# Thermal Characterization of Phase Change Materials by Differential Scanning Calorimetry: A Review
## 4 PCM Properties Achieved by DSC
### Enthalpy  
When talking about a PCM-based thermal energy storage, this refers to the fact that thermal energy is stored as latent heat during mostly solid-liquid transition. It is possible to use other kinds of transition, such as solid-gas and liquid-gas, to store energy. However, solid-liquid transition is the most popular due to the low volume change and independence of melting point from pressure [45]. The most relevant parameter in PCM applications is their enthalpy change in a specified temperature range because it shows the amount of energy that can be stored or released to or from a PCM. In order to design thermal storage systems and commercial products based on PCM, studying the enthalpy-temperature relationship of the PCM is important. The mentioned relationship and the other properties are determined using calorimetric analysis, mostly differential scanning calorimetry (DSC). As shown in Figure 11, in order to calculate transition enthalpy, one can integrate the area under the heat flow curve (red region) over the temperature range and consider a calibration constant derived from the DSC software. To represent the total enthalpy (black curve), the heat capacity can be calculated from the heat flow data, then multiplied by the temperature difference, Equations (15) and (16). [PERSON] et al. [54] mentioned that there is a large range reported for transition enthalpy of PCMs in the literature. [PERSON] et al. [9] also reported that, for salt hydrates, there are few papers that indicate the measurement uncertainties, while it is important to signify the related uncertainty in reporting the enthalpy value. Therefore, in their study, they reported the average values and related uncertainty. \[H=\int_{T_{1}}^{T_{2}}C_{p}(T)\cdot dT=\int_{T_{1}}^{T_{2}}\frac{\frac{d\rho}{ dT}}{\frac{dT}{dT}}dT=\int_{T_{1}}^{T_{2}}\frac{d\varphi}{dT}dT \tag{15}\] \begin{table}
\begin{tabular}{p{42.7 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline
**Ref.** & **PCM** & **Objective** & \multicolumn{1}{p{113.8 pt}}{**Recommendations to Determine the Transition Temperature**} \\ \hline
[54] & Not precise & Recommendations concerning accurate property measurements & Low heating rate (\(\sim\)2 \({}^{\circ}\)C/min) Sample in good thermal contact with DSC pan Multi point calibration or use of a calibrant with a close melting point to the sample Reporting the test conditions \\ \hline
[64] & RT27 26.8 \({}^{\circ}\)C & Accurate determination of PCM melting range & Proposed a new method to determine actual endset of melting that is not dependent on the heating rate \\ \hline
[57] & Paraffin-based 15 \({}^{\circ}\)C & Investigating the influence of heating rate and sample mass on transition properties of organic and inorganic PCMs & By increasing mass and heating rate, peak and endset temperatures shift to higher values. In case of hydrated salts, high heating rates hide more information about the kinetics. To achieve smaller deviation with larger sample, lower heating rate should be preferred. \\ \hline
[63] & Hexadecane 18 \({}^{\circ}\)C & Physical modelling of a heat transfer inside a DSC sample & In order to describe accurately the melting process inside a DSC cell, use lower heating rate. In case of mixture of PCMs, high heating rates hide more information about the kinetics of melting. \\ \hline
[65] & 23 organic and inorganic PCMs in the range of (\(-\)50 to 190 \({}^{\circ}\)C) & Establishing a consistent method to determine the phase transition temperatures and enthalpy & A combination of low heating rate (2 \({}^{\circ}\)C/min) for temperature measurement and high heating rate (10 \({}^{\circ}\)C/min) for enthalpy were used in a single temperature program. \\ \hline \end{tabular}
\end{table} 
Table 6: Studies on the transition temperature of PCMs. As mentioned previously, the enthalpy of fusion is obtained from the area under the fusion peak and principally, it should be independent of the heating rate.