Getting heat out of a box
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From: Tim Williams on 8 Aug 2010 13:12 "John Larkin" <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote in message news:btmt56p7sobm2av855raubd046a7sr8a1c(a)4ax.com... > Any others data points? Hmm, I've got a large power supply that occupies a 5 x 10 x 13" aluminum box (lots of free space). After a few hours, it gets maybe 20C above ambient. That's 360 in^2 (not counting the bottom, which is against the table). Measured power 100W, so the thermal conductivity is about 0.2 C/W, or 72 in^2*C/W. I may be grossly off with my power estimate, and the top panel may not contribute much by convection, being in stall. Eating mashed red potatoes. Not just redskin, these are red *all the way through*. It looks like strawberry ice cream, and is exactly as delicious, but savory instead of sweet. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: whit3rd on 8 Aug 2010 15:57
On Aug 8, 9:48 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >A wall-wart in a plastic case with circa 10 square inches of area > >has no difficulty in shedding 4W. Metal should dump heat faster. > Why would metal dump heat faster? Convection would be the same, > radiation generally better for plastic. It's because of turbulent flow; the local cooling of a bit of plastic in airflow doesn't cause heat flow laterally from nearby plastic surfaces that are in 'dead air', but lateral heat flow in a metal case will be significant. Admittedly, turbulent flow outside the box would have to exist for this to be important, but laminar flow is not common in uncontrolled environments. |