Unidirectional freezing of phase change materials saturated in open-cell metal foams

An experimental and theoretical study of the unidirectional freezing of water as a PCM filled in metal foams has been carried out. Particular concern is placed upon determining how the contact conditions between the metal foam and the cold wall influence the freezing process, as well as exploring the local thermal equilibrium between the metal foam and the PCM. To address these questions, three contact conditions were considered, i.e., natural contact, applied pressure, and bonding with a high thermal conductivity adhesive. To explore the local thermal equilibrium, temperatures on foam ligaments and within the pores were measured individually using thermocouples. For the current copper foam/water PCM system, the three different contact conditions were found to have similar freezing rate. This indicates that in practice one can simply embed metal foam blocks into PCMs with no need of bonding them to the cold wall via sintering, thermal adhesive or other methods, thereby reducing the costs of devices in thermal energy storage systems. Effects of foam properties, including porosity and pore density on the freezing rate, were also discussed.