Experimental study on the melting heat transfer of octadecane with passively adding graphene and actively applying an electric field

The low thermal conductivity of organic phase change materials (PCMs) has seriously obstructed the performance of thermal latent-heat thermal storage (LHTS) system. For the first attempt, we experimentally studied the phase-change heat transfer characteristics of octadecane inside a horizontal cavity with the passive addition of nano graphene and the active application of an electric field. The effects of nano graphene weight ratio, direct current (DC) voltage magnitude and polarity on melting heat transfer and their corresponding mechanism are then examined. Results are reported for the real-time melting process, the liquid fraction, and the evolution of absorbed energy. The velocity fields obtained by particle image velocimetry (PIV), the temperature fields measured by fiber Bragg grating (FBG) sensors, and the current-voltage curves are reported to reveal the heat transfer enhancement mechanism. The absorbed thermal energy is increased by 33.6% when nano graphene is added alone. A single electric field promotes the energy absorption by 153.5% where electric field driven flow develops. The net charge is generated by the conduction mechanism. For composite PCMs’ melting, the absorbed energy is enhanced by 124.8% at most when the cavity's bottom wall is exposed to -10.0 kV. However, when +10.0 kV is applied to the bottom wall the electrophoretic deposition takes place, and the combined augmentation effect on absorbed thermal energy is 111.2%. The present results provide a reference for improving the LHTS system's performance through sole or synergistic heat transfer enhancement method.