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Heatsink USA Extruded aluminum heatsinks, specializing in small custom cut orders

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Old 21st January 2009, 05:43 PM   #21
labjr is offline labjr  United States
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Quote:
Originally posted by tms0425

This is from the Conrad site regarding their powder coating:

"Coating Material
Textured black polyester powder coating has been chosen as the standard finish on all coated Conrad heatsinks and provides:

* a quality, durable and attractive finish capable of withstanding elevated temperatures,
* increased thermal dissipation in the order of 5% to 8% (depending on the heatsink) under natural convection."

Wow! I actually thought power coating would run hotter than if it were bare or anodized. That's interesting.
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Old 21st January 2009, 05:47 PM   #22
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Also powder coating will not change color over time link anodizing.

-David
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Old 21st January 2009, 05:51 PM   #23
pooge is offline pooge  United States
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Originally posted by labjr


How about powder coating? Does this change the thermal properties? I have friends who work in metal production and can easily have stuff powder coated. Anodizing is not so easy to have done, because it's not as popular as it used to be.

I believe Conrad does this, but I have no knowledge of its thermal properties. A black color is used to promote radiant heating, but that is not the primary mode of heat exchange, which is convection (after conduction from the transistor through the heat sink). So it is important for any coating to not inhibit convection cooling.

Fins that are very deep or very long can inhibit air movement through the fins, because the resistance to air movement will increase, and the air will move around and outside of the fins and not draw out the heat. Therefore, if fins are made deeper and longer, the spacing between adjacent fins must increase. It is all a balancing act, like everything else. You just don't make the fins deeper or longer in the expectation that it will be better, especially from a standpoint of economy of materials; at least not without determining the cost/benefit of doing so as opposed to other changes that may be of better benefit.
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Old 21st January 2009, 05:52 PM   #24
labjr is offline labjr  United States
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I guess I wouldn't powder coat the mounting surface. The bare aluminum is hard and flat enough to mount the output devices?
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Old 21st January 2009, 06:00 PM   #25
pooge is offline pooge  United States
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Quote:
Originally posted by tms0425

This is from the Conrad site regarding their powder coating:

* increased thermal dissipation in the order of 5% to 8% (depending on the heatsink) under natural convection."

I would be interested to know more about this. This statement is unclear what is being compared to what. As this range is in the range of radient improvement for a black color vs. a low emissivity natural color, I'm wondering if the improvement is only to just the radiant cooling (without speaking to any possible reduction of convection cooling), or to the total amount of radiant and convective heat exchange.
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Old 21st January 2009, 06:21 PM   #26
tms0425 is offline tms0425  United States
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Quote:
Originally posted by pooge



I would be interested to know more about this. This statement is unclear what is being compared to what. As this range is in the range of radient improvement for a black color vs. a low emissivity natural color, I'm wondering if the improvement is only to just the radiant cooling (without speaking to any possible reduction of convection cooling), or to the total amount of radiant and convective heat exchange.
No idea, just copied the quote from their site. I know it is very durable and does seem to stay black over time unlike most anodized ones.

The surface finish for mounting the transistors is also very flat and clean, so I doubt any added machining is necessary in most cases.
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Old 21st January 2009, 06:42 PM   #27
labjr is offline labjr  United States
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Quote:
Originally posted by pooge



I would be interested to know more about this. This statement is unclear what is being compared to what. As this range is in the range of radient improvement for a black color vs. a low emissivity natural color, I'm wondering if the improvement is only to just the radiant cooling (without speaking to any possible reduction of convection cooling), or to the total amount of radiant and convective heat exchange.
Heatsink design seems pretty complicated to me. However, I would have thought powder coating insulates the aluminum inhibiting some of the convection of the heatsink.
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Old 21st January 2009, 06:50 PM   #28
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One would not want to coat the mounting surface with anything, Mounting surfaces should always be bare aluminum or copper.

Aluminum oxidizes over time and eventually corrodes. Notice how some bare aluminum shows evidence of pitting covered by a white colored film?

The oxidation and any corrosion does impact thermal efficiency.

-David
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Old 21st January 2009, 06:58 PM   #29
tms0425 is offline tms0425  United States
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Quote:
Originally posted by hifimaker
One would not want to coat the mounting surface with anything, Mounting surfaces should always be bare aluminum or copper.

Aluminum oxidizes over time and eventually corrodes. Notice how some bare aluminum shows evidence of pitting covered by a white colored film?

The oxidation and any corrosion does impact thermal efficiency.

-David
Obviously true. I should have noted that the transistor mounting surface on the Conrads is definitely NOT coated.
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Old 21st January 2009, 07:40 PM   #30
AndrewT is offline AndrewT  Scotland
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the applied coating type is only part of the question.
That determines the emissivity and the thermal conductivity.
In addition one must ask how thick the coating is and what surface texture it has.
All these will affect the overall dissipation ability.
I suspect Conrad are comparing a bare untreated aluminium heatsink to their black powder coated version.

Be careful with most powder coating shops. The coatings are often very thick and become very effective (plastic) insulators.
A very fine mist spray of black lacquer is usually better but never looks as good.
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