Improving the heat storage/release rate and photo-thermal conversion performance of an organic PCM/expanded graphite composite block

A phase change material (PCM) with both high thermal storage/release rate and good photo-thermal conversion performance not only is a good working medium for thermal energy storage system but also show potential use in solar thermal utilization. Herein, a strategy of further improving thermal characteristics of an organic PCM/expanded graphite (EG) composite was explored. In this work, PA is selected as PCM. Specifically, the PA/EG composite was pressed into round blocks with different EG packing densities, and it is shown that the block that has the EG packing density of 320 Kg/m(3) exhibits both large enthalpy and high thermal conductivity. Then, two carbon materials, carbon fiber (CF) and graphite sheet (GS), were introduced into the optimal EG-based binary block to prepare two series of ternary blocks with different mass ratios of CF (GS) to EG, respectively. It is found that the ternary blocks containing GS always exhibit larger enthalpy and higher thermal conductivity than the ones containing CF at every identical mass ratio. The suitable mass ratio of GS to EG has been selected as 0.5, at which the obtained ternary block possesses a thermal conductivity of 16.5 W/mK, showing an increase by ca. 24%, while its enthalpy just decreases very slightly, as compared with the binary one. Moreover, it is revealed that the introduction of GS makes the ternary block exhibit accelerated heat storage and release rates and enhanced photo-thermal conversion performance. These good characteristics along with excellent thermal reliability endow the PA/GS/EG block with potential applications.