Hi Low density (1 or 2 lb / cu ft) urethane foam is going to be a better insulator than styrofoam. I believe it's reasonably opaque at IR.
Bob On Mar 10, 2010, at 8:23 PM, Bruce Griffiths wrote: > There's a small problem with my calculation and the published figures for the > thermal resistance of styrofoam. > If the measurements include radiative transfers the thermal resistance per > unit area of a styrofoam slab should reach a limiting value (when the > radiative transfer component dominates) as the thickness is increased. > Possibilities > > 1) My calculation is incorrect. > > 2) Infrared absorption in thick styrofoam slabs is significant. > > 3) The tabulated figures for the thermal resistance of styrofoam are merely > scaled up from the values measured with thin sheets. > This gives misleading values for thick sheets if the tabulated values include > radiative transfer. > > Bruce > > Bob Camp wrote: >> 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. >> >> > > > > _______________________________________________ > 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.
