Optimization of Heat Storage Devices of Stepped Phase Change Packed Bed at Different Cut-Off Temperatures

In recent years, the contradiction between global energy shortage and high energy consumption has intensified. The development of solar phase change energy storage technology is of great significance to the transformation of building energy structures. The heat storage devices of the spherical capsule cascade phase change packed bed can fully use medium and low-temperature solar energy, and the optimization design of heat storage cut-off temperature can improve the thermal performance and operation economy of the heat storage tank. On this basis, this paper conducts the following work: Firstly, based on the physical model of a two-dimensional packed bed heat storage tank and the mathematical model of dispersion-concentric transient heat transfer, the heat storage and release process of a single phase change capsule packed bed heat storage tank and a two phase change capsule packed bed cascade phase change heat storage tank were numerically simulated by FLUENT software, with the heat storage cut-off temperature analyzed by single factor. Then, the characteristics of heat storage and release cycle of cascade phase change heat storage tank are investigated. Also, the concepts of heat storage optimization rate and heat storage efficiency optimization rate are put forward. Finally, according to the numerical simulation results, the effective utilization rate of phase change materials in the second-stage cascade phase change heat storage is higher. Meanwhile, appropriately sacrificing the heat storage in the later stage of heat storage can improve efficiency performance indicators such as the average heat storage rate. When the heat storage performance and heat storage efficiency are of the same importance, the dimensionless heat storage cut-off temperature of the primary device and the secondary device is about 0.6.