Molecular dynamics simulations on the binary eutectic system Na2CO3-K2CO3

摘要

Molten carbonate salts as phase change materials have received particular attention for high-temperature thermal energy storage and heat transfer applications due to desirable thermal characteristics such as wide operating temperature range, low causticity and excellent thermal stability. In this study, molecular dynamics (MD) simulations were performed on the binary carbonate salt Na2CO3-K2CO3 (58-42 mol%) based on an effective pair potential model, a Born-Mayer type combined with a Coulomb term. The temperature dependences of thermodynamic properties including the density, sheer viscosity and thermal conductivity were simulated in detail from 1000 to 1400 K, which were all difficult to achieve from experiments on account of high-temperature extreme conditions. Moreover, the radial distribution functions (RDF) and coordination number curves of the binary carbonate salt were characterized to explore the mechanisms of their temperature dependences from microscopic view. The simulation results suggested that the changes of thermodynamic properties with temperature were induced by the distance changes between ions. Besides, it can be concluded that the high bond energy in the strong covalent bond C-0 of molten carbonate salts must contribute to the large specific heat capacity in comparison with that of molten un-oxyacid salts.