Parametric investigation of charging and discharging performances of a cascaded packed bed thermal energy storage system

The packed bed thermal energy storage (PBTES) system employing cascaded phase change material (PCM) is useful for low-grade waste heat recovery and utilization. The performance of a cascaded PBTES system is parametrically investigated in the present study. A one-dimensional concentric dispersion model is developed and validated by the experimental results. The average heat transfer rates of a cascaded PBTES system at various volumetric ratios of PCM capsules are numerically investigated, and the cascaded PBTES system of a volumetric ratio of hydroquinone: adipic acid: erythritol =3:6:1 is found to be the best configuration in the cyclic charging and discharging processes. Furthermore, the comparison of the thermal behaviors of the cascaded and non- cascaded PBTES systems shows that the PCMs in each layer of a cascaded PBTES system complete the phase change at nearly the same time, leading to a larger heat transfer rate compared to the non-cascaded one. The average heat transfer rate of a cascaded PBTES system with the volumetric ratio of 3:6:1 is about 6.96 % higher than that of the non-cascaded one for the cyclic process. In addition, the results show that the average heat transfer rate of the cyclic process of the PBTES system is improved by employing the cascaded PCMs, while the enhancement ratio of average cyclic heat transfer rate is found to decrease from 10.57 % to 1.35 % as the mass flow rate increases from 20 kg.h1 to 100 kg.h1 and to decrease from 10.32 % to 0.91 % as the capsule diameter increases from 20 mm to 100 mm