Investigation on Thermal Properties Enhancement of PEG/CNT Composites as PCM for Thermal Energy Storage
Volume Title: 1
Department of Polymer Engineering and Color Technology, Amirkabir University of Technology
Polyethylene glycol (PEG) as a phase change material (PCM) can be used for thermal energy storage (TES). Melting point and phase change enthalpy of this material are in appropriate range; 20.3 ℃ and approximately 100 J/g, respectively. However, its low thermal conductivity (~ 0.2 W/m.K) limits its application. Therefore, in this project thermal conductivity of PEG was enhanced by utilizing carbon nanotubes (CNT). In order to achieve good compatibility, CNT was first functionalized with surface modification by acid nitric. The modification caused agglomeration which results in improper dispersion. Hence, sonication and planetary ball mill were used for breaking up the agglomerates. The optical microscope (OM) images showed that planetary ball mill was more effective and reduced the cluster size to 2 µm. Then, composites of PEG/CNT were synthesized successfully with CNT loading of 1 and 2 wt.%. Thermal conductivity of the composites were investigated and showed approximately 60% improvement in thermal conductivity of PEG with 2 wt.% CNT. Other thermal properties were studied by differential scanning calorimetry (DSC). The results showed negligible change in phase change enthalpies. Melting and crystallization enthalpy of PEG with 2 wt.% CNT reduced by 1.3 and 5.7%, respectively. It was also observed that the supercooling degree of PEG/CNT composite decreased by 46.20% in comparison to the neat sample. It reveals that CNT also acts as nucleating agent for PEG. Also, specific heat capacities (CP) of PEG and the composite with 2wt.% CNT versus temperature were calculated from DSC results.