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TRG-TRC010-EN 17
period two
Refrigeration Cycle
notes
Refrigerant leaves the evaporator as saturated vapor ➀ and flows to the first-
stage impeller of the compressor. There, the refrigerant vapor is compressed to
a higher pressure (P
1
) and temperature ➁. Cooler refrigerant vapor that flashed
within the economizer is mixed with the refrigerant discharged from the first-
stage impeller, reducing the heat content of the mixture ➂. The second stage of
compression further elevates the pressure (P
c
) and temperature of the
refrigerant ➃.
Energy provided to the compressor is imparted to the refrigerant as an increase
in pressure and superheat. Superheated refrigerant vapor leaves the
compressor and enters the condenser.
Water flowing through the condenser absorbs heat from the hot, high-pressure
refrigerant vapor, causing it to desuperheat ➄ and condense into saturated
liquid ➅ before leaving the condenser to travel to the first expansion device.
The first expansion device reduces the pressure (➅ to ➆) of the refrigerant to
the second-stage impeller inlet pressure (P
1
). This pressure drop causes a
portion of the liquid refrigerant to evaporate, or flash. The evaporating
refrigerant absorbs heat from the remaining liquid refrigerant, reducing its
enthalpy from ➆ to ➇. The resulting mixture of liquid and vapor enters the
economizer ➆. Here, the vapor is separated from the mixture and routed
directly to the second-stage impeller inlet ➂ and the remaining liquid travels on
to the second expansion device ➇.
Just before it enters the evaporator, the liquid refrigerant flows through a
second expansion device that reduces its pressure (P
e
) and temperature to
evaporator conditions ➈. The cool, low-pressure mixture of liquid and vapor
enters the distribution system in the evaporator shell and absorbs heat from
water that flows through the tubes. This transfer of heat boils the liquid
refrigerant, and the resulting saturated refrigerant vapor is drawn back to the
compressor ➀ to repeat the cycle.
2-stage centrifugal chiller
Refrigeration Cycle
1
1
2
2
3
3
4
4
6
6
7
7
pressure
pressure
enthalpy
enthalpy
evaporator
evaporator
condenser
condenser
2-stage
2-stage
compressor
compressor
expansion
expansion
devices
devices
8
8
9
9
P
P
e
e
P
P
c
c
P
P
1
1
5
5
economizer
economizer
Figure 25
trgtrc010_book.book Page 17 Wednesday, September 1, 1999 10:39 AM