Synergistic enhancement of D-Mannitol solidification using hybrid nanoparticles and wavy spine-crossbar fins in a cylindrical latent heat storage unit

Latent heat thermal energy storage systems play a pivotal role in enhancing the efficiency and reliability of solar thermal technologies, particularly under conditions of intermittent solar availability. However, the low thermal conductivity of conventional phase change materials (PCMs) limits their charging and discharging rates. In this study, a hybrid nano-enhanced D-Mannitol PCM is integrated with geometrically optimized wavy spine-crossbar fins to improve solidification performance in a concentric cylindrical enclosure. Three-dimensional simulations were performed using ANSYS Fluent, employing the enthalpy-porosity method to model the solid–liquid phase transition. The outer cylindrical wall was idealized as a constant-temperature boundary at 303 K, acting as a cold sink to ensure controlled radial heat removal, while the top and bottom surfaces were treated as adiabatic to suppress axial heat losses, and thermal interactions with the external environment were neglected. The numerical framework was validated against experimental data reported in the literature, confirming the reliability of the predictions. A parametric analysis was conducted to examine the combined influence of fin geometry, fin number, and hybrid nanoparticle concentration on solidification dynamics. Results indicate that increasing fin count and adopting increasing-width fins substantially enhance radial heat conduction and accelerate solidification. The four-fin increasing-width (FFIW) configuration with 6% TiO2+SWCNT yielded the maximum improvement, achieving a 36.84% reduction in solidification time and an 12.04% decrease in PCM temperature compared to the baseline case. Consistent performance improvements were also observed across other nanoparticle types and volume fractions, confirming the robustness and general applicability of the proposed strategy. Although the computational domain corresponds to a laboratory-scale enclosure, the proposed methodology and findings provide scalable insights that are highly relevant to the design of large-scale solar thermal energy storage systems.