Encyclopedia > Turbine

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A turbine is a shaft with a fan of blades mounted on it, known as the rotor. This is mounted inside a sealed casing that has a ring of nozzles mounted on it. The activating fluid is blown through these nozzles under high pressure. These jets impact on the turbine's blades and cause it to spin very, very rapidly. Speeds of over 10,000 rpm are common with some very small turbines exceeding 100,000 rpm.

There are two main types of steam turbine, depending on the shape of the blades and nozzles. Impulse and reaction require a large, separate boiler and condensor plant to work.

These are an adaptation of the jet engine. The air is drawn in through a compressor unit that is driven by the turbine shaft. This compressed air is passed into a combustion chamber where the fuel is injected and ignited. the very hot, high pressure exhaust gas is directed through a nozzle ring to impinge on the turbine blades. this spins the shaft at very high speed. The turbine shaft is coupled at one end to the compressor fan and the other is coupled to whatever the gas-turbine is driving, usually an electrical generator. A compound turbine has two separate stages, one high-pressure and the other low-pressure, linked together. A turbopump is a type of pump in which the fluid is moved by the blades of a high-speed turbine.

Problems with turbines are quite rare but any imbalance of the rotor blades can lead to vibration, which in extreme cases can lead to a blade letting go and punching straight through the casing. If water gets into the gas and is blasted onto the blades rapid erosion of the blades can occur, possibly leading to imbalance and failure. The control of a turbine with a governor is essential, as turbines need to be run up slowly, to prevent damage. Uncontrolled acceleration of the turbine rotor can lead to the overspeed trip being activated to shut off the activating gas supply to the turbine. If this fails then the turbine may continue accelerating until it breaks apart, often spectacularly, probably extremely dangerously. The high pressures inside the casing lead to problems in sealing[?] the output shaft(labyrinth seals[?]). Turbines are expensive to make, requiring precision manufacture and special quality materials. This purchase cost is offset by much lower maintenance requirements and the small size of a turbine when compared to its shaft power output. Electrical Power stations around the world use large steam turbines driving turbo-generators[?] to produce vast amounts of electricity.

See also wind turbine tesla turbine

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