Influence of tank-to-particle diameter ratio on thermal storage performance of random packed-bed with spherical macro-encapsulated phase change materials

Thermal energy storage material is always filled in the packed bed system in a random accumulation manner, and there is an interrelationship between the tank-to-particle diameter ratio (TPDR) and the porosity. Therefore, in this paper, the packed bed latent heat storage system is constructed based on spherical macro-encapsulated phase change materials (PCM). To study the influence of TPDR on the thermal performance of a randomly packed bed, a transient two-dimensional axisymmetric symmetry continuous solid phase model is developed. The experimental and numerical results are compared to verify the accuracy of the model. The heat transfer and pressure drop characteristics between air and PCM capsules are analyzed in detail. The results indicate that the average porosity reaches the maximum at around TPDR≈1.7 position, which is about 0.7. In the same packed bed, when the TPDR is larger, the pressure drop is more affected. The diameter of the heat storage ball changes from 25 mm to 75 mm, the TPDR is reduced by 66.7%, the heat storage of the PCM is almost unchanged, and the heat storage capacity of the stainless-steel spherical shell is reduced by 72%, and the heat storage capacity of the entire heat storage ball is reduced by 12%.