Balancing power density and storage capacity in cryogenic energy storage: A dynamic optimization of nano-enhanced phase change materials

The efficient recovery of cryogenic exergy from liquefied natural gas regasification is critically constrained by supply intermittency and the poor thermal conductivity of conventional organic phase change materials. This study proposes a composite material enhanced by copper nanoparticles to bridge this mismatch. The transient solidification process is numerically resolved utilizing ANSYS Fluent 2025 R1. Adopting a governing framework based on the homogeneous nanofluid model, the Boussinesq approximation, and negligible particle sedimentation, rigorous simulations elucidate the competitive interplay between enhanced thermal transport and modified fluid dynamics. The investigation reveals that incorporating copper nanoparticles fundamentally alters the solidification regime. While increased viscosity suppresses natural convection, evidenced by a 27% reduction in the Rayleigh number, this hydrodynamic penalty is overwhelmingly counteracted by thermodynamic gains from enhanced thermal diffusivity. The composite exhibits superior cold penetration, lowering the core temperature by an additional 50% compared to pure PCMs during the intermediate stage of solidification. This mechanism shift reconfigures the phase interface from a parabolic shape driven by buoyancy to a uniform and nearly vertical profile, reducing the total solidification time by 13.6% relative to the baseline. Furthermore, a substantial nonlinear 17.6% gain in dynamic discharge power is quantified against a corresponding linear 8.1% penalty in storage capacity at the maximum evaluated boundary. To systematically resolve this conflicting relationship, a comprehensive figure of merit analysis definitively identifies a 5 wt% concentration as the global optimum, offering a definitive solution for highly responsive cryogenic energy storage.