Comparative study on high temperature thermal stability of quaternary nitrate-nitrite mixed salt and Solar salt

Molten salts are applied in solar thermal power plant as heat transfer and heat storage medium. In this work, the thermal stability of quaternary nitrate-nitrite (QNN) mixed salt and Solar salt are studied under three constant temperature conditions (500 degrees C, 565 degrees C, 600 degrees C) for 1008h. The results show that the mass ratio of NO2-1/NO3-1 plays an important role in the thermal physical properties of nitrite/nitrate molten salt. The mass ratio of NO2-1/NO3-1 in Solar salt increases with the increasing of working temperature, which results in the decreasing of melting point and initial crystal temperature and the increasing of decomposition temperature. The average values of melting point and initial crystal temperature of QNN mixed salt are maximum 119 degrees C and 24 degrees C lower than that of Solar salt. Meanwhile, the maximum increase of average values of specific heat and thermal conductivity of QNN mixed salt are 14.26%, 8.18% compared with its base salt, respectively. When the working temperature is higher than decomposition temperature, average values of specific heat and thermal conductivity of Solar salt decrease because of the acceleration of nitrite formation. The viscosity values of QNN mixed salt and Solar salt decrease with the increasing of temperature. Based on the comparative analysis, QNN mixed salt has good application value in practical engineering applications.

Automated summary

The study found that the thermal physical properties of QNN mixed salt and Solar salt differ under different temperature conditions. QNN mixed salt has higher average specific heat and thermal conductivity compared to Solar salt, making it suitable for practical engineering applications.