Synergistic effect of heat and mass transfer for thermochemical heat storage based on a novel umbrella-shaped fin structure

Compressed CO 2 energy storage (CCES) is regarded as a prospective large-scale energy storage technology, with CCES systems incorporating heat storage devices playing a pivotal role in enhancing system efficiency. Salt hydrate-based thermochemical energy storage (TCES) provides benefits such as high energy storage density (ESD) and minimal heat dissipation, presenting broad application prospects. However, the inefficient heat conduction in the reactor of TCES systems restricts widespread implementation. An umbrella-shaped fin structure is introduced into a TCES reactor for the first time to enhance heat transfer performance. A transient analysis for thermal charging and discharging characteristics is investigated, with heat storage performance of different branch structures being compared. The response surface method (RSM) synchronizing with genetic algorithm (GA) is employed to minimize the hydration time, which is the major indicator of the combined effect of heat and mass transfer. The results indicate that there exists an upper boundary of optimal branch number where little effect on heat charging/discharging time is observed with its further increase. Considering the synergistic effect of heat and mass transfer, and manufacturing complexity, the umbrella-shaped fin structure with three branches exhibits optimal comprehensive heat storage performance. Compared with the single-branch structure, the dehydration and hydration times are effectively reduced by 41.97% and 45.45%, respectively. Although a more uniform temperature distribution enhanced heat transfer, the mass transfer was limited with higher branch numbers, proving that the synergetic effect should be considered comprehensively instead of traditional studies where the heat transfer was mainly considered in accelerating the reaction rate. Compared with the unoptimized structure, the optimized structure leads to a 19.52% reduction in charging time and a 17.41% decrease in discharging time. This study provides new insights into the structural design of high-performance TCES reactors. The proposed reactor design shows great potential for compression heat utilization in CCES systems and large-scale energy storage applications. Further experimental validation and scale-up studies under practical CCES conditions are needed to promote its engineering application.