The main goal of a refrigeration system which performs the reverse effect of a heat engine is to remove the heat from a low-level temperature medium (heat source) and to transfer this heat to a higher level temperature medium (heat sink). Figure 3.1 shows a thermodynamic system acting as a refrigeration machine. The absolute temperature of the source is TL and the heat transferred from the source is the refrigeration effect (refrigeration load) QL. On the other side, the heat rejection to the sink at the temperature TH is QH. Both effects are accomplished by the work input W. For continuous operation, the first law of thermodynamics is applied to the system.
Refrigeration is one of the most important thermal processes in various practical applications, ranging from space conditioning to food cooling. In these systems, the refrigerant is used to transfer the heat. Initially, the refrigerant absorbs heat because its temperature is lower than the heat source’s temperature and the temperature of the efrigerant is increased during the process to a temperature higher than the heat sink’s temperature. Therefore, the refrigerant delivers the heat.
The main refrigeration systems and cycles we will deal with are:
• vapor-compression refrigeration systems,
• absorption refrigeration systems,
• air-standard refrigeration systems,
• jet ejector refrigeration systems,
• thermoelectric refrigeration, and
• thermoacoustic refrigeration.
Before commencing on these refrigeration systems, we will first introduce the refrigeration system components and discuss their technical and operational aspects.