Effects of segmentation in composite phase change material on melting/solidification performance of triplex-tube thermal energy storage systems

In this work, a numerical evaluation of the melting/solidification performance of phase change material (PCM) filled inside a triplex-tube latent heat storage unit has been carried out. To enhance the melting/solidification performance, the porous Cu metal foam (MF) was embedded inside PCM (termed as composite PCM). Alternative segments of pure PCM and composite PCM have been allocated in such a way that both the pure PCM and composite PCM occupy the equal annular area (i.e., equal volumes). Influence of increasing number of segments was delineated on the melting/solidification rate, complete melting time, and thermal energy storage/recovery enhancement. The comparisons were drawn with reference to the model having two segments of PCM and composite PCM. The results show that the model containing 64 segments with alternate allocations of PCM and composite PCM has a faster melting/solidification rate than other models. With 32 alternate segments of MF, the full melting/solidification time reduced by 23%/77% with respect to the case with one segment of MF only. The melting/solidification performance gets saturated beyond 32 segments (M-5) and negligible variation (only ~1%) in the thermal performance was noticed upon further segmentation. Finally, the model M-5 proved as the best model considering the aspects of augmented melting/solidification rate and associated complexities. Moreover, the heterogeneity of MF applied in 32-segment model confirmed that the anisotropic MF results in an increased melting rate and leads over other random isotropic distributions of MF.