Steam Turbines


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. 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.

Category: Science