Gas Turbine
A turbine represents a simple but effective way to harness energy by changing the force of a moving fluid into circular motion. Gas turbines are essentially a refinement of an ancient technology that underwent a rapid development in the nineteenth and twentieth centuries.
Water turbines such as water wheels, which use the energy of moving water to drive grain mills, for instance, have been in use for millennia. Windmills, which came in use in the Middle East in the 900s and in Europe in the 1100s, formed the next major step in the development of the turbine. The invention of machines that burned fuel to boost the power output of the turbine took place quite early--there is a description of a simple steam turbine dating to 120 B.C.--but remained inconsequential until the mid-19th century, when the development of the steam turbine for industrial purposes came to represent a significant share of generated power. Steam turbines are still widely used, in such technological applications as nuclear power stations and ships, because they are smaller and lighter than equally powerful piston-engines.
Attempts to develop gas turbines were first undertaken in the early 1900's, with pioneering work done in Germany. The most successful early gas turbines were built by Holzwarth, who developed a series of models between 1908 and 1933. The first industrial application of a gas turbine was installed in a steel works in Hamborn, Germany, in 1933. In 1939 a gas turbine was installed in a power plant in Neuchâtel. The basic principles of the gas turbine involve the compression of a gas, usually air, in a compressor. The compressed air then passes into a combustion chamber where it is mixed with a burning fuel. The gas expands as a result of the combustion and rushes into the turbine chamber, which is fitted out with a series of fanlike wheels. The wheels turn, driving both the compressor and an electric generator. The earliest gas turbines proved much less efficient than steam turbines, because sufficiently powerful compressors were not yet available. A gas turbine is most efficient at extremely high temperatures, and materials that could withstand such temperatures had yet to be developed. In addition, it turned out that most fuels were not suitable, causing too much corrosion of the turbine blades.
However, the development of gas turbines received tremendous stimulus with the discovery that such engines were vastly more efficient for high-speed, high-altitude flight than the piston-and-propeller engines then in use in aircraft. In addition, gas turbines are small and light, making them particularly suitable for flight applications. In Great Britain, Frank Whittle, an air force cadet, received a patent on an aircraft gas turbine jet propulsion engine in 1930. At the same time, German engineers, particularly Hans von Ohain, were experimenting with the technology. The first gas turbine-powered craft, a Heinkel HeS3, flew in 1939. The British first flew a gas turbine engine in 1941.
The operating principles of gas turbines in jet propulsion are slightly different, since the turbine itself is mainly used to drive the compressor, and sometimes a propeller. The bulk of the escaping hot gas serves directly to produce forward thrust, as in a balloon "powered" by air escaping from the inlet valve. The gas turbine revolutionized both military and commercial aviation, and today all aircraft have some form of gas turbine engine. Missiles are also powered by gas turbines. Land-based applications of gas turbine technology remain rather limited, since steam turbines have far greater fuel efficiency and can operate on many different kinds of fuel. Gas turbines are mainly used as stand-by generators to handle system overloads and in pipeline pumping stations.
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