Melting and solidification of PCM in a tube-in-shell unit: Effect of fin edge lengths' ratio

•Effect of the fin edge length's rate ratio on the thermal performance of a shell-in-tube unit is investigated.•Melting time can be shortened by 21% as the fin edge lengths’ ratio decreased from 1 to 0.•The fins with the edge lengths’ ratio of 0 shows the best melting performance.•The fin edge lengths’ ratio has an insignificant effect on the solidification time.•Increasing the inlet temperature from 75 to 80 °C decreased the total melting time approximately by 23%. In this study, melting (charge) and solidification (discharge) characteristics of a phase change material (PCM) in a vertical annular gap between a heat transfer tube and a shell are investigated experimentally. Different heat transfer tube surface configurations as finless tube and finned tube are considered in order to optimize the thermal performance of the system. Fin geometries with various edge lengths’ ratios (upper edge length / lower edge length) are examined for different inlet fluid temperatures. For each configuration tested, transient temperature variations at some radial and axial points inside PCM are obtained. For the finless tube case, natural convection recirculation is obtained to be weak in the lower half region of the annulus when compared to that in the upper half. Results show that adding a conducting fin to the inner tube intensifies the recirculation in the lower half region of the annular space. Accordingly, it is disclosed that decreasing the fin edge lengths’ ratio (w1/w2) significantly shortens the melting time while it has an insignificant effect on the solidification time.