[Tfug] Cooling

[Eric M. Gearhart]

It's fun when you read it if you emphasize all the words in asterisks with the voice in your head :) 

Just joking around btw... please don't take it seriously Bexley :) 

Eric 

----- Original Message ----- 
From: "Bowie J. Poag" <bpoag at comcast.net> 
To: "Tucson Free Unix Group" <tfug at tfug.org> 
Sent: Sunday, November 25, 2007 6:51:13 AM (GMT-0700) America/Phoenix 
Subject: Re: [Tfug] Cooling 

I'm going to report you for *asterisk* abuse. 


Bexley Hall wrote: 
> 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