[Tfug] Cooling

[Patrick P]

 I usually mount one fan blowing out and one blowing in to create airflow.

> Date: Sat, 24 Nov 2007 10:05:21 -0800
> From: bexley401 at yahoo.com
> To: tfug at tfug.org
> Subject: [Tfug] Cooling
> 
> Hi,
> 
> I suspect this one is a bit harder to get a
> *definitive* answer -- in the general case.   :<
> *But*, who knows, maybe somebody out there
> actually *does* this sort of thing for a living!
> 
> I had to replace the fan in one of my tape
> drives (noisey).  Of course, fans exhibit
> *loads* of symmetry (i.e., there are 8 ways
> you can mount one -- though, ralistically, the
> choices boil down to exactly TWO!)  So, since
> I didn't make a deliberate note of the original
> fan's orientation, I had to think this one
> through...
> 
> Fortunately, the fan had a filter on it -- which
> makes the choice easy (you don't need to filter
> EXHAUST air)!  So, the fan should be oriented to
> blow air *into* the enclosure.
> 
> This makes sense for a tape device since it helps
> keep crud from getting into the mechanism.  Same
> principle as maintaining positive pressure in sterile
> environments, etc.
> 
> But, beyond this, any "rules" for air flow seem to
> be pretty vague... "ad hoc", almost.
> 
> In the past, ME's et al. have made these decisions
> in product designs in which I've been involved.
> And, I've never been able to infer any *real* rules
> as to "which is better" (and in which circumstances).
> 
> A common approach is to exhaust air from things like
> power supplies.  This makes sense if there are other
> fans in the device that can move the heated air
> generated by other components in the assembly.  Note
> that exhausting air pulled directly from a CPU's
> heatsink fits this same class -- the heat source is
> concentrated and, as such, you can readily pull air
> directly from it.
> 
> But, what about devices that don't have these nice
> identifiable hotspots?  Are there any rules as to
> why or when it is best to pull vs. push air?  I
> know the turbulence created by obstructions greatly
> affects the cooling ability of the air flow.  But,
> does the turbulence differ if the is air being
> *pushed*
> into that region vs. *pulled* though it?
> 
> (yeah, it's one of those questions that I can -- and
> probably *will* -- die without knowing but it *is*
> puzzling!)
> 
> Thx,
> --don
> 
> 
> 
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