Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!elroy.jpl.nasa.gov!decwrl!public!thad
From: thad@public.BTR.COM (Thaddeus P. Floryan)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: The Fanning of the Amiga
Message-ID: <3025@public.BTR.COM>
Date: 11 Jun 91 11:50:25 GMT
References: <3004@public.BTR.COM> <1339@cbmger.UUCP>
Organization: BTR Public Access UNIX, Mountain View CA
Lines: 57

In article <1339@cbmger.UUCP> peterk@cbmger.UUCP (Peter Kittel GERMANY) writes:
>[...]
>Well, one difference between light rays and air flow is that the path
>of the former is reversible, the one of the latter not. We have discussed
>this already with engineering and when I remember correctly they always
>told us: When the fan sucks the air out, it is much more possible to
>direct the flow (by choosing inlet openings) to areas inside the case
>that need cooling (processor, expansion cards,...), than it would be
>possible with a fan blowing into the case (please don't ask ME for
>details, I'm only a physicist... :-).
>[...]

Yes, I can see how the flow path "may" be easier to control, but the issues
of inside cleanliness and "best" cooling are ignored (or sidestepped (in the
interests of "economy")).

As a for-instance, I can look at ANY one of my Amigas at home or at the office
and clearly see where the air enters the systems due to:

	dust buildup at the expansion port connector (A1000),
	dust buildup around the external video/floppy connectors,
	dust buildup around the joystick connectors, and
	dust buildup in and around the floppy drive(s).

The dust buildup around the floppy drive(s) is the worst ... what has happened
to me many times is the optical sensor that detects the write-protect tab on a
floppy gets obscured thus permitting the floppy to be (potentially) written-to
(which is NOT nice in a virus-infested real-world).

Though it's been nearly 30 years since I've taken any course in thermo-dynamics
(and I've forgotten most of it/them :-), I'd like to cite one practical, real-
world observation that anyone can verify:

	a fan blowing ONTO a power supply will keep the supply cooler than
	will a fan sucking air OVER a power supply.

Since one of my companies used to make the power supplies for modem companies
such as Ven-Tel, Racal-Vadic, and others (over 25,000 power supplies a month),
I have a large notebook of measurements of various tests made using fans and
YSI thermocouples regarding power supply heating, cooling, and related probs.

If you want to perform a simple test for yourself, quickly go do some exercise
and work up a sweat.  Then choose to cool off by either:

	(a) standing in front of a fan blowing on you, or
	(b) standing behind a fan sucking air around you.

I'm sure you'll quickly agree that choice (a) cools you better!   :-)

Choice (a) is similar to a case-mounted computer fan blowing IN over the power
supply and other heat-generating parts.  If it takes two fans to cool a case
such as the Amiga's, so be it.  There ARE quiet fans which can move a LOT of
air efficiently (I have 5 cases here in my lab operating that way to show
anyone who cares to visit (cases from IBM and from some outfit named "Systems
Integrators, Inc." that I acquired surplus).)

Thad Floryan [ thad@btr.com (OR) {decwrl, mips, fernwood}!btr!thad ]