Abstract

Heating solids arranged in a packed bed is a simple method to store sensible thermal energy. This study focuses on cylindrical packed-bed configurations, where a temperature profile develops along the stacked solids and moves towards the system's outlet. Therefore, the availability to store thermal energy in the packed bed decreases over time and the exhaust energy outside the storage increases. To address this challenge, the present work introduces a novel operational metric to monitor the thermal state of packed-bed storage systems. This operational metric relates the stored potential in the system with an ideal stage, and its definition enables constraining the system's operation with a simple mathematical condition, which is a significant outcome from the traditional approach of using arbitrary temperature limits to stop the charging process. Its calculation requires the measurement of the top and bottom temperatures of the packed bed and knowing the system's maximum operating temperatures. When applying the mathematical condition, the required charging time to reach that stage and the cut-off temperature can be obtained. A parametric analysis correlated these operating quantities to design data to predict their value given the design conditions. This work provides a new perspective on the dynamic operation of cylindrical packed-bed sensible thermal energy storage systems, offering a simple yet effective strategy to enhance system performance.