A numerical study on regulating the latent heat storage process of Fe3O4-paraffin wax composite materials by using gradient magnetic field

Serving as the regulatable external force, the magnetic nanoparticles induced force inside the magnetic field can be an efficient way to handle the heat storage of phase change materials. The deep understanding on the relation between the thermomagnetic convection and externally applied gradient magnetic field is no doubt essential. In this paper, the impacts of gradient magnetic field on the melting process of Fe₃O₄-paraffin wax composite phase change materials are identified through a numerical simulation. Particularly, the effects of some key parameters of nanoparticle concentration, heating surface temperature, and gradient magnetic field strength on the heat storage performance of phase change materials are discussed in depth. It is found that the angle (θ) between the volumetric force and the normal direction of the heating surface dominates the phase change heat storage effect in the cavity. Compared to the case with only gravity-force (θ = 90°), the cases with θ larger than 90° can enhance the phase change heat storage process, while those with θ less than 90° weakens it. Note that when the magnetic field gradient is in the same direction as the heat transfer direction, the heat storage performance of the phase change material decreases and vice versa increases. Moreover, the increase of heating surface temperature, nanoparticle concentration, and magnetic field strength can positively accelerate the heat storage process. The gradient magnetic field of 0.8 and -0.8 T·m⁻¹ would decrease and increase the specific volume heat storage power by 26.49 % and 29.04 % in sequence, compared to the no magnetic field case.