Steam Turbine
The earliest known steam turbine was built by Hero of Alexandria in the first century A.D. Called the Sphere of Aeolus, the device consisted of a hollow sphere that could be made to rotate at high speed by feeding the interior of the sphere with steam, which escaped through small spouts resembling elbows. In 1629 Giovanni Branca told how a wheel could be turned by allowing jets of steam to hit vanes attached to the wheel's outer rim. However, the significant drawback to this simple idea was the need for the wheel to revolve with unheard of velocity to absorb even a useful fraction of the energy of the steam.
The first steam turbines with any commercial use were those built in 1831 by William Avery in the United States. About 50 of his crude turbines were made and used in sawmills and even on a locomotive. But they were finally abandoned because they needed constant repair and would not maintain a constant speed.
In 1883, Gustav de Laval constructed a simple steam turbine, consisting of a wheel with blades on its perimeter, that he used to power small machines such as his cream separators. Laval's impulse turbine spun too fast (up to 30,000 rpm) to be used without step-down gears, and since it did not capture much of the energy from the steam that passed through it, it couldn't compete with other efficient engines in use at the time.
Seeing that a more efficient turbine would have tremendous commercial potential, Charles Parsons designed a practical one. Parsons's turbine had a rotor consisting of a drum with several sets of vanes attached to a shaft. Moving steam caused the drum to rotate as it pushed the vanes on its way through the turbine. Other stationary blades forced the steam against those that rotated, making use of as much energy as possible. The steam then continued until it encountered another set of turbine blades designed to work with the same steam at a slightly lower pressure. Because the steam expanded as it passed through the turbine, Parsons made the second set of blades larger and the exhaust end wider than the intake end. His turbines, while they had the ability to operate at slower speeds, could also be designed to spin as fast as 18,000 revolutions per minute with a high degree of efficiency. They were, however, prone to leakage between the moving blades and the casing of the turbine.
Parsons set up two of his turbines at a power station in England, thereby providing the first electricity by steam turbine. He also applied his technology to ships. He built a 100-foot (30 m) vessel, the Turbinia, which reached speeds near 20 knots (37 km/hr). Eventually, with three propellers this ship achieved the distinction of the fastest afloat when it reached 34 knots (63 km/hr). His engines provided high speeds with less vibration than the traditional reciprocating steam engines. Later, much larger steam engines (70,000 horsepower) drove famous liners like the Mauritania and Lusitania.
Around the turn of the century, two other engineers built upon the foundations laid by de Laval and Parsons. Auguste Rateau, a Frenchman, and Charles Curtis, an American, introduced modifications to turbine designs which vastly increased efficiency. The Curtis turbine, a kind of Laval turbine with many rows of blades, could produce the output of a piston engine at one-third its cost and one-tenth its size. In 1897, Curtis sold the rights for his design to the General Electric Company, which produced a working model in 1902. Rateau's multi-stage impulse turbine, built around 1897, corrected some of the leakage problems encountered by Parsons's turbine.
Within ten years, steam turbines had become an essential power source in naval vessels and electric generation plants. Today's steam turbines still rank among the most important and powerful machines in the world. Just one turbine powering a generator can supply all the electricity needed by 3,000,000 people.
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