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The widespread application of phase change thermal storage systems is essential for reducing energy consumption and carbon emissions. In this study, a phase change thermal storage tank (PCTST) incorporating a double U-tube and filled with 53 semi-refined paraffin as the phase change material (PCM) is developed. An experimental platform equipped with axial and radial temperature sensors is constructed to investigate the influence of heat transfer fluid (HTF) inlet temperatures (67, 70, 73, 76, and 79 degrees C) on the PCTST' thermal performance. The results show an asymmetric phase interface, with faster melting observed at the center than at the edges, forming a frustum-shaped interface that is wider at the top and narrower at the bottom. At 79 degrees C, the melting time is reduced to 330 min, 56.0 % shorter than the 750 min recorded at 67 degrees C. The movement rate of the valley points of the interface increases by 73.2 %. The final average temperature response exhibits nonlinearity across the tested inlet temperatures, with values of 61.9, 64.7, 66.7, 68.4, and 71.0 degrees C, respectively. Additionally, the radial average temperature difference decreases from 0.5 degrees C to 0.1 degrees C. These findings provide valuable experimental data for optimizing the structure and operating parameters of large-scale PCTSTs.