For D@ Br@b($)!'s entertainment:
Case fans are rated at ½ to 2½ mm of water column. I estimated that a 2 meter chimney at 60 °C inside and 25 °C outside would produce only ¼ mm of water column (0.25 kg/m²) before frictional losses. Flow rate is proportional to the square root of the pressure difference, so it's at best only 70% as good as a low-rpm nearly-silent fan. On the other hand, the chimney would add cooling that is four to eight times as good as the case by itself. That's a significant difference, even if it may not be sufficient.
http://www.engineeringtoolbox.com/air-p ... d_156.html
Specific heat of dry air at 60 °C is 1009 J per kg per °C. If we're heating the air from 25 °C to 60 °C and we're dissipating 100 watts = 100 joules per second, then we need air flow:
m dot = q dot ÷ Cp ÷ delta T
100 J/s ÷ 1009 J/kg°C ÷ (60-25) °C = 0.0028 kg/s x 60 s/min x 60 min/hr = 10.2 kg/hr ÷ 1.067 kg/m3 = 9.6 m3/hr = 5.6 ft3/min
I believe that this is doable with a 4" (DIN100) pipe with less than the 0.0003 psi of pressure difference that we have available.
