Molecular Dynamics Simulation of Thermophysical Properties and the Microstructure of Na 2 CO 3 Heat Storage Materials

In recent years, heat storage technology has attracted wide attention in the fields of renewable energy storage for its relatively high melting point, high heat storage capacity and economy, Na 2 CO 3 and eutectic salt mixtures containing Na 2 CO 3 are promising candidates in the field of solar energy storage. In this paper, a molecular dynamics (MD) simulation of Na 2 CO 3 was conducted with the Born–Mayer potential function. The simulated solid–liquid phase change temperature is 1200 K, and the error is 5.4%. The heat capacity at constant pressure ( C p ) is higher in liquid than in solid, the average C p of solid is 1.45 J/g and that of liquid is 1.79 J/g, and the minimum error is 2.8%. The simulation results revealed the change rules of density and thermal expansion coefficient of Na 2 CO 3 in the process of heating up, and these changes were analyzed by radial distribution functions (RDF) and angular distribution functions (ADF). Moreover, the RDF and ADF results show that the atomic spacing of Na 2 CO 3 increases, the coordination number decreases, and the angle distribution between atoms becomes wider as the temperature rises. Finally, this paper examined the microscopic changes of ions during the phase transition of Na 2 CO 3 from solid to liquid. It is concluded that the angle change of CO 3 2 − in the liquid state is more sharply. This study improves the understanding of the thermodynamic properties and local structure of Na 2 CO 3 and provides theoretical support for Na 2 CO 3 heat storage materials.