This study focuses on the thermal and frictional entropy generation characteristics of phase change material (PCM) in a triplex tube latent heat storage unit which is a promising technique for thermal management of lithium-ion batteries. Four different wavy structures for the triplex tube heat exchanger with variable waviness are considered, namely Case 1 to 4. Regarding the numerical analysis, the variations in mean temperature and liquid fraction of PCM are first revealed and presented where the crossflow heat transfer fluid in the system is considered water. Furthermore, thermal and frictional entropy generation rates in local and global means are separately discussed for both charging and discharging processes. The results showed that the difference in mean temperature and melting rates among the cases are more noticeable at the end of the process due to intensified natural convection, and Case 3 has 240 s (12.3%) shorter melting time compared to Case 1 and 4. Although solidification rates have similar trends in all cases, the solidification time is different, e.g., it is 110 s (5.2%) shorter in Case 4, compared to Case 1. The entropy generation trends are relatively similar during the solidification, while they are noticeably different in the melting process due to effect of liquid PCM flow.
