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Old 5th November 2013, 07:55 PM   #11
back is offline back  Greece
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Quote:
Originally Posted by Elvee View Post
Practically any type of paint will be better than bright aluminium regarding emissivity, including the ones that look rather light-colored: for far IR, which is what matters, most pigments and dyes appear black.

In theory the conductivity could matter, but in practice, with the thickness of the layer, the exchange surface and the thermal conductivity of organic polymers, the increase in thermal resistance will be modest. This means that in at least 90% of the situations, any type of paint will be preferable to bright aluminium.
Anodization or special paints are of course (slightly) better
well this is new.

anyway i will use sandpaper to make them rough i will use primer and then paint.i believe i will have a sucess since i was planing for two pairs of mosfet but know i will use one one so they are more than enough.

the only problem the paint will not degrade after some time.
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Old 5th November 2013, 07:59 PM   #12
jcx is offline jcx  United States
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radiation is only significant for tubz - typical finned Al heatsink work >80% in convection
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Old 15th November 2013, 05:13 PM   #13
AndrewT is offline AndrewT  Scotland
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and the surface that "conducts" the heat to the moving air flow must not be an effective insulator.

Conduction through the "finish" is VERY important.
Anodise is a very good conductor. The thickness of anodise makes the finish a better than a very good conductor.

I saw an estimate of 8% of the total finned heatsink dissipation is by radiation. I would not mind losing much or most of that 8%, if I knew that I was not ruining the conduction of the other 92% that still needs to be dissipated.
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Old 15th November 2013, 09:15 PM   #14
davym is offline davym  Scotland
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Black oxide is a better finish than anodise, thinner and more conductive but it's not something you can do in the kitchen at home.

http://www.birchwoodtechnologies.com/news/5283.html
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Last edited by davym; 15th November 2013 at 09:18 PM.
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Old 15th November 2013, 09:51 PM   #15
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Default Conrad heatsinks

Conrad heatsinks, a part mentioned and used by a number of DIY audio members, use a powder coated paint finish and they seem to work just fine.

I use fast drying flat black laquer from a spray can.
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Old 15th November 2013, 09:59 PM   #16
AVWERK is offline AVWERK  United States
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I assume you want a consistant looking finish and this is the reason for painting?
While I think its a bad idea and trying to get a good even coat down into the deeper sections will not look right (if it,s a deep finned one).. A better idea would be bead blasting of even sand blasting if you want a new look.
Anodizing is the way to bring it all home
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Old 19th November 2013, 12:19 PM   #17
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I did not see it mentioned: Where is the sink located? If it is inside a box, in the dark, it does not matter what colour it is, only the surface area is of importance. E
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Old 19th November 2013, 12:50 PM   #18
tinitus is offline tinitus  Europe
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are you saying amps run hotter when there is no light ?
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Old 19th November 2013, 01:18 PM   #19
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Lye, Sodium Hydroxide does a pretty good job of degreasing and etching the surface of aluminum.

You need to wash it very thoroughly afterwards.

Automotive sources have "self etching" paints and primers - but they are not thin.

I am very very surprised that Conrad uses a powder coat on heatsinks - a link to a discussion their site regarding that finish would be appreciated, especially what derating they apply. They may have specs for degC/W coated and uncoated that can be compared?

I'd not paint unless and until some specs emerge or other measurements.

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Old 19th November 2013, 02:20 PM   #20
tinitus is offline tinitus  Europe
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Conrad Heatsinks - Technical Details

Component Mounting Surface
Heatsink showing linished surface
Conrad heatsink showing machined
and linished surface.

The component mounting surfaces on Conrad heatsinks are machined, generally linished and remain uncoated. This surface preparation maximizes thermal conductivity between component and heatsink by:

Removing the relatively thick, thermally insulating surface oxide layer, formed as a result of any hot forming process with aluminium products.
Providing a flat, smooth surface ensuring maximum surface area contact between component and heatsink.
Keeping the junction between component and heatsink free of any thermally insulating coating.


sounds like they say a hard surface compromises heat transfer
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