A transformer that is L=20cm long, 6.2 cm wide, and 5 cm high is to be cooled by attaching a 10 cm × 6.2 cm wide polished aluminum heat sink (emissivity =0.03) to its top surface. The heat sink has seven 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 sink is to dissipate 20 W of heat and the base temperature of the heat 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 to supply to avoid overheating. (k=0.02681W/m˚C, Pr=0.7248, V= 1.726×10-5 m2 /s, )
A transformer that is L=20cm long, 6.2 cm wide, and 5 cm high is to be
cooled by attaching a 10 cm × 6.2 cm wide polished aluminum heat
sink (emissivity =0.03) to its top surface. The heat sink has seven 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 sink is to
dissipate 20 W of heat and the base temperature of the heat 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 to supply to avoid
overheating. (k=0.02681W/m˚C, Pr=0.7248, V= 1.726×10-5 m2
/s, )
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