## 3 Experimental Work
### Hysteresis Curves of Measurements  
In the measurements of the pure PCM sample, the hysteresis is not clearly visible; in fact, it is minimal, due to differences in the charging and discharging process. During charging, the dynamic itself is relatively high, which is due to the transition of the PCM from the solid to the liquid phase, while the internal heat transfer improves with an increase in the liquid fraction. In the discharge process, the curve reaches an ideal level where there is almost no temperature drop in the PCM during the phase change. However, it is necessary to note that the process is exceptionally slow and inefficient from the point of view of the time course. The gradual transition to the solid phase on the PCM-HTF contact surface results in a decrease in the thermal conductivity, resulting in a decrease in the ability to transfer heat efficiently. The experimental results are shown in Figure 20.  
Figure 21 shows the application of the volumetric structure on the base of the copper matrix (0.0006 m \(\times\) 0.0085 m). The result in the charging process is only a slight change in the curve, and this is in the final phase where a significant amount of solid material changes phase to liquid in a short time. During discharge, there is a significant improvement in dynamics and a reduction in the total time compared to pure PCM of up to 75%. Such an improvement in the dynamics allows the use of latent heat for application in the reservoir due to the acceleration of the energy release in a sufficient time range.  
As shown in Figure 22, the copper spiral only slightly improves the dynamics of the process during the extraction of energy, while it is possible to observe a comparable process in the case of pure PCM. During the charging process it is possible to observe the influence of the location of the spiral, which is cross-sectionally on the inner radius of the beaker, and it is possible to confirm the theoretical conclusions from the point of view of the theory of boundary formation, which, in this case, is significantly influenced. There is a significant  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Property** & **Steel Twisted Matrix** & **Copper Matrix** & **Copper Spiral** \\ \hline Weight (g) & 11.7 & 36 & 21 \\ Volume (m\({}^{3}\)) & \(0.214\times 10^{-5}\) & \(0.49\times 10^{-5}\) & \(0.36\times 10^{-5}\) \\ Heat exchange surface (m\({}^{2}\)) & 0.052 & 0.017 & 0.008 \\ Weight \% comparison to paraffin & 19.5\% & 60.0\% & 35.0\% \\ Volume \% comparison to paraffin & 2.7\% & 6.1\% & 4.45\% \\ Heat exchange surface \% comparison to & 100.00\% & 33.47\% & 15.17\% \\ steel twisted matrix & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Characteristics of metal structures.  
In Figure 23 is presented a waveform with the application of a volumetric structure represented by a thin-walled spatial structure in the whole volume with flat metallic fibers (0.0001 m \(\times\) 0.00045 m). There are no significant changes in the charging process, similar to the case of pure PCM and PCM-copper spiral. In the discharge process, there is a significant shortening of time, which is demonstrated as an effective improvement in the heat transfer dynamics in the entire volume, even after the transition of the surface contact layer to the solid phase.