Measurement of enthalpy curves of phase change materials via DSC and T-History: When are both methods needed to estimate the behaviour of the bulk material in applications?

Abstract

Thermal energy storages (TES) based on solid–liquid phase change materials (PCM) use the latent heat of the phase transition from solid to liquid and vice versa. The enthalpy change within application relevant temperature ranges has to be determined via calorimetric measurements providing high accuracy. For the most part, enthalpy curves of PCMs are measured either via differential scanning calorimetry (DSC) or via the T-History method, but rarely with both methods. Combined DSC and T-History measurements allow an improved determination of enthalpy curves of PCM, since intrinsic material properties can be separated from properties of the investigated sample and effects of the applied methods. In order to study when both methods are needed to estimate the behaviour of the bulk material in applications, the enthalpy curves upon heating and upon cooling of nine PCM from different material classes were measured via T-History and DSC in both dynamic and step mode. These are: octacosane, decane-1,10-diol, RT80, methylurea, glutaric acid, magnesium chloride hexahydrate, erythritol, sebacic acid and hydroquinone. The comparison of enthalpy curves in terms of melting temperature, degree of subcooling and enthalpy change within application relevant temperature ranges demonstrates the necessity of combined DSC and T-History measurements for materials with volume dependent behaviour. Melting temperatures agree within the limits of RAL testing regulations and considerably less subcooling is observed for T-History samples. If the PCM under investigation can be characterised reasonably with both methods, enthalpy changes determined via DSC and T-History deviate by less than 5%.