Experimental and numerical investigations for effective thermal conductivity in packed beds of thermochemical energy storage materials

Highlights: • ETC of a packed reactor is a fundamental parameter in the designing of TCHS systems. • XDEM enriches DEM by adding chemical and thermodynamic states of individual particles. • At low temperature and pressure conduction is prominent than convection and radiation. • Better heat transfer is observed at higher vapor pressures because of natural convection. • At a certain high pressure, the effect of natural convection is not significant anymore. Salt hydrates are promising candidates for long-term thermochemical heat storage (TCHS) 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 understand the details of the heat and mass transfer processes in the packed beds of salt hydrates. Poor heat (in the closed systems) and mass transfer (in open systems) can be the bottleneck in this technology. The main objective of this work is to investigate how heat transfer will be affected by applied pressure, particle size, and packing arrangement through calculating/measuring the effective thermal conductivity of the packed beds of salt hydrates. This is achieved by applying and developing a CFD-DEM model and by experimental measurements in a vacuum oven. Comparisons are carried out for the numerical results at low and high ambient pressures with the experimental measurements, which show a very good agreement. The obtained results show the effect of natural convection in the packed bed when the higher vapor pressure is applied.