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►Gas Turbine:
This machine has a single-stage radial compressor and turbine, a recuperator, and foil bearings. A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. (Gas turbine may also refer to just the turbine element.) Energy is released when air is mixed with fuel and ignited in the combustor. A common mistake is that combustion increases the pressure of the gasses flowing through a turbine. In fact the heat addition stage of a gas turbine cycle incurs a slight pressure drop to facilitate flow through the engine. For all intents and purposes, however, the combustion process can be considered as occuring at constant pressure, with an increasing volume to accommodate the temperature rise, as explained by the ideal gas law. This in turn results in an increase in the velocity of the gas flow (see gas laws). This is directed over the turbine's blades, spinning the turbine and powering the compressor, and finally is passed through a nozzle, generating additional thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure. Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, generators, and even tanks. Theory of operation: Gas turbines are described thermodynamically by the Brayton cycle, in which air is compressed isentropically, combustion occurs at constant pressure, and expansion over the turbine occurs isentropically back to the starting pressure. In practice, friction and turbulence cause: a) non-isentropic compression - for a given overall pressure ratio, the compressor delivery temperature is higher than ideal. b) non-isentropic expansion - although the turbine temperature drop necessary to drive the compressor is unaffected, the associated pressure ratio is greater, which decreases the expansion available to provide useful work. c) pressure losses in the air intake, combustor and exhaust - reduces the expansion available to provide useful work.
As with all cyclic heat engines, higher combustion temperature means greater efficiency. The limiting factor is the ability of the steel, ceramic, or other materials that make up the engine to withstand heat and pressure. Considerable engineering goes into keeping the turbine parts cool. Most turbines also try to recover exhaust heat, which otherwise is wasted energy. Recuperators are heat exchangers that pass exhaust heat to the compressed air, prior to combustion. Combined cycle designs pass waste heat to steam turbine systems. And combined heat and power (cogeneration) uses waste heat for hot water production. |
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Gas Turbine Power Plant -
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