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 (w(1)/w(2)) significantly shortens the melting time while it has an insignificant effect on the solidification time.