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Gas Turbine engines

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Compressors

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Types of Compressors

Reciprocating air compressors are the type of

compressor found in most small shops, they are

positive displacement machines.

This means that they increase the pressure of the air

by reducing its volume, this is accomplished by a

piston moving up a cylinder compressing the air above

it.

Single-stage and two-stage reciprocatingcompressors are commercially available. Single-stage

compressors are generally used for pressures in the

range of 70 psi to 150 psi. Two-stage compressors are

generally used for higher pressures.

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Rotary Screw Compressors

Rotary air compressors are also positivedisplacement compressors. The most commonrotary air compressor is the single stage helicalor spiral lobe oil flooded screw air compressor,

consisting of two rotors within a casing wherethe rotors compress the air internally. There areno valves. These units are basically oil cooled

with the oil sealing the internal clearances. Sincethe cooling takes place right inside the

compressor, the working parts never experienceextreme operating temperatures making them

continious duty compressors.

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Centrifugal Compressors

The centrifugal air compressor is a dynamiccompressor which depends on a rotatingimpeller to compress the air.

In order to do this efficiently, centrifugalcompressors must rotate at higher speedsthan the other types of compressors.

These types of compressors are designed forhigher capacity because flow through thecompressor is continuous and oil free bydesign.

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Centrifugal compressors consist of three main

parts, as shown in Figure 1.

The first is a rotating impeller, which imparts

work to the gas by increasing its angular

momentum. The fluid static pressure and

absolute velocity (stationary frame ofreference) increase through the impeller

passage.

The second component is the diffusersection, often with vanes to increase the

effectiveness. The diffuser converts the kinetic

energy into the static pressure by decelerating

the fluid.

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The third and final component is a volute orcollector, used for collecting the gas from

diffuser and delivering to the outlet pipe. Avolute has two functions: collection anddiffusion.

The volute must collect and transport thefluid to the downstream system. It also raisesthe static pressure by converting kineticenergy (u2) to potential energy (static

pressure).

The latter function has performance benefits,as the discharge pressure is increased.

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Figure 1: Centrifugal compressor layout. (a) A cross-sectional

view, showing the impeller followed by a vaned diffuser, and a

volute. (b) An isometric view of the package.

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Examples of ApplicationImpeller of a compressor

E l f A li ti

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Examples of Application

Vaned diffuser for centrifugal compressor

E l f A li ti

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Examples of Application Turbo charger

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Axial Compressor