Experimental study on thermal performance regulation of composited phase change system using non-uniform magnetic field generated by a Helmholtz coil

This study investigates the impact of non-uniform magnetic fields on the thermal performance of porous media filled with Fe3O4 nano-enhanced phase change materials (NEPCMs). A specialized experimental apparatus was devised, encompassing a Helmholtz coil to generate inhomogeneous magnetic fields, an oil cooler, a direct current power supply, and an infrared thermal imager. The experimental findings revealed that the NEPCM subjected to a single-coil magnetic field in the left side with a 15 A current exhibited the highest heat storage efficiency of 2.09 J/s and the fastest melting rate of 5842.8 s. The uniform magnetic field at 30 A resulted in the longest melting time (7671.60 s) for the 3 wt% NEPCM, with an energy storage efficiency of 1.59 %. These observations suggest that the non-uniform magnetic field induces Kelvin force on the nanoparticles, thereby significantly enhancing heat transfer. Moreover, the energy storage capacity of NEPCMs with 1 wt%, 2 wt%, and 3 wt% Fe3O4 was augmented by 5.47 %, 9.55 %, and 37.85 %, respectively, in comparison to pure PCM. Contrary to the gradual temperature increase observed in uniform magnetic fields, the left-sided magnetic field induced a sharp inflection point in the melting process. Furthermore, applying a magnetic field with a 45 A current on the left side reduced melting time by 20.04 %, 23.46 %, and 16.50 % when compared to uniform magnetic fields at 15 A, 30 A, and 45 A currents, respectively. The findings extend the scope of previous studies by quantifying the influence of magnetic field gradient and current strength on heat storage efficiency, providing insights for the development of more effective thermal management systems.