# Storage Capacity in Dependency of Supercooling and Cycle Stability of Different PCM Emulsions
## 2 Materials and Methods
### Characterisation  
Every PCM dispersion was analysed in terms of its particle size distribution, melting and crystallisation behaviours, enthalpy and stability against thermal-mechanical stress. The particle size distribution was analysed using a laser diffraction particle analyser, LS13320, from Beckman Coulter GmbH, Europark Fichtenhain B 13, 47807 Krefeld, Germany. The measured values represented the particle diameter. The particle size distribution was measured after production and after the thermal-mechanical stability test. A DSC (Q200 from TA Instruments, Altendorstra(r)e 12, 32609 Hullhorst, Germany) was used to determine the melting/crystallisation temperature and the enthalpy of the fusion/crystallisation. The onset values were chosen as the melting/crystallisation temperature due to its independency of the heating rate. To identify the suitable heating rate for the dispersions, a heating and cooling rate test was performed conformal to the procedure developed in IEA ECES Annex 29/SHC Task 42 [18]. According to the heating rate test, the heating rate was determined to 1 K/min. The measurements were performed in T\({}_{\text{zero}}\)hermetic aluminium crucibles at the determined heating rate, and the temperature dynamic range varied depending on the melting point of the PCMs. The sample volume was 10 \(\mu\)L. A flow of dry nitrogen was used to purge the measuring cell with 50 mL/h during the measurements. The error of the DSC measurements was given with \(\pm\)5% for the enthalpy values and \(\pm\)0.1 K for the temperature values. For using PCM emulsions as heat or cold storage fluids, it is important to consider the degree of supercooling, especially when comparing it with water. Supercooling is increasing the necessary temperature range that must be applied to use the full potential of SC. In principle, the larger this temperature range is, the lower is the benefit of PCM systems in comparison to storages using water as the storage fluid. For the determination of SC, a temperature range for charging and discharging is defined as the \(\Delta\)T\({}_{\text{load}}\). The SF is given as the volume-specific sensible and latent heat within the temperature range of \(\Delta\)T\({}_{\text{load}}\) in comparison to the volume-specific sensible heat of water in the same temperature range. For the comparison, a value of 4.19 kJ/(kg\(\cdot\)K) as the specific heat capacity for water and a density at 20 \({}^{\circ}\)C of 0.998 kg/L were used [19]. As the material datasheets showed no difference in the densities of the used pure paraffins, density measurements were performed using the Parafol 18-97 emulsion. The density was measured 4 times at 35 \({}^{\circ}\)C using an Anton Paar DMA 4500 divecen from Anton Paar GmbH, Hellmuth-Hirth-Strasse 6, 73760 Ostfildern, Germany. It was determined as 0.872 kg/L with a standard deviation of \(\pm\)12 kg/L considering all 4 measurements. In this study, different temperature points were chosen to obtain different \(\Delta\)T\({}_{\text{load}}\) to determine the SC and SF (in the following, called methods a-d):  
* Temperature range between the start of melting (T\({}_{\text{m-start}}\)) and end of melting (T\({}_{\text{m-end}}\)). * Temperature range of \(-\)6 K from the end of melting (T\({}_{\text{m-end}}\)) taking only the melting curve into account. * Temperature range of \(-\)6 K from the end of melting (T\({}_{\text{m-end}}\)) considering the crystallisation curve (see Figure 1). * Temperature range between the end of melting (T\({}_{\text{m-end}}\)) and end of crystallisation (T\({}_{\text{c-end}}\)). T\({}_{\text{m-end}}\) is determined as the temperature where the difference of enthalpy between the crystallisation and melting curve is smaller than 0.2 kJ/kg the first time when subtracting the melting curve from the crystallisation curve, starting from the onset temperature of melting to higher temperatures. T\({}_{\text{c-end}}\) is determined in the same way but by decreasing the temperature.