🔍 Key Concepts

• Function of the metering device/expansion valve in a refrigeration cycle • Pressure and temperature change of the refrigerant as it passes the metering device • Meaning of sub-cooled, saturated, and superheated states

💭 Think About

• Trace the standard refrigeration cycle: compressor → condenser → metering device/expansion valve → evaporator. What is the purpose of the metering device in this sequence? • Does the metering device cause the refrigerant pressure to increase or decrease, and what does that do to its boiling/evaporation behavior? • Right after the metering device, is the refrigerant supposed to be fully liquid, fully vapor, or in the process of changing phase in the evaporator?

✅ Before You Answer

• Review definitions: sub-cooled liquid (temperature below saturation for its pressure), saturated mixture (at boiling point with both liquid and vapor present), superheated vapor (temperature above saturation for its pressure) • Confirm where in the cycle superheating normally occurs (in the evaporator outlet/suction line) versus where subcooling normally occurs (at the condenser outlet). • Ask: the evaporator’s job is to absorb heat as the refrigerant changes phase. In what condition must the refrigerant enter the evaporator to best absorb latent heat?