Outline Of Refrigeration Cycle - Komatsu PC88MR-10 Shop Manual

80 Appendix

Outline of refrigeration cycle

Outline of refrigeration cycle

The refrigerating cycle performs the following four processes. The refrigerant is liquefied and gasified
repeatedly while it is circulated in the cycle.
Compression (Compressor)
The compressor sucks in the refrigerant that has been vaporized in the evaporator and 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 temperature and
pressure at which it can be easily liquefied when cooled to the ambient temperature.
Condensation (Condenser)
The condenser cools and liquefies the high pressure 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 dehydrated in the modulator and cooled further in the sub-cool
section to increase the cooling efficiency.
In the compression cycle, the gaseous refrigerant 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.
(The condensation pressure varies depending on the condensation temperature of the refrigerant)
Expansion (Expansion valve)
The expansion valve reduces the liquid refrigerant pressure to a level where liquid refrigerant can be
easily evaporated by the throttle action (*1).
The action of reducing the liquid refrigerant pressure 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 refrigerant 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 temperature (evaporation pressure).
The expansion valve controls the refrigerant feed rate so that the optimum quantity of liquid 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 consequently, its pressure and temperature are reduced.
No heat is transferred from or to the outside during the throttle action.
Evaporation (Evaporator)
The evaporator evaporates the liquid refrigerant (superheated vapor).
The refrigerant evaporates, while absorbing an amount of heat necessary for evaporation (evaporation
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 refrigerant 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
The refrigerant circulates in the refrigeration circuit while repeating the refrigeration cycle to expel the heat
from inside the cab.
80-8
(ALL-K500-04A-K-00-A)
PC88MR-10