Experimental and numerical investigations on the melting behavior of Fe3O4 nanoparticles composited paraffin wax in a cubic cavity under a magnetic-field

The magnetic field application provides a method of active regulation for passive phase change. Nonetheless, the effects and mechanisms of the uniform magnetic field on phase change are still relatively limited. This study describes the effects of magnetic field and phase change based on the thermomagnetic convection model and the enthalpy-porosity method. The phase change nanocomposites are prepared by adding paramagnetic Fe3O4 nanoparticles into paraffin, and their properties were measured. The accuracy of the numerical model is verified by observing the phase interface development and temperature distribution. Subsequently, the effect and mechanism of dimensionless magnetic induction, nanoparticle concentration, magnetic Rayleigh number and magnetic field direction on the melting performance are numerically investigated. The results show that the positive magnetic field has a significant inhibitory effect on melting. The liquid fraction and stored energy in the melting have the most significant decrease of 10.54% and 68.6%, respectively. Meanwhile, the positive magnetic field suppression effect on melting increases with the magnetic Rayleigh number. In contrast, the negative magnetic field promotes global melting, which leads to the largest increase of 12.01% and 33.94% in the liquid phase fraction and stored energy under different magnetic Rayleigh numbers, respectively. In essence, the mechanism of magnetic field-regulated melting originates from the different motions of Fe3O4 nanoparticles in the liquid phase of phase change nanocomposites.