A general thermodynamic model for eutectics of phase change molten salts in concentrating solar power applications

Thermal energy storage technology with Phase Change Materials (PCM) is an attractive option to optimise energy resources and to recover and promote excess heat. The phase change behaviour of PCM requires advanced research to understand and better control the thermal energy storage using PCM, which is a crucial step to develop a powerful latent storage system. This paper aims to analyse the multiphysics phenomena of three regenerator configurations, horizontal case and two injection direction of Heat Transfer Fluid (HTF): top and bottom in vertical case. The study is done for the charge and discharge cycles of the solid-solid and solid-liquid phase transitions of PCM. First, the temperature dependence of the thermal and physical properties of paraffin as PCM is characterised. Second, an experimental study of an annular latent storage system was carried out. Also, an experimental mesh method was introduced to compare the energy behaviour of the three cases. Third, a numerical analysis of the experimental storage unit with low thermal diffusion is performed. The experimental results are confronted with the numerical results obtained with ANSYS Fluent and COMSOL Multiphysics commercial software. Last, the three configurations are compared to a reference case without gravitational field. The results show that specific mechanisms control the thermal and energetic behaviour of the regenerator. Furthermore, several parameters, such as storage density, distribution of energy storage rate in the different regenerator components (PCM, HTF, and heat exchanger), were analysed. Altogether, the results supply important information to understand the dynamics of passive storage systems.