Re: Apple IIGS Cooling

["Paul G." <carbide@egine.com>]

On Apr 11, 8:38 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> Paul G. wrote:
> > On Apr 10, 11:27 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
> >>No, not a loop.
>
> >>The "laptop coolers" are about 10"x9"x3/8" with two very thin, quiet,
> >>medium-speed fans that draw air into the narrow case and vent it out
> >>one of the long sides.
>
> >>When one is placed upside down on top of a IIgs case, hot air is drawn
> >>upward through the case lid and then exhausted gently backward (or
> >>forward if you are cold ;-), where natural convection ensures that it
> >>will not reenter the IIgs.  The hot air withdrawn is replaced by cool
> >>outside air coming in from all the other holes in the IIgs case (most
> >>of which are on the bottom).  The power supply will be in a sea of
> >>cooler air, with the slight pressure differential providing assisted
> >>convection cooling.
>
> > Ah, OK, so the "laptop cooler" exhaust is at 90 degrees to the intake,
> > that makes all the difference. My mistake, I thought they had axial
> > flow.  I have to disagree on the utility of the bottom vent holes,
> > though- they are there, but effectively negated by the metal RF
> > shield.  Someone wasn't clear on the concept of convective cooling-
> > the big vents need to be on top, as the volume of the hot exhaust air
> > is greater than the volume of the cool air coming in the bottom...
>
> Actually, the volume of air entering the case--mostly from the bottom--
> is *exactly* the same as the volume of air leaving via the top.
>
> Otherwise, we'd soon have a vacuum in the IIgs and it would implode.
> ;-)
>
> Air can quite easily flow around obstacles at low speed, and that is
> quite enough to change the air often enough to keep a IIgs cool.
>
> If you don't believe it, allow some smoke to waft around the case
> with a cooling fan on and watch the flows and rates.
>
> It is undeniable that the primary place where hot air collects is
> at the top of the case, and that's exactly the air that is removed
> by an "exhaust" fan on top of the case.

Heh heh!  Now this is fun.
I disagree- cold air is denser than hot, therefore the volume of hot
air exiting at the top is greater than the volume of cold air entering
at the bottom- air expands when heated. Therefore the holes at the top
should be larger than those at the bottom.

I also say the "primary place where hot air collects" is inside the
powersupply. ;-)  That's why I mounted my fan on the right front side
of the powersupply, where Apple helpfully supplied fan mounting
holes.

I just took a careful look at one of my IIgs's. There is a nearly
solid piece of sheetmetal across the bottom. At first glance it
appeared that there were some vent holes directly under the P/S, but
it turned out that the speaker is mounted over them, so they are for
sound.  The motherboard is also nearly solid. Lastly, the lid has
about 1/3 of the surface area covered with a solid RF shield.  It's a
very poor design for cooling, even with a fan.  Of course a fan is
going to help a lot over simple convection.
-Paul