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 CHAPTER 3. DYNAMIC COMPRESSORS
1 DESCRIPTION. Centrifugal and axial flow compressors are both categorized
as dynamic compressors. Dynamic compressors move gases by a process of
acceleration. The direction of airflow in the centrifugal compressor is
radial with respect to the axis of rotation. In the axial flow compressor
airflow is parallel to the axis of rotation. Centrifugal and axial flow
compressors are driven by electric motors or steam turbines. Operating and
maintenance instructions for electric motor and steam turbine drives are
contained in NAVFAC MO-205, Central Heating and Steam Electric Generating
Plants.
1.1 Centrifugal Compressor. The major components of a centrifugal compressor
are: impeller, shaft, casing, and diffuser/volute (figures 3-l and 3-2). In
the center of the impeller is the suction eye area, the center of low pressure
when the impeller is rotating. Figure 3-3 illustrates three basic impeller
designs. Air entering the suction eye is moved outward along the impeller
blades by centrifugal force with increasing velocity. The air leaves the
impeller through the diffuser to the volute where the air is slowed and the
velocity component of the air mass is partially converted into pressure. In a
multistage compressor the air exiting the volute is fed to another impeller-
diffuser-volute series to further increase the air pressure.
1.2 Axial Flow Compressor. The major components of an axial flow compressor
are: rotor with rows of blades, and a stator with rows of stationary blades
(figures 3-4 and 3-5). The moving blades accelerate the air, and the
stationary blades direct the flow of air into the next row of moving blades.
FIGURE 3-l. Simple Volute Pump
3-1
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