Radiative heat transfer (for a surface with an emissivity of 1) is
around 150uW/square cm /degreeC at 300K.
That's equivalent to about 10cm of styrofoam.
It seems unlikely that the radiative heat transfer component is included
in the thermal resistance rating for Styrofoam.
The radiative component is independent of insulation thickness where the
insulation doesnt absorb in the 10-30um infrared region.
Adding carbon black to the foam appears to increase the thermal
resistance of 25mm thick foam by about 10%.
Bruce
Bob Camp wrote:
Hi
That raises the interesting question of weather radiant transfer is already included
in the rated thermal resistance. My guess is that the 8" of foam is enough to
cover any radiation issues and still get you above 20 C / W.
Since you are probably starting with 1 or 2" slabs, including the aluminum foil
would be pretty easy. It can't hurt and it might help.
Bob
On Mar 10, 2010, at 7:29 PM, Neville Michie wrote:
I have been wondering about achieving the rated thermal resistance from plastic
foam,
the problem being that radiant transmission may be very strong through the foam.
What happens if you interleave concentric sheets of foam plastic with aluminium
foil? (taking care to keep the foil
on isothermal surfaces)
Will this stop the radiant transfer and leave only the thermal conduction of
the plastic foam?
cheers, Neville Michie
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