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发表于 2008-6-26 13:13:19
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来自 美国
let's run an simple estimation:
h_rad = 4*esp*sigma*(T*T0)^(3/2). sigma = 5.67*10^-8.
Assume T0 = 300K (room temperature) , T= 100C (373K) is the maximum junction temperature that LED can sustain, assume esp = 0.5 (very resonable considering roughness of the LED screen surface).
h_rad ~ 1 W/m^2-K
h_conv ~ 10 W/m^2-K
So maximum thermal radiation is 10% of that from heat convection... In addition, the LED should be embedded in side package, so the package surface participateing the radiation will have substainially lower temperature than junction temperature. So actual h_rad will be even smaller, e.g., less than 0.5 W/m^2-K.
On the other hand, the thermal property value even from measurement usually will have 10% uncertainty. so as first order it's reasonable to ignore the radiation.
[ 本帖最后由 iomega 于 2008-6-26 13:19 编辑 ] |
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