 It 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 turbine
Working 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

Efficiency
 To 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 turbine
 It 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.

Uses
 Turbines 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.

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MEN -Lecture 12 for fundamental of ME.pptx

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MEN -Lecture 12 for fundamental of ME.pptx