Thermal Performances of High-Temperature Thermal Energy Storage System with Tin Embedded in Copper Matrix by Theoretical Methods

There is a critical need to develop advanced high-temperature thermal storage systems to improve efficiencies and reduce the costs of solar thermal storage system. In this work, two typical systems composed with Cu as matrix and Sn as the phase change material (PCM) are explored, namely, the 3-deimentional (3D) structure system by embedding Sn particles into Cu matrix and the 2-deimentional (2D) structure system by embedding Sn wires into Cu matrix. Given the thermophysical properties of a nanomaterial could be importantly different from that of a bulk one, we thus firstly derive the thermophysical properties of PCM and matrix theoretically, like the thermal conductivity by kinetic method and the specific heat capacity based on Lindemann's criterion. And then, these properties are utilized to estimate the energy storage ability in both 3D and 2D structure system, and the influence of structure on heat transfer efficiency is theoretically investigated in both 3D and 2D structure system. Results turn out that 3D structure system is a better choice than a 2D structure system, because of larger specific surface area, a larger sensitive heat capacity and a larger thermal conductivity. When the feature size of the PCM decreases to be less than a critical value which is about 500 nm for Sn, the thermal conductivity of the system decreases exponentially while the heat storage capacity increases lineally. Moreover, when the feature size of Sn geometry is less than a critical value, which is 15 nm for 3D structure system and 25 nm for 2D structure, the Cu matrix can't play a role in improving the effective thermal conductivity of the whole system.

Automated summary

Developing advanced high-temperature thermal storage systems is crucial for improving the efficiency and reducing the costs of solar thermal storage. Two typical systems composed of Cu as the matrix and Sn as the phase change material (PCM) were explored in this study: a 3D structure system with embedded Sn particles and a 2D structure system with embedded Sn wires. The thermophysical properties of PCM and matrix were derived theoretically, and used to estimate the energy storage ability and investigate the influence of structure on heat transfer efficiency. Results showed that the 3D structure system was a better choice due to its larger specific surface area, sensitive heat capacity, and thermal conductivity. The thermal conductivity of the system decreased exponentially when the feature size of the PCM decreased below a critical value, while the heat storage capacity increased linearly. Moreover, when the feature size of the Sn geometry was below a critical value, the Cu matrix could not improve the effective thermal conductivity of the whole system.