>>I'm no kind of engineer or anything, so I'm not
>schooled in the heat dispersion capabilities of
>various >materials. Does anyone think the aluminum pan
>or the >penny mat would disperse the heat better than
>the >tile? Any other suggestions?
>
>
>Well, I just happen to be a Physicist, but
>unfortunately not a very good one ;) I don't do much
>with chemical makeup, which would determine the heat
>dispersion capabilities of various materials, but I do
>have a couple of thoughts. One, both aluminum and
>copper are excellent conductors. Two, ceramic
>materials are excellent insulators. I am not trying
>to contradict observations that a PB runs cooler on a
>tile counter (experimental evidence speaks for
>itself), but I would think a surface that conducts
>heat away from the machine would be far better than a
>surface that , in theory, prevents heat transfer.
>Besides, the penny tray is just so damn trick!
>Actually the absolute best tray would be a finned
>aluminum heat sink, like you find on your processor.
>Don't know exactly where to find one of these, but
>your favorite salvage yard would be a good place to
>start...
well, I'm a chemist, and heat transfer (dispersion) depends on the
compound makeup of the material (substrate) you use, which dictates its
heat capacity (ability to absorb heat), it's surface area to volume and
the bulk material's density/physical geometry. For instance, ceramics
aren't good for heat transfer (that's why we use them for insulators in
hot enviroments like the skin of the shuttle). And as our engineer
friend said, they are great for INITIALLY sucking up that heat... but
once the initial thermal differences are reduced, you are stuck with a
material that only very slowly disappates heat to the enviroment. And as
he mentioned, this disappation is a function of the surface area. Any
material in solid form is worse than the same material as, say, a
honeycomb. However, totally or mostly enclosed air gaps act to insulate.
Nearly open air gaps, on the other hand, can help radiate the heat if
air is allowed to pass or be pushed through them. For simple heat
transfer, metals are much, much better than ceramics, as is water. Water
has that unusual risk of going everywhere you don't want it to unless you
contain it, and it causes electrical shorts so me thinks the bathtub or a
block of ice is right out.
Back to metals. All metals transfer heat at different rates, but let's
ignore that for a second. Just for sheer comfort, take an Al (aluminum)
frying pan and put your 'book on it. Take a Fe (Iron) pan and do the
same. Which one works better? Well, it doesn't matter if Fe were to
edge out Al... you're going to choose the Al pan 'cause there ain't no
way you will be lugging an iron heatsink all over tarnation. Copper (Cu,
as in pennies before the mint changed to a mostly-Zinc, Zn, penny) is
also heavier (higher density) than Al, but that doesn't necessarily mean
they are better. Our resident chemistry student pointed out that Al has
great heat capacity characteristic. I don't know about its emissivity
(ability to radiate heat, another physical property related to cooling),
but its probably no worse than the other metals. But regardless of Al's
better properties, surface area can matter. The air gaps between the
pennies would form micro channels for convective cooling, 'though that
wouldn't be super efficient either, that would be helpful.
I've got the PERFECT device for you. Believe it or not, your lap is
probably the BEST place to cool the laptop. You are over 70% water, and
you have a huge surface area relative to a brick or a pan. You also
supply a built-in water circulating system, evenly distributing the heat
away from the bottom of the laptop to the bountiful surface of the
cooling substrate, your skin. And, as this marvelous cooler is flexible,
your skin actually conforms to the bottom of the laptop better than any
rigid accessory. By golly, you actually keep yourself around 37C most
all of the time. The book can climb to nearly double that temp under
normal operation, but you'll always attempt to remain at a laptop-lovin'
37C. Do note: for maximum efficiency, you should always use your laptop
sans pants, skirts or any garments below the waist. Awful shame that we
have a nervous system that senses heat and translates that to discomfort
is such a situation. But it's a minor drawback. It's also why we
started this thread, 'though. So, I guess we're back to pennies.
Sometimes cool outweighs (no pun intended - not much of one anyway) the
most efficient.
----
Paul Vail, [EMAIL PROTECTED]
http://home.att.net/~afterhoursconsulting/
----
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