As the key heat storage and transfer medium in concentrated solar power (CSP) systems, molten salts’ thermophysical properties, such as thermal conductivity, specific heat capacity, and thermal stability, critically determine the systems energy conversion efficiency and economic viability. However, conventional molten salts suffer from low thermal conductivity and limited energy storage density, restricting their application in high-temperature thermal energy storage. Recent advances show that doping with nanoparticles, such as Al 2 O 3 , CuO, and SiO 2 , can significantly improve these properties. Nevertheless, systematic studies on quaternary molten salt systems remain scarce. In this work, we focus on the quaternary eutectic salt H15 (15 wt% Ca(NO 3 ) 2 –5.95 wt% NaNO 3 –45.05 wt% KNO 3 –34 wt% NaNO 2 ), which demonstrates a high decomposition temperature of 597.4 °C alongside a relatively low melting point of 84.4 °C and high thermal energy storage density of 1052.41 kJ/kg. To overcome its thermal performance limitations, Al 2 O 3 nanoparticles (0.1 wt% to 3 wt%) were introduced to form a nanocomposite molten salt. The influence of varying nanoparticle loadings was assessed via DSC, HotDisk, SEM, and XRD to examine corresponding changes in phase transition behavior, thermal conductivity, viscosity, and material microstructure. This study provides theoretical and experimental support for developing high-performance, wide temperature-range thermal energy storage materials for advanced CSP systems.
Shijue Wang,Ju Xiao,Fei Yuan,Long Li,Yafei Guo,Yingchun Xie,Tianlong Deng
In order to separate cesium nitrate from the eluant mixture sodium nitrate solution, the phase equilibrium of the ternary system (NaNO 3 + CsNO 3 + H 2 O) at 338.15 K and 0.1 MPa was investigated using the isothermal equilibrium solution method, and the solubilities and physicochemical properties (density and refractive index) of the system were determined, experimentally. According to the experimental data, the phase diagram and physicochemical properties versus the composition diagram of the ternary system at 338.15 K were established for the first time. There is one invariant point (NaNO 3 + CsNO 3 ), two univariant curves, and two crystallizing regions corresponding to NaNO 3 and CsNO 3 . The phase diagram belongs to a simple-type ternary system, and neither double salt nor solid solution was formed. Based on the phase diagrams of this system at 298.15 and 338.15 K, the cycle separation process for CsNO 3 recovery from the eluant of sodium nitrate mixture solution was evolved. It is worth noting that 90.29 % CsNO 3 can be separated from the mixed solution after three cycles. It is significant for the green recovery of cesium nitrate from the eluent solution containing sodium nitrate effectively.
The coefficient of thermal expansion of inorganic salts increases with increasing temperature. The sintering temperature may affect the properties of the shape-stable phase change materials (SSPCMs). We study the SSPCMs with NaNO 3 -KNO 3 as the phase change material and Al 2 O 3 and expanded graphite (EG) as the skeletal support materials (SSMs) to achieve thermal energy storage over a wide temperature range. The effects of different sintering temperatures on the SSMs content, thermal conductivity and compressive strength of SSPCMs were studied. The results showed that as the sintering temperature increased, more SSMs were required to support the SSPCMs. The maximum NaNO 3 -KNO 3 mass percentages of the SSPCMs sintered at 300 °C and 450 °C were 82.8 wt% and 66.4 wt%, respectively. Samples with application temperatures higher than the sintering temperature may have problems stabilizing the shape. Sintering temperature had little influence on the thermal conductivity of the same SSPCMs. However, the compressive strength of the SSPCMs decreased with increasing sintering temperature. The addition of EG decreases the decomposition temperature of the composite and limits its application temperature range. The SSPCM-10/30 sintered at 450 ℃ showed good chemical stability performance, and the latent heat decreased from 56.01 J/g to 53.44 J/g. The compressive strength dropped from 30.7 MPa to 25.17 MPa before and after 20 cycles due to larger internal gaps and did not change much after 20 cycles.
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