Modelling of phase change in spheres for applications in solar thermal heat storage systems

Thermally stratified solar energy accumulation tanks are an effective technique that is widely used in solar collector systems. Thermal energy storage (TES) systems using phase change materials (PCM) is another technology that can be applied to accumulation tanks to improve thermal energy density. To analyze the impact of placing PCM inside the tanks, it is crucial to understand the parameters that describe the processes that take place in each of the PCM sphere. In this study COMSOL Multiphysic is used to analyze the energy accumulation in PCM through thermal conductivity, which is one of the first steps to full simulate PCM in stratified water environment. The assumption stated by other studies that for low Rayleigh numbers the thermal conductivity is the dominant heat transfer principle is tested by comparing the model to experimental data. The simulation results showed that the thermal conductivity method can be successfully used to model the process until the material has melted, suggesting that additional effects has to be considered to increase the accuracy of model