calling all Alluminum heatsink expert - Page 2

oreo57 · 10/27/2018, 10:04 PM

IR is invisible..

black anodizing for "this" is just the preferred "color" being more emissive than others (how much more?? sorry never compared blue to red to ect....
I posted enough for others to decide..

Painting is "never" recommended is false. A heat sink in a hood or even house for that matter will not be receiving much outside radiation..

https://www.overclockers.com/forums/...ences-comments

As I said.. believe what you want to believe.. Doesn't make it real though..Maybe YOU don't recommend it..

and yes "painting" can be tricky..
There are specialized paints for it but short of dipping and gobbining it on it.. err..works..

What do you want? What more do you need??

Quote:

This shows the emissivity of various materials. This number (from 0 to 1) is how close the material is to a perfect black body. As you can see shiny polished metal is very close to zero. Matt black rough metal surfaces are very close to 1. Another site I found suggested that black anodized aluminium gives emissivity number of 0.7-0.9, black enamel 0.85 -0.91 and black oil paint 0.92 - 0.95.

We are talking about internal "heat" radiating OUT.. not in..

OK got to agree w/ you on one point..
color matters little BUT that doesn't change the ORIGINAL premise of changing the raw aluminum heatsink to IMPROVE heat transfer be it "anodizing" or painting..

https://www.radianheatsinks.com/heat...ated-heatsink/

Quote:

Since E-coating is a paint it is necessary to make a performance comparison between Anodized and E-Coating to determine if there is a thermal impact. Radian has performed a convection test using a 3U test bench, die casted aluminum 356.0 Pin fin heatsink mounted to a dummy heater block and attached thermocouples. Heater was set to 10W and Fan speed was varied from 200-800 LFM. A picture of the test setup can be seen in Figure 4 and Figure 5 test results following. Looking at the differences E-Coating does show an average of 1C higher than Anodization with a total impact of approximately 0.1 C/W.

Scrubber_steve · 10/27/2018, 10:33 PM

"Practically speaking, a heatsink being coloured is entirely for looks, and will affect cooling less than surface area, airflow, material and the contact between the heat source and heat sink."

https://www.google.com.au/amp/s/www....erformance/amp

Scrubber_steve · 10/27/2018, 10:40 PM

A heatsink painted black is a bad approximation of a blackbody, more like a 'grey' body where the energy radiated by the formula above is multiplied by a constant (emissivity epsilon) which is less than 1. A better approximation would be a heatsink with microholes with depth about 7x their diameter (the whole appears black inside, try it). This is used by Ersa in their IR heating plates for PCB rework.

To conclude, painting heatsinks black does not contribute to their ability to dissipate heat by radiation.

https://www.eevblog.com/forum/projec...black-surface/

oreo57 · 10/27/2018, 10:46 PM

Quote:

Originally Posted by Twinfallz

"Practically speaking, a heatsink being coloured is entirely for looks, and will affect cooling less than surface area, airflow, material and the contact between the heat source and heat sink."

https://www.google.com.au/amp/s/www....erformance/amp

sorry, like I said , my bad, color makes little difference but how do you know it's "anodized" if a clear coat..?

Black is just common usage...and a minor part of raw vs non-raw aluminum.

Still I bet there are differences but not significant..
couple w/ different "processses" ect..

Fact is anodizing is usually important in passive cooling..

Scrubber_steve · 10/27/2018, 10:47 PM

The Color

A black object radiates the best - so all heatsinks should be black". True? Not really. Remember, most of the heat is dissipated using forced convection - and for this effect, the color is irrelevant. When doing a comparison test of two otherwise identical heatsinks with a different color, the measured performance difference is usually negligible. The main reason why heatsink manufacturers anodize their heatsinks is to make them look more attractive. Heatsinks exist in a variety of colors - black, silver, but also blue, green, gold, and red. For the performance, it doesn't make any major difference.

https://www.anandtech.com/show/437/2

oreo57 · 10/27/2018, 10:53 PM

Quote:

Originally Posted by Twinfallz

A heatsink painted black is a bad approximation of a blackbody, more like a 'grey' body where the energy radiated by the formula above is multiplied by a constant (emissivity epsilon) which is less than 1. A better approximation would be a heatsink with microholes with depth about 7x their diameter (the whole appears black inside, try it). This is used by Ersa in their IR heating plates for PCB rework.

To conclude, painting heatsinks black does not contribute to their ability to dissipate heat by radiation.

https://www.eevblog.com/forum/projec...black-surface/

you list one out of many...
Painting certainly isn't my "choice" Bl anodizing is....

I've shown where paint can help. like I said let others decide for themselves..
If I was so inclined I'd have no issue spraying a heatsink black..

do I need to quote a real study again??

Quote:

To test the influence of thermal radiation on the total heat transfer in buoyancy-induced convection, an untreated and painted/anodized version of each heat sink was tested. Both painting and anodizing increase the emissivity of the heat sink and, consequently, the heat transfer by thermal radiation......Figure 8 compares the thermal performance of the untreated finned heat sink, the 22 mm-high in-house-made aluminum foam heat sink (reticulated22) and the 22 mm-high solid aluminum block to that of their painted/anodized counterparts. By painting or anodizing, the thermal performance improved for each of the tested heat sinks. The aluminum foam heat sink, the finned heat sink and the aluminum block, respectively, dissipated on average 17%, 31% and 44% more heat after they were painted or anodized.

