[oreo57]

Originally Posted by Twinfallz

The color of a heatsink plays no part in its ability to radiate heat

I disagree and so does science..

In situations where convection is low, such as a flat non-finned panel with low airflow, radiative cooling can be a significant factor. Here the surface properties may be an important design factor. Matte-black surfaces will radiate much more efficiently than shiny bare metal.[17][18] A shiny metal surface has low emissivity. The emissivity of a material is tremendously frequency dependent, and is related to absorptivity (of which shiny metal surfaces have very little). For most materials, the emissivity in the visible spectrum is similar to the emissivity in the infrared spectrum[citation needed]; however there are exceptions, notably certain metal oxides that are used as "selective surfaces".

Also,
the effect of radiation heat transfer is
very important in natural convection, as it can be responsible of up to 25% of the total heat dissipation. Unless the
component is facing a hotter surface nearby, it is imperative to
have the heat sink surfaces painted or anodized to enhance radiation.

https://www.boydcorp.com/files/techn...-Heat-Sink.pdf


OR:

Effects of Anodising on radiant heat transfer in heat sink

Heat sinks cooled by natural convection may benefit from an anodized finish, but the added cost of the finish may not be justified when the part is used in forced convection cooling.

Surface emissivity limits the amount of heat transfer due to radiation cooling. With 1.0 being perfect (black body) emissivity anodized aluminum is 0.85 and unfinished is 0.05.

Heat transfer due to radiation is proportional to the heat sink surface area exposed to its surroundings and to the temperature rise above ambient (in absolute °K) raised to the 4th power (T Heat-sink - Tambient)4. In natural convection on small heat sinks with open fins, and a high benefit from anodizing by up to 45%.

Relatively large extrusions and those used at low temperature rise, as in many high power applications, will only gain up to 10% by the addition of an anodized surface.

With forced ventilation (using a fan) convective cooling is about 3 times higher than in natural convection. This changes the proportion of heat transfer due to radiation. An anodized finish will only add 4 -8% to the overall cooling effect in forced air. This percentage again, depends on fin spacing and heat sink dimensions. The color of the anodized finish makes little impact on emissivity since most radiational heat loss occurs at wavelengths higher than visible light.

As a thumb rule, if anodize is not required for aesthetic or corrosion protection, we suggest it only for small, open finned heat sinks in natural convection.

http://smlease.com/entries/heat-tran...r-in-heat-sink

Like I said, w/ fans.. not an issue..