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engineering methods were developed highly enough for a successful attempt.
Two men undertook it almost simultaneously. The Swedish engineer, Gustaf
Patrik de Laval, built his first model in 1883. He made the steam from the boiler
emerge from four stationary nozzles arranged around the rim of a wheel with a great
number of small inch, de Laval's turbine wheel rotated at up to 40,000 revolutions per
minute. He supported the wheel on a flexible shaft so that it would adjust itself to
fluctuations of pressure– which, at such speeds, would have broken a rigid shaft in no
time.
De Laval geared an electric generator to his turbine after he had succeeded in
reducing the speed of rotation to 3,000 r. p. m. His turbo-generator worked, but its
capacity was limited, and it was found unsuitable for large-scale power stations.
Although the simplest form of a machine has often proved the most efficient one in
the history of technology, this was not the case with the steam-turbine. Another
inventor, and another system, proved much more successful.
In 1876 Charles Parsons began to work on the idea of a steam-turbine, for
which he forsaw a wide range of applications. The reciprocating steam-engine, which
was unable to convert more than 12 per cent of the latent energy of coal into
mechanical power, was not nearly effiuient enough for the economical generation of
electricity – energy leaked out right and left from the cylinder, and the condenser.
Besides, there were limits to the size in which it could be built, and therefore to the
output: and Parsons saw that the time had come to build giant electric power stations.
As he studied the problem he understood that the point where most would-be
turbine inventors
1
had been stumped was the excessive velocity of steam. Even steam
at a comparatively low pressure escaping into the atmosphere may easily travel at
speeds of more than twice the velocity of sound – and high-pressure steam may travel
twice as fast again, at about 5,000 feet per second. Unless the wheel of a turbine
could be made to rotate at least at half the speed of the steam acting upon its blades,
there could be no efficient use of its energy. But the centrifugal force alone, to say
nothing of the other forces which de Laval tried to counter with his flexible shaft,
would have destroyed such an engine.
Parsons had the idea of reducing the steam pressure and speed, without
reducing efficiency and economy, by causing the whole expansion of the steam to
take place in stages so that only moderate velocities would have to be reached by the
turbine wheels. This principle still forms the basis of all efficient steam-tirbines
today. Parsons put it into practice for the first time in his model of 1884, a little
turbine combined with an electric generator, both coupled without reducing gear and
revolving at 18,000 r. p. m. The turbine consisted of a cylindrical rotor enclosed in a
casing, with many rings of small blades fixed alternately to the casing and to the
rotor. The steam entered the casing at one end and flowed parallel with the rotor
('axial flow'); in doing so it had to pass between the rings of blade – each acting
virtually as a nozzle in which partial steam expansion could take place, and the jets
thus formed gave up their energy in driving the rotor blades.
It was a more complicated solution of the problem than de Laval's, but it
proved to be the right one. The speed of 18,000 r. p. m. used the energy of the steam
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