# Thermal Characterization of Phase Change Materials by Differential Scanning Calorimetry: A Review
## 4 PCM Properties Achieved by DSC
### Enthalpy
However, in practice, the peak of fusion extends over a temperature range and is accompanied with enthalpy and heat capacity contribution. The extension of the peak width is limited for metals, but for organic compounds, it could be significant [27; 39; 42]. [PERSON] et al. [54] studied the influence of the scan rate on the transition enthalpy of PT37 (PureTemp), and the measured values were 203 \(\pm\) 20 J/g and 211 \(\pm\) 20 J/g for heating rates of 1 K/min and 10 K/min, respectively. It was mentioned that the latter value was in good agreement with the supplier's report (210 J/g). The enthalpy of eicosan (99% purity) was also measured, and the following values related to different heating rates were reported: 241 \(\pm\) 24 J/g at 1 K/min, 237 \(\pm\) 24 J/g at 2 K/min, 245 \(\pm\) 25 J/g at 5 K/min and 239 \(\pm\) 24 J/g at 10 K/min. There is, then, no clear trend for the transition enthalpy as a function of the heating rate [54]. The average value (241 \(\pm\) 16 J/g) matches well with their five replication experiments on the same PCM with 10 K/min heating rate (246 \(\pm\) 13 J/g). The DSC literature values range from (236 to 247) J/g, and the value obtained by adiabatic calorimetry is 247 J/g. Thus, it was concluded that the very low heating rate (less than 1 K/min) might undervalue the transition enthalpy. Therefore, it is recommended to use a heating rate within the range [1; 2; 3; 4; 5; 6; 7; 8; 9; 10] K/min [54]. [PERSON] et al. [57] studied the fusion heat of two paraffin-based and hydrated salt-based PCMs and observed that it is affected by both the heating rate and sample mass. However, this effect is greater for paraffin-based PCM than the hydrated salt-based one. For paraffin-based PCM, the fusion heat is changed by maximum 15% (with the same heating rate and different sample masses) and 24% (with the same sample mass and different heating rates). Furthermore, the start of the melting process was not apparent clearly on the enthalpy curve for paraffin-based PCM. [PERSON] et al. [45] investigated the effect of two modes of heating (dynamic and step methods) with six different heating rates from 0.2 to 10 K/min, and three masses on the enthalpy-temperature relationship of a commercial PCM named Rubithem 27 (RT 27). They considered 10% uncertainty in enthalpy (8h \(<\)10%) and 0.5 K uncertainty in temperature (8T \(<\) 0.5 K) between a heating and cooling curve. They did not observe the mentioned criteria in dynamic mode of operation even for the lowest heating rates. Moreover, they observed a larger temperature uncertainty for larger sample but the enthalpy uncertainty was smaller. They concluded that by the increasing heating/cooling rates, the enthalpy determination gets more accurate. However, it increases the uncertainty on the temperature. For the step mode of heating, the amount of uncertainty is less than the limit of (8h \(<\)10%; 8T \(<\) 0.5 K) considered by  
Figure 11: Heat flow and enthalpy plot of adipic acid as a function of temperature (personal data). the authors. Therefore, the step method is less sensitive to measurement parameters. [PERSON] et al. (2020) mentioned that \(\pm\)10 \({}^{\circ}\)C around the phase change can be considered an appropriate temperature range for PCM applications. Thus, a reasonable design can be made if the uncertainty remains below 10% for enthalpy and \(\pm\)1 \({}^{\circ}\)C for temperature. [PERSON] and [PERSON] (2020) conducted an experimental and numerical study on the cylindrical latent heat thermal energy storage (LHTES) containing spheres filled with paraffin RT20 that melts around 17 \({}^{\circ}\)C. The potential application for the LHTES was a storage for accumulating low-energy daily heat and cold in buildings. The apparent heat capacity is considered in the numerical model, and it was based on DSC method in dynamic mode of operation under heating rates of 5, 1 and 0.1 \({}^{\circ}\)C/min. Apparent heat capacity is considered as a parameter that shows evolving latent heat over the temperature range.