Thermal Characterization of High Temperature Inorganic Phase Change Materials for Thermal Energy Storage Applications

Abstract

As the importance of latent heat thermal energy storage increases for utility scale concentrating solar power (CSP) plants, there lies a need to characterize the thermal properties and melting behavior of phase change materials (PCMs) that are low in cost and high in energy density. In this paper, the results of an investigation of the melting temperature and latent heat of two binary high temperature salt eutectics are presented. Melting point and latent heat are analyzed for a chloride eutectic and carbonate eutectic using simultaneous Differential Scanning Calorimetry (DSC) and Thermogravimetric Analsysis (TGA). High purity materials were used and the handling procedure was carefully controlled to accommodate the hygroscopic nature of the chloride eutectic. The DSC analysis gives the values of thermal properties of the eutectics, which are compared with the calculated (expected/published) values. The thermal stability of the eutectics is also examined by repeated thermal cycling in a DSC and is reported in the paper along with a cost analysis of the salt materials.

Thermal Conductivity of Molten Carbonates with Dispersed Solid Oxide from Differential Scanning Calorimetry

“…No significant weight loss was observed, demonstrating a high thermal and chemical stability of the sample during the analysis [34]. The steady baseline of the DSC cooling curves (Figure 2) before the exothermic peaks also confirms the chemical stability and retention of the homogeneity of the sample [33,35]. The LNC in the sample mixtures had a liquidus temperature of ~495 °C [4].…”

“…Therefore, the DSC thermal conductivity measurement program (Table 2) was set up, considering the melting point of the molten salt mixtures along with a few other parameters, such as the thermal and chemical stability of the samples and the melting point of the metal disk. In Figure 1, the TGA weight loss detected before the first heating cycle was due to evaporation of moisture (<200 °C) and melting (~495 °C) of LNC (eutectic Li and Na carbonates) in the LNC-MO mixture [33]. No significant weight loss was observed, demonstrating a high thermal and chemical stability of the sample during the analysis [34].…”

“…The silicon paste at the interface could, however, also affect the homogeneity of the sample in the molten state. It is well-known that the LNC in the sample mixture undergoes a significant thermal expansion and contraction upon heating and cooling, with a liquidus temperature of ~495 °C [33,36]. Therefore, subjecting the sample to an appropriate thermal cycling (heating and cooling) could improve the thermal contact.…”

“…The endothermic peak is intense and well defined in the third heating cycle, but not even initiated in the first heating cycle. This illustrates that the repeated solid and liquid phase transition had established a better thermal contact after a few thermal cycles [33,34]. The heating curve recorded between 650 and 690 °C (Al melting behavior) in the third cycle (after establishing a better thermal contact) was used to determine the thermal resistance of the sample.…”

Una Revisión sobre Materiales para Almacenamiento de Energía Solar Térmica

“…Los hidratos de sal se utilizan normalmente a bajas temperaturas de funcionamiento en el intervalo de 30 a 50 • C. Tienen una fórmula general AB.nH 2 O, son sales inorgánicas que contienen agua de cristalización. Durante la transformación de estado, se produce la deshidratación de la sal [45]. Esto puede ocurrir de dos maneras.…”