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As it was already said the process of conversion of thermal to kinetic energy in impulse turbines takes place only in the nozzles and the main function of the moving blades is to convert the kinetic energy into mechanical work.

However, it was reasonable to construct a stage in which the change from thermal to kinetic energy occurs in both the nozzle and the moving blades. This was done by shaping the moving blades passages so that they behave as nozzles also. Such blades, in addition to changing the direction of the fluid relative to the blade, also operate to change the magnitude of its velocity relative to the blade. This scheme of operation characterizes the reaction stage.

Most reaction turbines are designed in order to optimize stage efficiency and blade loading and to maintain sufficiently high rotor blade velocity.

Lesson 7

Marine Gas Turbines

Part I

Слова и словосочетания к тексту:

a great scope	—	большой диапазон, область (применения)
attempt n	—	попытка
combustion chamber	—	камера сгорания
axial-flow rotating device	—	аксиально- проточный компрессор
centrifugal rotating device	—	центробежный компрессор
driving torque	—	вращающий момент
impinge v	—	сталкиваться , ударять
compressor-driving turbine	—	компрессорная турбина
extract from v	—	извлекать из, получать от

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Marine propulsion offers a great scope for gas turbines. Gas turbines work on exactly the same thermodynamic cycle as any ordinary diesel engine. It takes air from the atmosphere, compresses it, heats this compressed air by the direct burning of fuel and then makes the air to perform work as it re-expands to atmospheric pressure.

The gas turbine engine is a successful attempt to combine the compactness and simplicity (the absence of reciprocating parts) with the advantages of internal combustion demonstrated by the diesel engine which gives better efficiency.

Several major components are required by the gas turbine in addition to the turbine itself. The first major component is a compressor, which raises the pressure of air taken from the atmosphere by means of several devices. It is either a centrifugal or axial-flow rotating device that receives its driving torque directly from the turbine, since it is always mounted on the same shaft. The axial compressor is more efficient.

The second is the combustion chamber (or a combustor), in which the air from the compressor is heated by the injection and burning of fuel. This air is at high pressure, having suffered only a slight loss in pressure as it passed through the combustion usually in the 15000 to 2000 F temperature range. It is then expanded through a nozzle to convert part of its thermal and pressure energy into kinetic energy; the resulting high velocity air (or gas) stream then impinges on the blades of the turbine.

The marine gas-turbine engine could be adaptable to a wide range of vessels from small craft requiring several horse powers to naval vessels and large merchant ships both of which may require from 20.000 to 50.000 horsepower, per shaft. In addition to conventional propulsion service gas turbines are used for shipboard auxiliary service.

Notes

suffer v — нести

F (Fahrenheit) — температура по Фаренгейту

Part 2

Слова и словосочетания к тексту:

lubricating oil	—	смазочное масло
in series	—	последовательное соединение
air-craft jet engine	—	авиационный реактивный двигатель