Re: Effect of colour in SSD heatsinks

On 01/06/2025 22:48, piglet wrote:

Pimpom <Pimpom@invalid.invalid> wrote:

On 02-06-2025 01:29 am, Liz Tuddenham wrote:

>
A surface which radiates well will also absorb well.  If there are
other components nearby with higher surface temperatures, a 'radiating'
finish could be a disadvantage because it will absorb more energy than
it radiates.
>

There's that factor too. So a shiny golden heatsink may actually be
better than a black one.
>
>

 Black will be always be the best choice even though as others have written
the differences will be tiny.
 Folk in really hot desert countries wear black instead of white as although
black absorbs better it also radiates better - the wisdom of the ages?

That is more likely to be because white is so difficult to keep looking clean in such a water starved environment. The difference between visibly white and black materials in the thermal band IR is negligible. White has the advantage of reflecting heat away.
There is a good reason why tubes in solar hot water systems are black!
The tricky one is shiny polished metal which is a terrible radiator and so can get very hot in the sun. There are also a handful of designer metamaterials now which can lose heat by radiation in sunlight (ie become colder than their surroundings by losing heat skywards).
Telescope domes back before there was air conditioning were painted the whitest white that could possibly be manufactured and at great expense.
A highly loaded MgO pigment white that was painful to look at. It is still completely black in the thermal IR band and so loses heat by radiation but reflects most of the daytime sunlight.
It turned out that this super white was actually too good and after sunset it allowed a supercool layer of air to form on the dome surface and spill down through the dome slit creating turbulence aka dome seeing. Aircon takes up the slack inside the dome during the day.
Modern observatories now use a mixed white pigment combined with aluminium dust to create a surface that is effectively neutral for radiation losses after dark whilst still being very effective in daytime at reflecting sunlight away. Dome seeing is no longer a problem.
--
Martin Brown