Investigation on thermal performance of quaternary nitrate-nitrite mixed salt and Solar salt under thermal shock condition

Abstract Molten salts are subjected to heating-cooling thermal shock cycle in the operation of concentrating solar power (CSP) plant. In this work, the quaternary nitrate-nitrite (QNN) mixed salt and Solar salt are comparatively studied under different thermal shock conditions. After 500 thermal shock test cycles, morphological and structural analysis of samples are carried out by wavelength dispersive x-ray fluorescence (WD-XRF), Fourier-transform infrared (FTIR), x-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Meanwhile, thermos-physical properties of samples are comparatively analyzed. The results show the average melting point and average initial crystal temperature of QNN mixed salt are maximum 135°C, 82.6°C lower than that of Solar salt, respectively. The decomposition temperature of QNN mixed salt is maximum 52.1°C higher than that of Solar salt. The specific heat of QNN mixed salt increases with the increasing of thermal shock temperature. The specific heat and thermal conductivity of QNN mixed salt maximally increase 15.46% and 9.8% compared with its base salt, respectively. Meanwhile, the thermal conductivity and viscosity of QNN mixed salt are slight higher than that of Solar salt. The Solar salt viscosity decreases with the increasing of thermal shock temperature.