Role of Filling Patterns of Metal Foam in Shell-And-Tube Thermal Storage Tank: A Critical Review

The low thermal conductivity of phase change materials (PCMs) limits the charging and discharging rates of shell-and-tube latent heat thermal energy storage (LHTES) systems. This review examines metal-foam enhancement from a spatial and system-level perspective. PCM classifications and heat-transfer mechanisms of metal-foam/PCM composites are summarized, followed by a critical assessment of porosity, pore density, pore size, specific surface area, permeability, and matrix material. Shell-side, tube-side, bilateral, partial, graded, and hybrid filling strategies are compared with attention to conduction enhancement, natural convection, storage capacity, pressure loss, and material use. Representative studies show that copper foam can raise the effective conductivity of RT-82 from 0.2 to 1.88 W·m−1·K−1. Bilateral configurations reported in the reviewed studies reduce melting or charging time by 72.2% to 84.9% relative to their specified reference cases, while a graded shell-side configuration reduced charging time by 68.67%. Hybrid configurations can provide additional enhancement, but their effects are not necessarily additive. Cross-study comparisons are strongly dependent on PCM properties, geometry, boundary conditions, HTF conditions, and reference configurations. The review therefore emphasizes regime-dependent design rather than maximum conductivity alone. Partial and graded configurations are particularly promising for coordinating conductive pathways with natural-convection regions while reducing material and hydraulic penalties.