Circuit hoards are mounted to interior vertical surfaces of a rectangular duct o

Question

Circuit hoards are mounted to interior vertical surfaces of a rectangular duct of height H = 400 mm and length L = 800 mm. Although the hoards arc cooled by forced convection heat transfer to air flowing through the duct, mil all of the heat dissipated by the electronic components is transferred to the flow Some of the heat is instead transferred by conduction to the vertical walls of the duct and then by natural convection and radiation to the ambient (atmospheric) air and surroundings. which arc at equivalent temperatures of T. 20 degree C. The walls are metallic and. to a first approximation, may be assumed to be isothermal at a temperature T Consider conditions for which the electronic components dissipate 200 W and air enters the duct at a flow rate of m = 0.015 kg/s and a temperature of T = 20 degree C. If the emissivity of the side walls is , = 0.15 and the outlet temperature of the air is T , = 30 degree C, what is the surface temperature T To reduce the temperature of the electronic components. it is desirable to enhance heat transfer from the side walls. Assuming no change in the air flow conditions, what is the effect on T, applying a high emissivity coating (epsilon, = 0.90) to the side walls? If there is a loss of air flow while power to be dissipated, what are the resulting values of T for epsilon = 0.15 and epsilon = 0.90?

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Circuit hoards are mounted to interior vertical surfaces of a rectangular duct o

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