Gas Turbine

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Introduction:-

??????????? A gas turbine unit for power generation or a turbojet engine for production of thrust primarily consists of a compressor, Combustion chamber and a turbine. The air as it passes through the compressor, experiences an increase in presser. There after the air in fed to the combustion chamber leading to tan increase in temperature. This high pressure and temperature gas in then passed through the turbine, where it is expanded the required power is obtained.

Turbines, like compressors, can be classified into radial, axial and mixed flow machines.? In the axial machine the fluid moves essentially in the axial direction through the rotor. In the radial type the fluid motion is mostly radial. The mixed-flow machine is characterized by a combination of axial and radial motion of the fluid relative to the rotor. The choice of turbine type depends on the application, though it is not always clear that any one type is superior.
Comparing axial and radial turbines of the same overall diameter, we may say that the axial machine, just as in the case of compressors, is capable of handling considerably greater mass flow. On the other hand, for small mass flows the radial machine can be made more efficient than the axial one. The radial turbine is capable of a higher pressure ratio per stage than the axial one. However, multistaging is very much easier to arrange with the axial turbine, so that large overall pressure ratios are not difficult to obtain with axial turbines. In this chapter,

We will focus on the axial flow terbine

Generally the efficiency of a well-designed turbine is higher than the efficiency of a compressor. Moreover, the design process is somewhat simpler. The principal reason
For this fact is that the fluid undergoes a pressure drop in the turbine and a pressure rise in the compressor .The pressure drop in the turbine is sufficient to keep the secondary layer generally well behaved and the secondary layer separation which of the occurs in compressors because of an adverse pressure gradient, can be avoided in turbines. Offsetting this advantage is the much more critical stress problem, since turbine rotors must operate in very high temperature gas. Actual blade shape is often more dependent on stress and cooling considerations than on aerodynamic considerations, beyond the satisfaction of the velocity-triangle requirements.
Because of the generally falling pressure in turbine flow passages much more turbine in a giving blade row is possible without danger of flow separation than in an axial compressor blade row. This means much more work and considerably higher pressure ratio, per stage.
In recent years advances have been made in turbine blade cooling and in the metallurgy of turbine blade materials. This means that turbines are able to operate successfully at increasingly high inlet gas temperatures and that substantial improvements are being made in turbine engine thrust, weight, and fuel consumption.

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Gas Turbine Efficiency

The allegedly impending crises of fuel shortages, fuel price rises and of global warming hang over the society of western society in the twenty first century and as a result businesses and governments alike are searching for more environmentally friendly and cost effective sources of energy. Such energy sources are intended to replace the fossil fuels such as petrol, oil and natural gas (the use of which greatly exacerbates the problem of global warming through the production of greenhouse gases such as carbon dioxide, carbon monoxide and nitrous oxides), sources of energy which are (according to reports) due to run out by the turn of the twenty second century.

However, it may not be necessary to find new and renewable energy sources (which may not prove to be any more environmentally friendly than our existing sources) if we are able to make our current sources of energy, such as the means of producing electricity via gas turbines, more productive and cost efficient.

Gas turbines generate electricity either as primary or secondary units, such as in natural gas-fuelled power plants where they are combined with steam turbines. The hot stream of gas (resulting from the combustion of the natural gas) or the steam produced by the steam turbines turns the blades of the gas turbine, producing mechanical energy which is then transferred to a generator which in turn creates electricity.

However, the performance of these gas turbines may be hindered by the simple fact that they are not being cleaned thoroughly enough, resulting in lower productivity and an output far below their potential. There are, however, a range of turbine cleaning solutions that are suitable for use on any and all gas turbines and compressors are they in the aerospace, maritime or power generation industries resulting in gas turbine efficiency.

The use of such cleaners can also result in businesses experiencing considerable long term cost savings, such as those experienced by the Ministry of Defence in regards to using such a product on their military and search and rescue helicopters, resulting in an estimated saving of ?7000 per engine as the engine cleaner dealt effectively with excessive salt fouling as well as acting as an inhibitor of corrosion, meaning that only one wash with this particular cleaner was required. Such products are still being used by the MOD as the army stationed in Iraq and Afghanistan use it on their aircraft engaged in combat and humanitarian operations, as do the Royal Navy (who use them extensively on the gas turbines used to propel their vessels).

 

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