Trane TRG-TRC003-EN notes

TRG-TRC003-EN 21

period three

Refrigeration Cycle

notes increase the pressure of the resulting refrigerant vapor to 280 psia [1.93 MPa].

This increase in pressure raises the temperature at which the vapor would

condense back into liquid to 121.5°F [49.7°C].

In order to condense the refrigerant vapor at this higher temperature, a

substance at a temperature less than 121.5°F [49.7°C] is needed. Ambient air or

water is generally available at temperatures less than this.

A compressor, condenser, and expansion device form the rest of the system

that returns the refrigerant vapor to a low-temperature liquid, which can again

be used to produce useful cooling. This cycle is called the vapor-compression

refrigeration cycle.

In this cycle, a compressor is used to pump the low-pressure refrigerant vapor

from the evaporator and compress it to a higher pressure.

This hot, high-pressure refrigerant vapor is then discharged into a condenser.

Because heat flows from a substance at a higher temperature to a substance at

a lower temperature, heat is transferred from the hot refrigerant vapor to a

cooler condensing media, which, in this example, is ambient air. As heat is

removed from the refrigerant, it condenses, returning to the liquid phase. This

liquid refrigerant is, however, still at a high temperature.

Finally, an expansion device is used to create a large pressure drop that

lowers the pressure, and correspondingly the temperature, of the liquid

refrigerant. The temperature is lowered to a point where it is again cool enough

to absorb heat in the evaporator.

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Figure 33