Planning Spraying the top plate of a cpu cooler.

I struggled to find the colour of orange I wanted at Halfords Sunday, and a ncie lady mixed me up a can of what turned out to be Lamborgini Orange. I am sure if you are still concerned about the high heat resistant issue, they might be able to mix you up a tin in a colour of your choice?
It was near enough £14 for a 300cl standard can of spray paint (can of coke size)
Might be a bit dearer for a heat resitant paint mind ???
Alternatives ...brake calaper paint

 

oh cool, so i wonder what the science behind that is then? I thought maybe because it is covering the surface of the Heatsink, the heat would take longer to travel through as there is two materials, and maybe paint has less heat disserpation properties than the metal?

I'm sure the black bird had special paint though, it had properties to absorb radar as well.

 

The thing is, there are lots of different kinds of paint, and different methods of application.

Adding a layer of paint is an additional layer of thermal resistance. However, the claim is that different colored materials will radiate heat better or worse, depending on what color they are and how reflective they are. Flat black is supposed to radiate the heat most effectively, because it is the least reflective material.

However, my knowledge on that area is fuzzy. If done right, a coating that radiates heat better than exposed copper or aluminum could lower temperatures.

One important distinction is the two ways with which surfaces dissipate heat. There is radiative heat, which comes in the form of infrared radiation emitted from the surface. There is convection heat, which comes in the form of another material making physical contact. AFAIK, the convective heat transfer is independent of what color the object is, just the surface area and the amount of the other material. In the case of a CPU heatsink, the guy with the most surface area and the best airflow has the coolest CPU.
Radiative is a little more complicated. I think that is where the color and reflectivity become significant factors. Different surfaces will radiate heat differently, and painting could improve that.

However, that doesn't mean that you should go out and rattle-can your Fenrir black.

I saw an impromptu test on a forum where a guy took two metal bars, one black and one unfinished, and mounted thermal probes in them and heated them with a high-power LED.

With no airflow, the black one was noticeably cooler, because it was radiating heat better.
With a small fan, there was no temperature difference, because the amount of heat transferred by convection is much larger than the amount transferred by radiation. And that was just a metal bar - in a heatsink, there is so much more surface area, so convection is a much higher portion of the cooling performance than radiation.

Remember, for radiation to be useful, it has to not hit the things. If two adjacent heatsink fins are both radiating heat into each other, that doesn't help. It's only the outside fins, that radiate heat into the case, that would help. Whereas with airflow, air can flow between the fins, so having more fins improves cooling performance.

 

hhmm this is really interesting, especially the test you were talking about with the two metal bars.

So I guess the question is, does a CPU produce more radiative heat or more convective heat?

Well Bit-Tech's test with the Fenrir Xmas edition showed exactly the same results as the regular Fenrir, so the paint had absolutly no positive or negative effect, apart from making it look a lot cooler (forgive the pun).

So if the only factor of the HSF is the space between the fins to allow the air to pass through, then it may be a probability that the paint may reduce this space if not applied thinly enough.

 

Conduction, convection, and radiation aren't types of heat, they're methods of heat transfer. The CPU transfers heat to the heatsink with conduction (direct physical contact). The heatsink transfers most of its heat to the ambient air by forced convection (blowing cool air on it). There is a little bit of radiative heat, but not much - if you blocked the airflow, it would overheat very quickly. And, it's not the spacing so much as it is the total surface area of the fins. The Fenrir and TRUE and the other good ones have tightly spaced fins, to maximize the amount of surface area within a given size constraint. If you reduced the number of fins, or reduced the size of the fins, it wouldn't cool as well.

Here is the test I was referencing:

http://www.candlepowerforums.com/vb/showthread.php?p=1715962#post1715962

 

+rep

Like the others have said, if your heatsink is travelling at over 2100mph, made of titanium, and full of cameras, you have bigger problems than just the colour scheme. The Blackbird was painted dark blue to increase radiative heat emission efficiency but with a ΔT of up to 600K at 85,000ft I'm not sure there's much to be learnt from that. Your cooler does almost all of it's work via convection - most of the radiative heat of the lower fins is soaked up by the fins above them, is my guess, so special radiative paint won't help much.

If you want to paint it - and I think it'll look good, too - mask it, primer it, and then paint just the top two with rattlecans. That should do the trick nicely.

 

What I was really trying to say was, that it wont make any difference if you paint the top 2 fins.

After this I think I will grab a couple of intel stock coolers and test unpainted, then paint it and see what happens.

 

It's going to be negligible.

 

Tell you what, I'm going to spray my whole heat sink (except the bottom obviously) in a week or so, we'll see what happens

Tests before and after @ stock and OC'd levels? Hardware Monitor accurate enough?

 

I'd love to see that.

 

Would love to see the comparison.....

 

This just screams at me that painting it black -might- improve the cooling performance. I really think I should have a go at this?

So, preparation wise? Steel wool the top, cover the base with tape and then what's the appropriate method of spraying? Gentle amounts applied in multiple layers or going to town on it and blowing any excess off with a hair dryer or what? I obviously want to avoid it being streaky/running...

 

Probably thin coats. Not sure what kind would work best.

Just keep this in mind

The amount of heat transferred by radiation is very small to the amount transferred by having a fan blowing over it.

With no blowing air, he found a 20 degree difference between the bare heatsink and the black heatsink.

With a fan blowing over the heatsink, it cooled them both off significantly, and there was not a difference in temperatures.

What this means is that this concept applies heavily to passive heatsinks and other silent PC stuff. where the total size of the heatsink is large and the airflow is small. With large airflow, the amount of cooling done by the air is so much greater that the emission difference becomes insignificant.

 

It is amazing this exact same topic comes up every now and then on our 2 stroke motorcycle forum when people are talking about spraying radiators.
As Altron has explained the amount of heat dissipated by radiation versus convection is so small is is almost inconsequential.

 

Oh, well I'll record some statistics anyway, but seems like it won't have too much of a negative effect on the cooling

 

Just sprayed my Ultra120, used Upol acid etch primer then matt black enamel
went a bit heavy on primer & had to resand down still doesn't look bad though

 

nice!! what brand paint did you use?

 

I used Halfords own matt black enamel £6.99.

I could have made a much better job if I had taken my time, the primer coat determines how good the paint will look.

Do very thin coats of primer, let it dry DON'T over do it like I did! Made the mistake of touching it before fully dry where it was applied too thick!

 

Very nice! How is the texture? Is it smooth or a bit bumpy because of the primer?

 

no, its very smooth, its got a few pits were i sanded the primer, if yoy put the primer on sparingly the finish will be awesome!