An heat sink must dispose a thermal power of 325W keeping the base temperature at 75°C when the environment is at 25°C (

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An heat sink must dispose a thermal power of 325W keeping the
base temperature at 75°C when the environment is at 25°C (h=15
W·m-2 ·K). The heat sink base is 15x15 cm, the step is of 5 mm and
thickness of the fin is 1 mm. Verify if it’s convenient to use the
heat sink to dispose the thermal power and then calculate the
length of the heat sink if it’s made of brass (λ=105 W·m-1 ·K) and
then calculate its efficiency.