Page 179 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Compressor Best Practices Best Practice 3 .13

Fig 3.13.7 Impeller with side plate removed

Fig 3.13.4 Impeller with side plate removed

Fig 3.13.8 Impeller with side plate removed

Since the head (energy) produced by the blade is pro-
portional to the tip speed (unchanged) and the tangential ve-
locity (increased), we can see that the reduction of flow through
Fig 3.13.5 Impeller with side plate removed
the blade has resulted in increased head or energy imparted to
the fluid. Practically, this makes sense, since the slower the gas
proceeds through the vane, the more time it has to pick up
energy imparted by the blades, and as a result will increase the
energy produced within the impeller. Therefore it can be seen
for all dynamic blades and impellers which increase the energy
of the fluid by the action of the vane on the fluid can increase
fluid energy only at a lower flow rate, assuming the speed of the
impeller and the inlet angle of the fluid to the blade remain
unchanged.

Blading types

Backward lean
The previous discussion focused on the characteristic of
a backward leaning vane. Most turbo machinery vanes are of
this type, since they produce a greater head rise from impeller
design point to the low flow operating point. The low flow limit
Fig 3.13.6 Impeller with side plate removed of operation for centrifugal compressors is known as surge.

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