"Al Dykes" wrote:
> You are picking *one* aspect of the many that affectthe cooling parts
> in a box. You also freely jump between the macro and micro effects.
> What is optimal in one is occasionally sub-optimal in the other.


I am picking "*one* aspect* to write about that is often denigrated
by "experts" as being undesirable. You can read countless
"modder" sites that advise keeping the air flow "smooth" to cool
the interior parts of a computer as much as possible. I merely
point out that if a part is to be cooled by a forced flow of fluid past
and over it (such as by forced draft of air), turbulent fluid flow cools
the part better than laminar fluid flow. That it is putting the flow
past the part to be cooled that is more important than merely
getting bulk air in and out of the case is evidenced by the transition
to dedicated fans on the heatsinks of CPUs and GPUs. The
designers don't just put bigger fans or more fans on the walls of
the case to get more air-per-minute in and to get more air-per-
minute out of the case, they instead put interior re-circulating flow
fans right at the heatsink. That this causes "pre-heated" or "used"
air to re-circulate against the heatsink in secondary - what is
important is that air is brought into contact with the heatsink as
much as possible, despite that the bulk flow through the case is
unchanged. This increased air speed at the surface of the
heatsink that does not affect the bulk flow of air is a form of
turbulence. It really doesn't matter whether this turbulence is
generated an eighth of an inch or a quarter of an inch or six
inches away - it's just turbulence, and it's effect is to scrub down
through the thin boundary layer of air that surrounds all objects
to make maximum contact with the object itself. In weatherman's
terms, in increases the "chill factor".

In practical terms, I can give my Dell ATX case as an example
of a design that takes advantage of turbulence to cool. There is
volume of space at the bottom of the case in which fresh air
sweeps in the from the lower front, straight back to the lower part
of the motherboard and the expansion cards. The main hard
drive plastic cage could easily have been mounted anywhere in
that cavity, and its mounting cage could have been conveniently
attached at any number of places. But the HD is mounted vertically
with its circuit board facing the front and about !/2" from the vent
holes - despite that this impedes the incoming air. Not only
does this put the HD's circuit board in the field of maximum
turbulence caused by the vent holes stamped in the metal case,
but it causes more turbulence in the case immediately behind it.
If the designers were designing for maximum bulk air flow through
the case, they failed. If they were designing for optimal cooling,
they did quite well because in 7 1/2 yrs, I haven't had a HD (or any
other part) in the PC fail. In fact, when I touch the 7,200 rpm HD,
it feels no warmer than my body temperature.

That turbulence cools parts is evidenced in countless fields of
science and engineering. That turbulence alone can cool objects -
of course not! If that were true, there would just be fans inside
cases and the cases would be sealed shut. What I point out is
that turbulence is NOT BAD, and that turbulence is turbulence -
be it generated by friction of the flow against the part itself that
is to be cooled, or somewhere upwind of that part.

*TimDaniels*