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Steam Engine

  A steam engine converts the heat energy of pressurized steam into mechanical energy. This usually consists of steam driving a piston inside a closed cylinder. Its development was to spark one of the greatest changes that have occurred in human history.

A major fallacy that has arisen with the steam engine is that James Watt (1736 - 1819) invented it totally on his own, and that his idea stemmed from watching a kettle boil. His steam engine was, in fact, an adaptation of earlier inventions. In 1698, Thomas Savery devised a steam pump that was used to lift water from mines. His pump was very inefficient and because it never had a safety valve, it tended to blow up. His invention was improved by Thomas Newcomen in 1712, whose ideas were reliable and safe. Newcomen allowed the steam from the boiler to enter the lower part of the cylinder, so driving the piston upwards. At the top of the stroke, the cylinder was then cooled and the steam was condensed back into water. This created a partial vacuum which forced the piston down to its original position. The piston was attached to a beam which was connected to a pumping rod at the other end. Although his engine worked well, it was highly inefficient, and it was not until Watt saw a model of Newcomen\'s engine that vast improvements were made.

Watt\'s first major concept was to design a separate condenser. This meant that the cylinder did not need to be heated and cooled during every cycle so reducing dramatically the fuel consumed. He also invented the so-called ‘sun and planet’ gearing system that allowed the crossbeam to drive a large flywheel instead of a pumping rod. His discoveries led to the double-acting steam engine which used both the upstroke and downstroke, which again was more efficient that Newcomen\'s engine which only acted as a pump during the downstroke.

Steam engines, as well as being used in the mining industry, were also used in other industries, such as the iron manufacturing and textile industries. One large engine was used to drive a shaft running through a factory and belt drives delivered power to individual machines. Its implications were vast, as the heavy toil of working using manpower alone was superseded.

Steam power meant that factories could now be set up instead of manufacturing items on a cottage industry scale, as vast amounts of power were available to drive machinery. This revolutionized the way people lived, as more and more were forced to live in cities near their places of work. This led to a rapid expansion in population growth within these industrial zones, as villages became towns and towns became cities.

Steam power also revolutionized transport, as shipping and then railways adapted the steam engine. As well as the transportation of goods becoming cheaper and more reliable, the new transport opened up one of the biggest industries in today\'s modern society, that of tourism.

Although reciprocating steam engines are no longer a major power source, their development and use was one of the pioneering factors in the Industrial Revolution, that changed the world forever.

The thermodynamic properties of steam are, however, vital in the operation of most electrical power generating stations, coal-fired boilers and nuclear reactor heated boilers produce superheated steam to drive the turbines which deliver power to the electric generators. A typical power station turbine will have a large diameter shaft passing through the turbine carrying multiple rows of discs on which blades of complex form are mounted. Steam is introduced at one end of the turbine through a ring of nozzles and it impinges on the blades on the first disc developing force on each blade to make the disc rotate and thus the shaft. The steam coming from the first row of blades is deflected by fixed blades secured to the casing of the turbine so that it impinges on the blades on the next disc at the correct angle, and this process is repeated at each disc. A large turbine may have as many as 20 discs, each one being of larger diameter than its predecessor as the steam travelling through the turbine expands in volume. After the last set of blades the steam is directed downwards onto the set of pipes which comprises the condenser. The steam passes over the outside of the pipes and cooling water is pumped through them. AA

Further reading J.D. Storer, The History of the Steam Engine.



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