Comparison between Impulse and Reaction Steam Turbines

In Impulse Turbine, steam completely expands in the nozzle itself. 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. Thus the pressure drop occurs gradually and continuously over both the fixed and moving blades.

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

In Reaction Turbine, Blade passage is of variable cross-sectional area (converging type) due to expansion of steam.

In Impulse Turbine, As pressure remains constant in moving blades, the relative velocity of steam passing over the moving blades remains constant

In Reaction Turbine, Continuous expansion of steam means relative velocity in the moving blades increases.

In Impulse Turbine, Blades are of symmetrical profile types : hence, manufacturing of blade is simple.

In Reaction Turbine, The blade shapes are of aerofoil and non-symmetrical type; hence manufacturing is difficult.

In Impulse Turbine, Because of large pressure drop, the steam speed and the running speed are high.

In Reaction Turbine, Due to small pressure drop, the steam speed and the running speed are low.

In Impulse Turbine, Because of large pressure drop in the nozzles, the number of stages are less. The size of an impulse turbine for power output is comparatively small.

In Reaction Turbine, Because of small pressure drop in each stage, the number of stages are more for the same pressure drop. Hence 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.


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