Melting of Phase Change Materials With Volume Change in Metal Foams

Melting of phase change materials (PCMs) embedded in metal foams is investigated. The two-temperature model developed accounts for volume change in the PCM upon melting. Volume-averaged mass and momentum equations are solved, with the Brinkman-Forchheimer extension to Darcy's law employed to model the porous-medium resistance. Local thermal equilibrium does not hold due to the large difference in thermal diffusivity between the metal foam and the PCM. Therefore, a two-temperature approach is adopted, with the heat transfer between the metal foam and the PCM being coupled by means of an interstitial Nusselt number. The enthalpy method is applied to account for phase change. The governing equations are solved using a finite-volume approach. Effects of volume shrinkage/expansion are considered for different interstitial heat transfer rates between the foam and PCM. The detailed behavior of the melting region as a function of buoyancy-driven convection and interstitial Nusselt number is analyzed. For strong interstitial heat transfer, the melting region is significantly reduced in extent and the melting process is greatly enhanced as is heat transfer from the wall; the converse applies for weak interstitial heat transfer. The melting process at a low interstitial Nusselt number is significantly influenced by melt convection, while the behavior is dominated by conduction at high interstitial Nusselt numbers. Volume shrinkage/expansion due to phase change induces an added flow, which affects the PCM melting rate.