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re: a bubble wall?
25 apr 1996
andreas haffner wrote:
>nick pine wrote:
>> david davis wrote:
>> >i have to agree with george. logic tells me you have provided numerous
>> >small wet paths for energy transfer via the bubble walls. before the
>> >bubbles transfer relied on convection in the air in the space.
>>
>> a lot of little convection paths in series will have more thermal resistance
>> than one big one...
>misunderstanding here, i think:
perhaps so...
>before you had one large convection path
right...
>with the bubbles you have many small convection paths and additionally many
>*conduction* paths.
that may not be so bad... water has a us r-value of about 0.25 ft^2-hr/btu
per inch, as i recall, eg for downward heat conduction. so what would we have
as the simple aggregate conductive thermal resistance owing to the water films,
from one side of a wall to the other, if the 4" wall space were filled with
a regular matrix of 1/4" cubical bubbles with a 0.0001" (approx 12 micron,
on the order of an 80 f black body ir wavelength) wall thickness, ie if the
wall cross section were 2500 parts air and 1 part water in each direction?
a 2500 x 2500 foot wall would have the equivalent of a 1 ft^2 thermally
conductive water shunt 4" thick with a us thermal resistance of 1, so the
wall would have an effective thermal conductance of 1/(2500^2 ft^2) or
an r-value of 6,250,000. not bad :-) this is more easily investigated by
experiment. we need a few more serious 12 year old scientists...
nick
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