Macroencapsulation of Phase Change Materials for Thermal Energy Storage

The use of a latent heat storage system using phase change materials (PCMs) is an effective way of storing thermal energy. Latent heat storage enables high-energy storage density which reduces the footprint of the system and the cost. However, PCMs have very low thermal conductivities making them unsuitable for large-scale use without enhancing the effective thermal conductivity. In order to address, the low thermal conductivity of the PCMs, macroencapsulation of PCMs has been adopted as an effective technique. The macroencapsulation not only provides a self-supporting structure of PCM and separates the PCM from thermal fluids but also enhances the heat transfer rate. The current work involves study of various concepts of encapsulation of low cost inorganic PCMs. Sodium nitrate (NaNO3), a low cost PCM, was selected for thermal storage in a temperature range of 300 - 500˚C. Various techniques like electroless coatings, coatings using silicates, coatings with metal oxide (SiO2) and sand encapsulation are discussed. A novel technique of metal oxide coating was developed where firstly a high temperature polymer, such as, polymer (stable \u3e 500˚C) was coated over PCM pellets, and cured, so that the pellet becomes insoluble in water as well as several organic solvents and later the metal oxide is coated over the pellet using self-assembly, hydrolysis, and simultaneous chemical oxidation at various temperatures. The coated PCM pellets were characterized