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Thursday, March 3, 2011

TURBINES

The main difference between the turbine and other types of engine is that its only movement is rotary, or turning. Its name comes from Latin turbo, meaning something that spins or twirls.
Turbines can be driven by steam water, gas or air. A steam turbine consists of a cylinder shaped casing containing a drum shaped rotor, or turning part. Steam from the boiler is led through nozzles fixed to the casing so that jets of steam strike blades are mounted in a ring round the rotor.
Water turbines are used for driving generators in hydroelectric power station. There are two types, impulse turbines and reaction turbines. Both make use of the energy of falling water which increases in velocity as it falls under the influence of gravity. The distance of fall or head, corresponds to steam pressure. A high head or steam pressure results in high water or steam velocity.

Gas turbines work on the same principle as steam or water turbines, but are driven by hot gas which is produced by burning liquid fuel such as paraffin, heavier oils, or gas in air. The gas is compressed by a rotary compressor, heated by burning the fuel, and blown into the gas turbine. Developed originally to drive aircraft, their outputs and sizes have been increased tremendously. They are now used widely for ship propulsion and in power stations.
Tiny air turbines, driven by compressed air and turning at 250.000 r.p.m are used for dentists drills. At this speed the drilling of a tooth is quickly completed and there is less vibration than with an electric drill.

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