Experimental study on the melting performance of magnetic NEPCMs embedded in metal foam subjected to a non-uniform magnetic field

This experimental study aims to evaluate the melting performance of non-magnetic and magnetic nano-enhanced phase change materials (NEPCMs) composited with metal foam inside a cavity heated from the left in a non-uniform magnetic field via thermochromic liquid crystal (TLC) visualization. The evolutions of solid-liquid interface and mushy zone during melting are captured by TLC technique and temperature distributions are recorded by ten thermocouples. The effects of particles concentrations of NEPCM (0 wt%, 1 wt%, 3 wt%, 5 wt%), filling arrangements of metal foam (filling height, porosity gradient direction) and directions of magnetic field (left, right) are studied with emphasis on the heat transfer and energy storage characteristics including liquid fraction, energy stored and Nusselt number. The results show that comparing to pure PCM, the 3 wt% Al2O3 NEPCM maximizes the enhancement of melting performance for decreasing complete melting time as 29.32% and increasing energy storage as 0.26%. For partial porous filling, as the filling height increases, the melting rate firstly increases then decreases, but energy stored shows the opposite trend. The filling height of 3/4h is considered as the optimal filling height with 43.51% decreasing of complete melting time and only 6.81% decreasing of energy stored. For gradient porosity filling, positive gradient has faster melting rate (62.16% amplification), but negative gradient has less energy loss (only 6.30% reduction). Under a non-uniform magnetic field, the convection of magnetic NEPCM is greatly suppressed by the Kelvin force, with 6.76% and 19.59% increasing of complete melting time and 0.07% reduction and 2.45% growth of energy stored for left and right magnet cases, respectively.