Investigation of pinacone hexahydrate as phase change material for thermal energy storage around 45 °C

Phase change materials (PCM) with a transition temperature around 45 °C can be used in various applications, e.g. as intermediate storages for heat pumps in space heating systems, for the thermal protection of battery systems or to increase the efficiency of dishwashers by preheating water. At that temperature level, typical PCMs are either salt hydrates or organic materials like paraffins and fatty acids. Salt hydrates usually provide higher volumetric enthalpy changes, whereas for organic PCMs, corrosion is generally less problematic. Organic hydrates combine the advantages of salt hydrates and organic PCMs. For the diol pinacone, the existence of a hexahydrate with a melting temperature around 45 °C and a high melting enthalpy of about 300 J/g was reported in literature. To investigate the applicability of pinacone hexahydrate as a PCM, we conducted a detailed calorimetric characterisation of its phase change. DSC and T-History measurements were performed to determine the enthalpy curves for melting and crystallisation. We measured an enthalpy change of (340 ± 17) J/g ((332 ± 17) kJ/l) between 32 °C and 47 °C, which is a suitable operating temperature range. In addition, enthalpy changes within 15 K around the phase change of PCMs with similar melting temperatures (docosane, lauric acid, zinc nitrate tetrahydrate) were measured and confirmed the promising properties of pinacone hexahydrate for compact thermal energy storage.