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Re: CPU recommendations - comments

On Mon, May 05, 2003 at 05:31:52PM +0100, Karsten M. Self wrote:
> on Sat, May 03, 2003 at 12:54:20AM -0700, Paul Johnson (baloo@ursine.dyndns.org) wrote:
> > On Fri, May 02, 2003 at 11:11:32PM -0700, Alvin Oga wrote:
> > > havent tested the blowing down vs sucking up heat ... think its
> > > sorta the same issue in that the air still has to make a 90degree turn
> > > within the heatsink but should work better for exhausting ( less
> > > turbulence )
> > 
> > That was the assumption I was going by, since it's easier to decrease
> > pressure in a confined space (like that between, say, a fan and the
> > base of a heatsink) then it is to increase it.
> Suction isn't directional.
> Richard Feynman has a good story about this from his IIRC Princeton
> days, trying to work out whether a bent-arm sprinkler (the sort that
> spins when it sprays water) would spin opposite-wise when sucking.  It
> doesn't.  Featured in _What Do You Care What Other People Think_.

(plays with piece of bent rubber tubing and some water) Yes it does.
Care to post a quote?

Re turbulence - as John Hasler has said, this is desirable...

Whether it is easier to decrease or increase pressure in a confined
space depends on all sorts of things to do with the shape of the
inlets / outlets, whether the flow becomes turbulent or not, how the
efficiency of the fan varies with density etc.

In the case of the CPU heatsink/fan assembly, how well either approach
works is also affected by existing airflows inside the case, the
temperature of the air in the "intake" region, positioning of nearby
cables and cards... most of the factors are pretty indeterminate, and
the effects of any one are small. Experimentation is really the only
way to sort it out for any individual setup; it is unlikely that one
person's tweaks will be equally effective in someone else's box.


Be kind to pigeons
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