Systematic melting point adjustment for certain salt hydrates.

Abstract

High operating temperature Phase Change Materials (PCMs) have various applications in industrial waste heat recovery and hybrid compressed air - thermal energy storage system. However, there is still a lack of detailed knowledge in terms of their thermal storage properties that hinders their wide-spread use in industry. In this study, one aims at characterizing the thermal properties, including melting point and enthalpy of two high temperature PCMs using Differential Scanning Calorimetry (DSC) according to the International Energy Agency (IEA) protocol. The selected organic PCMs are adipic acid 99% and PureTemp151® bio-based (commercially available PCM) with a melting point of 151 °C and a latent heat of over 200 J/g. One studies the effect of heating rate and the mass of sample in DSC procedures on transition temperature and enthalpy. Finally, thermal performance of PCMs is quantified through several cycles of melting and solidification. In recent years, the latent storage community presented hundreds of novel phase change materials (PCM, pure substances and mixtures) usable for various applications. Enthalpies of fusion and melting points are two major thermophysical properties needed when deciding whether a PCM is suitable for a specific application. Oftentimes, a promising PCM for an application must be rejected because its melting point is deviating from the ideal melting point (MP) by a few degrees Celsius. Even though the basic principle of using additives to achieve melting point depression has been known since many years, it has been rarely applied to manipulate the MP of promising PCMs. This study reports preliminary experiments conducted on tampering with melting points of specific, promising salt-based PCMs. Finding a systematic pathway to influence the melting point of salt hydrates using mixtures or additives could revolutionize the discovery of new and suitable PCMs for specific applications.