You are designing an enclosure which houses a PCB. Mounted outside the enclosure on its top is a set of aluminum fins, as seen in the sketch below. The enclosure (and fins) are 150mm deep long. There is no forced airflow. Neglect the thickness of the enclosure walls. Neglect heat transfer out of the sides and bottom of the enclosure. If the PCB produces 4000 W/m2: a) Most industrial-grade ICs have a maximum temperature of 85oC. If you must keep your PCB below this what is the maximum thermal resistance from the PCB to the air surrounding the fins? Assume the air around the fins stays at room temperature. b) If the top of the enclosure (and bottom of the fin base) runs at 50°?, what is the effective thermal conductivity above the PCB? Hint: Because the air inside the enclosure is trapped and heats up, any air properties NOT given below are calculated at the average air temperature (T1+T2)/2. c) What is the temperature at the base of the fins?
You are designing an enclosure which houses a PCB. Mounted outside the enclosure on its top is a set of aluminum fins, as seen in the sketch below. The enclosure (and fins) are 150mm deep long. There is no forced airflow.
Neglect the thickness of the enclosure walls. Neglect heat transfer out of the sides and bottom of the enclosure.
If the PCB produces 4000 W/m2:
a) Most industrial-grade ICs have a maximum temperature of 85oC. If you must keep your PCB below this what is the maximum thermal resistance from the PCB to the air surrounding the fins? Assume the air around the fins stays at room temperature.
b) If the top of the enclosure (and bottom of the fin base) runs at 50°?, what is the effective thermal conductivity above the PCB? Hint: Because the air inside the enclosure is trapped and heats up, any air properties NOT given below are calculated at the average air temperature (T1+T2)/2.
c) What is the temperature at the base of the fins?
d) What is the efficiency of the fins?
e) What must the convection coefficient be to eliminate all of the heat? Ignore the area of the base.
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