Trane TRG-TRC003-EN notes

TRG-TRC003-EN 37

period five

Review

notes Refrigerant enters the evaporator as a cool, low-pressure mixture of liquid and

vapor. It absorbs heat—from the relatively warm air or water to be cooled—and

boils. The cool, low-pressure vapor is then pumped from the evaporator by the

compressor. This increases the pressure and temperature of the refrigerant

vapor. The resulting hot, high-pressure refrigerant vapor enters the condenser

where it rejects heat to ambient air or water that is at a lower temperature, and

condenses into a liquid.

This liquid refrigerant flows from the condenser to the expansion device. The

expansion device creates a pressure drop that reduces the pressure of the

refrigerant to that of the evaporator. At this low pressure, a small portion of the

refrigerant boils off, cooling the remaining liquid refrigerant to the evaporator

temperature. The cool mixture of liquid and vapor refrigerant travels to the

evaporator where it absorbs heat and boils, repeating the cycle.

Period Four discussed the use of the pressure–enthalpy (P–

) chart to analyze

the refrigeration system.

The pressure–enthalpy chart plots the properties of a refrigerant—pressure

versus enthalpy. Enthalpy is a measure of heat quantity per pound [kg] of

refrigerant. The chart includes an envelope (curve) that indicates when the

refrigerant exists as a subcooled liquid (to the left of the envelope), a mixture of

liquid and vapor (inside the envelope), or a superheated vapor (to the right of

the envelope).

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