Mina Mirparizi
Cold thermal energy storage systems are widely employed in refrigeration, food preservation, and thermal management applications; however, their performance is often constrained by the inherently low thermal conductivity of phase change materials (PCMs), which limits the rate of solidification.Improving heat transfer during the freezing process therefore remains a central issue in the design of efficient storage systems.The present work examines the solidification behavior within a cold energy storage unit featuring a non-conventional container geometry with an elliptical cooling wall.Two enhancement strategies are considered in combination: the dispersion of a ternary nanoparticle mixture (TiO 2 -Ag-Al 2 O 3 ) in the base fluid at a volume fraction of 0.015%, and the incorporation of a metal foam structure to promote conductive heat transfer.A transient numerical model is established using a Galerkin-based finite element approach with adaptive mesh refinement to accurately capture the evolution of the solid-liquid interface.The results indicate that the addition of ternary nanoparticles leads to a reduction in total freezing time of approximately 13.12%, while the introduction of metal foam yields a substantially greater reduction of 82.35%.When both techniques are applied simultaneously, the freezing time decreases by 84.66%, demonstrating a clear synergistic effect.A comparative analysis further shows that the influence of foam porosity on the advancement of the solidification front is approximately 6.27 times greater than that of nanoparticle concentration.These findings suggest that structural enhancement through porous media plays a dominant role in accelerating heat transfer, and that prioritizing internal thermal pathways offers a more effective design strategy than relying solely on modifications of fluid properties.The results provide a quantitative basis for the development of high-efficiency cold energy storage systems in engineering applications.