Experimental study on the solidification and melting performances of magnetic NEPCMs composited with optimized filling metal foam in a uniform magnetic field

The present study experimentally investigates the magnetic nano-enhanced phase change material (NEPCM) filled with different strategies of metal foam in a uniform magnetic field for the solidification and melting processes. The thermochromic liquid crystals (TLC) technology is used to evaluate, compare and analyze the effects of magnetic field, partial filling (H = 0 h, 1/4h, 2/4h, 3/4h, 4/4h) and gradient porosity (positive and negative). The evolution of phase change interface, the temperature distributions and differences, solidification/ melting rate, energy released/stored, and Nusselt number are comprehensively analyzed. The results show that the magnetic field inhibits convection but accelerates local heat transfer by the Kelvin force. As the porous filling height increases, the solidification rate and energy released increase firstly and then decrease. Comparing to pure PCM, the H = 3/4h case has the excellent solidification performance for 2.08 times increase and energy released for 40.22% improvement. The melting rate is advanced with the growth of filling height, but the energy storage capacity gradually decreases. In terms of heat transfer performance, the positive gradient porosity case owns best temperature uniformity and fastest phase change rate. Compared with pure PCM, its solidification rate and energy released are increased by 4.30 times and 36.7%, and melting time is reduced by 64.29%, but the energy stored is lost by 16.44%. As for the energy storage, the negative gradient porosity case can release and store more energy at the same time as maintaining high heat transfer performance.