Air temperature inside totally enclosed plastic box with resistor dissipating 6W inside it?

[waveboy]

Hi,
Supposing you have a totally sealed hollow plastic rectanguloid box. Dimensions are 150mm by 60mm by 40mm
Wall thickness is 1mm
Plastic thermal conductivity is 0.2
There are extremely thin electrical wires going into the box. These wires supply 6W of power to a small resistor (Resistor dims = cylinder of size D=5mm by length = 30mm) which is in the box. There is no ventilation gaps where the wires go through the plastic box.
The box exists in an ambient air temperature of 30 Degrees C.

Please may i ask...How hot is the air temperature inside the box?

 

[IRstuff]

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[EdStainless]

Thank you IR, I have seen open power supplies in 45C ambient with vigorous fan cooling have specific components reach 95C.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[waveboy]

Seriously? You didn't think to mention ppg 25 through 29, which describes all the heat sink aluminum that's inside?

Thanks, but the heatsink metal is just floating inside the sealed plastic enclosure, its not connected to any of the components.

At 230VAC and max power (65W), the coldest component is 85.5 degc (as shown) . That means that internal ambient must be less than 85.5degc, which is very surprising since external ambient is 40degc.
(and this is a totally enclosed plastic case....as you know, a strong insulator).
How is the heat getting out of that plastic...it appears that plastic is such a good thermal conductor, that i am surprised there are not plastic cooling fins on the outside?

 

[3DDave]

The plastic is a terrible conductor, but if it is thin enough it is not a barrier. Paper doesn't conduct heat well either, but there are demonstrations of paper cups being used to boil water over a fire; the paper is thin enough to conduct heat that the water keeps it cool enough not to burn.

Fins would make the plastic thicker where the fins are and decrease the conduction.

 

[IRstuff]

I ran the math for the plastic already a week ago.

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[chicopee]

Before anyone gets too involved L.I. alluded to radiant heat. Solar radiation can be problematic if the plastic box has any color beside white-- and even white plastic can get pretty warm so is the box to be shaded from the sun?