In Figure (12), which represents the heat transfer rate during the solidification process over time, three distinct regions are observed. The first region witnesses a short, rapid increase in the heat transfer rate. This increase is attributed to the solidification of the adjusting PCM to the fin surfaces. The second region is characterized by a fast decrease in the heat transfer rate over time, as the solid PCM layer is generated, ultimately covering the fin surfaces. These first two regions correspond to stage one in the liquid fraction contour. Once the fin surfaces are fully covered by the solid PCM layer, the heat transfer rate decreases gradually over time due to the slow expansion of the solid PCM layer width.