Enhanced thermal conductivity of form-stable phase change materials using carbon nanofiber-expanded graphite hybrid structure

Abstract

Inorganic hydrated salt phase change materials (PCM) play a vital role in field of thermal energy storage and temperature control because of their high latent heat. However, inherent low conductivity of hydrated salt PCMs limits greatly their efficien cy in practical application. In this study, a hydrated salt (disodium hydrogen phosphate dodecahydrate)/carbon nanofiber-expanded graphite hybrid form-stable composite PCM (DSP/CNF-EG) is prepared using a physical mixing and the impregnation method. The enhanced thermal conductivity is achieved by the fill of CNF into the low thermal conductivity regions of EG. The thermal conductivity of DSP/CNF-EG is increased by 3.69 times compared with that of pure DSP, which is as high as 2.486 W m−1·k−1. Differential scanning calorimetry (DSC) indicates the outstanding latent heat (208.9 J g−1) and the suitable phase change temperature (33.7 °C) of the DSP/CNF-EG composite. Scanning electron microscopy (SEM) demonstrates that the thermal conductive reinforcements are formed by the addition of CNF. Moreover, Raman spectra results suggest that the hydrated salt is packaged well within the CNF-EG hybrid structure. Furthermore, the prepared DSP/CNF-EG composite maintains a good thermal stability after 200 thermal cycles. The obtained results indicate the DSP/CNF-EG composite is an excellent candidate used for thermal energy storage in building.