Green Building Bible, Fourth Edition |
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Posted By: WillInAberdeenU =Â ÎµÏƒ(T^4 â€“ t^4)/d
binomial series:
T^4-t^4
= T^4-(T-d)^4
= T^4 - T^4(1 + 4(d/T) - 6(d/T)^2 + â€¦. Â )
Drop the terms beyond (d/T)^2 which are very small so:
T^4-t^4 = 4 T^3 d
And so
U = 4Â ÎµÏƒ T^3
Plug in Îµ = 0.9;Â Ïƒ=5.67E-8 and T=310K gives:
U = 6 W/m2K
Or try different Kelvin temps to give the corresponding U's.
Posted By: SteamyTeaSo no one has taken view factor and reciprocity into account then
Posted By: WillInAberdeen
Or some "fearsome maths", never be a feartie! Using: Â hot temp = T ,Â cold temp = t,Â temp difference = d = (T -t)
U =Â ÎµÏƒ(T^4 â€“ t^4)/d
Posted By: mike7R Dawkins?Was Simon Mitton
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