Experimental development of hybrid nitride-based PCM with sand stones for enhanced thermal energy storage

Thermal energy storage technologies are gaining significant interest in the modern era as they help reduce the strain on renewable energy resources and optimize thermal energy used. Phase change heat storage is particularly appealing due to its high energy density, low heat loss, and excellent thermal stability. This study enhances the thermal properties of phase change materials (PCMs), including thermal conductivity, stability, and economic/environmental impacts. The proposed design introduces a novel PCM combination, LiNO₃-NaNO₃-NaCl integrated with the sandstones for thermal energy storage. The inclusion of the sandstones significantly improves the PCM's thermal stability, exhibiting only an 8 % mass loss after exposure to 650 °C and a mere 1.5 % reduction in storage capacity after 600 thermal cycles. Additionally, the thermal conductivity increases from 0.46 W/m·K to 0.98 W/m·K with the incorporation of the sandstones. Structural analysis reveals that the PCM-sandstone composite maintains a well-organized structure with strong mechanical bonding. In the material's morphology, NaCl appears in crystalline form, while NaNO₃ is observed as bright spots. The melting point of the PCM sandstone composite is 96 °C, while solidification occurs at 130 °C. The specific heat capacity is measured at 1250 J/kg·K, and the material's density is 1700 kg/m³. The thermal efficiency of the energy storage system reaches 86 % with the addition of sandstones, and the exergy efficiency is also recorded at 86 %. Furthermore, the cost reduction achieved by integrating sandstones into the PCM is 9.09 %, while CO₂ emissions are reduced by 8.11 %.