Difference between the Impulse and Reaction turbine

Today we discuss about the main difference between the impulse and reaction turbine , how differentiate both type of turbine according to steam flow , pressure computing , according to size and efficiency .
Steam Turbine working Principles
Based on working principle the steam turbine is classified as two types these are follows
1. Impulse type turbine
2. Reaction type turbine

Impulse type Turbine Working:

In the impulse type turbine working pressure of steam drops and the velocity increases as the steam passes through the nozzles. When the steam passes through the moving blades of steam turbine the velocity drops but the pressure remains the same when the steam exhaust outside the steam turbine
The fact that the pressure does not drop across the moving blades of steam turbine, it is the major feature of the impulse turbine. The pressure at the inlet of the moving blades is same as the pressure at the outlet of moving blades.

Reaction type Turbine Working:

reaction type turbine having rows of fixed blades alternating with rows of moving blades. The steam first expands in the stationary or fixed blades where it gains some velocity as it drops in pressure. After that steam enters in the moving blades where its direction of flow is changed thus producing an impulse force on the moving blades. In addition, however, the steam upon passing through the moving blades, again expands and further drops in pressure giving a reaction force to the blades.
This process is repeated as the steam passes through additional rows of fixed and moving blades.
Note that the steam pressure drops across both the fixed and the moving blades while the absolute velocity rises in the fixed blades and drops in the moving blades.
The major feature of the reaction turbine is the fact that the pressure does drop across the moving blades. We can say that, there is a pressure difference between the inlet to the moving blades and the outlet from the moving blades.
In Impulse type turbine steam expands in the nozzle firstly. Hence its pressure remains constant on both ends of the moving blades.

In Reaction Turbine, Fixed blades act as nozzles. Hence steam expands both in fixed and moving blades continuously as it passes over them. Hence the pressure drop occurs gradually and continuously over both the fixed and moving blades.
In impulse turbine only kinetic energy is used to rotate the turbine.

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Difference between the Impulse and Reaction turbine

in impulse turbine the same flow rate & operating condition the efficiency of impulse turbine is very low
in reaction turbine the same flow rate & operating condition the efficiency of the reaction turbine is high

In Impulse Turbine, Blades Passage is of constant cross section area, as there is no expansion of steam.

Cross-sectional area (converging type) of Blade passage is of variable due to expansion of steam in reaction turbine .

In Impulse Turbine pressure remains constant in moving blades during the relative velocity of steam passing

Relative velocity in the moving blades increases during continuous expansion of steam In Reaction Turbine,
The Cost of impulse turbine is much lower when compare to reaction turbine for same power rating.
Reaction turbine cost is much higher due to the critical shape of rotor

Manufacturing of steam turbine blade is very simple because of blade profile is symmetrical in impulse turbine .

Manufacturing of steam turbine blade is very difficult because of the blade shapes are of aerofoil and non-symmetrical type.
In Impulse Turbine the steam speed and the running speed are high because of large pressure drop,

The steam speed and the running speed are low in reaction turbine due to small pressure drop
impulse turbine widely used in petrochemical and refineries
Reaction turbine widely used in Power plants

Due to large pressure drop in the nozzles the number of stages are less in impulse turbine so the size of an impulse turbine for power output is comparatively small.

Due to small pressure drop in each stage so the number of stages are more for the same pressure drop in reaction turbine , so that the size of the reaction turbine for the same power output is large. Reaction turbines are multi-stage turbines only.

Impulse Turbine Occupies less space per unit power

Reaction Turbine Occupies more space per unit power

Impulse Turbine is Suitable for small powers

Reaction Turbine is Suitable for medium and higher powers.
In impulse turbine the steam may or may not be admitted to the whole circumference
In reaction turbine the steam must be admitted over the whole circumference.
Multistage impulse turbine having three type of compounding they are

1. Pressure Compounding

2. Velocity Compounding

3. Pressure – Velocity Compounding

in reaction turbine no compounding is available
In impulse turbine the direction of steam flow is radial to the direction of turbine wheel.
In reaction turbine the direction of steam flow is radial and axial to the turbine wheel.

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