Influence of metal foam morphology on phase change process under temporal thermal load

Abstract

Variable morphology metal foams, embedded in phase change materials (PCMs), enhance heat transfer performance without sacrificing the volume available for the PCM. The present study is a numerical investigation of the effect of aluminum metal foam, having varying morphology, on the unidirectional melting process of n-octadecane under pulsating heat flux boundary condition. The interdependencies of metal foam morphology, mean porosity, pulse duration, average heat flux, and system size on the progress of melt fraction and isoflux surface temperature are studied. The effect of two graded and one uniform metal foam morphologies, three pulses, two average wall heat fluxes, two system sizes, and five different mean porosities are analyzed. The positive gradient of metal foam porosity (i.e., the increase in the porosity with distance from the isoflux surface) limits the increase in the surface temperature by more than 15 °C when compared with the uniform metal foam. As well as, graded metal foam reduces temperature fluctuation under pulse heating load by more than 20%. However, the positive gradient of metal foam has adverse effects on the overall melting time. The effect of metal foam morphology on heat transfer is observed to increase with the average heat flux, system size, and mean porosity of metal foams. In the presence of heating from the top, as discussed in the present study, melting processes are driven by heat conduction due to the limited presence of advection. Therefore, the significance of enhancement in effective thermal conductivity is higher in the presence of isoflux boundary on the top surface.