33.3.
Refrigeration System
In an air-conditioner’s refrigeration system, the refrigerant picks up heat from the passenger compartment and is pumped to the condenser where it gives up its heat to the outside air, and then flows back through the system to pick up more heat. The system is shown schematically in Fig. 34.2. Refrigerant is recycled in a closed system. Freon-12 is used as the heat transfer medium in an automatic air-conditioner refrigeration system. This refrigerant has a good heat transfer property in the required temperature range and does not corrode system components.
Fig. 33.2. Heat removal from passenger compartment to outside air.
During operation, the refrigerant continuously changes its phase from liquid to gas and then back to liquid again. The refrigeration system works on vapour compression cycle, where four distinct activities such as compression, condensation, expansion (throttling), and evaporation of the refrigerant take place. The four major components of the refrigeration system responsible for above four functions are respectively compressor, condenser, expansion valve and evaporator. The composite system has been shown schematically in Fig. 34.3. Heat from the passenger compartment evaporates the refrigerant in the evaporator, thereby changes its phase from liquid to vapour and cools the air. The vapour is then pumped from the evaporator by the
Fig. 33.3. Schematic composite diagram of an automotive air-conditioning refrigeration system.
compressor, which compresses the vapour to increase its pressure. This high pressure, high temperature vapour passes through the condenser where it is cooled with outside air and condensed into high pressure liquid. This liquid is throttled down to a lower pressure in the expansion valve before passing to the evaporator. This constitutes a continuous cycle in which heat is carried from the evaporator placed in the passenger compartment to the condenser where it is given up to outside air.
