**1.1 Isobaric heat absorption process**

From **Figure 1**, point 4 to 1, the working fluid has low pressure and temperature in a vapourized form at constant pressure and temperature in the evaporator. The latent heat absorbed in the evaporator by the working fluid is expressed in Eq. (1). The phase change occurs as the refrigerant isentropically compressed by the compressor and moves to the next stage.

**Figure 1.** *P-h diagram of a vapor compression cycle.*

*Impact of Working Fluids and Performance of Isobutane in the Refrigeration System DOI: http://dx.doi.org/10.5772/intechopen.99121*

### **1.2 Isentropic compression process**

The isentropic compression takes place in the compression line. The vaporized refrigerant from the evaporator is compressed isentropically from stages 1 to 2 by the compressor. Work done on working fluid by the compressor is given in Eq. (2). The compression force increased the refrigerant's pressure and temperature, resulting in the rise of pressure and temperature, as shown in **Figure 1**. And refrigerant attains its superheated state at point 2.

#### **1.3 Isobaric heat rejection process**

The superheated refrigerant was de-superheated at constant pressure through the compressor outlet temperature to the condenser temperature at point 20 . Then, condensation occurs due to the natural air that inter-phases with the condenser's extended surface, resulting in heat rejection from the refrigerant. Thus, reducing the temperature by condensation at the condenser enables the refrigerant to attain a sub-cool state at point 3 at constant pressure and constant temperature along the 2<sup>0</sup> and 3 as shown in **Figure 1**, and the heat loss is expressed in Eq. (5).

#### **1.4 Isenthalpic expansion process**

In this isenthalpic process, the pressure at the upstream consistently higher than the pressure at the low stream. The capillary tube (CT) is used in practice to replace the expansion or throttling valve in a vapor compression refrigeration system (VCRS). This component aims to drastically reduce the pressure of the refrigerant that throttles through stages 3 and 4. It is assumed that there is no heat gain or loss because the process is adiabatic, that is, h3 = h4, as displayed in **Figure 1**. Therefore, the refrigerant throttled down the capillary tube and moved to the evaporator inlet at point 4.

In cooling systems, emphasis is always on domestic refrigerators and air-conditioning (AC) systems. There are various types of refrigeration and AC systems. RS can be classified base on the kind of energy input and the refrigeration process as:
