Effects of scale, interface, and salt ratio on phase change characteristics of mesoporous complex nitrate for thermal energy storage

Developing clean and sustainable energy technologies has become crucial in light of the growing concern worldwide regarding energy security and climate change. Thermal energy storage technology has emerged as one of the key technologies for achieving sustainable energy development. Research on developing and improving mesoporous composite phase change materials (CPCM) with mixed nitrates as the phase change core material has gained immense attention. The objective is to thoroughly understand the transformation rules governing the phase change characteristics of mesoporous complex nitrate. This study integrates molecular dynamics simulation with an experimental approach to investigate the impact of scale, interface, and the mixing ratio of salts on the phase change properties of CPCM, exploring the competitive relationships among these factors. The results indicated that the phase change temperatures of the mixed nitrate follow the order T (9:1) > T (4:6) > T (6:4) > T (5:5) depending on the ratio of NaNO3 and KNO3. The latent heat associated with the phase change of the CPCM increases with the content of NaNO3. When comparing different matrix materials with the same ratio of mixed salts, the CPCM with Al2O3 as the matrix exhibits the highest phase change temperature and latent heat. For the same ratio of mixed salts, the phase change temperature initially increases and then decreases with the increase of mesopores scale, while the latent heat increases with the enlargement of scale. Thus, the interfacial effect significantly impacts the phase change temperature. When considering the impact of interfacial effects and scale effects on phase change temperature, it was evident that the interfacial effect was dominant in the scale ranges of 3–5 nm and 7.5–10 nm, whereas the scale effect is dominant in the 5–7.5 nm. We found that the ratio of salts played a dominant role in the latent heat for CPCM compared to scale and interfacial effects.