Investigation of a packed bed cold thermal storage in supercritical compressed air energy storage systems

The packed bed cold thermal storage can be adopted as the cold storage/heat exchanger in supercritical compressed air energy storage systems. In the packed bed, the compressed air at supercritical pressure can efficiently transfer cold energy with packed particles. This study investigates the dynamic thermal behavior of the packed bed by a two-dimensional numerical model. After validation, the model is used to simulate the fully cold discharging and charging processes and calculate the effects of the air mass flow rate and the working pressure. Due to the dramatic changes of air properties around the critical temperature, very special evolutions of the thermocline region are revealed. Besides, the thermocline region in the cold discharging process is much thicker than that in the cold charging process. Before the thermocline region reaches the outlet, as high as 94.4% of the total cold energy can be charged, and the output mass flow rate oscillates and is lower than the input mass flow rate for the cold charging process. The results also show the increase of the air mass flow rate accelerates the cold charging and discharging processes but hardly affects the trends of the outlet temperature, the cold charging/discharging energy, or the pressure drop of the packed bed. The increase of the working pressure has little effect on the cold discharging process, while it decreases the pressure drop along the packed bed and affects the evolutions of the outlet temperature and the cold discharging energy.