## 4 Conclusions  
We investigated the thermophysical properties of MnCl\({}_{2}\cdot\)4H\({}_{2}\)O PCMs with various initial phases by using DSC and a heat flow meter, and the following conclusions were derived:  
1. The melting/solidification temperature, latent heat, and thermal diffusivity were measured for MnCl\({}_{2}\cdot\)4H\({}_{2}\)O PCMs, and the properties were provided. The melting temperatures of the PCMs under single phase were about 28 to 33 \({}^{\circ}\)C. Specimens 1 and 2, having a dual or slurry phase, led to superheating issues. The latent heat of the PCMs under the endothermic process was 146 to 176 J/g with a temperature range of 23 to 45 \({}^{\circ}\)C. The latent heats of as-received PCMs under the endothermic process were similar or higher than those of the commercial products with operating temperatures of 20 to 50 \({}^{\circ}\)C.
2. In the endothermic process, the PCMs with a liquid or dual phase exhibited superheating because of the insufficient holding time in the initial stage until the PCMs were fully solidified. Another cause of this was the low thermal diffusivity of the PCMs based on the thermal diffusivity measurement in this study.
3. In the exothermic process, more severe supercooling was observed in the DSC measurement. The high cooling rate and low thermal diffusivity of the PCMs used in this study caused inhomogeneous solidification, phase segregation, and, consequently, supercooling. Homogenization treatment prior to DSC could mitigate the supercooling issue, such as an increase in solidification temperature of about 15 \({}^{\circ}\)C compared with what was used for the as-received and treated PCMs. However, the treatment could not fully eliminate the supercooling issue.
4. The diffusivities of PCMs were measured as between 9.76 \(\times\) 10\({}^{-6}\) and 2.35 \(\times\) 10\({}^{-5}\) mm\({}^{2}\)/s. The diffusivities of PCMs in the solid phase were higher than those in the liquid phase. The Fourier numbers of the PCMs were much lower than those in the references. The insufficient time for heat transfer resulted in high heating and cooling rates, and a very low level of thermal diffusivity was responsible for supercooling. Specim 3 was the best PCM due to its high conductivity and high thermal diffusivity.  
Accurate measurements of the thermophysical properties of PCMs were necessary prior to the design and application of PCMs. DSC was extensively used in the measurements, but homogeneity in the initial state, and proper heating and cooling rates considering diffusivity, were ensured to avoid superheating and supercooling.  
\begin{table}
\begin{tabular}{c c c} \hline
**PCM** & **\(\mathbf{\alpha_{\text{solid}}}\) (mm2/s)** & **\(\mathbf{\alpha_{\text{liquid}}}\) (mm2/s)** \\ \hline Specim 1 & 1.34 \(\times\) 10\({}^{-5}\) & 1.22 \(\times\) 10\({}^{-5}\) \\ Specim 2 & 1.40 \(\times\) 10\({}^{-5}\) & 9.76 \(\times\) 10\({}^{-6}\) \\ Specim 3 & 2.35 \(\times\) 10\({}^{-5}\) & 1.60 \(\times\) 10\({}^{-5}\) \\ Specim 4 & 1.56 \(\times\) 10\({}^{-5}\) & 1.07 \(\times\) 10\({}^{-5}\) \\ \hline \end{tabular}
\end{table}
Table 4: Thermal diffusivities of the PCMs.  
Conceptualization, K.-E.M., J.-W.J., J.-K.K., C.W. and S.Y.; methodology, K.-E.M., J.-W.J., J.-K.K., C.W. and S.Y.; investigation, K.-E.M., J.-W.J., J.-K.K., C.W. and S.Y.; writing--original draft preparation, K.-E.M.; writing--review and editing, C.W. and S.Y.; project administration, K.-E.M.; All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.