Multiple-segment metal foam application in the shell-and-tube PCM thermal energy storage system

This study describes a new approach for heat-transfer enhancement in PCM-based shell-and-tube thermal energy storage systems by employing multiple-segment or cascaded metal foam. The principle is based on the fact that temperature gradient across the PCM during the phase change reduces significantly in the heat flow direction thus affecting the heat transfer rate and resulting in a poor overall storage performance. This study suggests using multiple-segment metal foam with porosity cascading in the heat flow direction so that a state closer to uniform temperature distribution can be achieved. A mathematical model that considers natural convection during charging and discharging of the system in addition to non-Darcy effects of the porous foam was developed and validated. The influence of using different cascading arrangements of the metal-foam on the evolution of the solid-liquid interfaces, distribution of isotherms and profile of the liquid fraction was investigated. The use of non-cascaded single-segment foam versus the use of cascaded multi-segment foam was also investigated and compared for the same system's volume usage. Results from the study show that energy storage and recovery times can be substantially shortened by foam cascading in the PCM/metal foam composite.