Change Of State Of Refrigerant - Kubota KX080-3 Workshop Manual

WSM KX080-3 Mechanism

(2) Change of state of refrigerant

The concept of the air conditioning system is as
follows. When liquid Freon is sprayed, it expands
and turns into very cold gas. It is so cold that it
freezes and looks snow-white (even under atmo-
spheric pressure). If the sprayed Freon is left as it
is, it will be lost. It should be therefore recovered
and reused. Freon continues to carry out a cooling
function while changing its state from liquid to gas
and vice versa.
The temperature of the
refrigerant should
lower than the cabin
temperature inside the
vehicle and higher than
the atmospheric temper-
ature outside the vehi-
cle. As a refrigerant
(heat-exchanging
medium), Freon is used
which makes it possible
to provide such tempera-
ture changes relatively
easily.
The principle of the air conditioner is as follows. By means of the expansion valve, the refrigerant in liquid form is rapidly
expanded and turned into low-temperature gas. This low-temperature gas is passed through the evaporator, which is so
designed that heat in the cabin can be absorbed effectively, and the cabin is cooled. Then the refrigerant in gaseous form,
which has absorbed heat in the cabin and increased its temperature a little, is compressed by the compressor and becomes
high-pressure and high-temperature gas. By means of the condenser, this high-pressure and high-temperature gas is air-
cooled and turned back into liquid. At this time, the refrigerant emits into the atmosphere the heat absorbed from the cabin.
This circulating system is called Refrigerant Cycle .
The following p-H diagram describes each state of refrigerant.
Liquid
Condenser
Heat emission
Saturated
liquid
Expansion
valve
Wet
saturated
liquid
Heat absorption
Liquid + Gas
Evaporator
Enthalpy h
Cabin
be
Evaporator
Drawing heat from
surroundings
Dry saturated vapor
Heating
Gas
Compressor
Dry saturated vapor
Cooling
Spray
Rapid cooling
Gas
Expansion valve
Expansion
Condensation
Evaporation
Compression
Compressor
1: Dry vapor
1 2: Adiabatic compression by means of com-
pressor
2: Superheated vapor
2 2 3: Isobaric change by means of condenser
(condensation through heat emission)
3: Saturated liquid
3 4: Isoentropic change by means of expansion
valve (restriction phenomenon)
4: Wet vapor
4 1: Isobaric and isothermal change by means of
evaporator (evaporation through heat absorption)
The cycle is thus completed.
Function of expansion valve
Sending a proper amount of refrigerant in liquid form
from the high-pressure condenser side to the low-
pressure evaporator side (flow control)
Turning high-pressure refrigerant into low-temperature
and low-pressure wet vapor
VI-M-4
VI Air Conditioner
Freon
Liquid
Atmosphere
Recovery
Condenser
Emitting heat
Refrigerant
outside