Thermophysical properties of SWCNT/molten carbonate composite phase change material: A molecular dynamics study

Abstract

Carbonate molten salts are considered the most competitive heat storage medium for the next-generation concentrated solar power (CSP) systems. This research presents a material composition design strategy aimed at improving the thermophysical properties of carbonate molten salts through the development of carbonate molten salt/single-walled carbon nanotubes (SWCNT) composite phase change material (CPCM). The mechanism of thermophysical property improvement was investigated using molecular dynamics (MD) simulations, focusing on aspects such as microstructural evolution, thermal diffusivity, and energy variation. The thermal properties including density, thermal conductivity, specific heat capacity, and viscosity of the CPCM with different mass fraction of SWCNT (1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%) were predicted in the high-temperature range of 1150 K to 1450 K. The results indicate that as the increasing mass fraction of SWCNT, leads to a substantial enhancement in both the thermal conductivity and specific heat capacity of the system. When the mass fraction of SWCMT is 5 wt%, the maximum increments are 16.41 % and 3.00 %, respectively. Simultaneously, it is observed that an increase in SWCNT mass fraction restricts the migration of molten salt ions, leading to a reduction in the self-diffusion coefficient of the system and an increase in shear viscosity. The research outcomes offer valuable insights for the design and implementation of molten salt-based elevated temperature thermal energy storage materials in next-generation CSP systems.