Metal wool is an emerging heat-transfer enhancer to improve the power density of thermal energy storage (TES) systems using phase change materials (PCMs). Previous experimental studies showed that metal wools can be placed in different ways and positions into TES tanks. Therefore, measuring the effective thermal conductivity of a metal wool-loaded PCM matrix is essential for determining the direction of maximum thermal-conductivity enhancement, given the anisotropic nature of metal wools. Most existing studies report the effective thermal conductivity of such matrices through steady-state measurements in TES tanks. This study uniquely assesses the effective thermal conductivity of a metal wool-loaded PCM matrix in all three axial directions of the samples. Copper and stainless-steel 434 are the metal wools, while n-octadecane and sodium nitrate are the PCMs examined in this study. Various metal wool-loaded PCM matrix samples were developed by varying the metal wool weight fraction in the PCM. Incorporating 20 wt% stainless-steel metal wool into the PCM enhances the effective thermal conductivity by 55% to 90% along all three axial directions compared to the bulk PCM. A maximum enhancement of 649% was observed for the copper metal wool-loaded n-octadecane matrix samples, along the direction aligned with the metal wool fibres. Results demonstrate that the anisotropic characteristics of metal wool become relevant when assessing the effective thermal conductivity of a metal wool-loaded PCM matrix, especially for PCM loaded with high thermal conductivity metal wool. Conclusions from this study also support the numerical simulation of TES systems, enabling more precise modelling for real-world applications. • Influence of metal wool on the PCM effective thermal conductivity was assessed. • Effective thermal conductivity was measured in all three directions of the samples. • Cu metal wool addition improved PCM effective thermal conductivity compared to SS. • Cu metal wool anisotropic nature became evident with increased addition to PCM. • A maximum of 649% enhancement was observed for the Cu n-octadecane PCM matrix.
López-Román et al. (Fri,) studied this question.