Will Matney wrote:
> All,
>
> I had to brush up a little on this as it's been a long time since I took any
> thermodynamics ,,,
>
This is an interesting thread. The one point that has not been
mentioned is that the visible color (black or bare aluminum or whatever)
has little to do with heat radiation. Unless you're talking about very
high temperatures (red hot and beyond), the radiation that matters is in
the infrared. You want a surface that is "black" in the infrared.
(Black means that it absorbs all radiation that falls on it. Physics
tells you that a black surface is also the most efficient heat radiator
at any given wavelength.)
The reason that bare steel or aluminum gets very hot in the sun is that
its surface is "blacker" in the visible sunlight than it is in the
infrared, so the absorbed visible light energy from the sun can't easily
radiate in the infrared. We used TiO2-based white paint to minimize the
problem on radioastronomy dishes-- it reflects in the visible, but is
"black" in the infrared. This is not the usual heat sink problem, but
it indicates that painting your heat sinks "Titanium white" might not be
such a bad idea! -- especially if your equipment needs to work in
direct sunlight.
I agree that convection and conduction are the most important ways to
dump heat at low or moderate temperatures, and any paint is likely to
insulate more than it helps.
73 Martin AA6E
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