The effectiveness of extended surfaces on a horizontal, cylindrical heat source/sink was studied experimentally during solid-liquid phase change heat transfer. Melting and freezing experiments were performed in a test cell suitable for photographic and shadowgraphic observations using a circular cylinder with three rectangular fins parallel to the axis and evenly distributed around the circumference of the heat exchanger. Results are reported for n-heptadecane as the phase change material. Orientation of fins on the heat exchanger with respect to the gravitational field are found to have more influence on the melting than on the freezing processes. The use of fins was found to be more effective for melting than for freezing. The instantaneous local and circumferentially averaged heat transfer coefficients at the heat source surface for melting from a cylinder with fins were usually within ±20 percent of those for melting from a bare cylinder. During solidification the degree of heat transfer enhancement due to finning is greatest when the frozen layer is thin and decreases as the layer grows thicker.

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