Determination of thermo-physical properties and stability testing of high-temperature phase-change materials for CSP applications

This paper presents the thermo-physical properties and stability testing results of six high-temperature phase-change candidate materials for potential use as a cascaded storage system for concentrating solar power applications. This type of storage is a promising technology because it offers a higher utilization of the possible phase change and a more uniform heat-transfer fluid outlet temperature, compared with the single phase-change material (PCM) storage system. The tested materials were inorganic eutectic PCMs with reported phase-change temperatures between 300 °C and 600 °C. Four PCMs were made from carbonate salts (Na2CO3, K2CO3, and Li2CO3) and two from chloride salts (NaCl, MgCl2, and KCl). The phase-change temperature, phase-change enthalpy, and specific heat of these PCMs were measured using a differential scanning calorimeter. Large material samples were tested in an oven subjected to multiple melt-freeze cycles. The results showed that the carbonate PCMs have a very high degree of sub-cooling in the initial cycles, which decreased in subsequent cycles. The chloride PCMs have a negligible degree of sub-cooling. There is some disagreement between the measured and reported thermo-physical property values of the tested materials, which demonstrates the uncertainty associated with published property values. One carbonate PCM and one chloride PCM were recommended as promising latent heat storage materials.