Enhanced thermal storage performance with non-linear porosity distribution in copper foam-PCM composites

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Phase change materials (PCMs) are increasingly utilized in thermal energy storage systems due to their high energy density and capability to maintain a constant temperature during phase transitions. However, the low thermal conductivity of PCMs poses a significant challenge, often mitigated by embedding PCMs within high-conductivity metal foams. While linear and layered porosity distributions in metal foams have been extensively studied, the potential benefits of non-linear porosity distributions remain underexplored. This study aims to bridge this gap by numerically investigating the effects of non-linear porosity distributions of copper foam on the melting behavior and thermal performance of palmitic acid. The paper thoroughly explains how different melting regimes influence the optimal choice of porosity distribution. Using the Enthalpy-Porosity approach and the Local Thermal Non-Equilibrium model, various positive and negative porosity gradients in both x and y directions were examined. The results demonstrate that positive porosity gradients significantly improve the melting rate and energy storage performance. Specifically, a positive gradient in the x-direction reduced the melting time by 10.4 %, while a positive gradient in the y-direction achieved a 16.74 % reduction compared to uniform porosity configuration. Building on these findings, the study then explores two-dimensional (2D) porosity distribution optimization, leading to further enhancements. The optimized 2D configuration achieved a 22.67 % reduction in melting time and a 32.38 % increase in the average energy storage rate compared to the uniform porosity scenario.