Hitachi 7E300020, Технический каталог, Страница: 23 / 158

2. Features and benefits
TCGB0075 rev.0 - 11/2012
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2.2.3 SMART cascade cycle
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Concept of normal cascade cycle
There exist some cycles which could require working at very low evaporation temperatures. For this type of application a
single refrigerant is not able to evaporate at low temperatures with positive pressures (higher than 1 atm) and to conden-
sate at high temperatures with pressures not too high with a good performance.
In this situation it must resort to an installation consisting on two single-stage cycles (high and low temperatures), thermally
connected by an intermediate heat exchanger. This cycle is known as cascade cycle.
The low temperature cycle use a refrigerant (R-410A) which allows to evaporate at very low temperatures at positive pres-
sures, but condensing in the intermediate heat exchanger at pressures not too high by transferring heat to the evaporator
of the high-temperature cycle, where is circulating a different refrigerant (R-134a) at lower temperature. The condensation
of the low-temperature refrigerant (R-410A) causes the evaporation of the high-temperature refrigerant (R-134a).
R-410A
R-410A
R-134a
R-134a
H
2
O
Air
Pressure
P
COND
(R-134a)
P
COND
(R-410A)
P
EVAP
(R-134a)
P
EVAP
(R-410A)
Enthalpy