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"Will black anodized chassis dissipate heat better than clear"

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2004

Q. We are an electronics manufacturing house dealing with 16 amp triac circuitry in an anodized aluminum chassis. We produce 100,000 - 150,000 pieces per year and have always used the clear anodized aluminum chassis. I remember reading somewhere that a chassis anodized BLACK will tend to dissipate the heat out of the chassis more efficiently than a clear anodized unit. Is this true ? Is there any documentation "out there" to back this statement up?

Edward Linkus
electronics mfgr - Shamokin, Pennsylvania, USA

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What you are referring to is called emissivity in Thermodynamics. Will black anodize have a higher emisivity than clear anodize? Yes; but not much, the emissivity of black anodize is about 0.86, its about 0.83 for clear. This is about the same as oil paint, any color. Heatsinks are anodized and dyed black for looks and corrosion resistance, not because it provides any useful improvement in cooling.

Paul Yursis [deceased]
- Columbia, Maryland, USA

Ed. note: it is our sad duty to advise of the passing of Paul Yursis in August 2005.
Here is a brief obituary by Mike Caswell.

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2004

I disagree with the first response - Black anodize does dissipate heat better than clear anodize, that is why most aluminum heatsinks get black anodized.

David A. Kraft
- Long Island City, New York

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The difference between 0.86 and 0.83 is about 1%. I don't consider this a useful improvement, but you might. In the course of our business, we routinely test the thermal performance of our heatsinks (commercially available extrusions designed for this purpose). 1% holds up well for natural convection, it's about 1.5% for forced air, as other things come into play with this. Most of our heatsinks are black, because we like the way they look.

This is not intended to beg the issue, rather its to address a commonly held misconception.

Everyone has noticed that a dark colored object will be appreciably warmer than a similar but light colored one after exposure to sunlight. This is due to the substantial differences color makes to thermal absorption by radiation. It's natural to assume that the effect will be the same when the direction of heat flow is reversed. Unfortunately this is not true, absorption by radiation is very different than emission by radiation, color or shade has little effect on heat flowing out. BTW, this is also why a "Radiometer" will spin when put in sunlight.

Paul Yursis [deceased]
- Columbia, Maryland, USA

Ed. note: it is our sad duty to advise of the passing of Paul Yursis in August 2005.
Here is a brief obituary by Mike Caswell.