A preliminary study to determine the charging cut-off temperature in a packed bed cryogenic energy storage system

The charging process in a packed bed cryogenic energy storage system is said to be complete when the temperature of the carrier gas at the bed outlet reaches a cut-off temperature. This temperature cannot be arbitrarily chosen since it dictates the thermodynamic performance behavior during the transient operation which in turn governs the cost of storage. In this paper, we consider the second law performance of packed bed system under various inlet mass flow rates and packing diameter during charging to gain insights into the selection of cut-off temperature. The results indicate that the charging exergy efficiency first increases and then decreases as the bed is charged. The time gap between the peak exergy efficiency and charge completion increased with increase in particle diameter and decrease in mass flow rate. The optimal cut-off temperature may be selected by representing the efficiency and energy stored in the bed in terms of cost.