Effects of Thermal Cycling Operation on Solar Thermal Energy Storage, Morphology, Chemical/Crystalline Structure, and Thermal Degradation Properties of Some Fatty Alcohols as Organic PCMs

Thermal cycling stability of phase change materials (PCMs) is one of the key parameters for real-scale thermal energy storage (TES) applications. Fatty alcohols as PCMs possess significantly large amount of energy storage capacity with suitable low and medium melting temperature ranges for thermal regulation of food carriers, textiles, and so forth. However, their thermal cycling performances have not been investigated thoroughly before. With this regard, this work aims to investigate the effects of thermal cycling operation on latent heat TES (LHTES) characteristics, morphology, chemical/crystalline structure, and thermal degradation properties of three kinds of fatty alcohols. Differential scanning calorimetry (DSC) is adopted for the measurement of thermal properties of 1-hexadecanol (HD) 1-dodecanol (DD), and 1-octadecanol (OD) after 3000 thermal cycles. The morphological and chemical/crystal structures of these PCMs were carried out by scanning electron microscopy, Fourier-transform infrared (FT-IR), and X-ray powder diffraction (XRD) before and after thermal cycling treatment. The DSC results showed that the pristine HD, DD, and OD have relatively higher LH between 234 and 277 J/g and melting temperature between 21 and 56 °C. The melting and solidification enthalpies of the cycled PCMs were not reduced by more than 9.4%, with a slight variation of-0.51-1.0 °C in melting point. The FT-IR and XRD results confirmed outstanding chemical and crystalline structure stability of all cycled PCMs. The thermogravimetric analysis findings revealed that the selected PCMs had good cycling thermal degradation stability. The outcomes of this investigation demonstrated that cycled HD, DD, and OD are favorable PCMs with excellent cycling thermal and chemical performances for low to medium temperature-passive solar TES applications.