Brian Beesley wrote:
> On Wednesday 20 August 2008 19:40, Keith Alexander wrote:
>   
>>  No need
>> to do anything electrical, just change which side of the fan is facing
>> "out." Thoughts, anyone?
>>     
> Used to be that this was thought to be a Bad Idea, mostly because you can't 
> pump air out without it leaking in somewhere, which was usually through the 
> floppy disk drive - where the heads got coated in the crap that got dragged 
> in along with the air. So it was generally agreed that the idea was to have a 
> positive pressure in the case. Maybe dirty floppy drive heads are no longer 
> an issue, but the principle that the inflowing air will be dirty is still 
> valid.
>
> Fact of the matter is, the leading edges of the blades will accumulate crap 
> anyway, this will reduce their efficiency leading to less air flow & higher 
> temps in the box.
>
> Some of my cases have several fans, some blowing in, some out (usually one 
> more blowing in than out). They all get dirty. The worst build up is around 
> the CPU heatsink fins, I have to vaccuum these out every six months or so. 
>
> If you want to keep the innards of the case clean, then the only real option 
> is to use a fanless cooling system - i.e. a massive finned case acting as a 
> heat sink, maybe assisted with Peltier cooling modules or incorporating a 
> miniature refrigerator to carry the heat away.
>
> Regards
> Brian Beesley
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>   
Thanks, Brian. I hadn't thought of that. You're absolutely right, of 
course. If air is being sucked OUT of the case, it's also going to be 
drawn IN somewhere else. Though I still hang on to one, most newer cases 
do NOT have floppy drives, but I suppose dust and lint COULD get sucked 
in through the gaps in the tray of your CD/DVD drive, and possibly cause 
problems.

Re: "positive pressure." I used to work as a central office tech. for 
the phone company, and I remember hearing that phone switching offices 
near the seashore in Florida were kept under "positive pressure" to keep 
the salt air from corroding the relays. Less of a problem now, as there 
are fewer and fewer relays to be seen in telephone offices. These days, 
all you hear are fans, not relays clacking.

Keith Alexander

-- 

"My view of reality is that it's always been a grim place
to be...but it's the only place you can get Chinese food."

Woody Allen

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