Page 433 - Mechanical Engineers' Handbook (Volume 4)

422 Refrigeration

2 BASIC PRINCIPLES
Most refrigeration systems utilize the vapor compression cycle to produce the desired re-
frigeration effect. A less common method used to produce refrigeration is the absorption
cycle, which is described later in this chapter. With the vapor compression cycle, a working
fluid, called the refrigerant, evaporates and condenses at suitable pressures for practical
equipment designs. The ideal (no pressure or frictional losses) vapor compression refriger-
ation cycle is illustrated in Fig. 1 on a pressure–enthalpy diagram. This cycle has no pressure
loss in the evaporator or condenser, and no heat or frictional losses in the compressor.
There are four basic components in every vapor compression refrigeration system: (1)
compressor, (2) condenser, (3) expansion device, and (4) evaporator. The compressor raises
the pressure of the refrigerant vapor so that the refrigerant saturation temperature is slightly
above the temperature of the cooling medium used in the condenser. The condenser is a heat
exchanger used to reject heat from the refrigerant to a cooling medium. The refrigerant enters
the condenser and usually leaves as a subcooled liquid. Typical cooling mediums used in
condensers are air and water. After leaving the condenser, the liquid refrigerant expands to

Figure 1 Simple vapor compression refrigeration cycle. 3