A numerical study on effects of axially and radially cascaded phase change material on charging/discharging time of paraffin based packed bed thermal energy storage

This study manifests the improvement in the charging and discharging time of the encapsulated PCM arranged in packed bed thermal energy storage. The combined effect of the aspect ratio (ratio of height to diameter of the packed bed) and cascaded configurations of phase change materials (PCMs) integrated with the solar water heating system is analyzed numerically. The mathematical model is validated by the experimental study available in the literature. Initially, an optimal aspect ratio of the packed bed is predicted for charging/discharging. And then, PCMs are arranged in different layers in the packed bed based on the optimal aspect ratio to analyze the combined effect of PCM configurations and optimal aspect ratio. The charging and discharging time were decreased with an increasing aspect ratio to 2.5. Afterward, an increased aspect ratio showed a trivial change in the charging and discharging time of latent heat thermal energy storage (LHTES). Furthermore, at an optimal aspect ratio of 2.5, PCMs were arranged in the packed bed with both axial (parallel) and combined axial-radial layers (parallel and series) to see the impact of the cascaded configuration. Charging and discharging time of combined axial-radial layers configuration was respectively found to be 17.21% and 18.5%, less than charging time without layers.