Effect of nanoparticle clusters on the specific heat capacity of a molten carbonate for thermal energy storage

Fused carbonates are promising heat storage materials for next-generation thermal energy storage technologies. Nanocomposite phase change materials (NPCMs) can often improve the thermal performance of a single-phase change material (PCM). In this paper, the effect of nanoparticles (SiO2) on the specific heat capacity (SHC) of molten salt (Na2CO3:K2CO3 = 58:42 mol%) was investigated by molecular dynamics (MD) method, and the intrinsic mechanism of the change of SHC was revealed from a microscopic perspective. The results showed that the SHC first rapidly increased and then gradually decreased with increasing nanoparticle loading. The SHC of the NPCM increased by 0.336 % to 4.299 % with nanoparticle loadings of 0.2–0.8 wt%, and the SHC of the NPCM was as high as 4.299 % with a nanoparticle loading of 0.2 wt%. In addition, Fb is defined in this paper to reflect the effect of the interaction between the nanoparticles and PCM on SHC. The decline in the Fb value with increasing nanoparticle loading indicates that the interaction is enhanced, and enhanced interaction was most clearly observed with a nanoparticle loading of 0.2 wt%. The interaction between nanoparticles and PCM leads to the separation of amorphous carbonate molten cations into different components, and this separation changes the distribution of Ecoul and Elong, which in turn increases the SHC of the NPCM. This work is a key guide for the selection and optimal design of new molten salt nanocomposites.