We just need to agree to disagree on this point..

oreo57 · 10/27/2018, 10:56 PM

Quote:

Originally Posted by Twinfallz

The Color

A black object radiates the best - so all heatsinks should be black". True? Not really. Remember, most of the heat is dissipated using forced convection - and for this effect, the color is irrelevant. When doing a comparison test of two otherwise identical heatsinks with a different color, the measured performance difference is usually negligible. The main reason why heatsink manufacturers anodize their heatsinks is to make them look more attractive. Heatsinks exist in a variety of colors - black, silver, but also blue, green, gold, and red. For the performance, it doesn't make any major difference.

https://www.anandtech.com/show/437/2

Probably referring more to FAN driven systems FORCED convection.. and w/ that I agree .. no need to anodize paint ect...

Quote:

The main reason why heatsink manufacturers anodize their heatsinks is to make them look more attractive.

DO NOT mix passive vs active cooling..
NOT at all...passive cooled heatsinks are anodized for a physical reason. Increasing radiative heat transfer...Period. no argument is possible.
Re PAINT
:
https://scholarsmine.mst.edu/cgi/vie...masters_theses

Scrubber_steve · 10/27/2018, 11:34 PM

Ok, so anodizing increases emissivity, but the color of the anodize is unimportant. So, as i said the color of a heatsink plays no part in its ability to loose heat.

How heat sink anodization improves thermal performance.

For electronics cooling, however, the advantages of surface anodizing are the dielectric isolation of the cooling components from their electronics environment, and the significant increase in their surface emissivity.

The pores created by acidic anodizing on aluminum can easily absorb dyes. Colored dyes are often used on heat sinks for cosmetic and marketing purposes. The color of anodization has no impact on radiation heat transfer. A clear anodized surface has the same emissive characteristics as a black anodized surface.

https://www.qats.com/cms/2010/11/09/...e-part-1-of-2/

oreo57 · 10/28/2018, 01:59 AM

Yes, I got sloppy and caught up in "black" my bad..
most "commercial' passive LED heat-sinks are black.

The orig. point was referring to the o/p's "plate' and if it could be improved if using it passively..

Painting or anodizing would help..

Scrubber_steve · 10/28/2018, 02:04 AM

Quote:

Originally Posted by oreo57

Yes, I got sloppy and caught up in "black" my bad..
most "commercial' passive LED heat-sinks are black.

The orig. point was referring to the o/p's "plate' and if it could be improved if using it passively..

Painting or anodizing would help..

I would just roughen up the surface of it to create more surface area. Better yet, grind slots in it, or even better again, use a table saw to cut slots in it

Even drilling holes in it would increase surface area & improve its performance

10/27/2018, 10:33 PM	#27
Scrubber_steve I'm really very likeable Join Date: Aug 2016 Location: Down Under Posts: 676	"Practically speaking, a heatsink being coloured is entirely for looks, and will affect cooling less than surface area, airflow, material and the contact between the heat source and heat sink." https://www.google.com.au/amp/s/www....erformance/amp

10/27/2018, 10:40 PM	#28
Scrubber_steve I'm really very likeable Join Date: Aug 2016 Location: Down Under Posts: 676	A heatsink painted black is a bad approximation of a blackbody, more like a 'grey' body where the energy radiated by the formula above is multiplied by a constant (emissivity epsilon) which is less than 1. A better approximation would be a heatsink with microholes with depth about 7x their diameter (the whole appears black inside, try it). This is used by Ersa in their IR heating plates for PCB rework. To conclude, painting heatsinks black does not contribute to their ability to dissipate heat by radiation. https://www.eevblog.com/forum/projec...black-surface/

10/27/2018, 10:47 PM	#30
Scrubber_steve I'm really very likeable Join Date: Aug 2016 Location: Down Under Posts: 676	The Color A black object radiates the best - so all heatsinks should be black". True? Not really. Remember, most of the heat is dissipated using forced convection - and for this effect, the color is irrelevant. When doing a comparison test of two otherwise identical heatsinks with a different color, the measured performance difference is usually negligible. The main reason why heatsink manufacturers anodize their heatsinks is to make them look more attractive. Heatsinks exist in a variety of colors - black, silver, but also blue, green, gold, and red. For the performance, it doesn't make any major difference. https://www.anandtech.com/show/437/2

10/27/2018, 11:34 PM	#33
Scrubber_steve I'm really very likeable Join Date: Aug 2016 Location: Down Under Posts: 676	Ok, so anodizing increases emissivity, but the color of the anodize is unimportant. So, as i said the color of a heatsink plays no part in its ability to loose heat. How heat sink anodization improves thermal performance. For electronics cooling, however, the advantages of surface anodizing are the dielectric isolation of the cooling components from their electronics environment, and the significant increase in their surface emissivity. The pores created by acidic anodizing on aluminum can easily absorb dyes. Colored dyes are often used on heat sinks for cosmetic and marketing purposes. The color of anodization has no impact on radiation heat transfer. A clear anodized surface has the same emissive characteristics as a black anodized surface. https://www.qats.com/cms/2010/11/09/...e-part-1-of-2/

10/28/2018, 01:59 AM	#34
oreo57 Registered Member Join Date: Apr 2013 Posts: 1,793	Yes, I got sloppy and caught up in "black" my bad.. most "commercial' passive LED heat-sinks are black. The orig. point was referring to the o/p's "plate' and if it could be improved if using it passively.. Painting or anodizing would help..