[rescue] This Just In: HP to buy Compaq

[Greg A. Woods]

[ On Saturday, September 15, 2001 at 23:40:30 (-0400), G W Adkins wrote: ]
> Subject: Re: [rescue] This Just In: HP to buy Compaq
>
> Actually it's more appropriate than you might think, since calorie exchange
> from the heatsink is determined largely by the surface area of the object
> and the difference in temperature between it and the surrounding air, more
> air exchanges per minute mean better cooling (of course...).  Exchanges per
> minute is a function of air velocity and distance across the object...  Make
> a little more sense?

Yes, that does help.  After I said what I said about "the depth of the
heat sink" it began to work in and eventually I realized that 

I was also being seriously confused by Intel's use of the phrase "case
to ambient temperature resistance" until after I re-read just now the
section on IC power dissipation from my old Lenk textbook on ICs and I
realised they meant the IC package case, not any enclosing chassis. :-)

>  Ultimately, the more familiar CFM divided by enclosed
> volume still boils down to air velocity, (i.e. how much time does some
> discrete volume of air remain in contact with the surface before being
> replaced by cooler air)

indeed -- with the caveat that pulling 100 CFM of air from a 10
cu. ft. box doesn't mean you've exchanged all the important air ten
times per minute.  Internal obstructions can create air pockets in the
worst and least obvious places, as can other internally generated air
currents (eg. from a cpu fan, etc.)

I opened the front door on my network cabinet yesterday and discovered
that some of my router gear was much warmer than I desired it to be,
despite the fact the cabinet has six 4" high-speed muffin fans blasting
enough air into it that the doors blow open without good restraint.

The floor (most of the air exhausts out the bottom) is quite warm and
breezy, but it seems the strange opposing fan orientations in the DEChub
(power supplies blow up, other units blow down) are changing the way air
flows in the cabinet sufficiently that they seem to be causing dead-air
vortices which never mix with the rest of the cabinet air.  I guess I'll
have to do some ducting to try to get the power supplies to circulate
differntly (or simply pull them appart and flip their fans!).

-- 
							Greg A. Woods

+1 416 218-0098      VE3TCP      <gwoods at acm.org>     <woods at robohack.ca>
Planix, Inc. <woods at planix.com>;   Secrets of the Weird <woods at weird.com>