# Storage Capacity in Dependency of Supercooling and Cycle Stability of Different PCM Emulsions
## 3 Results and Discussion
### PCM Emulsions
#### 3.1.2 Storage Capacities  
The DSC results are summarised in Table 2 for all the PCM emulsions. The melting enthalpies are in a range between 53 und 61 kJ/kg, which is on the level expected for odd-numbered paraffins due to the melting enthalpy of the first-phase transition of the used bulk paraffins. The even-numbered paraffin emulsions show a melting enthalpy that is less than 35% of the available bulk paraffin's melting enthalpy (see HfPCM-1 st-35% in Table 2). This is due to the induction of a second-phase transition through the emulsification process. In comparison to the pure paraffins, all emulsions show a high degree of supercooling (\(\Delta\)T = T\({}_{\text{m-offset}}-\) T\({}_{\text{c-onset}}\)) that is listed in Table 2 and shown in Figure 4 for all the emulsions. Supercooling is reduced with an increasing melting temperature and samples with lower purity. Additionally, those emulsions prepared using paraffins with an odd number of C atoms in their hydrocarbon chain show a lower degree of supercooling than emulsions with even-numbered paraffins. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Dispersed PCM** & \(\mathbf{T_{m-end}}\) & \(\mathbf{T_{m,onset}}\) & \(\mathbf{T_{m,offset}}\) & \(\mathbf{T_{c,onset}}\) & \(\mathbf{\Delta T}\) & \(\mathbf{\Delta Hf_{m}}\) & \(\mathbf{\Delta Hf_{c}}\) & \(\mathbf{\Delta Hf_{PCM-m-1 st-35\%}}\) \\ \hline  & \({}^{\circ}\)C & \({}^{\circ}\)C & \({}^{\circ}\)C & \({}^{\circ}\)C & \(\mathbf{K}\) & \(\mathbf{kJ/kg}\) & \(\mathbf{kJ/kg}\) & \(\mathbf{kJ/kg}\) \\ \hline P16-97 & 18.2 & 16.2 & 17.9 & 11.6 & 6.35 & 55.6 & 59.5 & 75.95 \\ P16-97/P18-97 & 21.5 & 18.4 & 21.0 & 18.3 & 2.69 & 57.9 & 58.2 & 52.85 \\ L17 & 21.7 & 19.6 & 21.8 & 17.5 & 4.31 & 60.6 & 57.8 & 57.05 \\ P17-97 & 21.9 & 20.1 & 21.9 & 18.0 & 3.87 & 60.6 & 62.4 & 55.65 \\ RT27 & 26.5 & 23.9 & 26.4 & 23.4 & 2.95 & 53.1 & 54 & 53.55 \\ P18-97 & 27.6 & 25.1 & 27.5 & 23.0 & 4.48 & 58.2 & 62.5 & 78.05 \\ P19-90 & 32.0 & 29.0 & 31.6 & 28.8 & 2.8 & 60.17 & 60.93 & 54.25 \\ P19-97 & 32.4 & 29.9 & 32.0 & 28.8 & 3.22 & 59.3 & 62.3 & 58.45 \\ P20Z & 36.0 & 31.4 & 35.9 & 32.9 & 3 & 59 & 59.1 & 73.85 \\ \hline \end{tabular}
\end{table} 
Table 2: Summary of the main DSC properties for the PCM dispersions, with \(\Delta\)T = T\({}_{\text{m, offset}}-\) T\({}_{\text{c-onset}}\). Figure 3: Particle size distribution of PCM dispersions with 35 wt.% of different PCMs dispersed in water. Figure 5 depicts the enthalpy curves for all PCM emulsions dependent on the temperature. The graph reveals that all emulsions have at least two-phase transitions in the measured temperature range, except the one prepared with a mixture of P16-97 and P18-97. It might have a second transition below the measured temperature range, but this could not be proved, as it was not possible to cool further down due to the freezing of the emulsion's water fraction. The curves also show that those emulsions prepared with mixtures of paraffins (P16-97/P18-97, RT27) show broader melting and crystallisation ranges than those using pure paraffins. Figure 6 compares the enthalpy curves of L17, P17-97 and the mixture of P16-97/P18-97 emulsions. It is visible that L17 and the P16-97/P18-97 mixture offer almost the same enthalpy differences in the main transition range, whereas P17-97 melts at a higher temperature and shows a higher change in the enthalpy. Both the bulk PCM L17 and P17-97 have around 210 kJ/kg, while the blend of P16-97/P18-97 is 28% lower with 151 kJ/kg. After emulsification, the enthalpy of this mixture is only about 4.5% lower than that of the L17 and P17-97 emulsions (57.9 k/kg versus 60.6 kJ/kg). A similar effect can be seen for the P18-97 and RT27 emulsions. While the enthalpy of bulk RT-27 is 31% lower, it is only 14% lower when it is emulsified. Despite the melting enthalpy for the bulk P16-97 being slightly higher (217 kJ/kg) than that of P20Z (211 kJ/kg), emulsified P20Z shows, with 59.0 kJ/kg, a slightly higher melting enthalpy than the emulsified P16-97, which provides 55.6 kJ/kg.