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TRG-TRC010-EN 23
period three
Compressor Capacity Control
notes
In a multistage centrifugal compressor, the operating characteristics of
each impeller are modulated by the impeller’s own set of inlet vanes.
This example shows 2 impellers in series. These impellers share the task of
compressing the refrigerant. Centrifugal water chillers are generally available
with 1, 2, or 3 impellers.
The forces that act on the refrigerant vapor within the centrifugal compressor
impeller can be broken down into 2 components. One component acts to move
the refrigerant away from the impeller in a radial direction. This component is
called radial velocity (V
r
).
The second component acts to move the refrigerant in the direction of impeller
rotation. This component is called tangential velocity (V
t
).
Together, these components generate the resultant velocity vector (R), the
length of which is proportional to the amount of kinetic energy in the
Multistage Compressor
inlet vanes
inlet vanes
impellers
impellers
Figure 33
V
V
r
r
R
R
V
V
t
t
Impeller
Figure 34
trgtrc010_book.book Page 23 Wednesday, September 1, 1999 10:39 AM