• The performance of single stage systems shows that these systems are adequate as long as the temperature difference between evaporator and condenser (temperature lift) is small.
•
There are many applications where the temperature lift can be quite
high. The temperature lift can become large either due to the requirement of very low
evaporator temperatures and/or due to the requirement of very high condensing
temperatures. For example, in frozen food industries the required evaporator
can be as low as –40 oC, while in chemical industries
temperatures as low as –150oC may be required for liquefaction of gases. On the high temperature side the
required condensing temperatures can be very
high if the refrigeration system is used as a heat pump for heating
applications such as process heating, or drying.
•
A multi-stage system is a refrigeration
system with two or more low-side pressures. Multi-stage systems can be
classified into:
a)
Multi-compression systems
b)
Multi-evaporator systems
c)
Cascade systems, etc.
•
Two concepts which are normally integral to
multi-pressure systems are,
i) flash
gas removal.
ii) intercooling.
.
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