[Amps] Anodizing aluminum, painting etc.

[Martin AA6E]

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