Semi-empirical Density Estimations for Binary, Ternary and Multicomponent Alkali Nitrate–Nitrite Molten Salt Mixtures

  • Thomas BauerEmail author
  • Alexander Bonk


For sensible thermal energy storage in Concentrating Solar Power (CSP) plants, a molten salt mixture of 60 wt% sodium nitrate (NaNO3) and 40 wt% potassium nitrate (KNO3), known as Solar Salt, is commonly utilized. The paper presents semi-empirical estimation results of the density of Solar Salt and alternative molten salt mixtures with low melting temperatures in a range from 70 °C to 140 °C. These mixtures are Hitec, HitecXL, LiNO3–KNO3–NaNO3 and a multicomponent mixture. The paper shows that density values of mixtures can be closely predicted from single salt densities. The paper examines different estimation rules for mixtures. The quasilinear volumetric additivity rule (QVAR) is known for ternary reciprocal systems. For the first time, the presented work extends the QVAR to multicomponent mixtures. Temperature-dependent densities of selected salt mixtures of the system Ca,Li,K,Na//NO2,NO3 were estimated. Estimations are motivated by a fast and reliable method compared to time-consuming and error-prone measurements of several mixtures.


Concentrating Solar Power (CSP) Hitec HitecXL Multicomponent salts Quasilinear volumetric additivity rule 

List of symbols


Density coefficient g/cm3


Temperature-dependent density coefficient g/(cm3K)


Molar volume cm3/mol


Molar volume of i cm3/mol


Molecular weight g/mol


Molecular weight of i g/mol


Density g/cm3


Mol fraction of i 1


Temperature °C


Deviation of estimated density value %


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Authors and Affiliations

  1. 1.German Aerospace Center (DLR)Institute of Engineering ThermodynamicsCologneGermany
  2. 2.German Aerospace Center (DLR)Institute of Engineering ThermodynamicsStuttgartGermany

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