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TRG-TRC010-EN 25
period three
Compressor Capacity Control
notes
Consider a given-diameter compressor impeller that rotates at a constant
speed. As the load on the chiller decreases, the inlet vanes partially close and
the flow rate of refrigerant through the compressor drops. Radial velocity (V
r
),
which is proportional to refrigerant flow, decreases as well.
Even though the speed of rotation and diameter of the impeller are constant,
the tangential velocity (V
t
) (which is proportional to the product of impeller
rotational speed and impeller diameter) drops because of the pre-swirling of
the refrigerant caused by the inlet vanes.
The result is a shorter resultant velocity vector (R), which means that less static
pressure is generated.
Compressor Unloading
V
V
r
r
R
R
V
V
t
t
V
V
r
r
V
V
t
t
full load
part load
R
R
Figure 36
trgtrc010_book.book Page 25 Wednesday, September 1, 1999 10:39 AM