Effects of expanded graphite on NaNO3/semi-coke ash shape-stable phase change composites for thermal energy storage
Yaxuan Xiong, Xi Tian, Xiang Li, Jing Ren, Qian Xu, Yuting Wu, Yulong Ding
Abstract
As an alkaline industrial solid waste with a porous structure , semi-coke ash can have adverse effects on the environment if accumulated or buried in large quantities. The research group has previously used this material in combination with NaNO 3 to prepare a shape-stable phase change composite. Building upon the previous research team, this work manufactured the shape-stable phase change composite by cold-compression hot-sintering method using NaNO 3 as the phase change material , semi-coke ash as the skeleton material and an innovative addition of expanded graphite as the thermal conductivity enhancer to enhance thermal conductivity of phase change material . Then, key thermal performance, mechanical strength , chemical compatibility, microscopic morphology , economic efficiency and emission reduction capacity were investigated. Results demonstrated that the sample SS2 with 0.5 wt% expanded graphite performed best, which also presented a mechanical strength of 113.82 MPa, a thermal conductivity of 1.844 W/(m·K), and an excellent thermal energy storage density of 424.91 J/g between 100–400 °C; Both the thermal performance and mechanical strength of sample SS2 decreased to some extent after the heating/cooling cycles; The semi-coke ash, expanded graphite, and NaNO 3 showed excellent chemical compatibility while both the thermal energy storage cost (0.022 ¥/kJ) and the raw material carbon emissions (1041 kg) of producing per ton sample SS2 in this work were far below traditional shape-stable phase change materials.