Multi-scale experimental analysis on the coupled effects of ultrasonic field and magnetic field on the melting and energy storage performances for hybrid nano-enhanced phase change materials

This study experimentally investigates the coupled effect of ultrasonic field and magnetic field on the melting performance of magnetic (Fe3O4) and non-magnetic (Al2O3) HNEPCM by means of infrared thermography and EDS element identification. A visualization platform is built to evaluate the interconnections between the dynamic evolution of melting fronts, heat transfer mechanisms and phase change performances of HNEPCM subjected to different external field strategies. The results demonstrate that the ultrasonic field allows the activation of the flow heat transfer process in the liquid region through cavitation and acoustic flow effects, enabling more homogeneous nanoparticle dispersion and greater heat transfer efficiency. Moreover, the more ultrasonic power is applied, the shorter the phase change process takes place, which is reduced by 10.18 %, 57.52 %, 66.37 %, 72.13 % for 0 W, 16 W, 32 W, 48 W, respectively, comparing to pure PCM case. Magnetic field actively regulates the distribution of magnetic and non-magnetic nanoparticles at the melting front, forming nanoparticle "thermal conduction layer" and reducing non-Newtonian effect. The coupled effect draws on their characteristics, the heat transfer performance is enhanced in the early stage but suppressed in the later stage compared with 16 W ultrasonic field case. In comparison with pure PCM, the melting time is reduced by 52.2 % and TES efficiency is improved by 72.7 %. From the comprehensive point of view, although the coupled effect owns great potentials in controllability, the 48 W middle ultrasonic strategy harvest the greatest improvement with the exceptional heat transfer capability.