Thermal performance analysis and optimization of cascaded packed bed latent heat storage tank

The packed bed tank with multiple phase change materials (PCMs) is one of the most efficient latent heat energy storage techniques. This study presents insight into the influence of the latent heat arrangements on the cascaded packed bed tank, providing a new idea for designing multi-PCM packed bed tank, which concerns the screening of PCMs. In this study, a parametric study is conducted to optimize the latent heat of the multi-PCM packed bed tank for the charging and discharging process. A developed two-dimensional model is used to predict the thermal behaviors of the heat transfer fluid and PCMs in packed bed tanks, which is verified by experiment. The results showed that the case with uniform latent heat arrangement exhibits the best overall thermal performance, which obtains the lowest standard deviation of average heat-exchange zone travel velocities for the charging and discharging cycle process. Moreover, the relationship between the efficiency and the standard deviations of the heat-exchange-zone travel velocities is unearthed, and its effectiveness is verified by an actual cascaded PCMs packed bed tank. The charging/discharging/overall efficiency increases with a decrease in the standard deviation of the heat-exchange-zone travel velocities of the PCM layers. This relationship can be used as a new PCM selection method for the cascaded latent heat storage tank. In addition, the actual cascaded packed bed unit with a different latent heat is optimized by variable capsule diameters.