Jim Tonne wrote:
> Roy wrote:
>
>
>
>> Black bodies radiate and absorb heat many times
>>more efficiently than a white or shiny body.
>
>
> I have heard it said that this is largely true at extreme
> temperatures. Might be nice to have someone dissipate a
> "real world" amount of power (say 100 watts) in a heat
> sink of raw aluminum and do it again with an identical
> sink that is black. I have a hunch that the heatsinks will
> have similar temperatures.
It will depend a lot on the situation - reasonable convection will
dominate over radiation, so black won't make much difference where
there's forced air, or vertical orientation with free airflow. Many
heatsink profiles have the fins much too close together to get efficient
'unblown' convection. Convection efficiency goes up with temperature
rise above ambient, but I think radiation goes up faster.
>
>> Try wearing a nice black tee shirt in the direct sun as
>>compared to a white one.
>
> Absolutely no question here but isn't this a case of
> absorbing heat as opposed to radiating it?
My physics is a lot of years old, but I thnk it works the same both ways
round. If you wear a black shirt and go out into cold air, you will
chill faster than if you wear white.
Steve
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