Thermal performance augmentation of metal foam infused phase change material using a partial filling strategy: An evaluation for fill height ratio and porosity

Infusion of a metal foam in a phase change material (PCM) used for a latent heat thermal energy storage (LHTES) system significantly improves the melting performance. The presence of metal foam in PCM, however, suppresses the natural convective transport, increases the cost, and depletes the TES capacity. An optimum thermal conductivity enhancer (TCE) density strategy is developed in the present study to determine the effective metal foam distribution and concentration. The primary objective of the strategy is the local installation of the metal foam mass at the high-temperature gradients region (high thermal potential) and elimination of the same at the region of low-temperature gradients (lower thermal potential) for the efficient use of the metal foam. Thus, the melting performance of the various fill height ratios (i.e. 0.25H, 0.5H, and 0.75H) and the metal foam porosities (0.97, 0.95, 0.92, and 0.90) are studied and comprehensively compared. To accomplish this, an in-house numerical code is developed using an enthalpy porosity approach supplemented with the local thermal non-equilibrium (LTNE) technique. Results show that the incorporation of the metal foam-PCM composite (MFPC) only at the lower portion of the enclosure enhances the total thermal transport. Further, the metal foam with the full height (H) and 0.75H require nearly the same total melting time and show that the total melting time increases as the fill height ratio further decreases. The influence of varying the porosities with the fixed fill height ratio of metal foam shows that if the porosity decreases, the total melting time decreases with a penalty of less TES capacity. By means of economic assessment, it is recommended that if the economy and TES capacity are major concerns of the thermal performance, a high porosity metal foam should be chosen with a compromise on the total melting time. Similarly, the LHTES systems targeting the higher melting rate can be designed with a low porosity metal foam, which increases the cost and reduces the TES capacity.