The Turbine is a Prime Mover in which a Rotary Motion is obtained by Centrifugal Force brought into action by changing the Direction of Jet of a Fluid escaping from a Nozzle at High Velocity.
This Turbines are classified by several ways.The most important and common division being with respect to the action of the Steam and they are as,
03)Combination of Impuse and Reaction Turbine.
Difference between Impuse and Reaction Turbine:-
In an Impulse Design of Steam Turbine,there is an attempt to attain no Expansion of Steam within the Moving Blades and as such its Pressure remains constant while passing over the Blades.
The Expansion of Steam,however,takes place in a set of Stationary Nozzels which lower its Pressure but impart a High Velocity to it.The Velocity attained in a properly designed Nozzel depends upon the Pressure drop through it.
Impuse Turbine Design may be classified as Single Stage,Multi Pressure Stage,Multi Velocity Stage and Combination of Multi Pressure and Velocity Stage.
The term Pressure Stage refers to unit of Nozzels combined with Moving Blades in which the Energy of the Steam resulting from each Pressure drop,isutilised.
The Velocity Stage refers to the number of Moving Blades in which the energy of the Steam in each Pressure drop is absorbed.
In case of Reaction Turbine the Steam expands as it flows over the Blades which,therefore act as Nozzles.In fact it is this drop in Pressure that gives a Reaction and hence Motion to the Rotor.
A pure Reaction Turbine,comprises of two or more Radial Tubes rotating and communicating with another pipe or turnnion through which Steam is supplied to Nozzle which are screwed into the ends of the Radial Pipes and arranged with their Axis in the Tangential Direction.
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