Refrigeration Cycle Overview

Overview

This lecture introduces the basic refrigeration cycle, its main components, and essential refrigeration terms, focusing on the process of heat transfer and phase changes in refrigerants.

The Four Main Components of the Refrigeration Cycle

• The compressor increases refrigerant temperature and pressure by compressing vapor.
• The condenser rejects heat from the refrigerant, causing it to change phase from vapor to liquid.
• The metering device decreases refrigerant pressure and temperature by creating a sudden expansion.
• The evaporator absorbs heat, causing the refrigerant to evaporate and change from liquid to vapor.

Key Processes in the Refrigeration Cycle

• The compressor starts the cycle by compressing low pressure, low temperature superheated vapor into high pressure, high temperature superheated vapor.
• The condenser cools the superheated vapor until it becomes a saturated refrigerant, a process called desuperheating.
• The saturated refrigerant then condenses into 100% liquid as more heat is rejected, with no change in temperature.
• The metering device rapidly reduces the pressure, creating a saturated low pressure, low temperature refrigerant.
• The evaporator absorbs heat, vaporizing the refrigerant back into a low pressure, low temperature superheated vapor.

Phase Change and Heat Transfer

• When heat is rejected, vapor condenses to liquid with no temperature change at the saturated temperature.
• When heat is absorbed, liquid boils to vapor with no temperature change, also at the saturated temperature.
• The cycle divides into high pressure/high temperature and low pressure/low temperature sections by the metering device and compressor.

Key Terms & Definitions

• Saturated Refrigerant — A state where refrigerant is both liquid and vapor in equilibrium at a specific temperature and pressure.
• Saturated Temperature — The temperature at which refrigerant changes state (boils or condenses) at a given pressure.
• Boiling Point — Another term for saturated temperature.
• Superheat — Temperature above the refrigerant’s boiling point at a given pressure; refrigerant is 100% vapor.
• Subcooling — Temperature below the boiling point at a given pressure; refrigerant is 100% liquid.

Action Items / Next Steps

• Watch the next videos in the series on the PT chart and the pressure-enthalpy (P-H) diagram.