Microstructural insights into the crystallinity and dispersion of copper oxide functionalized carbon nanofibers in paraffin composites for numerically simulated shell-and-tube thermal energy storage

Abstract

To overcome the poor interfacial bonding and irregular crystallinity arising from the separate mixing of different nanofillers in phase change materials (PCMs), CuO-functionalized activated carbon nanofiber (CuO-ACnF)reinforced paraffin wax composites were developed to promote heterogeneous nucleation and enhance thermophysical properties. The PCM composites were integrated into a shell-and-tube latent heat thermal energy storage (LHTES) system, with experimentally measured properties coupled to computational fluid dynamics and non-dimensional analyses to quantify conduction, convection, and phase transition during melting and solidification, enabling comparison of their energy storage and discharge capacities. CuO-ACnFs promoted filler-matrix interfacial bonding and heterogeneous nucleation, increasing thermal conductivity by 45.1 % and yielding a peak latent heat of 149.6 J/g for the composite with 3 wt% of the nanofiller. This balance of thermal conductivity, viscosity, and crystallinity increased the energy storage capacity by 26 % during melting and energy released by 25 % during solidification relative to those of paraffin wax. Unified correlations based on Fourier, Stefan, and Rayleigh numbers generalized phase change kinetics, decoupling material-specific effects from system-level thermal behavior. This study established an experimentally validated framework for engineering nanostructured phase change materials, optimizing material design to achieve high LHTES performance.