Question: A 12-cm-high and 20-cm-wide circuit board houses 100 closely spaced logic chips on its surface, each dissipating 0.05W. The board is cooled by a fan that blows air over the hot surface of the board at 35°C at a velocity of 0.5 m/s. The heat transfer from the back surface of the board is negligible. Determine the average temperature on the surface of the circuit board assuming the air flows vertically upward along the 12-cm-long side by
(a) ignoring natural convection and
(b) considering the contribution of natural convection.
Disregard any heat transfer by radiation. Evaluate air properties at a film temperature of 47.5°C and 1 atm pressure. Is this a good assumption?