Preparation and thermal energy storage properties of LiNO3-KCl-NaNO3/expanded graphite composite phase change material

Recent studies suggest expanded graphite (EG) can significantly enhance the thermal conductivity, stability, efficiency of phase change material (PCM). This study aims to investigate the thermal-physical properties of the LiNO3-KCl-NaNO3/expanded graphite composite PCM. The testing PCM samples were prepared using the Capillary Method with 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt% EG. When EG mass fraction is 25 wt%, no leakage was observed in the leakage test. The SEM image shows that the EG had intense absorption ability to the LiNO3-KCl-NaNO3 composites. The X-ray powder diffraction (XRD) comparison between the pure salt and the composite PCM suggests that no new substance produced after adding the EG into the eutectic LiNO3-KCl-NaNO3. Differential scanning calorimetry (DSC) curves of the composite PCM indicate that the latent heat was reduced dramatically when the EG and the eutectic LiNO3-KCl-NaNO3 were blended together. In the experiment, thermal conductivity and the compress density of the composite PCM show a strongly linear relationship. Also, the thermal conductivity of the PCM can be enhanced after adding the EG into the pure salt. Finally, the thermal performance of the latent heat system using the eutectic LiNO3-KCl-NaNO3 and the composite PCM were compared. Due to the high thermal conductivity, the charging rate of the system utilizing the composite PCM is much faster than the pure salt.