Is a black heatsink more effective?

[WX7G]

Actually aluminum objects get rid of heat even better than copper. I say again color has very little effect on a heat sink that is being swept with a fluid such as forced air in sufficient quantity.  

Copper is a far better heat conductor than aluminum and has more thermal mass so aluminum may give illusion of cooling quicker (because it has less thermal mass) Copper it pretty expensive to use these days and heavy too. Reason a lot of heat sinks are not paint is purely cost not because it does not help. You guys that like those boat anchor Astron power supplies. how many of those have you seen with bare aluminum shiny heat sinks?

Wrong.

The specific heat of copper is about 1/3 that of aluminum. So by mass copper stores about 1/3 the thermal energy that aluminum does.

By volume aluminum and copper store about the same thermal energy. This is because copper has about 3X the density.

[K8AXW]

Yes I do him credit for trying. /quote]

Absolutely!  Way to go TANAKASAN!  Since you have the setup already in place, perhaps you could replicate the experiment using a hole drilled into the heatsink center (Where the transistor is placed) and use a contact probe or bead.  This would be a great contribution to the ham comunity.

I have been living under the impression that a heatsink painted flat black was a better radiator than plain aluminum.  However, after reading some of the comments here about the paint retaining the heat within the aluminum, I'm having second thoughts.

[N6AJR]

Just put a fan on it and  keep going.. a fan blowing removes more heat than no fan..  and remember I am a fan of fan dipoles..)))

[W8JX]

Wrong.

The specific heat of copper is about 1/3 that of aluminum. So by mass copper stores about 1/3 the thermal energy that aluminum does.

By volume aluminum and copper store about the same thermal energy. This is because copper has about 3X the density.

Not exactly because while by weight copper stores 38.4% of heat that aluminum does, by volume copper stores 142% of the heat energy that Aluminum does.   Also these numbers are for pure aluminum which is rarely used in heat sinks. (alloys have lower heat capacities) Also, copper has  169% the thermal conductivity of pure aluminum. Furthermore copper's conductivity is 223% the conductivity of best aluminum alloy for heat conduction and 335% of the worst one.  Only silver is better than copper here but not by much (though silver has a lower heat capacity by weight than copper)   

[AA4HA]

Interestingly anodization actually increases the surface area of the heat sink at microscopic levels. Black is a better thermal conductor (look up "black body radiation" and "basic thermodynamics", this is first year college physics stuff).

If you seal an anodized finish you are actually closing off those pores that are opened up by the anodization etching process, this will reduce the ability of the object to radiate energy. This is also why most anodized surfaces are insulating (the sealant) instead of electrically conducting.

The color black in anodization is actually a dye that is added after the etching process. A sealer is added to keep the dye in place. You can look up the details of how anodization, dying and sealing at the Casewell web site.

[KB1GTX]

Anodize Black         0.88  0.88    1.00
Aluminum anodized  0.14  0.84      .17

.88 V .84,, and that is only if it's done right,, so don't paint it! 

[KB1GMX]

First of compared to conduction then convection radiation is the poorest way to rid heat.

So if you trying to keep transistors cool (using any reasonable metal heat sink) conduction is how the heatsink gets hot.  Convection either natural or by forced air(fluid) movement will remove the heat. Lacking that radiation will dissipate the heat but far slower.

In an ideal world a black anodized heat sink with forced air cooling would be best
(ignoring water and it's complications for now).  However the difference between
a black heatsink with forced air and a natural aluminum is very small.   I just went through
the whole exercise with a contact thermocouple. For my case it made less than 1 degree C
difference in a system dissipating nearly 18W.  While testing I closed the system in a sealed container without conduction to the container and the internal temps went though the sky (more than 100C) and heat sink color was not a help.  It took many times more time to
cool to 35C as well where the air cooled test never got hotter than 45C.  Radiation
is very inefficient in getting rid of heat.

It's very easy to test, mount a Dale power resistor to a heat sink and put DC on it.
Do not use an IF temp probe, use a contact thermometer or a thermocouple.

Paint is problematic as it's a coating and may add insulation.

FYI, computers for years(decades) have been cooling the CPU.  I've seen heatsinks of
almost every color ALL fan forced (or water cooled).

Also water cooling is conduction to conducting fluid(water) that conducts heat to
air via radiator(usually forced air).

This is not new science and the information is out there to evaluate the difference.


Allison

[W8JX]

FYI, computers for years(decades) have been cooling the CPU.  I've seen heatsinks of
almost every color ALL fan forced (or water cooled).

Best heatsink I ever had (and still do one a old system I used to overclock a LOT) was made out of copper with large diameter yet thin copper fins too. Coolest running CPU heatsink I ever had by far. For many years Intel used to use a copper slug for a core in a aluminum heatsink with fans for P4's to help get heat out of CPU and into heatsink.