**3.2 Thermoelectric refrigeration systems**

The thermoelectric refrigeration system (TRS) uses electricity to provide cooling effect utilizing the principle of two dissimilar metals to generate emf. There are two basic methods in obtaining this operation, which include Peltier and Seebeck effect.

## *3.2.1 Peltier effect*

This requires the flow of electric current through two dissimilar conductors, and the junction of the metals (conductors) either emit or absorb heat, which depends on the current that flows across the junctions. However, the flow of electric current is proportional to the heat gain or loss at the junction [12].

## *3.2.2 Seebeck effect*

In this process, direct heat is converted to electricity at the junction of various conductors (wire). This requires the generation of voltage along the wire that is subject to the temperature gradient and it results in thermoelectric power (see **Figure 2**) [13].

#### **3.3 Vapor absorption refrigeration systems**

The vapor absorption refrigeration system (VARS) comprises the same processes in the vapor compression system (VCS) such as compression, expansion, condensation, and evaporation. In the vapor absorption system, the working fluid used is ammonia, water, or lithium bromide. The refrigerant produces a cooling effect in the evaporator, and heat dissipates to the atmosphere through the condenser. The main difference between the two systems is the suction and compression of the refrigerant in the refrigeration cycle. In the VCS, the compressor sucks the refrigerant from the evaporator and compresses it to high pressure. The compressor also enables the flow of the refrigerant through the whole refrigeration system. In the VAS, the process of suction and compression is carried out by two

**Figure 2.** *Thermoelectric refrigeration systems.*

different devices called the absorber and the generator. The absorber and generator replace the compressor in the VAS (**Figure 3**) [14].
