A thorough investigation of thermochemical heat storage system from particle to bed scale

Salt hydrates are promising candidates for the long-term thermochemical heat storage (TCES) in the building environment. In such storage systems, the surplus of energy will be exploited in an endothermic reaction to dehydrate the salt hydrates. Once it is demanded, the stored energy will be released through an exothermic reaction by hydrating the salt, which results in an increase in the mass and temperature of salt particles as well as changes in the species of material. In order to construct an improved storage system, it is very important to deeply investigate the details of the (de)hydration processes in salt hydrates. Poor heat and mass transfer is the bottle neck in this technology. Therefore, the main objective of this work is to investigate how heat and mass transfer influence the (de)hydration in a closed TCES-system. The novelty of this work is to provide a high degree of detailed information about (de)hydration of TCM (thermochemical material) in a bed by calculating transport phenomena for each single particle while considering their interactions with each other. This is achieved by applying and developing the Extended Discrete Element Method (XDEM) as a numerical modeling tool and Thermogravimetric Analysis (TGA) measurements. Comparisons are carried out for the results of the hydration and dehydration process in a single particle with the measurements which shows a very good agreement. Moreover, impact of particle size on the hydration process is also studied. Further, simulations for the hydration process in a chain of six potassium carbonate (K₂CO₃) particles are performed in order to understand the mechanism of heat and mass transfer inside the packed beds.