A steam turbine works on the dynamic action of steam. Steam is caused to fall in pressure in a passage or nozzle. Due to this fall in pressure, certain amount of heat energy is converted into kinetic energy to give it high velocity. The high velocity steam impinges on the moving blades of the turbine and changes the direction of motion and thus gives rise to a change in momentum, therefore, a force. Essentially, the nozzles direct the steam so that it flows in a well-formed high velocity jet. Moving buckets convert this high-velocity jet to mechanical work in a rotating shaft.
In impulse turbines, there is a drop of steam pressure and consequent development of kinetic energy takes place solely in the stationary nozzles, and the work is obtained by the conversion of this kinetic energy into work on moving blades. In the reaction turbine, only a part of the kinetic energy conversion occurs in the stationary nozzles, whereas the remainder of the kinetic energy conversion is accomplished by a pressure drop in steam as it passes through the moving blades.
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