Page 130 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 3 .1 Compressor Best Practices

Fig 3.1.15 Typical axial compressor

centrifugal compressor is a machine of variable capacity, fixed compressor impeller can be reduced to a series of equivalent
energy or head for a given flow and is self-limiting. That is, orifices. The inlet of the blade row or impeller being one orifice,
there is a maximum pressure which the compressor can the exit being another and the eye and hub seals being additional
produce and a maximum horsepower which it requires. equivalent orifices.
Observing the curve of a typical dynamic compressor, one It should also be noted that both the suction and discharge
can see that the only place that a dynamic compressor can process system for a given point in time and flow rate can be
develop higher energy or head is at a lower flow for a given thought of as equivalent orifices placed at the inlet and discharge
speed. We will see in the next chapter how the system of the compressor flanges respectively.
combined with the compressor operating curve will de- In summary, the characteristics of positive displacement and
termine the operating point. It should be noted that the dynamic compressors are as follows:
operating curve of an axial compressor can sometimes ap-
proach that of a positive displacement compressor, in that its Flow e fixed for positive displacement, variable for dynamic.
volume range is small and almost approximates the positive Head e variable for positive displacement, fixed for dynamic.
displacement curve. Limiting characteristics for dynamic compressors e not self
The concept of an equivalent orifice is introduced in this limiting for positive displacement (requires relieving
section. Any typical axial compressor blade row or radial device).

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