Abstract
Molten chloride salt is recognized as a promising heat transfer and storage medium in concentrating solar power in recent years, but there is a serious lack for thermal property data of molten chloride salts. In this work, local structures and thermal properties for molten chloride salt—including NaCl, MgCl2, and ZnCl2—were precisely simulated by Born–Mayer–Huggins (BMH) potential in a rigid ion model (RIM) and a polarizable ion model (PIM). Compared with experimental data, distances between cations, densities, and heat capacities of molten chloride slats calculated from PIM agree remarkably better than those from RIM. The polarization effect brings an extra contribution to screen large repulsive Coulombic interaction of cation–cation, and then it makes shorter distance between cations, larger density and lower heat capacity. For NaCl, MgCl2, and ZnCl2, PIM simulation deviations of distances between cations are respectively 3.8%, 3.7%, and 0.3%. The deviations of density and heat capacity for NaCl between PIM simulation and experiments are only 0.6% and 2.2%, and those for MgCl2 and ZnCl2 are 0.7–10.7%. As the temperature rises, the distance between cations increases and the structure turns into loose state, so the density and thermal conductivity decrease, while the ionic self-diffusion coefficient increases, which also agree well with the experimental results.
Highlights
Received: 30 December 2020Concentrating solar thermal power (CSP) is a promising technique for high temperature solar energy utilization [1]
radial distribution function (RDF) of MgCl2 in polarizable ion model (PIM) have a good agreement with the experimental values [25]
There is a mean percentage error of 8.1% between simulated results and experiments from Nagasaka et al [15], so it proves that reverse non-equilibrium molecular dynamics (RNEMD) method is suitable for calculating the thermal conductivities
Summary
Concentrating solar thermal power (CSP) is a promising technique for high temperature solar energy utilization [1]. Molten chloride salts including LiCl, NaCl, KCl, MgCl2 , and ZnCl2 have been researched as promising heat transfer materials with high operating temperature [3]. Huang et al [25] computed the local structure of MgCl2 at 998 K by MD simulations, which agrees well with the experimental results by neutron diffraction technique except the distance of Mg-Mg. Gardner et al [26] calculated pair radial distribution functions, coordination numbers and internal pressure of ZnCl2 at 1200 K with different parameters in RIM, but the distances of Zn-Zn in all simulations are in excess of more than 23% of experimental value. The thermal and transport properties of molten chloride salts calculated by PIM and RIM are both compared with experimental data
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