Regulation mechanism of magnetic field on non-Newtonian melting and energy storage performance of metal foam composite nano-enhanced phase change materials

Abstract

A numerical study is conduced to explore regulation mechanism of magnetic field on melting heat transfer and energy storage performance of nano-enhanced phase change material (NEPCM) composited with metal foam. The enthalpy-porosity method, Darcy-Forchheimer model and local thermal non-equilibrium model are used to describe melting process, flow in porous media and coupling heat transfer, respectively. The proposed model is then verified by experiments using thermochromic liquid crystal thermometry. Effects of nanoparticles mass fraction (0%≤Φwt≤5%), magnetic number (0≤Mn≤7×106), and Rayleigh number (104≤Ra≤106) on the non-Newtonian fluids flow, melting heat transfer and energy storage characteristics are illustrated and discussed. Results show that the addition of Fe3O4 nanoparticles can effectively promote melting and induce non-Newtonian effect of molten NEPCM, but Φwt has no significant influence on the heat transfer. With the increase of Mn, the suppression effect of magnetic field on the whole melting process of NEPCM enhances at moderate Ra = 105, and natural convection is fully developed with a “force bridge” phenomenon of Kelvin force. For lower Ra (=104), natural convection becomes weaker and magnetic field presents a “force loop” phenomenon. For larger Ra (=106), natural convective heat transfer has absolute predominance and the suppression effect of magnetic field can be ignored. Moreover, the increase of Φwt and Ra have obvious positive contributions to heat storage and heat storage efficiency. At low Ra, the suppression effect of magnetic field on heat storage and total melting time leads to decrease in energy storage efficiency.