Hi Since styrofoam is being rated as a building insulation, it's reasonable to believe that the material on both sides is up around 1. I highly doubt that somebody tossing styrofoam in walls is going to add a radiation factor ...
In our application we're talking about a metal block inside a metal enclosure, polishing the surfaces could drop the emissivity by >10X. If the budget allows, you could gold plate the surfaces in addition to polishing them ..... Bob On Mar 10, 2010, at 8:01 PM, Bruce Griffiths wrote: > Oops forgot a factor of 4 > Radiative heat transfer for surface with an emissivity of 1 at 300K is about > 612uW/square cm/degree C > which is equivalent to about 25mm of styrofoam. > > Which raises the question what's the emissivity of the isothermal surface > used when measuring the thermal resistance of a slab of styrofoam? > > Bruce > > Bruce Griffiths wrote: >> 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 >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
