When compared with axial compressors, centrifugal compressors have the following five advantages:
They occupy a smaller length than the equivalent axial compressors.
They are not liable to loss of performance by buildup of deposits on the surfaces of the air channel when working in a contaminated atmosphere.
They are able to operate efficiently over a wider range of mass flow at any particular rotational speed (i.e., they alleviate problems of matching operational conditions with those of the associated turbine).
They are used mainly in small power units because the higher isentropic efficiency of axial compressors cannot be maintained for small machines.
Titanium is the preferable material because of its high resistance to corrosion.
The centrifugal compressor consists of a stationary casing containing a rotating impeller, which increases the velocity of the air, and a number of diffusers that decelerate the air converting a part of its kinetic energy to pressure. Figure 11.1 illustrates a centrifugal compressor.
Figure 11.2 illustrates the variation in the pressure ratio when a valve placed in the delivery line of the compressor running at constant speed is slowly opened. When the valve is shut and the flow is zero, the pressure ratio will have...
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