[Amps] making sinks black

[Peter Chadwick]

Somewhen back in the early 1970's (showing my age!) there was an article in one of the professional UK electronics magazines (long defunct). The people had done work on heat transfer from heat sinks. The main points I remember were:
1. Because the majority of heat loss is convection, radiation doesn't do a lot for normal (< 50 degC) temperature rises
2. Painting black doesn't help, because of the insulating effect of the paint, although a thin layer doesn't hurt too much. Anodising is a good method of providing a reasonable degree of corrosion resistance without adding to thermal resistance. Colour doesn't make a lot of odds because the main heat transfer is by convection.
3. Wide spaced deep fins were best, rather than lots of narrow spaced shallow fins
4. Turbulent air flow, using fan assistance, really helped.


My advice is to see if there's a local shop will anodise it, otherwise don't bother, unless for aesthetic reasons, plain aluminium won't do. If you need to improve the looks of plain aluminium after drilling, dip it in a caustic soda (sodium hydroxide, or lye) solution. Outdoors, 'cos the fizzing is hydrogen, so no sparks. After about 10 to 20 minutes, depending on the strength of the solution, remove. Ideally, soak for a few seconds (it doesn't need more) in a 20% nitric acid solution. Without nitric acid to dip it in, and less dodgy to use, a swab over with a cloth well soaked in vinegar, or even dip in vinegar. I don't recommend using the vinegar for culinary purposes afterwards, although it should be OK. The caustic dip gives a nice finish for a clear lacquer spray, or is not bad for a 'key' for the primer paint ot stick to.
73
Peter G3RZP