what is the difference between impulse and reaction turbines ?
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Answer Posted / vivek kumar singh
Impulse turbines------------
An impulse turbine has fixed nozzles that orient the steam
flow into high speed jets. These jets contain significant
kinetic energy, which the rotor blades, shaped like
buckets, convert into shaft rotation as the steam jet
changes direction. A pressure drop occurs across only the
stationary blades, with a net increase in steam velocity
across the stage.
As the steam flows through the nozzle its pressure falls
from inlet pressure to the exit pressure (atmospheric
pressure, or more usually, the condenser vacuum). Due to
this higher ratio of expansion of steam in the nozzle the
steam leaves the nozzle with a very high velocity. The
steam leaving the moving blades is a large portion of the
maximum velocity of the steam when leaving the nozzle. The
loss of energy due to this higher exit velocity is commonly
called the "carry over velocity" or "leaving loss".
Reaction turbines-------------
In the reaction turbine, the rotor blades themselves are
arranged to form convergent nozzles. This type of turbine
makes use of the reaction force produced as the steam
accelerates through the nozzles formed by the rotor. Steam
is directed onto the rotor by the fixed vanes of the
stator. It leaves the stator as a jet that fills the entire
circumference of the rotor. The steam then changes
direction and increases its speed relative to the speed of
the blades. A pressure drop occurs across both the stator
and the rotor, with steam accelerating through the stator
and decelerating through the rotor, with no net change in
steam velocity across the stage but with a decrease in both
pressure and temperature, reflecting the work performed in
the driving of the rotor.
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