Civil Engineering Reference
In-Depth Information
Fig. 12.1
A vapor-compression refrigeration system
The main components are the following:
• Evaporator where the heat transferred from a process source or from
a refrigerated space (cold region) results in vaporization of the refrig-
erant (also called coolant)
• Compressor where the gas refrigerant is compressed to a relatively
high pressure and temperature
• Condenser where the refrigerant condenses and the resulting heat is
transferred from the refrigerant to the cooler surroundings (warm
region)
• Expansion valve where the liquid refrigerant expands to the evapora-
tor pressure and leaves the valve as a two-phase liquid-vapor mixture
As a first step, let us consider an idealized reversible cycle which represents an
upper limit to the performance of the vapor-compression refrigeration cycle. This
means that there are no frictional pressure losses, and that the refrigerant flows at
constant pressure through the condenser and the evaporator. In addition, the com-
pression is assumed to be an isentropic process and the expansion through the
throttling valve an adiabatic process.
The main difference between the idealized and the actual cycle is in the
compression process. In the latter case it is only adiabatic and the entropy increases.
Pressure drops, which always occur in the cycle, are generally ignored.
