View Single Post
Old 13th Sep 2017, 7:13 am   #22
Craig Sawyers
Dekatron
 
Craig Sawyers's Avatar
 
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,939
Default Re: Re-anodising heatsinks?

Didn't you see my earlier post regarding dissipation being almost all convection and hardly any through radiation for a temperature rise of less than 40C? The colour of the heatsink is pretty much irrelevant for a temperature rise of less than 100C.

There is another effect that reinforces this idea called the "view factor". Think about how much each part of a finned heatsink area sees of the environment, and is capable of thermally radiating. Before you get very deep into the profile, each area of the heatsink sees progressively less of the environment, and the more it sees of the adjacent fin. Since the adjacent fin is at the same temperature there can be no radiative energy transfer - it can only radiate if it sees a cooler environment which it can only peek through the gaps between the fins.

All of which says: the colour of the heatsink does not matter if you can touch the heatsink without burning yourself. Cooling is close to 100% convection.

The colour of a heatsink is traditionally black for decorative reasons only, and alas reinforces the pseudoscience argument that thermal radiation assists dissipation to a significant degree.

Here is a link to a heatsink manufacturer that says the same thing http://www.abl-heatsinks.co.uk/heats...ace-colour.htm

Quote "The heat transfer from the heatsink occurs by convection of the surrounding air, conduction through the air, and radiation. Heat transfer by radiation is a function of both the heat sink temperature, and the temperature of the surroundings that the heat sink is optically coupled with. When both of these temperatures are on the order of 0 °C to 100 °C, the contribution of radiation compared to convection is generally small, and this factor is often neglected. In this case, finned heat sinks operating in either natural-convection or forced-flow will not be effected significantly by surface emissivity."

Craig

Last edited by Craig Sawyers; 13th Sep 2017 at 7:41 am.
Craig Sawyers is online now