Effect of Microstructure on Thermal Properties of EG/MA Shaped Composite Phase Change Materials

Myristic acid (MA) was used as the phase change material (PCM) and expanded graphite (EG) was used as the additive substrate. 21 kinds of EG/MA shaped composite PCM samples with different ratios were prepared by means of "melt blending-press forming " method with different molding pressure and pressing technology. The microstructure of the samples was characterized and analyzed, and then the samples were subjected to thermal property testing and thermal stability analysis to explore the relationship between the microstructure and thermal properties. Relevant experiments showed that EGII with high expansion degree not only improved the distribution uniformity of MA, but also significantly improved the liquid phase encapsulation during the phase transition. Better thermal stability was shown in the 50-cycle stability test. The melting point and enthalpy of the shaped composite PCM sample (24 wt% EG iota iota/MA) were 53.98 ? and 199.1 J g(-1), respectively. The addition of EG and the change of the pressing process can adjust the radial thermal conductivity and axial thermal conductivity of the samples. The radial thermal conductivity of the 16 wt% and 24 wt% EGII/MA samples consistently increased with increasing pressure in the molding pressure range of 10 MPa to 50 MPa, which is due to the larger pore volume of the more expansive EGII and the higher compressibility of the graphite flake layer in the composites. When the pressure was increased to 50 MPa, the radial thermal conductivity of 24 wt% EGII/MA slightly increased to 26.21 W m(-1)middotK(-1), which was about 140 times higher than the thermal conductivity value of 0.18 W m(-1)middotK(-1) for pure MA.