# Thermal Characterization of Phase Change Materials by Differential Scanning Calorimetry: A Review
## 5 Conclusions  
The current paper reviews studies that are focused on establishing a method or a protocol for DSC measurements of PCMs. This paper provides an introduction on calorimetric methods, calibration, and challenges in the characterization of PCMs' properties by DSC. The main limitation of calorimetry measurements based on DSC is the small sample size, especially for composite and heterogenous PCMs. However, using a proper method that addresses determining suitable heating rate, proper calibration and repetitions can yield reliable results. Following, the main conclusions for each property including the transition temperature, enthalpy, heat capacity, and thermal stability are summarized. Any improvement on the determination of the transition range improves the performance of PCM-based TES. Among the transition temperatures, the melting onset is less affected by the mass of PCM and the heating rate. Thus, it can be considered as the PCM melting point. It was observed that the shape of the transition peak is dependent on the heating rate, the heat of transition and thermal conductivity of the sample. Thus, in order to minimize the thermal gradient within the sample, using low heating rates is recommended. Multipoint calibration of the DSC machine, including a calibrant with a close melting point to the PCM, can improve accuracy in determining temperature. In case of salt hydrates and mixtures of PCMs, high heating rates hide more information about the melting kinetics. Depending on the application, the transition temperature of a PCM should be determined with an uncertainty of \(\pm\)0.5-1\({}^{\circ}\)C.  
Low heating rate might underestimate enthalpy due to the high signal to noise ratio. Thus, it is recommended, after a first measure using a low heating rate, to measure the heat flow with a higher heating rate to check the value of enthalpy. In case of a step mode heating, values with a very low uncertainty could be obtained but at the cost of consuming a large amount of time. However, a dynamic heating program is closer to the actual situation of a PCM in a realistic application. For heterogeneous PCMs, other calorimetric methods allowing larger samples, such as the T-history method, are recommended. Enthalpy-temperature graphs for both melting and solidification provide useful information for PCMs, though they are not widely interpreted in PCMs studies. It is also discussed that the IEA method is a reliable method to determine the enthalpy of PCMs. The maximum uncertainty on that quantity should be less than 10%. In PCMs characterization, measuring heat capacity is crucial for understanding the contribution of sensible heat in thermal storage and for indirect calculation of thermal conductivity. In DSC experiments, the three steps method can be used in the dynamic or area heating methods. The most important point is to apply exactly the same test conditions for blank, sapphire and sample measurements. The sample size for both sapphire and sample should remain in the same range. With the help of DSC experiments, one can estimate the thermal stability of a PCM faster than any other method. However, the sample is limited to a few milligrams. One can observe the change in the enthalpy value and in the peak shape during multiple cycles of melting and solidification. One can also conduct the thermal cycling of larger samples in a temperature-programmable oven, then test the sample in a DSC. According to the increasing demand for energy and environmental concerns, thermal energy storage is a promising technology to address these needs. This review paper highlights the important role of calorimetric characterization, especially DSC, in integrating PCMs in TES applications. This study summarizes the research on thermal characterization of PCMs by DSC with a focus on methods, approaches and recommendations to improve the accuracy of measurements for future studies.