Investigating the Synergistic Effects of Multi-Layered Porous Media and Multi-Phase Change Materials on Thermal Energy Storage Performance

• Cascaded PCMs (RT-65, RT-60, RT-55) improved melting time by 17% but reduced stored energy by 9%. • Using metal foams enhanced charging time by two orders of magnitude, significantly improving thermal response. • Gradient-increasing porosity with multiple PCMs achieved the best balance between charging time and stored energy. • Among tested PCMs, RT-55 provided the highest stored energy and shortest melting time. • Porous media reduced convection effects, making conduction the dominant heat transfer mechanism in PCM melting. This investigation explores the enhancement of thermal efficiency in concentric shell and tube thermal energy storage systems using multiple phase change materials (PCMs) and layered porous media. The investigation is done numerically to evaluate the impacts of the mentioned techniques on stored energy and melting time. Among the three PCMs (RT-65, RT-60, and RT-55), reservoirs with RT-55 showed higher stored energy and shorter melting times. Six arrangements of these PCMs were tested as multiple PCMs, revealing that cascaded PCMs improve melting times but reduce energy storage. For instance, the 65-60-55 arrangement reduced melting time by 17% but stored 9% less thermal energy compared to using only RT-55. The addition of porous media, particularly with varying porosities, significantly enhanced charging time by about two orders of magnitude. Various arrangements of porous media (stepwise/gradient increasing/decreasing porosity in the radial direction) with single/multiple PCMs were examined. The multi-increasing configuration (gradient-increasing porosity with multiple PCMs) and the single-90-94-98 configuration (only RT-55 with stepwise increasing porosity) exhibited optimal conditions for minimizing charging time while maximizing stored energy.