Numerical Analysis Of Salt Hydrate-based Sorption For Long Term Thermal Energy Storage

Thermochemical heat storage appears to be an attractive alternative solution for long-term heat storage, as it offers large energy capacity and negligible heat loss during long-term storage. Salt hydrate-based sorption is a typical thermochemical heat storage technology, and has become a new research hotpot for long-term thermal storage. In this paper, special attentions are paid on the research of sorption properties of pure hydrate salts and thermal performance of various sorption reactors. MgCl₂·6H₂O material, which offers a high storage density, shows the greatest potential in low-grade energy storage. For convenience of the simulation study, a fixed bed with porous MgCl₂·6H₂O material is chosen in this paper.Numerical investigation into the MgCl₂·6H₂O fixed-bed reactor was done in this paper. The dehydration of MgCl₂·6H₂O was modeled using the relations for the conservation of mass and energy. A kind of LDF model was developed to simulate material transportation in dehydration process.The CFD software FLUENT was employed in simulation research, which allows author to compile user-defined program to improve the performance. In order to test and verify the model, the temperature of two typical points was contrasted between the simulation and experiment results. It is found that the simulation predicts the experiment fairly well.Based on the dehydration process modeling and simulating, the contours of temperature, H₂O mass fraction, moisture content in the solid phase were analyzed. Typical parameters, such as fluid inlet velocity and solid initial temperature were analyzed to study the influencing factor in the dehydration process. It is found that fluid inlet velocity increased by 50%, the dehydration time reduced 41%, and if fluid inlet velocity was raised by 50%, the dehydration process would extend by 45%. Results showed that set the solid initial temperature at 30℃, the dehydration hours lengthened by 10%, and if the solid initial temperature was set at 60℃, the dehydration time would decrease by 8.5%.Finally, characteristics of the salt hydrates-based seasonal thermochemical storage technology are summarized and the future research directions are discussed.