Dynamic regulation of the photothermal conversion performances of nano-enhanced phase change material composited with ceramic foam subjected to external fields

This study aims to comparatively analyze the melting characteristics of magnetic Fe₃O₄ nano-enhanced phase change materials (NEPCM) assisted by optimum filling strategies of Al₂O₃ foam ceramics, ultrasonic field and magnetic field under solar radiation. A visualization experimental platform consisting of an ultrasonic field, a magnetic field, and infrared thermography is constructed and used to evaluate in detail the evolution of the melting front, the temperature distribution, and the heat transfer mechanism under different experimental conditions in a square cavity. The results show that the 1 wt% NEPCM using an ultrasonic field has the highest solar energy conversion efficiency of 39.99 % among the 18 experimental groups. This suggests that the cavitation effect and acoustic flow effect induced by ultrasound with a power of 40 W periodic ultrasonic mechanical vibration improve the uniformity of the distribution of magnetic nanoparticles, resulting in improved heat transfer properties. In the experimental group where a magnetic field is applied, the downward movement of the melting interface is accelerated due to the force of the magnetic field on the Fe₃O₄ nanoparticle. Under the effect of localized porous filling, the solar conversion efficiency of 1 wt% NEPCM is 31.57 % and the total energy storage is as high as 14.39 kJ. With the increase of concentration, the solar conversion efficiency and total energy storage decrease gradually. However, under the simultaneous effect of magnetic field and localized porous filling, the solar conversion efficiency and energy storage show an opposite trend. From a comprehensive point of view, the application of periodic ultrasound with a power of 40 W can effectively improve the photothermal conversion capacity of the PCM.