Melting and energy storage performance enhancement of rectangular cavity with metal foam by nano-PCM and recessed/protruding dimpled fin wall

Abstract

In this study, the melting and energy storage performance of a rectangular Latent Heat Thermal Energy Storage (LHTES) system containing a single wall recessed/protruding structure filled with fully metal foam (MF) was numerically analyzed under time-dependent natural convection conditions. A phase change material (PCM) enriched with Al₂O₃ nanoparticles at φ_vol.=1.0 and 5.0% volumetric concentrations was used in the system. Three different dimpled fins (DFs) geometries (spherical, square, and elliptical) were integrated into the recessed/protruding wall. This wall was kept at a constant temperature of T_wall=350 K, which exceeds the melting point of PCM, to ensure phase change. The governing equations were solved using the Brinkman-Forchheimer extended Darcy model, which includes the assumption of local thermal equilibrium (LTE) between PCM and MF. A numerical model based on the finite volume method (FVM) was developed and the enthalpy-porosity approach was used to analyze the melting process. A detailed comparative analysis of the performance improvement applications was performed within their categories and among themselves. The results were evaluated using the graphs and contours of the liquid fraction (β), temperature distribution, streamlines, Nusselt number (Nu), and energy storage parameters. It was observed that the incorporation of nano-PCM and DF significantly accelerated the melting process. The fastest melting was achieved using φ_vol.=5.0% and square DF. In particular, Al₂O₃ at φ_vol.=5.0% reduced the melting time by 4.0% due to providing a significant increment in thermal conductivity, while square DF led to a 21.0% reduction. However, increased thermal conductivity had an adverse effect on the time-dependent average Nu. It was further noted that the rise in φ_vol. within the PCM negatively impacted the stored energy. At the final stage of the melting process (t=750s), the PCM retained 5748.3 kJ.m⁻¹ of energy, which represented a 0.20% and 1.02% increase compared to the nano-PCM with φ_vol.=1.0% and 5.0%, respectively. Moreover, the geometry of the DFs considerably influenced the energy storage capacity, with square DFs showing an 3.20% improvement compared to finless configurations. In comparison, the spherical and elliptical DFs demonstrated increases of 2.71% and 1.37%, respectively. When applying φ_vol.=5.0% nano-PCM in square DF LHTES, the melting time was reduced by 24.5% compared to the finless case including PCM. However, the square DF case with PCM achieved the highest energy level among all configurations, reaching 5932.4 kJ.m⁻¹. This value represents a 3.20% increase over the finless PCM and a 3.01% increase over the square DF configuration with φ_vol.=5.0% nano-PCM.