A novel phase change materials used for direct photothermal conversion and efficient thermal storage

The inherent fluctuation of solar irradiation will seriously affect the stability of energy transfer of traditional photothermal conversion materials. Photothermal conversion phase change materials can combine the mechanisms of photothermal conversion and phase transformation to realize storage or release solar energy at constant temperature by phase transition, which can effectively overcome the instability of solar irradiation in time and space. In this paper, paraffin was selected as phase change matrix, meanwhile, the thermal conductivity enhancement (expanded graphite) and photothermal conversion reinforcement (carbon black nanoparticles) were respectively added by secondary vacuum penetration to prepare paraffin/expanded graphite/carbon black phase change materials for direct photothermal conversion. As a result, the extremely low thermal conductivity and poor spectrum absorption capacity of paraffin are greatly improved by expanded graphite and carbon black nanoparticles respectively on the basis of retaining the excellent phase transformation properties of paraffin. When the content of carbon black nanoparticles is 10 wt%, the isotropic thermal conductivity of the prepared material in solid phase and phase transformation respectively reach 10.54 W/mK and 20.53 W/mK, which increased by 31.94 times and 96.76 times when compared with pure paraffin. Meanwhile, the corresponding intrinsic photothermal conversion efficiency and effective thermal storage efficiency are up to 60.1% and 97.3%, respectively.