Vapour Compression Refrigeration

Introduction:

Currently the most common cycle used in automotive applications is the vapour compression cycle, e.g. R12 and R134a closed systems. The real world operation of the A/C system deviates from the ideal cycle.

VAPOUR COMPRESSION CYCLE

To understand the vapour compression cycle and other cycles it is important to understand the types of changes that a refrigerant goes through when used in an A/C system.

• A refrigerant in the ‘subcooled’ liquid region point a is at a temperature which is below its boiling point. If heat is continually added while maintaining constant pressure, the refrigerant’s temperature and enthalpy will increase.
• Its state will eventually approach ‘saturated liquid’ point b.This is where the liquid will start to vaporize. As the heat is continually added the liquid vaporises and continues to increase in enthalpy but not increase in temperature.
• The ‘saturated liquid’ vaporises until it becomes a ‘saturated vapour’ point b–c. The ‘saturated vapour’ at point c has no liquid because it has completely vaporized.