| Latent neat storage systems nave been applied in many fields such as solar energy systems, energy efficient buildings and industrial waste heat recovery, due to their high energy storage density and small temperature variation from storage to retrieval. In a latent heat storage system, energy is stored during melting and recovered during freezing of phase change materials (PCM). As a kind of solid-liquid phase change materials, paraffin wax has been widely used due to its chemical resistance, high heat of fusion, wide range of phase change temperatures, commercial availability, and low cost. However, it also has some inherent limitations, such as the leakage of melting paraffin and the low thermal conductivity.The paraffin/high density polyethylene (HDPE) phase change materials (PCM) were prepared by melt blending method, paraffin used as phase change material and HDPE used as support material. The microstructure, leakage rate and thermal performance of the composites were studied. And the influences of additives and preparation process on paraffin/HDPE shape-stabilized PCM leakage rate were explored. The results showed that paraffin and HDPE could be uniformly mixed. The phase change enthalpy of paraffin/HDPE shape-stabilized PCM was associated with the paraffin content. When added 0.1% DCP and 0.1% antioxidant 1010, the shape-stabilized PCM with a low leakage rate could be gotten by melt blending at 150℃The paraffin/HDPE/expanded graphite (EG) shape-stabilized PCM with high thermal conductivities were prepared by melt blending method, paraffin used as phase change material, HDPE used as support material and EG used as thermally conductive filler. The microstructure, thermal conductivity, leakage rate and thermal performance of the composites were studied. And the influences factors on paraffin/HDPE/ EG shape-stabilized PCM thermal conductivity were explored. The results showed that HDPE, EG and paraffin could be uniformly mixed. The leakage rate of phase change materials was increased when added the EG, but decreased with the increasing of EG content. When the EG content was close to 15 wt%, the leakage rate of PCM was less than 0.6%. The thermal conductivity of PCM was increased with the increasing of EG content. The thermal conductivity was up to 1.265 W/(m · K) when the EG content was 15 wt% and the increasing rate was up to 100%. The phase change enthalpy of PCM was not changed with the EG content.The effect of HDPE and EG on paraffin, and the distribution of EG were studied by dissolving the paraffin/HDPE shape-stabilized PCM and the paraffin/HDPE/EG shape-stabilized PCM into xylene. Thermally conductive mechanism of the paraffin/HDPE/EG shape-stabilized PCM was proposed. The results showed that the mesh structure formed by HDPE and the porous structure of EG have good effect on coating the paraffin. The mesh structure formed by HDPE was good to coating EG. Paraffin was absorbed by the worm-like EG in great quantities, and distributed in the space network structure formed by HDPE. When we added EG into paraffin/HDPE shape-stabilized PCM, thermal carrier changed from phonon to free electrons, which greatly improving the heat transfer rate. |
