[time-nuts] Thunderbolt stability and ambient temperature

Neville Michie namichie at gmail.com
Sat Jun 13 18:02:35 EDT 2009


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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