# Thermal Characterization of Phase Change Materials by Differential Scanning Calorimetry: A Review
## 3 Calorimetric Characterization
### Data Communication  
A phase change phenomenon in a PCM is described by four values, including phase change temperatures, phase change enthalpy, and heat capacities in the solid and liquid states [18]. Due to the mentioned challenges with PCMs for DSC characterization, such as showing melting range and subcooling, reporting just a single value for each parameter is not enough and a suitable way of data presentation is needed. [PERSON] et al. [6] concluded that the tabulation of stored heat in a temperature interval or the representation of the enthalpy curve as a function of temperature are accurate methods of data presentation. Plotting the graph of h(T) is of high importance compared to C\({}_{\text{p}}\)(T), since it includes \begin{table}
**Challenges** & **Explanations** & **Suggesions** & **References** \\ \hline High heat capacity & Thermal gradient inside a PCM sample is larger compared to other materials. Difference between apparent and real temperatures of the sample. & Smaller sample sizes, and lower heating and cooling rates, reduce the temperature shift. However, both of them lead to a weaker signal and a decreased accuracy in enthalpy. Using a method like IEA can help us determine the suitable heating rate. & [45] \\ \hline Subcooling & Subcooling deforms the cooling curve and gets stronger for smaller samples. External effects such as container or crucible wall. Small and moderate subcooling can be up to 5 and 10 \({}^{\circ}\)C, respectively. & Subcooling is a highly volume dependent phenomenon. So, at the DSC scale, PCMs show larger subcooling. & \\  & Subcooling deforms the cooling curve and gets stronger for smaller samples. External effects such as container or crucible wall. Small and moderate subcooling can be up to 5 and 10 \({}^{\circ}\)C, respectively. & Adding nucleating agents is a useful method to provide one with better temperature control over the solidification cycle. & [14; 26; 48; 52] \\  & & Combing DSC and T-history helps distinguish between real properties of a PCM and effects from test conditions. & \\  & & Adding nucleating agents is a useful method to reduce subcooling. & \\ \hline \hline \end{tabular} \begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multirow{4}{*}{\begin{tabular}{p{113.8 pt} p{113.8 pt}} \end{tabular} } & \multicolumn{3}{p{113.8 pt}}{Small sample might not be representative of bulk material. } \\  & Sampling & Repeating DSC tests by taking different samples. & [22] \\  & & Using methods such as T-history allows testing of a larger sample size. & \\ \hline \hline \begin{tabular}{p{113.8 pt} p{113.8 pt}} \end{tabular} & \begin{tabular}{p{113.8 pt}} Peak separation and incongruent phase \\ (mixture of several constituents) \\ \end{tabular} & \begin{tabular}{p{113.8 pt}} Large heating rates result in disappearing or \\ merging small peaks into a larger one. \\ Slow dynamic mode is recommended. \\ \end{tabular} & [46] \\ \hline Incomplete phase change process & \begin{tabular}{p{113.8 pt}} Partly melting/freezing due to the non-continuous load of energy \\ \end{tabular} & \begin{tabular}{p{113.8 pt}} Large heating/cooling rate would not simulate \\ correctly the real heat transfer into/out of PCM in the application. \\ Slow dynamic mode is recommended. \\ \end{tabular} & [46] \\ \hline Asymmetrical process of melting and solidification & \
\begin{tabular}{p{113.8 pt} p{113.8 pt}} In heat transfer modeling of PCMs, melting and solidification are assumed symmetrical \\ \end{tabular} &
\begin{tabular}{p{113.8 pt}} It is found out that melting and solidification are not symmetrical. Therefore, the enthalpy of a PCM is not only dependent on temperature, but also on the previous state of the PCM. & [53] \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Challenges in calorimetry measurements of PCMs. information on stored heat as a function of temperature, while C\({}_{\text{p}}\)(T) tends to infinity at the phase change temperatures, and thus lacks enough data points for representing the C\({}_{\text{p}}\) curve.