Preparation, optimization and thermal characterization of paraffin/nano-Fe3O4 composite phase change material for solar thermal energy storage

The latent heat thermal energy storage (LHTES) using phase change material (PCM) is one of the most effective measures to store and utilize solar energy. However, its thermal performance is seriously affected by the poor thermal conductivity of PCMs. In the present study, paraffin/nano-Fe3O4 composite PCMs were prepared to enhance the thermal conductivity of PCM and its preparation process was optimized. The thermo-physical properties of composite PCMs were comprehensively characterized and the enhancements of charging and discharging performance were evaluated numerically. Results show that the optimal preparation process is that the mass ratio of oleic acid and nano-Fe3O4 is 1:1, while the power of ultrasonic treatment is 200 W with the duration being 3 h. When the mass fraction of nano-Fe3O4 is 5 wt.%, the thermal conductivity of composite PCM can be enhanced by 53% at the solid state and 79% at the liquid state compared to that of pure paraffin, and the latent heat is reduced by 8.33% and 12.00% during the melting and solidification processes. In addition, it is found that 36.96% and 39.85% reductions in the total charging time and discharging time can be achieved by nano-Fe3O4; meanwhile, its heat stored and heat released decrease by 1.05% and 5.20% relative to the pure paraffin in the same volume.