Nonuniform concentrated nanoparticles enhancing melting of phase change materials in vertical shell-tube storage unit with annular fins

The nonuniform melting of phase change materials (PCM) in the widely used vertical shell-tube storage unit can significantly affect the thermal performance. To address this issue, the hybrid fins and nanoparticles is proposed in this study. With the employment of half-fins and full-fins, nanoparticles were dispersed uniformly and non-uniformly in different regions in the storage unit, respectively. Numerical method was developed to analyze the melting behaviors. The melting front, temperature and velocity distributions, as well as variations of liquid fraction, stored energy and uniformity index were examined. Results show that using full-fins decreases the bottom region heat runoff induced by the natural convection, and the nanoparticles with increasing concen-tration in the gravity direction enhances the heat conduction of the bottom region. A 23.8 % reduction of melting time is achieved with the nanoparticles concentration of 2.0 (top region)-4.0 (middle region)-6.0 vol% (bottom region). The enhancement potential of this design increases with the increase of nanoparticles concentration and decrease of PCM thickness. Furthermore, an optimized nanoparticles concentration of 3.5-2.0-6.5 vol% is rec-ommended, which reduces the melting time by 29.8 % and improve the melting rate uniformity by 94.0 %.

Automated summary

This study proposes a solution with hybrid fins and nanoparticles to address the nonuniform melting issue of PCM in the widely used vertical shell-tube storage unit, which significantly affects the thermal performance. By using half-fins and full-fins, nanoparticles are dispersed uniformly and non-uniformly in different regions of the storage unit. Numerical analysis reveals that using full-fins reduces heat runoff in the bottom region and increasing nanoparticles concentration enhances heat conduction. An optimized nanoparticles concentration of 3.5-2.0-6.5 vol% reduces melting time by 29.8% and improves melting rate uniformity by 94.0%.