# 7-28 A transformer that is 10-cm long, 6.2-cm wide, and 5-cm high is to be cooled by attaching a 10-cm x 6.2-cm-wide polished aluminum heat sink (emissivity = 0.03) to its top surface. The heat sink hasseven fins, which are 5-mm high, 2-mm thick, and 10-cm long. A fan blows air at 25°C parallel to the passages between the fins. The heat sinkheat sink is not to exceed 60°C. Assuming the fins and the base plate to be nearly isothermal and the radiation heat transfer to be negligible, determine the minimum free-stream velocity the fan needs tosupply to avoid overheating. Assume the flow is laminar over the entire finned surface of the transformer.to dissipate 12 W of heat, and the base temperature of theFIGURE P7-28Air25°C60°C-Fins0.5 cm10 cmTransformer5 cm12 W+6.2 cm -

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