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Cabin
environment
Cabin cooling
Heat extraction
Condenser
Compressor
Expansion
valve
Evaporator
Engine
environment
10.2 The simplified loop
The A/C loop uses the principle of the change of
state of refrigerant fluids in order to bring about heat
exchanges.
In a heat exchange the thermal flow is always from
hot to cold. This principle applies to the two heat
exchangers in the A/C loop: the evaporator and the
condenser.
Two changes in the state of the refrigerant fluid
in the exchangers are produced by controlling the
pressure in the A/C loop.
g
The higher the pressure, the higher the tempera-
ture at which the change in state occurs.
The three states of the refrigerant fluid in the loop
are LIQUID, DIPHASIC and GASEOUS. In the interme-
diate diphasic state, the fluid is partly gaseous and
partly liquid.
The state of the refrigerant changes in the course of
the exchanges of energy in the condenser and the
evaporator.
Increase gas pressure
â
increase temperature
Compressor
Condenser
Expansion valve
Evaporator
GAS COMPRESSION
Phase transition nr.2
â
heat transfer
EVAPORATION
Phase transition nr.1
â
heat transfer
CONDENSATION
Decrease pressure
â
decrease temperature
PRESSURE DROP
g
These changes of state in the evaporator and the
condenser are determined by two components
of the loop: the compressor and the expansion
valve.
g
The changes in the state of the fluid from liquid to
gas and vice versa allow large quantities of heat
to be transferred at a constant temperature.
Pressures in the condenser and the evaporator change
permanently according to the thermal exchanges that
take place with the outdoor air.
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