Experimental Investigations of the Effect of Ultrasonic Waves on the Thermal Performance of Nanoparticles Embedded Phase Change Material

Ultrasonication is the technique generally employed to break the agglomerated nanoparticles while synthesising nano-phase change material (PCM) composites. However, the particles tend to agglomerate when the composites undergo thermal cycling due to the absence of ultrasonication during the operation of energy storage systems. Ultrasonication using power ultrasonic waves is also found to be effective in enhancing the heat transfer rate. From this perspective, the primary objective of this research is to investigate the effect of ultrasonication on the particle agglomeration and heat transfer performance of nanoparticle-embedded PCMs during the charging and discharging processes. The melting and solidification experiments are carried out on Cu nanoparticles embedded-paraffin wax of 0.5 wt%, 1 wt%, 2 wt% and 3 wt% in a shell and tube module provided with two ultrasonic transducers at the bottom face for generating power ultrasonic waves. The results indicate that power ultrasound can minimize particle agglomeration and enhance the phase change rates. As compared to the system without ultrasonication, the melting time is reduced by a maximum of 30 %, whereas it is an 18 % reduction in solidification time. Although the melting rate increases with particle fraction, enhancement in solidification rate is observed only up to 2 wt% as the solidification time of the 3 wt% nano-PCM composite is greater than that of the 2 wt% nano-PCM composites. The effect of ultrasound on phase change is pronounced only during the natural convection domination period. Hence, optimization of the activation time and period of ultrasound is recommended.