Phase-change systems remain to be widely used for storage of thermal energy such as the energy harnessed by solar collectors. The major disadvantage of phase change materials (PCMs) is their low thermal conductivities, which drastically slows the phase change process and causes wide temperature variations within PCMs, while requiring heat transfer area. Metal foams are one class of porous media that possess thermal conductivities that are an order of magnitude higher than PCMs. When embedded in PCMs, the random internal structure and high porosity of metal foam enhance and accelerate the phase change process without significantly reducing PCMs’ heat storage capacity. Unlike traditional PCM systems, the distribution of the foam ligaments in PCMs makes the melting and solidification processes uniform and less dependent on location inside PCMs. This also leads to shorter charging and discharging times. The design, fabrication and characterization of a small PCM-metal-foam thermal storage system are described in this paper. The core of the system is a cylindrical shell composed of 90%-porous open-cell aluminum foam filled with Paraffin-based PCM. The foam occupies only 10% of the total volume. The shell walls were fabricated from copper. The system was tested in an open loop wind tunnel. Results for the convection heat transfer coefficient and the effect of volumetric flow rate on the system’s performance were obtained. The heat transfer rate from the system was computed and discussed.
Microlayered flow structure around an acoustically levitated droplet under a phase-change process
