Thermal response of annuli filled with metal foam for thermal energy storage: An experimental study

Latent heat thermal energy storage is a practical way to solve the intermittent of solar energy. However, the inherent low thermal conductivity of phase change materials (PCMs) hampers their widely-used applications. In this study, a visual experiment test rig was designed to investigate the effect of open-cell metal foam embedded into paraffin (PCM) on the thermal response of a shell-and-tube unit during charging process. High temperature water, selected as heat transfer fluid (HTF), was injected from top of copper tube. The evolution of solid-liquid interface in inside and outside views was captured and recorded by a high-definition camera. 3D interface model was reconstructed based on these interface images and melting fraction was thus calculated. T type thermocouples were arranged separately on the radial and axial positions inside the PCM. Heat transfer annuli filled with PCM and composite PCM were tested under different HTF injection velocities. Experimental results demonstrated that the involvement of open-cell metal foam can dramatically enhance the efficiency of thermal energy storage. Compared with pure PCM, the full melting time of composite PCM was reduced by 64%, and the temperature distribution was more uniformity. Increasing the injection velocities of HTF made little contribution to promoting charging process of two samples.