Numerical simulation of effective thermal conductivity and pore-scale melting process of PCMs in foam metals

Different foam metals combined with paraffin and other materials were analyzed to determine their effective thermal conductivity and the macroscopic thermophysical properties of the composite materials. A W-P model composed of six tetrakaidecahedrons and two irregular dodecahedrons was used to simulate the melting heat transfer process in open foam metal at pore-scale under constant temperature. The results show that the porosity and conductivity of the foam metal and the conductivity of the phase change material (PCM) have a significant influence on the effective thermal conductivity of the composite PCM, while the pore size has no obvious influence. The effective thermal conductivity of composite PCMs increased with increasing foam metal thermal conductivity, and increased more rapidly with lower foam metal porosity. The effective thermal conductivity of composite PCMs is related to the ratio of foam metal conductivity to PCM conductivity. The microstructure of the foam metal had an obvious effect on the solid-liquid phase distribution during the PCM melting process, where the heat was transferred mainly through the melted liquid PCM field. Conduction was the dominant heat transfer mechanism, and natural convection in the liquid PCM was weak for the confinement of foam metals. For heat transfer during the PCM melting process, conduction through the skeleton of the porous metal played the most important role. The PCM adjacent to the heating source and foam metal frame melted first, with the fusion zone gradually spreading to the pore center. The melting rate of the PCM increased with increasing boundary temperature and thermal conductivity of the foam metal, but decreased as foam metal porosity increased. During the melting process, the liquid phase fraction did not linearly grow with time; the melting rate was very large at the initial stage, but decreased gradually with time.