Constrained melting around one hot cylinder inside a horizontal square cavity is inefficient from an energysaving viewpoint because of the elevated thermal stratification and sluggish advancement of the melting front at the bottom. The situation is exacerbated by the low thermal conductivity of the phase change materials (PCM). To overcome it, four hot cylinders instead of one cylinder are selected in the same cross-section area. Besides, the base PCM is mixed with the small volumetric concentration of the nanometer-sized Cu particles to enhance the melting rate. It has to be clarified in which array the NEPCM is the most effective way. However, increasing the dynamic viscosity of the base PCM using nanoparticles may have a negative effect on the speed of the natural convection flow. Finally, the metallic porous matrix with the thermal characteristics of the Nickel-Steel alloys is inserted in the base PCM to enhance the thermal conductivity and melting rate and to abate the full melting time. The weakening of the natural convection effect within the porous structure could be worthy of attention. The enthalpy-based lattice Boltzmann method (LBM) with a D2Q9-double distribution function (DDF) model at the REV scale is used to model the ice melting in the absence of the subcooling.
