Hi,
Water must have a fairly high figure of merit for thermal buffering.
Unfortunately the lists of material properties are inaccurate, have
gross errors
and are inevitably listed in units such as tons per Degree F per inch
per square foot.
The tons refer to tons of ice per 24 hours, a good old reliable air
condtioning
unit.
The relevant measures are thermal conductivity, thermal heat
capacity, density
and thermal diffusivity.
Now there is an interesting comparison between copper and aluminium.
Copper has a specific heat of 0.09 and aluminium 0.2. (cal/gm C )
Copper has a relative thermal conductivity of 0.918 and aluminium 0.48
Copper has a density of 8.9 and Al 2.7
So the heat capacity of copper is 0.8 and Al 0.54 cal/C/cc when
calculated on a volume basis.
So water at 1cal/C/cc is better than copper, and twice as good as
Aluminium.
Where water really wins is on price, and being a liquid it will heat
with convective circulation
and so be much faster than the solids to reach equilibrium.
cheers, Neville Michie
On 14/06/2009, at 4:14 AM, Chuck Harris wrote:
Yes, but if it takes 20 years for 1 tsp of water to be lost, I just
don't see how that rules out the use of water as a thermal ballast.
Water's cheapness and availability in bulk makes it quite attractive
for this purpose.
If you don't trust plastic, use copper, or stainless steel, or...
If man can keep a vacuum in a vacuum tube for 100 years, surely
keeping a little water in a bottle or can isn't that hard?
Besides, I don't think we were talking about putting the water inside
of a crystal oven. We were talking about using water as a thermal
ballast to keep the closet/box your standard occupied at a more stable
temperature.
-Chuck Harris
J. Forster wrote:
Chuck, I don't dispute that you can contain water in plastic a
long time,
but, if some does escape it may not matter to the bottle contents,
but it
could well raise the humidity of the surround w/in a tightly sealed
oven/box/enclosure. Electronics does not much like high humidity.
-John
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