This work documents the study of two concepts of open reactors for thermochemical energy storage. While classical thermal storage uses sensible or latent heat to store thermal energy, thermochemical energy storage uses an endothermic / exothermic chemical reaction. The process studied is based on the hydration and dehydration of a reactive salt by a flow of moist air in order to release and store heat respectively. The first concept studied is a storage module composed by the pattern “one salt bed surrounded by an inlet and an outlet channel, placed in parallel”. The second concept is a storage module made of by tubes impregnated with the reactive salt on their intern face. In this configuration, the tubes and the impregnated salt layer length scales are in the order of micrometer. Both concepts are presented using the Constructal law of design.
In the first concept, air flows through the salt bed, corresponding to a forced convection through porous media problem, whereas in the second concept the air flow licks the impregnated salt and the chemical reaction occurs within the salt thanks to diffusion only.
The analytical part is based on the Constructal law approach. From the main trends in terms of pressures distribution the geometrical features are deduced to obtain the design of compact and thermally efficient systems.
Next, the discovered trends are backed up with numerical experiments. The geometrical dimensions are morphed with the purpose to move towards better performances. A ratio β between the heat produced by the chemical reaction within the entire module and the overall pumping power necessary to blow the fluid is determined to compare the configurations of each concepts.
In accord with Constructal design, the number of salt beds in the first concept is morphed to reach equipartition of imperfections. The results show that with this evolution, the ratio β increases. In the second concept, the salt volume must be allocated in such a way that the time for water vapor diffusion through the salt matches the time for hydration / dehydration.