## 3 Experimental Work
### Reference PCM Sample  
Further measurements focused on the melting and solidification processes of PCM over time. To compare the sensible and latent heat energy transfer, 60 g of PCM was placed in the samples, specifically, the paraffin mentioned above with a melting phase change of 48.2-51 \({}^{\circ}\)C. An amount of 60 g of this paraffin represents 80 mL. In Figure 9, a graphical progression of the melting of pure PCM can be observed.  
Since the measured sample contains one thermocouple, which is in the center or core of the paraffin, the image may not correlate with the real situation. This is due to uneven heating of the sample, due to the lower thermal conductivity of the paraffin. This means that the sample, i.e., the PCM on the shell, underwent a phase change much earlier than its core.  
In the first part of Figure 9, the curve of sensible heat transfer (State A) is shown, which lasts for 935 s; then, at a temperature of 48.2 \({}^{\circ}\)C, the second part of the graph starts with a phase change transition (melting of the PCM in the core) or the transfer of energy in the form of latent heat (image record State B). The end of the phase change occurs after the core melts at 52 \({}^{\circ}\)C at 1525 s. This means that the whole phase change took 590 s. In the third part of the graph, the curve again shows the acceptance of sensible heat up to the time of the end of the measurement.  
According to the parameters of the paraffin, it received 10,800 J in the form of latent heat during the phase change, since paraffin has a latent heat capacity of 180 KJ/kg. To express the amount of energy absorbed by the paraffin in the form of sensible heat, Equation (1) can be used. The heat capacity of the paraffin, according to the parameters in Table 1 and \(\Delta\)t = 34.3 \({}^{\circ}\)C, is 4527.6 J.  
The discharging or solidification process of the PCM is described in Figure 10. The figure shows the whole process of energy supply, mainly energy in the form of latent heat.  
The focus of this measurement is the amount of latent heat transfer to the heat transfer medium over time. In Figure 10, the progression of the onset of the solidification process of the PCM can be observed, which starts at a time of 395 s and a temperature of 53.5 \({}^{\circ}\)C. The temperature of the heat transfer medium is 33.5 \({}^{\circ}\)C at this point. The phase change  
Figure 9: Charging pure PCM sample.  
ends at 51.00 \({}^{\circ}\)C at a time of 4135 s. The heat transfer medium has heated to a temperature of 35.7 \({}^{\circ}\)C. In total, the phase change lasted 3740 s. From Figure 10, it can be determined that the phase change consists of two parts. These parts can be divided into a constant-temperature latent heat part and a mixed latent and sensible heat part. The latent heat part takes 2295 s and the mixed-phase part takes 1445 s which means that the latent heat part accounts for 61.36% of the total phase change time. During this section, the PCM heated the heat transfer medium from 33.5 \({}^{\circ}\)C to 35.7 \({}^{\circ}\)C, i.e., \(\Delta\)t = 2.2 \({}^{\circ}\)C. This can be calculated as follows:  
\[Q\ =\ m\cdot c\cdot\Delta\text{t}\ =\ 0.4\cdot 4180\cdot 2.2\ =\ 3678.4\ \text{J} \tag{22}\]  
The PCM supplied 3678.4 \(\text{J}\) to the heat transfer medium during the latent heat part of the phase change. During the mixed phase, the curve or temperature is in equilibrium and maintains the temperature of the medium at 35.7 \({}^{\circ}\)C. Two thermocouples were used in the experimental setup, one for measuring the temperature of the heat transfer medium and the other for measuring the phase change of the sample located in the core. Therefore, the measured state may be different from the real state due to the uneven solidification of the PCM both on the shell and in the core.