Outline Of Refrigeration Cycle - Komatsu PC200-8M0 Shop Manual

100 Air conditioner

Outline of refrigeration cycle

Outline of refrigeration cycle
The refrigeration cycle is comprised of 4 cycles. The refrigerant is circulated while repeatedly vaporizing and
liquefying.
1. Compression (Compressor)
The compressor sucks in the refrigerant that has
been vaporized
compresses it into a state where it can be easily
liquefied at the ambient temperature.
The gaseous refrigerant sucked into the
compressor cylinder is compressed to a temper-
ature and pressure at which it can be easily
liquefied when cooled to the ambient tempera-
ture.
2. Condensation (Condenser)
The condenser cools and liquefies the high pres-
sure and high-temperature gaseous refrigerant
sent from the compressor.
The heat released to the outside from the
condenser is called condensation heat.
The amount of condensation heat is the sum
total of the heat absorbed by the evaporator from
the air in the cab and the quantity of the work
applied (the value converted into a heat quantity)
by compression of the compressor.
The refrigerant liquefied in the condenser is sent
to the receiver drier, where moisture is removed.
In the compression cycle, the gaseous refrig-
erant and liquid refrigerant coexist.
The temperature (condensation temperature)
and the pressure (condensation pressure) at
which the gaseous refrigerant is liquefied are
proportional to each other.
Reference: The pressure varies depending on
the condensation temperature of the refrigerant.
3.
Expansion (Expansion valve)
The expansion valve reduces the liquid refrig-
erant pressure to a level where liquid refrigerant
can be easily evaporated by the throttle action
(*1).
The action of reducing the liquid refrigerant pres-
sure to a level where it can be easily evaporated
before it is sent to the evaporator is called
expansion.
The expansion valve, which reduces the refrig-
erant pressure, also adjusts the refrigerant flow
rate simultaneously.
The quantity of the liquid refrigerant that can be
evaporated in the evaporator depends on the
amount of heat (refrigeration load) to be
removed under the specific evaporation temper-
ature (evaporation pressure).
PC200, 200LC, 220, 220LC-8M0
in the evaporator
The expansion valve controls the refrigerant
feed rate so that the optimum quantity of liquid
and refrigerant is supplied to the evaporator.
(*1) Throttle action
If there is a narrow section in the passage
through which liquid is flowing at a constant rate,
a resistance to the flow will be generated.
The liquid expands when it passes through the
narrow section and rushes into the passage
where the sectional area is larger, and conse-
quently, its pressure and temperature are
reduced.
No heat is transferred from or to the outside
during the throttle action.
4. Evaporation (Evaporator)
The evaporator evaporates the liquid refrigerant
(superheated vapor).
The refrigerant evaporates, while absorbing an
amount of heat necessary for evaporation (evap-
oration heat) from the air around the cooling fins
(air in the cab).
After the heat has been removed, the cooled air
is sent into the cab by the blower fan, reducing
the temperature inside the cab.
The mist refrigerant that has been sent from the
expansion valve coexists with the evaporated
refrigerant in the evaporator
The temperature (evaporation temperature) and
the pressure (evaporation pressure) at which the
liquid refrigerant is evaporated are proportional
to each other.
The compressor sucks in the evaporated refrig-
erant in order to keep the pressure level in the
evaporator as low as possible so that the liquid
refrigerant can be evaporated at a much lower
temperature.
Relationship between refrigerant and defective
air conditioning
q The refrigerant circulates in the refrigeration cir-
cuit while repeating the refrigeration cycle to ex-
pel the heat from inside the cab.
q If there is an insufficient quantity of refrigerant,
all of it will be evaporated while it is passing
through the evaporator. This causes evaporator
efficiency to deteriorate, which will result in de-
fective air conditioning.
SEN06151-00
7
80-100