Thread: Fan on Heatsink
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  #9  
Old 28-11-2009, 11:52 AM
Menthu Rae
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Menthu Rae is offline
 
Join Date: Nov 2009
Location: Sydney, Australia
Posts: 6
I'm no expert, but I'm an engineering student and have completed a subject on thermodynamics and turbomachines...

You're dealing with an axial fan most likely - which causes negligible (if any) compression of air, as a result, PV = NRT doesn't apply...

What does apply is the thermodynamics of forced convection cooling. Without going into specifics and formulae, in general the effect of "blowing" or "sucking" air onto or from a heatsink will depend on the design of the heatsink, the volumetric flow rate of the fan and the ambient environment (including the enclosure) the heatsink is operating in.

Are you able to post any pictures of the setup? If you can then perhaps we can see why in your case sucking the air from the heatsink yields better heat transfer results than blowing.

Quote:
Originally Posted by mithrandir View Post
I guess blowing causes reduced cooling because they are being compressed and compressed gasses get hot. Sucked gasses provide additional cooling via expansion into the space left by the extracted gasses.

Boyle's Law + Charles' Law + Gay-Lussac's Law at work? PV=kT

Pressure x Volume = Konstant x Temperature
Quote:
Originally Posted by leon View Post
Don't quite know what all that means Andrew, but i expect your are right.

I tested it again today, and it proved right again, with extraction it cooled quicker and the temp went down from 21.5 degrees to 5.3 in five minutes.

Leon
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