Axial flow compressors characteristics

To be able to decide which type of compressor would best fit the job, we should first divide the compressors into three main categories positive displacement, centrifugaf and axial flow In general terms, positive displacement compressors are used for high pressure and low flow characteristics centrifugal compressors are used for medium to high pressure dehvery and medium flow and axial flow compressors are low pressure and high flow... 

Several types of compressor have characteristics intermediate between those of PD compressors and centrifugal or axial-flow compressors. These include the lobe type, sliding vane, and liquid piston. For all these, the discussion of compressor work and compressor efficiency applies just as well as the above-mentioned types. Descriptions of the mechanical arrangements of these can be found in texts on pumps and compressors [2]. 

Centrifugal compressors are dynamic compressors and are essentially constant pressure, variable volume machines and must be regulated in almost all applications. Before control can be discussed, the operating characteristics must be understood. The discussion to follow will be concerned with radial-flow compressors. Axial-flow compressors have similar characteristics curves, although the change in pressure rise is much greater with equivalent changes in compressor rotational speed. 

For ease of illustration we will consider the characteristics and behaviour of a centrifugal pump which is similar in behaviour to radial/axial flow fans and centrifugal/screw compressors. Figure 63 shows the mechanical connection of a flow valve to control the output of the pump or the discharge of the fluid through the throttle of the valve. Figure 6.39 illustrates the characteristics of the pump ... 

Characteristic curves—pressure against flowrate—of centrifugal and axial compressors usually have a peak. Figure 3.22 is an example. In order to avoid surging, the flow through the com-... 

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