# Thermal Characterization of Phase Change Materials by Differential Scanning Calorimetry: A Review
## 4 PCM Properties Achieved by DSC
### Enthalpy
It was found that the rate of phase change temperature changes rarely exceeds 0.2 \({}^{\circ}\)C/min. Therefore, the numerical results obtained with the lowest heating rate (0.1 \({}^{\circ}\)C/min) showed a good agreement with the experiments. However, they concluded that the heating rates of 5 and 1 \({}^{\circ}\)C/min are not suitable for determining the heat stored as a function of temperature. [PERSON] and [PERSON] (2020) emphasized on the importance of determining thermal properties of PCMs considering different heating and cooling rates. [PERSON] et al. (2020) with a collaboration of different laboratories and two international organizations performed three types of round robin tests (RRT) to determine the melting enthalpy of n-octadecane. The first RRT was carried out without any defined procedure, the second RRT with a procedure only for measurement, and the last RRT with a defined procedure for all steps, such as measurement, calibration and data analysis. They did not reach a repeatable data in the first round. This can be also considered as evidence of the data discrepancy we observed in the literature. When all the participants ran the DSC tests according to a predefined procedure, they reached a comparable result within \(\pm\)25 kJ/kg. During the third round of tests, they also applied a procedure for calibration, such as constructing a stable baseline. As a result, all participants reached accurate results for enthalpy and temperature, especially during heating. Unlike [PERSON] et al. (2019), [PERSON] et al. (2020) underlined the need for a low heating rate (below 1 \({}^{\circ}\)C/min) to get accurate results. Thus, all the tests were conducted under the heating rate of 0.2 \({}^{\circ}\)C/min with 5 min isothermal before and after each ramp. It was also recommended to run a baseline test (empty pan) before each sample measurement with the same conditions (such as same heating rate and pan). In the frame of the same organizations and groups (IEA-SHC Task 42 and IEA-ECES Annex 42), researchers from different universities and centers such as Fraunhofer ISE, ZAE Bayern, Germany, Universitat de Lleida, University of the Basque Country, University of Zaragoza, Spain, and Austrian Institute of Technology continued their experiments on developing a standard method for determining enthalpy curves of PCMs. The summary of this procedure can be seen in Table 7 and Figure 12. They started their measurements by following a procedure defined by German quality label PCM-RAL for determining heating rates ([PERSON], 2020). In this procedure (IEA), one should apply several cycles of heating and cooling and the heating and cooling rates should be reduced to half of the previous rate. Whenever the difference between the two inflection points (peak temperatures of the heat flow curves) for two consecutive heating rates reaches less than 0.2\({}^{\circ}\)C between two consecutive heating rates or 0.5 \({}^{\circ}\)C between heating and cooling of the same rate, the suitable heating rate is found. Measurements with the determined heating rate decrease the deviation and avoid unnecessary use of very low heating rates. However, the deviation in terms of total enthalpy may remain quite large. Further improvement is reached by measuring the same sample mass and applying a uniform calibration in all DSC machines. Furthermore, mathematically correcting the baseline can lead to a better convergence of the enthalpy curves at the end (Figure 13a,b). The overall procedure developed by the mentioned groups can be observed in Table 7 and graphically in Figure 12.  
For a mixture of different PCMs, the combination of phase equilibrium study with DSC results provides one with a robust method for determining the fusion heat and phase transition range by understanding the solid-liquid fraction at any temperature and related storage capacity in order to have a better system storage design. The storage density in any temperature range is a function of mixture and temperature range [8].