The invention of the water turbine was so successful that eventually, the idea came about for extracting power from steam. Steam has one great advantage over water-it expands in volume with tremendous velocity. To be the most effective, a steam turbine must run at a very high speed. No wheel made can revolve at any speed approaching the velocity that a steam turbine can. By utilizing the kinetic energy of steam flow, the turbine could achieve a higher efficiency. As a result, the steam turbine has supplanted the reciprocating engine as a prime mover in large electricity-generating plants and is also used as a means of jet propulsion. The action of the steam turbine is based on the thermodynamic principle that when a vapor is allowed to expand, its temperature drops.
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In turn, its internal energy is decreased. This reduction in internal energy is transformed into mechanical energy in the form of an acceleration of the particles of vapor. The transformation that occurs provides a large amount of available work energy. The essential parts of all steam turbines consist of nozzles or jets through which the steam can flow and expand. Thus, the temperature drops, and kinetic energy is gained. In addition, there are blades, on which high pressure steam is exerted. Stationary blades shift the steam onto rotating blades, which provide power. Also, turbines are equipped with wheels or drums where the blades are mounted. A shaft for these wheels or drums is also a basic component, as well as an outer casing that confines the steam to the area of the turbine proper. In order to efficiently use this contraption, it is necessary to have a number of stages. In each of these stages, a small amount of thermal energy is converted to kinetic energy.
If the entire conversion of energy took place at once, the rotative speed of the turbine wheel would be way too excessive. Steam turbines are really quite simple machines that have only one major moving part, the rotor. However, auxiliary equipment is necessary for their operation. Journal bearings support the shaft, and an oil system provides lubrication to these bearings. A special seal system prevents steam from leaking out, or outside air, from leaking in. A modern multistage steam turbine is inherently high in expansion efficiency, because of the ability to recover losses of one stage downstream. This is done through the process of reheating. Steam turbines are still in heavy use today, providing power to ships as well as many other things. They are used in the generation of nuclear power and they can operate with fuel-fired boilers for power generation. In factories, industrial units are used to power machines, pumps, compressors, electrical generators.