Numerical study on the cyclic cold storage performance in a solid-packed bed tank

An efficient cyclic cold storage system plays a crucial role in improving the performance of a Liquid Air Energy Storage system. Packed bed cold storage (PBCS) systems, widely researched and employed, demonstrate thermal stability, a broad operational temperature range, and cost-effectiveness. This study developed a two-dimensional transient cyclic solid-PBCS system using a porous media thermal non-equilibrium model, which was implemented in ANSYS Fluent software. During the cold charging and discharging periods, cryogenic nitrogen and nitrogen at ambient temperature were used as working fluids to exchange heat with the solid cold storage medium in the PBCS. Temperature distributions were analyzed during the cold charging, cold discharging, and the consecutive cyclic cold charging-discharging modes. The study systematically examined the impact of mass flow rate and the number of cold storage cycle on key system performance parameters, including heat exchange capacity and cyclic cold exergy efficiency. The results indicated that mass flow rate significantly affects the number of cycles required to reach a steady-state cyclic PBCS system, with higher mass flow rates necessitating more cycles. Optimal cyclic performance of the solid PBCS can be achieved at a moderate superficial mass flow rate. At a superficial mass flow rate of 0.32 kg‧s⁻¹‧m⁻², the cyclic cold charging exergy efficiency exceeds 99 % and cyclic cold discharging exergy efficiency can over 68 %. The stability of multiple consecutive cold storage cycles in the solid PBCS system is critical to the overall performance of LAES. These findings on the influence of PBCS cold storage cycles and fluid mass flow on system cyclic performance provide valuable theoretical guidance for the practical operation of PBCS cycles.