Investigation on thermo-physical properties of molten salt enhanced with nanoparticle and copper foam

HITEC salt (40 wt.% NaNO₂, 7 wt.% NaNO₃, 53 wt.% KNO₃) with a melting temperature of about 142°C is a typical phase change material for solar energy storage. Both aluminum oxide (Al₂ O₃) nanopowder and copper foam were applied to enhance pure HITEC salt, so as to retrieve the limitation of composite PCMs with single enhancement. Nanocomposite was synthesized with two-step methods at the beginning, then copper foam were infiltrated with nano-salt at high temperature. The morphologies of the composites were extensively characterized with Scanning Electron Microscope, X-ray diffraction and Fourier Transform Infrared Spectrometer, while the thermal behaviors were analyzed with Differential Scanning Calorimeter and Thermos-gravimetric Analyser. Results showed that special nanostructures were formed in the composite, and physical bonding was found between Al₂ O₃ nanopowder and salt. Theoretical prediction showed that the thermal conductivities of the composites were significantly enhanced about ten times, and the specific heat capacities of the composites were slightly decreased, which is beneficial for heat storage. Furthermore, the presence of porous copper foam and Al₂ O₃ nanopowder made the extrapolated onset and peak phase change temperatures shift slightly.