[time-nuts] Thermal time constant

[Bruce Griffiths]

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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