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Encapsulation of high-temperature inorganic phase change materials using graphite as heat transfer enhancer

Zhong, Yajuan, Zhao, Bingchen, Lin, Jun, Zhang, Feng, Wang, Haoran, Zhu, Zhiyong, Dai, Zhimin
Renewable energy 2019 v.133 pp. 240-247
cellulose, encapsulation, graphene, heat transfer, latent heat, models, pellets, phase transition, renewable energy sources, temperature, thermal conductivity, thermal energy, thermal expansion
A quasi-isostatic pressing technique for encapsulating spherical high-temperature inorganic phase change materials (PCMs) was presented in this work. To enhance the thermal conductivity of PCMs, graphite powder was dispersed into the PCM pellets. Meanwhile, cellulose particles, as sacrificial particles, were mixed with the PCM pellets to relieve the volumetric expansion of the PCMs during the phase change process. The effects of the latent heat, thermal conductivity, and thermal expansion behavior of the PCM/graphite capsule were investigated. The PCM capsules were able to work at temperatures up to 900 °C, including undergoing a solid-liquid phase change at 803 °C with a latent heat of 159.6 J g−1, and survived more than 300 thermal cycles as thermal energy storage devices. The thermal performance of the PCM capsules between 500 and 900 °C was numerically investigated using a modified one-dimensional (1-D) enthalpy-based model. The results indicated that the average heat transfer of the PCM capsules with graphite-dispersed core was significantly elevated during both the charging (by 92.5% for 99% charge) and discharging (by 168.4% for 99% discharge) processes, compared to the pure core PCMs.