## 4 Results  
### Experiments Without Thermal Spreader  
Figure 4a presents the measured temperature profiles of the heater (\(T_{H}\)) and the cover surface (\(T_{C}\)) for the experiment with package A (\(n\)-eicosane). Figure 4b shows the temperatures on the PCM package at various positions on the upper and lower surface. The temperatures read by the thermocouples located at the upper surface of the package (\(T_{UI}\)-\(T_{UA}\)) are illustrated in dashed lines, the ones located at the lower surface in full lines (\(T_{L1}\)-\(T_{L5}\)). The temperatures measured with the thermocouples with equal radial distances to the center (for example, \(T_{U2}\)/\(T_{L2}\)) are plotted in the same color. The melting temperature, \(T_{m}\), of \(n\)-eicosane is drawn as a dashed black line in the figure. At time zero, heat was generated from the heat source, resulting in a temperature increase of all thermocouples from their initial value, which was approximately 20 \({}^{\circ}\)C (room temperature). A maximum heater temperature of 115 \({}^{\circ}\)C was reached after 60 min. It is observed that the further the radial distance of the thermocouples to the heater, the lower the temperature increase was, showing that the package provides a very small amount of heat spreading above the bare setup case. The maximum temperature of the cover surface at the center of the setup was 58.5 \({}^{\circ}\)C after 60 min of charging. The temperatures of the thermocouples \(T_{C3}\) and \(T_{C3}\), which were placed on the cover at equal radial distance to the center, are very similar during both charging and discharging. In fact, the difference is within the measurement uncertainties of the thermocouples, which indicates the symmetrical nature of the experiment. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **PCM Package** & **Thermal Spreader** & \(P\) **(W)** & \(t_{on}\) **(min)** & \(t_{off}\) **(min)** \\ \hline \# 1 & - & - & 5 & 60 & 120 \\ \# 2 & A & - & 5 & 60 & 120 \\ \# 3 & B & - & 5 & 60 & 120 \\ \# 4 & - & Aluminum (0.4 mm) & 5 & 120 & 120 \\ \# 5 & A & Aluminum (0.4 mm) & 5 & 120 & 120 \\ \# 6 & B & Aluminum (0.4 mm) & 5 & 120 & 120 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: List of the performed experiments with constant power input. When comparing the curves of the two temperature sensors mounted on the PCM package at equal radial distance to the heater, e.g., \(T_{L1}\) and and \(T_{U1}\), it is observed that the temperature increase on the lower surface was greater than the one at the upper surface. After 4.5 min, \(T_{L1}\) reached the melting temperature of 35.6 \({}^{\circ}\)C. It took 11 min until \(T_{U1}\) reached the melting temperature. It may therefore be assumed that the PCM located closest to the center melted during this time span (4.5 to 11 min). \(T_{L3}\), which is the temperature of the lower surface of the PCM package at a radial distance of 25 mm to the center, reached the melting temperature after 28 min. \(T_{U3}\), on the upper surface of the PCM package at an equal radial distance to the center as \(T_{L3}\), reached the melting temperature after 45 min. Accordingly, it may be assumed that the melting front of PCM reached a radius of 25 mm within the time span of 28 to 45 min. \(T_{U4}\) and \(T_{L5}\) did not increase above the melting temperature, which indicates that the whole PCM did not melt during the experiment due to poor spreading within the PCM package, which shows that the low thermal conductivity of the PCM dominates over any possible heat spreading offered by the thin aluminized film making the package. The measured temperatures of the heater (\(T_{H}\)) and the cover surface (\(T_{C}\)) for the experiment with package B (dodecanoic acid) are illustrated in Figure 5a. PCM package B has the same volume and almost the same storage capacity as PCM package A, but its melting temperature is 7.4 \({}^{\circ}\)C higher than the one for package A.